Role of Mineralogy and Geochemistry in the Beneficiation of Jajarm
Total Page：16
File Type：pdf, Size：1020Kb
A.S. H. Alaug Mollai et al./ / Iranian Iranian Journal Journal of of Earth Earth Sciences Sciences 3 (2011)3 (2011) /153-167 / 134-152 153 Islamic Azad University Role of Mineralogy and Geochemistry in the Beneficiation of Mashhad Branch Jajarm Bauxite from North East Iran: Comparison with some other Bauxite Deposits of the World Habib Mollai * Department of Geology, Faculty of Sciences, Mashhad Branch, Islamic Azad University, Mashhad, Iran. Received 10 February 2011; accepted 12 August 2011 Abstract Two types of bauxite occur in the Jajarm Bauxite deposit, the first one is the hard bauxite and the other is the shaly bauxite or soft bauxite. The Al2O3 content ranges from 30% to 60% and SiO2 varies between 5% to 39%.The total tonnage is more than 22 million tons with a mean value of Al2O3 content between 47% to 48% , SiO2 around 10% and Fe2O3 ranges between 6.95 to 27% . The Jajarm bauxite deposit shows high concentration of active SiO2 and Fe2O3 in comparison with other bauxite deposits of the world. Efforts have been made in this research to delineate the characteristics of the Jajarm monohydrate bauxites, consisting of a diaspore and chamosite mixture, to improve their chemistry by different beneficiation techniques and optimize their processing, grinding and digestion conditions for alumina production The Jajarm bauxite shows politomorphic and micro- granular texture with several secondary textural elements. The size of diaspore grains (which is the main mineral component) are generally below 10 microns, with a homogeneous matrix. In addition, for the very hard bauxite we can not do any separation between the crystal grains and the matrix because of similar hardness for both with closely packed space filling and in consequence of the absence of well- defined grain boundaries. Based on the above studies, the Jajarm bauxite can be enriched neither by grain analysis nor by magnetic separation. In this research hard bauxite was crushed between 2 to 3 inches and then samples were washed with 5% HCl. The result of this laboratory studies shows that the silica modulus has improved from 1.05 to 2.56 which indicates an increase of 29% in the Al2O3 content. Jajarm laboratory s study shows that Jajarm bauxite deposit partially can be improved only by water treatment. Keywords: Mineralogy, Bauxite Deposit, Bauxite mineralogy, Beneficiation, Jajarm, Iran. 1. Introduction liberated from the ore. Metallurgical grade bauxite is beneficiated by mechanical screening and washing. In Bauxite ores in Iran have characteristics of most of the countries bauxite is subject to mineral diasporic type with high content of aluminum and iron dressing operations before being dispatched to the and low Al2O3 to SiO2 mass ratio. In diasporic bauxite consuming industries. The various processes used ore processing, silicates are easily over-ground and the (apart from crushing which forms the first stage in all fine silicate slimes are harmful to direct and reverse the flow sheets) are: 1- Screening, Scraping and flotation beneficiation of bauxite. The actual Washing 2- Magnetic separation and 3- Drying and beneficiation processes adopted are determined by the Calcination. Beneficiation by magnetic separation of nature and physical properties of ore and gangue iron is practiced on a limited scale, primarily on ore minerals, their mode of association with each other, the mined for abrasive and refractory industries. The method of exploiting the deposit and the end-use of the bauxite is usually dried and calcined before magnetic beneficiated product. In the small scale mining separation because the heating converts siderite operations selective mining is supplemented by hand- (FeCO3) to magnetite (Fe3O4), leaves pyrite (FeS2) as a sorting whereby ferruginous or siliceous impurities like magnetite residue and makes hematite (Fe2O3) and laterite, quartz, etc, are separated from bauxite on the other paramagnetic minerals strongly magnetic. basis of megascopic characteristics like color, texture Today's demand for aluminum in Iran is more than ,specific gravity etc. In large scale mechanized mining 140,000 tons per year. The capacity and actual the upgradation of ore by sampling, mineral dressing, production of aluminum in Iran by IRALCO is close to sorting, screening, and washing is not practicable, the 45,000 tons per year which requires an alumina feed of bauxite becomes inventible particularly when the ore about 90,000 tons per year, all of which is being body is mixed with deleterious constituents. The imported. At the present time the exact demand of mechanical beneficiation method for upgrading such bauxite for IRALCO is about 240,000 tons alumina bauxite can only be effective if the impurities are easily powder per year but the maximum feed is only about --------------------- 120,000 tons alumina powder which is exactly fifty *Corresponding author. percent of IRALCO requirement. The Jajarm alumina E-mail address (es): [email protected] plant has adopted the Bayer process to produce 154 A.S. AlaugH. Mollai et al./ / Iranian Iranian Journal Journal of of Earth Earth Sciences Sciences 3 3 (2011) (2011) /153-167 / 134-152 alumina from diasporic bauxite. The alumina produced Jajarm bauxite deposit, but there is no research has fully met the standards of metallurgical sandy reported on the beneficiation of Jajarm bauxite. alumina and each index has achieved or surpassed the planned capacity. The trial operation has been very 3. Regional and Geological setting of successful, saving 80 million US$ for Iran and creating Jajarm Bauxite Deposit thousands of jobs for the local population. This project has been acclaimed by the aluminum industry for From the tectonic point of view, Iran can be divided advanced Alumina technologies, thus laying a into two marginal active fold-belts located in the NE foundation for the expansion of aluminum market. (Kopeh Dagh) and in the SW (Zagros) resting on the We can compare Jajarm bauxite deposit with the Hercynian terrain and the Precambrian Arabian plate other bauxite deposits like those from China and [1] respectively (Fig.1). Between these marginal fold belts and Italy [2]. But in Iran we are faced with two are the Central Iran, Alborz, Zabol-Baluch and Makran problems, the first one is that the Jajarm deposit is a units [18]. In more detail, according to Stöcklin [16, very hard diasporic bauxite with a very fine texture and 17] and Nabavi [18] Iran can be divided into ten major the second point is that the SiO2 and Fe2O3 contents in litho-tectonic domains: Makran, Lut Block, Eastern this bauxite are very high. Therefore the improvement Iran, Kopet Dagh, Alborz Mountains, Central Iran of this bauxite is very important and the aim of this Block, Urumieh-Dokhtar zone, Sanandaj-Sirjan zone, research is to improve its chemistry by different Zagros fold belt, and Khuzestan plain. The boundaries beneficiation techniques and to optimize the of these units are usually marked by faults or in some processing, grinding and digestion conditions for cases by depressions (mainly tectonic). alumina production. The Jajarm Bauxite deposit is part of the eastern Alburz Range in the north of Iran The northern chain 2. Previous Investigations in the Region of the Alborz represents a branch of the Alpine- Himalayan Orogenic system and runs for 960 km The Alburz Range of mountains in general and the separating the Caspian Lowlands from the Central Iran Shemshak Formation in particular have been studied Plateau. The Alborz Mountains, form a gently sinuous by a number of Iranian and foreign geologists because E-W range across north of Iran. The Jajarm bauxite of their economic importance . Most of this work has deposit occurs in the Zoo mountain 600km north-east been listed by Harb in his PhD thesis, who studied the of Tehran, 400km west of Mashhad and 15km stratigraphy and tectonics of the area [3]. The Jajarm northeast of Jajarm town which is part of eastern bauxite was identified as a black layer by N. Valeh Alborz , which includes the main part of Iran and when he studied the aerial photograph of the area and Caucasia in the north and Arabian plate in the south. verified as bauxite in the field by Samimi Figure 2 shows the outline structural setting of the and Mallakpoor [4] who have analyzed hundred Jajarm area. The oldest formation in the area is the samples, which showed Al2O3 between 41.3 to 62.2 % Padha Formation (Devonian) and the youngest is the and SiO2 between 4 to 19.3 %. Balkay and Samimi [5] Lar Formation which belongs to the Late Jurassic [3]. summarized the status of bauxite exploration in Iran The bauxite deposit strikes E-W for about 16km. In and Jamshidpoor, [6] carried out research on the addition, the major tectonics have divided the Jajarm Alburz Range with special reference to the Shemshak mine into four deposits, from west to east which are Formation. The feasibility and techno-economical called Golbiny, Tagoei, Zoo, and Sangterash deposits studies were carried out by Alluterv-FKI [7]. Mollai et respectively. There are a number of minor north-south al. have published a paper on the geochemistry of faults that have displaced the ore body some times up Jajarm bauxite [8]. Davoodi et al. [9] presented a paper to two hundred meters. Two horizons of bauxite occur on the characterization of Alborz, Zagros and Central in the Zoo mountain, which are called A and B Iranian Plateau bauxites for the Tube Digestion horizons. The B horizon constitutes the Jajarm bauxite Process. Exploration and technology of Jajarm bauxite deposit. Prospecting and exploitation have been carried for alumina production were studied by Mollai [10]. out on this deposit, which has a late Triassic age (Fig. Jafarzadeh did his MSc thesis on mineralogy, 3). This deposit underlies the dolomitic rocks of the geochemistry and genesis of Jajarm Bauxite deposit Elika Formation and overlies the sequences of shale, [28].