Background

Due to the randomly distributed nature of uranium contamination, remediation strategies often concentrate on in-situ immobilization. Limestone can limit the migration of uranium through its spontaneous replacement reaction with phosphate, and achieve uranium immobilization.

Methods

In this study, the immobilization of uranium in the deposition process of hydroxyapatite was investigated. The effect of carbonate concentration on the reaction process was studied by adding Na₂CO₃.

Significant findings

The deposition process is accompanied by the immobilization of uranium by co-precipitation. The immobilization (92.6%) of uranium (0.52 mmol/L) is due to the formation of calcium uranyl phosphate, increasing carbonate concentration has a significant inhibitory effect on uranium immobilization, and the 50 Mm carbonate can reduce the uranium immobilization efficiency by nearly 20%. XRD, FTIR, Raman, XPS, EA and fluorescence spectroscopy proved that co-precipitation, complexation, and encapsulation were the main mechanisms of uranium immobilization. Through determining the ratios of type-A and type-B substitutions, it reveals the immobilization of uranium weakens due to the competition of carbonate and phosphate. Our study provides the deposition of uranium in the geosphere should be taken into account for remediation and radioactive pollution disposal.