Electrokinetics couples with the adsorption of activated carbon-supported hydroxycarbonate green rust that enhances the removal of Sr cations from the stock solution in batch and column

Abstract

Activated carbon-supported hydroxycarbonate green rust (GR-AC) was prepared, characterized, and used to remove Sr2+ ions from stock solutions. The electrokinetics coupling with the adsorption was further designed to enhance the uptake of Sr2+ ions in the fixed-bed column. The adsorption capacities (mg/g) of GR-AC experienced a U-shaped change over the pH of 2–13 for each concentration of Sr2+. The equilibrium adsorption capacities for the adsorbent in the initial concentrations of Sr2+ of 50, 100, 150, 200, and 250 mg/g were 48.36, 67.42, 73.25, 81.59, and 84.47, respectively. The pseudo-first-order and Elovich kinetic models were appropriate for modeling the adsorption of Sr2+ onto the GR-AC in the static equilibrium-adsorption experiments in terms of the whole pH range, while the intraparticle model was only suitable for the modeling in the alkaline aqueous environment. For the column-mode experiments, the changes in the voltage gradients, flow rates, and initial pH all had a significant effect on the removal of Sr2+ cations. A maximum breakthrough volume of 26.52 L was obtained in the orthogonal design. The correspondingly optimal combination of parameters determined for the column-mode experiments included the voltage gradient of 1.0 V/cm, the initial pH of 10, and a relatively slow flow rate of 5–15 mL/min. The application of EK enhanced the removal kinetics of Sr2+ from the stock solutions while had not significantly affected the interactions between Sr2+ and GR-AC. The specific reaction pathways determined for the Sr2+ removal was different with different pH ranges. The research provides an efficient method for removing radioactive Sr from wastewater in the future.