Experimental Study on Treating Waste Printed Circuit Boards by Molten Salt Oxidation

Abstract

The waste management of e-wastes is a significant challenge, especially for the disposal of waste printed circuit boards (WPCBs). An effective, economic and environmental-kind recycling technology is in great demand. Molten salt oxidation (MSO) is a robust thermal process, has the inherent capability of destroying organic constituents of wastes while retaining the inorganic constituents in the molten salt. In the present study MSO is employed for the disposal of waste printed circuit boards aimed at describing the treating method of WPCBs using MSO, and evaluating the efficiency of this alternative. Molten salt oxidation experiments of WPCBs have been conducted in a lab-scale molten salt reactor using a ternary carbonate salt (Li, Na, K)2CO3. The operation parameters investigated are the temperature of molten salts, the excess air factor and the residence time of the reactants in the salt bath. Results show that the retention efficiency of bromine is higher than 99.9%, irrespective of the operating conditions. The emissions of CO and SO2 decrease with temperature increasing, while the emission of NOx first decreases and later increases. And when the residence time is lengthened, the emissions of CO, NOx and SO2 decrease. Compared to the temperature and the residence time’s role, the effect of excess air factor on the emissions of CO, NOx and SO2 is relatively small. Over 95% of the copper in WPCBs are recycled. The fibreglass that is the main component of the ash content is dissolved by the molten carbonates and retains in the salt bath. The results of the present study show molten salt oxidation is an environmentally friendly and effective alternative technology for the disposal of WPCBs.