Hydrated sodium borate
Na2B4O7 -10H2O
Borax fuses at a low temperature and easily dissolves in different important elements like copper, chromium, cobalt, iron, nickel, and uranium giving different characteristic colours.
The History Says
Borax mining in the United States started with the production of borax from Borax lake in Tehama County in 1864. The discovery of cotton ball ulexite in the playa of Teel's Marsh by Frances Marion (Borax) Smith in 1872 ushered in the first major production of Borax in the United States. The center of cotton ball production then moved to Death Valley in 1880. The most famous operation was the Harmony borax works run by William Tell Coleman. This is the operation that become associated with the twenty mule team wagons. With the discovery of colemanite the Playa period started to decline.
The Present Scenario
Borax is used as a flux in the manufacture of artificial gems. Cubic boron nitride, commercially called 'Borazon' equals the diamond in hardness and has a greater resistance to oxidation under heat. Borazon can stand the temperature which is more than twice the temperature limit of a diamond i.e. about 900°C.
BORAX is a white powdery or granular substance used for refining gold and silver. Amongst the minerals, borax may be regarded to have taken a lead in industrial applications since early forties and now it is also regarded as a potential raw material for use as an additive in rocket fuel.
Borax is the most important boron mineral of industrial use. Boron minerals are many - as many as sixty are known - occuring as borates or complex boro-silicates, but only four borates are regarded as having any commercial importance. These are:
- Borax (Hydrated Sodium Borate)
Na2O, 2B2O3, 1OH2O : Na2O, 16.2%; B2O3, 36.6%; H2O, 47.2%. - Kernite (Hydrated Sodium Borate)
Na2O, 2B2O3, 4H2O : Na2O, 22.6%; B2O3, 51.1%; H2O, 26.3% - Colemanite (Hydrated Calcium Borate)
2CaO, 3 B2O3, 5H2O : CaO, 27.2%; B2O3, 50.9%; H2O, 21.9%. - Ulexite (Hydrated Sodium Calcium Borate)
Na2O, 2CaO, 5 B2O3, 16 H2O : Na2O, 7.7%; CaO, 13.8%; B2O3, 43.0%; H2O, 35.5%.
Besides, the above four boron minerals of commercial importance, two more borates, sassoline (H2BO3) the natural boric acid and boracite 5MgO, MgCl2, 7B2O3 are of some importance. Boro silicates are regarded to have been formed due to pneumatolysis. Borates have been derived from:
- Volcanic gases or hot springs near the volcanic activities, such deposits being predominantly borax and sassoline.
- As a result of drying up of shallow saline and alkaline Tertiary lakes called 'playa'.
Such types of deposits are found in Puga Valley, Kashmir, India and Tibet. The world's largest borax and kernite deposits found in Kramer district, California. Baron salts are also recovered as soluble compounds from saline lakes along with other salts, as for example, from Searles Lake, California, the USA.
Tincal is the name given to crude borax. The crude borax, mined chiefly in Tibet was sold in European markets under the name of tincal. Of all the Borates, borax and boric acid are the only two minerals which are utilized for commercial applications. Other borates are essentially a source of borax and boric acid and they are converted chemically into the above substance for industrial use. Kernite, when dissolved in water and evaporated, re-crystallizes with ten molecules of water.
| Hardness | Associated Minerals | Chemical/Typical composition | Colour | characteristics | Luster | Field Indicators |
| 2 - 2.5 | calcite halite hanksite colemanite ulexite and other borates | Na2O....16.25 % B2O3......36.51 % H2O.......47.24 % O............71.32 % | white to clear | sweet alkaline taste, alters to chalky white tincalconite with dehydration | vitreous | crystal habit, color, associations, locality, density and hardness |
Properties
Borax, Kernite, colemanite and ulexite all crystallize in Monoclinic system. Borax occurs as a white glassey mass, clear to translucent crystals and crystalline aggregates. It is easily soluble in water. The hardness varies between 2-2.5. Karnite sometimes resembles selenite crystals with platy cleavage. Its hardness is a little higher than that of borax and it is readily slouble in hot water. Colemanite resembles felspar or calcite. It can be easily distinguished by blow-pipe tests. It is insoluble in water but soluble in acids, giving rise to boric acid. Its hardness is 4-4.5. Ulexite is found to occur in association with other borates as a cotton-ball or a rounded mass with parallel or radiating fine fibres. It dissolves readily in acids and slowly in hot water. Its hardness is 1.
Sassoline crystallizes in Triclinic system and boracite in Cubic system. Sassoline is found as white scales and sometimes in prismatic crystals. It dissolves in water and alcohol. Its hardness is 1. Boracite occurs as cubic or octrahedral crystals, also massive and columnar. It is insoluble in water but soluble in hot acids.
Borax fuses at a low temperature and easily dissolves in different important elements like copper, chromium, cobalt, iron, nickel, and uranium giving different characteristic colours, the properties of which are utilized in the identification of minerals in borax-bead tests.
Industrial Applications
Borates are now listed as the most important and strategic minerals for their use as anti-knock agents in gasoline. Boron hydride has potential value as rocket fuel. The high energy fuel value have imparted by the addition of boron compounds has given borates considerable military significance. Another use of borates is the invention of organo-sodium borate (Liquibor) for use in hydraulic brake fluids in cars to provide lower volatility and built-in corrosive protection.
Product consisting of a combination of borax and trichlorobenzoic acid known as 'Benzabor' has been found most suitable in controlling deep-rooted perennials in the agricultural field. In the field of nuclear energy, boron (the B10 isotope) protects personnel from the harmful effects of reactors. Boron has the unique property of absorbing neutrons produced by nuclear reaction without the emission of harmful secondary gamma radiation. Another new organic borate is used, in combination with paraffin, for nuclear shielding. The elemental form of boron is being incorporated into polyethylene and rubber. Ammonium pentaborate is used in a 'poison' charge in atomic submarines.
Borax and boric acid are widely used in:
- food preservation
- detergents and soap
- electroplating
- fluxes
- the glass industry
- ceramic glasses
- enamels
- cosmetics
- pharmaceuticals
- pesticides
- refractories
- textiles
The glass and porcelain industries are the major consumers of boras and boric acid, consuming over 50% of the total production. The boric oxide behaves as a network - former in glass and ancillary industries and is a powerful flux. It is an essential component of heat-resisting boro-silicate glass, glass fibres, industrial, optical and other glass. In glass, enamels and glazes it controls thermal expansion, improves durability, assists the melting processes and is also a component of inorganic colours and decorations.
Boron, also, confers a low co-efficient of expansion, increases the resistance to mechanical and thermal shocks and gives a bright and pleasing appearance to glass. Between 15 to 50 parts of borax are used to each 1,000 parts of glass-sand batch. Borax and boric acid are used together in the manufacture of a number of boro-silicate glasses of low alkali content.
Some other areas where Borax is used:
- Medicine (boric powder)
- Leather processing
- Adhesive manufacture
- Corrosion inhibition
- Fertilizers correcting boron deficiency
- Ferrous wire manufacture
- Flame proofing
- Weed killers
- Timber preservation
Borax is used as a flux in the manufacture of artificial gems. Cubic boron nitride, commercially called 'Borazon' equals the diamond in hardness and has a greater resistance to oxidation under heat. Borazon can stand the temperature which is more than twice the temperature limit of a diamond i.e. about 900°C.
Mining
The mining of borates is dependent upon the mode of formation. Kramer deposits in California are worked both by open pit and underground method. The borate beds have been found there underlying between 40 to 300 metres from the surface. The deposits consist of thick beds of kernite and borax. The ulexite deposits in Turkey are mined by driving parallel adits. The Turkish ore is mainly ulexite mixed with colemanite, and priceite (Ca4B10O19.7H2O). The minerals are mined together and brought to the surface for further processing and refining. The borax salts, as found in the brine solution of the Searles lake, California, are pumped up, processes and refined from the mixed solution by the well-known fractional crystallization process commonly known as 'Troma process'.
Processing and Refining
Advantage is taken of the solubility of borates, especially borax and kernite, in separating clayey material by washing and recrystallization. Refined borax is produced by dissolving the crude material in hot water under pressure. The insoluble impurities are filtered off and the liquor is crystallized to give borax, or if boric acid is to be manufactured, the hot water solution is reacted with sulphuric acid. The reaction that takes place is as follows:
Na2B4O7. 10H2O +H2SO4 = 4H3BO3 + Na2SO4 + 5H2O
The ulexite or colemanite mined in Turkey is shipped to many European countries for processing into boric acid and borax. Ulexite and colemanite are treated in the same manner with sulphuric acid to convert them into boric acid. If borax is to be prepared, the boric acid is added to soda ash solution. Borax is also produced from colemanite by boiling the powdered mineral with sodium carbonate solution for about 3 hours. After filtering, the solution is allowed to crystallize to yield crude borax.
Borax is recovered from the Searles Lake deposits as a by-product of potash recovery. The lake is a solid salt-bed of complex composition. A saturated brine solution filling the interstices between the salt crystals 18 to 22 metres below the surface is pumped out through wells. The brine contains about 35% of solid in solution.
The average composition of the brine is as follows:
| KCl | 04.70 |
| NaCl | 16.35 |
| Na2CO3 | 04.70 |
| Na2SO4 | 06.96 |
| Na2B4O7 | 01.50 |
| Na3PO4 | 00.16 |
| NaF | 00.01 |
| Misc. | 00.30 |
| Total | 34.68 |
The seperation of salts present in the complex brine solution could be made possible by phase rule-study, first applied to German potash deposits at Stassfurt, and fractional crystallization. The Trona process of fractional crystallization has come to be known from the name of the locality in California where the plants for separation and processing of the salts from the Searles Lake are situated. The carbonation process of recovering borax is applied to the brine solution pumped from the lower level, which is comparatively richer in borax and sodium carbonate contents.
In the bicarbonate process, the brine solution is first precipitated by CO2; the remaining liquor is again blended with raw brine and sent to the vacuum crystallizers.
In the evaporation process, the brine is evaporated on a continuous cycle just to the point where potash becomes saturated. At this stage, sodium chloride (NaCl), licons (NaLi2PO4) and bukerite (2Na2CO3. 3Na2SO4) are crystallized and filtered. The resulting liquor is cooled in special crystallizers to remove potash. The other liquor from the potash plant is further sent to large crystallizers, where it is mixed with seed crystals to crystallize pentahydrate borax. It is further purified and dehydrated for export purposes.
The Searles Lake and Kramer deposits in California produce nearly two-thirds of the USA production and the USA alone is responsible for over 90% of the world supply.
World Resources
The world's largest known reserves of borates are located in USA, supplying nearly 90-95% of the world demand. Other principal countries possessing borate resources are:
- Turkey
- Italy
- Tibet
- Chile
- Argentina
- Bolivia
- USSR
Countrywise Brief
USA - California:
The chief sources of supply of borax are Kramer Lake and Searles Lake. Kramer Lake is situated midway between kern county in the east and Mojave Desert in the west. The deposits are 4.8 km. North of Boron town. Borax and kernite are found in Ricardo formations about 456m. thick lying over Saddleback lava, and overlain by conglomerate and alluvium having a maximum thickness of 91m. ricardo formations consist of footwall shale, blue shale and shale. The total thickness of the borate bed is 75 metres. It is estimated to contain at least 100 million tonnes of borates.
Other deposits are located in Owens Lake, Furnace Creek area, Inyo county and Death Valley, California. Large ulexite deposits are known to exist in Clark county, Nevada.
Turkey
Colemanite is the principal boron mineral produced in this country. The deposits lie in western Turkey as playa beds mixed with clay and marl. The mineral content varies from 30 to 70%. Small proportions of ulexite and priceite (Ca4B10O197H2O) are also found in the deposit.
Mines have been opened up in six areas namely Bigadic, Kucukler and Sindirgi in Balikesir Province; Kestelek in Bursa; Emet in Kutahya and Kirka in Eskisehir. Boron minerals are found as continuous beds of colemanite boulder in clay and marl strata underlying the hard limestone cap rock. The mineral horizones are usually found 10-20 metres below the upper Pliocene limestone. Mining is done mostly by the underground method though open pits are being developed for large-scale mining. The mined material is hand sorted and the ore is exported to European countries, USA, the UK and Japan.
Italy
This country exploits sassoline (natural boric acid) deposits of volcanic origin. It occurs with sulphur in the crater of a volcano in Lipari Islands, southern Italy. It is also found in the Tuscan lagoons, between Voltena and Massa Marittima. Boric acid is condensed in water and separates in large flakes which contain about 50% of the acid.
Argentina
This country is the second largest producer of ulexite, which is found as layers and nodules in playas in north-eastern Argentina adjacent to northern Chile. Only two bedded deposits are of Tertiary age; the remaining are located in a desert basin called "salaries". A number of salares are found in the desert basin usually associated with saline mineral and the reserves are supposed to be quite large and extensive.
Chile
Deposits of the playa bed types similar to those found in Argentina, also occur in the Atacama Desert of Chile. The basins near the coast contain mostly nitrates but the inland deposits are rich in borates. The most productive area is the Salar de Ascotan in Antofagasta Province.
Russia
Borate deposits are found along fracture zones on the north and south margins of a salt dome covering an area of 250 sq. km. The core of the salt dome consists of Permian marine evaporates, overlain by Mesozoic and Tertiary sediments. The salt dome is capped with gypsum and clay beds. Borates occur above salt replacing gypsum and clay. The chief mineral found in this bed is Szaibelyite, [Mg(BO2)OH].