Cr(III) and Fe(II) recovery from the polymetallic leach solution of electroplating sludge by Cr(III)-Fe(III) coprecipitation on maghemite

The separation of Cr(III) from the polymetallic leaching solution is a typical problem encountered during the recycling of electroplating sludge. In this paper, a novel method was proposed to recover Cr(III) and Fe(II) synchronously by forming the Cr(III)-Fe(III) coprecipitates on the surface of maghemite (gamma-Fe2O3) fine particles with Fe-2(SO4)(3) solution as the supplemental Fe source. The results showed that high Fe(III) to Cr(III) ratio in solution promoted the hydrolysis and precipitation of Cr(Ill). In addition, the maghemite particles, served as the crystal nuclei, could induce the formation of the core-shell structured Cr(III)-Fe(III) coprecipitates on its surface and accelerate the sedimentation of the coprecipitates in the magnetic field. By using a two-stage Cr(III)-Fe(III) coprecipitation process, the recoveries of Cr and Fe reached 96.17% and 99.39%, and the grades of Ni, Cu, and Zn in the coprecipitates were at 0.41%, 0.38%, and 0.22%, respectively. The obtained coprecipitates can be recycled as the feed material of chromium smelting after heat treatment. This method is simple and efficient for high-concentration Cr3+ solution treatment, which is beneficial for the sustainable development of resources and environment.