LEACHING OF A LOW-GRADE HEMATITIC LATERITE ORE USING FUNGI AND BIOLOGICALLY PRODUCED ACID METABOLITES

Heterotrophic microbial leaching of Greek nickeliferous laterites was investigated. A variety of microbial screening, adaptation and leaching techniques were used to determine microorganisms, media and optimum conditions for nickel and cobalt recoveries. Two bioleaching techniques were developed: (a) leaching in the presence of microorganisms and (b) chemical leaching at high temperature (95-degrees-C) with a solution consisted of the metabolic products obtained from the cultivation of fungus strains at 30-degrees-C in glucose and sucrose carbohydrate media. It was found that up to 55-60% of the nickel was extracted using the first technique (a) with fungi strains P2 (Penicillium sp.) and A3 (Aspergillus sp.) in almost 50 days. Losses of soluble nickel in the fungal biomass were found to be 3.5% and 10.8%, respectively. The cobalt recovery achieved was around 50%. Nickel recoveries obtained by the second technique (b) were in the range of 70-72%. Effectiveness of strains used was found to depend on their ability to produce hydroxycarboxylic acids, especially citric acid, and also other metabolites. Possibilities for future investigations are discussed.