Enhanced removal of iodide ions by nano Cu2O/Cu modified activated carbon from simulated wastewater with improved countercurrent two-stage adsorption.

A newly developed adsorbent nano Cu2O/Cu-modified activated carbon composite (nano Cu2O/Cu-C) was used to remove radioactive iodide ions (I-) from simulated wastewater. The emphasis of this research is to improve adsorption performance and obtain higher I- removal efficiency compared with the single-stage adsorption. To fully develop the amount of adsorption by nano Cu2O/Cu-C, and to increase the decontamination factor (DF) of I-, an improved countercurrent two-stage adsorption (ICTA) process was introduced. In the ICTA process, measures dealing with desorption of loaded adsorbent in the stage-two adsorption were taken and more extensive application of countercurrent two-stage adsorption (CTA) process could be made after the improvement to ICTA process in this study. Furthermore, in order to analyze the process and determine the I- concentration in the effluent, a calculation method was devised based on the Langmuir isotherm equations and adsorption accumulation principle. The mean DFs were 177, 166, and 89.7, respectively, when the initial I- concentrations were 5.00, 10.0, and 20.0 mg/L; and the adsorbent dosage was 1.25 g/L. These results were approximately 8.76, 8.97, and 6.79 times higher, respectively, than with conventional single-stage adsorption. The experimental values of the I- concentration were higher than the calculated ones, which could be ascribed to desorption of the residual loaded adsorbent and formation of CuI in the adsorption at stage 1. Formation of CuI in the adsorption at stage 1 was considered to be the predominant reason.