Separation of complexed mercury from aqueous wastes using self-assembled mercaptan on mesoporous silica

Separation of Hg(II) from potassium iodide/sulfate wastes was studied using a novel mesoporous silica material containing self-assembled mercaptan gro ups. The adsorbent, consisting of self-assembled mercaptan on mesoporous si lica (SAMMS) developed at Pacific Northwest National Laboratory (PNNL), was characterized as to its specificity, adsorption capacity, and kinetics for separation of mercury from potassium iodide/sulfate solutions. Aqueous spe ciation calculations indicated that a major fraction (92-99%) of dissolved mercury in the potassium iodide/sulfate wastes solutions existed as HgI42- species. The adsorption data showed that the mercury adsorption capacity of SAMMS material increased with decreasing iodide concentrations. The magnit ude of calculated free energy of adsorption indicated that mercury adsorpti on on this adsorbent is typical of soft acid-soft base interactions. High s pecificity for anionic complexes of Hg(II) by the SAMMS material was confir med by distribution coefficient measurements. The kinetics data indicated t hat the adsorption reactions occur very rapidly independent of Hg(II) conce ntrations and pH. These tests confirmed that SAMMS material can very effect ively remove strongly complexed Hg(II) from aqueous wastes.