3,032,391 Sttes ICC Patented May 1, 1962 1 2 hydroxide may thus be replaced by the calcium salt of 3,032,391 an organic or inorganic acid. PRODUCTION 0F CALCIUM BORATES According to the present invention, crystalline calcium Geottrey Robert Ball, Belvedere, and Godfrey Harold metaborate (CaB2O4) in the form of its tetrahydrate or Bowden, Epsom, England, assignors to United States hexahydrate is produced by reacting together borax, an Borax & Chemical Corporation, Los Angeles, Cah?, alkali-metal hydroxide (e.g. sodium hydroxide), calcium a corporation of Nevada hydroxide or calcium oxide, and a calcium salt (cg. No Drawing. Filed July 28, 1959, Ser. No. 829,956 Claims priority, application Great Britain Aug. 20, 1958 calcium sulphate or calcium chloride) or mixture of cal 2 Claims. (Cl. 23-59) cium salts, in an aqueous medium, and removing the 10 crystals of hydrated calcium metaborate so obtained. This invention relates to the production of crystalline The Word “borax” is used in this speci?cation to denote calcium borates, and more particularly to the production any sodium 1:2-borate, irrespectively of the number of of crystalline calcium 1,1-borate tetrahydrate and hexa molecules of water of crystallisation (if any). hydrate. Reaction is suitably effected at a temperature of 0° C. There is a large potential demand for pure calcium 15 to 100° C., and preferably at a temperature of 25° C. borate hydrates by the glass industry, and also they to 100° C. The pH value of the aqueous medium is are of great interest to the ceramic industry and in steel preferably 11 or higher. manufacture, as an alternative to the use of lime and Sodium hydroxide is the alkali-metal hydroxide nor boric acid. Calcium 1,1-borate (otherwise known as cal mally used, but it may, as already implied, be replaced cium metaborate) has a higher melting point (about 1, wholly or in part by other alkali-metal hydroxides as a 154° C.) than boric acid and sodium borates (the usual source of hydroxyl ions. suppliers of B203 in glass), and 'gives a more uniform The reaction mixture may be seeded with calcium melt when fused with other higher melting point ingredi metaborate tetrahydrate or hexahydrate according to ents. Whether the desired product is the tetrahydrate or the It is known that crystalline calcium 1,1-borate hexa 25 hexahydrate. The production of the tetrahydrate is hydrate may be made by several methods, e.g. by the re favoured by higher temperatures Within the ranges speci~ action in aqueous solution of borax with calcium oxide ?ed above, and when the tetrahydrate is in fact desired or hydroxide in the presence of sodium hydroxide. It is it is preferable to use a temperature above 40° C. also known that calcium l,l-borate tetrahydrate may be The method of the invention may be operated as a made by the reaction of borax and caustic soda in batch process or as a cyclic process. In a cyclic process aqueous solution with calcium hydroxide. the procedure may suitably comprise initially forming Although by using various combinations of sodium alkali-metal metaborate from borax and alkali-metal hy borates and calcium salts pure calcium metaborate can droxide, and then alternately (1) adding calcium hy be produced, the processes are often of low e?iciency in droxide or oxide, the calcium salt(s), and borax to the that comparatively little of the borate ion in the reactants 35 system, and (2) removing crystalline hydrated calcium is converted to calcium metaborate, and much of it may metaborate and one or more alkali-metal salt(s) cor remain as a sodium borate of slightly different responding with the calcium salt(s) used, for example Na2O/B2O3 ratio from the starting materials. Conse in accordance with the equations: quently a cyclic process in which the resultant sodium borate may be reconverted to the initial ratio is required for economic operation. The reaction of borax, sodium hydroxide and calcium hydroxide may be represented by the following equation In a cyclic process in accordance with the invention it (omitting water of hydration): is preferred that the molar proportions of calcium hy 45 éN?zO, 213203 + 6NaOH -\- 2C8(OH)2 = droxide or oxide to the calcium salt(s) should be sub W stantially 1:1, e.g. 0.95:1 to 1.05:1. The various materials used may be added in any order, and they may be used in various physical forms. Thus (Calcium (Sodium metaborate) borate» a solution of borax and alkali-metal hydroxide may for liquor) 50 example be added to a slurry of calcium hydroxide or if the sodium borate liquor is to be recycled, a sodium oxide and the calcium salt(s), or instead ?nely-divided borate having a molar ratio Na2O/B2O3 below 1.0 may calcium hydroxide or oxide and ?nely-divided calcium be added. This is done conveniently and economically salt(s) may be stirred into a solution of borax and alkali by the addition of borax: metal hydroxide. 55 The calcium oxide or hydroxide used should be as freshly calcined or slaked (respectively) as possible, he (Borax) _ should have as low a carbonate content as possible. Also If the borax is added as a solid it is clear that the con both the calcium oxide or hydroxide and the calcium centration of solids in the liquor will be increased, and as sulphate and/or other calcium salt(s) used should be there is a maximum permissible concentration, dilution 60 as ?nely divided as possible (suitably 80~90% of the of the liquor is necessary. The volume of the liquor in material passes a ZOO-mesh British Standard sieve). hand is therefore increased, and as it continues to in— When calcium sulphate is used as the (or a) calcium crease with each successive cycle a manufacturing proc salt, it is. preferred that it should be in the form of ess is not practicable. gypsum. It is of course to be understood that the calci The basic reason for impracticability of a cyclic proc 65 um salts used in the present method as reactants are cal ess involving reaction between sodium borate and calci cium salts other than calcium metaborate. um hydroxide is the rapid build-up of the sodium content As already indicated, sodium sulphate and/ or one or of the solution. We have found that this may be avoided more other alkali-metal salts are formed in the method by adding an anion which combines with the sodium of the present invention together with the hydrated calci ions to give a sodium salt which can be removed by 70 um metaborate. Normally, however, it is convenient that fractional crystallistation. The anion is conveniently in the separation of the alkal-metal salt(s) on the one hand troduced as a calcium salt. Some or all of the calcium and the calcium metaborate on the other hand should be 3,032,391 3 4 consecutive and not concurrent, i.e. it is normally prefer phate dihydrate and 0.5 gram of calcium metaborate able that the hydrated calcium metaborate should be al tetrahydrate “seed” at 18° C. The temperature was in lowed to crystallise out of solution ?rst and that the creased to and maintained at 50° C. for 5 hours, after alkali-metal salt(s) should ‘be removed from solution which the insoluble product was separated and found to subsequently. Usually the separation of the sodium sul be essentially crystalline calcium metaborate tetrahy phate and/ or other alkali-metal salt(s) may be e?ected drate. by an approprate change in temperature (normally a Sodium sulphate was crystallised from the mother reduction, but in the case of sodium sulphate itself either liquor by reducing the temperature to about 20° C. a reduction or increase, sodium sulphate having a maxi Example VI mum solubility at about 33° 0). However, principles 10 and methods of desulphation by removal of sodium sul A solution of the composition given in Example I was phate either as the anhydrous salt or as the decahydrate, added at 55° C. to a slurry containing 7.25 grams of according to temperature, are already well known. calcium hydroxide, 21.3 grams of calcium chloride hexa The invention is illustrated by the following examples. hydrate and 0.5 gram of calcium metaborate tetrahydrate 15 “seed” in 100 ccs. of water at 18° C. The mixture was Example I raised to 50° C. and this temperature was maintained for 150 grams of borax (Na2B4O7JOI-IZO) and 32 grams 5 hours with continuous slow stirring. An insoluble of sodium hydroxide were dissolved in 900 ccs. of water product which separated was essentially crystalline calci at a temperature of 55° C. and added to a slurry‘ com um metaborate tetrahydrate. prising 7.25 grams of ?nely-divided calcium hydroxide, 20 In any of the above examples, the calcium hydroxide 16.75 grams of ?nely-divided calcium sulphate dihydrate and calcium salt may be added in the form of dry ?ne and 100 ccs. of water. The mixture was stirred and 0.5 powders, the volume of the water used for the solution gram of calcium metaborate tetrahydrate added as of sodium hydroxide and borax being increased from 900 “seed.” The mixture was then maintained at a temper to 1000 ccs. to make up for the 100 ccs. used in the slur~ ature of 50° C. for 15 hours, being stirred slowly 25 ries of calcium hydroxide and calcium salt in Examples throughout. At the end of this time all the original cal I~VI.