Adsorptive Purification of Waste Cooking Oil Using Natural Maghnia Bentonite: Surface Charge and Multi‐Technique Characterization

ABSTRACT

Natural Maghnia bentonite was evaluated as a low‐cost adsorbent for the purification of waste cooking oil (WCO). A clay‐centric characterization combined physicochemical metrics (pH, density, moisture), UV–VIS spectroscopy, SEM, TGA, and ζ‐potential measurements of both the clay and the oil phase was conducted. After contact with WCO, the clay exhibited a shift in ζ from −20.6 to −24.6 mV and measurable changes in pH (from 7.9 to 6.1), density (from 1.15 to 1.25 g cm ⁻³ ), and moisture (from 4.0% to 0.5%), indicating strong interaction with acidic and polar residues. UV–Vis spectroscopy indicated the retention of chromophoric species on the recovered clay, while SEM micrographs revealed heterogeneous surface‐associated deposits compatible with oil‐derived material. TGA showed an increased thermally removable fraction in the treated bentonite, consistent with retained organic species together with the intrinsic thermal transformations of the clay. In the oil phase, treatment decreased total counts and moved ζ away from neutrality, consistent with improved dispersion stability. These results are consistent with a multimodal uptake process involving surface charge modification, retention of organic matter, and partial pore occupation.