Kenyan Iron Ore: Mining and prospects of processing

Kenyan Iron Ore: Mining and prospects of processing Prof. S M. Maranga* and Alvin Kiprono Bett* and Kyalo Ndeto* and Gilbert Bett** *Jomo Kenyatta University of Agriculture and Technology (Department of Mechanical Engineering) **Wanjala Mines Abstract Industrialization is one of the economic pillars in the Kenya Vision 2030 thus iron and steel will be prominent in the industrialization process. Kenya relies heavily on the importation of manufactured goods with iron and steel products forming the bulk of the raw materials. The country has some iron ore deposits and coal reserves among other input for steel making. The main deposits of the ore are found in Kishushe, Marimanti and Samia. The paper focuses on the iron ore from Kishushe location in the Coast region. The iron is mined and exported in semiprocessed state. The chemical composition of the ore has been analyzed. There are interests to produce steel from the local ore. The challenges are on the estimation of the deposits, the quality, beneficiation methods and the selection of the extraction technologies. Keywords - iron ore, magnetic separation, coal 1. Introduction Iron, Fe, is a common element accounting for around 5-6 % of the earth’s crust and the most used metal in many sectors in processed steel. The sources of iron are iron-rich minerals termed iron ores. Naturally iron is bonded with oxygen, water, sulphur or carbonate in a variety of minerals but the chief ores of iron are magnetite Fe 3 O 4 , containing 72.4 % Fe, black; hematite, Fe 2 O 3 containing 70 % Fe, red; limonite, 2Fe 2 O 3 ·3H 2 O, containing 59.9% Fe, brown; and the carbonate siderite, FeCO 3 , containing 48.3 % Fe, brown [1,2]. Also sulphides, pyrite, FeS 2 , and pyrrhotite, Fe x S (x=0-0.17) are ore sources. Iron ore deposits are formed by three geological processes [3]: direct sedimentation forming bedded sedimentary deposits resulting into two types of iron formation; banded ironformations and ironstones. Iron ore deposits of igneous origin formed because of magmatic segregation of iron-bearing minerals occurring as veins and tabular replacement bodies of magnetite and hematite. Iron-ore deposits formed by surface or near surface enrichment as less resistant minerals were removed. Chemical and physical weathering by soil forming processes of pre-existing iron-bearing minerals resulted in progressive concentration of iron oxides to form iron-rich deposits. Prof. S M Maranga Email: [email protected] Alvin K. Bett Email: [email protected]/ [email protected] Mathew Kyalo Ndeto Email: [email protected] Gilbert K. Bett Email: [email protected] 1.1. Mining Industry in Kenya Mining in Kenya is primarily for production of non-metallic minerals encompassing industrial minerals such as soda ash (trona), fluorspar, diatomite, natural CO 2 , kaolin, gemstone and limestone. Mining accounts for less than 1% of Kenya’s annual GDP [4]. Iron ores are mined from small-localized deposits that have not been fully developed/ explored and are largely sold to cement industries where they are used as additives in the manufacture of cement. Following global oil price increases, Kenya has been faced with an energy crisis, which has led to an increase in exploration activities for oil and gas reserves in the coastal and semi-arid parts of Kenya [7]. Metallic minerals are produced in some quantities for example gold, which is usually mined by residents in the western part of the country. Fig. 1 shows the mineral occurrence in Kenya. Coal reserves have been identified in Mui basin and feasibility study has been done [8]. 1.2. Iron Ore in Kenya In certain parts of Kenya and the neighboring countries, the smelting of iron ores by the use of charcoal was carried out in rural areas for the production of sponge iron. The product was used to make primitive implements and weapons but the craft practicaly died out as the result of increased trade with the industrialized countries, which were able to supply tools and other necessities at comparatively low prices [5]. Iron ore deposits in the country have not been fully explored. Iron minerals are of widespread occurrence in western Kenya, chiefly Nyanza namely as at Macalder mine which has banded ironstones as shown in Fig. 2, where they are frequently associated with the rocks of the goldfields formations [7]. Iron ore reserves exist in several locations and they include Meru, Ikutha, Taita, Embu, Lolgorien, Samburu and Funyula districts. Thus, the country has the primary raw material for setting up a steel plant. Iron ore exported monthly is 7,500 metric tons from Kishushe mines in Taita area [8]. 1.3. Steel Industry in Kenya In Kenya the direct and indirect consumptions of steel was projected to be 0.567 – 0.614 million tons in the year 1985 and 1.860 – 2.356 million tons in the year 2000 – 2015 (currently). Based on these projections the per capita iron and steel consumption was expected to increase from 20 -25 kgs in 1985 to 45 – 50 kg currently which is very low compared to the global per capita consumption of 300 kgs of steel. The iron and steel industry is owned by private sector and they are mostly involved in the rolling of steel products. The industry depends heavily on imported raw billets and from local scrap metal. Foundry a major sector in metal industry relies heavily on the local scrap. Currently, production of steel products in the country is estimated to be 600, 000 tons from steel rolling firms [6]. The source of energy for steel plants is electricity and coke. 1.4. Coal deposits Ministry of energy has drilled some blocks of coal reserves in Mui basin (Yoonye - Kateiko) to ascertain the availability of deposits. Laboratory results indicated that the coal ranks from peat trough lignite and sub-bituminious to bituminious grade with lignite and subbituminious most abundant. Summary of the analysis is as shown in Table 3 [8]. If exploited, other than the production of coke for the extraction of iron other potential uses of the mineral include; electric power generation, firing of kilns in manufacturing industries and boilers. Clean coal technology is the key to success in the use of coal. 1.5. Prospects of processing Iron ore From the three major sites identified (Kishushe, Marimanti and Samia) in Kenya to have substantial deposits of iron ore, besides the quality of the ores, the next step is to estimate the amounts. The selection of the methods for extraction of the metal follows. Studies on alternative beneficiation methods have been initiated to facilitate in the selection of the extraction technologies including a blast furnace. 2. Magnetic Separation of Iron Ore Iron ores should be of a good grade (above 65% Fe) to be used in blast furnaces. Low-grade ores are usually beneficiated/upgraded. Beneficiation technique for iron ore is important in order to achieve a maximized utilization of ore resources and to produce standard products [11]. Magnetic separation is used to separate natural magnetic iron ore (magnetite) from a variety of less-magnetic or non-magnetic materials. It may be conducted in dry or wet environment, with wet systems being commonly used. Magnetic separation operations can also be categorized as either low or high intensity where low intensity separators use magnetic fields between 1,000 and 3,000 gauss and normally used on highly magnetic material, such as magnetite. In high intensity separators fields as strong as 20,000 gauss are applied in separation of weak magnetic iron minerals, like hematite, from non-magnetic or less magnetic gangue material [3]. In separation process, particles are subjected to forces including gravity, drag and magnetic forces [9]. Materials are classified into two categories; diamagnetics that are repelled along the lines of magnetic force to a point where the field intensity is smaller thus diamagnetic substances cannot be concentrated magnetically because the forces involved are very small. Paramagnetics on the other hand are attracted along the lines of magnetic force to points of greater field intensity and can be concentrated in high intensity magnetic separators. Examples of paramagnets include titanium minerals namely ilmenite (FeTiO 3 ) and rutile (TiO 2 ), wolframite ((FeMn)WO 4 ), monazite (rare earth phosphate), siderite (FeCO 3 ), pyrrhotite (FeS), chromite (FeCr 2 0 4 ), hematite (Fe 2 0 3 ), and manganese materials [7]. For the Kishushe ore, the separation yielded values ranging from 84 – 98% iron ore. 3. Kishushe Iron Ore Deposits Taita-Taveta County has iron ore deposits in Kishushe, Mwandongo, Shelemba, Mwambirwa, Kasighau, Kamtonga, Daku and Oza locations (Fig 3) [9]. The site of study is Kishushe where the ore is mined by Sanghani groups/ Wanjala Mining Co Ltd. The county lies in the Mozambique belt, which is gelogically rich in metallic and gemstone minerals as shown in the Fig. 4 [8]. Iron ore exists in banded iron formation, reef and alluvial deposits. Mining methods applied are open pit mining for the reef deposits and mobile screening for the BIF and alluvial deposits. Both methods involve the clearing of vegetation such as trees, shrubs, grass, et al using a bulldozer, then removing topsoil and/ or loose rock if any unless it is gangue with substantial amount of iron pebbles which can be mined. Mobile screening would be the method to harvest rock pebbles that form a belt of 0.5-2m varying from point to point according to their depositation. However, the depth at which they occur also increases to the main vein/reef northwards as it dips also in the same direction and altitude. Reef mining proceeds sharply down with excavation of country rock to expose the vein of iron ore. Open pit mining is the cheapest method to mine and handle minerals at or near the earth surface so is the method that results in economical mining of iron ore in Kishushe. Iron ore vein dips at 60º in N-S direction and strikes at different levels due to geological formation of the ore due to the thrust force that allowed the hydrothermal fluid solidify on the fault planes. Heavy machinery such as hydraulic excavators especially Hyundai 450LC are used for development and exploitation of the ore. Other machinery include Powerplus bulldozer, Isuzu tipper truck etc. Rock sizes of approximately 152.4 - 203.4 mm are fed into jaw crusher. Jaw crusher reduces the ore sizes to <100mm and fed onto a vibrating screen. Ores sizes10-60 mm are conveyed directly to the magnetic separators; above 60 mm ores are fed into a cone crusher while less than 10 mm are magnetically separated using magnetic drums to collect iron fines. Magnetic minerals are stock piled in readiness for transportation to the port of Mombasa. The nonmagnetic rocks (mainly quartz) are stock piled on a separate area and further crushed into fines and beneficiated magnetically. The non-magnetic fines are used to refill the excavated areas. Iron fines are sold to the cement manufacturing industries within Kenya. (Fig 5-10 are samples of photographs taken at the site in Wanjala). The production of iron ore is estimated to be 100,000 tons per year on an average of three months a year due to enviromental challenges (rains). Iron ore exports from Kishushe for the year 2011 and 2010 are as shown in Table 4. Mining engineers and geologists in the mine carry out explorations in the surroundings and upon identification the samples are sent to the lab for analysis on the quality. The iron ores from Kishushe are mainly of two types: hematite and magnetite. Chemical analysis that has been carried out on these deposits are as shown in Tables 1 and 2 [10]. It is clear that the ores and are of good quality. The estimate of the quantity of the ore in the site was not available. 4. Conclusion There is interest in the country to exploit the iron ore deposits to make steel. However there is need to estimate the amount of deposits to ascertain that it can sustain steel making plant and selection of appropriate technology. The beneficiation methods of the local ores must be known as a part of anticipated processing of the ore to make steel. In the case of Kishushe the company, (Wanjala Mining Co. Ltd) has actually been mining and semi-processing the iron ore before exportation. The chemical composition of the ore has been determined. The company is interested in processing the ore to make steel. Beneficiation and selection of the most appropriate extraction technology is still a challenge that needs to be addressed. The beneficiation studies on going are geared towards the facilitation of Wanjala Mines to make informed decisions on extraction technology. Coal has been found in ample deposits and can be exploited to facilitate the iron ore processing industry. References 1. R. Khurmi and J. Gupta, Machine Design. Eurasia Publishing House, 2005. 2. G. Gustafsson, Simulation of iron ore pellets and powder flow using smoothed particle method. 2008: 12 ISSN: 1402-1757 ISRN: LTU-LIC–08/12–SE. 3. Environmental Protection Agency(EPA), “Extraction and Beneficiation of Ores and Minerals, Technical Resource Document, Iron,” vol. 3, 1994. 4. Website: www.ipckenya.org 5. C. G. B. Bois and J. Walsh, “Geological survey of Kenya minerals of Kenya,” Bulletin 1, 1952. 6. Draft Strategy Paper on Development of Iron and Steel Industry in Kenya by Ministry of Industrialization, April 2012. 7. P. M. W, “Iron ore in Kenya Colony,” Mines and Geological Department, 19th International Geological Congress, 1952. 8. Report on the Mining; Iron and Steel stakeholders forum held at utalii Hotel on 7th October, 2011. Promoting the Development of the Iron and Steel Industry in Kenya. Ministry of Industrialization. 9. “Wet low intensity magnetic separators (Technical specification),” www.metso.com. 10. B. A. Wills and T. Napier-Munn, Mineral Processing Technology, An Introduction to the Practical Aspects of Ore Treatment and Mineral. Elsevier Science and Technology Books, 7 ed., 2006. 11. Andreas Horn , Beneficiation of Iron Ore Challenges and Solutions. Allmineral, www.allmineral.com/de/download/.../Newsletter_ironore_0709.pdf 12. M. Mghanga, Mining in Taita Taveta County: Prospects Problems. Heinrich Boll Foundation, 2011. 13. D. B. Dow, W.J. Wairegi, Dr. W. L. Werneck, Dr. A. Horkel, Kenya-Austria Mineral Exploration Project, Report No. 6, vol 86, “The Wanjala Magnetite Project’’, Syposium, Appendix Table 1: Chemical analysis of samples from Wanjala (Ataca & Co.) Fe SiO 2 AlO 3 TiO 2 P S As Sn 61.19 10.84 .031 .02 .009 .008 nil .004 63.79 18.12 .082 .07 .005 .011 nil .022 in % Table 2: Chemical analysis of samples from Wanjala (Mines and Geology Department) Fe 2 O 3 P 2 O5 TiO 2 S 65.89 3.91 .02 Nil 82.26 Nil .08 Nil 84.66 Nil .08 Nil Table 3: Summary of coal analysis Lowest Highest Average Calorific values 12.6MJ/Kg 29.3 MJ/Kg 18 MJ/Kg Ash content 7% 42 % 30 % Volatiles - - 30 % Sulphur 0.5 % 4% 2.4 % Table 4: Kishushe iron ore exports Year Quantity (MT) Value (Kshs) Destination 2011 67,200 341,754,000.00 China 2010 23,318 37,593,800.00 China Figure 1. Map showing mineral occurance in Kenya (Source: Mines and Geology) Figure 2: Iron ore occurrence in Kenya Figure 3: Kishushe off Mombasa-Nairobi road 60Km (Google Maps) Figure 4: E. African Map Showing Mozambique Belt Figure 6: Magnetite ore. Figure 5: Stock piled ores Figure 7: Alluvial iron ore pebbles. Figure 8: Development and exploitation of reef iron ore. Figure 9: Site screening. Figure 10: Crusher plant.