Study On Treatment And Utilization Of Converter Steel Slag

With the fast development of steel and iron industry in China, the problem has become increasingly acute about treatment and utilization of steel slag.The comprehensive utilization rate of steel slag must reach 86% or morn than that in ' the Eleventh Five-Year Plan', and realize ' zero discharge ' of the steel slag. However, the fact is far away with the require of ' the Eleventh Five-Year Plan'. Especially the comprehensive utilization rate of converter slag is less than 10%. Therefore, the treatment and uilization level of converter slag directly affect the whole uilization level of steel slag in our country. As the by-product of steelmaking production,its comprehensive utilization of converter slag not only reduce environmental pollution,but also create huge economic benefit.That is a effective way of sustainable development.In this paper, the mineralogical characteristics and the comprehensive utilization technology of the converter steel slag(CSS) were studied.The results show that the phase compositions of CSS include tricalcium silicate in terms of hexagonal tabular, dicalcium silicate in terms of circle and perfect dense crystalline. The metallic iron and ferrous oxide associated with CSS ocuure as ball or cirle. The content of iron and magnetite is only 3.39%, a few calcium ferrites and fayalite also exists in CSS. The content of f-CaO is 3.93%.The results obtained by grinding-magnetic separation process show that the iron grade is 75.58% of magnetic product and the recovery of iron is 15.88% under the conditions of the grinding size less than 0.044mm, 0.08T magnetic field intensity. The phosphorus content is 0.1%, it shows that the magnetic product can be used the ironmaking or steelmaking raw material.The dephosphorization experiment shows that the dephosphorization is only 48% by alkali leaching. Make a comparison with alkali leaching process, it can be found that dephosphorization is much higher by acid leaching. A dephosphorization result of 90.28% can be obtained under the conditions of 3.5% sulfuric acid concentration, the 120min leaching time at 25℃. The phosphorus content decreases down to 0.068% and it is able to be used as sintering flux.A novel process is recommended to comprehensively utilize of CSS at last.Accrong to the acid-base balance theory, and combined with thermodynamic, analyse different types of phosphate exists at vanable pH value. During acid leaching, the phosphate is always existed in the system as phosphoric acid due to pH value at 1.0. However, during alkali leaching, pH value is changed to 13.0, phosphate most exists as PO₄^3- in the system, the precipitation may occur. So, the alkali leaching is ineffective.