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UNITED STATES PATENT OFFICE 2,018,955 PROCESS of MAKING CALCUM Sureate Winfieldpatterson, W

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UNITED STATES PATENT OFFICE 2,018,955 PROCESS of MAKING CALCUM Sureate Winfieldpatterson, W w Patented Oct. 29, 1935 2,018,955 UNITED STATES PATENT OFFICE 2,018,955 PROCESS OF MAKING CALCUM surEATE WinfieldPatterson, W. Wilmington,Beckert, Ardentown, Del, assignors and Gordon to Krebs D. Plgment & Color Corporation, Newark, N.J., a corporation of Delaware No Drawing. Application March 27, 1935, serial No. 13.222 16 Claims. (C. 23-122) The present invention relates to processes in or V. M. Goldschmidt's "Geochemische Verteil which calcium sulphate is precipitated from an ungsgesetze der Elemente" publ. Oslo 1926, Wol. aqueous medium and is particularly character VII page 32, who gives a series of ionic radii of ized by the presence in such medium of an agent, rareThe earth fact elements.that the ionic radii of the positive- called restraining agent, which inhibits or re ions effective in retarding crystal growth are of tards the crystal growth of the precipitated cal the same order of magnitude as that of the cal cium sulphate. cium ion (1.05A) may afford an explanation for Such restraining agents can be used in various their effectiveness in that their incorporation O processes of precipitating calcium sulphate from into the Crystal lattice may in Some manner re an aqueous medium, such as for instance in the sult in a deformation or distortion of the crystal action of a calcium compound upon a Sulphate , thus limiting the rate of growth. Furthermore, radical containing compound such as sulphuric the effective ions are also of high Valency which acid or a soluble sulphate, for instance, calcium may also be a contributing factor in influencing s chloride and sodium sulphate, or calcium nitrate their adsorption on certain faces of the growing and ammonium sulphate, or calcium acetate and potassium sulphate or magnesium sulphate, or crystal or actual incorporation in the crystal calcium hydrosulphid and zinc sulphate, in gen lattice.This explanation of. the mechanism of the ac eral in any metathetical reaction of this type. tion of Our novel restraining agent is given as O Our invention is similarly applicable in reactions a theory Only and should in no Way be COnsidered where sulphuric acid is allowed to act upon a as limiting our invention. It is supported on calcium compound such as calcium carbonate, the one hand by the fact that every compound lime, CaO, hydrated lime, or a decomposable cal containing a positive ion of an ionic radius of cium salt such as calcium chloride, etc. From at least 1.0 but less than 1.20 and a valency 25 a practical standpoint the use of our novel re greater than 2 which has been tested by us shows straining agents is particularly useful in the re an inhibiting or restraining effect on the crystal actions between sulphuric acid and lime, CaO; growth of calcium sulphate whereas no com calcium hydroxide, Ca(OH)2; and calcium car pound outside this range was found to be effec bonate, CaCO3. w tive and on the other hand, it was found that 80 The manner in which the calcium sulphate in some instances traces of the restraining agent has been formed seems to be of no influence upon had been adsorbed or otherwise associated with the action of the restraining agent, which seems the calcium sulphate precipitated in the presence to function entirely during the contact of the of such an agent. originally formed calcium sulphate particles with This is particularly noticeable with cerium 35 the aqueous medium from which the sulphate salts, which are detectable in calcium sulphate was precipitated. The action is noticeable in precipitated in the presence of such a salt. alkaline, neutral or acid media, though it is most Small, amounts of cerium salts do not notice pronounced in the latter which in the absence ably affect the color of the calcium sulphate of such restraining agents favor crystal growth. precipitated. When large amounts of cerium to Our novel restraining agents function as Crys salts, particularly tetravalent cerium salts, are tal growth inhibitors for the various calcium Sul adsorbed on the calcium sulphate, the resulting phate modifications such as gypsum (the di product is slightly colored, the colors ranging hydrate) and plaster of Paris (the hemi-hy from cream to sienna, and such colored calcium drate) which can be obtained by precipitation sulphate can be used to advantage as extenderss from aqueous media, and is particularly pro for other colored pigments. nounced for such of the calcium sulphate modi Similarly thorium compounds tend to be aSSO fications which are precipitated in an acicular ciated with the calcium sulphate precipitate. crystalThe form.restraining agents of Our invention are Compounds, which due to their commercial compounds which in aqueous solution form posi availability and effectiveness are particularly 50 tive ions which have an ionic radius of at least useful in our invention are compounds of tetra 10 but less than 1.2 Angstrom units and which valent thorium, cerium and uranium. A some have a valency greater than 2. what lesser efficiency are compounds of trivalent The data relative to ionic radii can, for in cerium and thallium or of other rare earth stance, be found in the 2nd Edition of Wyckoff's “The structure of Crystals", pages 192 and 193, metals, 2 2,018,955 below:The ionic radii of such elements are given alkalinity of the reaction medium have a marked influence upon the size of the calcium sulphate Ions within the abose limits particles produced. However, in all cases the addition of our restraining agents decreases the Ionic particle size of the resulting calcium sulphate, t in It is in general the experience that calcium units Sulphate of smaller crystal size is produced in a neutral medium such as in the reaction between a calcium salt and a sulphate such as calcium chloride and sodium sulphate, than in an acid ( medium. In cases where conditions are such that a product of relatively Small Crystal size is pro duced the effect of the restraining agent, al though very evident, is not as pronounced as in s Systems which foster rapid Crystal growth of the in the following table we list the ionic radii product. In order to actually evaluate and de of a number of other elements in various valency termine the true effectiveness of a specific agent stages. These are all outside the limits which we it is necessary to prepare a product following 20 found make the ions available in Our inventiton. a specified procedure both in the presence and These have been tested by us and it was in each absence of the restraining agent. 20 instance found that these ions had no influence We are describing in the following examples a upon the growth of calcium sulphate crystals. few of the operations in which we used our novel restraining agents for the preparation of calcium 25 ineffective ions Sulphate precipitates of Small crystal size. Eacample 1-A lime suspension was made by 25 Radius mixing 466 grams of hydrated lime to give a total on in A volume of 3 liters. This suspension was pebble units mill ground to obtain thorough and uniform dis integration. This suspension of calcium hydroxide was then 30 added slowly with constant agitation to 16.32 lbs. of an aqueous Sulphuric acid of 16.5% SO4 con taining 1.75 grams of raw rare earth metal com pounds figured as oxides, of which 0.60 grams were U2O5, 0.30 grams CeO2 and 0.10 grams Thoz. 25 Calcium sulphate precipitated. It was filtered and dried. It was of acicular form and the indi Our novel restraining agents are effective in vidual crystals were in the average noticeably amounts of from about 0.1 mol per cent of the smaller than the crystals obtained in the same element based on the calcium sulphate present, manner from a sulphuric acid which did not con- 40 up to the solubility of their sulphates in the re tain rare earth metal compounds. action mixture. From 0.2 to about 2 mol per Eacample 2-250 grams of a calcium hy cent of the effective element is the amount pre droxide suspension corresponding to 50 grams 45 ferred for commercial operations, though higher CaO was added while stirring to an 8%. Sull amounts can be used without noticeable disad phuric acid solution containing 2.2 grams cerous 6.5 vantage. oxalate. Calcium sphate in the form of very The effect of the agent is not manifest in exactly fine needles Was obtained. The amount of the same way in every case and for different types cerous oxalate present corresponded to 0.69 mol 50 of preparation. It was, for instance, found that per cent of Ce. in the use of a sulphuric acid solution containing Eacample 3-454 grams of an acid containing 0 small amounts of thorium an apparent change 19.0% SO4 and in composition entirely similar of crystal shape as well as size was noted. The to that of Example 1, was slowly added with smaller amounts of the agent caused the forma constant stirring to 200 grams of a 50% solu tion of needle-like crystals which appeared iden tion of CaCla. A very fine acicular calcium Su tical in shape with those formed with pure acid phate was formed. s but which were Smaller. By increasing the The amount of restraining agent present fig amount of thorium not only needle-like crystals ured in the same manner as in Example, 1 cor were formed, but in addition some broad, plate responded to 0.26 mol per cent. 80 like crystals began to appear.
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