Synthesis of Zn-Saponite Using a Microwave Circulating Reflux Method under Atmospheric Pressure

Smectite is a common clay mineral in nature. Due to its tendency to swell and its strong cation exchange capacity (CEC), smectite is prevalently used in industrial and technological applications. Numerous scholars have explored smectite synthesis, which usually involves autoclaving under high pressure. However, this approach requires an array of expensive equipment, and the process consumes time and energy. This study adopted self-developed equipment to synthesize zinc saponite (Zn-saponite), a type of trioctahedral smectite, using a microwave circulating reflux method under atmospheric pressure. Compared with the conventional hydrothermal methods, the proposed method entails fewer constraints regarding the synthesis environment and can be more easily applied to large-scale synthesis. The phase purity of the synthetic product was examined using X-ray diffraction and the CEC of the product was tested. The results revealed that the microwave circulating reflux method could synthesize Zn-saponite in 16 h under atmospheric pressure, and the CEC of the product reached 120 cmol(+)/kg. In addition, the product exhibited larger basal spacing and a 32% increase in CEC compared with Zn-saponite synthesized using a hot-plate under atmospheric pressure.