Valorization of Spent Bleaching Earth in HDPE Composites: A Green Process Approach Toward Industrial Waste Reduction

The increasing generation of solid industrial waste and the environmental burden associated with virgin polymer production call for the development of green processing strategies that reconcile material performance with ecological responsibility. This study proposes an environmentally driven approach for the valorization of spent bleaching earth (SBE), a solid waste generated in large quantities during vegetable oil refining, through its integration as an untreated mineral filler into a high-density polyethylene (HDPE) matrix.

A key environmental advantage of the proposed process lies in the complete elimination of any pre-treatment step for the SBE filler. Collected directly from an Algerian oil refinery (RAFH) processing soybean oil at 1500 t/day, the waste is used as-is, significantly reducing energy consumption, chemical use, and process-related emissions compared to conventional filler preparation routes. Physicochemical characterization of the SBE — including residual oil content (34.63 wt% by Soxhlet extraction), XRD structural analysis, and granulometric profiling — provides the basis for understanding filler-matrix interactions within a green formulation framework.

HDPE/SBE composites with filler loadings ranging from 10 to 40 wt% were elaborated by twin-screw extrusion and injection moulding at laboratory scale. The study encompasses a full lifecycle-oriented assessment structured across five phases: material characterization, composite processing and mechanical evaluation, thermooxidative and hydrothermal durability testing, recyclability assessment, and upscaling recommendations. Preliminary mechanical results confirm the technical viability of the approach, with tensile properties remaining acceptable up to 30 wt% SBE content.

By diverting refinery waste from landfill, reducing virgin HDPE consumption, and eliminating filler pre-treatment, this work outlines a replicable green process pathway applicable to various industrial waste-filled polymer systems, contributing to cleaner production and waste minimization objectives.