Remediation of Cd(ii)-contaminated soil by three kinds of ferrous phosphate nanoparticles

Abstract

The remediation of cadmium-contaminated soil has become a great concern because Cd will bring high health risk. Three kinds of iron phosphate nanoparticles, Fe₃(PO₄)₂, FeHPO₄ and Fe(H₂PO₄)₂, were synthesized to reduce the leachability and bioaccessibility of soil-bound Cd. The Cd leachability was evaluated by a toxicity characteristic leaching procedure (TCLP) and in vitro bioaccessibility was evaluated by physiological based extraction test (PBET). After equilibrating for 42 days, the concentrations of TCLP were reduced from 4.43 to 0.99, 1.42 and 1.63 mg L⁻¹ at a dosage of 4.5 mg PO₄ g⁻¹ soil with Fe₃(PO₄)₂, FeHPO₄ and Fe(H₂PO₄)₂, respectively. Meanwhile the bioaccessibility of Cd was reduced by 22.4, 10.6 and 20.7%. The results showed that the nanoparticles were highly effective at amending Cd in soils and the best material for immobilizing Cd was Fe₃(PO₄)₂. Results from sequential extraction procedures (SEP) showed a great decrease in exchangeable Cd and a concomitant increase in Cd residual fraction, suggesting that the formation of cadmium phosphate through precipitation was responsible for the decrease of Cd availability in soils. Moreover, because stable ferrous phosphate nanoparticles would bring less P residue than other soluble phosphate, they can be further optimized to prepare for practical application.