Parametric study of leaching processes using a GUI developed in Matlab (original) (raw)
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Improving the Control Structure of a High Pressure Leaching Process
The main purpose of the base metal refinery (BMR) as operated by Lonmin at their Western Platinum Ltd BMR, is to remove base metals – such as copper and nickel – from a platinum group metal (PGM) containing matte. The leaching processes in which this is done pose several challenges to the control of the process. The most significant of these is the slow dynamics of the process, due to large process units, as well as the continuously changing composition of the first stage leach residue, which is not measured on-line. This is aggravated by the fact that the exact leaching kinetics (and therefore the effect of the disturbances) are not understood well fundamentally. The slow process dynamics mean that controllers cannot be tuned aggressively, resulting in slow control action. The large residence times and off-line composition analyses of major controlled variables also mean that the effects of operator set point changes are visible only the following day, often by a different shift of operators. Dorfling (2012) recently developed a fundamental dynamic model of the pressure leach process at Lonmin‟s BMR. This dynamic model incorporates 21 chemical reactions, as well as mass and energy balances, into a system of 217 differential equations. The model provides a simulation framework within which improved control strategies can be investigated. The primary aims of this study are twofold. The first is to validate the model for the purpose of the investigation and development of control structure improvements. This is done by comparing the model to plant data, and adapting it if necessary. The second aim to reconsider the current control philosophy to the extent that is allowed by the model‟s determined validity. The current plant control philosophy aims to maintain a PGM grade of 65%, while the copper in the solids products of the second and third leaching stages should be below 25% and 3.5% by mass, respectively. Two areas of particular concern in this process that have been raised by Lonmin are the control of the temperature of the first compartment and the addition of pure sulphuric acid to control the acid concentration in the second stage leach. Dynamic plant data were used to calibrate the model, which was migrated from its received MATLAB platform to Simulink, to assist with control development. Flow rates were imported from the data, with some data values adapted for this purpose, due to mass balance inconsistencies. The outputs from the calibrated model were compared with corresponding data values. The model was found to be suitable for the investigation and development of the control structures of pressure, temperatures and inventories (termed basic regulatory control) and the acid concentration and solids fraction in the preparation tanks (termed compositional regulatory control). It was, however, found to be inadequate for the investigation and development of supervisory control, since it does not provide accurate compositional results. The leaching of copper is especially under-predicted, with the predicted copper concentration in the second stage product being approximately 46% lower than data values. The basic and compositional regulatory control structures were investigated. For each of these a base case was developed which aimed to represent the relevant current control structure, assuming optimal tuning. The variable pairings for the basic regulatory control were reconsidered using a method proposed by Luyben and Luyben (1997), since this part of the process does not permit the generation of a relative gain array (RGA) for variable pairing. The resulting pairing corresponds with Lonmin‟s current practice. Considering the temperature control of compartment 1, it was found that the addition of feed-forward control to the feedback control of the level of the flash tank improves the temperature control. More specifically, during an evaluation where the temperature‟s set point is varied up to 1%, the IAE of the temperature of compartment 1 was decreased with 7.5% from the base case, without disturbing the flash tank. The addition of feed-forward control allows for more rapid control and more aggressive tuning of this temperature, removing the current limit on ratio between the flash recycle stream and the autoclave feed. The compositional control was investigated for the second stage leach only, due to insufficient flow rate and compositional information around the third stage preparation tank. Variable pairing showed that three additive streams are available for the preparation tanks of the second and third stage leach to control the acid concentration and solids fraction in those tanks. Focussing on the second stage, the aim was to determine whether the acid concentration in the flash tank can be successfully controlled without the addition of pure acid to the tank. With four streams available around the second stage preparation tank to control its mass/level, the acid concentration and solids fraction, three manipulated variables were derived from these streams. The resulting pairings were affirmed by an RGA. Control loops for the control of acid concentration and solids fraction in the flash tank were added as cascade controllers, using the preparation tank‟s control as secondary loops. The added compositional control was evaluated in two tests. The first of these entailed the adding of typical disturbances, being the flash recycle rate, the solids and water in the feed to the second stage preparation tank and the acid concentration in copper spent electrolyte. In the second test the control system was tested for tracking an acid concentration set point. It was found that the cascade structure controls the acid concentration in the flash tank less tightly than the base case (with an IAE that is 124% and 80.6% higher for the two tests), but that it decreases the variation of solids fraction (lowering the IAE with 40.8% with the first test) in the same tank and of the temperature in the first compartment (lowering the IAE with 73.6% in the second test). It is recommended that the relative effects of these three variables on leaching behaviour should be investigated with an improved model that is proven to accurately predict leaching reactions in the autoclave.
Mass transfer simulation of liquid-liquid extraction systems using an educational software
Contemporary Engineering Sciences, 2018
In order to improve the learning process about the unit operation of Liquid Extraction, it is presented a GUI in Matlab® for designing extracting systems with different types of contact, where the stages reach the equilibrium between both liquid phases. The program called ExtractING is an application of theoretical studies and material balances presented in highly relevant documents and popular academic books, which has a general procedure that initiates by introducing feed and solvent quantities with their respective compositions, and a raffinate exit condition for multistage equipment. It is necessary to introduce the ternary system (solute, dissolvent, diluent) and an operating temperature to calculate equilibrium conditions with Van Laar activity model equations. Material balances, multiple iterative routines, and equilibrium diagrams were used to calculate raffinate and extract conditions in all the stages as well as the minimum number of stages needed for the required separation allowing the user to get the approximate size and cost of the equipment, making this software a powerful academic tool. With the program, it was compared the maximum separation for specified conditions between counter-current and crosscurrent equipment, the separation percentage behavior with an increasing feed quantity, and the separation behavior with variations of temperature.
EXTRACTION xtraction is a process whereby a mixture of several substances in the liquid phase is at least partially separated upon addition of a liquid solvent in which E the original substances have different solubilities. When some of the original substances are solids, the process is called leaching. In a sense, the role of solvent in extraction is analogous to the role of enthalpy in distillation. The solvent-rich phase is called the extract, and the solvent-poor phase is called the raffinate. A high degree of separation may be achieved with several extraction stages in series, particularly in countercurrent flow. crystallization, or adsorption sometimes are equally possible. Differences in solubility, and hence of separability by extraction, are associated with differences in chemical structure, whereas differences in vapor pressure are the basis of separation by distillation. Extraction often is effective at near-ambient temperatures, a valuable feature in the separation of thermally unstable natural mixtures or pharmaceutical substances such as penicillin. The simplest separation by extraction involves two substances and a solvent. Equilibria in such cases are represented conveniently on triangular diagrams, either equilateral or right-angled, as for example on Figures 14.1 and 14.2. Equivalent representations on rectangular coordinates also are shown. Equilibria between any number of substances are representable in terms of activity coefficient correlations such as the UNlQUAC or NRTL. In theory, these correlations involve only parameters that are derivable from measurements on binary mixtures, but in practice the resulting accuracy may be poor and some multicomponent equilibrium measurements also should be used to find the parameters. Finding the parameters of these equations is a complex enough operation to require the use of a computer. An extensive compilation of equilibrium diagrams and UNlQUAC and NRTL parameters is that of Sorensen and Ark (1979-1980). Extensive bibliographies have been compiled by Wisniak and Tamir (1 980-198 1). The highest degree of separation with a minimum of Processes of separation by extraction, distillation, On a ternary equilibrium diagram like that of Figure 14.1, the limits of mutual solubilities are marked by the binodal curve and the compositions of phases in equilibrium by tielines. The region within the dome is two-phase and that outside is one-phase. The most common systems are those with one pair (Type I, Fig. 14.1) and two pairs (Type 11, Fig. 14.4) of partially miscible substances. For instance, of the approximately lo00 sets of data collected and analyzed by Sorensen and Arlt (1979), 75% are Type I and 20% are Type 11. The remaining small percentage of systems exhibit a considerable variety of behaviors, a few of which appear in Figure 14.4. As some of these examples show, the effect of temperature on phase behavior of liquids often is very pronounced. Both equilateral and right triangular diagrams have the property that the compositions of mixtures of all proportions of two mixtures appear on the straight line connecting the original solvent is attained with a series of countercurrent stages. Such an assembly of mixing and separating equipment is represented in Figure 14.3(a). and more schematically in Figure 14.3(b). In the laboratory, the performance of a continuous countercurrent extractor can be simulated with a series of batch operations in separatov funnels, as in Figure 14.3(c). As the number of operations increases horizontally, the terminal concentrations E, and R3 approach asymptotically those obtained in continuous equipment. Various kinds of more sophisticated continuous equipment also are widely used in laboratories; some are described by Lo et a/. (1983, pp, 497-506). Laboratory work is of particular importance for complex mixtures whose equilibrium relations are not known and for which stage requirements cannot be calculated. In mixer-separators the contact times can be made long enough for any desired approach to equilibrium, but 80-90% efficiencies are economically justifiable. If five stages are required to duplicate the performance of four equilibrium stages, the stage efficiency is 80%. Since mixer-separator assemblies take much floor space, they usually are employed in batteries of at most four or five units. A large variety of more compact equipment is being used. The simplest in concept are various kinds of tower arrangements. The relations between their dimensions, the operating conditions, and the equivalent number of stages are the key information. Calculations of the relations between the input and output amounts and compositions and the number of extraction stages are based on material balances and equilibrium relations. Knowledge of efficiencies and capacities of the equipment then is applied to find its actual size and configuration. Since extraction processes usually are performed under adiabatic and isothermal conditions, in this respect the design problem is simpler than for thermal separations where enthalpy balances also are involved. On the other hand, the design is complicated by the fact that extraction is feasible only of nonideal liquid mixtures. Consequently, the activity coefficient behaviors of two liquid phases must be taken into account or direct equilibrium data must be available. mixtures. Moreover, the relative amounts of the original mixtures corresponding to an overall composition may be found from ratios of Line segments. Thus, on the figure of Example 14.2, the amounts of extract and raffinate corresponding to an overall composition M are in the ratio E , / R N = M R N / E , M. Experimental data on only 26 quaternary systems were found by Sorensen and Arlt (1979), and none of more complex systems, although a few scattered measurements do appear in the literature. Graphical representation of quaternary systems is possible but awkward, so that their behavior usually is analyzed with equations. To a limited degree of accuracy, the phase behavior of complex mixtures can be predicted from measurements on binary mixtures, and considerably better when some ternary measurements also are available. The data are correlated as activity coefficients by means of the UNIQUAC or NRTL equations. The basic principle of application is that at equilibrium the activity of each component is the same in both phases. In terms of activity coefficients this 459
Design and Fabrication of Multi-Purpose Mineral Leaching Equipment
2021
With much amount of money the nation had invested into the extractive sector of the economy, minerals are still mined and exported out of the country for beneficiation which results into much economic losses in the mining and extractive industries. The need to reduce the huge amount of losses expended on extracting valuable metals from ores by local miners and out springing cottage industries motivates this work. This report covers the design and construction of a laboratory size leaching equipment suitable for dissolution of clean pulverised minerals in acid and alkaline media via agitation and in-situ leaching techniques in single operation system. The dissolved metals are easily recovered from the solution by other techniques. The design and fabrication is based on the fundamentals of stoichiometric calculations and chemical reactions, engineering design drawings using AUTOCAD and INVENTOR softwares, material selection and safe environmental ethics. The equipment is produced from...
Development of a quick leaching test for monolithic materials by using factorial design
Talanta, 1998
A quick leaching test procedure for monolithic waste materials has been developed by a Nordic expert group using experimental factorial design. The Dutch quick leaching test proposal in which the wetting time of the test specimen is reduced by applying vacuum was chosen as a starting point. The influence of the following parameters were studied: vacuum, stirring, open or closed vessel, water renewal frequency, leachant quality and laboratory or batch differences. The study was performed with test specimens prepared from a cement stabilised soil containing As, Cr and Cu. The test specimens were immersed in water and the water was renewed at certain time intervals. The study clearly showed that the use of vacuum had a strong effect on the release rate and that the open vessel lowered the pH-values of the eluates due to uptake of carbon dioxide in the water. The results also indicate higher emissions when stirring was applied. The following test conditions are recommended: application of vacuum prior to testing, use of closed test vessel, use of stirring, a test time of 3 days with four water renewals after 15 min vacuum steps, and then after e.g. 2 h, 23 h and 3.2 days, use of demineralised water as leachant. The amount of water must be selected according to the size of the test specimen. A liquid to surface (L/A) ratio of 5-10 ml cm(-2) is recommended. All four eluates collected are filtered and analysed.
Minerals, 2015
Germanium recovery from coal fly ash by hydrometallurgical procedures was studied at the pilot scale (5 kg of fly ash/h). Results were used to design the equipment of a demonstration-sized plant (200 kg of fly ash/h). The process is based on hydrometallurgical operations: firstly a germanium extraction from fly ash by leaching and a consequent Ge separation from the other elements present in the solution by solvent extraction procedures. Based on the experimental results, mass balances and McCabe-Thiele diagrams were applied to determine the number of steps of the solvent extraction stage. Different arrangements have been studied and a countercurrent process with three steps in extraction and six steps in elution was defined. A residence time of 5 min was fixed in both the extraction and elution stages. Volumetric ratios in extraction and stripping were: aqueous phase/organic phase = 5 and organic phase/stripping phase = 5, so a concentration factor of 25 is achieved. Mixers and decanters were completely defined. The maximum extracted and eluted germanium was estimated and a global efficiency of 94% was achieved. The cost-effectiveness of the equipment was estimated using the Lang factors.
Hydrometallurgy, 2020
A generalized non-porous shrinking particle model (G NSPM) of leaching has been verified and used for numerical simulations. Unlike the commonly used "simple" non-porous shrinking particle model (S NSPM), the G NSPM assumes n−th order chemical reaction, the influence of the L/S ratio and non-ideal behaviour of the leach solution. The leaching of dead-burned magnesite with hydrochloric acid has been chosen to verify the proposed mathematical model, as the (apparent) reaction order for HCl, n, may be both positive and negative, depending on the HCl concentration. Comparison of the simulations with experiments revealed that the S NSPM does not reflect the qualitatively different leaching behaviour at positive and negative n, especially at near-to-stoichiometric HCl/MgO ratio. The G NSPM reflects the effect of n not only qualitatively, but also with acceptable accuracy. At the stoichiometric HCl/MgO ratio, the mean squared error of the predictions obtained using the S NSPM was 100-130 rel. % as compared to those provided by the G NSPM. The common effect of the reaction order, n, L/S ratio (represented by the reduced HCl/MgO molar ratio, ϕ) and non-ideal behaviour of the acid were studied in detail by means of numerical simulations. The values of parameters n and ϕ can alter the leaching behaviour qualitatively. In contrast, the activity coefficient of HCl only slightly modifies the shape of the kinetic curves, but does not change the overall picture. The error of the time for complete conversion of MgO calculated using the S NSPM can reach more than 100 rel. % for n = − 0.5 and even up to several hundred rel. % for n = 1, because the conversion vs. time curves predicted by the G NSPM are markedly skewed towards longer leaching times.
USING APLICATIVE SOFTWARE AND SOFTWARE TOOLS FOR THE PERFORMANCE OF LEACHING AND BIO-LEACHING
The refractory or low grade lead/zinc domestic ores in Republic of Macedonia are investigated by conventional separation technology or flotation separation. In the mean time, investigations are directed to the new possibilities of leaching by microorganisms – bioleaching. The paper is result of these technologies and investigations carried out for recovery of in the mentioned ores. Using Simplex EVOP and computer program Multisimplex performances are appropriate and most acceptable and excellent way for presentation of the leaching and bioleaching.