Phosphoric acid treatment of steelmaking dust and slag for agricultural soil conditioning: enhanced phosphorus incorporation and surface area

Steel industry residues are an abundant source of mineral materials that can be converted into valuable products for agricultural use. This study aimed to modify steelmaking slag (SS) and electric arc furnace dust (EAFD) with phosphoric acid (H3PO4) to produce phosphorus-enriched and porous materials suitable for soil conditioning. The residues were ground (< 0.297 mm) and treated with 10 mL of 85% H3PO4 per 10 g of solid, followed by drying at 300 °C for 3 h, washing, and neutralization. X-ray fluorescence analysis revealed a marked enrichment in phosphorus, with P₂O₅ contents increasing to 40.5% in modified SS (MSS) and 32.3% in modified EAFD (MEAFD). X-ray diffraction suggests partial amorphization and the formation of poorly crystalline phosphate phases, whereas SEM/EDS confirms phosphorus incorporation and surface modification. Nitrogen adsorption–desorption analysis revealed improvements in textural properties, with BET surface areas reaching 52.00 m² g⁻¹ for MSS and 8.50 m² g⁻¹ for MEAFD. Overall, phosphoric acid treatment transforms steel industry residues into functional materials with promising agronomic benefits through phosphorus supply and soil conditioning.