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 KHPO, Ca(HPO), CaHPO, and Ca(PO)), and the pathways and mechanisms of U passivation in the alkaline soil were revealed. The results showed that water-soluble P fertilizers, KHPO and Ca(HPO), were highly effective at immobilizing U, and significantly reduced the bioavailability of soil U. The exchangeable U was reduced by 70.5 ± 0.1% (KHPO) and 68.2 ± 1.9% (Ca(HPO)), which was converted into the Fe-Mn oxide-bound and residual phases. Pot experiments showed that soil remediation by KHPO significantly promoted crop growth, especially for roots, and reduced U uptake in crops by 94.5 ± 1.0%. The immobilization of U by KHPO could be attributed to the release of phosphate anions, which react with the uranyl ion (UO) forming a stable mineral of meta-ankoleite and enhancing the binding of UO to the soil Fe-Mn oxides. In addition, KHPO 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.