Transforming waste into resources: Circular economy assessment of phosphate mine waste rock as alternative road and railway embankments

The increasing dependence of road construction on natural aggregates is raising growing concerns about the depletion of finite resources, underscoring the need for alternative materials. In this context, this study explores the potential of phosphate mine waste rock (PMWR), a coarse by-product from phosphate extraction, as a geomaterial for transportation infrastructure embankment construction, offering a circular economy solution for the phosphate sector. Representative PMWR samples were collected from screening stockpiles in Benguerir (Morocco) and analyzed through a combination of geochemical, mineralogical, geotechnical, environmental, numerical, and economic methods. The results show that PMWR mainly consists of SiO₂ (33.16 wt%), CaO (28.14 wt%), and MgO (3.19 wt%), with quartz, calcite, dolomite, apatite, and mica minerals as the dominant phases. Environmental assessments confirmed that the material is non-hazardous. From a geotechnical perspective, PMWR exhibits moderate compaction properties (optimum moisture content of 18.2% and maximum dry density of 1.81 t/m³), but relatively low shear strength (ϕ′ = 22°, C′ = 10 kPa) and limited resistance to abrasion and fragmentation. These characteristics suggest that PMWR can be used in embankments, when compaction is carefully controlled. Stability analyses based on the simplified Bishop method indicate that embankments up to 15 m high can remain stable (safety factor > 1.5) when appropriate design measures are applied. The economic analysis shows that PMWR can be cost-effective within a transport distance of 33 km. Overall, this work highlights a practical and sustainable way to reuse mining waste, reducing pressure on natural resources while supporting more sustainable infrastructure development.