Effect of pyro-processing conditions on impurity removal and precious metal enrichment in waste printed circuit board (WPCB) recycling process

Abstract

The combinatorial effects of slag composition and O2-blowing conditions on silicon (Si) and iron (Fe) removal as well as gold (Au) and silver (Ag) enrichment from waste printed circuit boards (WPCBs) were investigated to optimize pyrometallurgical WPCBs recycling process. Regardless of the experimental conditions, the removal rate for Si and Fe was approximately 100%, except in slag-free operation. The Si removal rate was generally higher than the Fe removal rate at a given reaction time irrespective of experimental variables because the O2 affinity of Si is higher than that of Fe in molten copper, thermodynamically. The removal rate of impurities was clearly dependent on blowing conditions and slag composition, and a combinatorial operation of bottom-blowing and highly fluid slag favored the efficient removal of impurities. The maximum enrichment ratio of Au and Ag (CAu,AgMax) was about 10% and the possession rates of Au and Ag, RAu,Ag at CAu,AgMax were greater than 96%. The loss of Au and Ag can be minimized, i.e., RAu,Ag can be maximized by stopping O2-blowing before metal droplets are physically entrapped by molten slag, because metal droplet's entrainment is affected by slag viscosity, which contributes to the settling velocity of metal droplets. Consequently, it is very critical to appropriately control not only the slag composition but also O2-blowing conditions for both impurities removal and maximizing precious metals enrichment and possession.