Bioleaching of metals from ores and electronic scrap

Abstract

Low grade pyrite, sphalerite, complex Pb-Zn ore, nickel and copper containing sulphide ore’s bioleaching performances of pure un-adapted and metal ion-adapted cultures of different strains of Sulfobacillus thermosulfidooxidans as well as their consortium with acidophilic hetertrotrophs were analyzed in shake flasks studies. Maximum bioleaching potential was observed in case of mixed adapted consortium of Sulfobacillus thermosulfidooxidans strain RDB and Thermoplasma acidophilum. Orthogonal experimental array was designed for further co-optimization of process parameters for the enhancement of bioleaching efficiency. Then the technical feasibility to recover valuable metal ions from these ores by bioleaching process was tested in large columns at ambient temperature after optimization of process parameters in several small columns. Different pre-leaching and bioleaching strategies were adopted for maximum dissolution of metal ions from ores during column bioleaching studies. Changes in pH, redox potential, temperature, ferrous, ferric and total iron concentration, microbial growth and percent metals solubelization was observed periodically. Then bioleaching feasibility of electronic scrap by the selected moderately thermophilic strains of acidophilic chemolithotrophic and acidophilic heterotrophic bacteria was tested. These included Sulfobacillus thermosulfidooxidans of different strains, Thermoplasma acidophilum and an unidentified acidophilic heterotroph (code A1TSB). At scrap concentration of 10 g/L, a mixed consortium of the metal adapted cultures was able to leach more than 81 % of Ni, 89 % of Cu, 7 9 % of Al and 83 % of Zn. Then conical bubble reactor was fabricated locally and effect of hydraulic retention time on bioleaching potential was investigated and after that lab-scale columns with automated pH and temperature control were fabricated locally and bioleaching studies of electronic scrap in a bubble reactor was carried out. In case of column bioleaching studies the tolerance of bacterial cultures to mixed metal ions (Ag + , Al 3+ , Cu 2+ , Fe 3+ , Ni 2+ , Pb 2+ , Sn 2+ and Zn 2+ ) was improved markedly after nearly two year adaptation from 12 g/L to 20 g/L. The results from these studies demonstrate that 80 % Zn, 64 % Al, 86 % Cu and Ni 74 % can be recovered from electronic scrap by microbial leaching process using mixed adapted consortium of moderately thermophilic bacteria at column bioleaching level and 4 % Al, 6 % Zn, 5 % Cu and 7 % Ni can be leached out during preleaching. This finding may facilitate on industrial scale implementation of this process for recycling of metals from electronic scrap.