Reducing leachability and bioaccessibility of lead in soils using a new class of stabilized iron phosphate nanoparticles

This study prepared and tested a new class of iron phosphate (vivianite) nanoparticles synthesized with sodium carboxymethyl cellulose (CMC) as a stabilizer for in situ immobilization of lead (Pb(2+)) in soils. Batch test results showed that the CMC-stabilized nanoparticles can effectively reduce the TCLP (toxicity characteristic leaching procedure) leachability and PBET (physiologically-based extraction test) bioaccessibility of Pb(2+) in three representative soils (calcareous, neutral, and acidic). When the soils were treated for 56 days at a dosage ranging from 0.61 to 3.0 mg/g-soil as PO(4)(3-), the TCLP leachability of Pb(2+) was reduced by 85-95%, whereas the bioaccessibility was lowered by 31-47%. Results from a sequential extraction procedure showed a 33-93% decrease of exchangeable Pb(2+) and carbonate-bound fractions, and an increase in residual-Pb(2+) fraction when Pb(2+)-spiked soils were amended with the nanoparticles. Addition of chloride in the treatment further decreased the TCLP-leachable Pb(2+) in soils, suggesting the formation of chloro-pyromorphite minerals. Compared to soluble phosphate used for in situ metal immobilization, application of the iron phosphate nanoparticles results in approximately 50% reduction in phosphate leaching into the environment.