Molten salt shielded preparation of rice straw biochars doped by copper sulfide for elemental mercury capture

Biochar adsorbents are obtained from rice straw under an air atmosphere through a simple eutectic salt (K2CO3+Li2CO3) synthesis approach. Pristine biochars present relatively low mercury capture ability probably due to their small specific surface areas with less adsorption sites. Deposition of CuS can notably strengthen the mercury adsorption ability of the biochars. The best CuS content is 5 wt% associated with nearly complete mercury capture within 60–100 °C. The Hg0 removal ability of CuS-doped biochars are subtly degraded by NO and negligibly affected by SO2. Cu2+ and S2− species function as adsorption sites, resulting in the production of HgS accompanied by the reduction of partial surface Cu2+ ions into low-valence Cu+ ions.