Mimetite precipitation on Pb-clinoptilolite: an effective approach for arsenate removal from water

This short communication proposes a novel approach to arsenate remediation using in situ precipitation of mimetite [Pb 5 (AsO 4 ) 3 Cl], a sparingly soluble mineral phase with an apatite structure. The Pb 2+ source was provided by a lead-modified zeolite (clinoptilolite) loaded with approximately 70 g Pb/kg. It was reacted with arsenate (50 mg As/L) and chloride (20 mg Cl/L) at initial pH values of 2 and 7. Mimetite crystallized on and in the vicinity of zeolite due to the reaction of Pb(II) desorbed from zeolite with arsenate and chloride ions present in aqueous solution: 5 Pb 2 + desorbed from zeolite + 3 AsO 4 3 − contamination + Cl − supplied extra = Pb 5 AsO 4 3 Cl precipitated 5{{Pb}²⁺}desorbed\ from\ zeolite+3{{AsO₄³⁻}contamination}+C{{l}⁻}supplied\ extra={{Pb}₅}{{( {{AsO}₄} )}₃}{{Cl}precipitated} Mimetite formed rapidly resulting in efficient arsenate sequestration. At pH 7, arsenate removal reached 99.88% after 24 hr, with minimal lead release (<0.02 mg/L). These results demonstrate that lead-modified clinoptilolite is a promising material for a coupled sorption–precipitation mechanism which provides an effective strategy for arsenic immobilization in contaminated aqueous systems.