Borax (mineral)
Borax, also known as sodium borate, is a naturally occurring mineral that belongs to the borate group and is primarily found in alkaline lake muds. It appears as prismatic crystals or a white powder and is characterized by its chemical formula Na₂(B₄O₅)(OH)₄·8(H₂O). Major deposits of borax are located in the western United States, particularly in California’s Mojave Desert, as well as in regions of South America, Turkey, and Tibet. This mineral has been utilized for thousands of years, initially for ceramic glazes and later expanding its applications to include glass manufacturing, ceramics, agricultural chemicals, and various industrial processes.
Borax possesses numerous functional properties that make it valuable in many sectors, including as a cleaning agent, antiseptic, and pest control substance. It is known for its ability to dissolve in hot water and form glass-like beads when heated, which is useful in chemical analysis. However, while borax is effective in many applications, it is important to handle it with care as overexposure can lead to toxicity, particularly affecting the kidneys. Its diverse uses and historical significance highlight its role as a critical resource in both traditional and modern industries.
Borax (mineral)
Where Found
Borax, the most widespread of the borate minerals, is found in the muds of alkaline lakes along with minerals such as rock salt, sulfates, carbonates, and other borates. Large deposits are found in the western United States, South America, Turkey, and Tibet.
Primary Uses
Borax is essential to many industrial processes, notably the manufacture of glass and enamel. Other major users include the ceramics, agricultural, chemical, cleanser, and pharmaceutical industries.
Technical Definition
Borax (also known as sodium borate decahydrate, sodium pyroborate, birax, sodium tetraborate decahydrate, and sodium biborate) is an ore of boron with the chemical formula Na2(B4O5)(OH)4·8(H2O). Its average molecular weight is 381.4, composed of 12.06 percent sodium, 11.34 percent boron, 5.29 percent hydrogen, and 71.32 percent oxygen. Borax may be colorless, white, yellowish, or gray. Its hardness on the Mohs scale is 2 to 2.5. Borax occurs as prismatic crystals or as a white powder. Its specific gravity is 1.69 to 1.72. It is slightly soluble in cold water, very soluble in hot water, and insoluble in acids. It has a melting point of 75° Celsius and a boiling point of 320° Celsius. When heated above 740° Celsius, it fuses to form a “borax bead.”
Description, Distribution, and Forms
Borax is a member of a group of compounds known as borates, minerals that contain the element boron. Borax is an evaporite found in dried-up lakes and playas (desert basins). A sedimentary deposit that forms in arid regions, borax derives its name from būraq, an Arabic word meaning “white” that was used to refer to the substance. This widespread borate mineral is found in association with other evaporites, including rock salt, sulfates, carbonates, and other borates. Borax occurs as a white powder on the soil surface or in masses of short, prismatic crystals embedded in the muds of alkaline lakes. Borax is also present in many mineral waters and salt lakes. It commonly loses water to form tincalconite (Na2B4O7·5H2O).
The most widespread of the borate minerals, borax is notably found in arid regions near the sites of Pliocene lakes, where hot springs and volcanic activity are believed to be the source of the boron-rich brines that fed these lakes. Upon evaporation (hence its classification as an “evaporite”), deposits of borax and other borates formed. Buried accumulations of borax are often found in the centers of dried-up alkaline lakes, with outcrops of calcium and calcium-sodium boron minerals marking the periphery of the lake area.
In the United States, there are large deposits of borax in California, Nevada, and Oregon. Almost half the world’s refined borates come from Southern California. In California’s Mojave Desert, Searles Lake in San Bernardino County and Kramer in Kern County are two major borax deposits. At Searles Lake, borax is the most abundant of the four borate-bearing minerals found there. Borax is also the most abundant mineral in the Kramer borate deposit, the largest known reserve of boron compounds in the world. Other major deposits are located in Tibet, Argentina, and Turkey. In Argentina, for example, borax is mined at Salt Province (more than 4,000 meters above sea level) and at Tincalayu, Sijes, and the lakebeds at Salar Cauchari and Salar Diablillos.
History
Borax has been used commercially for thousands of years, with the earliest confirmed use in ceramic glazes traced to the tenth century c.e. The early Chinese, Persians, Arabs, and Babylonians knew of the mineral and its properties. It was introduced to Europe by Marco Polo about 1275 c.e. Europe’s earliest source for the mineral was Tibet, where tincal (crude borax) was used for making glazes and soldering gold. By the 1800’s, borax had gained widespread use in glassblowing and gold refining.
Italy, Tibet, and Chile were the principal world suppliers of borate minerals until extensive borate deposits were discovered in California and Nevada. An 1864 report on borax crystals found in the muds of Borax Lake in Lake County, California, was the first to publish the discovery of the mineral in the western United States. In the early 1880’s, borax was also found in Death Valley. The twenty-mule teams that hauled the material mined from Death Valley across the California desert to the railroad junction at Mojave became a widely recognized symbol for the borax industry in the United States.
Obtaining Borax
Borax may be obtained directly from dry lake beds on which the evaporite has formed, from open-pit borate mines, or from drilling for underground mines. At Searles Lake, borax is recovered by fractional crystallization from lake brine. Borax may also be made from other borate ores, including as kernite (Na2B4O7·4H2O), colemanite (Ca2B6O11·5H2O), and ulexite (NaCaB5O9·8H2O), or by the reaction of boric acid with soda. Crystalline borax readily effloresces—that is, it loses its water of crystallization to form a white powder—particularly upon heating.
Deposits of borate ores are found underground by drilling and then blasting to remove the sandstone that overlies the ore deposit. (Eventually such sites will turn into open-pit mining operations.) Huge shovels remove the rubble to get at the ore, which is then crushed and refined by mixing the crushed ore with hot water. Borates dissolve in the water, leaving the unwanted debris in solid form; the debris-free solution can then be pumped into tanks, which cool the solution so that the borates can crystallize and then be removed for drying, storage, and further processing.
Uses of Borax
The uses of borax are based on its many functional properties, which include metabolizing effects, bleaching effects, buffering effects, dispersing effects, vitrifying effects, inhibiting effects, flame-proofing effects, and neutron-absorbing effects. Borax has been used for centuries in making glass and enamels, and it has become an essential part of many other industrial processes. It is used in the manufacture of glass (notably heat-resistant and optical varieties), porcelain enamels, ceramics, shellacs, and glazes. It is a component of agricultural chemicals such as fertilizers and herbicides. It is used in the manufacture of chemicals, soaps, starches, adhesives, cosmetics, pharmaceuticals, insulation material, and fire retardants. In the textile industry, borax is used in fixing mordants on textiles, tanning leather, and spinning silk. It is effective as a mild antiseptic, a water softener, and a food preservative, although it is toxic if consumed in large doses. It is added to antifreeze to inhibit corrosion and used as a flux for soldering and welding. Borax is also a source of elemental boron, which is used as a deoxidizer and alloy in nonferrous metals, a neutron absorber in shields for atomic reactors, and a component of motor fuel and rocket fuel.
Borax also plays an important role in chemical analysis. Borax fused by heating is used in the “bead test,” a form of chemical analysis used in the identification of certain metals. Powdered borax is heated in a platinum-wire loop over a flame until the mineral fuses to form a clear glassy bead. The borax bead is then dipped into a small quantity of the metallic oxide to be identified. Upon reheating over the flame, the bead reacts chemically with the metallic oxide to form a metal borate, which gives the bead a characteristic color that helps identify the metal. For example, cobalt compounds yield a deep blue bead, and manganese compounds produce a violet one.
Perhaps the most familiar use of borax is as a cleansing agent. Borax combined with hot water will create hydrogen peroxide; it lowers the acidity of water, which facilitates the bleaching action of other cleansers. Borax also acts as both a disinfectant and a pesticide by blocking the biochemistry of both macro- and microorganisms, such as bacteria, fungi, fleas, roaches, ants, and other pests. These same properties, however, mean that people must avoid overexposure to borax lest it prove toxic to the kidneys and other organs (a typical symptom is red and peeling skin). Finally, borates such as borax enhance the power of other cleansing chemicals by bonding with other compounds in such a way that it maintains the even dispersal of these cleansing agents in solution, thereby maximizing their surface area and hence their effectiveness.
Bibliography
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