Synthesis of composite zeolite membrane by low-temperature water bath for efficient dynamic hardwater softening

In recent years, zeolite membrane has developed rapidly in the application of water treatment technology. However, the traditional zeolite membrane preparation process has the shortcomings of high temperature hydrothermal and other complex processes, which hinder its potential for large-scale industrial applications. In this study, a metakaolin/slag composite NaA zeolite membrane (GNaAM-20) on stainless steel substrate was prepared by composite geopolymer (metakaolin mixed with 20% slag) in a low-temperature water bath method, and GNaAM-20 was applied to the dynamic separation of Ca2+ from hard water. In this work, the mechanical strength (10.08 MPa) and crystallinity (92.13%) of composite zeolite membrane were enhanced by adjusting the slag content, so that a compact and higher removal efficiency zeolite membrane was prepared. The results showed that the GNaAM-20 had excellent acid resistance (pH = 1) with a removal efficiency of 92.03%, and the Ca2+ average removal efficiency by dynamic filtration after ten times of filtration (500 mL per filtration) was 91.2% using a 500 mg·L−1 Ca2+ solution. The maximum dynamic membrane adsorption capacity of GNaAM-20 was 102.54 mg·g−1. Compared with powder or gel adsorbents. GNaAM-20 virtually maintained its initial removal abilities after 5 regeneration cycles (average removal rate of more than 95%), and it had more significant advantages in terms of recycling and regeneration. Therefore, this study provides new ideas for achieving hard water softening and provides scientific guidance for industrial production.