Copper Recovery Originating from Galvanic Industry (original) (raw)

CPD NR3268

Conceptual Process Design
Process Systems Engineering
DelftChemTech - Faculty of Applied Sciences Delft University of Technology

Copper Recovery Originating from Galvanic Industry

Authors
Fredrick Aboka
Mo Osman Ahmed
Mariela Serrano
May Tampus
Yana Tatur

Keywords: copper recovery, waste-to-waste technology, starch hydrolysis, glucose degradation

Assignment issued : 5 October, 2001
Report issued : 1 November, 2001
Review date : 8 November, 2001
Appraisal : 12 February, 2002

Summary

Environmental regulations limit the presence of copper in the wastewater from industries to 3mg/l3 \mathrm{mg} / \mathrm{l}; furthermore, copper is a rather expensive commodity. Consequently, recovery of this metal is both necessary and attractive. Electrowining techniques are commonly used to recover copper, but it cannot be used when the streams contain hydrocarbons such as the waste stream, Multibond, from company A. As a result, this company is force to send their waste stream abroad for treatment paying 1.32 Euro/kg of waste.

The present project aims to recover copper via a hydrothermal process in the form of ( 99%99 \% pure) copper metal powder that can be sold to scrap industries in the area. The copper reduction will be achieved by combining a copper sulphate solution (copper II) waste stream and a carbohydrate waste stream under 12 bar and 185∘C185^{\circ} \mathrm{C} in a Kenics static mixer. The accessibility and the low or no-price for the feedstocks, make this design even more attractive. The copper reduction plant consists mainly of two units: reaction and separation. Thus making it a very simple process. Furthermore, the recovery is >99%>99 \% copper.

This process has already been made a reality in countries such as Chile where copper is abundant and the main export commodity. Currently new sites for this process are being developed and have been patented around the world.

Specifically, in company A the amount of copper recovered from the waste stream is 1.2 tons per year taking into consideration that company A is still under economical recovery so it is not working to its full capacity. The produced copper will be sold to scrap metal industries for the price 0.91 euro /kg/ \mathrm{kg}. With this production capacity, the design is not economically feasible, yet in the future when the company operates at its full capacity, or as the cost for treatment abroad will increase, this design will be with no doubt economically attractive.

In addition, designers recommend treating the five copper (II) containing waste streams of company A with this hydrothermal process. Advantages are that only one wastewater process will be applied in company A reducing the costs. Furthermore, the copper recovered will be increased to 65 tons per year, so the profit from its sales will around 59 million euro.

Table of contents
SUMMARY … I
TABLE OF CONTENTS … II
CHAPTER 1. INTRODUCTION … 1
1.1.COPPER … 1
1.2. INDUSTRIAL METHODS TO RECOVER COPPER METAL FROM WASTE STREAMS … 2
CHAPTER 2. PROCESS DEFINITION … 4
2.1. FEED STOCKS … 4
2.1.1.Carbohydrate stream … 4
2.1.2.Copper (II) sulphate stream … 5
2.2. REACTION: STOICHIOMETRY AND KINETICS. … 6
2.2.1. Degradation of starch … 6
2.2.2. Reduction of copper … 7
2.2.3. Optimal reaction conditions … 8
2.3. PRODUCTS … 9
2.4. Block SCHEME … 9
2.4.1. Separation … 10
CHAPTER 3. BASIS OF DESIGN (BOD) … 11
3.1. DESCRIPTION OF THE DESIGN … 11
3.2. PROCESS DEFINITION … 11
3.2.1. Process Concept chosen … 11
3.2.2. Block Scheme … 12
3.2.3. Thermodynamic Properties … 12
3.2.4. List of Pure Component Properties … 13
3.3. BASIC ASSUMPTIONS … 14
3.3.1. Plant Capacity … 14
3.3.2. Location … 14
3.3.3. Battery Limit … 15
3.3.4. Construction materials. … 15
3.3.5. Choice of Utilities … 15
3.4. ECONOMICAL ANALYSIS … 16
3.4.1. Economic margin … 16
3.4.2. Maximum allowed investment … 16
CHAPTER 4. THERMODYNAMIC PROPERTIES AND LIST OF PURE COMPONENTS … 18
4.1. Decomposition of H2O2\mathrm{H}_{2} \mathrm{O}_{2} … 18
4.2. THERMODYNAMIC PROPERTIES … 19
CHAPTER 5. PROCESS STRUCTURE AND DESCRIPTION … 21
5.1. CRITERIA AND SELECTION … 21
5.1.1. Storages … 21
5.1.2. Preheating … 22

5.1.3. Reaction … 22
5.1.4. Separation … 23
5.1.5. Purification … 24
5.1.6. Drying … 24
5.2. Process Flow Scheme (PFS) … 24
5.3. BATCH CYCLE DIAGRAM … 24
5.4. PROCESS STREAM SUMMARY … 25
5.5. Utilities … 25
5.6. PROCESS YIELD … 25
CHAPTER 6. PROCESS CONTROL … 26
6.1. Pressure CONTrol (PC) … 26
6.2. LIQUID CONTROL (LC) … 26
6.3. TEMPERATURE CONTROL (TC) … 26
6.4. Flow rate CONTrol (FC) … 26
6.5. PH CONTROL (PHC) … 27
CHAPTER 7. PROCESS STREAM SUMMARY, MASS BALANCE, AND HEAT BALANCE … 28
7.1. Stream BALANCE … 28
7.2. HEAT BALANCES … 29
7.2.1. Heat Exchanger E101 and E1012. … 29
7.2.2. Preheating stream in F101 and F102 … 29
CHAPTER 8. PROCESS AND EQUIPMENT DESIGN … 30
8.1. AGITATED STORAGE TANK T101 … 30
8.2. Storage tanKS T102 AND T103 … 30
8.3. HEAT EXCHANGERS E101 AND E102 … 31
8.4. ELECTRIC HEATERS F101 AND F102 … 31
8.5. REACTOR R101 … 32
8.6. HYDROCYCLONE S101 … 32
8.7. ROTARY DISK VACUUM FILTER … 33
8.8. PUMPS P101, P102 AND P103 … 33
8.9. PRESSURE ISSUES … 34
CHAPTER 9. WASTE TREATMENT … 35
CHAPTER 10. PROCESS SAFETY … 36
10.1. Dow Fire and Explosion Index Assessment … 36
10.2. CONCLUSIONS … 37
CHAPTER 11. ECONOMY … 38
11.1 INVESTMENT … 38
11.2. Production Costs … 40
11.3. CASH FLOW, ECONOMIC CRITERIA, COST REVIEW, SENSITIVITIES, AND NEGATIVE CASH FLOWS … 42
11.4 COMPANY’S SAVINGS … 44

CHAPTER 12. CONCLUSIONS AND RECOMMENDATIONS … 45
LIST OF TEXT SYMBOLS AND ABBREVIATIONS … 48
REFERENCES … 49

Chapter 1. Introduction

1.1.Copper

Copper is one of the most valuable resources in the world. Its electrical and thermal properties make copper a very precious commodity for wire and electrical devices. Figure 1.1 illustrates the copper consumption in the United States of America [1].

Figure 1.1 Functional consumption of copper in the USA
Copper can be obtained by mining or it can be recovered by applying electro-winning processes to waste streams containing copper such as the ones from galvanic industries.

The main goal of this project is to develop a conceptual process design for the recovery of copper metal (Cu0)\left(\mathrm{Cu}^{0}\right) from a waste stream containing copper (II) in a concentration of 20 g/l\mathrm{g} / \mathrm{l} in the form of copper sulphate (CuSO4)\left(\mathrm{CuSO}_{4}\right) from galvanic company A in the Netherlands.

This project will be based on the experiments done by Dr. ir. Van der Weijden, one of the project owners, who developed the method for the recovery of copper via waste-to-waste technology by combining a copper (II) containing waste stream with a carbohydrate waste stream in order to produce Cu0\mathrm{Cu}^{0}. Dr. Van der Weijden would like to check the feasibility of her laboratory experiments on an industrial scale. Furthermore, project owner, Ir. Niels van Wageningen, is doing simulations on particle size distribution of copper particles in a static mixer plug-flow reactor. With their combined objectives, this design project was conceived.

This method of copper recovery has been used in pilot plants simulations with plug flow reactors. Nevertheless, copper content in the waste stream was lower ( 2 g/l2 \mathrm{~g} / \mathrm{l} ) than that in present case ( 20 g/l)20 \mathrm{~g} / \mathrm{l}). Also, the new plug flow reactor with a static helix mixer will be designed in present research. Addition of static mixers to this reactor resembles a behavior of the ideal plug flow reactor thus improving the performance of the reactor. The use of this special reactor seems promising in terms of control and size distribution of formed copper particles (see Appendix E-i).

Recovering copper from the waste stream of company A yields economic as well as environmental benefits. As can be seen in figure 1.2, the global economic demand of copper is higher than 16000 metric tons. Thus, any possible project that recovers copper will be of interest to the world market. This project in particular intends to sell the recovered copper to scrap industries as 99%99 \% pure copper powder [2] at a price of 0.91 euro /kg/ \mathrm{kg} [3]. Apart from recovering copper, the copper (II) ion concentration of the waste stream will be reduced from 20 g/L20 \mathrm{~g} / \mathrm{L} to 0.097 g/L0.097 \mathrm{~g} / \mathrm{L}. This concentration is within the allowable range for any stream to be further treated in the wastewater treatment plant of company A.

Figure 1.2 The global demand for copper [1]

1.2. Industrial methods to recover copper metal from waste streams

A number of processes have been developed to recover copper metal from coppercontaining wastes. Examples of these processes are electro winning, cementation, and non-ionic reduction. Electro-winning processes use direct current to gather the positively charged copper metal ions at a cathode where they are eventually recovered by reclaiming the entire electrode or stripping the copper metal from it [4]. Cementation is the use of a more positive metal to dissolve and displace another metal with a less positive potential for instance, copper versus iron [5]. Non-ionic reduction utilizes hydrogen gas or carbon monoxide [5,6]. An alternative non-ionic reduction employs carbohydrates as a reductant under hydrothermal conditions [5,2]. The advantages and disadvantages of the various options are summarized in the table 1.1.

Table 1.1. Alternative Processes for recovering copper from galvanic industries.

As can be seen from table 1.1 above, a hydrothermal process with carbohydrates as the non-ionic reductant has more benefits compared to the other options. Hence, the process of choice in this design uses a carbohydrate containing waste to reduce copper (II) under hydrothermal conditions. These conditions are elevated temperatures (160−210∘C)\left(160-210{ }^{\circ} \mathrm{C}\right) and pressures (7-19 bar) [8]. Under these conditions, waste streams containing carbohydrates (e.g. starch, sawdust, molasses, paper) are able to reduce copper (II) into Cu0\mathrm{Cu}^{0}.

Dr. ir. Van der Weijden tried to patent this method. However, the patent could not be granted because, similar processes of copper reduction with carbohydrates had already been patented [9].

The hydrothermal process is economically attractive to both carbohydrate containing and copper (II) containing waste suppliers. The carbohydrate supplier benefits because there is no need to treat the waste in terms of COD and BOD content. Company A, the copper sulphate supplier, will be able to treat its waste on site and not send it to Belgium for treatment at an expense of 1.32 euro /kg/ \mathrm{kg}. The amount of waste to be treated is 66.343 ton/yr so the year expense for the treatment of the waste would be 87,572 euro/yr.

Chapter 2. Process definition

In this design, the copper (II) reduction will be achieved via a hydrothermal process as detailed in chapter 1 . This process can be summarized in figure 2.1.

Figure 2.1 Summary of hydrothermal process

2.1. Feed stocks

The carbohydrate containing waste stream and the copper sulphate-rich waste stream are the main feed stocks of this process.

2.1.1. Carbohydrate stream

Carbohydrates are polymers of sugar monomer units. In this hydrothermal process, the active components in the reduction of copper are the monomer units released during carbohydrate acid hydrolysis. The main hydrolysis products are glucose from starch, fructose and glucose from molasses, glucose from cellulose, and xylose from hemicellulose [2]. During the reaction these hydrolysis products will donate electrons to reduce copper ions and will degrade further. Example of such a reaction with glucose as a carbohydrate is shown in equation (2.7).

The carbohydrate containing waste stream can be selected from a variety of sources such as wood, paper, sugar processing industries (molasses), pulp industries (cellulose and hemicellulose, and grain processing industries (starch). Companies providing the carbohydrate waste were contacted. A possible supplier, a paper company, has a waste that contains cellulose and calcium carbonate. But the latter compound can be a problem in the process because additional purification steps would be required for the feed pretreatment. Another company contacted was a molasses supplier because this stream has proven to be a good copper reductant in previous experiments [9]. Unfortunately molasses is a by-product of the sugar industry and it is not considered to be a waste because it is used in animal feed and alcohol production. So, this feedstock will not be given for free, it will cost 113.64 euro/ton. The Xylose-containing waste available from a wood processing company located in Arnhem, which is around 72 km from company A, can give a high conversion and very pure product ( >99%>99 \% ) [2]. However, the concentration of xylose in the mentioned waste is too low (0.1 g/l)(0.1 \mathrm{~g} / \mathrm{l}). Therefore a concentrating unit at the wood processing company would be necessary to prevent excessive transportation costs. Finally, a grain processing company was contacted. This company is located 80 km from company A and has a starch-containing stream. This starch stream could be provided in large amounts and for the whole year. Furthermore, the concentration of the carbohydrate in this stream is 10 g/l10 \mathrm{~g} / \mathrm{l}; nevertheless representatives

of this company have agreed to concentrate the stream to 30 g/l30 \mathrm{~g} / \mathrm{l} in order to supply it. This concentration of starch achieves >99%>99 \% reduction of copper (II) [9]. The cost for this stream is still under discussion between the representatives of the grain processing company. Hence, for this design the only cost considered will be the transportation until more information is available. A disadvantage of using this stream is the production of carbon observed in experiments, so a purification step will be necessary. Table 2.1 compares the possible carbohydrate stream sources.

Table 2.1. Advantages and disadvantages of possible carbohydrates feed stocks.

Weighing the possibilities for the carbohydrate stream supply the price for transportation and the stream, and the concentration of carbohydrates in the stream were the essential factors to be considered. Consequently, the starch-containing waste was chosen for this design.

2.1.2 Copper (II) sulphate stream

The supplier for this stream has been pre-defined by the owner of the project as an integrated circuit company A. This company has five wastewater streams. Four streams already have electrolytic treatment processes in place yet the last stream, due to its contents cannot be treated electrolytically. For this reason, the owners of the project are interested in treating this last stream (Multi bond) with the hydrothermal process. The composition of this stream is summarized in table 2.2.

Table 2.2. Composition of copper wastewater stream [4]

2.2. Reaction: stoichiometry and kinetics

Following the hydrothermal process description of figure 2.1, the two feed streams will react in order to reduce the copper from the copper (II) waste stream according to equation (2.6) and (2.7) having as a limiting step the hydrolysis of the carbohydrate. Therefore, the carbohydrate-containing feed stream can be hydrolyzed before it is introduced to the reactor by adding a strong acid to the stream at high temperatures. However, it was realized that the copper (II) stream waste already contains a strong acid, H2SO4\mathrm{H}_{2} \mathrm{SO}_{4} (see table 2.2).

Mixing and preheating of the feed streams before introducing them to a reaction section was also investigated. But this option was ruled out because the reaction can start in the mixing vessel. This will lead to an overall lower degree of copper reduction. It was decided to pre-heat the two feed streams separately to the set-point temperature (185∘C)\left(185^{\circ} \mathrm{C}\right) and then feed them into the reactor where the hydrolysis of the carbohydrate and the reduction of the copper will take place simultaneously. Furthermore, better control of residence time and hence uniform size distribution of copper particles can be achieved if the reaction is started at optimum conditions inside the reactor. The scheme of the reaction with starch as a carbohydrate is shown in the equations (2.1-2.7).

2.2.1. Degradation of starch

The degradation of starch can be modeled by equation (2.1).

[C6H10O5]n→ (Glucose) S1C6H12O6→( HMF) S2C6H4O2O2→ S3CH2CO(CH2)2CO2H+HCOOH (Starch) \begin{aligned} & {\left[\mathrm{C}_{6} \mathrm{H}_{10} \mathrm{O}_{5}\right]_{\mathrm{n}} \xrightarrow[\text { (Glucose) }]{\mathrm{S}_{1}} \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6} \xrightarrow[(\text { HMF) }]{\mathrm{S}_{2}} \mathrm{C}_{6} \mathrm{H}_{4} \mathrm{O}_{2} \mathrm{O}_{2} \xrightarrow{\mathrm{~S}_{3}} \mathrm{CH}_{2} \mathrm{CO}\left(\mathrm{CH}_{2}\right)_{2} \mathrm{CO}_{2} \mathrm{H}+\mathrm{HCOOH}} \\ & \text { (Starch) } \end{aligned}

For this kinetic model a homogeneous first-order reaction can be described with equation (2.1) through equation (2.5) [2]. The value of k1\mathrm{k}_{1} was not available in literature, yet the conversion percent of starch into glucose was determined in Appendix G-iii to be 72%72 \%. For this calculation it was considered that 2.5 moles of copper (II) are reduced by 1 mol of glucose as suggested in literature [2].

d[Glu]dt=−k2[Glu]d[HMF]dt=k2[Glu]−k3[HMF]d[LaFa]dt=k3[HMF]\begin{aligned} & \frac{d[G l u]}{d t}=-k_{2}[G l u] \\ & \frac{d[H M F]}{d t}=k_{2}[G l u]-k_{3}[H M F] \\ & \frac{d[L a F a]}{d t}=k_{3}[H M F] \end{aligned}

the reaction rate constant ki\mathrm{k}_{\mathrm{i}} can be described via an empirical expression [5]:

ki=Pi[Ac]mie(−EiRT)(ki=1,2,3,…n)k_{\mathrm{i}}=P_{\mathrm{i}}[A c]^{m_{\mathrm{i}}} e^{\left(\frac{-E_{\mathrm{i}}}{R T}\right)} \quad\left(\mathrm{k}_{\mathrm{i}}=1,2,3, \ldots \mathrm{n}\right)

Literature values for the pre-exponential factors (Pi)\left(\mathrm{P}_{\mathrm{i}}\right), the exponents (mi)\left(\mathrm{m}_{\mathrm{i}}\right) and the activation energies (Ei)\left(\mathrm{E}_{\mathrm{i}}\right) are summarized in table 2.3.

Table 2.3. Kinetic Parameters for the degradation of glucose [2]

2.2.2. Reduction of copper

The main reaction can be described as
Cu2++2e−→Cu0\mathrm{Cu}^{2+}+2 \mathrm{e}^{-} \rightarrow \mathrm{Cu}^{0}
The electrons come from the oxidation of glucose into gluconic acid.
C6H12O6+H2O→C6H12O7+2e−+2H+\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}+\mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{7}+2 \mathrm{e}^{-}+2 \mathrm{H}^{+}
Glucose + water →\rightarrow gluconic acid +2e−+2H++2 \mathrm{e}^{-}+2 \mathrm{H}^{+}
As a result of these two reactions ( 2.6 and 2.7), protons, copper metal and carbon dioxide will be produced as can be seen in the overall equation (2.8).
12Cu2++[C6H10O5]n+7H2O→12nCu0+6nCO2+24nH+12 \mathrm{Cu}^{2+}+\left[\mathrm{C}_{6} \mathrm{H}_{10} \mathrm{O}_{5}\right]_{n}+7 \mathrm{H}_{2} \mathrm{O} \rightarrow 12 \mathrm{n} \mathrm{Cu}^{0}+6 \mathrm{n} \mathrm{CO}_{2}+24 \mathrm{n} \mathrm{H}^{+}
From equation (2.8) it can be seen that the production of hydrogen ions will lower the pH in the reactor. In order to maintain the pH in the reactor a strong base could be added. From literature, sodium hydroxide or potassium hydroxide [2] can be used for this purpose. Prices for pellets and solution of each of the salts were obtained. Potassium hydroxide pellets cost 32,000 euro per ton while sodium hydroxide pellets cost 1,452.27 euro per ton [10]. Therefore sodium hydroxide was chosen for the process. The choice between using solution or pellets of sodium hydroxide should be based on the amount needed for the process further on the design. The analysis of this is done in chapter 11, section 11.1. The cost of sodium hydroxide solution is 0.45 euro per kg according to Epenhuysen [11]. Nevertheless, company A already has a 9−m39-\mathrm{m}^{3} tank of 30%wtNaOH30 \% \mathrm{wt} \mathrm{NaOH} used for several of their processed. Therefore, the possibility of using their NaOH stock will also be investigated in chapter 11.

For the reaction section, three very important aspects are to be considered. First is carbon production of the process [5], which should be taken into account. Second is the final degradation product of sugars, which is carbon dioxide as can be seen from equation (2.8). The formation of carbon dioxide will be avoided by controlling the pH of the reaction with NaOH . So the reaction will not proceed to its end. Third is the presence of hydrogen peroxide ( 17 g/L17 \mathrm{~g} / \mathrm{L} ) in the copper (II) stream. This compound would be expected to have great influence in the reaction performance, such as increasing the pressure and temperature. Nevertheless, no negative oxidation effect of H2O2\mathrm{H}_{2} \mathrm{O}_{2} on copper reduction was observed during the experiments with and without hydrogen peroxide (Appendix B-i).

Furthermore, decomposition of H2O2\mathrm{H}_{2} \mathrm{O}_{2} will take place during storage of this stream. Hence, by the time this stream is fed to the design no H2O2\mathrm{H}_{2} \mathrm{O}_{2} will be present in the stream.

Experimentally, the reduction of copper has been plotted. The results are shown in figure 2.2. In this figure, the concentration of the degradation products of starch as well as copper reduction can be calculated at a given residence time.

Figure 2.2. Theoretical curves (210∘C)\left(210{ }^{\circ} \mathrm{C}\right) for cellulose (theoC), D-glucose (theoG), ydroxymethylfurfural (theoHMF), levulinic acid (theoL) and a Cu curve ( simCu⁡(a+b)\operatorname{simCu}(a+b) ) simulating a first order dependence on the disappearance of cellulose and glucose (simCu⁡(a))(\operatorname{simCu}(\mathrm{a})), and on the production of HMF and levulinic acid (simCu⁡(b))(\operatorname{simCu}(\mathrm{b})).

Introducing sodium hydroxide into the process reaction will lead to formation of salts. The impurities will be considered inert in the process. In the reactor, organics (watersoluble polymers) are present from the copper (II) stream as well as sulfuric acid. Moreover, organic compounds will be produced from the degradation of starch. The salts that will be formed from these organic compounds have been neglected in this design. The only salt that will be considered in the design will be sodium sulphate produced from the reaction of sodium hydroxide and sulfuric acid as shown in equation (2.9).

2NaOH(aq )+H2SO4→Na2SO4+2H2O2 \mathrm{NaOH}_{(\text {aq })}+\mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow \mathrm{Na}_{2} \mathrm{SO}_{4}+2 \mathrm{H}_{2} \mathrm{O}

2.2.3. Optimal reaction conditions

The temperature and pressure of the reaction were chosen based on original autoclave experiments made with Xylose where it has been observed that the optimal temperature and pressure for the main reaction of the process are 160∘C160^{\circ} \mathrm{C} and 7 bar. The 7 bar is a combination of 5 bar, provided to the system and 2 bar excess pressure provided by the purging of nitrogen gas (N2( g))\left(\mathrm{N}_{2(\mathrm{~g})}\right). Nitrogen gas was used for two reasons. One was to raise the pressure as explained above and the second one was to provide an inert atmosphere

for the reaction to avoid oxidation of the copper metal by the oxygen produced from the decomposition of H2O2( g)\mathrm{H}_{2} \mathrm{O}_{2(\mathrm{~g})}.

In addition, experiments where starch was used to reduce copper showed that optimal conditions where 185∘C185^{\circ} \mathrm{C} and 12 bar, and no nitrogen gas was used [9]. Therefore, the optimal conditions for this design were chosen at 185∘C185^{\circ} \mathrm{C} and 12 bar and no N2( g)\mathrm{N}_{2(\mathrm{~g})} will not be used in this design.

The mode of operation of the plant was chosen to be batch (see chapter 3, section 3.3.1). This decision was made because of the production capacity ( =1.2=1.2 ton copper metal particles per annum). Such a small capacity makes it unrealistic for the process to operate in a continuous mode [11,13][11,13].

2.3. Products

The products of this hydrothermal process will be copper metal, and a large acidic waste stream that should comply company A constrains for the waste water treatment plant [3]. The homogeneity and the purity of the product are important factors that will have a direct effect on the price at which the product will be sold. The more pure and homogeneous the product is the bigger the market that can be found for it. This process will be designed to produce 99%99 \% pure copper particles of homogeneous size. It has been given that the particle size ranges from 50 to 500 microns, yet the designers are still discussing with the owner for the specific size of the copper metal particles.

2.4. Block Scheme

After the analysis done previously in sections 2.1 through section 2.4, a potential inputoutput diagram showing the overall process of copper recovery from copper-containing waste could be obtained. The main feed stocks, products, and additional chemicals are included in the overall process described in figure 2.3. Figure 2.3 can be further divided into two main sections that are shown in figure 2.4.

Figure 2.3. Input-output diagram of the recovery of copper from galvanic industry

Figure 2.4. General process scheme for copper recovery originating from galvanic industry

2.4.1. Separation

The stream entering the separation section consists of copper metal and carbon particles suspended in a large acidic wastewater stream. There are two options for obtaining the copper particles from this mixture. Figure 2.5 shows the main process steps involved in the two options. Option 1 involves two steps while option 2 involves 1 step.

Option 1
Option 2
Figure 2.5. Options for copper recovery from reactor effluent.
For this design, option 2 was chosen since it involves fewer steps compared to option 1. Nevertheless the copper particles recovered from the separator will be wet and possibly contain some impurities. Hence, a purification and drying unit will be added to the design in order to recover dry copper particles from the process. It can be the case that a special equipment chosen will be able to perform separation and purification simultaneously. Consequently, figure 2.4 will be modified accordingly. Equipment choices will be further analyzed in chapter 8 .

Chapter 3. Basis of Design (BOD)

3.1. Description of the Design

Recovering copper from the waste stream of company A yields economic as well as environmental benefits. As can be seen in figure 1.2, the global economic consumption of copper is higher than 16000 metric tons. Thus, any possible project that recovers copper will be of interest to the world market. This project in particular intends to sell the recovered copper to scrap industries as 99%99 \% pure copper powder [2]. Apart from recovering copper, the copper (II) ion concentration of the waste will be reduced from 20 g/L\mathrm{g} / \mathrm{L} to 0.048 g/L0.048 \mathrm{~g} / \mathrm{L}. This concentration is within the allowable range for any stream to be further treated in the wastewater treatment plant of company A.

The reduction of copper (II) to copper metal will be achieved via a hydrothermal process. This innovative process combines two waste streams: carbohydrate stream and copper (II) stream under optimal conditions in a plug flow reactor with static helix mixers and produce 99%99 \% pure copper particles.

3.2. Process Definition

3.2.1. Process Concept chosen

3.2.1.1. Feed stocks

This waste-to-waste technology has two main feed stocks. The carbohydrate stream waste stream and the copper (II) waste stream. Weighing the possibilities of the supply, the price for transportation of stream, and the concentration of carbohydrate in the stream were important factors to consider when choosing the carbohydrate waste stream. Consequently, the starch-containing stream from company B was chosen as one of the feedstocks for this design. The copper (II) waste stream was pre-defined by the owner of the project as one of the waste stream of an integrated circuit, company A.

3.2.1.2. Reaction Stoichiometry and kinetics

In the main section of the design, the reactor, many reactions will be taking place simultaneously. The main reaction, reduction of copper produces copper metal, protons and gluconic acid. Nevertheless, some of the starch present in the reactor will degrade into leuvolinic acid and formic acid giving rise to a second reaction. And thirdly, the addition of sodium hydroxide to the reactor for pH controlling reasons creates a reaction with H2SO4\mathrm{H}_{2} \mathrm{SO}_{4} production sodium sulphate and water.

A problem is encountered when considering the kinetics of these reactions because in literature molecular weight of starch is not available as well as thermo dynamical properties of carbohydrates.

3.2.2. Block Scheme

All concepts chosen for this process are incorporated in the block scheme for the copper recovery process shown in figure 3.1 below.

Figure 3.1. Block scheme of the copper recovery process.
Notes: 1. Block □\square indicates combining or splitting of the streams.
2. Figures between brackets ( ) are ton/ton of product values.

The storage units of feeds and copper product, and the pre-heating units of feeds are not indicated in the block scheme. They will be shown later in process flow sheet. As result, the overall mass balance will be:

Total IN: 127.770 ton/yr (108.46)
Total OUT: 127.770 ton/yr (108.46)

3.2.3. Thermodynamic Properties

Thermodynamic properties of compounds used in this process are tabulated and presented in chapter 4 , section 4.2 .

3.2.4. List of Pure Component Properties

While finding values for table 3.1, most of the MAC and LD50 values for the pure components were very hard to find.

Table 3.1 Pure component properties of the compounds in copper recovery process

3.3. Basic Assumptions

3.3.1. Plant Capacity

The plant capacity is 1.2 tons of copper metal particles per annum (see chapter 7 and Appendix G-i). The small production capacity calls for batch mode of operation.

The amount of waste stored per day of copper (II) stream is 238 liters. On the other hand, starch will be stored every 20 days in amounts of 5000 liters. Because the starch storage tank is the limiting factor due to its smaller volume, the tanks will have to be emptied once the copper (II) storage tank contains 5000 liters. In other words, the installation will run every 21 days.

The company operates 250 days per year, so the copper reduction process will run 11 times per year. Every operation time will be based on an 8 hours day of continuous operation. The number of operators needed for the plant based on experience with similar processes will be one. This operator will do two shifts of four hours per operation day.

3.3.2. Location

The copper (II) waste stream producer -company A, and the starch-waste stream supplier -company B, are located in the south of Holland within the distance of 80 km from each other. This location is quite strategic in terms of transportation. The installation of the process can be located in company A or in company B. The amount of starch stream needed ( 61 ton per annum) is almost the same as the amount of copper (II) stream ( 66 ton per annum). So, there is no savings due to transport whether the installation is situated in company A or B. Nevertheless, the cost of transporting copper (II) waste will have a higher value. This value reflects the risks including spills of transporting a toxic waste. Hence, by treating the waste at company A the danger of polluting the environment by eliminating off-site shipments of toxic waste will be reduced.

Consequently, the installation will be situated in company A. Hence, every year the starch should be delivered 12 times in 6 -ton trucks. The transportation costs of this stream are calculated knowing that a truck rides 8 km per liter diesel and the price of diesel is 0.73 euro/liter. These calculations are summarized in chapter 11.

The area where the installation would rise is in the basement of company A where currently all wastewater treatment processes are installed. This area has been inspected by the designers and was determined that it is suitable working environment because it fulfills safety requirements and other two technicians work there.

3.3.3. Battery Limit

Streams crossing the battery limit are shown in figure 2.3. A detailed description of all streams that are passing the battery limit can be found in Appendix C-i. With reference to the block scheme diagram of figure 3.1, the major plant equipment may be identified as a reactor, a solid-liquid separator, a purifier and drier; two storage tanks: one for copper (II) containing waste and the other for starch containing waste, and a tank for sodium hydroxide solution.

The treatment of the acidic aqueous waste stream containing carbon particles occurs in a wastewater treatment facility (WWTP) existing outside the battery limit where the carbon is removed by micro filtration. Neutralization of the remaining waste will take place [21]. It is assumed that the existing waste treatment facility can handle the additional load [3]. A process water facility is also not included in the battery limit.

3.3.4. Construction materials

The materials for the reactor were chosen taking into consideration the acidity of the components and products, temperature, and pressure of the reaction. The pH in the reactor is 2 . Therefore acid-soluble materials such as iron cannot be used. It is also not possible to use amphoteric materials (aluminum, tin, zinc etc.) because they dissolve in both acidic and alkaline environments. Therefore, these materials are not suitable for the reactor. Metals such as copper, silver, platinum, rubidium, and titanium are not influenced by pH and can therefore used [17]. However, the precious metals will not be used because they are very expensive. That leaves the choice to rubidium and titanium. In addition, glass-lined vessels can be suitable alternatives.

The construction materials for the separation units will be chosen by considering the hardness of the copper particles containing stream that can cause erosion of the walls. In addition, the acidity of the copper-containing stream (pH=2)(\mathrm{pH}=2) is also important to consider.

3.3.5. Choice of Utilities

The utility that will be used in the process is steam. The possibility to apply heat integration in the installation is now being investigated by company A. However, steam is not available in company A; therefore, the designers will use electricity for the heaters, pumps, and motors needed in this process. The choice was also influence by the fact that the company generates its own electricity.

3.4. Economical Analysis

An economic plant life of 13 years from which one year was assigned for construction was assumed based on the criteria of Douglas [12].

3.4.1. Economic margin

The economic margin of this process can be calculated by subtracting the total value of feedstock’s and process chemicals from the total value of the product copper metal. The feedstocks are starch stream <stream 101>, copper (II) waste stream <stream 105> and the process chemical additionally used is NaOH30%\mathrm{NaOH} 30 \% wt solution <stream 109> (see Appendix E-ii).
The value of the both waste stream feed stocks is zero; nevertheless the transportation of the starch stream from company A to company B is a cost that should be considered. The total cost for feedstocks and chemicals has been done in detailed in chapter 11, table 11.6 and its value is 128.18 euro/year. The price of copper has been obtained from scrap companies in the area and quoted by company A to be 0.91euro/kg0.91 \mathrm{euro} / \mathrm{kg}. Therefore, the copper sales of 1.2 ton of cooper metal per year will give company A the total income of 1,920 euro per year. Hence, taking the values calculated previously will give an economic margin in euro of: (1,920−128,18)=1,791.82(1,920-128,18)=\mathbf{1 , 7 9 1 . 8 2} euro per annum
The economic margin calculated is not that high due to the small production capacity of this design ( =1.2=1.2 ton/year). Moreover, the margin will decrease when utilities are taken into account.

3.4.2. Maximum allowed investment

The maximum allowable investment is calculated by accumulating the economical margin over the expected lifetime of the plant. The value of economic margin is brought to its present value by compensating for an earning power of money of 10%10 \% (DCRFOF). This calculation followed Coulson and Richardson’s criteria [24] and is summarized in table 3.2 below.

Table 3.2. Maximum allowed investment

Total invest.
Disc Factor
Base year
1/(1+r2)r1 /\left(1+\mathrm{r}^{2}\right) \mathrm{r}
1/(1+r)2 N1 /(1+\mathrm{r})^{2} \mathrm{~N}
1/(1+r)2r1 /(1+\mathrm{r})^{\mathrm{2}} \mathrm{r}
1/(1+r)rN1 /(1+\mathrm{r})^{\mathrm{r}} \mathrm{N}
00

From table 3.2 the maximum allowed investment for this copper reduction plant was found to be 13,784.85\mathbf{1 3 , 7 8 4 . 8 5} euro.

Chapter 4. Thermodynamic properties and list of pure components

4.1. Decomposition of H2O2\mathrm{H}_{2} \mathrm{O}_{2}

Decomposition rate of H 2 O 2 into into oxygen and water, equation (4.1), increases with temperature, rough surfaces and contaminants, for example, Fe,Cu,Cr\mathrm{Fe}, \mathrm{Cu}, \mathrm{Cr}, or Mn ions up to levels below 1 ppm accelerate decomposition.[15]. In the Multibond stream copper (II) is present in the concentration of 20 g/L20 \mathrm{~g} / \mathrm{L} and it is originally at 45∘C45^{\circ} \mathrm{C}. Hence, it is realistic to assume that the initial H2O2\mathrm{H}_{2} \mathrm{O}_{2} present in the copper (II) stream decomposes during storing time of 20 days before it is being used in the process. The small amount of oxygen that will be formed from decomposition of H2O2\mathrm{H}_{2} \mathrm{O}_{2} is negligible and will be purged from the storage tank by means of a vent. Hence, the copper (II) stream that will be treated by this design will not contain any H2O2\mathrm{H}_{2} \mathrm{O}_{2} in it.

H2O2(g)→H2O(g)+12O2(g)−ΔH=25.24kcal molH_{2} O_{2(g)} \rightarrow H_{2} O_{(g)}+\frac{1}{2} O_{2(g)}-\Delta H=25.24 \frac{\mathrm{kcal}}{\mathrm{~mol}}

The use of nitrogen in the original process was eliminated as explained in chapter 2, section 2.2.3. In order to find the optimal pressure of the process a vapor-liquidequilibrium analysis is needed. A VLE of water with glucose at 12 bar performed by Aspen-plus will be used for the system.

Being aware that there are some impurities in this system mainly glucose, the mole fraction of water was calculated from the mass balance to be 0.98 . At this mole fraction, according to figure 4.2 the temperature of the stream can be raised up to 463∘K463^{\circ} \mathrm{K} or 190∘C190^{\circ} \mathrm{C} without having any vapor in the streams or reactor. Therefore, the optimal conditions for the process will be 185∘C185^{\circ} \mathrm{C} and 12 bar with a five degree possible deviation.

Figure 4.1. Boiling point or hydrogen peroxide versus concentration [15]

Figure 4.2. VLE for water with glucose.

4.2. Thermodynamic properties

The thermodynamic properties of all the components existing in this process were obtained and summarized in table 4.1. There will be some salts produced in this process. Consequently, the solubility of the rest of pertinent components and sodium sulphate are reported in table 4.2.

The heat capacity of copper (II) in the form of copper sulphate was not available in literature. In addition, no values for starch were obtained from literature as well as values for entropy, Gibbs energy and heat capacity for glucose, gluconic acid, HMF, and LaFa. Nevertheless, this data is not essential for our design because experimental data regarding starch decomposition was available.

Table 4.1. Thermodynamic properties for components in Copper Recovery Process [16]

Table 4.2. Solubility versus temperature [17]

Chapter 5. Process structure and description

The production of copper metal using waste-to-waste technology has been described in Chapter 2 in detail. Furthermore, a process has been already selected and block schemes have been made available. The details that have been left out about selected units operations and equipment will be done in this chapter.

5.1. Criteria and Selection

5.1.1. Storages

The location of the storage tanks will be in the basement of company A. This space is design for wastewater treatment and storage of chemicals of company A. The height of the basement is 3 meters.

Storage of Starch stream

Having decided to use the starch stream as one of the two feedstocks for the design will require a special storage for this feed. The reason being that starch precipitates very easily from solution, therefore an agitated tank will be used. A horizontal polyethylene (PE) tank is needed for this purpose.

Note: company A has a 6−m3PE6-\mathrm{m}^{3} \mathrm{PE} tank at disposal. Therefore, this tank will be modified into an agitated tank in order to lower the investment costs.

Storage of Copper II stream

The composition of this stream has already been mentioned in chapter 2. Due to its acid composition the stream has a pH of 1 . This should be taken into consideration when purchasing the storage tank.

Note: such a tank already exists at company A. Here the copper (II) stream is being stored in a 13−m313-\mathrm{m}^{3} Polyethylene high-density (PE-HD) tank at company A. This tank is located in a fireprotected area in the basement and is being emptied every 6 weeks in order to treat its contents at a wastewater treatment plant in Belgium.

Storage of sodium hydroxide

Sodium hydroxide solution was chosen for controlling the pH in the reactor in chapter 2. The storage for this solution should be designed taking into consideration the corrosive properties of NaOH solution specified in chapter 10.

Note: company A, already used this chemical for several of their processes. They store NaOH 30%30 \% wt in a 9−m39-\mathrm{m}^{3} PE-HD tank. This tank is located in a fire-protected area at the basement of the company.

5.1.2. Preheating

As mentioned in chapter 2, preheating of the two feedstocks will take place separately. At first the preheating was going to be done with steam. Unfortunately, the galvanic industry does not have any steam available. The alternatives of heating could be heating oil or electrical heating. Between these two the most economical will be electrical heating because the company produces its own electricity.

As the flow rate ( 24.2 L/min24.2 \mathrm{~L} / \mathrm{min} ) and the operation time (11 days per year) of the process are so small, and the company has no steam, electric heaters were chosen to heat both streams. The electrical heaters apply heat directly to the fluid to be heated with near 100%100 \% efficiency and maximum energy utilization, producing a rapid response to any temperature changes. Close, continuous, safer control of operating times and temperature is readily achieved.

Being aware that the electricity needed for this step can be large and therefore costly and moreover that the temperature of the reactor effluent is also at 185∘C185^{\circ} \mathrm{C}, it was decided to incorporate the concept of heat exchange into the design. The heat exchangers in this case will be between the reactor effluent and the two separate streams. This will make a total of two heat exchangers that will simultaneously cool the reactor effluent and heat the feedstocks before these enter the preheating units. The advantage of this technique is that less energy is needed to heat the streams at the preheating units and that the reactor effluent entering the separation unit will be at a lower temperature and therefore safer.

5.1.3. Reaction

For the reduction of copper (II) with a carbohydrate stream, a uniform particle size distribution and highly pure quality are desired for the copper particles to have a high market value. In order to obtain uniform particle size distribution, a very narrow residence time distribution in the reactor is necessary. This can be achieved in a batch reactor or a plug flow reactor. On the other hand, the plug flow reactor can yield a highly pure product. Table 5.1 compares the benefits and limitations of both reactors.

Table 5.1. Advantages and disadvantages of batch and plug flow reactors.

In this design, a plug flow reactor is preferred due to the following reasons:
i. A plug flow reactor is suitable for process control [8]. The reaction must be done at constant temperature, pressure, and pH .
ii. Hydrolysis of carbohydrates is optimized in a plug flow reactor [26].
iii. Smaller volume of the plug flow reactor (The system for recovery of copper will be installed in (an) already existing plant and there is potential space limitation. A plug flow reactor is suitable for this purpose.)

In real practice, ideal plug flow behavior is not achieved. It was suggested to apply a static mixer in the reactor in the form of helix by one of the owners [30]. The modeling of the Kenics static mixer that is very close to ideal plug flow was performed [30]. It was shown that formation of the copper metal particles occurs uniformly in the cross-section of the reactor and not at the walls, as it is the case when there is no mixer. Figures in Appendix E-i show the formation of the copper metal particles in the plug flow reactor with static helix mixer compared with one in the reactor without mixer. In addition, the accumulation of copper particles in the reactor can be avoided in a Kenics static mixer with the condition that the flow velocity is greater than or equal to the settling velocity of the copper particles. Energy consumption is also a very important consideration in choosing the type of equipment to be used. In a Kenics mixer, energy consumption is most economical [31]. The benefits of Kenics static mixers are further described in Appendix E-ii.

5.1.4. Separation

The reactor effluent contains mainly copper metal particles, carbon particles, and a large acidic waste stream. The product, copper particles, has to be separated from carbon and from the large wastewater at the same time. Because solid/solid/liquid separation is required the options between the equipment become narrower. Specifically, for this unit a centrifugal classifier or a hydrocyclone can be used. Centrifuges are more expensive due to the electricity needed for the process operation. The advantage of using a centrifugal classifier is the sharp separation of particles that can be obtained with this unit. On the other hand, a hydrocyclone is a simple, small space-consuming unit that not only concentrates the solids but also classifies and washes them. The only applicable disadvantage of the hydrocyclone in the design will be its susceptibility toward erosion due to copper abrasiveness towards its rigid walls. The inlet pressure of the flow is 11

bar, so no pump will be needed to raise the pressure of the hydrocyclone feed. Furthermore, the average size of copper particles is 100μ m100 \mu \mathrm{~m}, therefore these particles are big enough to be separated in the hydrocyclone. The advantages and disadvantages of the separation equipment options are summarized in the table 5.2.

Table 5.2. Choices for the separation unit

After reviewing the options, the hydrocyclone was chosen for this design.

5.1.5. Purification

This section will not be necessary because the hydrocyclone already took care of cleaning the product particles from carbon and waste-water.

5.1.6. Drying

The stream with the copper metal particles leaving the hydrocyclone will still be wet. Therefore, a drying unit is necessary. Because the production capacity of this plant is 1.2 ton per annum a simple drying unit such as a rotary disk vacuum filter will be sufficient. The only goal of this unit is to get rid of the water still present on the stream therefore the most economical unit was preferred. Other units such as the rotary drum filter, fluid beds, and belt filter were also investigated. Yet, they are more complicated units and more expensive.

5.2. Process Flow Scheme (PFS)

During the design the basic block scheme of the process has develop into a fully equipped Process Flow Scheme (PFS), Appendix E-iii. It represents the line-up of the various unit operations and their connection to process flows in a logical and clear way.

5.3. Batch Cycle diagram

Because the process is continuous no batch cycle diagram is necessary.

5.4. Process Stream Summary

The process stream calculations are described in chapter 7 and the process stream summary is shown in Appendix G-i.

5.5. Utilities

The summary of utilities is presented in Appendix E-iv.

5.6. Process Yield

The summary of the process yield is presented in Appendix E-v.

Chapter 6. Process Control

Process control is an essential aspect in any industrial installation. Good process control provides the desired quality of the product, helps to meet environmental constraints and avoids emergency situations.

Controllers can be used to keep temperature, pressure, flow rate, composition or liquid level in the optimum for the process range. Here the controllers used in the copper recovery process and their position is analyzed.

6.1. Pressure control (PC)

The reaction that obtains copper reduction in this design is performed under highpressure conditions. Pressure is increased to 12 bar by pumps P101, P102 and P103. Moreover the pressure is controlled by direct single loops regulating the power of the pumps.

6.2. Liquid control (LC)

No liquid control was used. It was decided that flow control and pressure control before the reactor is enough to prevent overflow. The potential cause of the overflow in the reactor, formation of two phases (vapor-liquid), is not possible in this process due to high-pressure operation (12 bar), which keeps the reaction components in the liquid phase.

6.3. Temperature control (TC)

The incoming copper and starch containing feed streams are preheated to optimum temperature of 185∘C185^{\circ} \mathrm{C}. Preheating is done by electricity in electric furnaces. Adjusting the amount of supplying electricity controls the optimum temperature of 185 oC . The addition of NaOH stream will cause heat loss of the two feedstocks; nevertheless, this stream is too small ( 1.63 kg/h)1.63 \mathrm{~kg} / \mathrm{h}) compared to the reaction volume. Hence, it will not influence the temperature in the reactor and preheating of this stream is unnecessary.

The effluent of the reactor has a high temperature. Feed-effluent exchange loops are applied to the starch containing feed stream first and then to the copper (II)-containing stream in order to take advantage of this temperature and lower utility costs.

6.4. Flow rate control (FC)

Feeds will be supplied from the storage tanks. The flow controllers are necessary. The flow rate controllers are applied after the pumps P101, P102 and P103.

6.5. pH control (pHC)

The optimum pH in the reactor is 2 . This value is going to vary due to the hydrolysis of the carbohydrate (starch) that produces protons. Due to these pH variations, enough amount of NaOH30%wt\mathrm{NaOH} 30 \% \mathrm{wt} solution will be added to the reactor. Furthermore in order to add a pH controller to the system, measurements will be done at the copper (II) waste stream feedstock with pH=1\mathrm{pH}=1. This control consists of a single loop controller that regulates the flow of NaOH30%wt\mathrm{NaOH} 30 \% \mathrm{wt} solution added to the reactor depending on the fluctuations of the pH at the feedstock stream.

Chapter 7. Process Stream Summary, Mass Balance, and Heat Balance

Mass and heat balances are essential tools for this plant. The law of mass and energy conservation applies to this plant at all times. This chapter is created for this reason. In it the quality of the design will be demonstrated by providing the mass and heat balances.

7.1. Stream balance

The process stream summary, mass balance and heat balance can be found in Appendix G-i and G-ii respectively. All pertinent calculations for the stream summary and mass balance are detailed in Appendix G-iii. The stream notations can be found in the Process Flow Scheme in Appendix E-iii.

While making this summary the first problem encountered was that the molecular weight of starch is not available. Therefore, the amount of this component in kmol per annum could not be calculated. Also, the amount of water in the feed stream <101> was calculated knowing that the carbohydrate feed stream is 30 g/L30 \mathrm{~g} / \mathrm{L} starch in water and for the process an amount of 30 g of starch is needed in order to reduce a copper (II) stream with 20 g/L20 \mathrm{~g} / \mathrm{L} copper (II). The composition of the copper (II) stream, <105><105>, was specified in chapter 2 , section 2.1 .

The amount of NaOH(1)\mathrm{NaOH}_{(1)} needed to maintain the pH of the reactor to 2 was calculated to be 0.03 ton per annum of sodium hydroxide. After these calculations were performed it was suggested that due to the small amount of NaOH needed for the process, to buy NaOH solution would probably be more economical. An economical analysis was made in chapter 11,section 11.1 and the solution was chosen.

Three reactions are taken into consideration while accounting for the components present in the copper slurry stream <111>. First the reduction of copper was taken into consideration. This reaction detailed in section 2.2 has the products: copper metal, gluconic acid, and protons. These compounds are found in stream <111⟩<111\rangle in quantities of 1.178ton/yr,1.455ton/yr1.178 \mathrm{ton} / \mathrm{yr}, 1.455 \mathrm{ton} / \mathrm{yr} and 0.019ton/yr0.019 \mathrm{ton} / \mathrm{yr} respectively. The unreduced copper (II) present in stream <111⟩<111\rangle is 0.012 ton per annum.

The second reaction considered is the degradation of the excess starch. Having calculated that 72%72 \% of starch needs to become glucose so a reduction of 99%99 \% can be achieved, leaves 28%28 \% of starch for degradation. Experimentally it was calculated that 15−20%15-20 \% of the starch will not degrade at all, the rest will become HMF and LaFa. The amount of this compounds in stream <111⟩<111\rangle were found by taking a residence time of 30 minutes and using figure 2.2. From figure 2.2 the specific concentrations for these compounds were 0.2 g/L0.2 \mathrm{~g} / \mathrm{L} of HMF, or 0.012ton/yr0.012 \mathrm{ton} / \mathrm{yr} and 0.8 g/LLaFa0.8 \mathrm{~g} / \mathrm{L} \mathrm{LaFa} or 0.048 tons per annum. Additionally, the concentration of glucose was found experimentally to be 4.0 g/L4.0 \mathrm{~g} / \mathrm{L} in stream <111><111> or 0.238 tons per annum

Finally, a third reaction was modeled for this process summary. This reaction is the pH controlling reaction. This reaction produces sodium sulphate and water, 0.058 tons/yr and

0.015 tons/yr respectively, while consuming all the NaOH added and an equimolar amount of H2SO4\mathrm{H}_{2} \mathrm{SO}_{4}. The excess amount of H2SO4\mathrm{H}_{2} \mathrm{SO}_{4} present in stream <111><111> was found to be 5.613 ton per annum.

7.2. Heat Balances

In order to find the overall heat balance of the process two sections are relevant. The first section is the heat exchangers and the second is the preheating section.

7.2.1. Heat Exchanger E101 and E1012

The optimal reaction conditions were determined to be 12 bar and 185∘C185^{\circ} \mathrm{C} in Chapter 4. Due to this, the reactor effluent stream <111><111> will be at 185∘C185^{\circ} \mathrm{C} as well. This hot stream was used in designing two heat exchangers that will increase the temperature of both streams <102><102> and <106><106> before entering the preheating units.

The heat duty of each heat exchanger was obtained with Aspen plus. The temperature increase in E101 for stream <103⟩<103\rangle was determined to be from ambient temperature to 171∘C171^{\circ} \mathrm{C} for the starch stream with a heat duty of 115.87 KW . The temperature increase of stream <107⟩<107\rangle that contains copper (II) in E102 was from room temperature to 41∘C41^{\circ} \mathrm{C} and the heat duty was 12.42 KW .

Another advantage of using these heat exchangers is that the stream entering the separation unit stream <113⟩<113\rangle is also cooled down to 24∘C24^{\circ} \mathrm{C}.

7.2.2. Preheating stream in F101 and F102

In this section of the design both the starch waste stream <103⟩<103\rangle and the copper (II) waste stream <107⟩<107\rangle are preheated separately. The starch stream is heated in the preheating unit from 171∘C171^{\circ} \mathrm{C} to 185∘C185^{\circ} \mathrm{C}. This stream is mainly water and starch. Water is the component with the lowest boiling point (100∘C)\left(100^{\circ} \mathrm{C}\right) and would be in the gas phase at the preheating temperature. Therefore, the preheating will take place under 12 bar that is the saturated steam pressure at 185∘C185^{\circ} \mathrm{C}. In this way the stream will be kept in the liquid phase. See chapter 4 , section 4.1 .

The copper (II) containing waste stream <105> first heated via heat exchanger E102 will be heated from 41∘C41^{\circ} \mathrm{C} to 185∘C185{ }^{\circ} \mathrm{C}. The original temperature of this stream is 45∘C45^{\circ} \mathrm{C}; nevertheless, because it is a small stream it will be accumulated in the existing 13−m313-\mathrm{m}^{3} tank in company A before processing it so it will cool to room temperature while in storage.

The calculation of the heat duty in each preheating section was done with Aspen Plus. The heat duty for heating the starch stream, F101, was found to be 13.66 KW and for heating the stream containing copper (II) in F102 was found to be 117.00 KW .

Chapter 8. Process and Equipment Design

The process block scheme has been developed to the Process Flow Sheet (PFS) in previous chapters. Calculations were developed in parallel from simple spreadsheet balance to advanced calculations for which specific application tools such as Aspen and MATCAD were used.
In this chapter the main design parameters of equipment chosen for this specific PFS is described. Also the equipment choice is given shortly. The more detailed information about choice of equipment can be found in chapter 5 of the present report. The detail calculations, final equipment summary and specification sheets are represented in Appendix H.

8.1. Agitated storage tank T101

Starch feed stock will be kept in the agitated storage tank T101. Agitation is needed because of the precipitation tendency of starch. The calculation of the agitated storage tank T101 is given in Appendix H-i. The results of the calculation are summarized in the table 8.1.

Table 8.1. Design parameters of agitated storage tank T101

8.2. Storage tanks T102 and T103

Copper containing solution to be processed and sodium hydroxide will be kept in the storage tanks T102 and T103 respectively. These tanks were not designed because they already exist at company A. The dimensions and materials of these tanks are summarized in the table 8.2.

Table 8.2. Data for storage tanks T102 and T103

8.3. Heat exchangers E101 and E102

The feed streams are preheated before entering the electric heaters by integration with the reactor effluent stream via two heat exchangers (E101 and E102). According to the flow scheme the reactor effluent is first combined with the starch-containing stream in E101. Then it flows to E102 where it preheats the copper (II)-containing stream. Application of such feed-effluent heat exchangers decrease the heat duty needed from electric heaters. The calculation of the heat exchangers was done with the aid of Aspen plus. The design parameters are summarized in table 8.3.

Table 8.3. Design parameters of heat exchangers E101 and E102

8.4. Electric heaters F101 and F102

Electric heating was chosen to preheat the feed streams. The design of the electric heaters is detailed in Appendix H-ii. The summary of the main parameters of the heaters is given in table 8.4.

Table 8.4. Design parameters of electric heaters F101 and F102

8.5. Reactor R101

A Kenics mixer is chosen as the reaction unit. The residence time distribution of the Kenics mixer closely approaches that of an ideal plug flow reactor. The reactor was modeled based on the equation of ideal plug flow reactor. The plug flow is expected to give higher recovery of copper metal particles. Also the quality of the copper particles is better in the plug flow reactor because the particle size distribution is very narrow. As described in chapter 5 the Kenics static mixer was used because it improves the uniformity of formed particles.

The design of the reactor R101 can be found in the Appendix H-iii. The results of the design are summarized in the table 8.5 .

Table 8.5. Design parameters of the plug flow reactor arranged in parallel, R101.

8.6. Hydrocyclone S101

The stream that leaves the reactor contains copper metal particles, some amount of carbon and acidic wastewater stream. The product, copper particles, has to be separated from carbon and water. Hydrocyclone was chosen as the equipment that will separate copper particles from liquid and simultaneously from carbon. Thus, no additional unit for purification is needed. Hence, there is a cost reduction.

The design of the hydrocyclone can be found in Appendix H-iv. Calculations were done in MATCAD based on the model described by Bradley [38]. The main characteristics of the hydrocyclone are summarized in table 8.6.

Table 8.6. Design parameters of the hydrocyclone

8.7. Rotary disk vacuum filter

Copper particles leaving the hydrocyclone contains 11 vol % of wastewater. It was decided to dry the copper particles in a rotary disk vacuum filter. This type of drying equipment was chosen because of its simplicity and because it is an appropriate device for drying small amounts of matter. In our case to amount of copper product to be dried is 1.2 tons per year.

The design of this equipment is described in Appendix H-v. Calculations were based on the example described in Perry’s handbook [17]. The main design parameters are given in table 8.7.

Table 8.7. Design parameters of rotary disk vacuum filter

Equipment summary and specifications sheets for all units are given in Appendix H-vi and H-vii.

8.8. Pumps P101, P102 and P103

The optimum pressure in the reactor is 11 bar. Therefore, pressure of the starch, copper (II), and NaOH feed streams has to be higher than 11 bar in order to let the streams flow inside the reactor. As a result, the pressure of the feedstocks is increased to 12 bar with the pumps P101, P102 and P103. Centrifugal pumps were chosen for pumps P101 and P102. When choosing pump P103, the small amount for NaOH solution used in the process (1.63 kg/h)(1.63 \mathrm{~kg} / \mathrm{h}) was taken into consideration. A centrifugal pump cannot be used to pump this stream since its capacity doesn’t allow dealing with small flow rates. A

positive displacement pump was chosen for this purpose. This pump can be applied for low flow rates.

The pumps specifications were obtained with Aspen. The results are shown in table 8.8.
Table 8.8. Design parameters of the pumps P101, P102 and P103

8.9. Pressure issues

The pressure needed in the reactor should not drop below 11 bar. Pumps that are installed upstream provide the pressure of 12 bar as previously explained. Pressure drop between the pumps and the reactor is negligible since the pumps are located close to the reactor (around 2 m ) resulting in a pressure drop of 0.131 bar and the pressure drop in each heat exchanger is also very small, 0.19 bar (see table 8.9). Calculations of the pressure drops can be found in Appendix H-viii. Consequently, the pressure at the entrance of the reactor will be considered to be 12 bar.

Table 8.9. Pressure drop between pumps and reactor

Pressure drop in the reactor was calculated to be very low 0.0035 bar. Hence, the reactor effluent will be considered to be at 12 bar. In addition, the pressure drop between the reactor exit and the hydrocyclone was calculated to be 1.04 bar taking into account heat exchangers and length of pipeline. As a result the stream entering the hydrocyclone has a pressure of 10.96 bar rounded off to 11 bar.

Chapter 9. Waste treatment

The aqueous waste stream from the copper recovery process contains 96.55mg/l96.55 \mathrm{mg} / \mathrm{l} of copper (II) ions. This is approximately 30 times above the limit of 3mg/l3 \mathrm{mg} / \mathrm{l} [14] allowed for copper (II) ion discharge by environmental laws. In addition, the waste stream is highly acidic (ca. pH 2 ). Consequently, the waste stream needs further treatment.

Fortunately, the existing wastewater treatment facility has extra capacity [3] to handle this additional waste from the copper recovery process. The treatment process ensures the company meets environmental regulations with regard to heavy metal ions such as copper (II) ions. In summary, the waste treatment process involves a neutralization step, heavy metal ion removal with Iron (III) chloride and sodium sulphite, filtration, and ion exchange.

Chapter 10. Process Safety

In order to evaluate potential risk from the copper recovery process, we calculated the Dow Fire and Explosion Index for the Multi bond waste storage unit and the tubular reactor. The choice of units to be included in the safety analysis was based on size, operating conditions, and properties of materials being processed. For example, starch storage tank was deemed not to pose significant hazard and was therefore not included in safety analysis. The units chosen for safety analysis were, Multi bond storage tank, sodium hydroxide storage tank and the tubular reactor.

10.1. Dow Fire and Explosion Index Assessment

The Multi bond waste storage tank contains mathrmCu++\mathrm{Cu}^{++}mathrmCu++ions 2%2 \% (wt/wt), H2SO4\mathrm{H}_{2} \mathrm{SO}_{4} (aq) 9.5%9.5 \% (wt/wt), H2O2\mathrm{H}_{2} \mathrm{O}_{2} (aq) 1.17%1.17 \% (wt/wt), water 87.33%87.33 \% (wt/wt) and negligible amount of organic substances. The presence of hydrogen peroxide enhances the normal hazards associated with flammable liquids, vapors, and gases. This is due to the propensity of H2O2\mathrm{H}_{2} \mathrm{O}_{2} to generate large amounts of oxygen in combination with a significant heating effect as it decomposes. Even if a flammable material is below its flash point and therefore normally considered to be in a safe region, the heat from decomposition of H2O2\mathrm{H}_{2} \mathrm{O}_{2} (ca. 25Kcal/mole25 \mathrm{Kcal} / \mathrm{mole} H2O2@25∘C\mathrm{H}_{2} \mathrm{O}_{2} @ 25{ }^{\circ} \mathrm{C} ) could raise the material above its flash point and convert a safe system into an unsafe one. Even dilute hydrogen peroxide can create potential problems. For example, 3%H2O23 \% \mathrm{H}_{2} \mathrm{O}_{2} generates 10 volumes of oxygen for each volume of H2O2\mathrm{H}_{2} \mathrm{O}_{2} decomposed [40].

Oxygen enrichment in confined spaces is therefore a real possibility. In addition, hydrogen peroxide can dramatically accelerate chloride ion corrosion effects on aluminum and its alloys and stainless steel. Furthermore, hydrogen peroxide is a very reactive, extremely powerful oxidizer. It will oxidize virtually all-organic materials and it is this property, which presents the most dangerous potential hazard. Dow Fire and Explosion Index calculation [41] for the multi bond storage tank with respect to hydrogen peroxide gave 50.64 indicating a light degree of hazard.

The Dow Index value for the sodium hydroxide storage tank was 36.96 , which is lower still. The reader is referred to Appendix J-i for Dow Fire and Explosion Index computations.

In the reactor, we have organic materials in the form of starch, glucose (starch hydrolysis product), gluconic acid as well as degradation products such as levulinic and formic acids. It is therefore clear from the facts already mentioned that the presence of hydrogen peroxide in the reactor would pose the greatest risk. In designing our process however, we have assumed that virtually all the peroxide is removed (via decomposition) in the storage. For the justification of this assumption, see chapter 4 , of this report. Nevertheless, the Dow Index calculation for the reactor was performed with respect to hydrogen peroxide (worst case scenario). The value obtained was 95.04 , which still indicates a moderate degree of hazard.

In addition, a limited hazard and operability study (HAZOP) was carried out on Multi bond waste storage tank and the reactor to help identify potential hazards and improve process safety. The results of this study are shown in Appendix J-ii.

10.2. Conclusions

The Dow Index values calculated for the two potentially most hazardous process units indicated light to moderate degree of hazard. The HAZOP study revealed a number of potential hazards and suggestions for process improvement and safety. These measures were implemented in the design. In addition, for the general safety of the operators, safety glasses and acid resistant gloves are recommended.

Chapter 11. Economy

In order to find the economic potential of this installation a detailed economic analysis is needed. This chapter deals with the capacity of this plant to earn back its investment, including the required profit that this plant will have.

11.1 Investment

The main installation for the reduction of copper (II) will take place at company A. It was brought to the attention of the designers that the main product of the galvanic company is to make circuit boards and not to clean its used water therefore little attention would be given to this project if it came to be expensive. Hence, the main goal of the designers is to keep the investment as low as possible to make it attractive for company A.

First, because of the small amount of sodium hydroxide needed for the process ( 0.033 tons/year), the possibility of buying solution instead of pellets was investigated. Table 11.1 summarizes these calculations.

Table 11.1. Calculation of the price value of NaOH(I)\mathrm{NaOH}_{(\mathrm{I})} for the process

The quantities presented in the table 11.1. were obtained from the stream balance calculations. Buying the pre-made solution is slightly cheaper than using pellets. In addition, pellets need a mixing tank where they can be dissolved and this will cost both for the utilities that are needed and in the investment of a tank. Consequently, NaOH solution was preferred for this process.

Secondly, the storage tanks were analyzed. After inspection it was found that company A has a 13−m313-\mathrm{m}^{3} storage tank for copper (II) waste, a 9−m39-\mathrm{m}^{3} storage tank for 30%wtNaOH30 \% \mathrm{wt} \mathrm{NaOH} and a not-in-use 6−m36-\mathrm{m}^{3} storage tank. All the storage tanks have their own pumps and are in good conditions. An economic evaluation was made and summarized in table 11.2. From this table, the savings that could be obtained if these storage tanks were bought adds to (26,272-818.18) or 25,455 euro. Hence, the pre-existing three tanks at company A will be used for this plant.

Table 11.2. Economic saving for using the existing storage tanks at company A

Having decided to buy NaOH 30% wt solution and to use the existing storage tanks with pumps, the total investment needed for this design can be assessed. For this evaluation, the fixed and working capital of this plant are needed.

Calculating Fixed and Working Capital:

The direct Capital costs were found using Lang’s method. For this the Purchased Equipment Cost (PCE) summary detailed in Appendix L-i, and table 6.1 from Coulson and Richardson’s [24] was used and summarized in table 11.3 below.

Table 11.3. Direct Costs

The indirect costs were taken to be in the order of 30 to 50%50 \% of the direct capital costs so the indirect costs will vary from 49,231 to 82,051 euro.

The Fixed Capital Costs according to Lang’s methods can be obtained as follows:
Table 11.4. Indirect Costs and Fixed Capital Costs in 1992

The total fixed capital in 2001 would be 172,308 euro. If the inflation is 7%7 \% per year and it takes one year to build the plant, the total fixed capital costs will be 184,370 euro.

The fixed capital is the total cost of the plant necessary for start-up. Nevertheless additional investment is needed to start and operate the plant until profit is earned, denominated working capital. If the fixed capital costs are taken as 80%80 \% of the total

investment costs, of which 14%14 \% for license costs and 6%6 \% for working capital, the total investment required by this plant is found to be 215,384 euro as shown in table 11.5.

Table 11.5. Total investment costs, license costs and working capital costs

11.2. Production Costs

For calculating the production cost of the copper reduction plant the approximation by Coulson and Richardson was taken as main reference. Furthermore, the license costs was set to zero in this analysis.

Calculation of raw material costs:
Table 11.6. Cost for Raw materials

Calculation of Utilities

The utilities needed for this process are summarized in Appendix E-iv. The cost of these utilities is summarized in table 11.7.

Table 11.7. Costs of Utilities

*Price of electricity based on the fact that company A makes their own electricity

Calculation of Operating Labor:

Based on experience with similar processes in company A, the plant requires 1 operator per day. This operator will be expected to work two shifts of four-hours each. The operation time of the plant is 11 days a year. Therefore the plant needs 1 operator in order to operate yearly. Because each operator costs 45,455 euro, the operating labor will be 1∗45,455=45,4551 * 45,455=\mathbf{4 5 , 4 5 5} euro.

Calculation of total production costs
Table 11.8. Total Production Costs

The production cost found above is 114 euro per kg of copper metal produced. This price is too high compared to the expected market value of 0.91 euro per kg of copper produced. The annual production costs adds up to136,685 euro. In conclusion this plant will not give an economic profit if run at a production rate of 1.2 ton per annum.

11.3. Cash Flow, Economic Criteria, Cost Review, Sensitivities, and Negative Cash Flows

Calculation of the NCF

Net Cash Flow (NCF) from Gross Income and Production Costs defined as the difference between the earnings and the expenditure at any moment when the plant is operating.
(prod. price - production cost)* production rate ==
(0.91(0.91 euro /kg−114/ \mathrm{kg}-114 euro /kg)×(1200 kg)=−135,708/ \mathrm{kg}) \times(1200 \mathrm{~kg})=-135,708 euro
The negative value for the Net Cash Flow complicates the economical analysis. However, the analysis will be pursued with the real values.

Cash Flow Diagram

In order to plot this diagram, the following values are needed and some assumptions were taken. These are summarized in table 11.9. It was assumed that the license costs are zero for the plotting of this diagram. Having a negative NCF means that there is no profit for this company therefore the plot is expected to lye in the negative cumulative cash flow.

Figure 11.1. Cash-Flow Diagram for the copper reduction plant

Table 11.9. Values and assumptions taken for constructing a cash flow diagram

As expected figure 11.1 represents the cash flow diagrams of a non-profit plant. Throughout the life of the plant, it is expected to lose money because there is no positive net cash flow in this plant. The life of the project was chosen as 13 years, from where 1 year is assumed for construction, and 12 years of production.

Calculating Rate of Return (ROR)

Calculating ROR using Coulson and Richardson approach and using points A, B, C, D, E and F found in the Cash Flow Diagram above will be as follows:

ROR == (cumulative net cash flow at end of project/life of project*original investment) * 100%100 \%
Where:
cumulative income =F−C=−1,738,205−(−382.564)=−1,355,645=\mathrm{F}-\mathrm{C}=-1,738,205-(-382.564)=-1,355,645 euro
Investment =C=−382,564=\mathrm{C}=-382,564 euro
life of project =13=13 years
Therefore ROR =1,355,645/(13∗−382,564)∗100=0.003=1,355,645 /(13^{*}-382,564) * 100=\mathbf{0 . 0 0 3}
Calculating Pay Out (Back) Time (POT)
The POT from the total investment or break-even point is denoted as the point D in figure 11.1. The copper reduction plant would never have a break-even point because it doesn’t earn any profit.

Calculation of Discounted Cash-flow rate of return (DCFRR), Net Future Value (NFV) and Net Present Value (NPV) at 8% interest

The Net future value, NFV, is equal to the NCF and has three different values depending on the life of the project, like shown below. Finally the total NPV of the project can be calculated as:
Total NPV =∑n=1n=αNFW(1+r)n=\sum_{n=1}^{n=\alpha} \frac{N F W}{(1+r)^{n}}
Where:

NFW == NCF of the respective year ( n )
0−120-12 years NCF=−135,818\mathrm{NCF}=-135,818 euro
12-13 years NCF= working capital or 13,827 euro
and t=\mathrm{t}= life of the project in this case 13 years
Therefore the total NPV =1,018,451=1,018,451 euro or 1 million euro

11.4 Company’s savings

Due to that this design is not economically feasible by itself, then the economics of this design are going to be evaluated in terms of how much money can the company save by adding this installation. If this installation is added, then the company will be able to treat its wastes on site instead of sending it to Belgium.

Table 11.10 Savings for Company A.

Unfortunately, the company will not save any money with this installation at the present production capacity. Instead, it will spend an extra 48,020.88euro per year as can be seen in table 11.10 .

Chapter 12. Conclusions and recommendations

The aim of this project was to design a hydrothermal process for copper recovery from one of the five waste streams containing copper (II) ions in company A. Currently; this waste is transported to Belgium for treatment. Company A is interested in the hydrothermal process as a viable (less costly) alternative to the present treatment. The company whose chief business is making circuit board’s emphasized that they will not consider this process unless it is less costly and safe.

Economics

During the design, we found, see chapter 11, that the hydrothermal process as designed did not satisfy Company A’s requirement of a less costly option. The main reasons for the negative economic return were the unavoidable small capacity of the copper recovery process and the low price of copper metal.

The problem of capacity can be improved to some extent if all the waste streams are considered for hydrothermal treatment. As already mentioned in chapter 2, Company A produces five waste streams containing copper ions. Four of these streams are treated by Electro winning. The remaining stream (Multibond), which is the subject of this design, cannot be treated by electro winning due to presence of organics. However, it is possible to treat the combined streams by the new process. Apart from the increase in capacity that would result from combining waste streams, the company would gain additional advantage of having one waste treatment process instead of two. It is also possible to consider treatment of copper containing wastes from other sources in the region.

In view of (i) the growing use of copper metal, (ii) the increasing awareness of the need to conserve the earth’s limited resources and (iii) the stricter laws protecting the environment from heavy metal ions such as copper, it is expected that (i) the price of copper metal will continue to rise (ii) the amount of wastes containing of copper (II) ion will increase and (iii) the demand for processes which can clean and recover valuable metals such as copper from aqueous waste streams will also continue to increase. We therefore expect that the hydrothermal copper recovery process will become economically attractive in the near future, as shown in the following analysis and summarized in table 12.1.

Table 12.1 shows that applying the designed hydrothermal method of copper recovery will cost company A 48,000 euro per year more than if the company sends their waste for treatment in Belgium. Despite this fact, the copper recovery process can bring a profit to company A if this company operates in the future or works at its full capacity. In the cases of operating with full capacity the waste would increase by a factor of 5 as shown in the table 12.1. Consequently, the amount of copper recovered by means of the present design would increase and so will the earnings of it.

Within the scenario that the design operates in the future ( =10=10 years from now), the price received for the copper produced is assumed to be at least 10%10 \% higher than in the present,

as well as all costs, and that treating the waste will cost at least twice as much. The costs of company A that will increase are: transport, raw materials, operators, and utilities. The transport for starch will increase due to the fact that this stream will have to be delivered every day. The cost of raw material will increase because the amount of NaOH solution will increase. Also, an additional tank for this solution will be needed. The number of operators will augment and the total utilities of this plant will be higher as well.

Table 12.1. Savings brought to the company by the design

As it can be seen in table 12.1 the savings that this plant will bring to the company are only increasing over time reaching values of 175,994.18 euro. Therefore, even though the process is currently not profitable, company A will save money by treating their wastes on site.

Prices

During the project design some uncertainties regarding the price were faced. The price of the starch-containing waste stream was not provided clearly by company B. Although the representatives of this company indicated that the price of this feedstock is compared to zero, they are still discussing the exact value of it.

In addition, the price for the produced copper particles has not yet been formalized. Both the scrap companies as well as company A have tried to make an estimation for the pure copper metal recovered in this plant. Hence, for the analysis an average price value was taken to 2NLG/kg2 \mathrm{NLG} / \mathrm{kg} or 0.91euro/kg0.91 \mathrm{euro} / \mathrm{kg}.

For a more precise economic evaluation it is recommended that quoted prices are used for these commodities.

Heat effects

Lack of information is a hindrance to intensively investigating the heat effects of this particular process. One way to solve this problem was to perform further experimental studies. In this design, it was assumed that heat effect could be neglected. However, problems would be encountered when (i) the hydrogen peroxide decomposition is considered and (ii) when setting up the operation into large scale. It is essential to know the heat effect of the process because it is a determining factor on the mode of operation of the reactor.

Reaction kinetics

Several simplifications were made to design the reactor. One of the most critical issues was the determination of the kinetic reaction rate constant. In this design, isothermal operation was chosen. However, there is a question about the certainty of the method of determining the reaction rate constant for copper reduction. The batch experimental data, from which the constant was obtained, was not under isothermal conditions. It is recommended that determination of the rate constant should be done isothermally. The size of the reactor depends on the speed of the reaction.

Another important issue is the extent to which the different reactions influence the reduction of copper. The kinetics of the reactions involved was oversimplified. To mention, the hydrolysis of starch to glucose is a determining step on the degree to which copper is reduced by the oxidation of glucose. In addition, glucose degrades into other products such as HMF, levulinic acid and formic acid and may further decompose into carbon dioxide and carbon. In the design of the reactor, these degradation reactions were simply neglected when in fact; the degradation of glucose into other products decreases conversion. Degradation of glucose should be considered because it does decrease selectivity and might also provide extra electrons for copper reduction. The reason for neglecting the degradation of glucose is that its mechanism is not yet known. One way to elucidate the selectivity of the process is to have the reaction kinetic data. As of this moment, there is no specific data on selectivity. However, it was assumed that the selectivity could be enhanced through pH control. Sodium hydroxide addition for pH control also posed a problem. We could not determine the exact points along the reactor where sodium hydroxide could be introduced.

Other issues that need to be considered are scale up, mass and heat transfer.

Safety

Safety analysis of chapter 10 showed that the greatest potential hazard in the hydrothermal process could result from the presence of hydrogen peroxide. Nevertheless, it was assumed that all the peroxide present in the waste stream would decompose while in the storage tank. The decomposition rate increases with temperature and is also accelerated by heavy metal ions. Unfortunately, we did not find specific data on the rate of decomposition

List of Text Symbols and Abbreviations

Table Text symbols

Table Abbreviations

References

1. http://marketdata.copper.org/graphs/b97f.html

2. Van der Weijden, R. D., J. Mahabir, A. Abbadi, M.A. Reuter (2001). “Copper reduction from copper (II) sulphate solutions by reduction with carbohydrates”. Submitted to Hydrometallurgy, February 2001

3. Data obtained through personal communications with company A.

4. http://www.kinetico.com/industrl/electroc.htm

5. Hage, J. L. T., M. A. Reuter. R. D. Schuiling, and I. S. Ramtahalsing (1999). “Reduction of copper with cellulose in an autoclave: an alternative to hydrolysis”. Minerals Engineering, 12(4), 393-404

6. J.Wodka,W.A.Charewicz, T.Janicki (1999). “Pressure reduction of copper(II) from highly acidic solutions containing arsenic”. Hydrometallurgy, 52, 177-187.

7. http://rotapan.com/rcopper.htm

8. Van der Weijden, R. D., A. J. Albornoz, R. A. Penners, and M. A. Reuter (2001). “Combined processing of various metals and organic (waste) streams”.

9. Van der Weijden, R. D. Data obtained through personal communications.

10. www.allchem.com/products/price.html

11. P.L.J. Swinkels. Data obtained through personal communications.

12. Douglas, J.M. (1988). Conceptual Design of Chemical Process. Mc-Graw Hill.

13. Grievink, J. (2000). “Supplementary Notes to the Lectures on Process Systems Design” (Process Systems Engineering Section).

14. Reker M., M. Lenart and S. Hamsberger. “Treatment and waste recycling of copper CMP slurry waste streams to achieve environmental compliance for copper and suspended solids”. Semiconductor Fabtech, 8th 8^{\text {th }} edition.

15. http://www.h2o2.com/intro/properties/physical.html#10

16. Lide, 2001

17. Perry, R. H. and D. Green (1998). Perry’s Chemical Engineers’ Handbook, 7th 7^{\text {th }} ed. McGraw-Hill International Editions.

18. Chemiekaarten, 16th 16^{\text {th }} Edition, 2000 Samenwerkingsverband- Chemiekaarten (TNO Arbeid, VNCI).

19. Sax’s Dangerous Properties of Industrial Materials, R.J. Lewis, 8th 8^{\text {th }} edition, 1992.

20. Dutch association of cost engineers (DACE). Prijzenboekie 21 ed., 2000.

21. Joost van Laarhoven, contact of the company A. Data obtained through personal communications.

22. www.edie.net/news/Archive/4581/cfm

23. www.metalparices.com

24. Sinnott, R. K. (1999). Coulson and Richardson’s Chemical Engineering: Chemical Engineering Design, 3rd 3^{\text {rd }} ed., vol. 6, Butterworth-Heineman, U.K.

25. Song, S. K. and Y. Y. Lee (1984). “Acid hydrolysis of wood cellulose under low water conditions”. Biomass, 6, 93-100

26. Abatzoglou, N., P.G. Koeberle, E. Chornet (1990). " Dilute acid hydrolysis of lignocellulosics; an application to medium consistency suspensions of hardwoods using a plug flow reactor". The Canadian Chemical Engineering Journal, 68, 627−638627-638.

27. Bienkowski, P. R., M. R. Ladisch, R. Nayaran, G. T. Tsao, and R. Eckert (1987). “Correlation of glucose (dextrose) degradation at 90 to 190∘C190^{\circ} \mathrm{C} in 0.4 to 20%20 \% acid”. Chemical Engineering Communications, 51, 179-192.

28. Jandova, J., T. Stefanova, R. Niemczykova (2000). “Recovery of Cu-concentrates from galvanic copper sludges”. Hydrometallurgy, 57, 77-84.

29. Mambote, R. C. M., M. A. Reuter, P. Krijgsman, and R. D. Schuiling (2000). “Hydrothermal metallurgy: an overview of basic concepts and applications”. Minerals Engineering, 13(8-9), 803-822.

30. W.F.C.van Wageningen. Data obtained through personal communications.

31. Pahl, M.H., E. Muschelknautz (1982). “Static Mixers and their applications”, 22, No. 2, 197-205.

32. http://www.geocities.com/chemforum/pitrend.htm

33. http://www.chemineer.com/Brochures/Kenics Web.pdf

34. Cybulski, A., K. Werner (1986). “Static mixers-criteria for application and selection”, 26, No. 1, 171-179.

35. McKetta, John J. (1992). “Heat Transfer Design methods”, Marcel Dekker, Inc.

36. P.Joshi, K.D.P. Nigam, E. Bruce Nauman (1995). “The Kinetix static mixer: new data and proposed correlations”, Chem. Ing. Journ., 59, 265-271.

37. Hobbs, D.M., F.J. Muzzio (1998). “Optimization of a static mixer using dynamical systems techniques”, Chem. Ing. Science, 53, 3199-3213.

38. Bradley, D (1965). “The hydrocyclone”. Pergamon press.

39. McCabe, Warren, Smith Julian and Harriott Peter. “Unit operations of Chemical Engineering”, Sixth edition, McGraw Hill, 2001

40. http://www.ee.surrey.ac.uk/SSC/H2O2CONF/mjeff.htm

41. Dow’s Fire and Explosion Index Harzard Classification Guide, 7th 7^{\text {th }}, ed., 1994.

42. http://www.reviso.leg.state.mn.us

43. Hage, JLT. “Autoclave Reduction of Jarosites and Other Metal Sulfates”. No 169. 1999.

44. Coker, Kayode. “Modeling of Chemical Kinetics and Reactor Design”. Butterworth-Heinemann. 2001

45. http://www.latech.edu

46. Gerritsen, & van den Bleek,. (2000). “Supplementary Notes to the Lectures on Chemical Reactor Engineering” (CRE section).