Remediation of environment contaminated by lead using synthetic and natural apatites

Abstract

Lead contamination is an environmental concern due to its effect on human health. One of the ways of remediating lead contamination is the in situ stabilization of this heavy metal. This can be achieved by converting different types of lead species into Pb-phosphates (pyromorphites), which are among the least soluble Pb-bearing solids. Synthetic hydroxyapatite (Ca5(PO4)3OH) and natural apatite can be used for this purpose. Both hydroxyapatite and some natural apatites are effective in reducing the aqueous Pb concentration to below 15 µgl-1 (EPA drinking water limit). The main mechanism in the case of hydroxyapatite is its dissolution and subsequent precipitation of pyromorphites. The mechanism and the effectiveness of natural apatites depend on the type of apatite, its composition, crystallinity and presence of impurities. Apatites are also effective in reducing the Pb concentration in leachets from contaminated soils in the pH range from 6 to 10. The percentage of Pb concentration reduction is from 60 to 99.9% depending on the type of contamination and type of apatite amendment applied. These data suggest that apatites have potential to provide cost-effective in situ Pb immobilization.