RU2214966C1 - Method for preparing calcium oxide - Google Patents

Abstract

FIELD: inorganic chemistry, chemical technology. SUBSTANCE: concentrate of isotope- -enriched calcium is dissolved in hydrochloric acid, solution is purified from impurities by precipitation of calcium oxalate in ammonia medium in the presence of tartaric acid, impurities of heavy metals are precipitated and separated as sulfides. From prepared solution calcium oxalate is precipitated repeatedly in ammonia medium in the presence of tartaric acid and calcium oxalate is dissolved in acid. Calcium carbonate is precipitated from purified solution with ammonia solution saturated with ammonium carbonate and calcium carbonate is separated and subjected for thermal treatment for two steps at 200-300 C and 800-850 C. Method for purification of calcium-containing concentrate provides rather complete separation of impurities and isolation of calcium without loss practically. Conditions for thermal treatment allows preparing the required chemical form of ready product. Proposed method provides isolation of 99.3% of isotope-enriched calcium as oxide with purification degree 99.96%. Method allows using standard equipment, available reagents being without significant consumption of electric energy. Method can be used for treatment of isotope-enriched calcium prepared by method of electromagnetic separation. EFFECT: improved preparing method, high yield and quality of product. 6 ex

Description

 The invention relates to the field of separation and purification of calcium oxide, including isotopically enriched obtained by electromagnetic separation.

 The principles of the separation and purification of isotopically enriched calcium is its maximum isolation at all stages of chemical processing and its production in the form of oxide containing a minimum amount of impurities.

A known method of producing pure calcium oxide ("Guide to inorganic synthesis", edited by G. Brauer. -M .: Mir, 1985, t.3, p. 996), including the dissolution of calcium carbonate in nitric acid, cleaning the solution in two stages - precipitation of the main amount of impurities by adding milk of lime to the solution and separating traces of impurities by precipitation of a part of calcium carbonate by passing CO ₂ into a hot solution at pH 6-7, precipitation from a purified solution of calcium carbonate, separation of the precipitate and its heat treatment at 800 ^o C.

The disadvantages of this method when using it to obtain isotopically enriched calcium oxide are:
- use for cleaning a solution of milk of lime, because natural calcium contained in the reagent will change the isotopic composition of calcium in the finished product;
- significant loss of calcium in the separation of traces of impurities.

 There is also known a method of purifying a solution of calcium nitrate (RF patent 1154206, C 01 F 11/36), comprising treating the solution with a mixture of hydrogen peroxide and ammonia and separating the precipitate of hydroxide impurities.

 The disadvantage of this method is the inability to clean from impurities of magnesium, aluminum and copper, which do not precipitate under these conditions.

Closest to the claimed technical solution is a method for producing purified calcium oxide from a concentrate (SU 767031, C 01 F 11/06, 04/03/78), including firing carbonate raw materials, previously aged at 100 ... 800 ^o C for 0.5 -1.2 h and treated with an aqueous solution containing calcium chloride and alcohol, followed by separation and feeding the solid phase for firing.

The disadvantages of this method when using it to obtain isotopically enriched calcium oxide are as follows:
- to obtain calcium oxide of a satisfactory degree of purification is possible only when using pure carbonate raw materials, while the initial concentrate for the production of isotopically enriched calcium oxide contains a significant amount of impurities that, when using this method, will be transferred to the final product (CaO);
- significant loss of calcium in the processing of carbonate raw materials, previously aged at 500-800 ^o With an aqueous solution due to the dissolution of calcium oxide, partially formed during heat treatment of carbonate.

 An object of the invention is to obtain calcium oxide containing a minimum amount of impurities with minimal calcium loss at all stages of chemical processing.

The task is achieved in that the concentrate is dissolved in hydrochloric acid, the solution is cleaned of impurities by precipitation of calcium oxalate in ammonia in the presence of tartaric acid, the precipitate of calcium oxalate is separated, calcined, the calcined calcium oxalate is dissolved at pH 2-3, precipitated and separated impurities of heavy metals in the form of sulfides, calcium is re-precipitated from the resulting solution in an ammonia medium in the presence of tartaric acid, calcium oxalate is dissolved in acid, and calcium carbonate is precipitated from the purified solution I ammonia solution, saturated ammonium carbonate, calcium carbonate precipitate is separated and subjected to heat treatment in two stages at 200-300 ^o C and 800-850 ^o C.

 A further increase in the temperature of the second stage of heat treatment is impractical, since this does not improve the results achieved, but increases the cost of electricity.

 In the claimed technical solution, the proposed method for cleaning the solution provides effective separation of impurities and obtaining a pure product with virtually no loss, and the heat treatment conditions allow to obtain calcium oxide, not containing an admixture of carbonate.

 The analysis of publicly available sources of information on the level of technology did not allow to identify a technical solution identical to the declared one, on the basis of which a conclusion is made about the unknownness of the latter, i.e. compliance presented in this application of the invention with the criterion of "novelty."

 A comparative analysis of the claimed technical solution with known technical solutions revealed that the presented set of distinctive features is unknown to a person skilled in the art, on the basis of which it is concluded that the invention presented in this application meets the criterion of "inventive step".

 The proposed method for producing calcium oxide was implemented as follows.

 Example 1

20 g of a concentrate containing 1.85 g of calcium and a significant amount of impurities, including copper, iron, chromium, lead, magnesium, aluminum and manganese, were dissolved in HC1 (1: 4) when heated. Tartaric acid was added to the solution at a rate of 15 g / l, ammonia to pH 10-11 and oxalic acid at a rate of 2.6 g per 1 g of calcium with an excess of 10 g / l. After the solution was sedimented for 10-16 hours, the precipitate of calcium oxalate was filtered off and the filtrate was analyzed for calcium content. It was less than 0.2 mg / L. The precipitate was calcined at 600 ^{° C.} and dissolved by adding hydrochloric acid to its aqueous suspension to pH 2-3. Heavy metal sulfides precipitated in the solution, passing gaseous H ₂ S for 30 min, and the precipitate of impurities was filtered. Tartaric acid was added to the solution at a rate of 5 g / L, ammonia to pH 10-11 and oxalic acid at a rate of 10 g / L. After setting the solution with the precipitate for 10-16 hours, the precipitate of calcium oxalate was filtered and calcined at 600 ^o C, the oxalate filtrate was analyzed for calcium content. It was <0.2 mg / L.

 The precipitate was dissolved in Hcl, adding it to a pH of 2-3. An ammonia solution (1: 2) saturated with ammonium carbonate was added to the solution to pH 11-12. The solution with the precipitate was thoroughly mixed and stood for 10-16 hours. The precipitate was filtered off and the filtrate was analyzed for calcium content. It was 2 mg / L.

Heat treatment of the precipitate was carried out first at 300 ^o C for 6 hours, and then at 850 ^o C for 6 hours to constant weight. Calcium oxide was analyzed for impurities and calcium carbonate. The impurity content was 0.021%. Calcium carbonate in the obtained product was not detected.

 Example 2

Calcium oxide was obtained as in example 1, but the second stage of heat treatment was carried out at 800 ^o C.

 The calcium content in the oxalate and carbonate filters was 0.2 mg / L and 2.6 mg / L, respectively. The amount of impurities in calcium oxide was 0.026%. Calcium carbonate in the obtained product was not detected.

 Example 3

Calcium oxide was obtained as in example 1, but the second stage of heat treatment of the precipitate of calcium carbonate was carried out at 750 ^o C. the Calcium content in the oxalate and carbonate filtrates was <0.2 mg / l and 3.2 mg / l, respectively. The amount of impurities in calcium oxide was 0.034%. The content of calcium carbonate is 0.97%.

 Example 4

 Calcium carbonate was obtained as in example 1, but did not carry out the deposition of sulfides of heavy metals. The calcium content in the oxalate and carbonate filtrates was <0.2 mg / L and 2.6 mg / L, respectively. The amount of impurities in calcium oxide was 0.904%, including 0.877% of lead. Calcium carbonate in the obtained product was not detected.

 Example 5

 Calcium oxide was obtained as in example 1, but the calcined precipitate of calcium oxalate was dissolved in excess hydrochloric acid to pH 1.

 The calcium content in the oxalate and carbonate filtrates was <0.2 mg / L and 3.4 mg / L, respectively. The amount of impurities in calcium oxide was 0.121%, including 0.091% manganese. Calcium carbonate in the obtained product was not detected.

 Example 6

 Calcium oxide was obtained as in example 1, but did not re-precipitate calcium oxalate in ammonia in the presence of tartaric acid, separating the precipitate, calcining it and dissolving in hydrochloric acid. The calcium content in the oxalate and carbonate filtrates was <0.2 mg / L and 2.8 mg / L, respectively. The amount of impurities in calcium oxide was 0.162%. Calcium carbonate in the obtained product was not detected.

 The proposed method for producing calcium oxide was tested in the production of stable isotopes. He allowed to isolate 99.3% of isotopically enriched calcium in the form of oxide with a purity of 99.96%.

 The proposed method allows the use of standard equipment, cheap and affordable reagents, does not require large energy consumption. The method is suitable from an environmental point of view, since the resulting ammonia filtrates are easily neutralized by acid.

Claims (1)

A method of producing calcium oxide from a concentrate, characterized in that the concentrate is dissolved in hydrochloric acid, the solution is cleaned of impurities by precipitation of calcium oxalate in ammonia in the presence of tartaric acid, the precipitate of calcium oxalate is separated, calcined, the calcined calcium oxalate is dissolved at pH 2-3, precipitated and impurities of heavy metals in the form of sulfides are separated, from the resulting solution re-precipitation of calcium oxalate in ammonia in the presence of tartaric acid is carried out, calcium oxalate is dissolved in acid, precipitated purified solution of calcium carbonate with a solution of ammonia saturated ammonium carbonate, calcium carbonate precipitate is separated and subjected to heat treatment in two stages at 200-300 ^o C and 800-850 ^o C.