RECOVERY OF PRECIOUS METAL FROM WASTE PRINTED CIRCUIT BOARD: UNDERSTANDING THE LEACHING PHENOMENON AND ITS OPTIMIZATION

Abstract

Recovery of precious metals from printed circuit boards (PCBs) using lixivient (thiourea ) was after adsorption on lowcost adsorbent prepared from waste tea powder. The influence of particle size of PCB (less than 75 μm-75-150 μm), thiourea dose (10-90 ml for 0.5g of PCBs), pulp density (0.00125-0.01125 g/ml), contact time (6-24 hr), ferric ion dose (0- 0.15 molar) and RPM (50-225) were studied for gold and silver leaching under batch mode. PCB sample with smaller particle size (>75 μm) leached higher amounts of gold and silver in the solution. Preliminary experiments showed 80 ml 0.5M TU dose best for leaching at pH 1.9-2.0 and at pulp density of 0.00125 g/ml after 15 h leaching time. Presence of 0.15 M ferric ions increased gold leaching rate. Leached liquor based on above discussed conditions showed an average of 2.220 mg/g of gold and 0.447 mg/g of silver leaching from 1g sample of PCBs. Optimization of thiourea dose, pulp density, ferric-ion concentration was carried in RSM through Box-Behnken Design. Second order quadratic polynomial model was developed for gold and silver using Design Expert Software to maximize both gold and silver recoveries. The optimum conditions suggested by model were found to be 100 ml 0.5M TU, 0.00125 g/ml pulp density and 0.15M ferric ion concentration. Adsorptive recovery of leached metal using low-cost pretreated waste tea powder was examined. Waste tea powder was found an effective material for recovery of metals from the leached liquor. Results of metal recovery on adsorbent were reported through SEM, EDS analysis.