Highly Efficient Antimonate Removal from Water by Pyrite/Hematite Bi-Mineral: Performance and Mechanism Studies

Pyrite/hematite bi-mineral (FeS2/alpha-Fe2O3) was obtained by thermal modification of pyrite. FeS2/alpha-Fe2O3 was investigated and developed as a promising adsorbent for antimonate [Sb(V)] removal. The influence of initial concentration, temperature, initial pH, contact time, and coexisting anions on Sb(V) adsorption performance of FeS2/alpha-Fe2O3 was investigated. FeS2/alpha-Fe2O3 exhibited good adsorption performance and excellent removal efficiency. The results of the Langmuir isotherm model indicated that FeS2/alpha-Fe2O3 had a large adsorption capacity (347.2 mg/g) for Sb(V) removal from water. High removal efficiency by FeS2/alpha-Fe2O3 was achieved over a broad pH range (2.5-10.7). The coexisting anions had little influence on Sb(V) adsorption by FeS2/alpha-Fe2O3. The pseudo-second-order and Dubinin-Radushkevich model analyses (E = 12.62 kJ/mol) suggested that FeS2/alpha-Fe2O3's Sb(V) removal process was chemisorption. The negative Gibbs free energy change and endothermic enthalpy change of 5.00 kJ/mol indicated that Sb(V) adsorption by FeS2/alpha-Fe2O3 was feasible, endothermic, and spontaneous. Additionally, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses indicated that Sb(V) formed an inner-sphere complex on thiol groups and hydroxyl groups surface sites on the surface of FeS2/alpha-Fe2O3. At last, the real environmental water application also confirmed the excellent adsorption performance of FeS2/alpha-Fe2O3. From a practical viewpoint, FeS2/alpha-Fe2O3 can be a hopeful alternative for the remediation of Sb(V) pollution because of its large uptake capacity, low-cost, reusability, and easy availability.