Natural clay membranes: a sustainable and affordable solution for treating dye solutions, coal mine washery waste, and aquaculture wastewater

In this study, we fabricated low-cost, sustainable inorganic membranes using a one-step dry compaction process that incorporates natural clay and edible glycerin, followed by sintering at low temperatures. Open porosity and permeability of the membranes were in the 33.6–45.2 % and 621.74–864.7 l/m².h.bar range, respectively. Regarding molecular weight cut-off (MWCO) and mercury porosity of membranes with 33.6 % and 45.2 % porosity, the average pore size of the former was ~10 nm, while it was increased up to 10–70 nm, 0.9–3 μm, and ~ 10 μm for the latter. The membranes were subjected to filtration for dye solutions, coal mine washery waste, and aquaculture wastewater, resulting in remarkable removal efficiencies. Specifically, the membranes achieved removal rates of 99.8 % for direct blue 71, 92.44 % for disperse red 74, and 99.1 % for red 2G in dye solutions. Furthermore, they demonstrated removal efficiencies of 99.19 % for turbidity and 94.2 % for chemical oxygen demand (COD) in coal mine washery waste. The membranes removed 98.5 % of total suspended solids from the fish farm effluent. During extended periods of operation, the clay membrane exhibited remarkable stability and minimal leaching of metal ions. Superior properties, including low-cost, nontoxic, and accessible precursors, one-step uni-axial fabrication process without the need for lubricant and plasticizer, low sintering temperature compared to commercial ceramic membranes, promising long-term chemical stability in highly acidic and alkaline media, recyclability, and reproducibility, make the as-prepared membranes an affordable and sustainable solution for treating wastewater in various industries, including textile, mining, and aquaculture, thereby mitigating the environmental impact of these industries.