Enhanced phytoremediation of uranium-contaminated soils by Indian mustard (Brassica juncea L.) using slow release citric acid

In this study, a novel slow release carrier for the controlled release of citric acid (CA), hydroxypropyl chitosan-graft-carboxymethyl-β-cyclodextrin (HPCS-g-CMCD) was synthesized by the grafting reaction of carboxymethyl-β-cyclodextrin (CMCD) with hydroxypropyl chitosan (HPCS), and the structural characteristics of HPCS-g-CMCD were confirmed by FT-IR, TGA, and NMR. Based on HPCS-g-CMCD and CA, slow release citric acid (SRCA) was prepared by a spray drying method. HPCS-g-CMCD carrier has a better slow release performance for CA compared to HPCS and CMCD, and CA release mechanism was attributed to a Fickian diffusion. Furthermore, the release behavior of uranium in contaminated soil could be effectively controlled by SRCA. The effects of SRCA on improving the phytoremediation capacity in uranium-contaminated soil were investigated using Brassica juncea, which were grown in pots containing soil with uranium at 56 mg kg⁻¹. After 50 days of growth, 5 mmol kg⁻¹ of CA, SRCA I, SRCA II, and SRCA III was applied, respectively. The results showed that slow release citric acid could enhance the uptake of uranium in Indian mustard. Uranium concentration in the root with SRCA I treatment was increased by 80.25% compared to the control, and the uranium removal efficiency of the SRCA I treatment was 1.66-fold greater than that of the control. Simultaneously, the leaching loss of uranium in SRCA I-treated soil was decreased by 37.35% compared to CA-treated soil. As a promising remediation strategy, SRCA-assisted phytoremediation may provide a kind of feasible technology with low leaching risk for remediation of uranium-contaminated soils.