Waste rock reprocessing to enhance the sustainability of phosphate reserves: A critical review

The continuous and growing demand for phosphate, especially by the fertilizer industry, has increased the exploitation rate of high-grade phosphate ores extracted from phosphate deposits. However, with the depletion of high-grade ore resources, the exploitation of low-grade phosphate ores and phosphate mine waste rock (PMWR) has become a necessity for cleaner production and sustainable resource conservation. Many scientific and industrial studies on the exploitation and beneficiation of low-grade phosphate ores were reviewed; however, the beneficiation of PMWR has rarely been studied in the previous literature. PMWR as a low-grade phosphate ore is characterised by high heterogeneity due to the large particle size distribution. This physical anisotropy of PMWR presents a crucial challenge for upgrading using sorting and further processing methods. The focus of this review was mainly on the recent advances in beneficiation technologies and their adaptability to reprocess PMWR to enhance the sustainability of non-renewable phosphate reserves. The technologies of PMWR reprocessing, such as mineralurgical methods (classification, flotation, gravity separation, and ore sorting), magnetic, electrostatic, and thermal separation (calcination), hydrometallurgical methods (acid leaching and bioleaching), and combined processes, are discussed in this paper. The final findings of this review paper allowed the identification of the relevant and suitable processing methods to recover phosphate from PMWR, including: i) ore sorting to reduce the challenges related to the high physical heterogeneity of PMWR; ii) gravity separation to preconcentrate the residual phosphate; iii) flotation to upgrade the phosphate grade by removing gangue minerals with a leaching process to dissolve carbonate minerals; and iv) calcination to reduce the carbonate content in the final product.