BIOLEACHING OF E-WASTE: STRATEGIES FOR ENHANCED GOLD RECOVERY

Abstract

GOLD BIOLEACHING FROM ELECTRONIC SCRAP MATERIAL (ESM) WAS EXAMINED USING BATCH CULTURES OF CHROMOBACTERIUM VIOLACEUM WHICH PRODUCES CYANIDE AS A SECONDARY METABOLITE. THREE APPROACHES WERE IDENTIFIED TO INCREASE THE CONCENTRATION OF CYANIDE IONS WHICH COMPLEXES WITH GOLD FROM ELECTRONIC SCRAP. IN THE FIRST APPROACH, MUTATIONS WERE INDUCED IN WILD C. VIOLACEUM TO ENABLE GROWTH AND CYANIDE PRODUCTION AT ALKALINE PH WHICH FACILITATED FORMATION OF GOLD- CYANIDE ION COMPLEX. IN THE SECOND APPROACH, PERFORMANCE OF SPENT MEDIUM LEACHING WAS EXAMINED WHERE CELL-FREE METABOLITE WAS USED FOR BIOLEACHING. IN THE THIRD APPROACH, HCN PRODUCTION WAS IMPROVED BY USING ENGINEERED STRAINS OF C. VIOLACEUM (PBAD AND PTAC) FOR BIOLEACHING WITH AN EXTRA COPY OF CYANIDE PRODUCING OPERON. ALL THREE APPROACHES SIGNIFICANTLY ENHANCED GOLD RECOVERY FROM ESM. FINALLY, IMPORTANT FACTORS AFFECTING GOLD BIOCYANIDATION WERE OPTIMIZED FOLLOWING CENTRAL COMPOSITE DESIGN AND SCALE UP STUDIES WERE PERFORMED IN BIOREACTO