Mercury removal by thiol-functionalized metal oxide-carbon black sorbent and mixed-matrix membranes

Aqueous mercury sorption is achieved using a novel thiol-functionalized metal oxide-coated carbon sorbent. The material is hydrolytically and thermally stable (up to 250°C) because of the formation of covalent siloxane bonds on functionalization and increased hydrophobicity. The particles were synthesized with a variety of morphologies; the base particles are ∼80 nm and a nonuniform metal oxide (including silica) coating less than 5 nm thick. This sorbent material has a high equilibrium capacity for mercury (∼60 mg/g) at concentrations up to ∼150 mg/L. The Langmuir constant for equilibrium sorption (k_a/k_d) is K = 16.9 L/mol. Packed column experiments using real water reduced mercury levels to below detectable limits. Mixed-matrix membranes (sorbent particles and polysulfone) were synthesized to combine the ease of surface functionalization on particles with advantages of polymer membranes. Membranes with up to 50 wt % particles were synthesized, with sorption capacities at 200 mg/g sorbent or greater due to dispersion of particles in the matrix and the use of small particles, which are impractical in packed column operations. A regeneration scheme is proposed using multifunctional particles (thiol and sulfonate moieties). Initial experiments showed that mild regeneration conditions (dilute HCl at pH 4) partially regenerated the sorbent particles.