Uranium removal from radioactive wastewater using biochar-based adsorbents: A review on synthesis, performance, and mechanism

With the expansion of nuclear power plants to meet increasing global energy demands, environmental pollution, particularly radioactive uranium (U) contamination, has emerged as a critical research area. Among the various water purification techniques, adsorption is widely utilized for treating radioactive wastewater because of its rapid kinetics, high selectivity, and operational simplicity. Given the significance of purifying uranyl [U(VI)]-contaminated water, this comprehensive review explores the removal of U(VI) from wastewater using different biochar-based adsorbents, focusing on their synthesis methods, adsorption performance, and governing mechanisms. Initially, an overview of the preparation methods for biochar-based adsorbents is provided, covering the synthesis techniques and the incorporation of (nano)composite materials. The discussion then describes four key aspects: (i) U speciation and the role of the solution pH; (ii) adsorption isotherms, kinetics, and thermodynamics; (iii) the influence of background ions, ionic strength, and organic substances on the adsorption behavior; and (iv) desorption characteristics. The improved U(VI) adsorption performance is primarily attributed to mechanisms such as surface complexation, precipitation, and ion exchange. Despite significant progress, further research is necessary to establish a comprehensive framework for the effective purification of U(VI)-contaminated wastewater.