The RO Phase Separation From Steel Slag

Using steel slag as cement admixture is one of the subjects of resourcefulutilization the industrial solid wastes. In order to solve the problem of using steel slagwith a low hydraulic activity and using as cement admixture with low amount andutilization, we investigated a new process of removing the inert mineral RO phase(about30%) from steel slag to enhance hydraulic activity minerals content.In this paper two kinds of steel slag were selected for analyzing the petrographycharacteristics, using optical microscopy (OM), scanning electro microscope (SEM) andX-ray diffraction. The selectivity of RO phase was discussed by gravity concentration,magnetic separation and electrostatic separation. The characteristic of the dissociationby grinding was examined and separation experiments of steel slag powder wereinvestigated.The results show that the percentage of RO phase in the steel slag is20%-30%, andthe average particle size is31-45μm which is smaller than silicate minerals, but biggerthan aluminoferrite mineral and f-CaO phase. The RO phase is a hard constituent withthe greatest density in the mineral composition, and it concentrates in the coarse fractionand the heavier components of steel slag powder. The RO phase content in the coarsefraction is2.3times greater than that of the fine fraction after air classification by aswirling separator. Since the RO phase belongs to a medium magnetic mineral, and theassociated minerals belong to non-magnetic minerals, the RO phase can be separated bya magnetic separator with medium magnetic intensity. The RO phase content in theconcentrates is5.1times greater than that of the tailings after magnetic separation. TheRO phase can be also recycled by electrostatic separation due to its electric conductivity.The RO phase content in the concentrates is3.1times greater than that of the tailingsafter electrostatic separation. The higher FeO/MgO mole ratio in RO phase’s chemicalcomposition is, the more efficient separation process will be. Oxidizing roasting of the steel slag manifests beneficial effect to magnetic separation of RO phase, butunfavourable function for electrostatic separation.The dissociation of steel slag by grinding reached70%when the cut size controlledin55-65μm. The smaller the partical size and the higher the evenness index of steel slagpowder are, the higher the dissociation will be. The dissociation of RO phase in steelslag by semi-industrial continous disc grinder is higher than by batch-type ball mill.The order of efficiency of the three separations: magnetic separation＞pneumaticseparation＞electrostatic separation. The higher the evenness index of steel slag powderis, the better the separations will be. The higher the dissociation of RO phase in steelslag by grinding is, the more effective the separations will be.