Characterization of Low-Cost Multi-Precursor Ceramic Membranes from Nigerian Agricultural and Biogenic Wastes for Synergistic Removal of Heavy Metals and Azo Dyes from Wastewater

Abstract

The contamination of water resources by heavy metals and recalcitrant azo dyes from textile and industrial effluents remains a critical environmental and public-health challenge, particularly in developing regions. Conventional ceramic membranes, while effective, are often prohibitively expensive due to high-purity raw materials. This study reports the optimized fabrication of a novel low-cost multi-precursor ceramic membrane using abundant, locally sourced Nigerian wastes and natural materials—sawdust, rice husk, snail shell, kaolin clay, and natural clay. Raw materials were pretreated, homogeneously mixed with binders and additives (boric acid, PVA, PEG, CTAB), uniaxially pressed into flat disks (40 mm diameter, 3 mm thickness), and subjected to controlled two-stage sintering. A top-layer coating of fine clay suspension (<2 µm) was applied to enhance selectivity. Comprehensive characterization of both precursors and the final membrane (optimal Sample 25) was performed using EDX, SEM, XRD, FTIR, TG-DTA, XRF, and BET surface-area analysis. The optimized membrane exhibited a high BET surface area of 255.52 m²/g, a hierarchical micro-mesoporous structure, crystalline phases including quartz, kaolinite, and zeolite, and surface functional groups (Si–O–Si, O–H, C–O) conducive to adsorption and ion exchange. SEM revealed irregular, porous morphologies ideal for high permeability and antifouling, while thermal analysis confirmed structural stability up to sintering temperatures. These properties support synergistic pollutant removal through size exclusion, electrostatic repulsion, adsorption, and Donnan exclusion. The developed membrane, integrated into a custom CAD-designed stainless-steel filtration unit, offers a sustainable, circular-economy approach that valorizes agricultural and biogenic wastes, significantly reduces production costs compared with commercial alumina/zirconia membranes, and aligns with UN Sustainable Development Goals for clean water and sanitation. This work provides a scalable, low-energy fabrication pathway for advanced ceramic membranes tailored for simultaneous heavy-metal and azo-dye remediation in real wastewater matrices.