Thesis Abstract

<p> This research investigated the sintering characteristics of sinter blends produced from<br>Agbaja iron ore concentrate of high phosphorus (P2O5 = 1.50 – 2.14%) and low silica<br>content and Itakpe iron ore concentrate of low phosphorus (P = 0.03%) and high silica in<br>order to produce fluxed sinters suitable for pig iron production. The ores (Agbaja and<br>Itakpe) were concentrated using conventional beneficiation techniques and then blended<br>in the ratios of 10-70% Agbaja and 90-30% Itakpe. The blends were mixed with coke<br>breeze, limestone and moisture to produce fluxed sinters. The physical and chemical<br>characteristics of the produced sinters vis-a-visa abrasion resistance, shatter index,<br>tumbler index, reducibility, reduction decrepitating and chemical composition were<br>determined. The results obtained revealed that both the physical and chemical properties<br>of the produced sinters compared favourably with existing blast furnace specifications for<br>sinters. However, the sinter with 10% Agbaja and 90% Itakpe possessed physical and<br>chemical properties that are close to the specified properties of sinter for use in the blast<br>furnace for Pig iron production. Therefore, sinter blend with 10% Agbaja and 90%<br>Itakpe iron concentrates can be recommended for use in blast furnace for the production<br>of pig iron. <br></p>

Thesis Overview

<p> 1.0 INTRODUCTION<br>In order to ensure the survival of any industry, raw materials input must be critical and<br>continuously be in supply both in large quantity and in good quality. Even though Nigeria<br>is blessed with large quantity of iron ore deposit of about three billions (3 x 109) metric<br>tonnes, these deposit cannot be used directly in pig iron production without beneficiation<br>because some of them are of low grade and contain impurities, which can be detrimental<br>to the properties of the steels to be produced. Some researches have already been carried<br>out on the beneficiation of some of these ores for use for pig iron production by, Adigwe<br>(1973), and Oloche et al., (1996).<br>Eventhough Nigeria is blessed with large reserves of proven and unproven iron ore<br>deposits, only one of the deposits in the proven reserves is currently being exploited and<br>processed that is the Itakpe iron ore deposit. This deposit has an estimated reserve of<br>about 200 millions (200 x 106) metric tonnes and has been earmarked to be supplied to<br>Ajaokuta and Delta steel plants. However, this deposit, based on the designed<br>requirement of the Ajaokuta plant, will only last for 25 years (Adigwe, 1983). This is<br>grossly inadequate for the establishment of a formidable foundation for a well- projected<br>and integrated iron and steel plants. Also the Agbaja iron ore deposit, eventhough the<br>largest iron ore deposit in Nigeria estimated at over 2 billions (2 x 109) metric tonnes, has<br>a very high phosphorous content in addition to its extremely fine grained texture. This<br>feature has discouraged its utilization to date (BRGM Report, 1983). With these apparent<br>problems it has become very necessary to find ways of using this vast deposit of iron ore.<br>2<br>The most probable way to utilize the large quantity of iron ore is by blending with other<br>iron ores with lower phosphorous content. Therefore, the objective of this work is to<br>blend Itakpe super concentrate of low phosphorous with the Agbaja concentrate of high<br>phosphorus so as to produce a sinter mix that can serve as feed to blast furnace for pig<br>iron production.<br>Kurt (1980) said that both sinters and pellets are used as feed with iron but sinters are the<br>common and suitable sources of feeds to the blast furnace. The process of sintering<br>comprises high temperature-treatment (above 10000C) of iron fines on a moving grate,<br>blended with fluxes and coke breeze (finely divided coke) to form hard lumps or iron-rich<br>material suitable for use as blast furnace feed (Williams, 1983). In iron ore sintering, the<br>aim is always to produce a strong but porous agglomerate from a sandy uncompacted<br>mass. Tupkary et al., (1998) also noted that in order to obtain smooth and hard “rapid<br>driving operation”, the burden charged in the furnace should ideally posses the following<br>physical and chemical properties.<br>Physical properties<br>1. A close size range with minimum of fines.<br>2. An ability to withstand the physical stresses incurred on being transported to<br>the furnace, charged to the hopper and the bells and, finally in the furnace.<br>3. Non –decrepitating nature.<br>4. An ability to withstand mild reducing condition at lower temperature without<br>breaking.<br>3<br>5. A good bulk reducibility so as to obtain closed equilibrium conditions<br>between solid and gas phases in the stack.<br>6. Low swelling tendency during reduction.<br>7. A high softening temperature with a narrow temperature range of fusion.<br>Chemical properties<br>1. A high percentage of iron to gangue ratio.<br>2. A low percentage of silica, alumina and a low alumina to silica ratio.<br>3. Good overall chemistry of the burden to ensure adequate desulphurization of<br>metal and absorption of coke ash in slag.<br>4. Good overall chemistry to ensure clean slag and metal separation at minimum<br>temperature and free flow of both slag and metal.<br>In addition, sintering is also carried out to improve size grading and reducibility of iron<br>ore concentrate to avoid wasting of fines, reduction of the quantity of coke used in the<br>blast furnace and lastly to use up waste materials from blast furnace flue dust.<br>The quantity of sinter produced by the integrated blast furnace route has risen from<br>371.2mt in1982 to 422.7mt in 1994, accounting for 55.0% to 57.9% of total crude steel<br>production. Therefore more than 50% of the total liquid iron production during this<br>period was supplied via the blast furnace for which sinters remain the major iron feed<br>stock. However, Pellets are gradually replacing sinters to a certain degree, depending on<br>available local process, economic and environmental circumstances with the global<br>4<br>output of the two products in 1994 standing at 534.3mt and 224.7mt for sinter and pellet<br>respectively (Madugu, 2001).<br>Iron ore sintering is a complex thermo-chemical process and the qualities of sinters being<br>produced affect the blast furnace performances in terms of fuel consumption, smooth<br>operation, and rate of production. (Nath et al., 2004). Presently, the proportion of sinters<br>in the charge of most blast furnaces amounts to 90% of the total weight of charge.<br>Recently, the use of sinters is gradually increasing as mines produce more dusty,<br>complex and lean ores, which need to be ground to a very fine particle before<br>beneficiation. The world trend for use of sinters in pig iron production via the<br>conventional blast furnace (acid and basic) is given in Appendix 1.0. Ogg et al., (1977)<br>observes that the production and use of sinter for pig iron and hot metal manufacture<br>continues to grow in 90% of the world’s steelmaking areas. This expansion is often faster<br>than the growth of iron production, showing that the use of sinter in the blast furnace will<br>continue to increase since the iron content of the ores to be sinter is generally rising and<br>thereby lower the slag volume in the blast furnace.<br>1.1 Statement of problem<br>Agbaja ore deposit has an estimated reserve of about 2 billions (2 x 109) metric tonnes,<br>containing high phosphorus (P2O5 = 1.5-2.14%) and low silica, because of this, the<br>deposit is not suitable for pig iron production. Phosphorus exists in iron ores as<br>phosphorus pentoxide (P2O5) and this cannot be reduced during beneficiation technique<br>and agglomeration. Kudrin (1989) observes that the effects of the phosphorus on the<br>machined iron properties and steel are enormous. In order to use Agbaja iron ore, it is<br>5<br>imperative to blend the ore with Itakpe iron ore with a reserve of about 200-300 million<br>metric tonnes having low phosphorus (0.03%) and high silica to take care of the high<br>phosphorus in Agbaja iron ore and also to provide large source of iron ore for sinter<br>production.<br>1.2 Aims and Objectives of the Study<br>The main aim is to determine the optimum-blending ratio, the ratio at which the two ores,<br>when blended will produce sinters with physical and chemical properties that are suitable<br>for pig iron production via the blast furnace process. The results obtained will also be<br>compared with the minimum standard specifications required of sinters for pig iron<br>production via the blast furnace route.<br>1.3 Justification and Significance of the study<br>The Agbaja iron ore deposit exists in large quantity and it is very close to Ajaokuta.<br>Because of high phosphorus associated with it, there is the need to intensify effort in<br>order to find the means of utilizing the ore economically. One of such means/alternatives<br>is by blending which is the main focus of this research work.<br>If this research is successful, it will find a solution to the use of Agbaja through blending<br>with Itakpe iron ore for the production of sinters for Ajaokuta Steel Company. This will<br>augment the source of raw material input for pig iron production at Ajaokuta Steel<br>Company. Also the sinter to be produced could be exported as this will attract foreign<br>exchange earning.<br>6<br>1.4 Limitations of the research<br>As a result of non-availability of some equipment, certain tests, like swelling index, hot<br>compression strength and low temperature characteristics may not be carried out. <br></p>