Biosorption and biocrystallisation of gold

A review of the geochemistry and processing of gold and the present research and industrial applications of biological processes in metal recovery has been carried out.The field of biohydrometallurgy is discussed with particular emphasis on the biosorption and bioreduction of gold.Although biohydrometallurgical gold recovery is not practised industrially at present there is a great interest in this type of process both from a theoretical and process viewpoint.The research in this thesis considers mechanistic aspects of gold biohydrometallurgy and describes a process for recovery of gold from 0.1-10 mg/1 gold, acidic chloride, media.Preliminary investigations of the microorganisms Bacillus subtilis, Aspergillus niger, Spirulina platentis and Chlorella vulgaris indicated that all these organisms concentrate gold from aqueous gold(III) chloride.Comparisons of the influence of pH on adsorption and comparative adsorption isotherms showed that Chlorella gave the most efficient adsorption (loading in excess of 10% by weight) in the range pH 3-3.5 and Spirulina was also relatively efficient and more easily available than Chlorella.In the pH range 1-2, gold was selectively adsorbed in the presence of copper, zinc and iron.Similar results were obtained with platinum and palladium.