Speciation of a Pb and Zn contaminated soil reacted with various P amendments: A molecular-scale prospective Luke R. Baker 1, G.M. Pierzynski 1, G.M. Hettiarachchi 2, K.G. Scheckel 3, M. Newville 4, and S. Indraratne 5. 1 Department of Agronomy, Kansas State University, Manhattan, KS, USA; 2 The University of Adelaide/CSIRO, Australia; 3 USEPA, Cincinnati, OH, USA; 4 GSECARS, University of Chicago, USA; 5 University of Peradeniya, Peradeniya, Sri Lanka; Objectives Introduction Extraction and processing of metal ores has contaminated soil and water resources with heavy metals throughout the world. Natural weathering processes acting on contaminated land and mining wastes have dispersed metal contaminants to surrounding soils, streams, and ground water, further endangering humans and ecosystems. Studies have shown that the addition of P amendments to Pb and Zn contaminated soils reduces the bioavailability of these metals. At this time we are unsure if the source of P influences the efficiency and rate of reaction product formation. These observations can be made by molecular scale studies that allow us to investigate redistribution/speciation of Pb and Zn upon addition of different P sources to contaminated soils. To investigate the reaction products that are formed over time in similar environments when different P amendments are added to a Pb and Zn contaminated smelter slag at the molecular level Sample/Thin Section Preparation The contaminated material was a smelter slag that was collected near a Pb/Zn smelter from Dearing, KS A small amount of the contaminated material brought to 25% gravimetric water content was placed in a plastic container Phosphorus (P) treatments were added in a line across the center of the container onto the soil P Treatments: Phosphoric Acid (PA) Rock Phosphate (RP) Monammonium Phosphate (MAP) Ammonium Polyphosphate (APP) Triple Super Phosphate (TSP) Treatments were covered with additional contaminated soil (25% gravimetric water content), covered, incubated for 1 month or 12 months (data not shown), dried, and impregnated with Buehler EpoThin® two part (epoxy/hardener) resin (Beuhler LTD., Lake Bluff, IL, USA) A petrographic trim saw was used to cut through the resin blocks (Fig. 1) and expose the P treated smelter slag Thin sections (< 30 μm) were prepared on polystyrene plastic slides with the exposed P treatment directly cemented to the plastic μ-XRF, -XANES/-EXAFS, and -XRD Analysis XRF maps were collected near the point of P application (on average ~300 x 500 μm) and points of interest (POI) were then determined for Pb and Zn (Fig. 2) For each POI, the following analyses were performed: Pb XANES (13,035 eV); Zn EXAFS (9658 eV); μ-XRD (17,500 eV) The linear combination fitting (LCF) procedure was used to reconstruct the Pb and Zn using all of the combinations possible from the known Pb and Zn compounds Pb XANES spectra were fit due to high background noise (Fig. 3) Zn k 2 -weighted EXAFS were fit (Fig. 4) For μ-XRD, the data were processed using the Fit2D software package for integrating 2-D Debye-Scherrer rings to one-dimensional 2θ scans Results: μ-XRF, Pb and Zn μ-XANES Fig 1. Picture illustrating a treated resin block. Pb Zn Fig 2. X-ray fluorescence maps of selected elements for the 1 month rock phosphate treatment. Area of a single map is 300 by 500 μm. The color scheme employed ranges from white-yellow for high fluorescence signal to blue-black for low fluorescence signal. The arrows indicate points of interest where μ-XANES and/or μ-XRD was employed. Similar maps were collected for all other treatments to determine POI’s. Table 1. Results for Pb XANES linear combination fitting for selected POI’s for each treatment at 1 month. Typcial uncertainties for LCF are PbCO 3 = cerussite; PbFe 12 O 19 = magnetoplumbite; PbS = galena; Fe 4 PbO 7 = plumboferrite; PbAl 3 (PO 4 ) 2 (OH) 5 *H 2 O = plumbogummite; Pb 5 (PO 4 ) 3 Cl = pyromorphite. Table 2. Results for Zn EXAFS linear combination fitting for selected POI’s for each treatment at 1 month. Typical uncertainties for LCF are Zn 4 Si 2 O 7 (OH) 2 *H 2 O = hemimorphite; ZnSiO 4 = willemite; Zn 3 (PO 4 ) 2 *4H 2 O = hopeite; ZnO = zincite. Note: No MAP treatment for Zn, spectra were not good. Results:μ-XRD Conclusions Fig 5. The 2-dimensional diffraction pattern obtained (A) at the GSECARS beamline. Minerals indicated from the pattern include: PbCO 3 = cerussite; PbFe 12 O 19 = magnetoplumbite; PbS = galena; PbAl 3 (PO 4 ) 2 (OH) 5 *H 2 O = plumbogummite; and Pb 5 (PO 4 ) 3 Cl = pyromorphite. Red lines in (B) indicate plumbogummite, green- pyromorphite, and blue- cerrusite. A B Thanks to Dr. Mickey Ransom, the staff at GSECARS Argonne National Laboratory, Ellen Burke, and Grace Vaillant for their assistance in thin section preparation, sample analysis and lab work. Acknowledgements * and $ indicates POI’s that are eight ~300 to 400 microns or ~25 microns, respectively, from the point of P application # Indicates if μ-XRD was able to confirm LCF findings for XANES spectra. Y = yes; MS = Major Species identified PbCO 3 PbFe 12 O 19 PbSFe 4 PbO 7 Sorbed PbPbAl 3 (PO 4 ) 2 (OH) 5 *H 2 OPb 5 (PO 4 ) 3 ClXRD # Control Y RP* MS RP $ Y TSP* Y TSP $ Y PA* Y PA $ Y MAP* Y MAP $ Y APP* Y APP $ Y Fig 3. The normalized XANES spectra of selected Pb points of interest for each treatment. Zn 4 Si 2 O 7 (OH) 2 *H 2 OZnAlSilicateZnSiO 4 Zn 3 (PO 4 ) 2 *4H 2 O ZnSO 4 ZnOXRD # Control Y RP* MS RP $ Y TSP* Y TSP $ MS PA* MS PA $ Y APP* Y APP $ Y * and $ indicates POI’s that are eight ~300 to 400 microns or ~25 microns, respectively, from the point of P application # Indicates if μ-XRD was able to confirm LCF findings for EXAFS spectra. Y = yes; MS = Major Species identified Fig 4. The normalized Zn-EXAFS spectra of selected points of interest for each treatment in k-space. LCF was used in an attempt to reconstruct the spectra in k- space. TSP was able to induce the formation of Pb/Zn phosphate more effectively than all other granular fertilizer treatments In general, fluid P sources appear to be more effective at producing Pb/Zn phosphates as compared to the equivalent granular sources The combined use of different synchrotron based techniques, μ-XANES/EXAFS and μ-XRD, helped to enhance species identification providing us with less uncertainty A quick and simple μ-XRD pattern can be used to confirm the LCF procedure All P treatments produced Pb phosphate minerals as indicated by both μ-XANES and μ-XRD analysis Distance from the application point and the form the fertilizer, fluid or granular, has major implications on whether Pb phosphates will form Of the two fluid fertilizer P treatments, PA and APP, PA was more effective at forming plumbogummite (a more soluble Pb phoshpate mineral) both near and at ~350 microns from the point of application, but APP was the only treatment to induce the formation of pyromorphite (highly insoluble Pb phosphate) All P treatments were able to induce Zn phosphate formation as indicated by μ- EXAFS and μ-XRD APP was more effective at producing Zn phosphates that PA Distance from the application point has major implications on whether Zn phosphates will form 12 month samples will be evaluated using the same techniques to determine treatment effectiveness Future Research