You are here:
FORMATION OF CHLOROPYROMORPHITE IN A LEAD-CONTAMINATED SOIL AMENDED WITH HYDROXYAPATITE
Citation:
Ryan*, J A., P. Zhang, D. Hesterberg, J. Chou, AND D. E. Sayers. FORMATION OF CHLOROPYROMORPHITE IN A LEAD-CONTAMINATED SOIL AMENDED WITH HYDROXYAPATITE. Glaze, W.H. (ed.), ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 35(18):3798-3803, (2001).
Description:
To evaluate conversion of soil Pb to pyromorphite, a Pb contaminated soil collected adjacent to a historical smelter was reacted with hydroxyapatite in a traditional incubation experiment and in a dialysis system in which the soil and hydroxyapatite solids were separated by a dialysis membrane i a slurry during incubation. A crystalline precipitate formed on the dialysis membrane was identified as chloropyromorphite. Soluble species measured in the soil slurry indicated that dissolution of solid-phase soil Pb was the rate-limiting step for pyromorphite formation. Sequential chemical extraction was used to identify Pb species in field-moist soil incubated with hydroxyapatite. The first four fractions of extractable Pb decreased and the recalcitrant extraction residue fraction increased by 35% of total Pb at 0d incubation and by 45% after 240d incubation. The increase in the extraction residue fraction in the hydroxyapatite amended 0d incubated soil as compared to the control soil illustrates that the chemical extraction procedure itself caused changes in extractability. Thus, the chemical extraction procedure cannot easily be utilized to confirm changes occurring in amended soils. The further increase in the 240d incubation s compared to the 0d incubation implies that the reaction also occurs in the soil during incubation. Extended x-ray adsorption fine structure spectroscopy indicated that the 240d incubated hydroxyapatite treatment caused a change in the average, local molecular bonding environment of soil Pb. Low-temperature EXAFS spectra (chi data and radial structure functions - RSFs) showed a high degree of similarity between the chemical extraction residue and synthetic pyromorphite, providing additional evidence that the change of soil Pb to pyromorphite is possible by simple amendments of hydroxyapatite to soil.