Hydroxyapatite (HAP) has been recognized as an effective absorbent for uranium. Recognizing and revealing its fate in coordinating with uranyl ions (U(VI)) under various conditions are vital for its practical application. In this work, HAP nanoflowers were synthesized by a simple wet chemical method, and the immobilization properties of HAP on U(VI) and U(VI) phase transformation during immobilization process were investigated systematically using a host of experimental methods and advanced characterization techniques. The results show that HAP can effectively immobilize U(VI) at high concentrations (50–3000 mg/L), with a maximum U(VI) adsorption capacity (q) of 10,200 mg/g and a distribution ratio (K d ) higher than 1.16 × 10 5 mL/g. Under the presence of sufficient U(VI) and a pH around 1.5 ∼ 3.0, HAP can rapidly react with U(VI) to form Autunite (Ca(UO 2 ) 2 (PO 4 ) 2 ·3H 2 O) with a nanoflake morphology, which is demonstrated excellently long-term stability. A moderately low pH that enables form adequately free calcium ions and phosphate groups via hydrolysis of HAP is essential to the mineralization of U(VI). This work is expected to pave the way for the use of HAP to develop highly efficient immobilization agents for the remediation of uranium-contaminated scenes and presents a comprehensive insight into the mechanisms of long-term U(VI) stabilization.
Column reactors and batch experiments were conducted to investigate the performance and mechanism of uranium (U) immobilization enhanced by extracellular polymeric substances (EPS) from anaerobic granular sludge (ANGS). Successful remediation of anoxic U-contaminated groundwater was achieved using ANGS-inoculated column reactors (all higher than 98% of U removal rate for the three columns at hydraulic retention time of 72-h), and parameters (hydraulic retention time, nitrate content, the type and content of the external carbon sources) influenced the reactor performance. 306-day column studies implied the enhanced U immobilization by EPS, where EPS acted as energy source, electron donors and U reservoir with a contribution of 3.5–6.8% to total U removal by ANGS. Results in 26-h batch experiments further demonstrated that U immobilization performance of ANGS could be promoted (6.4–22%) by EPS through adsorption and reduction. EPS induced the precipitation of U(VI) and U(IV) particulates, and amino and carboxyl groups were the main functional groups for EPS binding with U. Complexation was confirmed between humic acids in EPS and U. The interaction mechanisms between U and EPS were directly evidenced to involve complexation, induced particulate formation and reduction.
In this work, hydroxyapatite (HAP), an environmentally friendly material was prepared with Phosphogypsum (PG) as calcium source, and uranium immobilization gel spheres were prepared by chitosan (CS) embedding, which would reduce HAP agglomeration while providing an abundance of uranium-loving groups, realizing “treating waste for waste”. The optimum pH for U(VI) removal was determined to be 4, the optimum dosage was 0.2 g/L, and q max = 350.88 mg/g through batch experiments. When C 0 = 10 mg/L, it was found that the removal rate of U(VI) by HAP-CS could be up to 99.92 %, and the residual uranium concentration was 0.008 mg/L, which meets the national emission standard. The removal rate of uranium can reach 95.92 % by applying it to high concentration uranium ore wastewater. CS was found to have good biocompatibility with HAP by SEM, FTIR, XRD, and XPS characterization. Meanwhile, we found that Ca, –OH, and P-O play a dominant role in the uranium removal process, and the main mechanism of uranium removal by Hydroxyapatite-Chitosan gel spheres (HAP-CS) is surface complexation, ion exchange, and dissolution–precipitation binding. The HAP-CS has high uranium removal efficiency, simple solid–liquid separation, and good biocompatibility, and can be used to treat actual uranium-containing wastewater.
危险品化学品经营许可证（带存储）