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

Abstract 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: <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="block"> <m:mrow> <m:msub> <m:mrow> <m:mn>5</m:mn> <m:msup> <m:mtext>Pb</m:mtext> <m:mrow> <m:mn>2</m:mn> <m:mo>+</m:mo> </m:mrow> </m:msup> </m:mrow> <m:mrow> <m:mtext>desorbed</m:mtext> <m:mo> </m:mo> <m:mtext>from</m:mtext> <m:mo> </m:mo> <m:mtext>zeolite</m:mtext> </m:mrow> </m:msub> <m:mo>+</m:mo> <m:msub> <m:mrow> <m:mn>3</m:mn> <m:msubsup> <m:mrow> <m:mtext>AsO</m:mtext> </m:mrow> <m:mn>4</m:mn> <m:mrow> <m:mn>3</m:mn> <m:mo>−</m:mo> </m:mrow> </m:msubsup> </m:mrow> <m:mrow> <m:mtext>contamination</m:mtext> </m:mrow> </m:msub> <m:mo>+</m:mo> <m:msub> <m:mrow> <m:msup> <m:mrow> <m:mtext>Cl</m:mtext> </m:mrow> <m:mo>−</m:mo> </m:msup> </m:mrow> <m:mrow> <m:mtext>supplied</m:mtext> <m:mo> </m:mo> <m:mtext>extra</m:mtext> </m:mrow> </m:msub> <m:mo>=</m:mo> <m:msub> <m:mrow> <m:mtext>Pb</m:mtext> </m:mrow> <m:mn>5</m:mn> </m:msub> <m:msub> <m:mrow> <m:mfenced> <m:mrow> <m:msub> <m:mrow> <m:mtext>AsO</m:mtext> </m:mrow> <m:mn>4</m:mn> </m:msub> </m:mrow> </m:mfenced> </m:mrow> <m:mn>3</m:mn> </m:msub> <m:mo> </m:mo> <m:msub> <m:mrow> <m:mtext>Cl</m:mtext> </m:mrow> <m:mrow> <m:mtext>precipitated</m:mtext> </m:mrow> </m:msub> </m:mrow> </m:math> 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 (&lt;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.