Synthesis and characterization of low-cost zeolite NaA from coal gangue by hydrothermal method

Abstract

Abstract Through this investigation, we have demonstrated a low-cost preparation method of zeolite NaA from coal gangue. The well-developed zeolite NaA of 87.56% crystallinity was successfully prepared by hydrothermal alkali activation method, which required low alkali concentration (1.8\xa0mol/L) compared to other researches (3–6\xa0mol/L). The characterization results of product prepared at different conditions suggest that the purity and crystallinity of zeolite NaA are high at low alkali concentration and longer crystallization time. The Ca2+ exchange value of synthesized zeolite attained 265\xa0mg CaCO3/g compared to commercial zeolite, which is typically 340\xa0mg CaCO3/g. The basic structure parameters and thermal stability have also been studied. The results suggest that the obtained zeolite has a potential to be used as hard water softening agent. Moreover, the result of Rietveld quantitative phase analysis and Box-Behnken s response surface methodology showed that the weight fraction of zeolite NaA in product can reach 71.9%, and the crystallinity can attain 88.14% at the optimal condition of n(SiO2)/n(Al2O3) of 2.60, NaOH(aq) concentration of 1.86\xa0mol/L at 95\xa0°C for 10.08\xa0h.