Secondary steel mill slags with pulp and paper mill solid residues for soil amendment: Mineralogy, relevant physicochemical properties and trace element availability

Inter-industrial utilisation of solid residues for soil amendment was investigated by combining secondary steel mill slags with residuals from a pulp and paper mill. Sample analysis included mineralogical characterisation by X-ray diffraction, relevant physicochemical properties and trace element availability by the original three-stage sequential BCR extraction procedure (CH ₃COOH, NH₂OH·HCl and H₂O₂ + CH₃COONH₄) and residual fraction determination by acid digestion (USEPA 3051A). Respectively, the pseudo-total concentrations of trace elements were determined according to USEPA method 3051A. Consequently, the alkalinity of the samples (pH values 12.1-12.2) suggests significant buffering and acid neutralisation capacity with liming effect values (34.9%-35.6%, Ca-equivalents, d.w.) comparable to commercial ground limestone. This was supported by XRD, which only revealed the existence of portlandite [Ca(OH) ₂] an calcite [CaCO₃]. Additionally, the pseudo-total concentrations of trace elements were lower than the respective limit values for EU soil improvers (2006/799/EC). However, Ba and V recovery during sequential extraction (Ba: 40.1-56.0 mg·kg^-1, d.w., by CH ₃COOH; and V: 72.2-96.5 mg·kg^-1, d.w., by NH ₂OH·HCl) indicates potential phytoavailability.