Selective Recovery of Hg ²⁺ in Waste Acids by CuSe as High-Added-Value HgSe for Resource Utilization: Performance, Mechanism, and Application

Currently, there is a significant demand to selectively remove Hg2+ in waste acids from smelters before the coprecipitation of other heavy metal cations. In this study, CuSe was developed to selectively remove Hg2+ in waste acids as a high-added-value HgSe for resource utilization. CuSe displayed an exceptional capacity of 1.96 g g–1 for Hg2+ removal without any passivation of CuSe and an approximately 100% selectivity in the presence of other metal cations. X-ray diffraction (XRD) and theoretical calculations both demonstrated that the reaction product between CuSe and HgCl2 was primarily HgSe. However, XRD and transient reaction analysis both indicated that formed HgSe can further react with aqueous HgCl2 to form Hg3Se2Cl2. As the rate for Hg3Se2Cl2 formation was much less than that for HgSe formation, the product for Hg2+ removal by CuSe was mainly the mixture of HgSe and Hg3Se2Cl2, and the stoichiometric ratio of Hg2+ removal by CuSe was in the range of 1.0–1.5. To fully utilize CuSe for Hg2+ removal and to ensure approximately 100% Hg2+ removal efficiency, a technology of double transformation and double precipitation followed by thermal treatment was devised to recover Hg2+ in waste acids as high-added-value HgSe for resource utilization and solid HgCl2 for centralized control.