Remediation of arsenic and lead with nanocrystalline zinc sulfide

Nanocrystalline (1.7 +/- 0.3 nm) zinc sulfide with a specific surface area up to 360 m(2) g(-1) was prepared from the thermal decomposition of a single-source precursor, zinc ethylxanthate. Zinc ethylxanthate decomposes to cubic zinc sulfide upon exposure to temperatures greater than or equal to 125 degrees C. The resulting zinc sulfide was tested as a water impurity extractant. The target impurities used in this study were As5+, As3+, and Pb2+. The reaction of the nanocrystalline ZnS with Pb2+ proceeds as a replacement reaction where solid PbS is formed and Zn2+ is released into the aqueous system. Removal of lead to a level of less than two parts per billion is achievable. The results of a detailed kinetics experiment between the ZnS and Pb2+ are included in this study. Unlike the instance of lead, both As5+ and As3+ adsorb on the surface of the ZnS extractant as opposed to an ion-exchange process. An uptake capacity of > 25 mg g(-1) for the removal of As5+ is possible. The uptake of As3+ appears to proceed by a slower process than that of the As5+ with a capacity of nearly 20 mg g(-1). The nanocrystalline zinc sulfide was extremely successful for the removal of arsenic and lead from simulated oil sand tailing pond water.