CS240530B1 - Gassing) of pure calcium carbonate with spherulite shape; crystals - Google Patents

Abstract

Calcium carbonate is precipitated from a solution of calcium formate or calcium acetate, either by the action of the carbonate of at least one organic nitrogen base, or also by carbon dioxide in the presence of a 100% or greater amount of at least one organic nitrogen base; at a temperature of 0 to 90 °C. The method is particularly suitable for the production of up to micro-grained calcium carbonate, required for the production of honeycomb fillers and the like.

Description

The invention relates to a process for the production of pure calcium carbonate from calcium oxide and / or its hydration products in the form of a spherulite crystal powder.

Calcium carbonate is used in industry both in natural form and synthetic (so-called precipitated), mainly as mineral calcite (micronized limestone, floated chalk), less often than mineral aragonite. The third polymorphic modification of calcium carbonate, vaterite, occurs only very rarely in nature and its industrial production has not been described to date, as it is a highly volatile substance which, in the environment in which it is produced, transforms more or less rapidly into calcite or argonite [Pascal P .: Nouveau Traité do Chimie Minérale. Tom IV. Paris. Masson te Cie., Editeurs (1958); Decr W. A., Howie A. A., and Zussman J .: Rock-Forming Minerals. Vol. 5. London Longmans (1962)]. The vaterite crystals, as opposed to the calcite, which usually consists of gemstones, and from the aragonite, which consists of columnar to fibrous crystals, are generally spherical in shape. The pseudomorphoses of calcite also form a spherolithic appearance. under suitable reaction conditions by polymorphic conversion of vaterite. Since the 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 used, for example, as an isotropic filler or additive in plastic, rubber, dye, pharmaceutical, cosmetic , food and chemical industries. It is known that spherical fillers, unlike sharp edge and corner fillers, have little effect, for example on the viscosity of the matrix, and because they do not cause uneven distribution of stresses around the particles, improve the mechanical properties of composite materials (Katz HS and Milewski JV: Handbook of Fillers) and Reinforoements for Plastics (New York, Van Nostrand Reinhold Company, 1978).

However, these processes do not solve the production of calcium carbonate in the form of fine spherulite crystals.

However, according to the invention, the process for producing spherulite-shaped calcium carbonate can be carried out by precipitating calcium carbonate from a solution of calcium formate and / or calcium acetate by the action of an organic nitrogen base (s) carbonate and / or carbon dioxide in the presence of at least a stoichiometric amount of organic nitrogen base. or bases at a temperature of 0 to 90 ° C, preferably 20 to 70 ° C.

The advantage of the process according to the invention is not only the possibility of producing pure calcium carbonate, preferably in the form of a powder, but also of the desired structure, depending on the intended application of the spherulite crystal powder. Another advantage is the possibility to industrially produce up to micro-grained vaterite with a specific surface area of about 10 m, ² . g ¹ and, last but not least, the possibility of highly technically and economically valorizing the widely available, even falling off lime raw materials from various production plants.

For such production of pure calcium carbonate in the form of a spherulite crystal powder, it is of particular importance that the starting calcium raw material or intermediate is calcium formate and / or calcium acetate. Most often it is calcium oxide and / or calcium hydroxide together with other inorganic and organic additives, in which calcium oxide or its hydration products are usually converted into solution by the action of a leaching solution. The leaching solution can also be recirculated.

Further advantages and details of the method according to the invention are also evident from the examples.

Example 1

Aqueous solution containing 100 wt. parts of calcium formate, 100 wt. parts of monoethanolamine and 700 wt. parts of water are precipitated with carbon dioxide at 30 ° C with stirring. After reaching pH 7.5, the formed calcium carbonate as a spherulite vaterite is separated by filtration and washing with distilled water with suction and drying at 80 ° C. The obtained vaterite powder has a specific surface area of 10.61 m ² . g ^_1 . Under otherwise similar conditions, but using calcium chloride instead of calcium formate, a calcite powder having a specific surface area of 0.43 m ^{2 is obtained} . • g ' ¹ ·

Example 1 a d 2

Aqueous solution containing 100 wt. parts of calcium formate, 140 wt. parts of diethanolamine and 700 wt. parts of water are precipitated with carbon dioxide at 45 ° C with stirring. After reaching pH 8, the precipitated calcium carbonate is separated by centrifugation and washing with demineralized water, the residual soluble impurities are removed from the solid phase by decanting with demineralized water, and the calcium carbonate precipitate in the form of a spherulite calcite is dried at 200 ° C.

Example 3

To a solution containing 100 wt. parts of calcium acetate and 400 wt. parts of water at 15 ° C with stirring is added a solution prepared by reacting diethanolamine (130 parts by weight) dissolved in water (200 parts by weight) with carbon dioxide (final pH of the solution is 7.5) until the calcium carbonate precipitates completely. in the form of a spherulite vaterite, which is separated from the solution by filtration and washing with demineralized water in a filter press and drying at 100 ° C.

Claims (1)

SUBJECT Process for producing pure calcium carbonate having a spherulite crystal shape, characterized in that the calcium carbonate is precipitated from a solution of calcium formate and / or calcium acetate by the action of carbonate to find an organic nitrogen base or bases and / or carbon dioxide in the presence of at least a stoichiometric amount of organic nitrogen or bases base at a temperature of 0 to 90 ° C, preferably 20 to 70 ° C.