Valorization of purified mining phosphate sludge as a functional filler in ethylene-vinyl acetate–coated cellulose-based packaging papers

As demand increases for sustainable fiber-based packaging, this study introduces a novel use of purified phosphate sludge (P-PS), a mining by-product, as a functional filler in cellulose-based paper. Initially considered hazardous due to its toxic element content, P-PS is rendered safe through acid leaching, washing, and calcination, removing up to 96 % of toxic elements and yielding a material enriched with over 85 % SiO₂. Incorporated at concentrations from 10 to 90 wt%, P-PS enhances structural integrity by forming hydrogen bonds between its silanol groups and cellulose hydroxyl groups. To improve surface properties, a thin layer of ethylene-vinyl acetate (EVA) is applied via thermocompression (100 °C, 5 min), encapsulating the filler and increasing water resistance. Coated papers with 10-40 wt% P-PS show enhanced morphology, thermal stability, and hydrophobicity, with contact angles reaching 121°. Mechanical testing reveals significant gains in stiffness (>2700 MPa), tensile strength (+11.78 %), and ductility (+75.62 %). This study demonstrates the safe and valuable reuse of phosphate sludge in packaging materials, providing a waste management pathway while improving material performance.