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The development by bioleaching organisms of a tolerance to the toxicity of heavy metals was examined in a laboratory. The extracellular detoxification mechanisms of Aspergillus foetidus were determined, using a pulp containing 0.2-0.7% wt/v of weathered saprolitic nickel ore. The study used FTIR, CHNS and microscopy to confirm the participation of functional groups, and found that the primary detoxification method of A. foetidus was a change in surface chemistry. It also showed that a gradual acclimatisation was the best method for developing the tolerance to heavy metals. An un-acclimatised organism could dissolve 9% of the nickel after 25 days, while a tolerant one could dissolve 71% in the same period., The development by bioleaching organisms of a tolerance to the toxicity of heavy metals was examined in a laboratory. The extracellular detoxification mechanisms of Aspergillus foetidus were determined, using a pulp containing 0.2-0.7% wt/v of weathered saprolitic nickel ore. The study used FTIR, CHNS and microscopy to confirm the participation of functional groups, and found that the primary detoxification method of A. foetidus was a change in surface chemistry. It also showed that a gradual acclimatisation was the best method for developing the tolerance to heavy metals. An un-acclimatised organism could dissolve 9% of the nickel after 25 days, while a tolerant one could dissolve 71% in the same period.

The capability was studied of organisms and their metabolic acids for dissolving the metallic fractions from waste printed circuit boards. Factors considered included secondary reactions, solution pH, temperature and the nature of ligands in solutions or bio-acid constituents. The Cu-rich waste was leached for up to six hours in citric, malic, lactic, oxalic and sulphuric acids at 70-90 degrees with 1% w/v pulp density of waste while being shaken at 1 000 rpm. A comparison of Cu solubility in the various metabolic acids at pH 2.0 indicated that heterotrophic organisms and their organic acids are generally more effective in dissolving Cu metal to sulphuric acid generated by bacteria belonging to the genus Acidithiobacillus. At lower pH of 1.5 sulphuric acid provided greater dissolution. The results suggest that complexation of the organic acids predominate at higher pH and the acidification process at lower pH. There was generally very little difference in the activity of the organic acids at pH 2.0, with the exception of oxalic acid which promoted the precipitation of Cu. Increasing temperature reduced Cu solubility in sulphuric acid but Cu solubility increased with temperature in the presence of organic acids. The use of thermophilic heterotrophic fungi organisms may yield greater benefit in dissolving the metallic fractions of electronic wastes, in particular divalent metals. An overall Cu dissolution of 94% in citric acid at pH 1.7 showed the potential of bioleaching as a method for reprocessing the wastes., The capability was studied of organisms and their metabolic acids for dissolving the metallic fractions from waste printed circuit boards. Factors considered included secondary reactions, solution pH, temperature and the nature of ligands in solutions or bio-acid constituents. The Cu-rich waste was leached for up to six hours in citric, malic, lactic, oxalic and sulphuric acids at 70-90 degrees with 1% w/v pulp density of waste while being shaken at 1 000 rpm. A comparison of Cu solubility in the various metabolic acids at pH 2.0 indicated that heterotrophic organisms and their organic acids are generally more effective in dissolving Cu metal to sulphuric acid generated by bacteria belonging to the genus Acidithiobacillus. At lower pH of 1.5 sulphuric acid provided greater dissolution. The results suggest that complexation of the organic acids predominate at higher pH and the acidification process at lower pH. There was generally very little difference in the activity of the organic acids at pH 2.0, with the exception of oxalic acid which promoted the precipitation of Cu. Increasing temperature reduced Cu solubility in sulphuric acid but Cu solubility increased with temperature in the presence of organic acids. The use of thermophilic heterotrophic fungi organisms may yield greater benefit in dissolving the metallic fractions of electronic wastes, in particular divalent metals. An overall Cu dissolution of 94% in citric acid at pH 1.7 showed the potential of bioleaching as a method for reprocessing the wastes.

The leaching kinetics of Cu-rich electronic waste in citric acid were used to examine the potential for the ex-situ leaching of the waste with fungi organisms such as Aspergillus niger and their metabolic products. Waste with mean particle sizes of 350-720 micrometres was treated for 6- 24 hours at a liquid/solid ratio of 1g/ml, temperature of 50-90 degrees C, acid pH of 1.4-2.0 and shaking at 1 000 rpm. The leaching rate increased with increasing temperature. A kinetic model was developed to describe the leaching process based on an analysis of the kinetic data according to the particle shrinking model for liquid-solid systems. The kinetics were characterised by two stages, the first involving a generally slower rate and the later stage by a faster leaching rate. The difference in the kinetics could be attributed to the presence of copper oxide on the surface of the waste, which is relatively more stable compared to the metallic copper. The results show that bioleaching using metabolic products from heterotrophic organisms could be used to recover Cu from the waste., The leaching kinetics of Cu-rich electronic waste in citric acid were used to examine the potential for the ex-situ leaching of the waste with fungi organisms such as Aspergillus niger and their metabolic products. Waste with mean particle sizes of 350-720 micrometres was treated for 6- 24 hours at a liquid/solid ratio of 1g/ml, temperature of 50-90 degrees C, acid pH of 1.4-2.0 and shaking at 1 000 rpm. The leaching rate increased with increasing temperature. A kinetic model was developed to describe the leaching process based on an analysis of the kinetic data according to the particle shrinking model for liquid-solid systems. The kinetics were characterised by two stages, the first involving a generally slower rate and the later stage by a faster leaching rate. The difference in the kinetics could be attributed to the presence of copper oxide on the surface of the waste, which is relatively more stable compared to the metallic copper. The results show that bioleaching using metabolic products from heterotrophic organisms could be used to recover Cu from the waste.