RU2010003C1 - Method of calcium fluoride production - Google Patents

Abstract

FIELD: chemical technology. SUBSTANCE: aqueous suspension of calcium carbonate is treated with hexafluorosilicic acid solution by two stages. At the first stage treatment is carried out with a mixture of hexafluorosilicic acid and clarified solution obtained from the second stage. Precipitate is separated and treated with hexafluorosilicic acid taken at concentration 20-50% of stoichiometrically required at 40-80 C. Obtained calcium fluoride has, wt. -% : CaF₃ 95.6-98.6; CaCO₃ 0.2-0.6, and SiO₂ 0.8-1.2. Utilization degree is 94.7-95.0% . Method is used in hydro- gen fluoride reprocessing. EFFECT: improved method of production. 1 tbl

Description

 The invention relates to the technology of inorganic substances, in particular calcium fluoride from solutions of hydrofluoric acid.

A known method of producing calcium fluoride [1], including the interaction of 2.5-6.0% aqueous solution of hexafluorosilicic acid with ground calcium carbonate at a temperature of 1.7-54.5 ^about With and pH 3.5-6.7 with subsequent separation of the precipitate by filtration, washing and drying. The product contains 93-96% calcium fluoride and 4-7% silicon dioxide.

 The disadvantage of this method is the high content of silicon dioxide in the finished product.

In order to improve the quality of the calcium fluoride is provided a method [2], according to which the hexafluorosilicic acid solution having a concentration of not more than 4% is mixed with pulverized calcium carbonate, taken in an amount of not more than 85% from stoichiometry, at a temperature of 2-38 ^{° C} and pH 3, 5-5 for about 2 hours. The product contains 97-99% calcium fluoride and about 0.5% silicon dioxide. The disadvantages of the method include a low, not more than 85%, fluoride yield.

The closest in technical essence to the proposed is a method of producing calcium fluoride [3], in which an aqueous suspension of calcium carbonate is mixed with a solution of 5-30% hexafluorosilicic acid, taken in an amount of 101.5-117.6% of stoichiometry, at pH medium 2-3, and in the second stage at a temperature of 20 ^about With the pulp is mixed with calcium carbonate in an amount necessary to neutralize up to 9.9% of excess H ₂ SiF ₆ . The precipitate was separated from the suspension by filtration, washed and dried. The resulting product contains 93-95% calcium fluoride and 2-4% silicon dioxide.

The disadvantage of this method is the high content of impurities SiO ₂ .

 The aim of the invention is to reduce the content of impurities in the product while maintaining a high degree of fluorine utilization.

The goal is achieved a two-step treatment with aqueous calcium carbonate solution geksaftorkremnevoy acid slurry in the first stage treatment is carried out with a mixture geksaftorkremnevoy acid and the clarified solution from the second stage, and then the precipitate from the first stage is treated at a temperature of 40-80 ^{° C} geksaftorkremnevoy acid taken in an amount of 20- 50% of stoichiometry with a total consumption of hexafluorosilicic acid 103-105%.

At temperatures below 40 ^C in a second process stage the processing time increases significantly, and at a temperature above 80 ° ^C increase loss geksaftorkremnevoy acid with purge. A decrease in the consumption of hexafluorosilicic acid less than 20% in the second stage does not improve the quality of the resulting calcium fluoride, and an increase in the flow rate above 50% from stoichiometric to the initial calcium carbonate leads to an increase in energy consumption for heating hexafluorosilicic acid.

 The technological parameters of the first stage of the process are due to the need to stabilize the silicic acid sol formed in the process and do not fundamentally differ from the conditions of analogues and prototype.

Branch precipitation at stages of the process carried out by known methods - sludge or filtration and drying the precipitate is carried out at a temperature of 110-160 ^C. The product obtained contains 95-98% of calcium fluoride, 0.5-1.0% silicon dioxide and 0.2 -0.5% carbonate with a degree of fluorine utilization of 94.5-95%.

The distinctive features of the proposed method is the treatment of calcium carbonate in the first step a mixture geksaftorkremnevoy acid and clarified solution with the second-stage treatment of sludge produced in the first step, geksaftorkremnevoy acid taken in an amount of 20-50% of stoichiometry, at a temperature of 40-80 ° ^C.

 Comparison of the claimed technical solution with the prototype and other known technical solutions showed that similar features are not known, which allows us to conclude that the criterion of "significant differences".

PRI me R 1. In a reactor with a capacity of 2 m ³ with a mixing device, 100 kg of chalk containing 98.5% CaCO ₃ are charged, industrial water is supplied and a suspension of T: L = 1: 4 is prepared. Then, 645.42 l are supplied clarified solution containing 0.4% H ₂ SiF ₆ and the 172.33 l of 20% geksaftorkremnevoy acid solution and stirred for 30 min at 20 ^C. The resulting suspension was concentrated in a settling tank to T: l = 1: 2, the clarified part is sent to neutralization, and the lower discharge is fed to another reactor and subjected to processing for 30 minutes at a temperature of 80 ^about 40.55 l of 20% a solution of hexafluorosilicic acid, which is 20% of the stoichiometrically necessary calculated on the basis of the initial calcium carbonate. The pulp is thickened in a sump to T: W = 1: 2 and repulped with 500 l of circulating water in order to wash the sludge, after filtering the sludge is dried at a temperature of 120 ^o C.

The clarified part from the stage of repeated treatment of calcium carbonate with hexafluorosilicic acid and the filtrate from the stage of repulpation are mixed with a 20% solution of H ₂ SiF ₆ and sent to the first stage of obtaining calcium fluoride. The result is 77.533 kg of synthetic calcium fluoride with a content of CaF ₂ 98.5%, SiO ₂ 0.9%, CaCO ₃ - 0.2%. The degree of fluorine use is 95.08%. The total consumption of a 20% solution of hexafluorosilicic acid was 212.88 L at a density of 1.166 kg / L or 49.644 kg of 100% H ₂ SiF ₆ , which is 105% of the stoichiometrically necessary for the conversion of calcium carbonate in the feed.

 Experiments 2-7 were carried out by a similar method, the results are presented in the table.

 Experiment 8 was conducted according to the prototype method for comparing the quality of the resulting product.

A comparison of the results presented in the table shows that the quality of calcium fluoride obtained by the claimed method is higher than the product of the prototype method, since the content of the basic substance is 95.6-98.6% versus 92.3%, the impurity of SiO ₂ decreases up to 0.9-2.2% against 4.8%, while the degree of fluorine use remains at the level of the prototype method (94.7-98.0, against 94.3). (56) 1. U.S. Patent No. 2,780,521, cl. C 01 F 11/22, 1957.

 2. US patent N 2780523, CL. C 01 F 11/22, 1957.

 3. Application of Germany N 2307897, cl. C 01 F 11/22, 1974.

Claims (1)

METHOD FOR PRODUCING CALCIUM FLUORIDE, including treating a suspension of calcium carbonate with a solution of hexafluorosilicic acid, taken in an amount of 103 - 105% of stoichiometrically necessary, separating, washing and drying the product sludge, characterized in that, in order to reduce the high content of the content fluorine and treatment are carried out in two stages: first, a suspension of calcium carbonate is treated with hexafluorosilicic acid, taken in a mixture with a clarified solution from the second stage of treatment, the precipitate is separated, and ATEM last obpabatyvayut geksaftopkpemnievoy acid taken in an amount of 20 - 50% of stehiometpicheski necessary, at 40 - 80 ^o C, after which ppoduktsionny precipitate is separated and clarified pastvop shall send at step obpabotki appeared first.

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