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Process for Producing Borax Decahydrate Crystals

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The International Union of Pure and Applied Chemistry name for borax is sodium tetraborate decahydrate. The normal use of the expression “borax” alludes to a gathering of related mixes, recognized by their water content:

  • Anhydrous borax or sodium tetraborate (Na2B4O7)
  • Borax pentahydrate (Na2B4O7·5H2O)
  • The borax decahydrate (Na2B4O7·10H2O)

The Borax Decahydrate formula is often written as Na₂[B₄O₅(OH)₄]·8H₂O

(1) Field of the invention:
This invention relates to a process for the production of inorganic salts. More particularly, it relates to the production of borax decahydrate crystals of a controlled mean particle size and size range.

(2) Description of the prior art:
It is well known that Borax Decahydrate Na₂[B₄O₅(OH)₄]·8H₂O may be produced in commercial operation by continuous crystallization of the borax from aqueous liquors. However, borax crystals produced by such continuous crystallization techniques are of uncontrolled mean size and size distribution. Consequently, if it is desired to obtain borax crystals of a predetermined mean size and size range by these techniques, it is presently necessary to classify and/or screen the product. However, even when such procedures are used, generally only a small percentage of the total product is of the desired size range. As a result, the production of borax crystals of the desired size by Such prior techniques is a relatively inefficient operation.

A process for controlling the mean size and size range of borax decahydrate crystals produced from a magma containing Solid-phase borax and water saturated with borax. The temperature and solids concentration of the magma is controlled to produce two basic crystal size distributions, one having a mean particle size of less than about 45 mesh and the other having a mean particle size of greater than about 45 mesh. Borax crystals of the Smaller particle size are crystallized from the magma when the magma is maintained at a temperature of less than 115 F. and a solids concentration of greater than 0.25 grams of solid borax crystals per cubic centimeter of Solids-free mother liquor. Borax crystals of the larger particle size are crystallized from the magma when it is maintained at a temperature higher than 115 F. and a Solids concentration of fewer than 0.25 grams per cubic centimeter.

Summary of Borax Decahydrate Invention

The present invention provides a process for controlling the mean size and size range of borax decahydrate crystals produced by crystallization from an aqueous liquor. Broadly, the present process provides for the control of certain critical conditions during the crystallization of borax decahydrate whereby crystals having a predetermined mean size and size range are obtained. Thus, it has been discovered that the mean particle size and size range of borax crystals, crystallized from an aqueous magma containing aqueous mother liquor and Solid borax, may be controlled by controlling the temperature and Solids concentration of the magma. By the use of suitable size classifying procedures in the removal of the product from the magma, a further advantage is achieved in that the predetermined size range of the borax crystals may be limited to a value close to that of the desired mean crystal SZC. Advantageously, the process of this invention can be operated with the magma at such a slight degree of super Saturation that the apparatus generally does not become fouled with deposits of tightly adhering borax crystals. Generally, the magma is Supersaturated with less than about 2 percent of borax by the weight of the solution.