Title of Invention

"A PROCESS FOR THE PRODUCTION OF REFRACTORY GRADE BAUXITE FROM FERRUGINEOUS BAUXITE"

Abstract

A process for the production of refractory grade bauxite from ferrugineous bauxite which comprises calcining -10 mm ferrugineous bauxite with solid reductant such as herein described, at a temperature in the range 800-900 °C for a period of 30-60 min, crushing the calcined bauxite to below 3 mm size by known methods and subjecting to conventional low intensity magnetic separator to get refractory grade bauxite.

Full Text

This invention relates to a process for the production of refractory grade bauxite from fermgineous bauxite Iron and calcium are.objectionable impurities in bauxite for refractory, ceramic and abrasive applications. It is generally recognized that 2-2.5% Fe2O3 and 0.5 CaO are the upper permissible limits of iron and calcium in the bauxite. In India, the reserves of high grade bauxite suitable for refractory, ceramic and abrasive applications arc estimated to be 40 million tonnes which is equivalent to 1.5% of the total Indian bauxite reserves. These reserves are limited to west coast region of India. The refractory grade baaxite requirement in 1990 is around 14 thousand tonnes. In addition to this, the overall growth of consumption of refractory grade baaxite is estimated around 6% up to 2000 AD. On this basis, the available good grade baaxite, which is being so rapidly mined would sustain for 10-15 years only. Presently the domestic reserves of baaxite with sufficiently high alumina content, but too high iron content (more than 2.5% Iron) is bypassed in mining and stockpiled. The rapid depletion of high grade baaxite due to increasing consumption in refractory, ceramic and abrasive industry, necessitates utilization of lean and off-grade baaxites containing high iron (4% and above) and calcium (19o and above) as undesirable impurities. The present invention relates to process development for reduction of iron and calcium from lean and off grade baaxite by magnetize roasting followed by magnetic separation methods. The product so obtained by this process is suitable for refractory, ceramic and abrasive industries. Most attempts to remove iron from baaxite have resulted in marginal success, presumably because, the iron content present in the crude ore are too weekly magnetic and or too finely divided and poorly liberated to respond to magnetic separation used alone are in concert with other physical bcncficiation processing. The investigation results of researchers reveal the facts that by using Eritz high intensity magnetic separator, the products obtained contain 2.5% FejQj from feed samples of Alabama bauxite containing 2.7% and 8% F^Q* on a calcined basis. However, the recoveries arc limited to 17% onry. (Browning, J.S., MRI, Tcchn. Rep. Ser. T.R. No.5, 1978, p. 21). lanicelli reported the use of a small commercial high intensity wet magnetic separator to beneficiate Arkansas bauxite containing 10.7% F^Qj. The product contain 2.9% FezQ, on a calcined basis. (lanicelli, J, Mining. Eng. NY, Oct., 1953, pp 1470-71). Application of hydrocyclone and wet high intensity magnetic separation on beneficiation of gibbsitic sands and saprolites for potential use as refractory raw material, produce a product containing 4-5%Fe2Q, (White, J.C., Lnd. Eng. Chem. Res., 26(1), 1987, pp 7-11). Using SALA High Gradient Magnetic Separator (HGMS) on a Venezula ferrugineous bauxite containing 39% FezQ,, it is reported that 13% enrichment in the quality of baaxitc in the non-magnetic fraction with a recovery of 60% (Bolsaitis, P., et al., Int. J. Mineral. Process, 8, 1981, pp 249-263) could be achieved. The patent literature contain a number of references to treat various ores to increase the magnetic susceptibilities of iron minerals they contained. Hartiy describe a process in which pulverized hematite iron ore was roasted in a reducing atmosphere to produce a magnetic oxide (Hartley, H.J.C., US Pat. No.3,273,993, 1966). The available literature on application of magnetize roasting on bauxite is limited. The latest work by Sadler and Venkataraman reported on Alabama bauxite contain 2.7% FeiQj involves tine grinding and calcination with reducing gas (Hydrogen) followed by magnetic separation. The product so obtained contain 1.6% (Sadler, L.Y. and Venkataram, C., Int. J. \finer. Process, 31, 1991, pp 233-246). Literature pertaining on Indian bauxite for use in refractory, ceramic and abrasive industry is scanty. Bhima Rao et al., reported that a calcined non-magnetic product (-0.5 + 0.06 mm size) contain 2% FezQiwith 28% recovery from a crude sample containing 14% Fe2Qj (Bhima Rao, R., et al IM & FJ, March 1991, pp 17-19). The earlier reported ^literature on bene&ciatton ot Dauxitc.for use in retractory, ceramic and abrasive industries involve certain disadvantages. Use of HGMS and high intensity magnetic separators need very fine grinding which is high energy intensive step. The products obtained by this process is limited to low recoveries. Similarly, calcination by hydrogen gas for removal of iron also needs fine grinding. Further, the reductant applied for this purpose is not readily available. The main objective of the present invention is to develop a process for reduction of iron from lean and off grade bauxites using magnetizing roasting with solid reductanl/calcination followed by low/high intensity magnetic separation. The main aim of the invention is to remove iron content at coarser size bauxite samples so that the product obtained by dry magnetic separation can directly be used for refractory industry after further treatment of the product by acid wash or flotation. This product can also be used as a raw material in ceramic and abrasive industries. India is endowed with high alumina bauxite, but due to high iron and calcium appreciable quantity of bauxite reserves in the west coast region of Gujarat is being bypassed at mine site and stockpiled. Such raw material can directly be utilised by this new invention process. The advantages involvtd in this process arc (I) use of carbonacious material like coal, coke breeze as reductant, (ii) selective conversion of iron oxides present in the bauxite to magnetite, which render to increase the magnetic susceptibility, (iii) comminution of calcined product obtained by reduction roasting/simple calcination of bauxite requires less energy consumption due to liberation of iron at coarser size particles, (rv) removal of iron from the calcine using low intensity magnetic separator (drum/belt separators) improves the magnetic separation and reduces the power consumption and (v) this invention is totally a dry process. The main finding in this process is selective conversion of iron oxides present in the bauxite to a magnetite phase and also enhance^ the selective liberation of iron at coarser size particles. Due to increase of magnetic susccptabiliry of the product, low intensity magnetic separator can be used to remove iron. This process can make use of the stockpiled high iron (more than 4.0% FE2O3) containing bauxite as a raw material for refractory, ceramic and abrasive industries. On development of this technology, a processing plant can be put up at the west coast region of India. The process involves conversion of oxide phase of iron into magnetite by reduction roasting of the ore with solid reductant like charcoal/coke breeze/coal followed by comminution if necessary and magnetic separation of the calcine by applying low intensity magnetic separation or simple calcination of bauxite followed by comminution and high intensity magnetic separation. The summary of the main processing steps involved in the present invention arc (i) reduction roasting of -10 mm particle size bauxite in a rotary furnace followed by low- intensity magnetic separation of the calcined product, (ii) simple calcination of -10mm size i_ - . bauxite and size reduction of calcine to below 1 mm size folowed by high intensity magnetic separation. The products obtained by this process are suitable for refractory ceramic and abrasive application. Thus, the process of the present invention consists of (i) reduction roasting of -10 mm size bauxite containing 4.0% FejO3 with coke breeze 3-5% by weight for 30-60 min. at 800-900°C followed by natural cooling of the calcine to 300-400°C. This roasted calcine is subjected to low intensity magnetic separator (6000 gauss). A non-magnetic fraction (product) containing Fe2O3 2.5-2.6% with 70% Al2O3, recovery is achieved from a calcined feed containing Fe2O3 6.5-7.0%. (ii) calcination of-10 mm size bauxite containing 4.0% Fe2O3 for 30-60 min. at 800-900°C followed by comminution to below 1 mm size and high intensity magnetic separation". The non-magnetic fraction (Product) contain Fe2O3 2.4-2.6% with 63% Al2O3 recovery could be achieved from a calcined feed containing Fe2O3, 6.5-7.0%. The uniqueness of this process is selective reduction of iron oxide phase present in bauxite to a magnetite phase using indigcncoush/ available solid reductant. As a result of selective conversion of hematite to magnetite phase, low intensity magnetic separators could improve the reduction of iron in the product suitable for refractory, ceramic and abrasive applications, whereas the reported information by different researchers on reduction of iron from crude or calcined bauxite involves fine grinding followed by calcination and use of high intensity magnetic separators. This process involves high energy consumption and the product so obtained is not directly suitable as a raw material for refractory, ceramic and abrasive industries. The present invention consists of pyrometallurgical pretreatment of lean and off grade bauxite followed by beneficiation. The product obtained by this new technique could be a suitable raw material for use in refractory, ceramic and abrasive industries. In order to achieve this objective, percentage reductant, temperature, time of reduction and comminution to liberation size of iron phase in the calcine are to be suitably adjusted. The pretreatment has been done in a rotary furnace on 2 kgs scale with a solid reductant (coke breeze) 3-5% by weight. The temperature 800-900°C and reduction time 30-60 min. are maintained. During this step, the iron oxide present in the baaxite is converted to a magnetite phase. The naturally cooled calcine (300-400°C) is subjected to a low intensity magnetic separator (6000 gauss). The product thus obtained by this process is suitable as a raw material for refractory, ceramic and abrasive applications. In order to achieve the objective, the other pyrometallurgica] methods involving simple calcination followed by comminution and high intensity magnetic separation has been investigated on the bauxite sample of Jamnagar region, Gujarat. For this route, the -10 mm bauxite was calcined at 800-900°C for a period of 30-60 min. followed by comminution to below 1 mm size and subjected to magnetic separation by using high intensity (14000 gauss) separators. The product thus obtained is also suitable for refractory, ceramic and abrasive applications. However, this process is comparatively high energy intensive. Accordingly the present invention provides, a process for the production of refractory grade bauxite from ferrugineous bauxite characterized by calcining -10 mm ferrugineous bauxite with solid reductant such as herein described, at a temperature in the range 800 -900°C for a period of 30 - 60 min, crushing the calcined bauxite to below 3 mm size by known methods and subjecting to conventional low intensity magnetic separator to get refractory grade bauxite. The ferrugineous bauxite used may contain 4.5% Fe203, 53% AI2C>3, 2.7% CaO, 1.7% Si02/ 2.1% Ti02. The solid reductant such as coke breeze, coal, charcoal in an amount of 3 to 5% of bauxite may be used along with ferrigineous bauxite during calcinations. The intensity of magnetic field used for reduced bauxite may range from 5500 to 6500 and that for calcined bauxite may range from 12000 to 14000 gauss. Example 1 Reduction Roasting: 2 kgs of -10 mm bauxite sample containing AI203 53%, Fe203 4.5%, CaO 2.7%, Si021.7% and Ti02 2.1% was roasted with 5% coke breeze in a rotary furnace at 800°C for 30 min. duration. After the experiment, the charge was allowed to cool to 300°C and discharged. This calcined feed contained on an average AI203 74.5%, Fe203 6.5% , CaO 4.1%, Si02 2.4% and Ti02 3.0%. This feed was crushed to below 3 mm size and subjected to low intensity magnetic separator (6000 gauss). Bothe the magnetics and non-magnetics were weighed and analysed for alumina, iron and calcium. The non-magnetic fraction is a product. On an average, this product contain AI2O3 76.1%, Fe2O3 2.6%, CaO 3.6%, SiO2 3.0% and TiO2 3.5% with a yield of 64% and 70% AI203 recovery. The reduction in Fe2O3 by this process is 67%. Example 2 Calcination: 2 Kgs of-10 mm bauxite sample containing Al2O3 53%, FezO3 4.5%, CaO 2.7%, SiO2 1.7% and TiO2 2.1% was calcined at 900°C for 30 min duration. After the experiment the charge was allowed to cool to 300°C and discharged. This calcined feed contained on an average A12O3, 76.2%, Fe2O3 6.5%, CaO 4.6%, SiO2 2.4% and TiOz 3.0%. This feed was crushed to below 1 mm size and subjected to high intensity magnetic separator (14000 gauss). Both the magnetics and non magnetics were weighed and analysed for alumina, iron and calcium. Ths non magnetic fraction is a product. On an average, this product contain Al2O3 79.1%, Fe2O3 2.4%, CaO 4.1% with a yield of 61% and 63% Al2O3 recovery. The reduction in Fe2O3by this process is 72%. We Claim: 1. A process for the production of refractory grade bauxite from ferrugineous bauxite characterized by calcining -10 mm ferrugineous bauxite with solid reductant such as herein described, at a temperature in the range 800 -900°C for a period of 30 - 60 min, crushing the calcined bauxite to below 3 mm size by known methods and subjecting to conventional low intensity magnetic separator to get refractory grade bauxite. 2. A process as claimed in claim 1, where the ferrugineous bauxite used contains 4.5% Fe2O3 and 53% Al2O3. 3. A process as claimed in claim 1 and 2, where the solid reductant is coke breeze, coal, charcoal or any other carbonaceous material in an amount ranges from 3 - 5%. 4. A process as claimed in claim 1 to 3, where the calcined bauxite is crushed to below 1 mm size. 5. A process as claimed in claims 1 to 4, where the intensity of magnetic field employed for reduced sample is 6000 gauss and for calcined sample is 14000 gauss. 6. A process for the production of refractory grade bauxite from ferrugineous bauxite substantially as here in described with reference to example.

Documents:

57-del-1999-abstract.pdf

57-del-1999-claims.pdf

57-del-1999-complete specification (granted).pdf

57-del-1999-correspondence-others.pdf

57-del-1999-correspondence-po.pdf

57-DEL-1999-Description (Complete).pdf

57-del-1999-form-1.pdf

57-del-1999-form-19.pdf

57-del-1999-form-2.pdf