Remediation of uranium-contaminated alkaline soil by rational application of phosphorus fertilizers: Effect and mechanism

In alkaline soil, abundant carbonates will mobilize uranium (U) and increase its ecotoxicity, which is a serious threat to crop growth. However, the knowledge of U remediation in alkaline soils remains very limited. In this study, U-contaminated alkaline soil (tillage layer) was collected from the Ili mining area of Xinjiang, the soil remediation was carried out by using phosphorus (P) fertilizers of different solubility (including KH2PO4, Ca (H2PO4)2, CaHPO4, and Ca3(PO4)2), and the pathways and mechanisms of U passivation in the alkaline soil were revealed. The results showed that water-soluble P fertilizers, KH2PO4 and Ca(H2PO4)2, were highly effective at immobilizing U, and significantly reduced the bioavailability of soil U. The exchangeable U was reduced by 70.5 +/- 0.1% (KH2PO4) and 68.2 +/- 1.9% (Ca(H2PO4)2), which was converted into the Fe-Mn oxide-bound and re-sidual phases. Pot experiments showed that soil remediation by KH2PO4 significantly promoted crop growth, especially for roots, and reduced U uptake in crops by 94.5 +/- 1.0%. The immobilization of U by KH2PO4 could be attributed to the release of phosphate anions, which react with the uranyl ion (UO22+) forming a stable mineral of meta-ankoleite and enhancing the binding of UO22+ to the soil Fe-Mn oxides. In addition, KH2PO4 dissolution produces acidity and P fertilizer, which can reduce soil alkalinity and improve crop growth. The findings in this work demonstrate that a rational application of P fertilizer can effectively, conveniently, and cheaply remediate U contamination and improve crop yield and safety on alkaline farmland.

Automated summary

This study investigates the remediation of uranium contamination in alkaline soil by using different solubility phosphorus fertilizers. The results show that water-soluble phosphorus fertilizers, KH2PO4 and Ca(H2PO4)2, effectively immobilize uranium and reduce its bioavailability in soil. Pot experiments demonstrate that soil remediation with KH2PO4 promotes crop growth, particularly root growth, and reduces uranium uptake in crops. The immobilization of uranium by KH2PO4 is attributed to the release of phosphate anions, forming stable minerals and enhancing the binding of uranium to soil Fe-Mn oxides.