Resource recovery of steel slag: Effects of partial substitution for soilless culture medium on coriander cultivation after modification

To promote the resource utilization of steelmaking slag (SS) and reduce peat consumption, this study investigated the partial substitution of peat with modified steelmaking slag (MSS) for coriander cultivation. SS and iron tailings (1:1 w/w) were modified at 1550 °C to mitigate alkalinity and heavy metal risks. MSS of two particle sizes (20-60 mesh and 60-100 mesh) replaced peat in a standard mix (peat: perlite: vermiculite = 1:1:1 v/v/v) at weight ratios of 10%-40%. The results demonstrated that the modification significantly optimized the medium pH, EC, and heavy metal leaching profiles to meet coriander growth requirements. Optimal performance was observed at a 20% weight substitution ratio using 20-60 mesh MSS, where coriander growth parameters and soluble content matched commercial control levels. In conclusion, MSS serves as a safe and effective peat substitute within specific particle sizes (20-60 mesh) and weight replacement ratios (≤20%). This strategy not only mitigates ecological risks from slag alkalinity and heavy metals but also enhances the economic viability of soilless cultivation by reducing peat dependency and material costs.