Borax decahydrate

The most versatile of all borates as a synthetic reagent, orthoboric acid, B(0H)3, is the second most important refined borate product in terms of industrial tonnage. It is typically manufactured by reacting a borate ore, particularly kernite or colemanite, with sulfuric acid, Eqs. (8) and (9). 

Production processes have been developed for metaboric acid, but to date it has not become commercially important and is not currently produced in any substantial quantities. 

Boric acid is a white solid that crystallizes from water as waxy platelets. The crystal structure of boric acid consists of triangular B(0H)3 molecules interconnected by hydrogen bonding into planar layers 3.18 A apart, (Fig. 20) [88]. 

This structure accounts for the slippery feel of boric acid and the cleavage planes observed in boric acid crystals. Boric acid provides lubricity in products ranging from cosmetics to pencil leads. Although the tribological properties of boric acid have been known and utilized for many years, its lubricating properties were rediscovered in recent years by the materials science community [89]. 

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Table 7. Solubility of Boric Acid, Borax Decahydrate, and Borax Pentahydrate in Organic Solvents...

Rapid heating of either borax decahydrate or pentahydrate causes the crystal to dissolve before significant dehydration, and at about 140°C, puffing occurs from rapid vaporisation of water to form particles having as high as 90% void volume and very low bulk density (78). 

Solubihty data ia water are given ia Figure 5 and ia Table 9, solution pH ia Table 10, and the solubiUty ia organic solvents is given ia Table 7. Heats of solution ia water have been determined (68,73). The pentahydrate, ia contact with its aqueous solution, is metastable with respect to the tetrahydrate (kernite) at temperatures above 58.2°C and metastable to borax decahydrate below 60.6—60.8°C. Kernite can be slowly crystallised from a near saturate... 

Borax Decahydrate and Pentahydrate. Borax decahydrate and pentahydrate are produced from sodium borate ores, dry lake brines, colemanite, or magnesium borate ores. 

The derivatives plant is designed to aimuaHy produce 160,000 t of borax pentahydrate, 17,000 t of borax decahydrate, and 60,000 t of anhydrous borax. A reported 50,000 t of borax pentahydrate was produced in 1987. A sodium borate refinery is fed from stockpiled tincal ore or product from the concentration plant. The feed is dissolved using steam to give a solution 18% in The solution is then passed through a series of filters and sent to a... 

Anhydrous Borax. Anhydrous borax is produced from its hydrated forms, borax decahydrate or pentahydrate, by fusion (Pig. 6). Low temperature calcining is usually an intermediate step to remove water of hydration. This material is fed to a refractory brick-lined furnace and fused to a mobile Hquid at about 1000°C. 

Product Specifications. Specifications for the maximum allowable impurity levels for borate products are given in Table 12. Where maximum levels are not set, typical values are given. Typical levels of impurities generally fall well below the maximum specification. Both borax decahydrate and pentahydrate are sometimes overdried in manufacture and may give higher than theoretical assays. 

Decahydrate, Pentahydrate, and Anhydrous Borax and Bulk Calcium Borates. The bulk borate products, borax decahydrate and pentahydrate, anhydrous borax, boric acid and oxide, and upgraded colemanite and ulexite, account in both toimage and monetary terms for over 99% of sales of the boron primary products industry (6). Economic considerations for all these products are highly interrelated, and most production and trade statistics do not distinguish the various products. 

Refined or concentrated borax decahydrate and borax pentahydrate... 

Borax decahydrate occurs in nature as mineral, borax (tincal). It is one of the most common sodium borate ores. The compound has several industrial applications. The refined material is mostly used in household cleaning products. It is used to make pyrex and other horosilicate glasses. Borax is added to fertilizers in small quantities as a source of boron, as a trace nutrient for plants. High purity grade borax is used in cosmetics, toilet products and electrolytic capacitors. It also is used in fire retardants, adhesives and herbicides. 

Borax decahydrate is produced from borate ores, primarily colemanite and also from dry lake brines. When produced from its ore, the ore is crushed and then blended with B2O3. The blend is mixed with hot recycle liquor in a dissolving plant. Rock and clay particles from the liquor are removed over vibrating screens. The hquor is then fed to thickeners for settling of insolubles after which the underflow mud is washed with water. The strong liquor of borax hydrates is then pumped into continuous vacuum crystallizers for the separation of the pentahydrate first and then the decahydrate. The products are dried in rotary or fluid bed driers. 

Water of crystalization can be analyzed by TGA or DTA methods. The theoretical water content of borax decahydrate is 47.2%. The salt is digested with acid and the boron and sodium content may be measured by AA or ICP spectrophotometry. The compound may be identified by x-ray methods. 

Fig. 19. Borax structure, where x = 8 for borax decahydrate and x = 2.67 for borax pentahydrate...

Disodium Tetraborate Decahydrate (Borax Decahydrate). Disodium tetraborate decahydrate, Na2B40 101I, 0 or Na20 2B203 1 HI I (). formula wt, 381.36 monoclinic sp gr, 1.71 specific heat 1.611 kj/ (kg-K) [0.385 kcal/(g°C] at 25—50°C (68) heat of formation, —6.2643 MJ/mol (—1497.2 kcal/mol) (69) exists in nature as the mineral borax. Its crystal habit, nucleation, and growth rate are sensitive to inorganic and surface active otganic modifiers (70). 

To convert from kPa to mm Hg, multiply by 7.5. Values for the specific heat of aqueous borax solutions (73) Borax decahydrate, wt % as a function of weight percent decahydrate are Specific heat, k[/(kg-K)... 

NF-grade borax decahydrate is manufactured to conform to standards of the National Formulary, XV ed., for sodium borate. Maximum allowable impurity levels for technical anhydrous borax are SO2- 0.41% Si02, 0.21% A1203, 0.14% CaO, 0.03% MgO, 0.15% and Fe203, 0.02%. 

A substitution for Balanced Alkali can be made by mixing sodium hydroxide with borax, decahydrate (Appendix 3 Pharmacopoeia Balanced Alkali). 

Notes Borax is available as borax, pentahydrate, but most commonly as borax, decahydrate, the form used in photographic formulas. The old term for decahydrate is crystalline. Borax, decahydrate, and 20 Mule Team Borax are one and the same. 

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