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GIFU UNIVERSITY GIFU UNIVERSITY DEPARTMENT of CIVIL ENGINEERING Phosphorus-Induced Lead Immobilization in a Shooting Range Soil Using Poorly-Crystalline Hydroxyapatite and Incinerated Poultry Waste Yohey Hashimoto, Takatoshi Yoshida, Takeshi Sato Results and Discussion Objective To assess the effects of phosphorus amendments on immobilizing Pb and recovering soil biological properties. Materials and Methods A soil incubation study was conducted to assess the effect of P amendments on soil Pb immobilization up to 22 weeks. Amendments used were pure hydroxyapatite (HA), byproduct based hydroxyapatite(CHA), Ca3(PO4)2 (CP) and incinerated poultry waste (PW). Soil sequential extraction, XRD, TCLP were performed on Pb to assess immobilization. Enzyme activities of dehydrogenase, phosphatase, and urease were determined and were linked to soil Pb fractions. Reference for poorly-crystalline hydroxyapatites synthesized from industrial byproducts - Hashimoto, Y., and T. Sato. 2007. Removal of aqueous lead by poorly-crystalline hydroxyapatites. Chemosphere 69:1775-1782. Soil and Hydroxyapatite properties Sequential Extraction of Pb Activities of dehydrogenase and urase improved in the P-added soils relative to the non-amended soils. The addition of poultry waste had a low enzyme activity due probably to the excessive pH rise. Poultry waste was most effective in reducing bioavailable Pb, but may have an adverse impact on soil ecosystem and reestablishing the vegetation. The residual fraction was greatest in PW (80%) > CP (50%) > CHA (50%) > HA (15%) > Soil (7%). Reduction of carbonate fraction in PW, CP and CHA induced the increase of their residual fraction that could be related to pyromorphite. Ceramic-apatite (CHA) reduced soluble Pb more effectively than pure hydroxyapatite (HA) because CHA had greater solubility and surface area, enhanced P dissolution and Pb-P precipitation reactions. Amendments of poultry waste (PW), ceramic-apatite (CHA) and Ca3(PO4)2 (CP) reduced soluble Pb due probably to the formation of pyromorphite-like minerals. Phosphorus amendments except poultry waste improved soil enzyme activities. Although poultry waste was most capable of immobilizing soil Pb, it may give an adverse impact on enzyme activities, suggesting the importance in amendments from the soil biological perspectives. Pb toxicity to vegetation and soil microbes needs to be alleviated in shooting ranges Cerussite (PbCO 3 ) is the common species of Pb in shooting ranges Immobilization of Pb by Phosphorus Phosphorus amendments immobilize soil Pb via formation of pyromorphite Pb5(PO4)3Cl. Lower solubility than the other Pb species, and stable in an acid pH Three Difficulties in Remediation of Shooting Range Soils (in Japan) Severe & Broad Contamination Slope contamination Low Land Price Pb Mineralogy of P amended soils Soil pH and TCLP extractable Pb changes after 22 weeks Amendments pH TCLP-Pb (ppm) 22week 1 week 22 week HA (hydroxyapatite) 7.3 820 890 CHA (ceramic HA) 6.9 313 475 CP (Ca-phosphate) 6.5 47 62 PW (poultry waste) 11.2 0.05 0.05 Soil (w/o amend) 7.2 900 592 A pure hydroxyapatite (right) synthesized from ceramic waste has a greater surface area than the commercial one (left). Peaks of cerussite (PbCO3) and hydrocerussite [Pb3(CO3)2(OH)2] were observed in all soils, indicated as C and HC, respectively. Pyromorphite peaks were observed in the CHA and CP amended soils that had lower pH than the other soils. Immobilization mechanism of PW could be increased pH (~12). HA CHA CP PW No amendment Exchangeable Carbonate Fe/Mn Organic Residual HACHACPPW w/o amendment HACHACPPW w/o amendment Soil Enzyme activities – Dehydrogenases & Urease Conclusions Expensive cost --- Pb concn exceeds 10000 ppm 70% of Japanese land is hilly Annual precipitation exceeds 80 in. Recuperating the cost spent for the soil remediation is difficult via a real-estate deal. Erosion Cost effective technologies --- in-situ immobilization with P amendments Cost effective P-amendments Byproducts Pb Immobilization Reduced toxicity to soil ecosystems enzymes Poultry waste Stable Pb species Hydroxyapatite synthesized from ceramic waste
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