In situ stabilization of soil lead using phosphorus and manganese oxide

In addition to the formation of insoluble lead (Pb) compounds, adsorption i s another potentially important process controlling the bioavailability of Pb in soils. Less attention has been given to manganese (Mn) oxides, even t hough they are known to adsorb Pb more strongly than any other metal (hydr) oxides. This study was conducted to evaluate the effects of P and Mn oxide on bioavailable Pb in five metal-contaminated soils or mine spoils from Kan sas and Missouri. Cryptomelane was used as the representative Mn oxide. Nin e treatments were used: zero P, 5000 mg of P as triple superphosphate (TSP) or phosphate rock (PR), 2500 and 5000 mg of Mn oxide/kg, and combinations of Mn oxide and P as TSP or PR. Changes in bioavailable Pb over time were m easured using a modified physiologically based extraction procedure (PBET), and mineralogical changes were observed using X-ray diffraction. The addit ion of P or cryptomelane reduced bioavailable Pb in all five materials. The addition of P and cryptomelane together was more effective in reducing bio available Pb than the addition of either amendment alone in all materials. Reductions in bioavailable Pb in stomach phase extractions upon addition of P or P and cryptomelane ranged from 15 to 41% and 23 to 67%, respectively, compared to the unamended control. Similarly, a modified toxicity characte ristic leaching procedure (TCLP) indicated less soluble Pb in materials rec eiving P and cryptomelane compared to the control, P- or cryptomelane-treat ed samples. X-ray diffractometry analysis supported the PBET and TCLP resul ts, indicating that more "pyromorphite-like minerals" formed in the presenc e of both P and Mn oxide compared to the control. This new improved techniq ue to remediate Pb-contaminated soil and mine wastes has advantages over st andard methods.