Processes for gold recovery from electronic wastes using porous porphyrin polymers

Abstract

Electronic wastes containing precious metals have great potential as a sustainable source of such metals. Separation and refining, however, remain complicated, and none of the existing technologies have yet experienced commercialization. A novel porphyrin-based porous polymer, named COP-180, was recently introduced as a powerful adsorbent option, especially for gold, and in this study, aspects of desorption and recovery of adsorbed gold and regeneration of the polymer were investigated.According to ionic states of adsorbed gold, two approaches were introduced: physical and electrochemical processes. The elemental gold was separated via gravitational sedimentation using glycerol as a separation media. Recovery efficiency and purity of the collected gold were improved by adding a dispersing agent, sodium hexametaphosphate. The remaining gold on the adsorbent was then retrieved by desorption and plating. A hydrometallurgical approach on the basis of non-cyanide leaching agents was developed, and an acid thiourea-based solution was found to be suited for COP-180. The unaffected structure and desorption efficiency of COP-180 after its repeated use were proved the potential of its regeneration. Gold in the thiourea solution was then recovered as a film through electroless plating. Also, the application of the gold-thiourea solution to electroless nickel/immersion gold process was verified

corrosion resistance of the gold layer was comparable to the existing technology and deposition rate faster. All this clearly showed the use of gold-thiourea solution can indeed offer a workable option as a commercialized process. Electroplating was also made possible with lower energy consumption than the previous reports. The regeneration of thiourea was confirmed with the electroplating and leaching efficiency drop was marginal.The whole suggested processes appear to be a potential route especially as a closed-loop system for the purpose of gold recovery in electronic industry, and in so doing valuable resources are recovered with wastes treated in a simultaneous manner.