Chemistry of inorganic compounds – Carbon or compound thereof – Oxygen containing
Patent
1997-10-22
2000-03-14
Griffin, Steven P.
Chemistry of inorganic compounds
Carbon or compound thereof
Oxygen containing
423432, C01F 524
Patent
active
060369337
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to methods for producing crystalline materials by precipitation. According to one aspect of the invention it relates to the production of precipitated calcium carbonate. The invention thus relates particularly, but not exclusively, to the production of high purity calcium carbonate from relatively impure calcium source material.
BACKGROUND TO THE INVENTION
Calcium carbonate is a natural carbonate which is present in large quantities particularly in calcitic and dolomitic limestone. In raw impure form these products are used in various industries including the mining and cement industries. In purified crystalline form calcium carbonate is used in the production of paint, in toothpaste, paper coating and sizing and as an acid neutraliser or as a filler in pharmaceutical products, amongst other applications.
Despite the natural abundance of calcium carbonate as such pure calcium carbonate is a relatively expensive product due to the difficulties and expenses associated with conventional purification methods.
OBJECT OF THE INVENTION
It is an object of the present invention to provide a new method for producing precipitated calcium carbonate from a natural source material containing calcium values.
EP-A-49666 [Kalk Chemische Fabrik] teaches the preparation of calcium carbonate [vaterite] by reaction of a calcium ion containing aqueous solution with carbonate ions containing aqueous solution. Preferred are the use of a solution containing calcium nitrate and a solution of ammonium carbonate.
Chemical Abstracts, AN: 116:258510H of CN-A-1055718 [Zou et al] discloses the preparation of calcium nitrate from calcined [dolomite] ores [i.e. lime] by impregnation of the calcination product with ammonium nitrate solution. The resultant calcium nitrate solution is used for the preparation of calcium carbonate by carbonisation with CO.sub.2 -containing air.
WO-A-7900931 [Anderson] discloses a process for the preparation of white liquor for the sulphate pulping process, wherein quicklime is slaked with green liquor and the slaked lime formed is reacted with the sodium carbonate in the green liquor to sodium hydroxide in a causticizing process, the lime sludge formed being separated. According to that invention, the process from the slaking of the lime up to the separation of the white liquor and the lime sludge is carried out at a pressure above the atmospheric pressure. In a preferred embodiment, the process is also carried out at a temperature above the normal boiling temperature of the system.
SUMMARY OF THE INVENTION
According to the invention there is provided a method for producing precipitated calcium carbonate by reacting an aqueous solution of calcium nitrate [Ca(NO.sub.3).sub.2 ] with an aqueous solution of ammonium carbonate [(NH.sub.4).sub.2 CO.sub.3 ] and allowing calcium carbonate to precipitate from the resultant mixture containing nitrate [NH.sub.4 NO.sub.3 ] in the mother liquor, the process being characterised in that processes is prepared by slaking lime [CaO] in water in the presence of ammonium nitrate [NH.sub.4 NO.sub.3 ] to form calcium nitrate [Ca(NO.sub.3).sub.2 ] and ammonium hydroxide [NH.sub.4 OH] in solution, filtering the solution to render it solids free, and heating the filtrate to dissociate the ammonium hydroxide [NH.sub.4 OH] and to drive ammonia gas [NH.sub.3 ] from the solution; prepared by absorbing ammonia gas [NH.sub.3 ] and carbon dioxide gas in water, the ammonia gas preferably being derived from the step in [i] above in which the Ca(NO.sub.3).sub.2 solution is heated; during which calcium carbonate is precipitated from the mother liquor containing ammonium nitrate.
The precipitation reaction between the two reagent solutions which react to form the precipitated CaCO.sub.3 is preferably performed by feeding the solutions into intimate contact with one another in a contact zone of a reactor arrangement and immediately displacing the mixture from the contact zone, and allowing the resultant crystalline reaction product to precipi
REFERENCES:
patent: 2535999 (1950-12-01), Bouchard
Zou et al., "Manufacture of Magnesium Oxide and Calcium Carbonate", Chem. Abstracts., 116:26, 178, abstract No. 258510h, Oct. 1991.
Dmitrievskii et al., "Manufacture of Calcium Carbonate" Chem. Abstracts, 114:6, 175, abstract No., Feb. 45999w (1991).
Gomersall John Edward
Griffin Steven P.
Heiman Lee C.
Hendrickson Staurt L.
Nath Gary M.
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