Preparation and characterization of clay based ceramic porous membranes and their use for the removal of lead ions from synthetic wastewater with an insight into the removal mechanism

The present study explores the use of local clay from the United Arab Emirates (UAE) to prepare porous ceramic membranes (flat disk shape) for the purpose of removing toxic heavy metals from contaminated water. Four distinct ceramic membranes, crafted from locally sourced clay and incorporated with activated carbon and graphite, underwent careful and thorough preparation. The initial set of membranes was subjected to open-air sintering, resulting in the creation of mACA and mGrA membranes. Concurrently, a second set of meticulously prepared membranes underwent sintering under inert nitrogen conditions, yielding the formation of mACI and mGrI membranes, respectively. Prior to making the membranes, the clay material was characterized by thermogravimetric analysis (TGA), X-ray fluorescence (XRF), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction analysis (XRD). The clay presented the lowest weight loss compared to AC and Gr, implying that these two materials could be used as porogen agents. The X-ray fluorescence results indicated that the natural clay contained 65.5 wt% of silicon dioxide (SiO2), aluminium oxide (Al2O3), and iron (III) oxide (Fe2O3) falling within the class C category of clays according to ASTM. The FTIR analysis showed different clay regions allocated to various stretching and deformation vibrations of hydroxide, organic fraction, and (Si, Al, Fe)-O groups. The XRD analysis revealed the presence of kaolinite, illite, smectite and calcite phyllite phases in the clay mineral. The membranes were characterized using FESEM, with those containing AC (used as porogen) exhibiting large pores clearly visible on the surface, and were tested for the removal of lead (Pb2+) ions from synthetic wastewater. The removal efficiencies of the membranes were 33 %, 75.2 %, 100 % and 100 % for mACA, mACI, mGrA and mGrI respectively after 100 min operation. The wettability of the membranes was found to follow the order mACI < mACA < mGrI < mGrA, which corroborated well with water fluxes of 7, 8, 112 and 214 L h(-1) m(-2) recorded after 60 min duration and 1.0 bar applied pressure. The mechanisms of filtration of Pb2+ ions were adsorption for the AC-based membranes (mACA, mACI) and a combination of adsorption and size exclusion for the Gr-based membranes (mGrA, mGrI).