Acceleration of Hg⁰ Adsorption onto Natural Sphalerite by Cu²⁺ Activation during Flotation: Mechanism and Applications in Hg⁰ Recovery

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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.