Browsing by Subject "Hydrometallurgy"
Now showing 1 - 6 of 6
Results Per Page
Sort Options
- ItemOpen AccessAn electrochemical reduction process for the recovery of copper powder from a refinery effluent stream(2014) Bezuidenhout, Chandon; Petersen, JochenIn recent years a significant amount of research has gone into the development of a feed pretreatment process for the concentrate refined at Anglo American Platinum's Precious Metals Refiners (PMR). Such a process has the potential to significantly simplify the downstream refining process and reduce the number of unit processes required for purification. One of the considered options involves a high temperature oxidative roast process followed by a high temperature hydrochlorination process to volatilise base metal chlorides and other impurities. The resulting precious group metal (PGM) concentrate is cleaner and thus requires significantly less process steps to final product. The off-gas from hydrochlorination contains predominantly silver, copper, nickel and iron. This off-gas undergoes a quench-scrub to condense the base metal chlorides. The quench-scrub liquor undergoes a dechlorination process with sulfuric acid to precipitate AgCl(s). The filtrate from this process then undergoes an electrochemical reduction process to recover copper metal concentrate. The objectives of this study were to: i. Determine the operating conditions for an electrochemical reduction process aimed at recovering copper as a copper powder from a sulfuric acid stream containing copper, nickel and iron. ii. Develop a conceptual flowsheet for a batch electrochemical process and estimate the capital cost and operating cost.
- ItemOpen AccessEvaluating the effect of alternative neutralising agent and seeding on the zinc recovery through the Zincor iron removal circuit(2016) Taggart, Diane; Petersen, JochenZincor's average zinc recovery was 90.29 % (for the period of 1 January 2009 to 30 September 2011), which was well below the industry standard of 96 %. Due to limitations in Zincor's iron removal technology, the maximum achievable recovery was 94 %. The zinc loss through the iron residue was the second biggest contributor to the overall zinc losses, so that there was much room for improvement. The calcine used for neutralisation in the Iron Removal Stage contained a portion of insoluble zinc ferrite. The insoluble zinc loss through the iron residue was associated with the presence of the insoluble zinc ferrite, as well as the phenomenon of coating of unleached neutralising agent by iron precipitate. The soluble zinc loss was a function of the dewatering characteristics of the precipitate. The work included the evaluation of alternative neutralising agents to supplement or replace calcine, as well as the implementation of a seed recycle. A review of literature found that the use of an alternative neutralising agent that contained little or no zinc could potentially reduce the insoluble portion of the zinc loss. Secondly, the presence of seed could potentially reduce both the soluble and insoluble zinc losses by promoting agglomeration growth and providing additional surface area for precipitation to occur (thereby reducing coating of zinc-rich neutralising agents). The laboratory work evaluated a number of alternative neutralising agents, but focused on the use of DRC oxide and limestone for neutralisation. These were evaluated separately and in combination, with and without a seed recycle.
- ItemRestrictedInvestigating heap leaching – the effect of feed iron concentration on bioleaching performance(Elsevier, 2010) van Hille, Robert P; van Zyl, Andries W; Spurr, Nicholas R L; Harrison, Susan T LThis paper describes an investigation into the effect of iron concentration in the leach solution on the bioleaching of a low grade copper ore, where chalcopyrite was the dominant copper sulphide. The concentration of dissolved iron is primarily controlled by pH and the relative proportion of ferric to ferrous iron, with significant jarosite precipitation occurring above pH ≈ 1.8 in a highly oxidised system. The solution pH may be increased by the dissolution of acid soluble gangue and when iron oxidation is significantly higher than sulphur oxidation. The study was approached using two experimental systems. In the former, the leach solution was recycled through an ore bed of low aspect (reactor height divided by diameter) ratio for a portion of the experiment. During the recycle phase, no acid was added to the system and acid consumption by gangue material led to a pH increase (1.6–2.2). The resulting jarosite precipitation reduced soluble iron from 2.5 g/l to less than 250 mg/l. Copper recovery decreased, but not in proportion to the decrease in iron. This was partly attributed to adsorption on, or entrainment within, the jarosites. To study the effect of reduced iron concentration on leach performance under more controlled conditions, bioleaching was performed in packed bed column reactors with feed iron concentrations ranging from 5 g/l to 200 mg/l. Observations indicated an initial decreased rate of copper liberation with reduced iron concentration in the feed. The relationship between available Fe3+ concentration and copper liberation was not proportional. However, with time, the liberation of copper became independent of iron concentration in the percolation liquor. Further, the specific rate of copper liberation was consistently below the theoretical value on a basis of ferric iron concentration. The highest values of copper liberation were reported at the lowest iron concentrations. In summary, while increased iron concentration in solution may enhance the initial rate of leaching, mineral availability appears to dominate CuFeS2 leach kinetics through the majority of the leach. Furthermore, high iron concentrations in solution aggravate jarosite formation with concomitant retention of copper in the ore bed.
- ItemOpen AccessInvestigating the rheological behavior of Witbank coal water mixtures(2016) Owusu Gyebi, Prince; Deglon, DavidSouth Africa has large low-grade coal reserves. With the prospect of expanding its coal demands for exports and power generation, it is important that the beneficiation and transport of coal in the country are economical. The current mode of transporting coal has some drawbacks, which include inefficient rail infrastructure, long distances, and several environmental concerns related to air pollution, water pollution, and traffic risks. It is, therefore, important to investigate efficient means of coal transportation, which will also reduce environmental impacts. The transport of highly concentrated coal-water slurries through pipelines has attracted the attention of many researchers as an efficient and economical means of fine coal utilization. The primary objectives of this study are to investigate the importance of surface charge, solids concentration and particle size on the stability and rheological behaviour of Witbank coal. This work was carried out to arrive at a sounder discernment of the function of dispersion addition on coal-water mixtures rheology and stability.
- ItemRestrictedQuantification of growth and colonisation of low grade sulphidic ores by acidophilic chemoautotrophs using a novel experimental system(Elsevier, 2013) Govender, Elaine; Bryan, Christopher G; Harrison, Susan T LMicrobial colonisation of low grade sulphidic ores and subsequent growth in heap bioleaching systems has not been quantified rigorously. In this study, an experimental system simulating the sub-processes that occur at the agglomerate scale was used to quantify the colonisation, growth and propagation of Acidithiobacillus ferrooxidans in an unsaturated bed of crushed and agglomerated low grade chalcopyrite ore. The relative distribution of the microorganisms in the flowing leachate solution (‘PLS’), the stagnant interstitial liquid and weakly and strongly attached to the mineral surfaces was determined at various time points during the leach. There was a distinct difference in population dynamics in each of these discrete phases. The microbial cells present in the interstitial phase dominated the microbial population in the ore bed. Particularly, the microbial concentration in the free flowing PLS was found to be a poor representation of the ore-associated microbial population. The calculated growth rate of At. ferrooxidans in the PLS was unreasonably high when modelled as a continuous system, indicating that change in cell concentration in the PLS was dominated by transfer from the mineral ore associated population. However, the transfer rate was not correlated directly to changes in either the interstitial or attached population sizes. Therefore, unless transfer rates can be accounted for, PLS population dynamics do not accurately represent those in the column as a whole. Growth rates of microorganisms in the interstitial, weakly mineral-attached and strongly mineral-attached phases better predicted growth of At. ferrooxidans on the whole ore system owing to the dominance of the microbial location in these phases.
- ItemOpen AccessA study of the decay of acid cationic ion exchange resin(2016) Nesbitt, Allan Bernard; Petersen, JochenA study was undertaken on the decay of acid ion exchange resin from both a qualitative and quantitative perspective. The qualitative study concentrated on observing the impact on resin strength of varying electrolyte concentrations and varying di-vinyl benzene contents, during the loading phase. The phenomenon of osmotic shock in addition to resin cracking and swelling is clearly observed. A further qualitative study bore out the change in resin rigidity as the resin is artificially degraded through repeated loadings and regenerations performed by using a specially constructed device that cyclically loads and regenerates resin up to 1000 times in a three week period. Loss of resin rigidity was observed under these circumstances and was measured by means of observing changes in degree of swelling/contraction and changes in translucence. Quantitative study of the resin was limited to its characterisation through measurement of the equilibrium through the Mass-Action Law, capacity and resin kinetics. A study, of existing kinetic rigorous modelling methods and in particular the extensively published challenge of the multiple mechanism adsorption process, was undertaken. A rigorous model, that divorces the external and internal mass-transport parameters from the traditionally utilised lumped parameter, is proposed. All kinetic measurements were performed in a 1 litre closed circuit (finite system) consisting of a variable-pump, a five mL zero length column (ZLC) and a reservoir, allowing for the insertion of probes and sample extraction. An original method of model simulation for the purposes of fitting to kinetic data was developed and consists of determining the resin surface concentration from flux data assuming the applicability of Newton's Law of Cooling to the ionic flux through the external laminar layer. Simulation of flux inside the resin was achieved by assuming an internal homogeneous environment and the applicability of the Nernst-Plank equation that combines transport effects of both Fick's Law of Diffusion and inter-ion electrical forces to the flux of both the adsorbing and desorbing ions simultaneously, during the transient adsorption process.