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 [Pb₅(AsO₄)₃Cl], a sparingly soluble mineral phase with an apatite structure. The Pb²⁺ 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: 5Pb2+desorbed from zeolite+3AsO43−contamination+Cl−supplied extra=Pb5AsO43 Clprecipitated 5{{\text{Pb}}^{2+}}_{\text{desorbed}\ \text{from}\ \text{zeolite}}+3{{\text{AsO}_{4}^{3-}}_{\text{contamination}}}+\text{C}{{\text{l}}^{-}}_{\text{supplied}\ \text{extra}}={{\text{Pb}}_{5}}{{\left( {{\text{AsO}}_{4}} \right)}_{3}}{{\text{Cl}}_{\text{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.