Effect of Coal Source on Quallty of Bauxite for Refractories Applications

china,'s RefractoriesvL21,No1,2012Dr. Ye Guotian oblained his B Sc. from Wuhan University of Science and Technology in 1982, M. Sofrom Luoyang Institute of Refractories Research( Now Sinosteel Luoyang Institute of Refractories ResearchCo, Lid. )in 1985 and Ph. D from University of British Columbia(UBC)in 2005. His research interestsare mainly in refractory materials. He has authored or co-authored over 50 papers. Dr. Ye worked in WuhanScience and Technology until 1987 and Luoyang Institute of Science and Technology until 2001and joined Zhengzhou University since 2007Effect of Coal Source on Quality of BauxItefor Refractories ApplicationsZHANG Chuanyin, YE Guotian*, WANG QingfengSchool of Material Science and Engineering, Zhengzhou UniversityZhengzhou 450001, ChinaAbstractand calcium carbonates that are often present at differ-a Bauxite from Qing hen is calcined for refractent levels in bauxite deposits seriously offset the per-applications. Three fuel sources with different amounts offormance of refractories. Especially, iron oxide is aresidual ash and ferric oxide were used for bauxite calci- detrimental element in bauxite for refractory applicanation in a rotary kiln. It is found the quality, inclutions. The excess iron oxide in bauxite not only lowersding the content of ferric oxide, bulk density, apparentrefractoriness by forming low melting phases and makesporosity and water absorption, of the bauxite is highlythe refractory more susceptible to carbon monoxide at-influenced by the fuel source of rotary kiln. In essencetack 2 but causes undesirable discoloration of thefactories as wellthe effect of fuel on the quality of bauxite is attributed toAs known, impurities in raw ore are the parathe amount of ferric oxide introduced by the fuel. Intro- mount source of the iron oxide in bauxite for refractoriesduction of a modest quantity of ferric oxide is beneficialapplications. There has been a considerable interestfor promoting the densification of bauxite.over the years in investigating the effect of ferric oxideKey words: bauxite; iron oxide; bulk density; apparent porosity; fuel son the properties of bauxite-containing refractories andfinding an efficient process for removing iron fromChina's bauxite(3-5). However. there is no sufficient1 ntroductionattention paid to the impurity of iron oxide coming fromcoal for calcining raw ore of bauxite. Therefore, thisBauxite is a naturally occurring, heterogeneousvestigation has been made to clarify the effect of coalmaterial comprised primarily of one or more aluminumsource oquality of bauxite for refractories applicationshydroxides plus various mixtures of aluminosilicate(ka-alinite, etc.), silica(SiO2), iron oxide(Fe203),ti-tania TiO2), and other impurities in2 Experimental Procedureamounts. High alumina bauxite is widely used forThe raw ore of bauxite was mined from Qingzhenmanufacturing refractories and abrasives. However, Guizhou provinH中国煤化工6.2ma%major impurities such as iron, titania, silicon oxides AL,O, with 0.8CNMHGre of bauxiteCorresponding author.E-mail:gtyezzu@qg.com(YEGuotian)22 China's Refractories 2012/Effect of Coal Source on Quality of Bauxite for Refractories ApplicationsChina's Refwas crushed and then fed into a rotary kiln(1. 5 m x at 1 100 C for 30 min. The amount of ash residual of75 m), with particle size of 10-15 mm. The bauxite the two kinds of coal was obtained via calcining theparticles were calcined at 1 500C, heating up accord- coal at 815C until no mass change with time. Cheming to the curve shown in Fig. Ial compositions of the raw ore and the calcined bauxite as well as the ash residual were determined byX-ray Fluorescence(XRF, Bruker S2). Mineralogicalanalysis was carried out with X-ray Diffraction(XRDBruker D4). The bulk density, apparent porosity andk 80water absorption of the bauxite sintered were measuredby Archimedes method with immersing the specimensinto distilled water3 Results and DiscussionFig. 1 Temperature curve for calcining raw ore of bauxiteAccording to the XRF results in Table 1, the bauxTwo kinds of coal from Zhenfeng( Guizhou Prov- ite raw ore contains 76.2 mass alumina, 3. 3 mass%ince)and Yulin Shaanxi Province ) respectively, silica and 4.0 mass titanium oxide mainly. Ferricwere used as fuel of the rotary kiln. For the purpose of oxide is a relatively minor component, with the contentcomparison, raw ore of bauxite was also calcined at of 0.8 mass%. The mineralogical XRD pattem is shown1 500C with the fuel of coal gas. Different from calci- in Fig. 2, indicating the chief alumina mineral presentning with coal, there is no foreign impurities intro- in the raw ore is diaspore (AL 0,.H,0),with aduced into bauxite when calcining with coal gasminor amount of anatase TiO2) and muscoviteThe loss of ignition( Lon)of the raw ore was (KAl2(, A1)Oo(OH, F)2). These observations inmeasured by calculating the mass change after calcining dicate the bauxite is suitable for refractories applicationTable 1 Chemical composition of bauxite raw ore/massAl, O3M76.213.300.350.6014.17little bit higher than that in raw ore. However. in theDiasporebauxite calcined with Zhenfeng coal, the content of ferAnataseoxide is up to 2. 29 mass %, much highein the raw ore of the bauxiteTable 2 Chemical compositions of bauxite calcined with va-rious heat sources /mass %oHeat source Al, O, SiO, Fe, O, Ca0 MgO TiOCoal gas88.793.840.930.160.414.60Yulin coa87.963.931.010.170.414.564.532.290.260.364.920()Fig. 2 XRD pattern of bauxite raw oreThe change of ferric oxide in fired bauxite can beThe chemical compositions of bauxite calcined in explained by the analysis results of the two kinds ofrotary kiIn with Zhenfeng coal, Yulin coal and coal gas coal, as presented in Table 3. Comparing to Zhenfengare given in Table 2. It can be found that the content coal, Yulin coal is characterized by somewhat highof ferric oxide varies with the change of the fuel heat value, less ash residual and low content of ferricsource. The content of ferric oxide in the bauxite cal- oxide. This means the dosage of Yulin coal required forcined with coal gas is 0. 93 mass % This value is al中国煤化工 ite raw ore ismost equal to that in raw ore after deduction of loi 6 massCN MH Gat of Zhenfengfrom the result. The amount of ferric oxide in the baux- coal. In addition the contents of ash residual and fer-ite calcined with Yulin coal is 1. 01 mass % which is a ric oxide in the ash residual in yulin coal are lowerChina's Refractories 2012/1China's RefractoriesZHANG Chuanyin, YE Guotian, WANG Qingfengthan those in Zhenfeng coal. Therefore, Yulin coal in- than Zhengfeng coal doestroduces less contamination of ferric oxide into bauxiteTable 3 Analysis results on heat value of the two kinds of coal and the amount and chemical composition of their ash residualHeat valueHeat sourceAsh amountChemical composition/mass/(kel·kg-)/mass%o2O3O, Fe,,CaoYulin coal67177.8038.95l1.7015.516.38henfeng coal633318.6936.491.74The bulk density, apparent porosity and water ab- results in a lot of liquid phase with relatively low viscos-sorption are highly influenced by heat sources, as ity forming in the bauxite. Driven by the force of capilshown in Fig. 3. The bauxite sintered with Yulin coal lary tunnels, the liquid phase runs out of the sinteringpresents relatively high bulk density, low apparent po- bumps and hence aggravates the formation of kiln coatrosity and low water absorption. Whereas the bauxite It is a common phenomenon that aluminosilicate refrac-fired with coal gas shows generally low densification, tories containing relatively high amount of iron oxide arewhich is probably attributed to the comprehensive effect usually dotted with flux holes and bubbles which areof the quantity of the liquid phase and its viscositymainly attributed to iron oxide as a fluxing agent( 6)The formation of liquid phase depends highly on the Therefore, the bauxite sintered with zhenfecontent of ferric oxide introduced by fuelwhich includes relatively higher content of ferric oxide6r8.1r3.28becomes somewhat porous microstructurally, embodying25更Bulk density3.27in insufficient bulk density and medium apparent porosity in physical properties. On the other hand, when Yulin732623.25\Water absorptcoal is used, a modest quantity of liquid phase occurs inhe bauxite and thus benefits the densification process2763.24Apparent porosityl100Fig. 3 Physical properties of bauxite sintered with variousheat sourcesIn rotary kiln, the kiln coat increases with1.2reasing liquid phase. So, the quantity of liquid phaseformed in bauxite sintered can be correspondingly givenby the ratio of kiln coat formation, as shown in Fig. 4Coal gasYulin coalIn the case of firing with coal gas, there is no enough Fig. 4 Relationship between ratio of kiln coat formation andiquid phase formed in the bauxite due to no ferric ox-content of ferric oxideide introduced. Thus, coal gas has almost no promo-It can be observed in Fig. 5 that the bauxite firedtion effect on the densification process of bauxite and with Zhenfeng coal is darker than that with coal gas orroduces bauxite with lower bulk density and higherYulin coal. This result confirms that highcontent offerric oxide in bauxite causes undesirable discolorationHigh content of ferric oxide in Zhenfeng coal of the refractories中国煤化工CNMHGCoal gasn1 coFig. 5 Color of bauxite fired with various fuelsChina's Refractories 2012/1Effect of Coal Source on Quality of Bauxite for Refractories ApplicationsChina' s Refractories4 ConclusionReferencesThe ash residual of coal is one of the maj1] Bhima Rao R, Besra L, Reddy B R, et al. The effect ofies source introduced into bauxite calcined. Accordpretreatment on magnetic separation of ferruginous mineralsing to the above results, the content of ferric oxide inin bauxite[ J]. Magnetic and Electrical Separation, 1997auxite calcined with Zhenfeng coal is 50 mass% high-8(2):115-123er than that with Yulin coal because the former con-[2] Bhima Rao R, Veeresh M B, Banerjee G N. Effect of thertains higher amounts of ash residual and iron oxide. Itmal pretreatment on grindability and upgradation of bauxitehas been found in this work that the coal characterizedfor refractory applications[ C]. Light Metals 2002, Washion,2002:205-208by low ash residual and low content of iron oxide is[3] Sadler L Y, Venkataraman C. A process for enhanced re-beneficial to promote densification of bauxite during firmoval of iron from bauxite ores[ J]. International Journal ofng,while the coal with high amounts of ash residualMineral Processing, 1991, 31(3-4): 233-246and iron oxide produces bauxite with lower bulk density [4] Banerjee G N, Reddy B R, Bhima Rao R, et al. Effect ofand higher apparent porosity.magnetizing roasting on removal of iron from bauxite ore forfractory uses [J]. World Ceramics and Refractories1998(9):12-16.Acknowledgements[5] Banerjee G N, Bhima Rao R. Thermal shock for energyThe authors acknowledge National Natural Science Foundaconservation: a case study on ball milling of vanadiferoustion of China(50872125), National High-Tech R D Develmagnetite[ J]. International Journal of Metals, Materialopment Program of China(2009 AA032503)and Internationald process,2000,12(1):81-86s&T cooperation Program of China( 201ODFB50350)for [6] Guo Haizhu, Yu Sen. Handbook on Refractory Raw Materi-financial supportals[ M]. 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