Enhanced humification by carbonated basic oxygen furnace steel slag - I. Characterization of humic-like acids produced from humic precursors

► Carbonated steel slag accelerated the polycondensation of model humic precursors. ► Steel slag-HLA was strikingly similar to zeolite- and birnessite-HLAs. ► Steel slag-HLA is a complex organic material that is highly aromatic in nature. ► Steel slag is a promising material for use as an additive in composting.