Fate of Lead (Pb) & Phosphorus (P) in alkaline Pb-polluted soils amended with P and acidified The effect of acidification on Pb and P FIGURE 1 speciation in alkaline Pb-polluted soils that are amended with P to stabilize Pb is unclear. It was studied in alkaline Pb-polluted soils. Results indicated that the formation of pyromorphite, i.e. the Pb stabilized form, was limited in the acidified soil samples amended with fish bones or HPO. This was due to Pb and P3 4 leaching and PbSO formation in the HPO-4(s) 3 4 amended soil samples. In contrast, most Pb was inaccessible to the acidified soil solution or retained by organic matter, similarly to P, in fish bone-amended soil samples. Results had FIGURE 2 important implications on the applicability of this Pb stabilization method in alkaline soils. One of the most cost-effective methods to treat Pb-contaminated soils consists in adding a phosphorus-bearing material to the soil. Lead precipitates along with P to form a very stable mineral phase, pyromorphite (Pb(PO)Cl). The soil is acidified435 to maximize the formation of pyromorphite. The effect of acidification to alkaline Pb-polluted soil has never been reported in the literature. It was then studied in this investigation using a combination of synchrotron techniques. This was useful to determine the possible mechanisms that limit pyromorphite formation in alkaline Pb-polluted soils that are acidified and treated with P. Understanding these mechanisms represents a prerequisite to optimize the efficiency of the P-based method to remediate Pb-polluted soils. This was similar to the 2θ position of the most intense peak in IDENTIFICATION OF Pb & P CHEMICAL FORMS the XRD pattern corresponding to a pyromorphite reference (Fig. 1a). In contrast, none of the mineral phases present in areas The three soil samples studied were characterized in a previousof Garden Soil or Soil Near House, whose XRD patterns were investigation and were called “Soil Near Dump”, “Soil Near House”,extracted by MCR-ALS, could correspond to pyromorphite (data and “Garden Soil” [1]. All XAFS data was treated using SOLEILnot shown). Results from P K-edge XANES analyses indicated Synchrotron’s FASTOSH software [2]. In addition to collectingthat P was in the form of pyromorphite in all Soil Near Dump µ-XRD patterns at specific locations of interest in the P-amendedsamples as their corresponding XANES spectra and the one & acidified soil samples, µ-XRD patterns were collected using acorresponding to pyromorphite were similar to each other (Fig. 2D mapping technique and the data was processed by PCA and 2). The chemical form of P in all Garden Soil and Soil Near House MCR-ALS. In at least one XRD pattern extracted by MCR-ALS in samples, including the control samples and those acidified and a sample area corresponding to Soil Near Dump, the 2θ positionamended with P, could be similar to a P organic form and did of the most intense diffraction peak was at 13.3 ± .1 ° (Fig. 1b). 32