FEASIBILITY STUDY ON THE USE OF IRANIAN BAUXITES IN THE FABRICATION OF SHAPED REFRACTORY & HIGH ALUMINA CEMENTS. R. Naghizadeh 1, J. Javadpour 1, M. Naeemi 2, M.T. Hamadani 3 and H. R. Rezaie 1 1 Iran University of science & Technology, Iran 2 Pars Refractory Production co., Iran 3 Tabriz University, Iran Abstract: Calcined bauxites are important raw materials in the production of high alumina shaped & monolithic refractories. Presently most bauxites used in the Iranian refractory manufacturing sector are imported from china. Although Iran s bauxite deposit is not amongst the highest in the world, it is our belief that it might be a useful source Al 2 O 3 in the production of part of refractory needs in the country. With this in mind chemical and mineralogical studies were carried out on bauxite samples taken from several chosen mines. By comparing the results with those from the imported samples it is concluded that the bauxite deposit from some of the mines have the potential to be used in the fabrication of high Al 2 O 3 refractories and others are more suitable for use in the cement producing industries. 1. INTRODUCTION High Al 2 O 3 refractories are manufactured with the use of sillimanite, mullite, calcined bauxite, and tabular alumina and some type of refractory clay as raw material. Calcined bauxites are usually used in the production of refractory bricks with the alumina content in the range of 75-90% [1]. These types of bricks have applications in steel ladles, EAF roofs, cement producing furnaces, aluminum melting furnaces, etc. Around 85% of world bauxite deposits are consumed in the Al-Producing industries. The remaining is used in refractory, abrasive, cement & chemical industries [2]. Bauxite productiom was reported to be around 135.7 million tons in the year 2000. It was expected to show a yearly increase of 0.8% up to year 2006 [3]. Major deposits of quality refractory bauxite have been found in Guyana, China and Brazil [4]. The bauxite used in the Iranian refractory industry is mostly imported from china. The major phase in the calcined chinese bauxite is corundum with some tielite (Al 2 O 3.TiO 2 ), mullite and glassy phase connecting corundum particles. The mullite content in the calcined bauxite varies according to their rigion, for example samples from Shanxi mine contains high amounts of mullite while the samples from Guizhou mine contain much less mullite. The presence of mullite in the calcined bauxite provides several advantages such as improvement in the thermal shock, creep resistance and mechanical strength in the products. In addition mullite has solubility for harmful impurities such as TiO 2 (max, 3.3%) and Fe 2 O 3 (max. 1.2%) and this way it can reduce the damaging effect on impurities to a large extent [5]. High alumina cement as hydraulic binder is prepared by sintering or melting bauxite and/or alumina with limestone. There are five components (Al 2 O 3 CaO, SiO 2, FeO and Fe 2 O 3 ) in the refractory cements fabricated using bauxite. These components lead to the formation of several phase such as CA, C 12 A 7, C 2 AS, C 2 S ferrites (CF, C 2 F and C 6 A 2 F), Q phase[(c 22 (AFe +3 ) 12 (MFe +2 ) 8 S)] and glass in the cement [6,7]. In order minimize the amounts of unwanted phases in the cement, the percentage of SiO 2 and TiO 2 should be controlled in the bauxite. There are several bauxite mines in Iran. The major aim of this section study is to investigate the feasibility of these domestic bauxite deposites for use in the production of refractory high alumina cements. 444
R. Naghizadeh, J. Javadpour, M. Naeemi, M. T. Hamadani.and H. R. Rezaie. 2. BAUXITE MINES CONSIDERED FOR SHAPED REFRACTORY APPLICATIONS 2.1. Raw Materials and Calcination Process The bauxite mines studied were located near Isfahan, Damavand s shahbolaghi near Tehran and the Bigglar mine in Gazvin. The bauxite deposits in these mines are estimated as 6.7 milion tons, 800,000 tons, and 300,000 tons respectively. Chemical analysis for the typical samples taken out of these mines along with the chemical analysis for the two type of imported bauxites are presented in Table 1. As shown in this table the bauxite deposits from are d as supper and High class. Table 1. Chemical analysis of typical domestic and imported bauxites Bauxite type (mine) Al 2 O 3 SiO 2 Fe 2 O 3 TiO 2 CaO+MgO K 2 O+Na 2 O Super 81 75.29 10.9 14.3 1.36 1.53 3.59 3.28 1.38 0.81 1.68 2.15 Shahbolaghi 69.80 12.90 2.2 12.7 0.84 0.13 Biglar 64.8 21.7 1.13 12.15 0.32 0.22 86 89.1 5.05 4.59 4.81 1.98 3.53 3.23 0.99 0.5 _ 0.34 The mineralogical constitution of the domestic bauxite sample are given in Table 2. Table 2. Mineralogical constitution of the domestic bauxite samples Bauxite type (mine) Minerals Present Super Diaspore-kaolinite-Anatase Diaspore-kaolinite-Anatase Shahbolaghi Boehmite-Rutile-Kaolinite Biglar Diaspore-Anatase-Quartz-Kaolinite Table 3. Physical and mineralogical characteristics of calcined bauxite samples Bauxite type (mine) Mineralogical constitution PCF ( o C) Open Proosity (vol.%) Super >1750 >1750 17 15 Shahbolaghi Corundum-Rutile-Mullite-Tielite >1730 8.77 Biglar Corundum-Rutile-Mullite-Tielite >1730 7.61 5.1 11.9 The calcination of the bauxite samples from mines was performed at 1620 o C while samples from shahbolaghi and Bigglar were calcineed at 1500 o C. The calcined samples were characterized with regard to their physical properties and mineralogical content, the results which are shown in Table 3. 2.2. Sample Preparation and Property Evaluation Both domestic and bauxite samples were size screened and were mixed with 15% of clay binder prior to forming stage. After pressing and drying, the samples were heated in an electrical 445
furnace and they were held for 3 hours at the maximum temperature. The maximum heating temperature and the results of the physical and mechanical property tests on the heat treated samples are shown in Table 4. Table 4. Physical and mechanical properties of various bauxite samples Firing Bauxite type CCS Pa Type of clay binder Temperature (mine) ( o (Mpa) (vol%) C) Super Zedlitz kaolin 1500 110 21 1500 120 20 Zedlitz kaolin 1500 75 22 Shahbolaghi CC-31kaolin 1450 60 22 Biglar CC-31kaolin 1450 58.8 24 CC-31kaolin 1450 100 17.6 The microstructure of the samples prepared using shahbolaghi and Biglar bauxites were examined by SEM & EDS analysis. The results of these examination is shown in Fig. 1. 4000 Biglar 2500 Shahbolaghi Fig. 1. SEM micrograph of typical samples prepared using shahbolaghi and Biglar bauxites 2.3. Discussion Based on the results shown in tables I, II the bauxite samples from mine can be classified as diaspore - kaolinite type This sample contains a rather high amount of SiO 2 which has the tendency to encourage the formation of mullite phase in the calcination. As was mentioned previously the presence of mullite is useful in the improvement of the mechanical properties. For example the CCS values for the samples prepared using bauxite is clearly higher than the samples prepared using chinese bauxite (Table 4). Again from Tables 1 & 2,one can conclude that bauxites from shahbolaghi and Biglar are of boehmite and diaspore types respectively and contain high amounts of TiO 2. This impurity shows itself as rutile phase after calcination (Table 3). On the other hand the acceptable levels of SiO 2 and alkalies content in these bauxites may lead to the formation of some mullite in the microstructure which can balance the negative effect of TiO 2 to some extent. Based on the physical and mechanical properties and the microstructure shown in Fig. 1. It seems that, these bauxites can be used in a limited 446
R. Naghizadeh, J. Javadpour, M. Naeemi, M. T. Hamadani.and H. R. Rezaie. alumina refractory applications. It should also be mentioned that the strength of the samples prepared using these bauxites are comparable in those of commercially available bricks. 2.4. Concluding Remarks Bauxite samples from mine have the potential to be used in the high -Al 2 O 3 refractory applications. Bauxite samples from shahbolaghi & Bigglar are more suitable for high alumina application where the Al 2 O 3 content in the ranges 50-60%. 3. BAUXITE MATERIALS FOR HIGH ALUMINA CEMENT 3.1. Raw Materials Bauxite samples from the province of Yazd, Dehdasht and Bookan were studied as potential candidates for use in the preparation of high alumina cements. The present bauxite deposits for these mines are estimated to be around 1.7million tons, 750,000 and 800,000 tons respectively. The chemical and mineralogical data for these bauxites are presented in Tables 5 and 6 respectively. Table 5. Chemical analysis of bauxite samples from different regions. Bauxite type (mine) Al 2 O 3 SiO 2 Fe 2 O 3 CaO MgO TiO 2 K 2 O+Na 2 O L.O.I Dehdasht Yazd Bookan 56.11 44.41 48.54 10.3 15.4 5.43 12.7 23.07 27.21 4.22 1.25 3.32 0.37 1.11 0.34 1.35 4.57 2.32 0.54 0.36 0.19 14.59 9.51 11.98 Dehdasht Yazd Bookan Table 6. mineralogical constitution of the bauxite samples from different regions. Bauxite type (mine) Minerals Present Boehmite-Calcite-Hematite-Diaspore-Kaolinite Diaspore- Hematite-Anatase-Chlorite-Quartz Diaspore- Hematite-Chlorite-Feldspar 3.2. Preparation of High Alumina Cements In formulating the raw materials for the preparation of high alumina cements we made use of the above bauxites and limestone from Azarshar with 98% purity. The formulations were adjusted so that the CaO/Al 2 O 3 ratio remained close to unity. After mixing the raw materials were transferred to a refractory crucible and heated at 1500 o C for 3hrs in an electrical furnace. After cooling to room temperature, the specimen were subjected to x-ray diffraction (XRD) studies. The results showed the presence of large amounts of nonhydraulic C 2 AS phase in the samples prepared from Yazd & Bookan bauxites. In the sample prepared using dehdasht bauxite the three phases in the decreasing order were C 2 AS, CA and CA 2 as detected by XRD. In order to get a more desirable phase distribution in the clinker samples, it was decided to add 20wt% commercial Al 2 O 3 with 99% purity and a mesh size of below 230 to the dehdasht bauxite / Azarshar limestone mixture. In this new formulation the relative amounts of phases in the decreasing order were CA, C 2 AS and CA 2. After a milling process the properties of the calcined clinker was evaluated and compared to that of Fondu- Lafarge cement. The results of the comparison is shown in Table 7. Table 7. Properties of dehdasht and Fondu - Lafarge cement. Setting time (Vicat) Cement type Surface area(blain) (Cm 2 /gr) (Min.) Refractoriness PCE ( o C) initial final Dehdasht 3345 85 70 1450 Fondu-Lafarge 3383 100 90 1440 447
3.3. Discussion Based on the information provided in table V, the bauxite samples from yazd and Bookan mines contains large amounts of iron oxide. In addition the SiO 2 content in yazd bauxite is also on the high side. These and the mineralogical characteristics of these 2-types of bauxites makes the formation of other non-hydraulic amorphous phases next to C 2 AS highly probable. Therefore the bauxites from these mines are not recommended to be used in the fabrication of refractory cements. Our study shows that the bauxite sample from Dehdasht mine is the most suitable candidate for high alumina cement application. However, the high SiO 2 content in this sample makes the C 2 AS still the predominant phase in the clinker prepared using this bauxite. However, the addition of Al 2 O 3 to this bauxite led to the formation of more calcium aluminate phases in the microstructure. The properties of the alumina added Dehdasht cement were more comparable to that of Fondu Lafarage cement (Table 7). 3.4. Concluding Remarks The bauxite samples from bookan and Yazd areas are not the considered to be a suitable sourc of Al 2 O 3 in the fabrication of high alumina cement. Addition of Al 2 O 3 in the dehdasht bauxite makes it a good candidate in the high alumina cement application. REFERENCES 1. N. Nasr, E. Shennawi, D. Messiha High alumina refractories made of calcined bauxite and synthesis alumina mixture Interceram NR., 1981, PP.494-496. 2. Russel, A. Refractory bauxite, the changing face of supply Industrial Mineral, 1997, PP.39-43. 3. The Economics of bauxite & alumina Roskill Infurmation Services Ltd. 4. Sepulvda P., Studart, A. R, Panddfelli V. C., Characterization and properties of refractory bauxites Interceram Vol.48 No.6, 1999, PP.398-406 5. Green. C. R, White J., Solid solubility of TiO 2 in mulite in the system Al 2 O 3 TiO 2 SiO 2 Br. Ceram, Trans. Vol. 73, No. 3, 1979, PP73-75. 6. A. Sourie, F. P. Glasser Studies of the mineralogy of high alumina cement clinkers Br. Ceram. Trans. 90, 1991, PP 70-71. 448