| Abstract
| - In addition to the formation of insoluble lead (Pb)compounds, adsorption is another potentially importantprocess controlling the bioavailability of Pb in soils. Lessattention has been given to manganese (Mn) oxides, eventhough they are known to adsorb Pb more strongly thanany other metal (hydr)oxides. This study was conducted toevaluate the effects of P and Mn oxide on bioavailablePb in five metal-contaminated soils or mine spoils fromKansas and Missouri. Cryptomelane was used as therepresentative Mn oxide. Nine treatments were used: zeroP, 5000 mg of P as triple superphosphate (TSP) orphosphate rock (PR), 2500 and 5000 mg of Mn oxide/kg,and combinations of Mn oxide and P as TSP or PR. Changesin bioavailable Pb over time were measured using amodified physiologically based extraction procedure (PBET),and mineralogical changes were observed using X-raydiffraction. The addition of P or cryptomelane reducedbioavailable Pb in all five materials. The addition of P andcryptomelane together was more effective in reducingbioavailable Pb than the addition of either amendment alonein all materials. Reductions in bioavailable Pb in stomachphase extractions upon addition of P or P and cryptomelaneranged from 15 to 41% and 23 to 67%, respectively, comparedto the unamended control. Similarly, a modified toxicitycharacteristic leaching procedure (TCLP) indicated lesssoluble Pb in materials receiving P and cryptomelanecompared to the control, P- or cryptomelane-treated samples.X-ray diffractometry analysis supported the PBET andTCLP results, indicating that more “pyromorphite-like minerals”formed in the presence of both P and Mn oxide comparedto the control. This new improved technique to remediatePb-contaminated soil and mine wastes has advantages overstandard methods.
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