Modeling, Simulation, Optimization, and Experimental Verification of Mercury Removal onto Natural and Sulfur-Impregnated Zeolite Clinoptilolite-Assessment of Feasibility for Remediation of Mercury-Contaminated Soil

In this paper, a series of equilibrium and kinetic experiments of Hg(II) removal in a single-stage batch reactor on natural (NZ) and sulfur-impregnated zeolite (SZ) were performed. Batch sorption of Hg(II) on zeolites was studied using different isothermal and kinetic models. It was found to be best described by the Brouers-Sotolongo isotherm and the Vermeulen's approximation, which were applied in optimizing the mass and contact time in two-stage cross-current and counter-current flow batch reactors based on the desired criterion of 99.9% removal efficiency. Mathematical models for minimizing zeolite mass and contact time were developed and experimentally verified. The optimum minimum masses of NZ and SZ were calculated for all systems, and a significant saving in SZ consumption was found when the counter-current design was applied. The toxicity characteristic leaching procedure (TCLP) was applied to mercury contaminated soil from the Idrija mine region in Slovenia to evaluate potential soil toxicity. The results showed that the soil is extremely contaminated and represents hazardous waste. The addition of zeolites significantly reduced the concentration of leached Hg, with the most satisfactory results obtained with SZ. It was found that at the lowest dose of 0.25 g of SZ, the leached Hg concentration was reduced below the maximum concentration criterion of 0.2 mg/L according to the TCLP test. This study revealed that SZ could be a potential sorbent for in situ remediation of mercury contaminated soil.