Optimized cementitious immobilization of simulated cesium and barium radionuclides in borate waste solution by natural zeolite additives

This study investigates the immobilization of cesium and barium contaminants in borate waste solutions using clinoptilolite-bearing and mordenite-bearing additives within cement matrices, with a focus on their adsorption capacity. These zeolites were incorporated at varying ratios into blends of Portland cement (PC) and calcium sulfoaluminate cement (CSAC). A batch adsorption experiment was conducted, utilizing borate waste solutions containing trace concentrations of simulated cesium-137 radioisotopes and its metastable decay product barium-137, to evaluate their effectiveness in reducing the leachability of these contaminants after a 28-day solidification period. The experimental setup included a comprehensive analysis involving ASTM standard leaching tests over 11 days, alongside compressive strength testing, scanning electron microscopy (SEM), and X-ray diffraction (XRD) for morphological and chemical assessment at the cement mineral level. Inductively coupled plasma optical emission spectroscopy (ICP-OES) and mass spectroscopy (ICP-MS) analyses were conducted on the leachate from the solidified cement pastes to study the physical and chemical changes of the cement pastes matrices. Results showed that cement paste matrices with untreated clinoptilolite-bearing samples exhibited the highest cesium adsorption capacity in the boric acid liquid waste, whereas KCuHFC-treated zeolite-bearing (i.e., clinoptilolite-bearing and mordenite-bearing) samples showed diminished capacity for cesium adsorption from the boric acid liquid waste. The use of 5% clinoptilolite in the PC/CSAC blend produced optimal physical and chemical stability, highlighting its potential for effective cesium immobilization in waste management.