CS239182B1 - A method of producing calcium carbonate with spherulite crystals - Google Patents

Abstract

Calcium carbonate with a spherulitic crystal form is produced from predominantly calcareous raw materials through the intermediate formation of a solution of calcium formate or acetate, which is a condition for the formation of spherulitic crystals. Usually, after the separation of the undissolved suspension from the solution, calcium carbonate with a spherulitic crystal form is precipitated and separated by treatment with ammonium carbonate and/or carbon dioxide in the presence of a stoichiometric or superstoichiometric amount of ammonia and/or ammonium hydroxide at a temperature of 0 to 90 degrees C. The leaching solution is usually recirculated after replacing losses.

Description

The present invention relates to a process for the production of calcium carbonate in the form of a powder consisting of spherulite crystallites with raw materials mainly consisting of calcium oxide and / or its hydration products, or their precursors mixed with other inorganic and organic admixtures.

Calcium carbonate CaCOs is used in industry both in natural form and synthetic (so-called precipitated), especially alcohol mineral calcite (micronized limestone, floated chalk), less often than aragonite mineral.

The third polyinorphic modification of calcium carbonate, vaterite, occurs very rarely in nature and its industrial production has not been described hitherto as it is a highly volatile substance that transforms more or less rapidly in the environment in which it is produced, depending on the reaction conditions to calcite or to aragonite (Pascal P .: Nouveau Traité de Cbimie Minerals. Tom IV. Paris, Masson et Cie., Éditeurs (1958); Deer WA, Howie RA and Zussman J .: Rock-Forming Minerals. Vol. 5 London Longmans (19-2)).

The vaterite crystals, as opposed to the calcite which forms the convex crystals and from the aragonite which forms the column crystals, are generally spherical in shape. The spherulite appearance is also retained by pseudomorphoses of calcite, formed under appropriate conditions by polymorphic conversion of vaterite. Since vaterite and calcite spherulites can be prepared with different defined grain sizes (e.g. in the range of 0.1 to 10 µm), the spherulite calcium carbonate can be advantageously utilized, e.g., in its use as an isotropic filler in plastic, rubber, dye, paper, pharmaceutical, cosmetics, food and chemical industries.

Although this problem largely solves the way according to MS. However, it does not exhaust all possibilities and does not unequivocally determine the conditions of the type of calcium compound intermediates necessary for the deliberate production of powdered calcium carbonate with a spherulite crystal shape.

According to the invention, the process for producing spherulite-shaped calcium carbonate from predominantly calcium raw materials is carried out by precipitating a spherulite-shaped calcium carbonate (crystals by the action of ammonium carbonate and / or oxide) from a solution of calcium formate and / or calcium acetate. carbon dioxide in the presence of a stoichiometric or above stoichiometric amount of ammonia and / or ammonium hydroxide at a temperature of 0 to 90 ° C, preferably 20 to 70 ° C, and separated, wherein the leaching solution containing ammonium formate and / or acetic acid ammonium salt containing an aqueous solution of ammonia and / or ammonium carbonate is preferably recirculated after loss compensation.

An advantage of the process according to the invention is the production of up to micro-grained calcium carbonate powder in the form of spherulite crystals based on widely available calcium raw materials, including quicklime, often high in silicon, aluminum, iron, as well as falling calcium hydroxide from acetylene production from calcium carbide. ap.

Another advantage is the possibility, depending on the needs, of producing powdered calcium carbonate of predetermined crystals and grain, of high purity, free of chlorides, sulphates or other undesirable anions.

The process according to the present invention is an Lys-closed production cycle without harmful gaseous pollutants or effluents, since the recovered leaching solution containing, for example, either ammonium formate and / or ammonium acetate is returned to production, recirculated, treated to calcare raw material (e.g. calcium hydroxide] to form a formate or calcium acetate, etc.

Suitable inorganic nitrogen bases are ammonia, resp. ammonium hydroxide.

Carbon dioxide can be used as pure, whether in the form of gas or as a solid, so-called carbon dioxide. dry ice, also in the form of an aqueous solution, but most often mixed with other gases, such as carbon monoxide, nitrogen, argon, oxygen, methane, natural gas and the like.

Further details of the method are both in MS. No. 207 300, to which this invention is essentially based and in the following examples.

Example 1

100 wt. parts of calcium hydroxide are fed to 1,500 wt. parts of a warm (20 ° C) aqueous solution containing 2:20 wt. parts of ammonium formate and 20 wt. parts of ammonia. The filtered solution is simultaneously fed with carbon dioxide and ammonia in such a ratio that the reaction medium is low in pH 8 to 9.

Calcium carbonate precipitates from the reaction system at 35 ° C in the form of a spherulite vaterite, which is separated from the solution by centrifugation, washing with 0.5% by weight aqueous ammonium formate under suction and drying at 6 ° C under reduced pressure ( 1.3 kPa] gas atmosphere.

Example 2

1Ό0 wt. parts of quicklime composition

91.1% by weight of calcium oxide, 8.2% calcium carbonate, 0.3% silica, 0.2% alumina, 0.1% iron oxide, ground and sieved through a 0.06 mm sieve, is added in portions of up to 1,650 wt. parts of a warm (20 ° C) solution containing 250 wt. parts of ammonium formate and 1,400 wt. parts of water.

From the solution heated to 54 ° C by reaction heat, the insoluble residue is separated by filtration and from the filtrate cooled to 30 to 40 ° C with concurrently supplied carbon dioxide and ammonia, fed at a rate such that the reaction medium lows pH 8 to 9. The calcium carbonate in the vaterite mineral spherolite is further dried, the vaterite yield reaching 99%. Its specific surface is 9 m ² .g ^-1 .

Under otherwise similar conditions, but using equivalent amounts of ammonium chloride instead of ammonium formate, pure calcium carbonate is again obtained, but in the form of a calcite mineral with a specific surface area of 0.4 m ² . g ^_1 .

Example 3

100 wt. parts of dried waste

2 of lime from the production of acetylene from carbide with a composition of 82.3% by weight of calcium hydroxide, 13.3% of calcium carbonate, 0.3% of calcium. magnesium and 0.1% coke, 1.2% iron oxide are added in portions to 1300 wt. parts of a 40 ° C warm solution containing 245 wt. 0.1 parts by weight of ammonium acetate; parts of ammonium carbonate and 1100 wt. parts of water. From the resulting solution of calcium acetate was removed by filtration, the insoluble residue and the filtrate, at a temperature of 24 ³ C and at a pH of 8 to 9 at the same time by feeding carbon dioxide and ammonia precipitated calcium carbonate as a mineral vaterite. The yield is 118 wt. parts of vaterite containing more than 99% by weight of CaCO3. Decantation of the water is transformed into the vaterite spherulitic pseudomorphs of calcite on the same particle size and the same specific surface area (10.5 m ² .g J ^_1 that precipitated was originally vaterite.

Claims (1)

SUBJECT Process for producing a spherulite-shaped calcium carbonate from predominantly calcium raw materials, characterized in that, as a rule, the spherulite-shaped calcium carbonate and / or carbon dioxide in the presence of ammonium carbonate and / or carbon dioxide is precipitated from the calcium formate and / or calcium acetate solution. of a tric or above-stoichiometric amount of ammonia and / or ammonium hydroxide at a temperature of 0 to 90 ° C, preferably 20 to 70 ° C, and separated, wherein the leaching solution containing the ammonium formate and / or the acetic acid ammonium salt is optionally containing an aqueous solution of ammonia and / or ammonium carbonate, is preferably recirculated after loss compensation.