Steel slag co-products for sustainable soil health and phosphorus nutrition in agriculture

Efficient phosphorus (P) management is essential for sustainable agriculture. However, global dependence on finite phosphate rock reserves and the environmental impacts of conventional P fertilisers highlight the urgent need for alternative nutrient sources. Steel slag, an abundant by-product of steelmaking, has emerged as a promising secondary P resource with additional agronomic benefits, including liming capacity, silicon provision, and improved soil quality. During iron and steel production, P is transferred from iron ore into slag, accumulating in the dicalcium silicate–tricalcium phosphate (C 2 S–C 3 P) phase, which enables targeted P recovery. Recent studies have advanced P enrichment, phase separation, and the development of slag-based fertilisers. Despite these advances, challenges remain in optimising P extraction, understanding nutrient dynamics in various soil types, and ensuring the environmental safety of steel slag application. With growers’ emphasis on sustainable P fertiliser practice, the potential of steel slag as an alternative P source is evaluated. P recovery technologies from the steel industry, agronomic uses of steel slag, and associated environmental concerns are examined to support future research and the development of circular sustainable strategies for enhancing soil health and agricultural productivity.