Dolf Bruinsma - Academia.edu (original) (raw)

Papers by Dolf Bruinsma

Vapor recompression has become the standard heat pump technology in distillation and substantial ... more Vapor recompression has become the standard heat pump technology in distillation and substantial energy savings in the order of 50% have been achieved. Economic applications of VRC are limited to column temperature differences of about 30 C, which is only one fifth of the across the pinch columns in operation. 2 generation heat pump systems based on further heat integration and novel heat pump equipment do not only increase the potential energy savings but also extend the application range to columns with a larger temperature difference.

Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie, 2014

Vapor recompression has become the standard heat pump technology in distillation and substantial ... more Vapor recompression has become the standard heat pump technology in distillation and substantial energy savings in the order of 50% have been achieved. Economic applications of VRC are limited to column temperature differences of about 30 0 C, which is only one fifth of the across the pinch columns in operation. 2 nd generation heat pump systems based on further heat integration and novel heat pump equipment do not only increase the potential energy savings but also extend the application range to columns with a larger temperature difference.

Solvent Extraction and Ion Exchange

ABSTRACT The suitability of the organophosphorus-based extractants, DiOPA, Ionquest 801 and D2EHP... more ABSTRACT The suitability of the organophosphorus-based extractants, DiOPA, Ionquest 801 and D2EHPA was evaluated for the selective extraction of Zr and Hf from an (NH4)3Zr(Hf)F7 acidic solution using both dispersive and pertraction solvent extraction (SX). A stock solution of (NH4)3Zr(Hf)F7 was dissolved in either HCl or H2SO4 (0.1–8 M). The following extraction variables were investigated: type and concentration of the acidic solution, the contact time, and extractant to metal ratio. Subsequently, the stripping was investigated using (NH4)2CO3, CaCl2, H2SO4 and C2H2O4 in the concentration ranges of 0–2 M. During extraction, scrubbing and stripping using D2EHPA, CaCl2 and C2H2O4, the Zr purity was increased from 97.2% to 99.0%. When extracting from 4 M H2SO4 with 9 wt% D2EHPA, a Hf selectivity of 32% was observed where after stripping with C2H2O4 resulted in a 98.7% recovery of Zr. With 1.2 M CaCl2 as stripping liquor, almost no Hf and 75% Zr stripping was obtained. During the pertraction 72% Hf and 44% Zr extraction was achieved after 180 min when extracting with 9 wt% D2EHPA from 4 M H2SO4. Pertraction based stripping with 1.2 M C2H2O4 yielded 75% of both Zr and Hf, while stripping with 2 M CaCl2 resulted in 58% Hf stripped with almost no Zr stripping.

Hydrometallurgy, 2016

Abstract Commercial alkaline dissolution molybdenum-99 ( 99 Mo) producers are currently not recov... more Abstract Commercial alkaline dissolution molybdenum-99 ( 99 Mo) producers are currently not recovering enriched uranium (U) from 99 Mo production waste which has a unique actinide and fission product composition. During the development of a process to recover U from 99 Mo production residue, the suitability of non-dispersive membrane based solvent extraction (MBSX) for this process was investigated. The residue was dissolved in nitric acid (HNO 3 ) and extracted using tributyl phosphate (TBP). Acetohydroxamic acid (AHA) was added to the feed to prevent co-extraction of plutonium (Pu). Complete U extraction with MBSX was achieved at low U(VI) concentrations in the feed while more than one MBSX contacting step was required for high U(VI) concentrations. Ammonium carbonate ((NH 4 ) 2 CO 3 ) was investigated as an alternative stripping solution to traditionally used dilute HNO 3 . Almost complete U(VI) stripping (99%) from 7500 mg L − 1 U(VI) in the organic phase was obtained in a single contacting step with 0.5 M (NH 4 ) 2 CO 3 . Practically none of the characteristic fission products present in the 99 Mo production residue were extracted with AHA and also neither influencing U(VI) nor fission product extraction. The study has shown that MBSX was suitable for selective extraction (with AHA added) and stripping (0.5 M (NH 4 ) 2 CO 3 ) of U(VI) from a simulated 99 Mo production residue.

Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie

$Research paper thumbnail of Refining aluminium scrap by means of fractional crystallisation: Basic experimental investigations$

Recycling of aluminium is an effective way of enhancing the efficient use of energy and limiting ... more Recycling of aluminium is an effective way of enhancing the efficient use of energy and limiting the burden on the environment. Where cascade recycling is an established way of using reclaimed aluminium, closing the recycling chain is currently hampered by the unavailability of suitable techniques for refining contaminated scrap on an industrial scale. To overcome this problem, purification based on fractional crystallisation appears to be a promising option. This implies that the material is to be processed in the semi-solid state; that is, at a temperature where a solid and a liquid phase co-exist. In the current paper, it is shown that zone melting can serve as an indicative test for assessing the refining potential of fractional crystallisation processes, since they are both based on the same thermodynamic principle. Next, the results of zone-melting experiments are presented for some representative aluminium model alloys. The BPS-model (developed by Burton, Prim and Slichter) i...

Advanced Materials Research, Nov 5, 2014

The suitability of Liquid-liquid extraction (LLE) for the selective extraction of chemically simi... more The suitability of Liquid-liquid extraction (LLE) for the selective extraction of chemically similar tantalum (Ta) and niobium (Nb) mixtures was investigated by determining the influence of the acid concentration, extractant to metal mole ratio (E:M) as well as the ageing of the feed on extraction using the extractants, bis (2-ethylhexyl) phosphate (D2EHPA) and di-iso-octylphosphinic acid (PA). The system consisted of a solvent in varying E:M ratio’s, diluted in cyclohexane with 3% (v\v) 1-octanol added as modifier and a feed solution containing sulphuric acid and 100 ppm of the NH4TaF6 and NH4NbF6 complexes. Depending on the acid concentration, extraction percentages (%E) of up to 100% for Ta and 10-20% for Nb were attained. An initial lack of repeatability in experimental results was shown to be caused by variations in the age of the feed solution. The change in extraction trends expressed as a normalized %E for the aged feed solutions were nearly identical for both extractants when using 3, 6, 9 and 14mol/dm3 H2SO4. For the 3 and 6mol/dm3 solutions, the %E decreased significantly within the first 4-5 hours of ageing. At 9mol/dm3 the %E remained stable for feed ages up to 3.5 hours before declining, while the %E remained near constant at 14mol/dm3even after ageing for 24 hours.

Advanced Materials Research, 2014

Tantalum (Ta) and niobium (Nb) are two metals with similar chemical and physical properties and are found together in nature. One form of Ta is tantalum pentafluoride, which is stable in reducing environments, is corrosive resistant and stable under harsh conditions. Ta is currently used in nuclear reactors with a wide variety of uses and advantages. For these applications, pure Ta is needed to insure high value catalysts, contrary the higher the purity grade the more expensive the production of these high value catalysts. One way of ensuring an economic viable process for the production of high purity Ta, is to find a cost effective way to separate Ta from Nb. Ungerer et al. studied the separation of Ta and Nb, using safer chemicals and techniques for the environment in a solvent extraction (SX) process. During this study, separation was achieved in a sulphuric acid (H2SO4) medium with the extractants diiso-octyl phosphinic acid (PA) and di-(2-ethylhexyl) phosphoric acid (D2EHPA). The main obstacle during this study was the speciation of Ta and Nb, springing the question of why separation occurred with some extractants and not with the others. One method for determining the speciation of the compounds in a reaction mixture is by using computational techniques for molecular modelling. Several molecular modelling programs are available which uses various mathematical equations and approximations. Progress in computational chemistry over the last 20 years has made quantum mechanical calculations on large molecules, chemical systems as well as on macromolecule reactions possible. Calculations based on the density-functional theory (DFT) are now, not only used on light elements and small molecules, but also on metal complexes, heavy metals and especially on metal separation in SX. With these models at hand, SX processes were modelled within realistic margins to fit the experimental setup in a small scale laboratory. It is anticipated that the advances from this work will provide the possibility to determine, with good approximation, the outcome not only of the proposed Ta SX experiments, but also SX in general, before embarking on expensive, time consuming experiments and environmental unfriendly waste generation. In this paper molecular modelling was used to compile a partial energy profile for a proposed reaction mechanism for the reaction of tantalum- and niobium pentafluoride (TaF5, NbF5) with water to form tantalum- and niobium hydroxides. In the process, possible species that may form during the reaction were identified and evaluated.

Solvent Extraction and Ion Exchange

Membranes

In the Pyror process, electrowinning (EW) is used to recover acid and iron from spent leaching so... more In the Pyror process, electrowinning (EW) is used to recover acid and iron from spent leaching solutions (SLS), where a porous Terylene membrane acts as a separator between the cathode and anode. In this study, a novel anion exchange membrane (AEM)-based EW process is benchmarked against a process without and with a porous Terylene membrane by comparing the current efficiency, specific energy consumption (SEC), and sulfuric acid generation using an in-house constructed EW flow cell. Using an FAP-PK-130 commercial AEM, it was shown that the AEM-based process was more efficient than the traditional processes. Subsequently, 11 novel polybenzimidazole (PBI)-based blend AEMs were compared with the commercial AEM. The best performing novel AEM (BM-5), yielded a current efficiency of 95% at an SEC of 3.53 kWh/kg Fe, which is a 10% increase in current efficiency and a 0.72 kWh/kg Fe decrease in SEC when compared to the existing Pyror process. Furthermore, the use of the novel BM-5 AEM resul...

Journal of the Chemical Society, Chemical Communications, 1987

... SOC., Chem. Commun., 1984, 1596. A. Araya, TJ Barber, B. M. Lowe, DM Sinclair, and A. Varma, ... more ... SOC., Chem. Commun., 1984, 1596. A. Araya, TJ Barber, B. M. Lowe, DM Sinclair, and A. Varma, Zeolites, 1984, 4, 263. J . F. Cole and H. W. Kouwenhoven, ACS Advances in Chemistry Series, 1973, no. 121 (Molecular Sieves, 3rd International Confer-ence), p. 583. ...

Thermochimica Acta, 2010

The kinetic parameters of the reduction of barium sulphate to barium sulphide using carbon monoxi... more The kinetic parameters of the reduction of barium sulphate to barium sulphide using carbon monoxide fractions of 2.4-9.6% and temperatures of 850-1000 • C, using an isothermal thermogravimetric method, were obtained. This reaction has shown to be temperature and carbon monoxide concentration dependent. By variation in temperature, at constant CO fractions, an average activation energy of 149 (±10) kJ/mol was observed. By changing the CO fraction at constant temperature, it is suggested that the reduction reaction is first order in CO. An overall reaction rate equation is proposed.

$Research paper thumbnail of Refining aluminium scrap by means of fractional crystallisation: Basic experimental investigations$

Mixing and Crystallization, 2000

Science and Technology of Crystal Growth, 1995

Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie, 2014

Vapor recompression has become the standard heat pump technology in distillation and substantial ... more Vapor recompression has become the standard heat pump technology in distillation and substantial energy savings in the order of 50% have been achieved. Economic applications of VRC are limited to column temperature differences of about 30 0 C, which is only one fifth of the across the pinch columns in operation. 2 nd generation heat pump systems based on further heat integration and novel heat pump equipment do not only increase the potential energy savings but also extend the application range to columns with a larger temperature difference.

Solvent Extraction and Ion Exchange

Hydrometallurgy, 2016

Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie

$Research paper thumbnail of Refining aluminium scrap by means of fractional crystallisation: Basic experimental investigations$

Advanced Materials Research, Nov 5, 2014

Advanced Materials Research, 2014

Solvent Extraction and Ion Exchange

Membranes

Journal of the Chemical Society, Chemical Communications, 1987

Thermochimica Acta, 2010

$Research paper thumbnail of Refining aluminium scrap by means of fractional crystallisation: Basic experimental investigations$

Mixing and Crystallization, 2000

Science and Technology of Crystal Growth, 1995