Silt from mining siltation ponds poses environmental risks and hazards, necessitating research into sustainable valorization techniques. One of the unexplored ways to do so is to use them as sustainable fillers for polymer composites. This study investigates the use of silt from mine waste, sourced from siltation ponds of a mining company in the southern Philippines, as a sustainable filler in unsaturated polyester resin (UPR) composites to advance a circular economy. The silt, processed to <1 micron and treated with sodium silicate, was incorporated at 1%, 3%, and 5% weight percentages. Composites underwent tensile and flexural strength tests, with silt characterized by FTIR and XRD to confirm compatibility.

Tensile tests revealed that the 5% filler composite had the highest Young's modulus (437.064 MPa) and toughness (361.473 J/m³), surpassing the UPR control (308.363 MPa and 322.866 J/m³). Flexural tests showed that the 1% filler composite had the highest flexural modulus (1276.413 MPa) and maximum stress (58.716 MPa), while the 3% filler composite balanced stiffness (1061.621 MPa), strength (47.890 MPa), and toughness (617.153 J/m³). ANOVA confirmed significant differences in tensile (p=0.019) and flexural properties (p=0.007). Fracture analysis using a digital microscope indicated mixed brittle and ductile mechanisms, with rougher surfaces in higher filler composites suggesting improved energy dissipation. FTIR and XRD verified silt’s suitability, with the presence of phyllosilicates detected in the sample. Future work should include SEM analysis of fractured surfaces to investigate microstructural interactions and a UTM with higher capacity to accurately assess compressive strength. These findings reveal that mine waste-derived silt can be used as a sustainable filler for enhancing UPR composite mechanical properties, supporting eco-friendly material development.