Integrated approach to sustainable utilization of phosphate waste rock in road embankments: experimental insights, stability analysis, and preliminary economic evaluation

This paper highlights an issue that has not received much attention which is the use of phosphate waste rock (PWR) in road embankments. This study focuses on the valorization of marly clay and marly limestone lithologies, which are abundant but often unused or undervalued, being simply deposited around mine sites. Investigating the potential use of these materials in road embankments requires a combination of experimentation, stability analysis, and economic evaluation. The materials were collected from mining trenches in the Benguerir mine (Morocco). The samples were subjected to i) chemical and mineralogical characterization; ii) environmental characterization; and iii) geotechnical characterization. The results of the characterization show that the samples are chemically dominated by CaO (12 - 33wt.%), SiO2 (23 - 38wt.%), and MgO (7 – 9wt.%); mineralogically, the main phases are quartz, calcite, dolomite, apatite, and clay minerals. The environmental characterization classified the studied materials as non-hazardous waste. In terms of geotechnical characterization, the marly limestone and marly clay belong to the A3 and R33 categories, which means that they can be successfully used as a sustainable alternative material for the embankment. This finding supports their safe utilization. The stability analysis reveals that embankments up to 10m in height can be constructed with marly clay without significant physical instability risks. Satisfactory safety factors (SF) were found (SF=1.97 for H=5m and SF=1.54 for H=10m). For marly limestone, the height limit is less than 10m (SF=1.74 for H=5m and SF=1.33 for H=10m), but it can be increased to 10m by adding a bench of rock fill with a safety factor of 1.64. Finally, an economic evaluation demonstrates that PWR can be used as embankment materials within a radius of 28km around the mine site. It appears to be a cost-effective alternative compared to conventional materials.