Title : Chemical and mineralogical evaluation of phosphate mining waste from the Pratápolis Mine – Minas Gerais, Brazil: Potential for soil remineralizers
Abstract:
The Pratápolis sedimentary phosphate deposit, located in Minas Gerais, Brazil, is inserted in the geological context of the Passos Nappe, within the southern portion of the Brasília Fold Belt. The ore is associated with a metasedimentary sequence of the Bambuí Group (Neoproterozoic age), mainly hosted in metasiltstones and tectonic breccias, forming phosphorites and phosphocrete. The Morro Verde Mine extracts two main products: reactive natural phosphate for fertilizer production and dolomitic limestone. In the mining area, lithologies such as limestone, phosphorites, phosphosiltstones, phyllites, and cherts have been identified. Commercial phosphorites present medium (8–15% P2O5) and high grades (average of 27% P2O5), while lower-grade materials (3–8% P2O5) are accumulated in waste piles. This accumulation represents an environmental liability, as large volumes remain unused and may affect soil and water dynamics.A sustainable alternative is the evaluation of this waste as a potential soil remineralizer. Waste piles were systematically sampled by levels, and the material was crushed and milled to a particle size of 0.3 mm (50 mesh). Mineralogical analyses using proximal remote sensing and X-ray diffraction (XRD), along with chemical analyses of the rock powder, were conducted to assess compliance with the criteria established by Brazilian regulation (IN No. 05/2016). Spectral data indicated characteristic features of goethite (600–1000 nm) and montmorillonite (~1400 nm). XRD analyses identified muscovite, fluorapatite, and quartz. Chemical results showed 9.51% CaO, 1.35% MgO, 6.47%P2O5, 0.14% K2O, 4.64% Fe, 0.24% S, and 0.22% MnO, with a base sum of 11%. Potentially toxic elements were below regulatory limits. Although K2O did not reach the minimum required value (1%), the material contains relevant levels of Ca, Mg, and P, indicating potential for soil acidity regulation and nutrient supply. Agronomic trials are required to confirm nutrient availability and effectiveness in soil fertility and plant development.
