| Steel slag is a bulk solid waste discharged from the steelmaking process by converters or electric furnaces.Its main chemical composition is CaO,MgO,Fe2O3,Si O2,Al2O3,etc.,while its mineral composition includes C3S,C2S,C2F,RO phase,f-CaO,f-MgO,etc.At present,the utilization of steel slag is extremely low because of its low hydration activity,poor grinding property and instability.C3S and C2S content in steel slag is relatively lower than that of clinker due to the low content of CaO,andγ-C2S with low hydration activity is formed during cooling process,which makes steel slag low hydration activity.Many more residual iron phases,including RO phase,particulate magnetic iron and oxides,exist in steel slag,which makes it high density and poor grinding property.There are higher content of RO phase,f-CaO,f-MgO in steel slag,they will swell during hydration,and the swelling reaction is almost uncontrollable,so the volume stability of steel slag is poor.Traditional pretreatment methods,such as hot stewing,hot splashing and granulation can improve the poor stability of the slag to a certain extent,but the chemical nature and physical properties of the steel slag are not fundamentally changed.Reduction process is expected to separate/recover the iron and reconstruct the slag system,which is one of the most effective ways to full components utilize steel slag.In Panzhihua-Xichang region of Sichuan province,large amount of steel slags with about 20%of TFe and 2%of V2O5content are discharged.Traditional utilization ways of V-bearing steel slag inevitably resulted in the inefficient loss of strategic Fe/V metal resources.Based on above,a melt-reduction process was proposed to separate Fe/V metal resources from V-bearing steel slag,meanwhile,reconstructed reduction tailings would also be obtained by composition regulation and cooling method design.Results showed that:（1）Fe/V reduction rate was closely related to the quaternary basicity（R）of the slag system,appropriate increase of R within 1.4 was conducive to the reduction of vanadium oxides,while it had little effect on the reduction of iron oxides,the maximum reduction rate of Fe and V could reach 96.8%and 69.2%,respectively,when steel slag was reduced at 1600℃for 30min.（2）Quartz sand,Coal-fired slag and the composite of quartz sand and high aluminum slag regulator were used as reduction and reconstruction aids,respectively,water-quenching and air-quenching reduction tailings（WCS and ACS）were thus obtained when the steel slag was reduced at 1600℃for 30min.Grindability of the reduction tail slag was greatly improved compared to that of raw steel slag,but it would be decreased with the increase of R.Specific surface areas of WCS and ACS after 60 minutes grinding was 460～550m2/kg and453～517m2/kg,respectively.That is,the grindability of ACS was slightly poorer than that of WCS.（3）Glassy phase content and polymerization degree of tailing slag would be influenced by R,reduction and reconstruction aids,cooling methods,while R had a greater impact.Glassy phase content of the reduction tailings decreased with the increase of R,its content would be above 90%when the R of reduction tailings was below 1.0.Polymerization of the reduction tailings increased with the increase of R,it would get lower when R of reduction tailings was below 1.0.（4）WCS and ACS powders were obtained through 60 minutes of grinding.Fluidity ratio of mortars with WCS or ACS was greater than 95%.Activity index of WCS can reach 94%for3d,121%for 7d,and 120%for 28d.Activity index of ACS can reach 80%for 3d,112%for7d,and 114%for 28d.WCS and ACS with the activity index comparable to that of S95granulated blast furnace slag powder could be prepared when CaO/MgO≈5,3<Si O2/Al2O3<4and R≤1.1.（5）Hydration heat release of the cementitious material system containing WCS or ACS decreased,the total hydration heat release during 7d reduced by 57.62 J/g for WCS and63.59 J/g for ACS compared to that of Portland cement.Pore structures of the hardened pastes containing WCS or ACS refined,the proportion of harmless and less harmful pores in the paste would be increased.Better activity index of the reduction tailings and economic benefits were observed by the using of Coal-fired slag as the reduction and reconstruction aid. |
