Different Processing Methods of Illie Clay for the Development of Zeolites

Alkaline and alkaline-thermal activation were used in an attempt to synthesize zeolites using the sedimented illite fraction of raw Devonian clays from the Kuprava clay pit in Latvia. The Si/Al molar ratio of these clays is 2.79. Thermal and hydrothermal treatments were conducted using 6M and 10M NaOH solutions, along with different curing environments. The treated samples were analyzed using XRD, FTIR, and SEM, and were compared to the raw and calcined illite fraction samples. The main phase that forms after alkaline treatment is hydrosodalite (Na8[AlSiO4]6(OH)2∙2H2O). Using a higher concentration of NaOH leads to a significant increase in hydrosodalite formation. Increasing the curing temperature from 120°C to 600°C slightly reduces hydrosodalite formation due to the crystallization of the nepheline (Na3K(Al4Si4O16)) phase. This phase forms relatively intensively when the chemically treated samples are cured in a nitrogen environment at 600°C, thereby reducing the formation of hydrosodalite. The characteristic layered-fused structure of clay minerals remains in all chemically treated samples when cured at 600°C in air, but it does not remain when cured at the same temperature in nitrogen. The intensive formation of hydrosodalite is mainly achieved through hydrothermal treatment, along with a primary treatment using 10M NaOH. Considering the calculated size of the crystallites, treatment with 6M NaOH and curing at 120°C can also be seen as beneficial for hydrosodalite formation.