Self-modified iron-based materials for efficient chromium (VI) removal: Efficacy and mechanism

Hexavalent chromium (Cr(VI)) is a typical carcinogenic contaminant, and the prerequisite for its efficient remediation is the low-cost and high-efficiency removal materials. Thus, in this study, we propose an outstanding Cr(VI) removal iron-based materials derived from the self-modification of secondary minerals by simple pyrolysis and explore their Cr(VI) removal mechanism. The resulting materials, C-AJ (from ammoniojarosite) and C-Jar (from jarosite) exhibited excellent Cr(VI) removal efficiencies, with maximum Cr(VI) removal capacities of 96.9 mg/g and 70.7 mg/g, respectively. Their excellent Cr(VI) removal capacities are mainly attributed to the self-modification of two minerals to form Fe(II) and the retained SO₄^2-, and the N escape of ammoniojarosite [(NH₄, H₃O)Fe₃(OH)₆(SO₄)₂] further promotes the formation of active sites and brings higher Cr(VI) removal ability. Moreover, C-AJ and C-Jar have similar Cr(VI) removal mechanisms involving reduction and absorption. The reduction process, primarily driven by Fe(II), contributes significantly, while the adsorption process, mainly influenced by sulfate, plays a minor role. In addition, the iron-based material exhibits high resistance to interference from pH changes, maintains strong Cr(VI) removal ability in the presence of anions and organic acids, and does not pose a risk of secondary pollution. This study demonstrates that simple pyrolysis of iron-based minerals can induce self-modification, resulting in highly active Cr(VI) removal materials, which presents a potential low-cost and efficient Cr(VI) remediation solution.