Optimization analysis and mechanism exploration on the removal of cesium and the solidification of secondary residue wastes in electrokinetics

Abstract

The fallout of the radioactive nuclide cesium (Cs) has posed its potential environmental threat to human health and ecosystem during the Fukushima accident. Thus, Cs decontamination from radioactive wastewater is strongly required for treating similar occurrences. In this work, a coupling method was applied to achieve Cs+ removal and solidification in one conducting system. Ammonium molybdophosphate (AMP) was loaded to blast furnace slag (BFS) particles for the preparation of adsorbent (BFS-AMP) and binder. The maximum adsorption capacity of BFS-AMP for Cs+ was 23.36 mg/g obtaining at the pH of 8 and the initial concentration of 500 mg/L in the equilibrium adsorption experiments. Cs+ uptake confirmed to the pseudo-first-order kinetic model. Electrokinetics (EK) not only increased the adsorption capacity of BFS-AMP also enhanced the migration of Cs+ ions from the anode to cathode in the electrolyzer. The transfer of Cs+ ions from liquid to solid in the electrolyzer was controlled by both voltage gradients and flow rates. The solidification of EK-treated BFS-AMP mortar was mainly dominated by the mass ratios (wt.%) of alkali activator to adsorbent and the initial pH values. Cs+ leaching from the solidified products of EK-treated BFS-AMP mortars ranged from approximately 1.18 × 10−7 to 9.54 × 10−6 g cm−2∙d−1. The electromigration, geopolymer stabilization, and hydration encapsulation were concluded as the main incorporation mechanisms for Cs+ ions transferring from the stock solution into the BFS-AMP-based solidification in the electrolyzer.