Archive | 2021
Characterisation of Tailings from Itakpe Iron Ore Mine, Itakpe, Nigeria
Abstract
Knowledge of tailings characteristics is required for utilisation and management purposes in the mining and construction industry. Tailings from the mine waste dumps at Itakpe iron ore mine were collected and analysed in the laboratory to determine their chemical and physical characteristics and these include; permeability, porosity, specific gravity, particle size distribution, chemical composition and bioavailability factor of element. Geochemical speciation with quantitative X-ray powder diffraction was used to evaluate the chemical and mineral composition of Itakpe iron ore tailings. The aim is to offer base line data necessary to assess metal mobility and bioavailability. The distribution of heavy metals such as Cu, Ni, Cd, Cr, Zn and Fe was determined using multistep sequential extraction. The results obtained indicate that the permeability is 6.24 x 10-3 cm/sec; porosity is 35%; and specific gravity is 3.58. The tailings are well graded and is sand gravel. Nickel and Zinc was found to be considerably high in exchangeable and bound to carbonates fraction which are mobile region and is bound to Fe – Mn oxides which is slightly mobile region but the higher concentration of Ni found in residual fraction. The implication of this result is that Nickel and Zinc partially enter into the food chain. Chromium and Cadmium concentration result indicated that these metals can easily enter into the food chain because of their presence in the mobile region and their higher mobility percentage. Introduction The Itakpe iron ore mine came into existence as a result of the Federal Government of Nigeria desire for rapid industrialisation of the country through the iron and steel industry. The Itakpe iron ore deposit is the principal source for the iron and steel industry. As a result of the low grade of the Itakpe iron ore (36%), beneficiation is required. The beneficiated iron ore from Itakpe is expected to feed the Ajaokuta Steel Complex, Ajaokuta Kogi State and Delta Steel Company Aladja Delta State, Nigeria. Specifically the mine was created in 1979 as Associated Ores Mining Company Limited (AOMC) and went through name changes before becoming National Iron Ore Mining Project Limited (NIOMP) in 1992. The corporate objectives of NIOMP are as follows: (i) to produce and supply 100% of the iron ore requirements of the Ajaokuta Steel Company Limited (ASCL) amounting to 2.15 x 106 tons per year assaying 63% Fe (ii) to produce and supply 40% of the iron ore requirements of the Delta Steel Company, Aladja (Warri) (DSC), Nigeria amounting to 550,000 tons per year assaying 67 to 68% Fe as per initial design of Itakpe plant (iii) to export the concentrates to the international market after local needs have been satisfied (iv) to represent the interest of the Federal Government of Nigeria in foreign iron ore mining projects (v) to arrange and coordinate the exploitation of other locally available raw materials required by the major steel plants [1]. In the process of exploitation of the iron ore, wastes rocks are generated. Waste rocks at the Itakpe iron ore mine are associated rock mined during the exploitation of the deposit, while the tailings are waste generated during iron ore beneficiation [2]. Tailings are the products remaining after the extraction of metals by physical and chemical methods. At the Itakpe iron ore mine, the tailings are the bye-product of iron ore beneficiation. Tailings are mixtures of crushed rock and processing Sustainable Geoscience and Geotourism Submitted: 2020-08-06 ISSN: 2624-8220, Vol. 4, pp 1-8 Revised: 2021-04-13 doi:10.18052/www.scipress.com/SGG.4.1 Accepted: 2021-04-21 CC BY 4.0. Published by SciPress Ltd, Switzerland, 2021 Online: 2021-04-30 This paper is an open access paper published under the terms and conditions of the Creative Commons Attribution license (CC BY) (https://creativecommons.org/licenses/by/4.0) fluids from mills, washeries or concentrators that remain after the extraction of economic metals, minerals, mineral fuels or coal from the mine resource [3]. About 400,000 tons of tailings had been produced since the beneficiation of the ore started in 1993 at the Itakpe iron ore mine [4], while it can be estimated that about 632 million tonnes of iron ore tailings are generated yearly in Western Australia [5]. The tailings produced from the beneficiation of the ore were dumped in a waste pile lying there unutilised until recently when the petroleum industry in Nigeria started using it to coat pipelines to prevent corrosion. At the Itakpe iron ore mine, the ratio of waste to ore is 4:1. The ratio of tailings to concentrate is commonly very high, generally around 200:1 [6]. For instance, it has been reported that in Western Australia, on average, the production of 1 tonne of iron ore results in the generation of 2 tonnes of iron ore tailings [7]. In Brazil, it is estimated that for each tonne of beneficiated iron ore, 400 kg of tailings are produced, and based on the 2014 production, about 275.5 million tonnes of waste was disposed of in landfills and tailing dams in 2014 [8]. Also, the output of iron tailings was around 500 million tons in 2015 [9]. Itakpe tailings are stockpiled in an open space of land dump, which may post environmental pollution issue if erosion occur and the possibility of the disposed tailings causing acid mine drainage and leaching of heavy metals to harm people and environment. The total heavy metals in tailings samples is an effective method to identify environmental contamination but it is not enough to evaluate the impact of each element in probable pollution of the ecosystem [10]. However, speciation of metals in tailings and solid wastes is often studied to determine the impact of each metal on the environment whereby the target metals are fractionated into several fractions using extractant solutions of increasing strength [11; 12; 13; 14]. Mineralogical techniques such as electron microscopy and X-ray diffraction (XRD), among others instrumental methods, are repeatedly engaged to elaborate on the data acquired by chemical speciation [15]. The iron ore tailings of Itakpe have been produced over three decades, its characteristics as it relates to pollution attributes has not been linked together; the study therefore examined these linkages to determine the leaching potential of the tailings. Therefore, it is very important to evaluate metals mobility/bioavailability base on the combine use of physical, chemical speciation mineralogical methods to actually ascertain the distribution of the metals which is the focus of the research. Tailings Characterisation The characteristic of the tailings depends on the type of ore mined. Tailings vary considerably in their chemical and physical characteristics and these characteristics include: mineralogical and geochemical compositions; specific gravity of tailings particles; settling behaviour; permeability vs. density relationships; soil plasticity (i.e. Atterberg limits); consolidation behaviour; rheology/viscosity characteristics; strength characteristics; pore water chemistry; and leaching properties [16; 6]. Further disaggregation of characterisation of tailings indicates both the physical, mechanical and chemical properties. Common physical properties of tailings are; grain size, density, bulk density, specific gravity, porosity while some of the mechanical properties are shear strength and permeability. Some chemical properties of mine tailings include pH, chemical composition etc. The chemical composition of tailings depends on the mineralogy of the ore body, the nature of the processing fluids used to extract the economic metals, the efficiency of the extraction process and the degree of weathering during storage in the dammed impoundment [3]. The major components of Itakpe iron ore mine tailings are 71% of SiO2 and 2.62 % Al2O3 as shown in Table 1. The Fe (total) of 15% indicates that a sizeable amount of iron could still be further extracted as the beneficiation process improves. This shows that the ore recovery is not total. The tailings is 2 SGG Volume 4