SOLUBILIZATION OF ZINC-OXIDE FROM FILTER DUST WITH PENICILLIUM-SIMPLICISSIMUM - BIOREACTOR LEACHING AND STOICHIOMETRY

Filter dusts from metal-processing industries contain valuable metals which should be recycled. Some disadvantages of conventional recycling methods can be avoided by applying biohydrometallurgical methods. Fungi are suitable for such processes because they are fairly resistant to heavy metals. Furthermore, leaching activity occurs in a pH range from 2 to 7. This is important because filter dusts generally raise the pH of the medium. Leaching of zinc from zinc oxide contained in filter dust was possible in a bioreactor (stirred tank reactor) especially constructed for this purpose. Zinc solutions of 0.41 M were obtained after 9 days of leaching. The zinc concentration was doubled compared to leaching experiments in shake-flask cultures. The solubilization of zinc oxide was caused by the action of protons originating from citric acid produced by the fungus. A further increase in solubilized zinc seemed difficult to achieve, because zinc and citric acid precipitated at the high zinc and citric acid concentrations present at the end of the leaching period. The lack of a cheap growth substrate for the fungus appeared to be the greatest handicap toward an application on an industrial scale.