EFFECTS OF NO3-, CL-, F-, SO42-, AND CO32- ON PB2+ IMMOBILIZATION BY HYDROXYAPATITE

Remediation of Pb-contaminated wastes has received considerable attention recently. We have previously shown that hydroxyapatite [Ca5(PO4)3OH] can reduce Pb2+ concentrations below the EPA action level (72.4 nmol L-1) and, thus, has the potential for in situ Pb2+ immobilization against leaching. This research investigated the effects of NO3-, Cl-, F-, SO42-, and CO32- on hydroxyapatite-Pb2+ interactions. Solutions containing initial Pb2+ concentrations of 24.1-482 mumol L-1 were reduced to below 72.4 nmol L-1 after reaction with hydroxyapatite, except in the presence of high levels of CO32- and Pb2+. Concentrations of Cl-, F-, and SO42- decreased, whereas NO3- and CO32- concentrations were unchanged after reaction with hydroxyapatite. Hydroxypyromorphite [Pb5(PO4)3OH] precipitated after the reaction of hydroxyapatite with Pb2+ in the presence of NO3-, SO42-, and CO32-, while chloropy romorphite [Pb5(PO4)3Cl] and fluoropyromorphite [Pb5-(PO4)3F] formed in the presence of Cl- and F-, respectively. The ability of hydroxyapatite to rapidly remove Pb2+ from solution in the presence of high levels of NO3-, Cl-, F-, SO42-, and CO32- demonstrates its great potential for reducing the environmental impact of Pb2+-contaminated wastes.