Promoting elemental mercury immobilization performance from smelting flue gas over a wide temperature range via cobalt-doped copper sulfide adsorbents.

Abstract

Copper sulfide (CuS) sorbent exhibits great potential for gaseous elemental mercury (Hg⁰) decontamination, but it still suffers from a narrow operating temperature. Therefore, designing advanced CuS sorbents that have a high activity level for capturing Hg⁰ and thermal stability at a high temperature range is challenging. Herein, we propose a metal doping strategy to fabricate a bimetallic sulfide adsorbent. Benefiting the unique structure and composition, a mesoporous structure and an abundance of unsaturated sulfur sites ensure that Cu_xCo_(1-x)S_y provides a desirable level of adsorption for Hg⁰. The experimental results indicate the optimum Co doping mass concentration of 5 %. The Cu_0.95Co_0.05S_y not only performs satisfactory Hg⁰ adsorption at elevated temperatures (Hg⁰ average adsorption efficiency of over 97.3 %, Hg⁰ average adsorption rate of over 2.7 μg/g/min), but also presents an exciting regeneration and recycle performance (a Hg⁰ adsorption efficiency of over 94 % after 10 cycles). The adsorption capacity of Cu_0.95Co_0.05S_y at the breakthrough threshold of 25 % reaches 5.22 mg/g, surpassing most of metal sulfide sorbents for Hg⁰ immobilization at 150 °C. As far as Hg⁰ adsorption is concerned, the composition of typical smelting flue gases has almost no effect. According to further studies, unsaturated coordination short-chain sulfur (S₂^2-) sites are essential for adsorption of Hg⁰ and are capable of directly forming α-HgS from Hg⁰. In both the contrast experiment and density functional theory calculations, the cobalt doping strategy enhances the thermal stability of the active S₂^2- ligand and the Hg⁰ adsorption properties. This study not only provide a prospective adsorbent for Hg⁰ sequestration at wide temperature range, but also explores a method of utilizing gaseous contaminants for resource utilization.