Research On The Selective Leaching Of Phosphorus From Dephosphorization Slag

The productivity of steelmaking slag in China is huge,while its comprehensive utilization ratio is lower,resulting in severe resources waste and environmental burden.Steelmaking slag consists of large amounts of valuable components,such as CaO,FetO,MgO,which is regarded as extremely valuable metallurgical resources.Therefore,it could be recycled in the sintering and steelmaking process.However,the existence of P2O5 in steelmaking slag hinders its utilization in metallurgical process.Consequently,the separation and recovery of P from steelmaking slag is the key technology to achieve its efficient resource utilization.In this study,based on the previous researches,the selective leaching was adopted to separate and extract P from dephosphorization slag.The effect of slag composition on the dissolution behavior of dephosphorization slag was studied.In this research,increasing Fe2O3 or P2O5 content in slag was beneficial for improving the dissolution ratio of P and hindered the dissolution ratio of Fe.Furthermore,as the pH decreased,the dissolution of P and Fe was promoted significantly.When the pH decreased to 5,the dissolution ratio of P in the high-Fe2O3 content dephosphorization slag reached 85%while that of Fe was only 2.8%.At pH=5,the dissolution ratio of P from steelmaking slags with different P2O5 contents were all over 81%and those of Fe were less than 6%,achieving the efficient removal of P.The recovery of P from the leachate by chemical precipitation was studied.The obtained precipitate was composed of 50.9 mass%CaO and 23.9 mass%P2O5.It had a high solubility in the 2%citric acid solution,indicating that it could be used as a slowreleased phosphate fertilizer.The effect of leaching conditions on the dissolution behavior of P was investigated and the kinetics of leaching process was analyzed.Decreasing pH and particle size had a significant effect on the selective leaching of P while increasing reaction temperature had a little effect on that of P.When particle size was less than 53 μm and leaching was conducted at 25℃ at pH=5,the dissolution ratio of P reached 85.1%and that of Fe was 6.7%.The kinetic model of selective leaching of P conformed to the shrinking core model which was controlled by the diffusion though product layer model.The dissolution rate was determined by the diffusion rate of H+and phosphate ions through the residue.The activation energy in this leaching process was 7.46 kJ/mol.By using selective leaching and chemical precipitation,the P in dephosphorization slag was dissolved effectively and recovered,and the P-removal residue could be reused in ironmaking or steelmaking process,achieving an efficient resource utilization of dephosphorization slag.