Preparation of geopolymer inorganic membrane and purification of pulp-papermaking green liquor

Abstract

This paper describes a low-cost and highly efficient metakaolin-based geopolymer composite membrane (support + dense layer) at normal pressure and <70 °C. The support was fabricated using geopolymer foam materials and shows a large water flux and good mechanical properties. The dense layer was prepared using a dip-coating process with geopolymer paste on the porous geopolymer support surface. This study explored the influence of the foam agent content on the support membrane microstructure, water flux and compressive strength, and determined that the optimal foam agent content is 1.0 mass%. By adjusting the viscosity of the geopolymer paste in accordance with the water flux and removal rate, the thickness of the dense layer was determined as 500 μm. The composite membrane shows a distribution of pore sizes (approximately 0.09 μm of dense layer), amorphous structure, high permeable water flux (245 kg·m−2·h−1), good interface combination and can be reused. The preliminary ultra-filtration test (0.2 MPa operation pressure) demonstrates that the geopolymer-based composite membrane can effectively treat suspended particles in wastewater and is expected to be applied in the field of wastewater treatment. We then used the composite membrane in the pulp-papermaking green liquor at different temperatures, and it was found that the SS (suspended solids) of the filtrate can be decreased to 3.45 mg/L at 80 °C or to 0.79 mg/L at 30 °C, far below the industrial requirements of green liquor recycling (SS < 20 mg·L−1).