CaO-SiO 2-Ti02-Al203-MgO Slag

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1 ISIJ Intrnatinal, Vl. 5 ( 5), N., pp Sulphur Distributin and Carbn-saturatd btwn lrn at CaO-SiO 2-Ti02-l-MgO Slag 77K TangXin and Xu Chusha Dpartmnt f Mtallurgy, Chngqing Univrsity. Sichuan, 600, P. R. China. (Rcivd n Octbr 7. l accptd in final frm n January 27. /5) In this papr, th slag-mtal quilibrium xprimnts wr prfrmd t invstigat th ffct f Ti02 cncntratin in th slag and basicity (R=wtlCaO/wtlSi02) n th sulphur distributin rati (Ls) btwn CaO-Si02-Ti000l-8lMgOslag and carbn-saturatd irn at 77 K. Sulphid capacitis (Cs) wr calculatd basd n th sulphur distributin rati. Th sulphur distributin rati and sulphid capacity f CaO-Si02-Ti02-5/l-80/0MgOstag incras with incras f basicity and with dcras Ti02 Cncntratin in th slag. Th rlatinshlp btwn sulphid capacity f CaO-Si02JTi02-5ll-8lMgO slag and ptical basicity was als invstigatd. Th xprimntal rsults ar usful fr smlting vanadium titanifrrus magntit f blast furnac. KEYWORDS: sulphur distributin rati; sulphid capacity; quilibrium; carbn-saturatd irn; CaO-Si02T Ti02~U-MgOsystm.. Intrductin Rcntly 0mBF, basd n vanadium titanifrrus magntit, has alradly madgrat prgrss. But in practic, th sulphur distributin rati f slags cntaining Ti02 is lwr. With th dvlpmnt f irn & stl industris, sm smallr BF, such as 00-00m BF, spcially in Sichuan, China, start t mak us f th vanadium titanifrrus magntit. Hwvr, th thrtical study fr th sulphur distributin rati and sulphid capacity f slags cntaining Ti0 Iacks fr ths smallr BF. Thrfr, in th prsnt wrk, a 00m BF is cnsidrd t b an bjct f study. 50/0 l, 8 / MgO f slag and th slag amunt f 800kg/t Fc ar dtrmind by th prductin rsults. Using th slag-mtal quilibrium mthd, th ffcts f Ti02 cncntratih and basicity f slag n sulphur distributin rati wr invstigatd at 77K. 2. Calculatin f Sulphid Capacity Th ability f mtallurgical slag t cntain sulphur is dfind by th sulphid capacity as xprssdby Eq. ( ), ) Cs = (/ S)( P,/ Ps.) /2.() whr, (ls) is th massprcntags f sulphur in slag, P, andps, ar th partial prssur f 02, S2, rspctivly. P, may b calculatd using Eqs. (2) and () undr th cnditin f carbn-saturatd irn,2) [C]satd+ 2=CO......(2) G~=-68778T J/m0)...() Ps, is btaind frm th fllwing ractin assuming Hnry's law /2S2=(S)...() G~= TJ/m0)...(5) Using th variatin f fr nrgy f Eqs. () and (5), th Eq. () in lgarithmic frm yilds: LgCs=LgLs-Lg fs+ LgPc0+I 0/T (6) whr, Ls (/ S)/[/ S] = Pc is th partial prssur f CO, atm was ad ptd,) fs is th Hnrian activity cfficint f sulphur disslvd in th mtal. Th valu ffs usd is calculatd as fllws: Lgfs=:x[li]......(7) whr, : is th intractin cfficint,) [ll] is th massprcntags f lmnt i in th mtal. Equatin (6) is vry usful bcaus it rlats th sulphid capacity Cs t th sulphur distributin rati Ls. In th cas f knwntmpratur and chmical cmpsitins f irn, th Cscan bcalculatd using Eq. (6). Exprimntal Mthds.. Prparatin f Matrials Slags wr prpard by mixing apprpriat wights f pwdrdcao,si02, Ti02, l and MgO, drid 57K fr 2.0 h. Thmixing ratis ar shwnin Tabl. Th irn was takn frm th Panzhihua lrn & Stl C., and prpard by mlting practic irn and high purity FSin a graphit crucibl using inductin furnac. at 67 C 5 isij

2 ISIJ Intrnatinal, Vl. 5 (5), N. Tabl l. Chmical cmpsitins f slags and xprimntal rsult. Exp. Mixd cmpsitins f slags (wt'/.) CaO Si02 Ti02 l MgO [s] (S) Ls Cs x lo ll , , , ,OO , l OO O.OO O.OO OO O.O O Ọ O O l l.ll l l.28 l l.02 l O O Tabl 2. Chmical cmpsitins f irn. ~(wt/) C Si P S V Ti , l Obsrvatin hl 2Fumactub MSi2rd Crucibl 5 Slag 6 Irn 7 Crucibl supprt 8 Inrt gas inlt Thrmcupl schmatic diagram f th xprimntal apparatus mplydin th prsnt wrk. Th fllwing prcdur was:.0g f irn cntaining 0. / Swasplacd in ach graphit hl. - r gas was flwn in th furnac at th flw rat f OOOml/min. - Whn th systm tmpratur rachd th rquird tmpratur 77K, th graphit crucibl was placd and hld fr 0min, thn adding 6.0g f plltizd slag n th irn surfac. - Thsampls wr quilibratd fr 2.5 h. Thchic f th quilibrium tim will b xamindin th fllwing sctin. - t th nd f ach xprimntal run, th crucibl was rapidly withdrawn frm th furnac and qunchdin a stram f r gas. Thmtal and slag wr sparatd and crushd. - Th chmical analysis f sulphur fr mtal and slag was carrid ut using th cmbustin analysis mthd. 8 Frg. l. Schmatic diagram f xprimntal apparatus. Th chmical cmpsitins f usd irn ar shwnin Tabl 2. Thgraphit crucibl fr quilibrium study was prpard by drilling hls f.0mminnr diamtr and 80.0mmdpth ach in a graphit f 80.0 mm innr diamtr and 00.0mmlngth. This allwd t quilibrat diffrnt sampls simultanusly..2. Exprimntal Prcdur vrtical MSi2high tmpratur furnac was usd. Th tmpratur variatin at th cnstant hat zn f 00.0mmlngth was kpt within 5'C. Tw sts f thrmcupl f Pt-60/0Rh/Pt-000Rh wr usd t masur th systm tmpratur. Figur I shws th. Rsults and Discussin.. Chic f Equilibrium Tim xprimnt was carrid ut tb dtrmin th quilibrium tim accrding t sulphur cncntratin in mtal and slag. Figur 2shws th chang f sulphur cntnt with tim. It wasfundd that sulphur cntnt did nt vary aftr 2.0h. Th quilibrium tim thrfr was chsn as 2.5 h in th prsnt wrk..2. Effct f Basicity Tabl Iists all I th xprimntal rsults, including sulphur cncntratin in mtal and slag, th calculatd btwn Ls and Cs. Figurs and shwth rlatin Ls, Cs and R (=wt/cao/wt/si02) rspctivly. s sn in th figurs, Ls and Cs incras with incras f basicity. This can b xplaind qualitativly by th inic structur f slags. t th lwr basicity, th CaOcntnt C 5 ISIJ 68

3 ISIJ Intrnatinal, Vl. 5 (5), N. 0,5 '~0. ~ c! *Jrll :) v.i (f) ~] 2O.8.G ~) Il. T=77 l Fig. 2. O 0 80 TIME (min) Changf sulphur cncntratin in mtal and slag with tim (wt% )+ (Vvt ) D= (wt%si02)*0.6 (wt~~ i 02) Fig.. 80 l :77 l GO u]l J ~O wt~ti02: 0.8.O s 5.2 ~: wt%cao/wt%si02 Rlatin btwn R and Ls fr CaO-Si02-Ti02 5'/.l-8"/*MgO systm at 77K. T: 77K Frg. 5. Rlatin btwn B and Ls fr CaO-Si02~H02-5'/.l-8 "/.MgO systm at 77K. ~' ~P. J. T=77K : (wt~~o)*(wt B: ) ~:~Si ~SiO) 02) *0.6(~(~~li02) *0.6(~(~~li 02) Frg. 6. Rlatin btwn B and Ls fr CaC~Si02-Ti02-50/0l-8 lmgosystm at 77K. Fig.. ~O~2 0.8 n:wt~)ctlld wt~~'i02 : 5 0 IS wt~,si Rlatin btwn R and Cs fr Ca(~Si02-Ti02-50/0l-8 lmgosystm at 77K. in th slag is lss, s that nly a fw fr 02~ ins xist. This rsults in lw sulphur distributin ratis and sulphid capacity f slags. s basic xids incras, th Si02 ntwrks ar brkn int smallr anin grups and th prprtin f fr xygn starts t incras. Thrfr, th sulphur distributin rati and sulphid capacity f slag will incras. Th rsults f Tsa and Katayama5)fr Ca(l~Si02- l-mgosystm and Brwn6) fr CaO-Si02-Ti02- MgOsystmandCaO-Si02-Ti02lsystmshwd that incrasing th CaO, MgOcntnt in slag r dcrasing Si02 cntnt in slag can incras th sulphur capacity Cs. In rdr t furthr study th ffct f basicity n Ls and Cs, th mdifid slag basicity, B, dfind by Yang and Zha0,7) xprssd by Eq. (8), was cnsidrd. B= (~lcao + /.MgO)/('0Si /Ti02) """(8) Figurs 5and 6indicat th rlatin btwn Ls, Cs andb fr CaC~Si02-Ti02-50/0l-8 /. MgO systm. sxpctd, Ls andcsincras with th mdifid basicity B. Cnsidring th Ls and Csbing xprssd by a linar crrlatin with B, th fllwing quatins ar btaind. LgLs = 0.702B Rc () = 6 C 5 ISIJ

4 80 GO u]0 J Fig. 7. O Fig. 8. O a Ti02 ISIJ Intrnatinal. Vl. T:77K Y~t~CaO/wt~S CL Wt% Effct f Ti02 cncntratin n Ls fr CaC~Si02- Ti00/0l-800MgOsystm at 77K. l : 77 wt~lo/wt~si O Ti02 wt'~) Effct f Ti02 cncntratin n Cs fr Ca(~Si02- Ti02-5"/.l-8~/.MgO systm at 77K, U J0 I T= 77 ~r ~'t~a ~~st~~. 8 -,-.2 5 O 5 I 02 Wt~, Frg.. Rlatin btwnprcnt dcras fls andti02 cncntratin fr CaC~Si02-Ti00/0l-80/0MgO systm at 77K. LgCs=0.287B-.870 Rc= (I O) whr, Rc dnts th crrlatin cfficint... Effct f Ti02 Th ffcts f Ti02 cncntratin in slag n Ls and Cs ar shwnin Figs. 7 and 8, rspctivly. It can b sn frm Figs. 7and 8 that Ls and Cs dcras with th incras f Ti02 cncntratin in slag at th givn 5 (5). N. wtcx) - Si G t Itp ~ ~~ O 27 7 / l:~o /\.O*r~ \ ~~ ~ 5 7 Fig. r. Is-sulphur distributin rati curvs f Ca(~Si02- Ti02-5"/.l8'/.Mg systm at 77K. basicity. This is bcausin th basic slags Ti02 xists as Ti0~~ ins, cnfirmd by Smmrvill and Bll.8) Thrfr, Ti02 in slags frms th anins which mak th fr 02~ ins dcras. In th thr wrds, th highr Ti02 in slags is, th lss CaO in slags is. Hwvr, th basicity f slag is givn, th highr th Ti02 cncntratin f slag is, th mr th prcnt dcras f Ls. This ffct is mr clarly sn in Fig. whr th prcnt dcras f sulphur distributin rati (LS), xprssd by Eq. ( ), ar drawn against Ti02 cncntratin. LS (/) = ((Ls-Lsa)/Lsa) x 000/0...( ) whr, Lsa is sulphur distributin rati withut Ti02, Ls is sulphur distributin rati at givn Ti02 cncntratin. Frmth rsults mntind abv, in rdr t furthr clarify th rlatinship f Ls, Rand Ti02 cncntratin in slag, using rgrssin mthd, Eq. ( 2) canb btaind. Ls = 56, (/Ti02) (/Ti02) (R - I.O) (R - I.O) (/Ti02)(R...(2) I.O) - Basd n th Eq. ( 2), th is-sulphur distributin rati curvs ar shwnin Fig. 0. It wasfund in Fig. 0 that th is-ls curvs wr nt paralld. In thr wrds, whn basicity r Ti02 cncntratin in slags changs, th variatin f Ls is diffrnt... Optical Basicity Ssinsky and Smmrvill) hav shwnthat thr is a crrlatinship btwn ptical basicity () and Cs f CaO-basdslags. Kunisadaand lwai l) havpintd ut that Cs f Na-basdslags is th functin f ptical basicity. Fr CaO-Si02-Cslag th rlatin was cnfirmd by naclt, L and Hays.) Th ptical basicity f an xid, dfind by Duffy and Ingram,2) is rlatd t th Pauling's lctrngativity (X) f th catin by Eq. (). i=.6(xi-0.26)......() Slags ar xid slutins and th ptical basicity f a C 5 ISIJ 70

5 Tabl. ISIJ l ntrnatinal, Vl. 5 (5). N. Pauling's lctrngativity f xids, 2) CaO MgO TiO 2 Si02 l.o JD J? Fig ~..2. H)-Ls H'- Cs : f T=77 l OG 0.62 O~ O.8. c 0..2 Rlatin btwn Ls, Cs and fr Ca(:~Si02- Ti02-50/0l-8'/MgO systm at 77K. slag is calculatd using ml fractins and ptical basicity f individual xids. Tabl Iists Pauling's lctrngativity f varius xids. Th rlatinships f Ls, Csahd wasshwnin Fig.. Thcrrlatin quatin ar: LgLs=I Rc=0....() LgCs=.6 - l0.6 Rc=0.0...(5) It is sn frm rsults btaind abv that th ptical basicity mthd is usful fr rsarching th sulphur distributin rati and sulphid capacity f slags cntaining Ti02' 5. Cnclusins Basd n th quilibrium study abv, th rsults btaind ar summarizd as fllws: Jr) () With th incras f Ti02 cncntratin in slags, th sulphur distributin rati and sulphid capacity dcras. Th highr th Ti02 cncntratin f slags is, th mr th prcnt dcras f Ls and Cs. (2) Ls and Csf slags cntaining Ti02 incras with th incras f basicity and th mdifid basicity. Th rlatin ar: LgLs = 0.702B Lg Cs = 0.287B () Thrlatin f Ls, RandTi02 cncntratin can b xprssd in th prsnt wrk: Ls = (/Ti02) + 0'055(/Ti02) (R - I.O) (R - I.O)2 =. 50(/Ti02)(R - I.O) () Optical basicity can b usd t study sulphur distributin rati and sulphid capacity f slags cntaining Ti02, th crrlatin quitin at 77K is, LgLs = LgCs = REFERENCES ) F. D. Richardsn and G. Withrs: J. Irn Stl Inst., 65 (50), 66. 2) x. G. Huang:ThPrincipl f Mtanufgy. ChngqingUnivrsity Publishr, Chngqing, (80), 7. ) J. x. Chn: Handbkf Frquntly UsdDiagramsand Data fr stlmaking, Th Publishing Husf Mtallurg, Bijing, (8), 22. ) J. Taylr: J. Irn Stl Inst., 2 (6),. 5) T. Tsa and H. G. Katayama: Trans. Irn Stl. Inst. Jpn., 26 (06), 77. 6) 7) 8) ) O) ) 2) S. D. Brwn, R. J. Rxburgh. I. Ghita andh. B. Bll: Irnmaking Stlmaking, (82), 6. Z. P. Yangand L. R. Zha: J. Nrthast Inst., (8), 7. I. D. Smmrvill and H. B. Bll: Can. Mtall. Q., 2 (82), 5. D. J. Ssinsky and I. D. Smmrvill: Mdtall. Trans. B, 7 (86),. K~Kunisada and H. Iwai: ISIJ Int., (),. N. M. naclt. H. G. L and P. C. Hays: ISIJ Int., (), 5. J.. Duffy and M. Ingram: J. Inrg. Nucl. Chm., 7 (75),. 7 C 5 ISIJ