Acidophilic strains for the valorization of metal bearing wastes

The present work deals with bioaugmentation strategies with acidophilic chemoautotrophic Fe/S-oxidising bacteria for the mobilization of metals from different solid wastes: end of life industrial catalysts, sediments contaminated with heavy metals, fluorescent powders coming from a cathode ray tube glass recycling process. The performed experiments were aimed at assessing the performance of bacteria for such different solid matrices, also focusing on the effect of solid concentration and of different substrata. The achieved results have evidenced that metal solubilisation results to be strongly influenced by the metal speciation and partitioning in the solid matrix. No biological effect was observed in Ni, Zn, As, Cr mobilisation from marine sediments (34%, 44%, 15%, 10% yields, respectively). On the other hand, for spent refinery catalysts (Ni, V, Mo extractions of 83, 90 and 40%, respectively) and fluorescent powders (Zn and Y extraction of 55% and 70%, respectively), the improvement in metal extraction observed in the presence of a microbial activity confirms the key role of Fe/S oxidizing bacteria and ferrous iron. A negative effect of solid concentration was in general observed on bioleaching performances, due to the toxicity of dissolved metals and/or to the solid organic component.