Selective removal of Hg2+ from acidic wastewaters using sulfureted Fe2TiO5: Underlying mechanism and its application as a regenerable sorbent for recovering Hg from waste acids of smelters

Abstract

The selective removal of Hg²⁺ from waste acids containing high concentrations of other metal cations, such as Cu²⁺, Zn²⁺, and Cd²⁺, which are discharged from nonferrous metal smelting industries, is in great demand. Herein, sulfureted Fe₂TiO₅ was developed as a regenerable magnetic sorbent to recover Hg²⁺ from waste acids for centralized control. Sulfureted Fe₂TiO₅ exhibited an excellent ability for Hg²⁺ removal with the capacity of 292-317 mg g^-1 and the rate of 49.5-57.6 mg g^-1 h^-1 at pH=2-4. Meanwhile, it exhibited an excellent selectivity for Hg²⁺ removal that not only the coexisting Cu²⁺, Zn²⁺, and Cd²⁺ can scarcely be adsorbed but also Hg²⁺ adsorption was hardly inhibited. The mechanism and kinetic studies indicated that the Fe²⁺ in the FeS₂ coated on sulfureted Fe₂TiO₅ was exchanged with Hg²⁺ adsorbed at a Fe²⁺ to Hg²⁺ mole ratio of 1:2. Meanwhile, most of the Hg²⁺ removed by sulfureted Fe₂TiO₅ can be thermally desorbed primarily as ultra-high concentrations of gaseous Hg⁰, which can finally be recovered as liquid Hg⁰ for centralized control in combination with existing Hg⁰-recovery devices in smelters. Moreover, the spent sulfureted Fe₂TiO₅ could be regenerated for duty-cycle operations with re-sulfuration without a remarkable degradation of the Hg²⁺-removal performance. Therefore, Hg²⁺ recovery using sulfureted Fe₂TiO₅ may be a promising, low-cost, and environmentally friendly technology for the centralized control of Hg²⁺ in waste acids discharged from smelters.

Keywords: Hg(2+) removal; Isomorphous substitution; Kinetic analysis; Nonferrous metal smelting; Selectivity; Waste acids.