Precious Metals Recovery from Waste Printed Circuit Boards by Gravity Separation and Leaching

Abstract

This study focuses on the recovery of valuable metals, such as gold, silver, and copper, from the printed circuit boards of waste computers, using physical separation followed by leaching methods. Characterization studies revealed that resins and glass fibers were attached as grain together with base and precious metals. A hammer mill was employed as a second stage crusher to disintegrate the different components of the printed circuit board, thus improving the selectivity and recovery of metals. Separation studies using a laboratory-scale shaking table showed that 33% of the feed was removed as a light product and 96.8% of Au, 96.7% of Ag, and 97.7% of Cu were recovered in heavy fraction. Leaching the light fraction using 3 M H2SO4 and 0.33 M HNO3 at 80°C for two h resulted in greater than 90% extraction of Cu. Au and Ag were dissolved at room temperature with a leaching solution of 0.2 M S2O32-, 0.02 M CuSO4, and 0.2 M NH3.H2O, which provided a recovery of more than 59% of Au and 98% of Ag within eight h. Direct leaching tests using optimized conditions were also implemented on the crushed sample, and 45% of Au, 87.6% of Ag, and 70.8% of Cu were extracted.