Eco-friendly and low-cost removal of bromine from waste printed circuit board smelting ash by mechano-chemical leaching

Abstract

Waste printed circuit board smelting ash (WPCB-SA), which is generated in the waste printed circuit board (WPCB) smelting process, is considered a hazardous waste because it contains substantial amounts of highly toxic inorganic bromides. Therefore, disposing inorganic bromides from WPCB-SA has become an environmental concern worldwide. In this study, a mechano-chemical leaching technology was developed to convert hazardous bromides in WPCB-SA into value-added products. By optimizing the removal and recovery conditions, 96.76% of the bromides in WPCB-SA could be removed, and a high recovery yield of NaBr was obtained. The mechano-chemical process was simulated to theoretically optimize the conditions affecting the performance. The experimental results indicate that the optimal mechano-chemical leaching conditions include a NaOH concentration of 4.5 mol L⁻¹, a liquid–solid ratio of 3 mL g⁻¹, a grinding disc gap of 3 μm, a rotational speed of 2500 rpm, and a leaching time of 20 min. After mechano-chemical leaching, the Br-containing leachate was purified via neutralizing precipitation, evaporative crystallization, and methanol purification, for efficiently removing impurities (Pb, Zn, Sn, and Cl); thus, NaBr was obtained as the final recovery product with a purity of 98.71%. The advantages of the as-proposed technology include: (1) no toxic SO₂/HBr/Br₂ flue gas release, (2) reduced removal time, (3) decreased energy consumption, and (4) less water and reagent consumption, in contrast to conventional technologies for removing Br from WPCB-SA. This study provides an environmentally-friendly, efficient, and cost-effective approach for removing hazardous inorganic bromides from WPCB-SA.