Effect of Nature Gas Injection on Reducibility of Wustite Prepared from Baharia Iron Ore Sinter

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1 Effect of Nture Gs Injection on Reduciility of Wustite Prepred from Bhri Iron Ore Sinter 1 M. Bhgt*, 2 K. S. Adel Hlim, 3 H. A. El-Kelesh, 4 M. I. Nsr Centrl Metllurgicl Reserch nd Development Institute (CMRDI), P.O.Box 87-Helwn, Ciro, 11421, Egypt 1 M_hgt7@yhoo.com; *m_hgt7@yhoo.com; 2 khsd99@yhoo.com; 3 He_chemist24@yhoo.com; 4 minsr@hotmil.com Astrct-The min method for iron production is the lst furnce. It emits out 2 illion tons CO 2 per yer, which hs the lrgest contriution in glol wrming. Using thermogrvimetric technique, wustite smples prepred from Bhri iron ore sinter were isothermlly reduced t 9-11 o C y different rtios of H 2 /CO/CO 2 /N 2 which is somewht simulting the composition of the reducing gs in cse of nturl gs injection with low oxygen enrichment in the lst furnce. The reduction extent for wustite from iron ore sinter is clerly enhnced to e in the rnge of 54-69% comprtively with tht reduced with coke gses (3-5%) s industril dt. Enhncement of wustite reduciility decreses the remining quntity of unreduced wustite, which descends to high temperture region t which reduction depends minly on solid cron tht will consequently led to reduction of coke consumption nd CO 2 emission. The reduction rte of wustite smples is independent on either the rection temperture or the H 2 concentrtion in the reducing gs mixture due to the wter gs shift rection. The reduction rte of wustite smples t initil stges re most likely controlled y the comined effect of chemicl rection nd gseous diffusion mechnisms while t finl stges re most likely controlled y interfcil chemicl rection mechnism. Keywords-Iron Mking; Wustite; Nturl Gs; Iron Ore; Sinter; CO 2 Emission I. INTRODUCTION Glol climte chnge cused y green house gses hs roused wide concern in interntionl society. According to Interntionl Pnel on Climte Chnge (IPCC) report, there re four principle greenhouse gses result from humn ctivities i.e. cron dioxide, methne, nitrous oxide, nd the hlocrons. Among these gses, CO 2 mkes the lrgest contriution to glol wrning [1]. Since the iron nd steel industry is energy intensive, CO 2 plys the most importnt role mong these green house gses. The iron nd steel industry is emitting out 65 million tons CO 2 per yer s the fourth iggest industry using fossil fuels [2]. The mount of CO 2 emissions from iron nd steel industry ccounts for gret shre of the totl CO 2 emissions from industry [3]. Thus, reducing CO 2 emissions in iron nd steel industry is urgent for environmentl protection nd sustinle development. Some previous investigtions hndled the CO 2 emission reduction. Christer Rymn et l [4] studied reduction of CO 2 emissions from integrted steelmking y optimized scrp strtegies. An importnt spect of the demonstrted clcultions is tht high scrp dditions to n integrted system does not lwys ct s liner CO 2 diluent. It is importnt to optimize nd lnce the different processes in the considered system to ensure glol optiml solution. Hisrn technology could reduce CO 2 emissions from lst furnce steelmking y more thn 5 percent [5]. The 2 million project is one of the inititives tht hs sprung up under the uspices of ULCOS (ultr-low CO 2 steelmking), consortium of Europen steelmkers tht hs drwn up the world s most dvnced progrm to reduce the steel industry s cron footprint. The 6 tp Hisrn pilot plnt will hrness new process tht mkes the production of liquid iron from virgin rw mterils in just single step possile, eliminting two of the three production steps required in lst furnce iron mking. Hisrn opens the prospect of 2% improvement in steel industry energy efficiency. Also five lst furnce compnies hve joined together to reduce cron dioxide (CO 2 ) emitted y the steel industry y 3% [6]. The gretest chllenge is considered to e the development of technology for using hydrogen for the reduction of iron ore, or put more simply, technology for using hydrogen s the reduction gent to reduce the mount of coke inserted into the lst furnce. The oxygen enrichment hs n insignificnt effect on the performnce indices [7]. The injection of nturl gs reduces CO 2 emission ut increses the energy consumption s compred to trditionl iron mking. The injection of geologiclly older solid nturl fuels, e.g. high-, med-, or low voltile cols, reduces CO 2 emission, with simultneous reduction of energy consumption indices. Jcco C. M. Frl et l [8] studied one possile wy of decresing CO 2 emissions, which is to pply CO 2 removl involving recovering of cron dioxide from energy conversion processes nd storing it outside the tmosphere. Since the 198 s, the possiilities for recovering CO 2 from therml power plnts hve received incresing ttention. Andrzej Zieik et l [9] studied the energy nlysis of lst furnce system operting with the corex process nd CO 2 removl. COREX export gs cn e utilized in severl wys: s fuel gs in metllurgicl CHP, s uxiliry fuel or hot reducing gs in the lst-furnce process (fter CO 2 removl), s reducing gent in the direct reduction of ore (e.g. MIDREX) or s rw gs for the production of synthesis gs. The injection of COREX gs or lst-furnce gs fter the removl of CO 2 into the therml reserve zone influences the consumption of coke, in this wy to reduce the emission of hrmful components nd CO 2 from the cookery. Also it influences the mount of lst furnce gs nd its chemicl energy, the mount of electricity generted in the lstfurnce gs pressure recovery turine, the consumption of lst-furnce gs in the Cowper stoves nd the mount of lst-furnce gs feeding the gs system of the ironworks. Compring to conventionl BF iron-mking system, direct CO 2 emissions of COREX is higher while the totl emission depends on the utiliztion wy of export COREX gses [1]. If the export gses re used for power genertion nd the credits of CO 2 emission re ccounted, the COREX smelting ME Volume 1, Issue 1 April 212 PP Americn V-King Scientific Pulishing

2 reduction processes cn hve dvntges over conventionl BF iron-mking system in CO 2 emissions only when the COREX is joined with high-efficiency generting units where the efficiency is greter thn 45% nd CO 2 emission fctor of the grid is higher thn.9 kg CO 2 /kwh. On the high temperture region of lst furnce (BF) the finl reduction step from the wustite (FeO) phse to iron (Fe) depends on direct reduction with solid cron, which is considered s one of the min fctors for CO 2 evolution in the lst furnce. Thus enhncement of the wustite reduciility efore the high temperture region will decrese the coke gsifiction nd so decrese the evolved CO 2. The Egyptin iron ores of El-Bhri Osis is the min feedstock for the four lst furnces of the Egyptin Iron nd Steel Co. In the present investigtion, comprtive reduction ehvior of synthesized pure chemicl wustite nd wustite prepred from Bhri iron ore sinter ws studied t K using H 2 /CO/CO 2 /N 2 gs mixture which is somewht simulting the composition of the reducing gs in cse of nturl gs injection with low oxygen enrichment in the lst furnce. II. EXPERIMENTAL In the present study, two different types of wüstite smples were used for the experiments. The first one is pure chemicl smple tht is tken s reference nd the other is mde of sinter of Bhri iron ore. The pure wustite smples were prepred y the reduction of pure hemtite. A regent grde (A.R) hemtite powder (99.9%) ws compcted in cylinder shpe. These compcts were sintered t 1473 k in ir for 24 hrs. After tht the sintered compcts were crushed nd reduced to wüstite using CO/CO 2 gs mixtured t rtio of 1/1 with totl flow rte of 1 l/min t 1273 K. Due to the nonstoichiometric chrcter of the wüstite, the rection ws extended, fter the initil reduction, for out 6 hrs to ssure the homogeneous structure distriution of the ction vcncies nd holes on the formed wüstite. Pure wüstite powders were compcted into riquettes of out 1 gm weight, 7 mm dimeter, nd 5 mm height. For preprtion of the other smple, Bhri iron ore sinter ws delivered from the Egyptin Iron nd Steel Co. in Helwn. The chemicl nlysis of this sinter s received from the compny is shown in Tle I. The sinter smples were crushed nd reduced to wüstite using CO/CO 2 gs mixture t rtio of 1/1 in totl flow rte of 1 l/min t 1273 K. furnce constnt hot zone. First, nitrogen t flow rte of 1 liter/min ws introduced. Then fter the smple soking for 1 min. t the reduction temperture, the reducing gs mixture t flow rte of 1 liter/min ws introduced. The weight loss resulted from oxygen removl from the riquettes ws recorded with time t intervls. At the end of the experiment, the sket with the reduced riquettes ws removed nd dropped y relesing its suspension wire from the lnce, into conicl flsk contining cetone to prevent pyrophority of the reduced smple. The fired nd reduced smples were exmined with the id of reflected light microscope (Meiji CK 39), scnning electron microscope (JEOL, JSM-541), X-ry diffrction nlysis ((JSX-6P JEOL diffrctometer with copper trget) nd pore size distriution (Micromeritics Pore Sizer 932). III. RESULTS AND DISCUSSION A. Chrcteriztion of Prepred Wüstite Smples The nneled pure wüstite compcts nd those prepred from Bhri sinter were chrcterized with XRD nlysis. Wüstite phse clerly ppered in XRD chrts, ut in cse of sinter smples, it ws ccompnied y other phses ppered such s Ferroustmite (C.5 Fe.5 SiO 3 ) nd C 2 SiO 4 due to the presence of impurities in the ore. From XRD nlysis, the verge crystlline size ws clculted using the diffrctions peks from Scherer s formul s shown elow: D =.9 λ / β cos θ (3.1.1) Where D is the crystllite size, λ the X-ry wvelength, β the rodening of the diffrction pek, nd θ is the diffrction ngle [12]. It ws found tht the crystlline size increses from 85.4 nm for pure wüstite to 92 nm for wustite prepred from sinter. Also it cn e oserved tht the totl porosity of nneled pure wüstite is 37.28% ut for wüstite prepred from sinter of Bhri iron ore is 34.76%. Fig. 1 shows the reltion etween incrementl pore volume nd pore dimeter for nneled pure wustite compcts nd those prepred from sinter of Bhri iron ore. It cn e noticed tht the pore size distriution in pure wüstite compcts nd those prepred from Bhri iron ore minly rnged etween 1-4 nd.5-.3 µm. Pure wustite compcts hve higher numer of lrge pores wheres wustite prepred from Bhri iron ore hs higher numer of smll pores. TABLE I THE CHEMICAL ANALYSIS OF BAHARIA IRON ORE SITER Fe SiO 2 CO FeO MgO B % 9.8% 9.92% 15.44% 1.75% 1.1% The prepred wustite smples were then reduced in thermo-grvimetric pprtus t K using H 2 /CO/CO 2 /N 2 gs mixture. The reduction ssemly nd gs flow system used in this study were previously mentioned [11]. The course of reduction ws followed up y mesuring the weight loss s function of time under controlled conditions of temperture nd gs composition. For ech reduction experiment, the furnce ws heted up to the required reduction temperture, nd then the smple ws weighed nd plced in pltinum wire sket. The smple ws then grdully introduced into the furnce so s to void therml shock crcking nd positioned in the middle of the incrementl intrusion, ml/g pure wustite sinter pore dimeter, m μ Fig. 1 the pore size distriution for nneled pure wustite nd those prepred from sinter of Bhri iron ore. ME Volume 1, Issue 1 April 212 PP Americn V-King Scientific Pulishing

3 The microstructure of oth wustite smples is mtrix of gloulr wüstite grins forming reltively less dense structure with homogeneously distriuted mcro- nd micropores. On the other hnd, the microstructure of wüstite prepred from sinter showed some chnges compred to the pure one s the grins tended to e lrger nd connected to ech other. Also the pores re connected to ech other to give lrger mcropores with denser wüstite grins reltive to those in the pure one. B. Reduction Behvior of Wustite Smples Using thermo-grvimetric technique, oth wüstite smples (pure nd those from iron ore sinter) were isothermlly reduced t the temperture rnge 9-11 o C y different rtios of H 2 /CO/CO 2 /N 2 (Tle II) which is somewht simulting the composition of the reducing gs in cse of nturl gs injection with low oxygen enrichment in the lst furnce. The H 2 /CO rtio ws in the rnge of out.8-1 tht determines the suitle conditions for reduction in the lst furnce to void the unfvorle excess of nturl gs nd CO [13-17]. The reduced smples were chrcterized y XRD. It ws found tht the wüstite is reduced grdully to metllic iron. The influence of reduction temperture nd reducing gses composition on the reduction ehvior nd structurl chrcteristics of the reduced products ws studied in order to elucidte the kinetics nd mechnisms of reduction. TABLE II THE VARIOUS GAS COMPOSITIONS APPLIED FOR ISOTHERMAL REDUCTION OF WUSTITE SAMPLES Reduction extent (%) Tempertur e Fig. 3 Effect of reduction temperture on the reduction ehvior of pure wustite smples reduced y H 2 / (H 2 +CO+CO 2 ) = Gs composition, vol% H 2 /(H 2 +CO+CO 2 ) H 2 CO CO 2 N Temp., o C Tempertu ) Effect of Temperture: Pure Smples: The isotherml reduction curves of pure wüstite compcts reduced y H 2 /(H 2 +CO+CO 2 )=.38,.41 nd.44 t 9-11 o C re given in Fig. 2-4 respectively. For ech single reduction curve, the rte of reduction ws highest t the erly stges nd decresed s reduction proceeds till the end of reduction Tempertur e Fig. 2 Effect of reduction temperture on the reduction ehvior of pure wustite smples reduced y H 2 / (H 2 +CO+CO 2 ) =.38 Time, min. Fig. 4 Effect of reduction temperture on the reduction ehvior of pure wustite smples reduced y H 2 / (H 2 +CO+CO 2 ) =.44 The reduction cme to its completion for ll smples reduced y ll gs compositions t 9-11 o C. The effect of temperture on the rte of reduction hs chrcterized ehvior tht t the initil stges the rection rte incresed with incresing temperture ut grdully ecomes independent on reduction temperture. Nmely, for H 2 /(H 2 +CO+CO 2 )=.38 the rte decresed y incresing reduction temperture from 95 o C till 11 o C ut t 9 o C rection hs the lowest rte in this rtio. This phenomenon is due to the possiility of wter-gs shift rection H 2 + CO 2 = CO + H 2 O The equilirium of this rection is t 8 o C, t higher tempertures the rection shifted to direction of CO formtion, which increses percent of CO higher thn H 2 in the medium. Since CO hs reducing power lower thn H 2, so the reduction rte decresed y incresing reduction temperture. Also, for pure wustite compcts reduced y H 2 /(H 2 +CO+CO 2 )=.41 nd.44, the reduction rtes re independent of temperture due to wter-gs shift rection. ME Volume 1, Issue 1 April 212 PP Americn V-King Scientific Pulishing

4 The totl reduction process in the lst furnce lsts for 12 min, ut the reduction sttus t 9 min ttrcts more ttention ecuse it is the time needed for the urden to pss through the temperture region of 9-11 o C in lst furnce. From isotherml reduction curves of pure wustite, it ws found tht t 9-11 o C the reduction extent fter 9 min ws in the rnge of % which is greter thn tht of pure wustite smples 5-75% isothermlly reduced coke gses (CO/CO 2 /N 2 ) tht studied y the present uthors previously [18]. At lower H 2 content, the totl porosity decreses y incresing reduction temperture from 53.6% to 28.22% for pure wustite compcts reduced y H 2 /(H 2 +CO+CO 2 )=.38 t 95 o C to 15 o C respectively. The reltion etween incrementl pore volume nd pore dimeter for pure wustite compcts reduced y H 2 / (H 2 +CO+CO 2 ) =.38 t 95 nd 15 o C respectively showed tht the pore size distriution rnged etween 1-1 μm nd micropores rnged etween µm for oth smples. The incrementl intrusion vlue for smples reduced t 95 o C is higher thn tht reduced t 15 o C which reflects incresing of pores size nd pores numer y decresing reduction temperture which is lso confirmed y SEM microgrphs s shown in Fig. 5, for pure wustite smples reduced y (H 2 +CO+CO 2 ) =.38 t 95 nd 15 o C respectively. Fig. 5 SEM microgrphs of pure wustite reduced y H 2 / (H 2 +CO+CO 2 ) =.38 It cn e oserved tht the structure of smples reduced t 95 o C contins smll grins with some mcro- nd micropores ut y incresing temperture, the grins tended to e lrger nd connected to ech other forming dense structure with lower porosity. Accordingly, the fster reduction rte t 95 o C incresed the porosity of the formed metllic iron compred with reduction t 15 o C. At higher H 2 percents, totl porosity increses y incresing reduction temperture from 33.1% to 56.88% for pure wustite compcts reduced y H 2 /(H 2 +CO+CO 2 )=.44 t 95 o C to 15 o C respectively. The pore size distriution rnged etween 1-1μm nd micropores rnged etween.5-.8 µm for oth smples s shown in Fig.6 of pure wustite compcts reduced y H 2 /(H 2 +CO+CO 2 )=.44 t 95 o C to 15 o C respectively. The incrementl intrusion vlue for smples reduced t 15 o C is higher thn tht for 95 o C which reflects incresing of pores size nd pores numer y incresing reduction temperture s confirmed y SEM microgrphs for pure wustite smples reduced y (H 2 +CO+CO 2 ) =.44 t 95 nd 15 o C. Incrementl volume, ml/g Temperture, pore dimeter, μ m Fig. 6 The reltion etween incrementl intrusion volume nd pore dimeter for pure wustite reduced y H 2 / (H 2 +CO+CO 2 ) =.44 t 95 nd The structure of smples reduced t 95 o C is fine nd grins gglomerted with ech other. But y incresing temperture the grins tended to e lrger nd connected to ech other with mny mcro- nd micro-pores inside them. Accordingly, the fster reduction rte t 15 o C incresed the porosity of the formed metllic iron compred with reduction t 95 o C. 2) Smples from iron ore sinter: The rte of reduction ws highest t the erly stges nd decresed s reduction proceeds till the end of reduction. The reduction rte t the erly stges incresed y incresing the rection temperture ut fter tht the reduction rte ecomes independent on temperture. This is owing to the phenomenon of wter-gs shift rection. On the other hnd from isotherml reduction curves, it ws found tht the reduction extent fter 9 min ws in the rnge of 54-69% which is reltively higher compred with the wustite from iron ore sinter reduced with coke gses (3-5%) s given y industril dt or (34 48%) from previous study for present uthors [18]. The isotherml reduction curves of wüstite from iron ore sinter reduced y H 2 /(H 2 +CO+CO 2 )=.41 t 9-11 o C re given in Fig o C Temperture, o C Fig. 7 Effect of reduction temperture on the reduction ehvior of iron ore sinter smples reduced y H 2 / (H 2 +CO+CO 2 ) =.41 ME Volume 1, Issue 1 April 212 PP Americn V-King Scientific Pulishing

5 The totl porosity increses y incresing reduction temperture from 74.1% to 95.37% for iron ore sinter reduced y H 2 /(H 2 +CO+CO 2 )=.41 t 9 o C to 11 o C respectively. Fig.8, shows the reltion etween incrementl pore volume nd pore dimeter for wustite from iron ore sinter reduced y H 2 / (H 2 +CO+CO 2 ) =.41 t 9 nd 11 o C respectively. Incrementl volume ml/g Incrementl volume, ml/g Pore dimeter, m pore dimeter, Fig. 8 The reltion etween incrementl intrusion volume nd pore dimeter for iron ore sinter reduced y H 2 / (H 2 +CO+CO 2 ) =.41 t: ) 9 o C ) 11 o C It cn e noticed tht, for smples reduced t 9 o C, the pore size distriution rnged etween μm nd micropores rnged etween.1-.8 µm. But for smples reduced t 11 o C, the pore size distriution rnged etween μm nd micropores rnged etween.2-.6 µm. The incrementl intrusion vlue for smples reduced t 11 o C is higher thn tht t 9 o C, nd they hve very wide rnge of mcro-pores tht reflects incresing of pores size nd pores numer y incresing reduction temperture. This is confirmed y SEM microgrphs s shown in Fig.9, for iron ore sinter reduced y H 2 / (H 2 +CO+CO 2 ) =.41 t 9 nd 11 o C respectively. It cn e oserved tht the structure of the smples reduced t 11 o C contins whiskers with mny micro-pores, nd lrge numer of mcropores ut y decresing temperture the whiskers disppered nd grins tended to e smller with lower numer of mcropores forming more dense structure µ µ m Fig. 9 SEM microgrphs of iron ore sinter reduced y H 2 / (H 2 +CO+CO 2 ) =.41 t: ) 9 o C ) 11 o C 3) Effect of Reducing Gs Composition: Generlly it ws found tht the percent of H 2 in the reducing gses hd significnt effect on the reduction of wüstite. The reduction rte incresed y incresing H 2 concentrtion in the reducing gs mix either t high or low tempertures. The difference etween reduction rtes of vrious reduced smples decresed y decresing reduction temperture till 9 o C t which the curves overlpped t finl reduction stges. The isotherml reduction curves of pure wüstite compcts reduced y H 2 / (H 2 +CO+CO 2 ) =.38,.41 nd.44 t 9 nd 11 o C re given in Fig. 1 (, ) respectively H H content Fig. 1 Effect of reducing gses rtio on the reduction ehvior of pure wesite t: ME Volume 1, Issue 1 April 212 PP Americn V-King Scientific Pulishing

6 Journl of Metllurgicl Engineering (ME) The internl structures of different pure smples reduced y H 2 / (H 2 +CO+CO 2 ) =.38,.41 nd.44 t constnt tempertures re exmined y SEM. It cn e noticed tht t higher rection temperture (15 o C) the produced metllic structure reltively ecomes denser y decresing the H 2 concentrtion from.44 to.38. This is lso confirmed y the mesured totl porosity for reduced products t higher temperture, which decreses from 56.88% to 28.22% y decresing percent of H 2 gs from 44% to 38% respectively. This cn e ttriuted to the reltively slower rection rte t lower H 2 concentrtion. Fig. 11 shows the reltion etween incrementl pore volume nd pore dimeter for pure wustite compcts reduced y H 2 / (H 2 +CO+CO 2 ) =.38,.41 nd.44 t 15 o C. Incrementl volume, ml/g Pore dimeter, Fig. 11 The reltion etween incrementl intrusion volume nd pore dimeter for pure wustite reduced y H 2 / (H 2 +CO+CO 2 ) =.38,.41 nd.44 t 15 o C It cn e noticed tht the pore size distriution minly rnged etween 1-1 μm nd micro-pores rnged etween µm for ll smples. The incrementl intrusion vlue for smple reduced with H 2 gs percent.44 is higher thn the others nd it hs greter numer of mcro- nd micro-pores. This mens tht pores numer incresed y incresing H 2 gs percent in reducing gs. On the other hnd, the totl porosity for reduced product t lower temperture decreses from 53.6% to 33.1% y incresing percent of H 2 gs from 38% to 44% respectively. Fig.12 shows the reltion etween incrementl pore volume nd pore dimeter for pure wustite compcts reduced y H 2 / (H 2 +CO+CO 2 ) =.38,.41 nd.44 t 95 o C μ m H content µm for ll smples. For mcro-pores, the incrementl intrusion vlues incresed y decresing percent of H 2 in reducing gs composition which reflects tht the smples reduced y lower H 2 percents hve higher numer of mcro-pores. On the other hnd, for micro-pores the incrementl intrusion vlue incresed y incresing H 2 percents tht confirms incresing rte of reduction y incresing H 2 percent of reducing gs from.38 to.44 ecuse micropores re minly responsile for reduction progress. This lso confirmed y studying the internl structure of compcts reduced y H 2 / (H 2 +CO+CO 2 ) =.41 nd.44 t 95 o C which showed tht micropores incresed y incresing percent of H 2 in reducing gs nd lrger metllic iron res were formed with lower hydrogen concentrtion. 4) Smples from iron ore sinter: The isotherml reduction curves of wüstite smples from iron ore sinter reduced y H 2 / (H 2 +CO+CO 2 ) =.38,.41 nd.44 t 1 o C re given in Fig.13. Generlly, it is cler tht the reduction rte is independent of gs rtio which is due to wter gs shift rection: H 2 + CO 2 = CO + H 2 O By incresing percent of H 2 in reducing gs the wter gs shift rection shifted to direction of CO formtion so the rte of reduction decresed due to the lower reduction strength of CO compred to tht of H 2. However, the rection ws not complete t ll rection conditions Fig. 13 Effect of reducing gses rtio on the reduction ehvior of iron ore sinter t 1 o C The internl structure of different smples reduced y H 2 / (H 2 +CO+CO 2 ) =.38 nd.44 t constnt tempertures (1 o C) re exmined y SEM s shown in Fig. 14, respectively..5 Incrementl volume, ml/ g pore dimeter, m μ Fig. 12 The reltion etween incrementl intrusion volume nd pore dimeter for pure wustite reduced y H 2 / (H 2 +CO+CO 2 ) =.38,.41 nd.44 t 95 o C It cn e noticed tht the pore size distriution minly rnged etween 1-11 μm nd micropores rnged etween Fig. 14 SEM microgrphs of iron ore sinter reduced t 1 o C y ME Volume 1, Issue 1 April 212 PP Americn V-King Scientific Pulishing

7 It cn e noticed tht the produced metllic iron hd dense structure t higher H 2 concentrtion while t lower H 2 concentrtion porous structure ws formed. The porosity mesurement confirmed the ove oservtions tht the totl porosity decresed from 87.86% to % y incresing reducing gs rtio from.38 to.44. The reltion etween incrementl pore volume nd pore dimeter for wustite from iron ore sinter reduced y H 2 / (H 2 +CO+CO 2 ) =.38,.41 nd.44 t 1 o C showed tht the pore size distriution minly rnged etween μm. For smples reduced y H 2 / (H 2 +CO+CO 2 ) =.38, ut for gs rtio =.44 the pore size distriution is slightly wider to 3 μm wheres it minly rnged etween μm. For smples reduced y H 2 / (H 2 +CO+CO 2 ) =.41 tht reflected the presence of gret numer of pores with vrious dimeters. The micro pores rnged etween μm for ll smples. The incrementl intrusion vlues reflected tht reltively y incresing H 2 concentrtion in the reducing gs, numer of mcro-pores nd micro-pores decresed. B. Rte Controlling Steps nd Mechnisms of Reduction In order to predict the rte controlling mechnism t oth the initil nd finl stges of reduction, the vlues of pprent ctivtion energy (E ) re clculted from Arrhenius eqution eq. (3.3.1): K r = K o e E / RT (3.3.1) Where K r is the reduction rte constnt, K o is the frequency fctor, R is the gs constnt nd T is the solute temperture. The ppliction of different heterogeneous gssolid mthemticl models nd the internl structure of prtilly reduced compcts were exmined nd correlted with ech other. The reltionships etween the logrithm of the rte of reduction (dr/dt) nd the reciprocl of the solute temperture 1/T re plotted t oth initil (2%) nd finl (8%) rection stges for pure wüstite smples reduced y H 2 / (H 2 +CO+CO 2 ) =.44 t 9-11 o C. From the otined results, the pprent ctivtion energy (E ) is clculted t the initil nd finl stges s shown in Tle III: TABLE Ⅲ THE APPARENT ACTIVATION ENERGY (EA) CALCULATED AT THE INITIAL AND FINAL REDUCTION STAGES FOR PURE WUSTITE SAMPLES REDUCED BY DIFFERENT RATIO OF REDUCING GAS Rection stge E vlues t different rtios of H 2 / (H 2 +CO+CO 2 ), (kj/ mole) % of Reducing gs =.38 =.41 =.44 Initil Finl The vlues of ctivtion energy indicte the type of mechnism [19]. The clculted ctivtion energy vlues indicte tht the reduction t the initil stges for pure wüstite reduced y H 2 / (H 2 +CO+CO 2 ) =.38,.41 nd.44 re most likely controlled y comined effect of oth gseous diffusion nd interfcil chemicl rection mechnisms while t the finl reduction stges it is most likely controlled y interfcil chemicl rection mechnism. In order to confirm the vlidity of the reduction mechnism, the following mthemticl formultions eq. ( ) derived y Szekely et l. [2-23] ws tested ginst the experimentl results: (1) t * (P F (X))= X+(1-X) ln(1-x) (3.3.2) For gseous diffusion mechnism (2) t * (G F (X)) = 1- (1- X ).5 (3.3.3) For chemicl rection mechnism (3) t * ( 1 + 1/σ 2 ) = G F (X) + P F (X) = 1- (1- X ).5 + X + (1- X ) ln (1-X) (3.3.4) For the mixed control mechnism where X = frctionl reduction degree, t * = dimensionless time, σ = gs-solid rection modulus. By pplying the different mthemticl formultions derived from gs-solid rection model, it ws found tht stright lines were otined on pplying the mixed control of the chemicl rection nd gseous diffusion mechnism t the initil rection stges of pure wustite smples reduced y H 2 / (H 2 +CO+CO 2 ) =.38,.41 nd.44. Also the stright lines were otined on pplying the chemicl rection mechnism t the finl rection stges of ll smples. Fig.15, show the mthemticl formultions plots for pure wustite smples reduced y H 2 / (H 2 +CO+CO 2 ) =.41 t initil nd finl reduction stges respectively. 1-(1-x).5 +x+(1-x)ln(1-x) 1-(1-x) Temperture, o C Time,min. Temperture, o C Fig. 15 Appliction of the control mthemticl eqution for pure wustite reduced y H 2 / (H 2 +CO+CO 2 ) =.41 t vrious reduction stges: ) initil ) finl ME Volume 1, Issue 1 April 212 PP Americn V-King Scientific Pulishing - 2 -

8 This ws in good greement with the suggested controlling mechnisms from the clculted ctivtion energy vlues t oth initil nd finl reduction stges for ll smples. The microstructure of pure wüstite compcts prtilly reduced y H 2 / (H 2 +CO+CO 2 ) =.44 to 2% reduction extent t 1 o C ws exmined y reflected light microscope s shown in Fig.16. It ws oserved tht some micro nd mcro-pores were oserved in homogeneous distriution with the produced metllic iron nd wustite grins tht reflected the ility of gs ccess nd successful iron nucletion in these smples. At the sme time, dense structure of connected wustite grins ws detected. So, oth gseous diffusion nd interfcil chemicl rection mechnisms re controlling the rection s concluded ove y E clcultions. The microstructure of pure wüstite compcts prtilly reduced y H 2 / (H 2 +CO+CO 2 ) =.44 to 8% reduction extent t 1 o C ws exmined y reflected light microscope s shown in Fig.16. It ws oserved tht the formed metllic iron structure looks very porous with the presence of mny micro nd mcro-pores in homogeneous distriution for ll smples. These oservtions confirm the concluded rection controlling mechnisms y E clcultions. Rection stge Initil Finl E vlues, (kj/ mole) The vlues of ctivtion energy indicte the type of mechnism. The reduction t the initil stges for wüstite from iron ore sinter reduced y H 2 / (H 2 +CO+CO 2 ) =.41 is most likely controlled y comined effect of oth gs diffusion nd interfcil chemicl rection mechnisms while t finl stges is most likely controlled y interfcil chemicl rection mechnism. 1-(1-x).5 +x+(1-x)ln(1-x) Temperture, (1-x) o C Temperture, Fig. 17 Appliction of the control mthemticl eqution of wustite from iron ore sinter reduced y H 2 / (H 2 +CO+CO 2 ) =.41 t: Fig. 16 Photomicrogrph of pure wustite smples prtilly reduced to vrious reduction extent t 1 o C y H 2 / (H 2 +CO+CO 2 ) =.44: ) 2% (x=4) ) 8% (x=2) The pprent ctivtion energy (E ) is clculted from the reltionships etween the logrithm of the rte of reduction (dr/dt) nd the reciprocl of the solute temperture 1/T t oth initil (2%) nd finl (6%) rection stges for wüstite from iron ore sinter reduced y H 2 / (H 2 +CO+CO 2 ) =.41 s shown in the following tle: TABLE IV: THE APPARENT ACTIVATION ENERGY (EA) CALCULATED AT INITIAL AND FINAL REDUCTION STAGES FOR WÜSTITE FROM IRON ORE SINTER REDUCED BY H2/ (H2+CO+CO2) =.41 By pplying the different mthemticl formultions derived from gs-solid rection model, it ws found tht stright lines were otined on tht pplying the mixed control mechnism t the initil rection stges of wustite smples reduced y H 2 / (H 2 +CO+CO 2 ) =.41, nd t finl stges stright lines were otined on tht pplying the chemicl rection mechnism s shown in Fig.17, respectively. This ws in good greement with the controlling mechnisms suggested from the clculted ctivtion energy vlues t oth the initil nd finl reduction stges. The microstructure of wustite from iron ore sinter prtilly reduced y H 2 / (H 2 +CO+CO 2 ) =.41 to 2% nd 6% t ME Volume 1, Issue 1 April 212 PP Americn V-King Scientific Pulishing

9 1 o C ws exmined y reflected light microscope. At initil reduction stges, some micro nd mcropores were in homogeneous distriution with the produced metllic iron nd wustite grins tht reflected the ility of gs ccess nd successful iron nucletion in these smples. While t finl reduction stges metllic iron grins were formed with the presence of mny micro nd mcropores in homogenous distriution forming porous structure, which reflected the esier gs ccess in this smple. The concluded mechnism (interfcil chemicl rection) explined the SEM oservtion in Fig.9 for whisker formtion. During the metllic iron formtion under pure chemicl control, iron is fed to the nucleus down very steep grdient, which sustntites the extreme ssumption tht the rte of the trnsport mechnism is much higher thn tht of further reduction. Growth then tkes plce without ny significnt removl of oxygen round the nucleus condition which leves it no other possiility thn to grow outwrds [24]. IV. CONCLUSIONS Wüstite smples (pure nd those from iron ore sinter) were isothermlly reduced t 9-11 o C y different rtios of H 2 /CO/CO 2 /N 2. The reduction rtes of oth wustite smples re independent on neither the rection temperture nor the H2 concentrtion in the reducing gs mixture due to the wter gs shift rection. The reduction extent fter 9 min. for pure wustite smples is clerly enhnced to e in the rnge of % comprtively with tht reduced with coke gses CO/CO2/N2 (5 75%). By the sme mnner, the reduction extent fter 9 min for wustite from iron ore sinter is clerly enhnced to e in the rnge of 54-69% comprtively with tht reduced with coke gses (3-5%) s industril dt or (34-48%) from previous study for present uthors. During reduction of pure wustite, t lower H2 percents the totl porosity decresed y incresing reduction temperture while t higher H2 percents, the totl porosity incresed y incresing reduction temperture. During reduction of wustite from iron ore sinter, the totl porosity incresed y incresing reduction temperture. During reduction of pure wustite, t higher rection temperture, the produced metllic structure reltively ecomes denser y decresing the H2 concentrtion while t lower temperture, porosity decresed y incresing percent of H2 gs. During reduction of wustite from iron ore sinter, the produced metllic iron hd dense structure t higher H2 concentrtion while t lower H2 concentrtion porous structure ws formed. The reduction process of pure smples nd wüstite from iron ore sinter t initil stges is most likely controlled y the comined effect of chemicl rection nd gseous diffusion mechnisms while t finl stges is most likely controlled y interfcil chemicl rection mechnism. REFERENCES [1] Interntionl Pnel on Climte Chnge, The physicl science sis. IPCC, Genev, Switzerlnd, 27. [2] Andres orth, Nikol Anstsijevic nd Heinz Eicherger, Minerl Engineering, vol. 2, pp , 27. [3] Zhiji Hung, Xio Ding, Ho Sun nd Siyue Liu, Journl of clener production,vol. 18, pp , 21. [4] Christer Rymn nd Mikel Lrsson, ISIJ Interntionl, vol. 46, No. 12, pp , 26. [5] (29) posted Nov 3. [6] (29) [7] R. Petel, W. Hutny nd J.T. Price, Advnces in Environmentl Reserch, vol. 6, pp , 22. [8] Jcco C. M. Frl, Chris A. Hendriks nd Kornelis Blok, Energy Conversion nd Mngement, vol. 36, Issues 6-9, pp , [9] Andrzej Zieik, Krzysztof Lmpert nd Mrcin Szeg, Energy, vol. 33, pp , 28. [1] HU Chngqing, HAN Xiowei, LI Zhihong nd ZHANG Chunxi, Journl of Environmentl Sciences Supplement, pp. S116 S12, 29. [11] A. A. El-Gessy, M. I. Nsr nd M. Bhgt, Ironmking Steelmking, vol. 27, pp. 117, 2. [12] B. D. Cullity nd S. R. Stock, Elements of X-Ry Diffrction, 3rd edition, pp. 167, Prentice Hll, 21. [13] V.N. Andronov, Modern Blst Furnce, Lirry of Sint Petersurg Stte Technicl University, pp. 1, Russi, 21. [14] V.N. Andronov, The influence of Different Fctors on the Possile Minimum Coke Consumption in the Blst Furnce, Lirry of Sint Petersurg Stte Technicl University, p. 142, Russi, 21. [15] K.S. Adel Hlim, Ph.D. Thesis, Sint Petersurg Stte Technicl University, Russi, 21. [16] V.N. Andronov nd K.S. Adel Hlim, Journl of ferrous metls (Cherny Metll), No.8, pp.25-3, 21. [17] K.S. Adel Hlim, V.N. Andronov nd M.I. Nsr, Ironmking nd Steelmking, vol. 36, No.1, pp , 29. [18] M. Bhgt, K. S. Adel Hlim, H. A. El-Kelesh nd M. I. Nsr, minerl processing nd extrctive metllurgy, vol. 12, No. 2, pp. 12, 211. [19] M. I. Nsr, A. A. Omr, M. H. Khdr nd A. A. El-Gessy, ISIJ Interntionl, vol. 35, pp. 143, [2] J. Szekely, J. W. Evns nd H. Y. Sohn, Gs-Solid Rection, Acdemic press, N. Y, [21] H. Y. Sohn nd Szekely, Chem. Eng. Sci., vol. 27, pp. 763, [22] B. L. Seth nd H. U. Ross, AIME, vol. 233, pp. 18, [23] W. M. Mc Kewn, AIME, vol.218, pp. 2, 196. [24] R. Nicolle nd A. Rist, Metllurgicl Trensctions B, vol. 1B, pp. 429, ACKNOWLEDGMENT This work is fully supported y the Science nd Technology Development Fund (STDF), Egypt nd is grtefully cknowledged. ME Volume 1, Issue 1 April 212 PP Americn V-King Scientific Pulishing