Metallurgical Analysis of Ugunoda Clay Deposit, Nigeria for Use as a Refractory

Transcription

1 Metallurgical Analysis of Ugunoda Clay Deposit, Nigeria for Use as a Refractory AYE, A.E Department of Foundry Engineering Technology, Federal Polytechnic, Idah, Kogi State Nigeria aaron1963a@yahoo.com OYETUNJI, A Department of Metallurgical & Materials Engineering, Federal University of Technology, Akure, Ondo State Nigeria akinlabioyetunji@yahoo.com Abstract The mineralogical composition as well as the refractory properties of Ugunoda clay samples obtained from three different locations in Ofu Local Government Area of Kogi State, Nigeria was studied. The mineralogical analysis was performed using the atomic absorption spectrometer (AAS). To determine the refractory properties, physical property tests, vis-à-vis, bulk density, cold crushing strength, porosity, firing shrinkage, loss on ignition and refractoriness were done. Results showed that Ugunoda clay composed mainly of silica (61.60%) and alumina (17.44%). The physical/refractory characteristics examined confirmed that the clay belong to the fire clay class and is useful for refractory and ceramic applications. Keywords- Mineralogical analysis, clay, refractory, properties, applications INTRODUCTION Refractory materials are class of materials capable of withstanding high melting temperature (Fasuba, 2001). They are used in industries where various types of furnaces are employed to get their end products. About 80% of the total refractory materials are being consumed by the metallurgical industries for the construction and maintenance of furnaces, kilns, reactor vessels and boilers. The remaining 20% are being used in the nonmetallurgical industries such as cement, glass and hard ware (Ndaliman, 2007). is therefore, indispensable materials in high temperature processes (Mark, 2010). The most useful and most available refractory material is clay. Clays are fine grained rock which when suitably crushed and pulverized becomes plastic when wet, leather hard when dried and on firing is converted to a permanent rocklike mass (Bain, 1971). Clay is composed of silica (SiO 2 ), alumina (Al 2 O 3 ) and water (H 2 O) plus appreciable concentration of iron, alkali and alkaline earth, and contain groups of crystalline substances known as clay minerals such as quatz, felspar and mica (Sani et al, 2013). The refractories need of Nigeria, a developing nation, is potentially enormous. It was estimated that the Ajaokuta Steel Company and Delta Steel Company will, at full capacity, respectively require 43,503 and 25,000 tonnes per year of fireclay refractories for their activities; and these products are sourced from abroad (Adondua, 1988). Onyemaobi (2002) further observed that most of the refractories consumed in this country are sourced from abroad whereas there are many clay deposits in Nigeria that could be used as refractories (Oyetunji et al, 2009) and (Oyetunji and Opaluwa, 2009). The country expends a lot of foreign exchange importing refractoriness. A number of deposits, however, were found suitable for use as refractory raw materials if properly processed (Hassan, 2001). Therefore, the development of our local materials for the production of 25

2 refractories to meet our industrial and technological requirements is not only justified but imperative. This work focuses on the mineralogical analysis of Ugunoda clay in Ofu Local Government Area of Kogi State. The properties covered in the course of this work are compositional analysis, Loss on Ignition (LOI), bulk density, porosity, shrinkage after firing, cold crushing strength and refractoriness. MATERIALS AND METHODS The raw materials for the study were clay obtained from Ugunoda in Ofu Local Government Area of Kogi State. The clay samples were excavated from three different locations. The clays as mined in lump form were sun-dried and crushed to suitable sizes. The crushed samples were then thoroughly mixed to represent the actual composition of the clay deposit. They were the ground and sieved with mesh of three different aperture sizes. The sieved samples were then graded into coarse (75μm); medium (200μm) and fine (600μm). The three aggregates were mixed with water added for proper plasticity to make molding easier. Molding was done mechanically using the hydraulic press machine that produced rectangular bricks having the following dimension; 16 mm length, 50 mm breadth and 100 mm heigth. Mineralogical Analysis The mineralogical analysis of the clay sample was carried out using the Atomic Absorption Spectrometer (AAS) in accordance with Akinola et al 2013 and the result presented in Table 1. Loss on Ignition Porcelain crucible of known weight (W 1 ) was used for the test. 25gms of the dried samples was placed into the crucible (W 2 ) and heated gradually on the Bunsen burner and later transferred into the muffle furnace where it was heated to 1000 o c for 1 hour. It was removed, cooled in the desiccators and weighed (W 3 ). The % loss on ignition (Akinola et al 2013 was then determined as follows: The test specimens measuring about 16 mm length, 50 mm breadth and 100 mm heigth were fired at 110 o C for 2 hours and weighted (W a ). The specimens were then suspended in water for about 30 minutes; the weight (W b ) while suspended in water was noted. It was then removed from water and the weight (W c ) of the soaked samples in air noted. The bulk density was then determined by the expression This was determined by the immersion method. The samples were weighed in air (W 1 ) and carefully submerged in water for one hour until the samples were soaked and can no longer absorb water. The samples were removed and excess water on it was dried off with foam. The weight of the soaked samples were taken (W 3 ). Prior to this, the weight of the samples suspended in water was noted (W 2 ). Percentage porosity was calculated as follows: 26

3 Shrinkage after Firing The test samples were dried at 110 o C for 2 hours and the dimensions noted. The samples were then fired to 1000 o C and furnace cooled. The dimensions were again noted and recorded. The dimensional changes were used to calculate the linear shrinkage as shown below: Cold Crushing Strength The test pieces were air dried for 24 hours and even dried at temperature of 110 o C for 12 hours and then fired in a furnace at a temperature of about 1000 o C for 6 hours and then cooled to room temperature. The test pieces were taken to tensiometer where load was applied axially to the test pieces until crack was noticed. The load at which the specimen cracked was noted, which represents the load required for determining Cold Crushing Strength of the test specimen. Cold Crushing Strength (CCS) was then determined using equation (Sani, et.al, 2013): The refractoriness or softening point was determined using the pyrometric cone equivalent (P.C.E.) method. Test cones were prepared by mixing each clay sample with sufficient quantity of water to make the Clay become plastic and molded by hand into a cone shape. The samples were then dried and fired to a temperature of 900 o C in a muffle furnace. Pyrometric cones designed to deform at 1300 o C, 1400 o C, 1600 o C were placed round the samples and the temperature rose to above 1000 o C at 10 0 C per minute. The heating was discontinued when the test cone bent over and leveled with the base of the disc. (g/cm 3 ) Firing Shrinkage (%) The pyrometric cone equivalent (P.C.E.) of the samples was recorded to be the number of standard pyrometric cone corresponding to the time of softening of the test cone. RESULTS AND DISCUSSION Results The results obtained from the research work were averages of a minimum of three repetitions for most of the tests carried out on the sample. The results obtained are presented below: Table 1: Mineralogical Composition of Ugunoda Clay Sample Oxide Al2O3 SiO2 Fe2O3 CaO MgO Na2O K2O P2O5 % Composition Table 2: Properties of Clay Sample DISCUSSION Mineralogical Composition The results presented in Table 1 indicates that the clay has some traces of both sodium and potassium oxides. The presence of these oxides which are principal components of feldspar mineral serve as a very good flux to help bring down the fusion point of the clay, hence reducing the refractoriness of the clay (Nwajagu, 1994 and Mukoro, 2002). The alumina content of the clay sample agreed with what was reported by literature that in Nigeria, the major refractory clay deposits containing alumina silicate are kaolinitic and fire clay in nature with alumina content less than 45% (Aderibigbe, 1989). Cold Crushing Strength (Kg/cm 2 ) ND Loss on Ignition (%) ( o C) (PCE 28)

4 Refractory Properties The key physical properties of the clay which were investigated to determine its refractory properties are shown in Table 2. The clay has a bulk density of 2.03g/cm 3 which is within the range for fire clay (Chesti, 1986) and those reported for local clays in Nigeria (Chukwuogo, 1984). Bulk density is an important property consideration as far as transportation is concerned in selecting a material for use as refractory. The clay has a porosity of 22.55% which is within the acceptable range of 10 30% suggested for refractory clays (Chester, 1973). affects the permeability, heat conductivity, and strength and temperature fluctuation. It also depends on grain sizes and firing temperature (Chesti, 1986). Firing Shrinkage The clay sample has a firing shrinkage of 13.29%. Shrinkage after firing is an important property in the selection of refractory raw materials because the greater the shrinkage, the greater the difficulty in holding finishing tolerance. High shrinkage also enhances the danger of cracking in the firing kiln. Cold Crushing Strength The clay sample has a cold crushing strength of 173.2kg/cm 2. This shows that the clay offer moderate resistance to abrasion. However, cold crushing strength is affected by the firing temperature, amount of water, the manufacturing processes, the particle size and the extent to which the particles are bonded together. Cold crushing strength is a useful indicator of the ability of a refractory to withstand handling and impact at low temperatures. Loss on Ignition The Loss on Ignition value for this clay is 8.45%. The weight loss on ignition depends on the presence of carbonaceous matter. The carbonaceous matters are burnt off and water held between the particles got lost (Akinola et al, 2013). The softening point of the clay given in pyrometric cone equivalent (PCE) as well as the corresponding temperature is indicated in Table 2. Ugunoda showed a refractoriness of 1660 o C (PCE 28) which is an indication of good refractoriness because the normal range for fire clay refractoriness is 1500 o C 1700 o C (Abdullahi, 2007). CONCLUSION From the obtained results the clay can be used as refractory raw materials in the lining of furnaces for the melting of metals with moderate melting points. It is recommended that in using the clay for refractory applications, that refractoriness under load test, resistance to slag attack, thermal conductivity and electrical conductivity should be done. References Abdullahi, M.Y. and Sumaila, U. (2007). Characterizationof Some Nigeria Clays as Refractory Materials for Furnace Lining. Continental Journal of Engineering Sciences, Adamawa, Pp Aderibigbe, D.A. (1989). Local Sourcing of Raw Materials and Consumables for Iron and Steel Industries in Nigeria Challenges for the future. Raw Materials Research and Development Council of Nigeria (RMRDC) 28

5 Adondua, S. (1988). Indigenous Refractory Raw Material base for Nigeria Steel Industry. Journal of the Nigerian Society of Chemical Engineers (NSCHE)(7):2, Pp Akinola,A. O. Fapetu, O. P. and Oyetunji A. (2013). Investigation into the Properties of Akure Laterite for Furnace lining. Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) 4 (3): Pp Scholar link Research Institute Journals, jeteas.scholarlinkresearch.org. Bain, J.A. (1971). A Plasticity Chart as an Aid in Identification of assessment of Industrial Clay, P.19. Chester, J.H. (1973). Refractories, Production and Properties. The Iron and Steel Institute, London. Pp. 4-13, Chesti, A.R. (1986). Refractories, Manufacture, Properties and Applications, (1 st ed.)new-delhi: Prentice-Hall of India Private limited. Pp. Pp Chukwuogo, C.E.B. (1984). Physico- Chemical propertyof some Nigeria Clays. Research and quality Control, Delta Steel Company Ltd. (DSCL), Ovwian-Aladja. Fasuba, O.A., Egunlae, O., and Jimoh, B. (2001). Metallurgical analysis of Orin-Ekiti alumina clay deposit for use as a refractory. Journal of Engineering Technology and Industrial Application. Vol. I, No.4, Pp Hassan, S.B. (2001). Effects of silicon carbide on some refractory properties of kankara clay. Proceeding of the Nigerian Metallurgical Society, 18 th Annual Conference, Pp Mark, U. (2010). Characterization of Ibere and Oboro Clay deposits in Abia State, Nigeria for refractory applications. International Journal of Natural and applied Sciences,Pp Mukoro, E.E. (2002). Local production of pyrometric (Seger) cones for control of kilntemperature. Proceeding of Nigeria Metallurgical Society (NMS), 19 th Annual Conference, Pp Ndaliman, M.B. (2007). Refractory properties of termitehills under varied proportions of additives, A.U. J.T 10 (3). Pp Nwajagu, C.O. (1994). Foundry Theory and Practice, Enugu: ABC Publishers Ltd., Pp Onyemaobi, O.O. (2002). Mineral Resource Exploitation, Processing and Utilization A sine Qua Non for Nigeria s Metallurgical Industrial Development, Inaugural Lecture Series 5 of FUTO. Opaluwa A. I. and Oyetunji A. (2012). Evaluating the Baked Compressive Strength of Produced Sand Cores Using Cassava Starch as Binder for the Casting of Aluminium Alloy T- Joint Pipe. Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) 3 (1): Pp Scholar link Research Institute Journals, 2012 (ISSN: ) jeteas.scholarlinkresearch.org. Oyetunji A; Bankole, L.K. and Alhassan, A.O. (2009). Binding Characteristics of Mbushi and Ewekoro Clays of Nigeria in Foundry Moulding Sand. Global Journal of Engineering and Technology.( Volume 2, No. 4, December 2009), Pp Indian. Oyetunji A. and Opaluwa I. (2012). Study the Compressive Strength of Produced Sand Cores Using Clay and Starch as Binder for the Casting of Aluminium Alloy T-Joint pipe. The International Research Journal of Engineering and Technologies. Vol. 4 Issue 3. Pp Science Record Journals Sani, A., Bashir, G., Danshehu, B.G. and Isah, A.D. (2013). Studies on the Chemical and Physical characteristics of selected clay samples. International Journal of Engineering Research and Technology (IJERT), Vol.2 Issue 7. Pp