Study on the strength of cold-bonded high-phosphorus oolitic hematite-coal composite briquettes

International Journal of Minerals, Metallurgy and MaterialsVolume 21, Number 5, May 2014, Page 423Do:10.1007/s12613-01409256Study on the strength of cold-bonded high-phosphorus oolitic hematite-coalcomposite briquettesWen Yu2), Ti-chang Sun2), Zhen-zhen Liu2),Jue Kou2), and Cheng-yan Xu.2)1)The Key Laboratory of the Ministry of Education of China for High-Efficient Mining and Safety of Metal Mines, University of Science and Technology Beijing, Bei-2)School of Civil and Environmental Engineering, University of Science and Technology Beijing, Beijing 100083, China(Received: 3 December 2013; revised: 19 December 2013; accepted: 28 December 2013)Abstract: Composite briquettes containing high-phosphorus oolitic hematite and coal were produced with a twin-roller briquette machineusing sodium carboxymethyl cellulose, molasses, starch, sodium silicate, and bentonite as binders. The effect of these binders on the strengthof the composite briquettes, including cold strength and high-temperature strength, was investigated by drop testing and compression testingIt was found the addition of Ca(OH)2 and Na2 CO3 not only improved the reduction of iron oxides and promoted dephosphorization duringthe reduction-separation process but also provided strength to the composite briquettes during the briquetting process; a compressive strengthof 152. 8 N per briquette was obtained when no binders were used. On this basis, the addition of molasses, sodium silicate, starch, and betonite improved the cold strength of the composite briquettes, and a maximum compressive strength of 4046n per briquette was obtained byusing starch. When subjected to a thermal treatment at 1200 C, all of the composite briquettes suffered from a sharp decrease in compressivestrength during the initial reduction process. This decrease in strength was related to an increase in porosity of the composite briquettesX-ray diffraction(XRD)and scanning electron microscopy(SEM) analyses showed that the decrease in strength of the composite briquettecould be caused by four factors: decomposition of bonding materials, gasification of coal, transportation of byproduct gases in the compositebriquettes, and thermal stressKeywords: hematite; briquetting; binders; compressive strength; porosity; direct reduction proces1. Introductionstrength to withstand stresses induced during their handling,trCold-bonded ore-coal composite pellets have been de- Binders play an important role in the cold-bonding pelletizato[1-3] and to redtion process, and different binders have been utilized. Benzinc, and lead from the waste materials of iron and steel tonite, ground blast furnace slag, cement, lime, hydratedplants [4-11]. The advantages of these pellets include (1)a lime, and sodium silicate have been used as inorganic bind-high reaction rate due to the closeness of the reactants, (2) ers, whereas starch, pitch, dextrin, molasses, and dextrosethe ability to use non-coking coal as a reductant, and(3) have been used as organic binders. Moreover, some combiwithout high temperature induration process. Several indus- nations of inorganic-organic binders have also been em-trial processes such as Inmetco, ITmk3, and Fastmet proc- ployed. The compressive strength of the composite pelletsesses in which a rotary hearth furnace is used as the reduc- has been reported to vary from 50 to approximately 1000 Ning equipment have been developed to treat cold-bonded per pellet [1-3,8-11]composite pellets [12-13]. In addition, the charging of aHigh-phosphorus oolitic hematite ore is one of the mostshaft furnace and rotary kiln with cold-bonded composite refractory iron ores in China because iron oxides andpellets as a burden material has been reported in Refs. [1-2, fluorapatite in this ore are so intimately intermixed that ben-5-9]. Cold-bonded composite pellets must have sufficient eficiation of the iron ore by conventional mineral processino University of Science and Technology Beijing and Springer-Verlag Berlin Heidelberg 2014中国煤化工≌prgrCNMHG424Int J. Miner. Metall. Mater, VoL. 21, No 5, May 2014methods is unfeasible [14. A new process known asTable 1. Particle size distribution of raw materials wt%coal-based direct reduction and the magnetic0.074+method have been developed to produce direct reductionlaterial0.074mm0.045mm0.045mmiron(DRI) from high-phosphorus oolitic hematite ore472275813.39[15-20]. In this process, hematite is reduced to metallic iron23.3847.001105by coal and then the roasted product is ground to liberatemetallic iron, which is subsequently separated by magnetic Experimental procedureseparation. Most investigations related to this method have 2.2.1. Preparation of composite briquetteshe composite briqueffects of the reduction and separation parameters as well as laboratory-scale twin-roller briquette machine.First,finehe effects of different additives and coals on dephosphoripowders of iron ore, coal and additives were mixed with anzation and the recovery of iron. Few researches have fo- appropriate amount of water(8wt%-12wt%); the mixturescused on the pelletization of the mixtures of iron ore, coal, were subsequently briquetted in the briquette machine.Thend additives. Zhou et al. [15] have conducted experiments dosages of coal, Ca(OH)2, and Na, CO, were 25wt%, 15wt%with composite briquettes, but they did not investigate the and 3wt%, respectively; these dosages were determined inour previous study [20]. The dosages of binders were deter-In our previous work [20], we studied the function of mined by referring to Refs. [1, 10, 21]. The coCa(OH)2 and Na2CO3 as additives in the reduction of the briquettes are shown in Table 2. a piece of briquetteligh-phosphorus oolitic hematite-coal composite briquettes; weighed 8-10 g and had an almond shape with the dimerthe results showed that the additives can promote the reduc- sion of 14 mm x 25 mm x 25 mm. The wet briquettes weretion of hematite and decrease the P content of DRI. We ob- cured naturally for 3-4 d under ambient atmosphere. Curingtained a dri with 92 6wt% Fe and 0.07wt% P at a recoverynsidered to be complete when the strength of the briof 91.79wt%dding 15wt% Ca(OH)2 and 3wt%Nastant for 2-3After theWe prepared the composite briquettes using a die and punch composite briquettes were cured, their strength was testedbut did not investigate their strength. In the present studythe mixtures of high-phosphorus oolitic hematite, coal, and Table 2. Composition of the briquettes with different bindersadditives were briquetted with a twin-roller briquette ma- Iron Coal/ Ca(OH)2/ Na,CO,/Binderchine. Sodium carboxymethyl cellulose(Na-CMC), molas- ore wt% wt%ses, sodium silicate, bentonite, and starch were used as bind6993174810.492.10ers, and the cold-bonding strength and high-temperature 69.62 1741 10.44 2.09 Na-CMC: 0.44wt%rength of briquettes with various compositions were studied. 65.36 16.34 9.80 1.96 Molasses: 6.54wt%2. Experimental65.3616.349.801.96 Sodium silicate: 6.54wt%65.3616.341.96 Bentonie: 6.54wt%2.1. Raw materials65.3616.341.96 Starch: 6.54wt%High-phosphorus oolitic hematite ore samples used inthis work were obtained from Hubei Province, China; the 2.2.2. Briquette quality testingnature of the ore has been described elsewhere [20]. Coal(1) Drop tests. In the drop tests, the composite briquettesused as a reductant in this study was obtained from Ningxia were dropped repeatedly from a height of 0.5 m onto aProvince, China. The industrial analysis(air dry(ad)of the 10-mm-thick steel plate until they broke. The average ofcoal was 11.77wt% moisture. 17.56wt% ash. 24.86wt% five such test results was taken as the final valuevolatiles. and 45.8lwt%o fixed carbon. The iron ore and coal(2)Compression tests. The composite briquettes werewere crushed to 100% passing a I mm sieve for use in the tested on a compressive strength testing instrument. Theexperiments, and the particle size distribution of the samples arithmetic mean of four such test results was calculated asis given in Table 1. Lime hydrate, sodium carbonate, sodium the final valuecarboxymethyl cellulose(Na-CMC)and sodium silicate(3)High-temperature strength testing. Reduction roastingused in the experiments were of analytical reagent grade. was performed in a muffle furnace with a tempSoluble starch(made from potato) was of chemical reagent trol programgrade Molasses and bentonite were industrial productscrucible with tla yH中国煤化工 a clay-graphiteCNMHGnd 75 mm,re-w. Yu et al, Study on the strength of cold-bonded high-phosphorus oolitic hematite-coal composite briquettes425spectively. When the furnace temperature reached 1200C, presence of Na2 CO3 promoted carbonate bonding betweenthe graphite crucible was placed inside the furnace and the particles [23]. These results mean that the addition ofheated for the desired time; the furnace temperature returned Ca(OH)2 and Na2 CO3 can not only promote the reduction ofto 1200.C after approximately 30 s. After the prescribed hematite and improve dephosphorization during the reducleating period, the crucible was removed from the furnace tion-separation process [20], but also serve as a binder dur-and then covered with coal powder to cool. After the re- ing the briquetting process. Moreover, as evident from re-duced briquettes had cooled, their compressive strength and sults in Table 3, the binders play a very important role inporosity were testedimproving the strength of the briquettes. The drop number(4)Porosity of the briquettes. The porosity of the bri- and the compressive strength of the briquettes prepared withquette was calculated as followsNa-CMC as a binder were 12. 3 and 250.2 n per briquetteTrue density-Apparent density x100%,respectively. Na-CMC is a linear polymeric derivative ofPorosity-cellulose that is used in numerous industries; it forms poly-where the true density of the briquettes was measured by themer bridges at the point of contact between particles, andpycnometer method, and the apparent density of briquettesen the briquettes [21]. whewas measured by a simple technique based on the Ar- was added, the drop number was 25.8 and the compressive73.8Ngth of the bri23. Analysis and characterizationwas obvious and may stem from the fact that the molassesX-ray diffraction(XRD, Rigaku DMAX-RB, Japan)us-not only bonds the particles by itself but also catalyzes theing Cu Ka radiation and a secondary monochromator wereformation of calcite when combined with Ca(OH)2 [9]used to identify the formed phases; the samples wereComposite briquettes made using sodium silicate as a binderscanned over the 20 range of 10 to 90. Scanning electronhad a drop number of 10.2 and a compressive strength ofmicroscopy(SEM) and X-ray energy-dispersive spectr166.1 N per briquette In the presence of water, sodium sili-copy( Carl Zeiss Evo 18)analyses were performed on thecate forms a viscous liquid that can bind particles together;samples mounted in epoxy resin and polishedafter it has dried, the sodium silicate forms a hard glassysubstance that provides strength to the briquettes [24]. Ben3. Results and discussiontonite is a standard binder used for iron ore pelletization3.1. Effect of binders on the cold strength of composite while meeting with water, it swells and creates strong bondsbetween particles [24. with the addition of bentonite, thedrop number and compressive strength of the briquettesThe strength of composite briquettes prepared using dif- were 12.2 and 232. 0N per briquette, respectively. The dropferent types of binders is shown in Table 3number and compressive strength of composite briquettesprepared using starch as the binder were greater than 50 andTable 3. Strength of composite briquettes4046N per briquette, respectively; these results were thebest obtained in this study. Starch used in the experiment isDrop numberopressive strength /Nper briquettea soluble starch that exhibits good solubility in room-temperature water; it also forms polymer bridges between particles and therefore provides strength to the briquettes [1]In summary, organic binders were observed to be moreMolasseseffective than inorganic binders in this study. Furthermore166.1compared with inorganic binders, organic binders offer anBentonite2320additional advantage of not contaminating the briquettes orStarch404.6diluting their iron content because such binders are burnedoff during the roasting process [24]We observed that, when no binder was added to the br- 3.2. Relationship between the compressive strength ofquette, their drop number was 6.0 and their compressivestrength was 152. 8 N per briquette. This can be attributed tocomposite briquettes and reduction timethe fact that Ca(OH) absorbs CO2 from air and forms中国煤化工 s prepared usCaCO3, which binds particles together [22]. In addition, the ing various bindedYHCNMHGWIIn Fig I42IntJ. Miner. Metall. Mater vol 21, No 5, May 20141500tion of the briquettes will deteriorate the permeability ofz1300burden and increase the dust content in stack gases [12-13MolassesSodium silicateIn a rotary kiln, the presence of fine powders is one of theBentonStarchmain causes of ring formation [26]. Therefore, the burdenmaterial in shaft furnaces and rotary kilns must not onlypossess sufficient cold strength to withstand stresses duringtransportation but also have sufficient strength to withstandstresses induced during reduction in the furnace. The compressive strength of cold-bonded high-phosphorus oolitichematite-coal composite briquettes sharply decrthe initial reduction, which may adversely affect the per-Reduction time/minformance of shaft furnaces and rotary kilns. However, wherFig. 1. Compressive strength versus reduction time.a rotary hearth furnace is used as a reactor, because no relative movement occurs between the briquettes and the fuThe compressive strength of the composite briquettes de-nace and because the feed layer is only a few centimeterscreased sharply with the increase in roasting time during the thick [12-13], the strength requirement for the briquettes isinitial reduction processes. The compressive strength of the primarily to remain intact before the reduction process.Thecomposite briquettes prepared without additional binder de- strength of the composite briquettes prepared without addicreased to a minimum of 276n per briquette after 5 min. tional binder is sufficient for normal operation;thereforeThe compressive strength of the composite briquettes pre- the addition of binders is not necessary under these circumpared using starch decreased to a minimum of 22. 4 n per stancesbriquette after 6 min, and that of the briquettes prepared us-ing Na-CMC, molasses, sodium silicate, and bentonite de- 3.3. Effect of reduction time on the porosity of compositecreased to the minima of 30... and 90 13N per briquettesbriquette after 4, 6, 3, and 5 min, respectively. The greatestThe relationship between the compressive strength ofstrength loss occurred during the first 3 min. The strength of pellets and their porosity has been reported [24, 27).Hencethe composite briquettes prepared without additional binder we studied the change in porosity of composite briquettesand that of the briquettes prepared using Na-CMC, molasses, during the reduction process. Composite briquettes preparedsodium silicate, bentonite, and starch decreased by 73. 58%using bentonite and starch and those prepared without addi85.54%,88.25%0,81.80%0,53.48%, and 87.37%o, respec- tional binder were selected to investigate the effect of poros-tively. After reaching their minima, the compressive strengths ity; the results are shown in Fig. 2of all of the investigated composite briquettes increasedsharply with increasing reduction time. In addition,coldgth did not determine the briquette behavior dduction. For example, when starch was used as a binder, thecold compressive strength of the briquettes was 4046N perbriquette, which was the highest value among the investi-gated briquettes; however, the lowest strength of these bri35quette at high temperature was 27.6n per briquette, whichwas the second lowest value. this fact has also been notedby other researchers [8]Bentonite- StarchNumerous researchers have reported that self-reducingbriquettes lose strength at high temperature; in general, thisstrength loss is considered to be caused by decomposition ofReduction time/minbinders and swelling of the briquettes [6, 8-9, 11, 25]. TheFig 2. Porosity versus reduction time.decrease in compressive strength during reduction maycause the breakage and pulverization of the briquettesFig. 2 shows that the porosity of composite briquettes in-hich will bring about significant adverse impacts on the creased with theproduction. For example, in a shaft furnace, the pulverizacreased wi中国煤化工 ter reaching aCNMHGw. Yu et al, Study on the strength of cold-bonded high-phosphorus oolitic hematite-coal composite briquettesmaximum value. The porosities of unreduced compositeAccording to results in Fig 3. the iron occurs in the formbriquettes prepared without additional binder and of those of hematite in the unreduced briquette and the gangues areprepared using bentonite and starch were 24.01%, 24.79%, quartz, calcite, and portlandite. Since the mixtures do notand 20.79%, respectively. After the briquettes were heated contain calcite, the calcite in the briquettes can be inferred toat 1200C, the maximum porosity of the three briquettes have formed due to the carbonation of Ca(OH)2 during cur-were 55. 19%, 52.80%, and 58.23%, corresponding to the ing, which resulted in increased strength. In addition, the inreduction time of 6, 4, and 5 min, respectively. The com- tensity of the diffraction peak of calcite diminished with theparison of Fig. 2 and Fig. 1 reveals a strong correlation be- increase of reduction time and disappearedween the porosity and compressive strength of the reduced quette were reduced for 4 min. This disappearance of calbriquettes. As the porosity of the briquettes increased, their cite results from the fact that calcite decomposes into CaOand CO2 at 825C, which may be the main reason why thehereafter increased with the decrease of porosity. Further- strength of the composite briquettes decreased during themoalthough the composite briquettes prepared using first reduction process. When the briquettes were reducedstarch exhibited the lowest porosity before being reduced, for 2 min, the diffraction peaks associated with magnetitethey exhibited a higher porosity than the briquettes prepared were observed; peaks attributable to wustite and metallicusing starch and no binder after they were reduced for 2-8 iron appeared after 3 min of reduction. As the roasting timemin. This higher porosity may be due to the fact that starch was extended, the intensity of the iron diffraction peakswas burned away and left behind pores when heated at high gradually increased, and new gangue minerals, such as fayatemperature. This increased porosity may also explain why lite and akermanite, were generated. Because the metallicorganic binders fail to provide strength under high tempera- iron will agglomerate as the reduction proceeds and becausefatal3.4.Relationship between phase transformation and re- particles together, the metallic iron and fayalite may be theduction timenew bonding phases and improve the strength of the briXRD was used to study the effect of phase transitions onthe strength of the composite briquette. The composite bri- 3.5. Briquette microstructurequette made without additional binder were selected. TheSEM was used to investigate the morphological changesXRD patterns of the mixtures of iron, coal and additives, the in composite briquettes during the reduction process. Theunreduced briquette, and the briquettes reduced for different SEM images of the composite briquettes prepared withouttime are shown in Fig 3additional binders before and after being reduced for differ69 8 minIn the unreduced briquette(Fig. 4(a), a compact struc-ture in the mixtures of iron ore coal and additives is formedby compressive force and with the aid of the bonding effectof CaCO3. Several fissures were observed, which may haveformed during the sample preparation procedure, which in-cluded cutting and polishing processes. Since the coldbonded briquette was brittle, it was inevitably damagedduring the cutting and polishing processeUnreduced briquettThe SEM image of the briquettes reduced for 2 min indicated the presence of numerous pores(Fig. 4(b), whichMixturescan be explained by four effects: (1) the decomposition of1020304CacO, resulted in the loss of bonding force between parti20/(°)cles;(2)the gasification of coal left a gap between the coalI- hematite, 2- quartz, 3- portlandite: 4- calcite; 5- magnetiteparticles and other particles; (3) several types of byproductalcium oxide: 8netallic iron: 10gases were generated during the reduction process, and theakermanitetransport of these gases in the briquette will also destroy theFig 3. XRD patterns of mixtures, unreduced briquettes, and original structureduced briquettes.stresses generaYH中国煤化工d(4) thermalCNMHGs because theyInt J. Miner. Metall. Mater, VoL. 21, No 5, May 2014have different thermal conductivities and coefficients of briquette was reduced for 6 min( Fig 4(d), its porosity inthermal expansion. All of these effects cause damage to the creased continuously and its original structure was combond phase between particles, which results in increased pletely destroyed. However, more metallic iron was formedosity and a loss of strength. As evident in Fig. 4(c), the and the degree of melting of the newly formed phases inporosity of the briquette obviously increased and the dense creased, which caused the strength to start to increase. Afterstructure of the briquette became very loose when they were 8 min(Fig. 4(e)), the porosity of the briquette obviously de-reduced for 4 min; hence, the strength of the briquettes de- creased because newly formed phases melted. Althoughcreased continuously. Moreover, a few metallic iron parti- some large pores were present in the briquette the newlyobserved in the outermost layer of the briquette. When a gether, which resulted in improved strength. on linked to-cles(white particles) and a slight melting phenomenon were formed phase filled cracks and the metallic iron linked to-Fissure100mumFig. 4. SEM images of compositeiquettes:(a) unreduced briquettes(b)reduced for 2 min;(c)reduced for4 min;(d)reduced for 6 min;(e)re-duced for 8 minThe other composite briquettes prepared using additional quette had a compressive strength of 150 n per briquettbinders also suffered from binder decomposition, coal gasi- adding 15wt% Ca(OH)2 and 3wt% Na2CO3 due to carbfication, transportation of byproductstresses; they therefore also exhilstrength during the initial reduction processcan improve the strength of the composite briquetteshighest compressive strength value of 4046n per briquette4. Conclusionswas obtained when starch was used as a binder(2) The compressive strength of all of the investigated(1) High-phosphorus oolitic hematite-coal composite bri-ite bl中国煤化工 ring the initialCNMHGw. Yu et al, Study on the strength of cold-bonded high-phosphorus oolitic hematite-coal composite briquettesreduction process. After the first 3 min, the strength of the [8 M C Mantovani, C. Takano, and P.M. Buchler, Electric arccomposite briquettes prepared without an additional binderfurnace dust-coaland of those prepared using Na-CMC, molasses, sodiumcomposition, and additives on swelling and zinc removal,silicate, bentonite, and starch as binders decreased byIronmaking Steelmaking, 29(2002), No 4, p. 25773.58%.85.54%88.25%,81.80%.53.48%, and 87.37% [9] M.C. Mantovani and C. Takano. The strength and the hightemperature behaviors of self-reducing pellets contain3)A strong correlation was observed between the poros- [10R. Sah and S K. Dutta, Effects of binder on the properties ofity and the compressive strength of the composite briquettesiron ore-coal composite pellets, Miner:. Process. Extr: Metall.during the reduction process. As the porosity of the bri-Rev,31(2010,No.3,p.73ettes increased, their compressive strength decreased[11 C. Takano and M B Mourao, Comparison of high tempera(4)During the initial reduction process, the compactture behavior of self-reducing pellets produced from iron orestructure of the unreduced briquettes was damaged due toth that of dust from sintering plant, IS/J Int, 41(2001),the decomposition of the binder, the gasification of coal, thetransportation of byproduct gases and the thermal stresses, [12] B. Anameric and S K. Kawatra, Properties and features of di-rect reduced iron, Miner Process, Extr Metall Reand this change in structure resulted in the strength loss. Ashe degree of melting increased and more metallic iron[13] B. Anameric and S.K. Kawatra, Direct iron smelting reducformed. the strength of the briquettes was improvedion processes, Miner Process. Extr: Metall. Rev., 30(2008)Acknowledgements[ X.G. Bi, J D. Zhou, Z.C. Huang, Y Jin, and w. Xiong, Present investigation situation of dephosphorization processesThis work was financially supported by the Nationalfor high phosphorus content iron ores, Henan Metall.Natural Science Foundation of China(No. 51134002)15(2007),No.6,p.3.[15] J C. Zhou, Z.L. Xue, H F. Zhang, and Z.Q. Li, Study onReferencesphosphorus removal technology of high-phosphorus oolitichematite, Ironmaking, 26(2007), No. 2, p[16] D W. Yang, T C. Sun, H F, Yang, C.Y. Xu, C.Y. Qi, and Z X[1] B B. Agrawal, K.K. Prasad, S B Sarkar, and H.s. Ray, Coldbonded ore-coal composite pellets for sponge ironmakingLi, Dephosphorization mechanism in a roasting process fordirect reduction of high-phosphorus oolitic hematite in westart 1. Laboratory scale development, Ironmaking SteelmakHubei Province, China, J. Univ. Sci. Technol. Beijing,ig,27(2000,No.6,p.421[2] B B. Agrawal, KK. Prasad, S B Sarkar, and H.S. Ray, Cold32(2010),No.8,p.968[17 Y.L. Li, T.C. Sun, C.Y. Xu, and Z.H. Liu, New dephosphobonded ore-coal composite pellets for sponge ironmakingPart 2. Plant trials in rotary kiln, Ironmaking Steelmaking,rizing agent for phosphorus removal from high-phosphorusclitic hematite28(2001),No.1,p.23direct reduction roasting, J Cent3]SK. Dutta and A Ghosh, Study of nonisothermal reductionSouth Univ. Sci. Technol, 43(2012), No. 3, p. 827.of iron ore-coal/char composite pellet, Metall. Mater: Trans[18 C.Y. Xu, T.C. Sun, J. Kou, Y L. Li, X.L. Mo, and L G. Tang,B,25(1994),No.1,p.15Mechanism of phosphorus removal in beneficiation of higl44] Y.S. Lee, D.W.Ri, S.H. Yi, and I. Sohn, Relationship be-phosphorous oolitic hematite by direct reduction roastingtween the reduction degree and strength of DRI pellets pro-with dephosphorization agent, Trans. Nonferrous Met. Socduced from iron and carbon bearing wastes using an RHFchina,22(2012),p.2806simulator, /S/Int, 52(2012), No 8, p 1454[19 Y.S. Sun, Y.X. Han, P. Gao, Z.H. Wang, and D Z. Ren, Re-5] N.A. El-Hussiny and M.E. H. Shalabi, A self-reduced inter-covery of iron from high phosphorus oolitic iron ore usingmediate product from iron and steel plants waste materialscoal-based reduction followed by magnetic separation, Int Jusing a briquetting process, Powder Technol, 205(2011), NoMiner. Metall. Mater, 20(2013), No. 5, p. 41-3,p.21720]W. Yu, T.C. Sun, J Kou, Y.X. Wei, C.Y. Xu, and Z.Z. Liu,16J. Aota, L, Morin, Q. Zhuang, and B. Clements, Direct re-The function of Ca(Oh)2 and Na,CO, as additive on the reduced iron production using cold bonded carbon bearing pelduction of high-phosphorus oolitic hematite-coal mixed pellets: Part 1. Laboratory metallisation, Ironmaking steelmaking,lets,Shmt,53(2013),No.3,p.42733(2006),No.5,p.426.21]YX. Wei, T.C. Sun, W, Yu, Y.Y. Cao, and Z.Z. Liu, Mecha[7] Q. Zhuang, B. Clements, J Aota, and L. Morin, DRI produc-nism of sodium carboxymethyl cellulose for improving thetion using cold bonded carbon bearing pellets: Part 2. Rotarystrength of briquettes made of hematite ore and coal, Univkiln process modelling, Ironmaking Steelmaking, 33(2006),中国煤化工2No.5,p.429[22] J. Pal,SGHD Ghosh and dCNMHG430Int J. Miner. Metall. Mater, VoL. 21, No 5, May 2014Bandyopadhyay, Development of fluxed iron oxide pelletsking: mechanical behavior, Miner: Process. Extr. Metallstrengthened by CO, treatment for use in basic oxygen steelRe,24(2003),No.3-4,p.233.making, IS/ Int, 49(2009), No 2, p. 210[26] Z.C. Huang, J.J. Xu, X.G. Zong, and Q.Y. Liu, The require23]Q. Wang, Iron Ore-Coal Composite Briquettes Technology,ments of the furnace burdens in the cold-bonded pellet directMetallurgy Industry Press, Beijing, 2005, p. 16reduction process, Sintering pelletizing, 24(1999), No. 6, pganic and inorganic binders on strength of iron oxide pellets, [27 Z.C. Huang, L.Y. Yi, and T. Jiang, Mechanisms of strengthMetall. Mater. Trans. B, 44(2013), No. 4, p. 1000decrease in the initial reduction of iron ore oxide pellets.25 C. Takano and M.B. Mourao, Self-reducing pellets for ironPowder Technol., 221(2012), p. 284中国煤化工CNMHG