New insights into the mechanism of selective flotation of copper and copper-tin alloy

Abstract

Waste printed circuit boards (WPCBs) are an integral part of e-waste, and they contain many valuable metals like Cu, Sn, etc. In order to recycle metal from WPCBs, electrostatic separation, wet gravity separation, air current separation, etc., have been used to separate metals from nonmetals, and the metal product has usually contained a high grade of copper and a low grade of tin. Because copper and tin can form an alloy, it is difficult to separate the two by smelting. Therefore, selective flotation of copper and copper-tin alloy (solder) was investigated in this study, with the aim of decreasing the content of tin in the rich copper product. Under optimized conditions, a rich copper concentrate with Cu grade of 61.12%, Cu recovery of 75.93%, Sn grade of 1.78%, Sn recovery of 8.46%, and a rich tin tailings with Sn grade of 40.93%, Sn recovery of 91.54%, Cu grade of 40.50%, Cu recovery of 24.07% were obtained. Moreover, during the flotation process, the adsorption capacity of ammonium dibutyl dithiophosphate (ADD) on the surface of copper was significantly higher than that on the surface of solder, which is the main reason for the flotation separation of copper and solder. Cu(II) on the surface of copper and solder was reduced to a lower valence state by ADD, and the ADD was oxidized to (ADD)2; but the (ADD)2 did not stably adsorb on the surface of either copper or solder. The adsorption product of ADD on the surface of copper and solder was Cu(I)-ADD precipitate; the adsorption sites of ADD on the solder surface were copper atoms.