RU2412906C1 - Method of producing high-purity barium carbonate - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to production of highly pure carbonates of alkali-earth metals used in optical glass manufacturing and fibre optics. To obtain barium carbonate, first, initial barium nitrate solution undergoes pre-treatment with aluminium nitrate in amount of 2% of the weight of anhydrous barium nitrate and with alkali to pH 8.0-8.3, followed by separation of the solution from the precipitate. Barium carbonate is then chemically deposited from the cleaned barium nitrate solution using carbon dioxide gas which is fed into the reactor simultaneously with the cleaned barium nitrate solution and a stream of ammonia gas or its aqueous solution. Chemical deposition is carried out using stoichiometric amounts of reagents, temperature of 42-45°C, pH 7.8-8.2 and while stirring the reaction mixture at 900-1000 rpm. The obtained product is separated via filtration, washed with clean water and dried at 115-125°C.

EFFECT: invention increases efficiency of the process of producing barium carbonate and purity of the obtained product.

2 cl, 4 ex

Description

The present invention relates to methods for producing alkaline earth metal carbonates, in particular high purity barium carbonate, which can be used as a starting product in the chemical industry, optical glassmaking, in the manufacture of oxide ceramics, conductive materials and other technical fields.

One of the requirements for barium carbonate used in the above areas of technology is a high degree of purity and the minimum possible content of limited impurities.

A number of known methods for producing barium carbonate, limited by the content of chlorine and sulfur. For example, it is known to obtain barium carbonate with a low content of chlorine and sulfur impurities by treating an aqueous suspension of barium sulfide with dilute nitric acid at 60-70 ° C, then treating the resulting suspension with steam at 85-95 ° C, and treating the resulting purified solution of barium nitrate sodium carbonate to form a precipitate of barium carbonate (RU 2096329, C01F 1/18, 1997), containing a mass fraction of chlorides in terms of chlorine ion at the level of 0.003%, mass fraction of total sulfur in terms of SO ₄ -ion -0.15% . The main disadvantage of this method, as noted in another patent (RU 2195428, C01F 11/18, 2002), is the insufficiently complete separation of barium in a barium-containing solution due to the partial oxidation of barium sulfide and the formation of insoluble sulfate. In addition, the barium carbonate obtained by the considered method contains impurities of other alkaline earth elements and impurities of sodium, which does not allow to achieve a high degree of purity and to obtain a product of high purity. Barium sulfide as a feedstock is proposed in another known method for producing barium carbonate (RU 1373686, C01F 11/18, 1991). An intermediate in this method is barium chloride obtained by treating barium sulfide with hydrochloric acid, the aqueous solution of which is then treated with sodium carbonate. The product obtained by the last cited method is also contaminated with impurities of sodium and, in addition, impurities of heavy metals.

Barium carbonate, limited by the content of a number of impurities, is obtained by another known method (RU, 2195428, C01F 11/18, 2002), where barium sulfate is used as the starting product, which is alloyed with a mixture of soda, oxalic acid and sodium nitrate and washed with water. Then, the resulting barium-containing concentrate is treated with 20-23% nitric acid to form a solution of barium nitrate, which is subjected to further purification. For this, an aqueous solution of barium nitrate is evaporated to form a wet salt, which is then washed with concentrated nitric acid and dissolved in water. Then, barium carbonate is precipitated from the purified solution of barium nitrate by adding to it a saturated solution of ammonium carbonate in ammonia with a concentration of at least 5%. Barium carbonate obtained by this method contains a total of 0.013% impurities, including 0.005% Ca and 0.0011% Sr. The main disadvantage of this method, selected as a prototype, is the low degree of purity of the obtained barium carbonate, which does not meet the requirements for products for optical glassmaking and fiber optics.

Barium carbonate having a high degree of purity, corresponding to the requirements for highly pure products for optical glass melting and fiber optics, is obtained in a new highly efficient way. A new method for producing highly pure barium carbonate involves pretreating an initial aqueous solution of barium nitrate with 2% aluminum nitrate, based on the weight of anhydrous barium nitrate, and with alkali to pH 8.0-8.3, followed by filtration separation of the solution from the precipitate, subsequent chemical precipitation of barium carbonate from the purified solution of barium nitrate with a carbonizing agent, which is used as gaseous carbon dioxide, which is introduced into the reactor simultaneously with the flows of the purified solution waste of barium, gaseous ammonia or its aqueous solution, and the chemical deposition process is carried out using stoichiometric amounts of reagents, a temperature of 42-45 ° C, pH 7.8-8.2 and a stirring speed of the reaction mixture 900-1000 rpm, after which the precipitated product is filtered off, washed with high purity water and dried at 115-125 ° C. The precipitated product is dried in a fluidized bed dryer.

The new method, as well as the prototype method, includes the stage of purification of the initial product, and then the stage of chemical precipitation of barium carbonate from a solution of barium nitrate with a carbonizing agent. However, the new method has significant differences from the prototype method, which are both at the stage of preliminary purification of the initial product, and at the stage of chemical precipitation of barium carbonate.

The preliminary purification of the initial barium-containing solution, which is a solution of barium nitrate, in the new method is carried out by treating it with aluminum nitrate, which is added to the product to be purified in an amount of 2% by weight of anhydrous barium nitrate, after which it is alkalinized to pH 8.0-8.3 and separated from the precipitate by filtration. This treatment of the initial solution of reactive qualification containing impurity ions at the level of 0.0001-0.00001 wt.% Ensures its deep purification to form highly pure barium nitrate containing the following impurity ions (wt.%): Fe - 0.000003, Mn - 0.0000008, Cu - 0.0000004, Ni - 0.0000005, Cr - 0.0000006, Co - 0.0000005, Al - less than 0.001 wt.%, Which is confirmed by chemical-spectral analysis.

At the stage of chemical precipitation in the new method, carbon dioxide gas is used as the carbonizing agent, and not ammonium carbonate, as in the prototype method. The use of carbon dioxide gas as a carbonizing agent enhances the carbonization process compared to the use of carbonates. A prerequisite for the precipitation process in the new method is the presence in the reaction medium of a stoichiometric amount of ammonia or its aqueous solution. Ammonium nitrate formed during the reaction in the form of an aqueous solution is processed into a reactive product for further use. Instead of gaseous ammonia, it is possible to use its aqueous solution, which is more environmentally acceptable than the use of gaseous ammonia.

The deposition process is carried out at certain technological parameters (mixing speed, temperature, pH of the medium), significantly affecting the efficiency of the process. The reaction mass in a reactor equipped with a turbine stirrer is mixed at a speed of 9000-1000 rpm. Such intensive mixing ensures maximum contact in the zone of gas and solution deposition and optimal absorption of gaseous carbon dioxide and ammonia. In the case of a decrease in the stirring speed of the reaction mixture below 900 rpm, the efficiency of the deposition process decreases, since the solubility of gaseous carbon dioxide in the solution decreases, which, in turn, leads to undesirable breakthroughs of gaseous carbon dioxide and, consequently, to an uneconomical increase in the flow rate . An increase in the rotation speed above 1000 rpm does not lead to an increase in the efficiency of the process, however, the energy intensity of the process increases. Significantly affects the efficiency of the process and its temperature regime. It is optimal to carry out the deposition process at a temperature of 42-45 ° C. In the case of a decrease in temperature below 42 ° C, complete precipitation of calcium carbonate is not observed, which is explained by the partial binding of ammonia and carbon dioxide until a stable by-product is formed - ammonium carbamate (NH ₄ COONH ₂ ). Raising the temperature above the claimed limit (above 45 ° C) is also undesirable, since this leads to a decrease in the solubility of gases in solution, to their significant slip and large losses, and hence to a decrease in the efficiency of the process.

To carry out the deposition process in an efficient mode, it is also necessary to maintain the pH of the reaction medium at a certain level, namely, at a level of 7.8-8.2, which is ensured by maintaining a stoichiometric ratio of ammonia to carbon dioxide (at a level of 2: 1 with respect to a solution of barium nitrate ). In the case of decreasing the pH value below 7.8, incomplete precipitation of barium carbonate occurs, in the case of increasing the pH above 8.2, the precipitation process is violated with a sharp decrease in the yield of the final product.

The precipitated barium carbonate in the form of a suspension continuously enters the collection tank through the side nozzle of the reactor, and from there it is periodically drained to a vacuum filter, where it is washed several times from the mother liquor with high purity water until there are no nitrate ions. The use of high purity water in the washing stage helps to maintain a high degree of purity in the final product. For washing, for example, high purity water of special grade is used. 27-5, in which, according to TU-6-09-2502, the content of 27 impurities of cations and anions is regulated and which in total contains impurities at the level of 10 ^-5 wt.%, And individual impurities at the level of 10 ^-6 -10 ^-7 mass .%. At the last stage, pasty barium carbonate with a moisture content of about 20-25% is dried in a fluidized bed dryer at a temperature of 115-125 ° C. The specified temperature conditions are optimal for this process. Increasing the drying temperature above 125 ° C leads to a significant increase in energy costs for heating and cleaning large volumes of air, which is a drying agent, and a decrease in temperature below 115 ° C leads to an increase in the duration of the process and a decrease in productivity. The drying process is optimally carried out in a fluidized bed dryer, since this helps to increase the efficiency of the drying process, which intensifies the whole process.

The new method is illustrated by the examples below.

Example 1. The initial 8% aqueous solution of barium nitrate (500 ml), prepared by dissolving reactive purity barium nitrate in distilled water and then purified by filtration from mechanical impurities, is poured into a reactor made of organic glass and equipped with a stirrer. 2.0 g of crystals of aluminum nitrate nanohydrate are introduced into the reactor, stirred until the crystals are completely dissolved and 10% sodium hydroxide is introduced to pH 8.0-8.3, mixed until the impurities are coprecipitated on the formed precipitate of hydrated alumina, the precipitate is settled and the precipitate is separated off clarified solution from the precipitate on a vacuum filter. The purified barium nitrate solution (chemical spectral analysis) contains the following limited impurities (wt.%): Fe - 0.000003, Mn - 0.0000007, Cu - 0.0000005, Co - 0.0000005, Ni - 0.0000005 Cr is 0.0000005. The initial reactive qualification barium nitrate contains limited impurities (wt.%): Fe - 0.0003, Mn - 0.00007, Cu - 0.00008, Co - 0.000005, Ni - 0.00004, Cr - 0.00005.

Example 2

An 8% solution of purified barium nitrate (1 L), technical ammonia gas (GOST 6221-89) containing 99.9 vol.% NH ₃ (22.8 L) are continuously fed into a reactor equipped with a jacket and a stirrer, and technical carbon dioxide gas (GOST 2050-76) containing 98 vol.% CO ₂ (11.4 l), and the reaction mass is constantly stirred at a speed of 900 rpm at a temperature of 42 ° C until a pH of 7.8 is established. A suspension containing barium carbonate formed during the precipitation reaction from the reactor through the side fitting continuously enters the collection tank equipped with a stirrer, from where it is periodically drained onto a vacuum filter. On the filter, the precipitate of barium carbonate is washed with high purity water until the nitrate ions are practically absent in the wash water (less than 0.001 wt.%). The washed paste with a moisture content of 25% is dried in a fluidized bed dryer at a temperature of 125 ° C. Get 60 g of the finished product (barium carbonate), which is 99.99% of theoretical. The resulting product contains impurities (wt.%): Fe - 0.00001, Mn - 0.000005, Cu - 0.000003, Co - 0.0000005, Ni - 0.0000005, Cr - 0.0000005.

Example 3. The method is carried out analogously to example 2, but with a few changed some process parameters. Namely, when using as a reagent a solution of barium nitrate, gaseous carbon dioxide and gaseous ammonia in the same stoichiometric quantities as in example 1, the chemical deposition process is carried out at a speed of rotation of the stirrer 1000 rpm and at a temperature of 45 ° C and pH 8.2. The washed paste with a moisture content of 20% is dried at a temperature of 115 ° C. The yield of barium carbonate is 99.99% of theoretical. The resulting product has the same degree of purity as the product of example 2.

Example 4. The process is carried out analogously to example 2, only instead of gaseous ammonia, a stream of an aqueous ammonia solution (151 ml) is continuously introduced into the reactor simultaneously with streams of barium nitrate and gaseous carbon dioxide, for which an aqueous solution of ammonia of the brand name 17-4 with a concentration of 25 wt.%. Get the product with a yield of 99.99% and the same degree of purity.

Thus, the new method provides the highest possible yield (99.99%) for the production of high purity barium carbonate that meets the requirements for the purity of products for optical glassmaking and fiber optics.

Claims (2)

1. A method of producing high purity barium carbonate, including the preliminary purification of barium nitrate, chemical precipitation of barium carbonate from a purified solution of barium nitrate with a carbonizing agent and the isolation of the product, characterized in that the initial solution of barium nitrate is treated with aluminum nitrate in an amount of 2% by weight of anhydrous barium nitrate and alkali to a pH of 8.0-8.3 and filtered, and the chemical precipitation of barium carbonate is carried out in the presence of ammonia or its aqueous solution when used as carbonizing a carbon dioxide gas that is introduced into the reactor simultaneously with the stream of a purified solution of barium nitrate, as well as a stream of ammonia gas or its aqueous solution, and the chemical deposition process is carried out using stoichiometric amounts of reagents, temperature 42-45 ° С, pH 7.8- 8.2 and a stirring speed of the reaction mixture equal to 900-1000 rpm, and the filtered product is then washed with high purity water and dried at 115-125 ° C. 2. The method according to claim 1, characterized in that the washed barium carbonate is dried in a fluidized bed dryer.