Slag-Metakaolin Geopolymer Membranes for Textile Wastewater Treatment: Microstructural Engineering, Filtration...

The development of sustainable and effective membranes for industrial wastewater treatment is a significant challenge in environmental protection. In this work, slag and metakaolin-based geopolymer membranes were prepared and optimized for textile wastewater treatment. Three slag contents (30 wt%, 50 wt%, and 70 wt%) were considered. They were synthesized and systematically compared with respect to their structural, microstructural, mechanical, filtration, and dielectric properties. Specifically, it was found that the membrane with 50 wt% slag (GM-50) retains a good balance between porosity (34.65%), compression, and permeability results. Structural data confirmed the formation of a hybrid C-A-S-H/N-A-S-H geopolymer framework, whereas SEM measurements revealed an integrated, uniform pore structure beneficial for filtration. The GM-50 membrane exhibited excellent filtration performance, achieving high removal efficiencies of turbidity, COD, and color in textile wastewater. Apart from filtration performance, the dielectric properties of the optimized membrane were characterized using impedance spectroscopy over a broad frequency range (10¹-10⁷ Hz) and temperature range (30°C-180°C). The inferred transport mechanisms arise predominantly within a structurally heterogeneous geopolymer matrix and are driven by thermally activated hopping processes. Maxwell-Wagner-Sillars interfacial polarization dominated the dielectric behavior, and non-Debye-type relaxation characteristics indicated that the material's structural heterogeneity and pore connectivity were key factors. The synergistic structural, functional, and dielectric characterization confirmed that the optimized GM-50 membrane is a feasible and sustainable option for textile wastewater treatment with direct relevance to electrical transport properties of geopolymer-based materials.