Mine waste rock reprocessing using sensor-based sorting (SBS): Novel approach toward circular economy in phosphate mining

Abstract

Phosphate extraction and processing generates large volumes of phosphate mine waste rock (PMWR) that still contains non-negligible amounts of residual phosphate. Due to the increasing demand for phosphorous (P), in particular by the fertilizer industry, PMWR can become a potential resource for P beneficiation if cost-effective methods are applied. The main objectives of this study are to:i)characterise PMWR from the Ben Guerir mine site (Morocco);ii)evaluate the efficiency of hand- and sensor-based sorting (SBS) to recover the lost phosphate; and.iii)upgrade the P2O5 content in the concentrate.Samples were collected from different locations in the PMWR piles and divided into two main fractions: >30 mm and < 30 mm. The coarse fraction (>30 mm) was sorted using three main SBS technologies to separate phosphate from gangue materials: dual energy X-ray transmission (DE-XRT), near-infrared combined with color (NIR/color), and color technologies. The fine fraction was processed with the conventional flowsheet used by the mine.Chemical and mineralogical characterisation showed that the composite sample contained up to 17.5 wt% P2O5, with an abundance of fluorapatite, calcite, quartz, and dolomite. The hand sorting demonstrated that >50 wt% of the PMWR within the coarse fraction (>30 mm) was in the form of indured phosphate (IndP). The remaining lithologies were represented by phosphated flint, flint, silexite, limestone, and marl. In terms of sorting efficiency, the tests highlighted the performance of DE-XRT for materials characterised with a difference in atomic density. The use of DE-XRT allowed a P2O5 recovery of 70 wt%, with an increase of the P2O5 content from 13.5 wt% to 18.5 wt%. The remaining lithologies were successfully separated using SBS technologies. Materials sorting is an interesting technology that can reduce the environmental footprint of PMWR by recovering the lost phosphate and valorising the remaining lithologies for civil engineering applications.