Remediation of lead contamination in shooting range soil by the amendment of four types of phosphate chemicals

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1 Remediation of lead contamination in shooting range soil by the amendment of four types of phosphate chemicals Bin Hua John Yang June 17, 21 Department of Agriculture and Environmental Sciences Lincoln University of Missouri, Jefferson City, Missouri

2 Background information Outline Objectives and methods Results and discussion Solution extraction SEM/EDS XRD analysis

3 Lead contamination in shooting range In the US, the total amount of Pb expended as munitions in hunting and recreational shooting has exceeded 3 million tons in the last century Lead weathering occurs as soon as lead bullets contact with soil, air and water. Within 6 13 years, 5 17% of the metallic Pb bullet may be transformed into Pb oxide, carbonate and sulfate. Complete transformation may take 1 3 years Pb mobilization is induced by the weathering of metallic Pb, followed by the dissolution of these weathering products.

4 Obstacles in shooting range remediation In shooting range, Pb concentration often exceeds 1, mg kg -1 soil because of spent lead bullets Pb weathering is slow and could last up to several hundreds years Due to their remote locations, the shooting ranges have a lower land price than urban areas, indicating that recuperating the cost spent for soil remediation will be difficult via real-estate deals after the remediation process has been completed.

5 Pb immobilization by different phosphate sources Amendment materials Contamination sources References Synthesized Hydroxyapatite PbCl 2, Pb(NO 3 ) 2, soil Pb Ma (1994); Zhuang and Ryan (1999) Soluble phosphate PbCl 2, Pb(NO 3 ) 2, soil Pb Cotter-Howells (1994); NaH 2 PO 4, KH 2 PO 4, H 3 PO 4 Yang (21) Phosphate rock PbCl 2, Pb(NO 3 ) 2, soil Pb Ma and Rao (1999); Garrido (26) Biosolids PbCl 2, Pb(NO 3 ) 2, soil Pb Brown (23) Deydier (27)

6 Solubility of several phosphate compounds

7 Objectives and methods Objectives To demonstrate that the treatments using phosphate chemicals could effectively immobilize high concentration of lead in shooting range To evaluate the efficiency of different types of phosphate chemicals in terms of lead immobilization and to identify the products after the treatment. Methods Soil preparation Immobilization treatment Solution extraction Treated soil characterization using SEM/EDS and XRD

8 Methods (cont d) Sample I.D. O.M. % CEC meq/1g Total P % ph STL Texture Total Pb ppm Sand % Silt % Clay Clay loam 45,

9 Methods (cont d) Sample ID T1 T2 T3 T4 T5 Chemical H 3 PO 4 (8%) KH 2 PO 4 CaHPO 4 P-fertilizer Control Dosage 5.69 ml 7.15 g 7.15 g g Water 1 ml 1 ml 1 ml 1 ml 1 ml Soil 1 g 1 g 1 g 1 g 1 g

10 Methods (cont d) Sequential extraction: 1. Water soluble and exchangeable 2. Bound to carbonate 3. Bound to Fe-Mn 4. Bound to organic 5. Residual Limitation: In situ transformation

11 Methods (cont d) Solution extraction, SEM/EDS, and XRD 1. Distilled, deionized water to simulate storm rain-off 2. Toxicity characteristic leaching procedure (TCLP) solution (ph = 2.88) to simulate landfill leachate 3. Concentrated nitric acid with microwave assisted digestion; using NIST 2711 Montana soil for quality control 4. SEM/EDS 5. XRD analysis

12 Extractable lead after phosphate amendment weeks 6 weeks Pb (ppm) Pb (ppm) H3PO4 KH2PO4 CaHPO4 Fertilizer Control Different phorsphous sources H3PO4 KH2PO4 CaHPO4 Fertilizer Control Different phorsphous sources (a) extracted by Millipore water after 2 weeks; (b) extracted by TCLP (ph = 2.88) after 2 and 6 weeks.

SEM/EDS of T2 treated with KH 2 PO 4 2 Si 15 Counts 1 P Pb 5 2 4 6 kev

13 SEM/EDS of T2 treated with KH 2 PO 4 2 Si 15 Counts 1 P Pb kev Counts Pb 12 P Si kev Counts 25 Si 2 15 P Pb kev

SEM/EDS of T4 treated with fertilizer 12 Counts 1 8 6 4 P Pb 2 2 4 6

14 SEM/EDS of T4 treated with fertilizer 12 Counts P Pb kev Counts Pb P Counts P Pb kev kev

SEM/EDS of T5 (control without adding any phosphate compound) 25 2 Pb Counts 15 1

15 SEM/EDS of T5 (control without adding any phosphate compound) 25 2 Pb Counts kev 3 35 Counts Pb Counts Pb kev kev

16 XRD spectra of sample T2, T4 and T5 1 Intensity (arbitrary units) PbCO3 s5 s2 s

17 Summary The soil treatments with KH 2 PO 4 and fertilizer ((NH 4 ) 3 PO 4 as the effective composition) were most effective, resulting in over 99% reduction of TCLP leachable Pb within two-week period, as compared to the control sample The X-ray diffraction (XRD) and leaching tests indicated that lead carbonate present in untreated soil has been transformed into insoluble lead phosphates by the treatment Solid-phase analyses using SEM/EDS revealed that phosphorous in treated soils were closely associated with lead, suggesting the formation of insoluble pyromorphites or pyromorphite-like minerals.

18 Acknowledgements Financial support from USDA is gratefully acknowledged. Moussa Bakari (Lincoln University) Kristina Norris (Lincoln University)

19 Thank you! Questions?

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