Material conversion from waste sandstone cake into cation exchanger using alkali fusion

An inorganic cation exchanger was synthesized from waste sandstone cake using the alkali fusion method. We used two starting materials: one was the original cake and the other was leached cake, which was prepared from the original cake by acid-leaching with 1 M HCl solution. Each starting material was mixed with NaOH powder (the weight ratio of NaOH/sandstone = 1.6) and then heated at 600 °C for 1 h to make a fused material. This fused material was then added to distilled water and agitated for one day, then heated at 80 °C, 120 °C, and 160 °C for 8 h in reaction bombs under autogenous pressure in order to synthesize the cation exchanger. From the original cake, a mixture of zeolite-X and hydroxysodalite was synthesized at 80 °C, hydroxysodalite alone was synthesized at 120 °C, and a mixture of hydroxysodalite and tobermorite was synthesized at 160 °C. From the leached cake, zeolite-X alone was synthesized at 80 °C, a mixture of zeolite-X and hydroxysodalite was synthesized at 120 °C, and the hydroxysodalite alone was synthesized at 160 °C. By increasing the synthesis temperature, the cation exchange capacity (CEC) of the product from both cakes decreased, and at each synthesis temperature the product from the leached cake had a higher CEC than did the original cake. The product with the highest CEC was the zeolite-X alone synthesized from the leached cake at 80 °C, which had a CEC of 230 cmol/kg.