A quantitative XANES evaluation of the TCLP applicability in phosphate-induced lead stabilization for firing range soils

An acidic (pH 5.2) firing range soil, FDR26 in New Jersey, with Pb content of 6,017 mg kg⁻¹, was amended by adding 2.5 wt% fish bone grains. The leaching test, toxicity characteristic leaching procedure (TCLP), and spectroscopic technique, non-destructive X-ray absorption near edge structure (LCF-XANES), were employed to determine the leaching behavior and Pb speciation prior to and after the TCLP test. The TCLP-Pb was 209 mg L⁻¹ after the standard 18 h of tumbling and was increased to 288 mg L⁻¹ after an extended tumbling time of 96 h. The XANES of TCLP residue confirmed the existence of extractable Pb species following the 18 h extraction. TCLP-Pb was also reduced to 1.4 mg L⁻¹ after phosphate addition followed by 28 days of curing. LCF-XANES results revealed the transformation of metallic Pb into insoluble pyromorphite precipitates during the leaching test. The acidic extraction solution significantly increased the dissolution of phosphate source and Pb species, and resulted in improved Pb immobilization.