Productive use of steelmaking by-product in environmental applications – II: Leachate geochemistry, ecotoxicity and environmental radioactivity

Detailed laboratory studies have indicated that the HIsmelt steelmaking by-product has the ability to neutralise acidity and hence, may have potential application as an environmental amendment. Prior to widespread environmental use, however, an ecotoxicological characterisation of the by-product leachate and an environmental radioactivity risk assessment are required. Ecotoxicity testing indicated that the HIsmelt steelmaking by-product softwater leachate, adjusted from its natural pH of 10.6–8.0 prior to use, was of low toxicity to Chlorella algae and the marine bacterium Vibrio fischeri, and not toxic to the cladoceran Ceriodaphnia dubia. Leachate metal concentrations in HIsmelt by-product were low. Relative to stringent health-based guidelines for Australian drinking water, the HIsmelt softwater leachate only exceeds the pH guideline of 6.5–8.5. The acidic toxicity characteristic leaching procedure (TCLP) HIsmelt leachate compares favourably with TCLP leachates from international steel-making by-products with low trace element concentrations reflecting low solid-phase concentrations. The HIsmelt steelmaking by-product exhibited low to moderate U and Th decay chain radionuclide activities with an absorbed dose rate of 65 nGy/h. Given the low ecotoxicity, low leachate trace elements concentrations and acceptable radioactivity, the HIsmelt steelmaking by-product has potential applications as a construction material or as a soil amendment to ameliorate acidity. However, based on the results of the synthetic softwater leachate tests, it is likely that the HIsmelt steelmaking by-product will require mixing with other materials to reduce leachate pH prior to use as an environmental amendment.