Synthesis of NaP1 zeolite from silica waste as an absorbent for the removal of Cs+ and Sr2+ from aqueous solution

Abstract

For effective utilization of silica waste discharged from an industrial process for manufacturing synthetic quartz glass, GIS-NaP1 zeolite as an adsorbent for removing Cs+ and Sr2+ from an aqueous solution was hydrothermally synthesized using silica waste as the raw material. The experimental parameters in the hydrothermal process, such as reaction temperature, reaction time and molar ratio of SiO2:NaOH:H2O, were studied to examine their effects on the formation of zeolites. The samples obtained were characterized by XRD and FE-SEM, and the pore size distribution and the BET surface area were also determined by nitrogen adsorption–desorption. The samples mainly consisted of GIS (NaP1 and NaP2) and ANA (analcime), and the composition varied depending on the synthesis conditions. Under the conditions of a reaction temperature of 140 °C, reaction time of 48 h and SiO2:NaOH:H2O molar ratio of 1:1.0:39, a NaP1 zeolite sample with small amounts of NaP2 and analcime was successfully obtained. The adsorption kinetics and isotherms for Cs+ and Sr2+ were well described by the pseudo-second-order model and the Langmuir model, respectively. The results demonstrate that the hydrothermal process can effectively transform silica waste into zeolites with good performance for the removal of Cs+ and Sr2+ from aqueous solutions.