Co-doped ZnS with large adsorption capacity for recovering Hg0 from non-ferrous metal smelting gas as a co-benefit of electrostatic demisters

Abstract

The installation of electrostatic demisters (ESDs) makes possible the use of sorbent injection technology for recovering Hg⁰ from non-ferrous smelting gas. ZnS, as a typical smelting raw material, could be a promising candidate due to the sulfur boding site for mercury. However, the low reaction rate and poor adsorption capacity limited its application. In this study, Co was incorporated into ZnS to enhance adsorption activity for recovering Hg⁰. Co_0.2Zn_0.8S exhibited the best Hg⁰ capture performance among the modified sorbents. The Hg⁰ adsorption capacity was up to 46.01 mg/g at 50 °C (with 50% breakthrough threshold), and the adsorption rate was as high as 0.017 mg/(g min). Meanwhile, SO₂ and H₂O had no poison effects on Hg⁰ adsorption. The chemical adsorption mechanism was proposed, which was Co³⁺, and sulfur active sites could immobilize Hg⁰ in the form of stable HgS, following a Mars-Maessen reaction pathway. The spent sorbent will release ultrahigh concentration mercury-containing vapor through the heating treatment, which facilitated centralized recovery of Hg⁰. Meanwhile, inactivated sorbent can be used as smelting raw material to recover sulfur resources. Therefore, the control of Hg⁰ emission from non-ferrous smelting gas by Co-adopted ZnS was cost-effective and did not form secondary pollution.