Agrogeological potential of schists from the Rio das Velhas Supergroup: A study of mining co-products from the Itabira Iron Mine, Minas Gerais, Brazil

Schists derived from iron mining operations in the Quadrilátero Ferrífero, Brazil, show potential for use as soil conditioners or rock dust remineralizers (REM). Among them, schists from the Rio das Velhas Supergroup, Nova Lima Group, are noteworthy. This study evaluated the agrogeological potential of these schists as soil remineralizers and as inputs for CO 2 capture. A composite sample was prepared from three schist samples collected in the Itabira region. Samples were homogenized and ground to below 0.3 mm, with 84% of the mass composed of particles smaller than 0.075 mm. To assess the pH increase in the soil-rock mixture as a function of application rate, different rock powder doses were tested in four soil types, two clayey and two sandy. Doses applied to sandy soils ranged from 0 to 150 mg per 10 g of soil (equivalent to 0 to 15 t ha −1 , assuming incorporation in the 0–10 cm layer). For clayey soils, doses ranged from 0 to 300 mg per 10 g of soil (equivalent to 0 to 30 t ha −1 ). Chemical analysis revealed a sum CaO + MgO + K 2 O of 16.36%, SiO 2 content of 44.85%, MgO of 7.56%, K 2 O below 1%, and a theoretical CO 2 sequestration potential of 245 kg CO 2 t −1 of material applied to soil. The main paragenesis includes actinolite (∼26%), chlorite (∼21%), calcite and dolomite (∼15%), quartz (∼18%) and albite (∼14%). Quartz volume is below 25%, meeting the requirement established by Brazilian Normative Instruction N°. 05/2016 for classification as a remineralizer. However, the K 2 O content is below the minimum threshold set by the same regulation (<1%). Results indicated that doses between 50 and 150 mg per 10 g of soil (corresponding to agronomic doses of 5 to 15 t ha −1 in the 0–10 cm soil layer) stabilized pH between 5.5 and 6.5 after 24 and 72 h of incubation, evidencing the schist's effectiveness in neutralizing soil acidity. The 90-day incubation experiment showed that schist application significantly improved soil chemical properties by increasing calcium and magnesium levels while reducing acidity. Furthermore, the observed levels of CaO and MgO, together with the mineralogy, suggest a high CO 2 sequestration potential through enhanced weathering. Therefore, despite the K 2 O concentration being below the minimum threshold required for registration as a remineralizer, the material shows potential as a soil conditioner and as a source of Ca, Mg and Si for blended agromineral formulations.