Process for Phosphorus Recovery from Phosphorus-concentrated Steelmaking Slag and Decreasing Slag Volume

Steelmaking slag contains a considerable amount of phosphorus, which is widely used in human society. Phosphorus recovered from steelmaking slag will provide a new resource, and reusing the steelmaking slag, from which phosphorus has been removed, in the steel manufacturing process reduces the total slag volume. In this study, phosphorus was separated from phosphorus-concentrated slag, which was produced through the oxidation of high-phosphorus hot metal using a small amount of steelmaking slag. The leachate of the phosphorus-concentrated slag was obtained by agitating the slag in citric acid at pH=3 using a mill pot containing mill balls. To separate phosphorus from the leachate by the precipitation of calcium phosphate, the pH of the leachate was increased by adding NaOH solution to increase the pH from 3 to 11, and by adding Ca(OH)2 solution or Ca(OH)2 powder to increase the pH from 3 to 11. The recovery ratio of phosphorus was over 75% for these methods. The P2O5 content in the recovered precipitates was over 30 mass%, which is higher than that in natural phosphorus ores. It is calculated that 50% of phosphorus in hot metal could be recovered as precipitates, and when the leaching residue was recycled for hot metal dephosphorization, the amount of slag emissions was reduced by 34% compared to the current hot metal dephosphorization operation. It is suggested that phosphorus can be recovered from steelmaking slag and slag emissions can be decreased through slag treatment processes such as slag reduction, dephosphorization, acid leaching, and precipitation.