The rate of gaseous Hg 0 adsorption onto natural sphalerite increased by approximately 1.9−7.7 times after Cu 2+ activation during flotation of the natural sphalerite to remove impurities. Via a new pathway involving CuS, physically adsorbed Hg 0 was oxidized by CuS to HgS on natural sphalerite after Cu 2+ activation. In a similar intrinsic ZnS pathway, physically adsorbed Hg 0 was oxidized by ZnS to HgS. The rate of the CuS pathway for Hg 0 capture was generally significantly larger than that of the intrinsic ZnS pathway. Thus, Hg 0 adsorption onto natural sphalerite was notably accelerated after Cu 2+ activation. However, the kinetic analysis indicated that the capacity of natural sphalerite for Hg 0 capture did not vary. Because the properties of the activated sphalerite for Zn smelting were barely degraded after Hg 0 capture, the spent activated sphalerite for Hg 0 capture can be reused for Zn smelting. Moreover, most of the gaseous Hg 0 captured by activated sphalerite can be recovered eventually as liquid Hg 0 in the condenser unit of Zn smelters. Thus, Hg 0 recovery by activated sphalerite is a cost-effective and environmentally friendly technology to recover Hg 0 from Zn smelting flue gas, thus replacing the complex and dangerous Boliden−Norzink process.

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In this study, CuS x /TiO 2 was developed to selectively remove Hg 2+ from waste acids. X-ray photoelectron spectroscopy and X-ray diffraction analyses demonstrated that there were two reaction routes for Hg 2+ removal by CuS x /TiO 2 , corresponding to the two types of copper sulfides (i.e., CuS and Cu 2 S). The CuS route with the product HgS occurred regardless of the presence of Cl − , while the Cu 2 S route with the product Hg 2 Cl 2 only occurred with Cl − . Therefore, Cl − exhibited a remarkable promotion on Hg 2+ removal. Kinetic analysis demonstrated that the CuS route was markedly faster than the Cu 2 S route, which accounted for the rapid removal of Hg 2+ . CuS x /TiO 2 showed excellent performance for Hg 2+ removal at pH 2.0 with an adsorption rate of 16.3 mg g −1 min −1 , and removed Hg 2+ can be recovered as liquid Hg 0 as a co-benefit of Hg 0 recovery units in smelters. Therefore, CuS x /TiO 2 was a promising sorbent for Hg 2+ recovery in waste acids for centralized control.