New Approach for Mining Site Reclamation Using Alternative Substrate Based on Phosphate Industry By-Product and Sludge Mixture

Mining soils are generally characterized by soils having a coarse texture and low fertility, which makes revegetation a very difficult and delicate operation, especially in arid and semi-arid zones. The main objective of this work is to evaluate different substrates that can both contribute to the successful reclamation of phosphate mining soils and the valorization of phosphate by-product and sewage sludge. The study was carried out in pots under a greenhouse on Italian ryegrass (Lolium multiflorum). The experimental design is a randomized complete block with ten treatments, four repetitions from five substrates: phosphogypsum (PG), phosphate sludge (PS), sewage sludge (SS), topsoil from mining (TS) and phosphate waste rocks (PWR); this corresponds to soil after rock phosphate extraction. Nitrogen fertilization was applied to treatments after soil depletion in treatments not receiving sludge. An aerial biomass measurement and nutrient analysis were carried out for the three cuts. The results showed that a proportion of 65% of PG enriched the substrate in phosphorus by improving the crop yield. The addition of 5% of SS contributed to a significant improvement of ryegrass aerial biomass. In the absence of SS application, the addition of nitrogen is required to maintain crop growth. For large-scale application, TS can be mixed with PS, SS and PG for mine site reclamation.