Alkali Conversion of Waste Clay into Zeolitic Materials using NaOH and KOH solution

Abstract

Alkali conversion from waste clay in a NaOH and KOH solution was attempted to synthesize the zeolitic materials. Waste clay was added into 2 mol/L NaOH or KOH solution, then heated at 90, 120, 150 and 180 °C for 20 h to obtain the product. Waste clay mainly comprised three crystalline phases, quartz (SiO₂), albite (NaAlSi₃O₈) and clinochlore ((Mg, Fe)₅Al(Si₃Al)O₁₀(OH)₈), and one amorphous phase. In NaOH solution, zeolite-P (Na₆Si₁₀Al₆O₃₂·12H₂O) was formed at 90°C and 120°C, whereas the three mineral phases in raw waste clay remained, and analcime (NaAlSi₂O₆･H₂O) was formed above 150°C. In KOH solution, chabazite (K₂Al₂Si₄O₁₂･6H₂O) and zeolite K-H (K₂Al₂Si₄O₁₂･xH₂O) were formed at 90-150°C and 150-180 °C, respectively. With increasing reaction temperature from 90°C to 180°C, the cation exchange capacity (CEC) of the product using KOH increases, while that of the product using NaOH decreases. Waste clay was added into 0-8 mol/L KOH solution, and then heated at 80, 130 and 180°C for 12 h to obtain the product. The product synthesized in 3 M KOH at 180°C indicates the maximum CEC, 1.29 mmol/g. The concentrations of Si and Al in the solution and crystallization in the product during the reaction explain the CEC of the product.