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

Pyrite/hematite bi-mineral (FeS₂/α-Fe₂O₃) was obtained by thermal modification of pyrite. FeS₂/α-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/α-Fe₂O₃ was investigated. FeS₂/α-Fe₂O₃ exhibited good adsorption performance and excellent removal efficiency. The results of the Langmuir isotherm model indicated that FeS₂/α-Fe₂O₃ had a large adsorption capacity (347.2 mg/g) for Sb­(V) removal from water. High removal efficiency by FeS₂/α-Fe₂O₃ was achieved over a broad pH range (2.5–10.7). The coexisting anions had little influence on Sb­(V) adsorption by FeS₂/α-Fe₂O₃. The pseudo-second-order and Dubinin–Radushkevich model analyses (E = 12.62 kJ/mol) suggested that FeS₂/α-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/α-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/α-Fe₂O₃. At last, the real environmental water application also confirmed the excellent adsorption performance of FeS₂/α-Fe₂O₃. From a practical viewpoint, FeS₂/α-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.