Tin and silver recovery from wave soldering dross

Abstract

This work proposes a method for the recovery of tin and silver from wave soldering dross produced during the manufacture of printed circuit boards. Samples of wave soldering dross were first subjected to carbothermic reduction to obtain an ingot containing the above metals plus other elements. This ingot was then subjected to electrorefining at different densities of electrical current, electrolyte flow rate, and cathode-anode separation distance, to determine the optimum conditions for recovering pure tin. Under such conditions, 82 wt% of the tin in the ingot was recovered at a purity of 99.94%. After subjecting ingots to continuous electrorefining under optimum conditions for 845 h, the slime collected at the anode was removed for the recovery of silver. This slime was subjected to thin-layer leaching with concentrated nitric acid. The leachate produced was subjected to copper-cementation; the silver adhering to the copper rod was collected by washing. This process recovered 92% of the silver in the wave soldering dross ingot at a purity of >99.6%. Some 99% of the copper entering the leachate from the copper rod during cementation was recovered by liquid-liquid extraction with 40% LIX84 (dissolved in EXXOL D100). This method could provide a rapid, inexpensive means of recovering pure tin and silver from wave soldering dross.