Mechanochemically Activated Microsized Zero-Valent Iron/Pyrite Composite for Effective Hexavalent Chromium Sequestration in Aqueous Solution

The activity of pyrite (FeS2) and microsized zero-valent iron (mZVI) is greatly limited by the passivating layer. This study indicated that hexavalent chromium (Cr(VI)) could be effectively sequestered by mechanochemically activated mZVI/FeS2 composite (MA-mZVI/FeS2), which was obtained from the mZVI/FeS2 mixture by mechanochemical technology. Compared with MA-mZVI and MA-FeS2, the Cr(VI) removal performance of MA-mZVI/FeS2 was significantly improved at a mZVI/FeS2 molar ratio of 1:9. The effects of initial concentration, coexisting anions, reaction time, and initial pH on Cr(VI) sequestration by MA-mZVI/FeS2 were investigated. During the removal process, the concentrations of different valence states of chromium and iron were measured to explore the Cr(VI) removal mechanism. Based on the experiments and characterizations, surface sorption accounted for 41.38% and reduction accounted for 58.62% at the Cr(VI) adsorption equilibrium of MA-mZVI/FeS2. The ball milling destroyed the passivating layer of MA-mZVI/FeS2, resulting in a rough surface. The corrosion of mZVI can be significantly accelerated by FeS2 due to the strong interaction between mZVI and FeS2 in MA-mZVI/FeS2, which led to the enhanced Cr(VI) sequestration. The practical application indicated that MA-mZVI/FeS2 had good Cr(VI) removal performance in real water samples. This study revealed that MA-mZVI/FeS2 can be a hopeful adsorbent for effective Cr(VI) sequestration in aqueous solution.