Comparing struvite, K-struvite and hydroxyapatite for the remediation of lead and cadmium contaminated soil

Heavy metal pollution leads to severe soil contamination and raises environmental concerns. Phosphorus-bearing minerals have been identified as effective and environmentally friendly agents for remediating contaminated soil. However, using recycled phosphorus for metal remediation remains limited. In this study, we investigated the potential use of recovered magnesium ammonium phosphate (MAP), potassium magnesium phosphate hydrate (KMP), and hydroxyapatite (HAP) to immobilize lead (Pb) and cadmium (Cd) in contaminated soil. The effectiveness of MAP, KMP, and HAP in modifying the chemical composition of Pb and Cd in the soil and reducing their mobility was demonstrated by the results. When added at dosages of 5:1 and 10:1, the extractable fraction of Pb decreased to 0.43–13.43 % of the control group. Similarly, the extractable fraction of Cd decreased to 49.18–76.44 % of the control group at the same dosages. Moreover, the application of these products resulted in an increase in soil pH value, urease activity, and bacterial Shannon index, thereby enhancing soil properties. The immobilization effects were more significant in Pb-contaminated soil compared to Cd-contaminated soil, and MAP and KMP exhibited a stronger passivation effect on Pb in comparison to HAP. For soil fertility improvement, a molar ratio of 10:1 was recommended, whereas a ratio of 5:1 effectively passivated Pb in contaminated soil. These findings provide evidence for the feasibility of utilizing MAP, KMP, and HAP in the immobilization of heavy metals in polluted soil.