Effect of oxalic acid on the selective flotation separation of Pb-activated sphalerite from galena

Abstract

The separation of sphalerite (ZnS) and galena (PbS) is challenging owing to activation of the sphalerite surface by unavoidable metal ions, such as lead ions (Pb²⁺) released from lead-containing minerals. In this study, oxalic acid (OA) was applied for the first time as an environmentally friendly reagent to deactivate the sphalerite surface in lead–zinc (Pb-Zn) flotation separation. Micro-flotation experiments showed that OA, at a concentration of 0.56 mM, significantly reduced sphalerite recovery. Single-mineral flotation tests demonstrated that sphalerite recovery decreased to 20 %, while galena recovery remained at 58.7 % after OA treatment. Further flotation tests on an artificial mixture of sphalerite and galena confirmed effective separation with OA treatment under mildly alkaline conditions, achieving recoveries of 83 % for galena and 17 % for sphalerite. Infrared spectroscopy and X-ray photoelectron spectroscopy analyses showed that OA removes Pb²⁺ ions from the surface of sphalerite by forming lead oxalate (Pb(II)-Ox) precipitates, which detach from the sphalerite surface, effectively cleaning it. This detachment prevents the adsorption of potassium amyl xanthate (PAX) by forming a dispersed lead oxalate-amyl xanthate (PbOx-AX) complex, which exposes the hydrophilic sphalerite surface and leads to its depression. In contrast, this interaction had a minimal impact on the floatability of galena.