Bioleaching of waste mobile phone printed circuit board in controlled redox potential compared to non-controlled redox potential

Abstract

The present study was conducted to carry out bioleaching of waste mobile phone printed circuit board (WMPPCB) in a high redox potential-controlled fed-batch process compared to the low redox potential batch process. Concomitant additions of WMPPCB achieved high redox potential bioleaching of WMPPCB. The pH of the bioleaching slurry was maintained at 1.50 for both high and low redox potential experiment. High redox potential was controlled to allow more Fe-oxidizing activity compared to sulfur oxidation process. The primary element in the WMPPCB was Cu (26.3%) along with Ni, Zn, Al, etc., analyzed by XRF, while XRD revealed the presence of metal sulfide/oxides. Both experiments were carried out in a 2-L stirred tank reactor and regular measurement of pH, redox potential, planktonic viable cell count, Fe2+, Fe3+, Fe (total), SO42-, Cu2+ concentration. The change in pH and controlling with acid addition showed that fed-batch bioleaching consumes 1.35 times lower sulfuric acid per ton WMPPCB than the batch process. Both the batch and fed-batch bioleaching supported first-order reaction and also followed as similar type of intermediate leaching kinetics, which is neither chemically controlled nor diffusion-controlled type. The leaching yield of copper was found to be best (98-97%) in both leach residue and leach liquor analysis. The acid requirement/ton WMPPCB and the bio-residue weight loss state a better fed-batch process. The fed-batch bioleaching was comparatively better than batch process, when compared all bioprocess dynamics parameters and leaching yield of various metals.