Study On Modification Of Stainless Steel Slag, The Magnetic Separation And The Preparation Of Cr-enriched Phase

This paper study on the modification of stainless steel slag, the magnetic separationand the preparation of Cr-enriched phase, H₃BO₃was added to modify the slag based ondetermining the chemical properties of factory slag and Cr distribution, then control theappropriate temperature and the amounts of additor in order to enrich Cr in the slag andenhance the growth of Cr-enriched phase. Magnetic separation method was used toseparate the Cr-enriched phase. Meantime, the Cr-enriched phase was synthesized byusing analytical reagent in different atmosphere under elevated temperature with an aim toinvestigate magnetism and density. All the results will provide a technical route for theseparation of the Cr-enriched phase from stainless steel slag.（1） The physical and chemical properties of the stainless steel slag was firstdetermined. It is shown that the main components are CaO, MgO, SiO₂, Fe₂O₃and Cr₂O₃（13.76wt%）, and the main mineral phases are: dicalcium silicate （2CaO SiO₂, C₂S）,merwinite （Ca₃Mg（SiO₂）₂, C₃MS₂）, spinel （Fe,Mg）（Cr,Fe）₂O₄and the matrix glass phase.Chromium is distributed in the spinel and matrix and the content of Cr₂O₃in the twophases is56.20%and2.47%, respectively.（2） The modification by adding H₃BO₃and growth of spinel were experimented. Theresults show that the H₃BO₃can enlarge the enrichment degree of Cr and enhance thegrowth of Cr-enriched phase. But the addition of H₃BO₃did not change the phasecompositions of the slag. Cr₂O₃in spinel is49.70wt%and the concentration degree canreach to87.11%, the Cr-enriched degree decreased with the increase amount of H₃BO₃, inaddition, when the holing time extend from5min to180min, the article size of Cr-enrichedphase can increase from22.18μm to35.63μm, the growing behavior of spinel was fitted toOstwald theory and JMAK model.（3） The separation experiment of Cr-enriched phase in stainless steel slag: theproportion of magnetic part was38.09%during magnetic separation process at the0.35Texternal magnetic field strength, separating60mins; the magnetic part was not completelydetached with non-magnetic part when the average size of slag was29.460μm, and theresultant was consistent with the statistic result of metallographic microscope; XRFdetection results showed that the components of magnetic portion and non-magneticportion were approximately same due to mineral magnetism and magnetic field strength.（4） Synthesis and magnetism detecting experiment of Cr-enriched phase: the spinelwas obtained after burdening （MgO, Al₂O₃, Fe₂O₃, and Cr₂O₃as raw materials,4%B₂O₃as fluxing agent）, compression moulding and high-temperature calcination, based on thecomponent of the as-separated spinel. XRD result showed that the main diffraction peaksof sample could be indexed as spinel; Ms was only0.6081emu/g and the as-obtainedsample showed non-magnetism or paramagnetism adding20wt%Fe₂O₃.Magnetic properties of the spinel synthesized can be obviously enhanced, and Msincreased to24.854emu/g at the sintering environment with a weak reducing atmosphere;it was inferred that the Fe³⁺was reduced to Fe²⁺or Fe partly, Ms was increased to28.120emu/g when10%FeSO₄7H₂Owas added to introduce Fe²⁺. This can providetechnical support for the followed magnetic separation, the content of multivalent ions(Fe³⁺/Fe²⁺and Cr³⁺/Cr²⁺) in the synthetized spinel needed to be further detection foroptimizing the reducing atmosphere of sintering process. Separation of Cr-contained phasein stainless steel slag will need a large number of experiments.