Impact of mercury speciation on its removal from water by activated carbon and organoclay

Abstract Mercury (Hg) speciation can affect its removal efficiency by adsorbents. This study assessed the removal of dissolved inorganic Hg(II) species (Hg(II)*), β-HgS nanoparticles (HgS NP), and Hg complexed with dissolved organic matter (Hg-DOM) by three sorbents: activated carbon (AC), sulfur-impregnated activated carbon (SAC), and organoclay (OC). The effect of ionic composition, solution ionic strength, and natural organic matter (NOM) concentration on the removal of each Hg species was also evaluated. The three adsorbents were all effective in removing Hg(II)*, Hg-DOM, and HgS NPs. Increasing ionic strength decreased the removal of Hg(II)* species due to the formation of ionic Hg species with lower affinity for the sorbents. Added NOM decreased the removal of Hg(II)* and HgS NPs by all sorbents with the OC sorbent being most susceptible to NOM fouling. On a surface area-normalized basis, the OC removed all types of Hg species better than the AC and SAC samples. Moreover, adsorbed Hg-DOM transformed to a β-HgS phase on the OC, but not for AC and SAC. These studies indicate that both Hg speciation and the water quality parameters need to be considered when designing sorbent-based emission controls to meet Hg removal targets.