Comparative Effects of Soxhlet Extraction and Thermal Treatment on the Physicochemical Properties of Spent Bleaching Earth for Sustainable Reuse

Abstract This study evaluates the effects of solvent extraction and thermal treatment on the structural, mineralogical, and physicochemical properties of spent bleaching earth (SBE) from a palm oil refinery, aimed at sustainable reuse strategies. The SBE was subjected to Soxhlet extraction using n-hexane, as well as another process through calcination between 300 and 1000°C. Products were characterized by XRF, XRD, TGA/DSC, laser granulometry, SEM/EDS, and FTIR. The raw industrial bentonitic material exhibited a typical aluminosilicate composition: montmorillonite, illite, and kaolinite. Solvent extraction virtually removed residual oil from the bleaching process of palm oil, without significant changes in chemical composition or crystalline structure, preserving lamellar morphology, although with an increase in amorphous content. In contrast, thermal treatment promoted transformations, including structural collapse of montmorillonite, dehydroxylation of clay minerals, and formation of thermally stable phases, as well as particle agglomeration. Thermal analysis along with chemical extraction indicated approximately 25 wt.% residual oil content, and mass loss of about 40 wt.% from volatile materials. Results show that solvent extraction favors partial reactivation for adsorptive applications, whereas calcination produces a structurally modified material with potential for ceramic applications, possibly contributing to circular economy practices in vegetable oil refining.