Leaching of precious metals from waste printed circuit boards with different leaching reagents / Ainin Syakirah Abdul Rahim and Chang Siu Hua

Electronics is the biggest and fastest-growing manufacturing sector in the world. The global production of electronic waste is increased 3-5% each year due to the lifetime of electronic devices is continually minimized. Waste printed circuit boards is one of the electronic wastes. The recovery of precious metals inside printed circuit boards is necessary to prevent the depletion of natural resources. This study was carried out to evaluate various leaching reagents for precious metals. The alternative leaching reagent must be identified to replace the conventional method of leaching which is cyanide leaching. This is due to the toxicity of cyanide solution. Since the use of cyanide as a liquid solution has contributed to serious water contamination in different metal recovery plants worldwide, this serious problem is to be solved by using more environmentally friendly leaching agents as alternators for the leaching process. SALSA method which is part of systematic literature review (SLR) is used to collect, synthesize, and analyze data. A total of six leaching reagents are identified and presented collectively in this review paper. There are several studies were considered to assist with the choice of non-cyanide reagents for the precious metal leaching. The environmental effects of leaching should be taken more attention to evaluate the best leaching reagent in order to develop an environmental friendly leaching for the recovery of precious metal from waste PCBs. A critical comparison of six leaching reagents is analyzed based on screening and scoring method. This method compared the total of six alternatives of leaching reagents with selected criteria like leaching rate, reagent cost, toxicity level, corrosivity level and its research level. From the result obtained, thiourea, thiosulfate and iodide leaching have been recommended to replace cyanide leaching more efficiently.