Rice straw-based biochar beads for the removal of radioactive strontium from aqueous solution

Biochars from agricultural residues have recently attracted significant attention as adsorbents for purifying contaminated water and wastewater. In this study, the removal of strontium from aqueous solutions was investigated using rice straw-based biochar (RSBC) beads in both batch and continuous fixed-bed column systems. The RSBC beads had negatively charged surfaces and exhibited a large surface area (71.53 m²/g) with high micro-porosity. The synthesized beads showed a maximum adsorption capacity of 175.95 mg/g at an initial strontium concentration of 10 g/L at 35 °C and pH 7. Furthermore, they showed a good selectivity toward strontium ions in the presence of competing ions such as Al^{3 +}, Mg^{2 +}, and K⁺. The effects of different operating conditions like flow rate and initial strontium concentration were investigated in the fixed–bed column reactor. The Thomas, Adams–Bohart, and Yoon–Nelson models were applied to the experimental data to predict the breakthrough curves using non-linear regression. Both the Thomas and the Yoon–Nelson models were appropriate for describing entire breakthrough curves under different operating conditions. Overall, RSBC beads demonstrate great potential as efficient adsorbents for the treatment of wastewater polluted with strontium in a continuous operation mode.