Expert paper DEPOSITS OF BORATE RAW MATERIALS AND THEIR INDUSTRIAL USE

Transcription

1 UNDERGROUND MINING ENGINEERING 14 (2005) UDK 62 FACULTY OF MINING AND GEOLOGY, BELGRADE YU ISSN ABSTRACT Expert paper DEPOSITS OF BORATE RAW MATERIALS AND THEIR INDUSTRIAL USE Vidanović Nebojša 1, Dimitrijević Bojan 1, Tokalić Rade 1 In this paper is given review of mineral-raw materials complex of boron compounds and main deposits of this rare ore-value in the world. With development of technology of modification borate raw materials, it has showed is their up to now industrial application. World practice are important for examination possibility exploitation and modification borate raw materials in our country and it has been initials for starting exploration «Top down«project in years colled «Energy, ecological and economy aspects device of technology extracting elementary boron of their compounds from domestic (local) raw materials which finance Ministry of Science and Environmental Protection, Republic of Serbia. Key words: boron, deposits boron, use boron INTRODUCTION Boron as raw mineral materials known in ancient period civilization development, that is in the age of the old Babilon, Egypt and Chinese culture. It is very wide implementation scale of borate and his compounds in domain of conventional technologies and contemporary technical solutions as well. That makes borate as one of the most important industrial raw materials. Rising of all metal and non-metal prices on worlds stock market exchanges indicate need for increasing attention to boron as a very important potential available in our country. BASIC CHEMICAL AND GEO CHEMICAL CHARACTERISTICS OF BORON Amorphous boron is brow powder with specific weight of 2.45 and atomic weight of Boron melt on approximately 2300 о C and it is volatile on this temperature in very small scale. By heating on atmosphere conditions in oxygen boron burn with spark and compose borontrioxide (B 2 O 3 ), but on the air it burn creating mixture of oxide and nitride. 1 Faculty of Mining and Geology University of Belgrade

2 158 Vidanović N.; Dimitrijević B.; Tokalić R.; Boron compounds shows, generally speaking, non-metals characteristics with three valence bonds. Free boron no exist in nature, it is contained in compounds as boron acid, in borate form: borax, tincal, kernite and as complex borates as: colemanite, sodium calcium borate and calcium borate. It is recorded that is boron acid in sea water, in the ground, in the most of botanic products, botanic ashes and some types of wine. Borates, fully oxygenated compounds of the element boron, represent >99% of boron compounds commercially produced and used worldwide. Naturally occurring boron is found exclusively combined with oxygen primarily in minerals as alkali metal or alkaline earth salts. Thus, the vast majority of industrial boron chemistry is concerned with B O compounds. Chemical reactions of borates are generally characterized by the interaction with the associated oxygen atoms and not with the boron atom directly. Like silicon the ability of boron to form strong covalent bonds with oxygen is fundamental to the chemistry of borates but unlike silicon, boron readily undergoes valence bond expansion having a coordination number of either three or four. Three coordinate boron is comprised of three covalent bonds to oxygen forming a trivalent or planar trigonal group found in the boric acid molecule, B(OH) 3, and bears no formal charge. As a consequence boric acid is mono basic and a weak Lewis acid. The central boron atom in boric acid is electron deficient and accepts an electron pair, as for example in the next equation, from the oxygen in water to form the borate ion. B(OH) 3 + 2H 2 O B(OH) 4 + H 3 O + (K a = 6 x in water) Four coordinate boron has four covalent bonds to oxygen forming a tetravalent or tetrahedral group found in the borate ion, B(OH) 4 having a formal negative charge on the central boron atom. Boron belongs to group of lithophilos elements, his Clark is 12 ppm and concentration factor is >10000, which indicate conclusion about level of occurrence of boron deposit in the nature. In endogenetic stage of forming, boron is characteristic for high temperature hydrothermal area where form easy volatile compounds with F, Fe, Sn, Mo, W etc. In the same conditions boron is in alkali solutions which are rich with fluoride while in volcanic emanations occur as gaseous halogenides which in reaction with water steam gives boron acid. In exogenetic conditions, boron from boron containing rocks of primary deposits of boron and other sources, alkalinize, or in other words in form of complex anions convert into cold water solutions (boron acid and easily volatile borate).

3 Deposits of borate raw materials MINERALS, ORES AND DEPOSITS OF THE BORON There are more than 200 minerals that contain boric oxide but relatively few that are of commercial significance. In fact four minerals comprise almost 90% of the borates used by industry: borax and kernite, both sodium borates; ulexite, a sodium calcium borate; and colemanite, a calcium borate. These minerals are extracted in California and Turkey and to a lesser extent in Argentina, Bolivia, Chile, Peru and China. China and Russia also have some commercial production from magnesium borates and calcium boron-silicates. These deposits furnish nearly all the world's borate supply at this time. In Table 1. are given the borate minerals of economic importance: Тable 1. - Borate minerals of economic importance: B Мineral Formula 2 O 3 % Borax Na 2 O. 2B 2 O 3. 10H 2 O 36,5 Main sources USA, Тurkey, China, Argentina Кernite Na 2 O. 2B 2 O. 3 4H 2 O 51,0 USA Colemanite 2CaO. 3B 2 O. 3 5H 2 O 50,8 Тurkey, Argentina, USA Ulexite Na 2 O. 2CaO. 5B 2 O. 3 16H 2 O 43,0 Тurkey, Chile, Peru, Argentina, Bolivia, China, Datolite 2CaO. B 2 O. 3 2SiO. 2 H 2 O 21,8 Russia Hydroboracite CaO. MgO. 3B 2 O. 3 6H 2 O 50,5 Argentina, Chile Asharite 2MgO. B 2 O. 3 H 2 O 41,4 China In ore, these occur with other minerals and some processing is required to produce usable borate products. For glass these may be refined chemicals or upgraded minerals. Boron deposits originates from different geological environments and physical-chemical processes. From particular economic significance are deposits which occurrence was linked with post magmatic gaseousliquid fluids in the endogenic stage of orogeny, that is infiltration and homogenous-sedimentary deposits in exogenic stage of orogeny. In series of endogenetic deposits, economically significant deposits are hydrothermal sediments, volcanogene-hydrothermal sediments and eshalated boron deposits originated in the zone of recent and fossil volcanic activity. Geologic environment of occurrences of first two orogene types usually are lake sediment basins with flood of borone hydrothermal fluids. Eshalated boron deposits compared with previous types are with less significant economic importance. Spatially and genetically considering, they are mostly connected with area of recent volcanic activity, where boron minerals are separated from fumarole and solphatare. In exogenetic conditions, boron are mostly concentraced in salty marine and lake basins, rarely in the fresh water environment (mineralized boron-bearing waters).

4 160 Vidanović N.; Dimitrijević B.; Tokalić R.; In The Pacific Ocean boron belts have produced deposits in North and South America and Asia and the Mid-Asiatic or Mediterranean boron belts have produced the deposits in Turkey. The two main borate producing regions are in Southern California and Turkey and supply about 80% of the world's requirements for borates. Sodium borates are extracted from the large deposit at Boron in the Mojave Desert and as a by-product of the Searles Lake brines operation near Death Valley. There are three main producing regions in Turkey; Kirka which produces borax, the Emet Basin which produces colemanite and the Bigadic Basin which produces colemanite and ulexite. In South America there are deposits of ulexite, tincal, colemanite and hydroboracite in Argentina, Chile, Bolivia and Peru that are exploited mainly for the local market. China has deposits of ulexite in Tibet and ascharite that occurs in the North East near to Korea; these are processed for local consumption. The unusual borosilicate mineral datolite is mined in the East of Russia at Dalnegorsk and is used mainly for production of boric acid. Sodium borate minerals are soluble in water and readily converted into borax pentahydrate; this represents the bulk of the sodium borate usage by industry. The main sources of this are Boron and Searles Lake in California, Kirka in Turkey and Tincalayu in Argentina. There are significant reserves of boron minerals in Serbia, situated in Baljevac on Ibar. This reserves are in the frame of following deposits: Pobrdjanski creek (cca 150,000 t) and Piskanja (cca 7,500,000 t). This deposits was explore by deep drilling and in less scale with mining exploration operations. FIELDS OF IMPLEMENTATION AND FINAL BORON PRODUCTS Boric oxide (B 2 O 3 ) is an important constituent of a wide range of glasses: glass wool for thermal and acoustic insulation, textile fibres for the reinforcement of plastics, enamels for steels and other metal substrates, ceramic glazes (for example tiles and tableware), optical glass and a diverse range of technical borosilicate glasses for lighting, laboratory, cookware, medical and LCD screens. Second major end uses are detergency, where sodium perborate is used as a bleach in washing powder and agriculture where boron is an essential trace nutrient for many crops. The third important area of application is metallurgy (alloyes on the base fero-boron and for polishing and glazing at steel and the other metallic substrate). Special importance boron has in production rocket-fuel, because is particulalarly accent their ctrategic importance. In Table 2. is showed of borate consumption by end use for a total of 1 5 million tones B 2 O 3.

5 Deposits of borate raw materials Table 2. Borate consumption by end use Final boron productions Insulation fibreglass Detergents, sodium perborate Textile fibreglass Borosilicate glass Frit and ceramics Agriculture productions Others % Borate BORATE RAW MATERIALS Criteria for the selection of borate raw materials for glass manufacture are no different to those for other raw materials: composition, impurities, consistency, price, availability and melt properties. Different glass types will have different criteria. For some, impurity levels are less important provided they are consistent, others will require high purity refined chemicals with ppm levels of impurities. Borates for glass may be broadly classified as mineral or refined, sodium or nonsodium containing and hydrated or anhydrous. These are listed in Table 3. Borates are relatively expensive compared to other batch components and the batch is formulated to minimise cost within the constraints of the glass composition, for example, borax pentahydrate is commonly used in sodium containing glass as it is more cost effective than using, for example, boric acid with soda ash. Two different borates may be used in the same batch, for example in some borosilicate glasses where borax pentahydrate and boric acid are used to adjust the Na:B ratio. Таble 3. Borate raw materials used for glass production Material Formula % B 2 O 3 Rafined chemicals: Sodium borates Borax pentahydrate Na 2 O. 2B 2 O. 3 5H 2 O 48,8 Nonsodium borates Аnhydrous, fused Mineral products: Sodium borates Nonsodium borates CONCSLUSION Borax decahydrate Boric acid Аnhydrous borax Boric oxide Ulexite Colemanite Hydroboracite Na 2 O. 2B 2 O. 3 10H 2 O B(OH) 3 Na 2 O. 2B 2 O 3 Na 2 O. 2B 2 O 3 Na 2 O. 2CaO. 5B 2 O 3. 16H 2 O 2CaO. 3B 2 O 3. 5H 2 O CaO. MgO. 3B 2 O 3. 6H 2 O 36,5 56,3 68, ,0 Borates are minerals that contain boron. Boron in traces amounts exist in rocks, soil, water and people. Boron-containing ores are rare in the nature, and their exploitation has been lasting for more than a cen-

6 162 Vidanović N.; Dimitrijević B.; Tokalić R.; tury. These minerals are emphasized in California and Turky, and in less measure in Argentina, Bolivia, Chile, Peru and China, and there are important resources in our country. China and Russia have got too, some commercial production from magnesium borates and calcium boronsilicate. Borates are essential micronutrients for plants and are a part of a healthy human diet. More than that, though, borates key ingredients in hundreds of products people use everyday. The simplified reason is that boron is a carbon-like mineral that has the ability to form bonds with oxygen compounds and hydrogen. This is important in applications as diverse as glassmaking, wood preservatives and detergents. In detergents, borates enhance stain removal and bleaching, stablize enzymes, provide alkaline buffering, soften water and boost surfactant performance. About 41 percent of the borates produced each year by Borax and others in the business are used in insulation fiberglass, textile fiberglass and heat-resistant glass. About 13 percent are used in ceramics and enamel frits and glazes as well as tile bodies. Another 12 percent are used in detergents, soaps and personal care products. Six percent of the borates produced are used as plant nutrients. The remaining 28 percent are used in several dozen other products. LITERATURE 1. Melor. Melor's modern nonorganic chemistry, Belgrade, Smith, R. A. History of the use of B2;O3 in commercial glass. Borate glasses, crystals and melts. Proc. Second Int. Conf. Borates glasses, crystals and melts Society of Glass Technology, Sheffield. P Simon, J. M. & Smith, R. A. Borates and their use in the glass industry. Proc. 18th International Congress on Glass Smith, R. A. & McBroom, R. B. Boron oxides, boric acid and borates. Encyclopedia of Chemical Technology. 4th Edition. Vol John Wiley & Sons, Chichester. P Bray, P. J. NMR and NQR studies of borates and borides. borate glasses, crystals and melts. Proc. Second Int. Conf. on Borates glasses. crystals and melts Society of Glass Technology, Shelfield. P Kral S., U.S. Borax: Still mining borates after 131 years, Mining Engineering, Vol. 55, Issue 7, pages 19-24, Roskill. The Economics of Boron Translations into English: Authors