Preparation method of high-purity cesium carbonate

Abstract

The invention relates to a preparation method of high-purity cesium carbonate, which comprises the following steps: by taking pollucite as a raw material, leaching with sulfuric acid, cooling and crystallizing to obtain crude cesium alum, recrystallizing to obtain high-purity cesium alum, adding at least one of cesium salt or cesium solution of which the cesium molar weight is greater than the aluminum molar weight in the production process in the recrystallization process, removing aluminum, converting, purifying and removing impurities, thereby obtaining the high-purity cesium carbonate. And carrying out evaporation concentration and carbonization crystallization to obtain high-purity cesium bicarbonate, and finally drying and decomposing to obtain a high-purity cesium carbonate product. Compared with a conventional method for preparing cesium carbonate through extracting cesium from pollucite and a conventional method for preparing high-purity cesium carbonate through an extraction method, the method has the advantages that the product purity is greatly improved, the content of cesium carbonate is larger than or equal to 99.999% wt in terms of Cs2CO3, the total amount of impurities including Li, Na, K, Rb, Ca, Mg, Al, Fe, SiO2 and heavy metal (in terms of Pb) is smaller than or equal to 0.001% wt, and especially the content of the same-main-group impurity Rb is smaller than or equal to 0.0001% wt.

Description

Technical Field

[0001] The invention relates to a method for preparing high-purity cesium carbonate, and belongs to the technical field of chemical production. Background Art

[0002] Cesium carbonate is a white crystal or powder and is a rare alkali metal salt. In recent years, it has shown important value in scientific research, nuclear industry and chemical analysis. Due to the application of highly radioactive isotopes of cesium as fuel and neutron source in nuclear reactors, cesium carbonate has become a key raw material for the preparation of cesium compounds. With the development of nuclear energy technology and the exploration of new materials, the demand for cesium carbonate has gradually increased, especially in the fields of nuclear medicine and radioisotope batteries. In civilian use, cesium carbonate is increasingly used in medical imaging, radioisotope batteries and environmental monitoring equipment. On the other hand, scientific research institutions and enterprises will increase the research and development of cesium carbonate extraction and purification technology, improve its purity and stability, and meet the special needs of high-tech fields. With the development of high-tech materials and applications, the purity requirements of cesium carbonate are getting higher and higher, especially for impurities such as rubidium. At present, the market can only achieve cesium carbonate with a purity of not less than 99.99%, and the lower limit of the impurity rubidium is generally 10ppm. To achieve this purity of cesium carbonate, rubidium and cesium are usually separated by extraction, and the purification process of cesium carbonate requires multiple recrystallizations. In some high-end application scenarios, the purity of cesium carbonate needs to reach more than 99.999%, and the impurity rubidium is required to be no more than 5ppm, or even lower.

[0003] The main raw material for producing and purifying cesium carbonate is cesium garnet. Ceium garnet, also known as cesium zeolite, is composed of Cs(AlSi2O6)·H2O. It is an isometric crystal system, and the crystals are aggregates of cubes and tetrahedrons; usually dense block aggregates, colorless and transparent, glass luster, hardness 6.5-7, shell-shaped fracture, density 2.86-2.90g / cm. Ceium garnet contains about 23.5% to 36.5% Cs2O, which is the mineral with the highest cesium content known. It is an important ore mineral for extracting cesium and preparing cesium salts. The main methods for extracting cesium from cesium garnet include acid method, alkaline roasting, chlorination roasting and direct reduction of ore. Alkaline roasting requires the addition of a large amount of flux, such as sodium carbonate, calcium carbonate, calcium oxide, etc., which brings difficulties to the separation and purification of cesium; the chlorination roasting method has complex equipment, large environmental pollution, and high environmental protection costs; the direct reduction method requires high temperature and high vacuum, high equipment cost, and industrial mass production is difficult to achieve. The acid process is relatively simple, mainly including sulfuric acid method, hydrochloric acid method, hydrofluoric acid method and hydrobromic acid method. Hydrochloric acid, hydrofluoric acid, and hydrobromic acid are all volatile, gas pollution is serious, working conditions are poor, and the leaching effect of hydrochloric acid is poor; sulfuric acid has a high boiling point, is not easy to volatilize, and has a good leaching effect. Moreover, because there is aluminum in cesium garnet, cesium alum can be directly obtained by leaching with sulfuric acid, and then purified by recrystallization. Therefore, the method of extracting cesium from cesium garnet with sulfuric acid has been widely used.

[0004] Since cesium garnet ore contains a variety of alkali metal elements such as potassium and rubidium, they are in the same main group and have very similar properties. They are all easy to form alum. Therefore, in the process of extracting cesium by sulfuric acid method, it is necessary to use the solubility difference of various alums to recrystallize the obtained cesium alum multiple times to achieve the purpose of removing potassium and rubidium and purifying to obtain refined cesium alum. The recrystallization process consumes a lot of energy, and each additional recrystallization will result in a loss of yield. How to efficiently remove potassium and rubidium impurities in cesium vanadium is the key to preparing high-purity cesium carbonate. For example, the patent application "New process for producing cesium carbonate from cesium garnet (CN101774613A)" discloses "including acid leaching - constant temperature filtration - precipitation of cesium alum - separation - crude cesium alum - two recrystallizations - refined cesium alum steps, characterized in that it also includes, aluminum sulfate removal - separation - cesium sulfate solution - sulfate radical removal - filtration - cesium hydroxide solution - one hydrogenation - one filtration - hydrogenated liquid - concentration and cooling - two filtrations - concentrated solution - two hydrogenations - three filtrations - concentrated clean liquid - concentrated cooling crystallization - centrifugal separation - cesium bicarbonate wet material - drying - cesium carbonate step", which mainly adopts two recrystallizations and "adjusts the liquid-solid ratio of cesium alum to water to 3 to 10:1", so as to achieve the purpose of reducing rubidium in the product and finally obtain a 99.9% cesium carbonate product. Chinese patent CN110078100A "A method for extracting high-purity cesium carbonate from cesium garnet" uses an extraction method to separate rubidium and cesium, and produces cesium carbonate with a purity of 99.99%, and the content of rubidium, potassium and sodium in the product is less than 10ppm. The non-ferrous metal industry standard "YS / T 756-2011" announced cesium carbonate with a purity of 99.99%, in which the Rb content is not more than 0.001%. However, the above cesium carbonates are difficult to meet the current requirements for the use of high-end materials. Summary of the invention

[0005] In view of the above shortcomings, the present invention provides a method for preparing high-purity cesium carbonate, which can prepare high-purity cesium carbonate with a cesium carbonate content of ≥99.999%wt in terms of Cs2CO3, especially with very low impurities, Li≤0.00005%wt, Na≤0.00005%wt, K≤0.00005%wt, Rb≤0.0001%wt, Ca≤0.00005%wt, Mg≤0.00005%wt, Fe≤0.00005%, heavy metals (in terms of Pb)≤0.00005%wt, Al≤0.0001%wt, SiO2≤0.0004%wt. It should be noted that according to the industry standard YS / T756-2011, the Cs2CO3 content is 100% minus the remainder of the sum of the measured values ​​of the impurities listed above. The present invention is achieved through the following technical solutions.

[0006] A method for preparing high-purity cesium carbonate comprises the following steps S1-S8:

[0007] S1 leaching: using cesium garnet as raw material, leaching with sulfuric acid to obtain leachate and leaching residue; preferably, the sulfuric acid concentration is 20-40%, the liquid-solid volume mass ratio of sulfuric acid to cesium garnet is 4:1-7:1, the temperature is 100-120°C, and the leaching is carried out for 4-12h.

[0008] S2 cooling crystallization: cooling and crystallizing the S1 leachate to obtain crude cesium alum and the first crystallization mother liquor; controlling the cooling crystallization temperature to be 10-50°C, preferably 30-50°C.

[0009] S3 recrystallization: dissolve the crude cesium alum in S2 and recrystallize it to obtain high-purity cesium alum and recrystallization mother liquor; preferably, the dissolution temperature of cesium alum during recrystallization is 90-105°C, the liquid-solid mass ratio is 4:1-7:1, and the crystallization temperature is 10-50°C, preferably 30-50°C. In order to improve the separation effect of rubidium and cesium, at least one of the cesium salts or cesium solutions in which the molar amount of cesium is greater than the molar amount of aluminum in the production process is added to the cesium alum solution in the step S3 recrystallization step, and the added amount is calculated in terms of the molar amount of cesium, and the molar amount of cesium added minus the molar amount of aluminum is 1-50 times the total molar amount of rubidium and potassium in the solution. The recrystallization step can be repeated once or twice or more.

[0010] S4 aluminum removal: dissolve the high-purity cesium alum obtained in S3, add an aluminum removal agent to remove aluminum, filter and wash to obtain a cesium sulfate solution, aluminum removal slag and slag washing water, and the aluminum removal endpoint pH is controlled to 8-10. The aluminum removal agent can be selected from at least one of CaO, Ca(OH)2 and Ba(OH)2.

[0011] S5 conversion: add Ba(OH)2 to the cesium sulfate solution obtained in S4 for conversion, filter to obtain cesium hydroxide solution and barium sulfate precipitate, wash the barium sulfate precipitate to obtain slag washing water II; preferably, the amount of Ba(OH)2 added is 1.05-2.0 times the molar amount of sulfate. Obviously, if Ba(OH)2 is purified by recrystallization, it is less likely to introduce impurities. When washing the barium sulfate precipitate, an appropriate amount of dilute sulfuric acid can be added to control the pH of the washing water to 1-6. The main purpose is to wash off the cesium ions entrained by the barium sulfate precipitate, thereby ensuring the total yield of cesium. The purity of the washed barium sulfate is also relatively high and can be sold as a by-product.

[0012] S6 purification and impurity removal: the cesium hydroxide solution obtained in S5 is purified and impurities removed, and a high-purity cesium carbonate solution and purified slag are obtained after washing and filtering; purification and impurity removal refers to the introduction of CO2 gas into the cesium hydroxide solution, controlling the end point pH=10-12, so that the cesium hydroxide is converted into cesium carbonate, and at the same time, the calcium and barium in the solution are precipitated. If the pH is too high, the cesium carbonate precipitation conversion rate is not high, and if the pH is too low, calcium and barium are easy to generate calcium bicarbonate and barium bicarbonate with higher solubility, and the purpose of impurity removal cannot be achieved.

[0013] S7 concentration and carbonization crystallization: The high-purity cesium carbonate solution obtained in S6 is evaporated and concentrated, and the concentrated high-purity cesium carbonate solution is carbonized and crystallized, that is, CO2 is introduced into the concentrated high-purity cesium carbonate solution under stirring conditions and the end point pH value is controlled in the range of 7-9, which can effectively prevent the carbonized cesium bicarbonate from decomposing into cesium carbonate again, and then solid-liquid separation is performed to obtain high-purity cesium bicarbonate and a second crystallization mother liquor.

[0014] S8 drying and decomposition: drying and decomposing the high-purity cesium bicarbonate described in S7, vacuum drying at 60-90° C. for 4-48 hours, then heating to 250-300° C. and keeping the temperature for 4-24 hours, to finally obtain a high-purity cesium carbonate product.

[0015] The cesium salt in which the molar amount of cesium is greater than the molar amount of aluminum in the production process includes the high-purity cesium bicarbonate obtained in step S7 and the high-purity cesium carbonate obtained in step S8. The cesium solution in which the molar amount of cesium is greater than the molar amount of aluminum in the production process includes the cesium sulfate solution in step S4, the slag washing water one in step S4, the cesium hydroxide solution in step S5, the slag washing water two in step S5, the high-purity cesium carbonate solution in step S6 and the second crystallization mother liquor in step S5. These materials all contain cesium ions or cesium compounds. When cesium carbonate is prepared for the first time, there is no cesium salt or solution in the above production process, and the first preparation can be completed first with cesium sulfate, cesium chloride, cesium nitrate, etc.

[0016] In order to improve the material utilization rate and reduce energy consumption in the production process, the solvent used for dissolving the crude cesium alum in step S3 can be at least one of pure water, the slag washing water 1 described in step S4, the slag washing water 2 described in step S5 and the cesium sulfate solution from which aluminum has been removed.

[0017] The separation of cesium and rubidium mainly utilizes the principle of ion crystal equilibrium. In the crude cesium vanadium solution, there are mainly Al 3+ , Cs + , Rb + , K + 、SO4 2- Plasma, and Al 3+ Molar amount and Cs + , Rb + , K + The total molar amount of alkali metal ions is equivalent, and the following reaction equilibrium of formula 1-formula 3 exists during cooling crystallization:

[0018] Formula 1: Cs + +Al 3+ +SO4 2- +12H2O CSAl(SO4)2.12H2O(crystal)

[0019] Formula 2: Rb + +Al 3+ +SO42- +12H2O RbAl(SO4)2.12H2O(crystal)

[0020] Formula 3: K + +Al 3+ +SO4 2- +12H2O KAl(SO4)2.12H2O(crystal)

[0021] According to the chemical properties of alkali metal elements, the larger the atomic number, the stronger the metallicity, and the lower the solubility of alkali metal alum salts. U.S. Patent No. 10738370B2 discloses the solubility data of anhydrous alum in Table 2 of the specification, see Table 1 below:

[0022] Table 1---Alum solubilities in g of anhydrous alum per 100ml of water

[0023]

[0024] It can be seen from the above table that at the same temperature, cesium alum has the lowest solubility and is preferentially crystallized. According to the cesium alum crystal molecular formula CsAl(SO4)2·12H2O, it is not difficult for those skilled in the art to understand that the volume product of cesium alum is mainly related to Cs + 、Al 3+ and SO4 2- concentration, that is, Ksp = [Cs + ][Al 3+ ][SO4 2- ] 2 Therefore, when Al 3+ Cs + As the concentration increases, it is easier to form cesium alum crystals. 3+ and SO4 2- When the concentration decreases, 3+ and SO4 2- When the concentration is reduced to a certain level, less or no RbAl(SO4)2·12H2O and KAl(SO4)2·12H2O crystals will be formed during the recrystallization process, thus achieving the separation of cesium from rubidium and potassium. + , K + Combined Al 3+ Content (equivalent to Rb + , K + The total molar amount of Cs + The amount of Rb in the recrystallization solution+ , K + Combined Al 3+ The amount of free Al in the solution is converted into CsAl(SO4)2·12H2O, thereby reducing 3+ The concentration of Rb + , K + It still exists in the solution in the form of ions, and finally achieves efficient separation of cesium from rubidium and potassium, improves the purity of cesium alum, and obtains high-purity cesium alum with low rubidium. In the present invention, at least one of cesium salts or cesium solutions in which the cesium molar amount is greater than the aluminum molar amount in the production process is added to the cesium alum solution in the step S3 recrystallization step, and the added amount is calculated in terms of cesium molar amount, and the added cesium molar amount minus the aluminum molar amount is 1-50 times the total molar amount of rubidium and potassium in the solution, which is based on this principle.

[0025] Compared with the conventional cesium extraction process of cesium from garnet and the extraction process of cesium extraction, the present invention can well realize the separation of cesium from rubidium and potassium, and prepare high-purity cesium carbonate with a content of ≥99.999% in terms of Cs2CO3, wherein the total amount of impurities Li, Na, K, Rb, Ca, Mg, Al, Fe, SiO2 and heavy metals (in terms of Pb) is ≤0.001%wt; specifically, Li ≤0.00005%wt, Na ≤0.00005%wt wt, K≤0.00005%wt, Rb≤0.0001%wt, Ca≤0.00005%wt, Mg≤0.00005%wt, Fe≤0.00005%, heavy metals (in terms of Pb)≤0.00005%wt, Al≤0.0001%wt, SiO2≤0.0004%wt, and Cs2CO3 content is the remainder of 100% minus the sum of the measured values ​​of the above impurities. The method of the present invention has simple process, the materials in the production process can be fully utilized, energy is saved, and wastewater discharge is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The present invention is a process flow chart for preparing high-purity cesium sulfate. DETAILED DESCRIPTION

[0027] In order to describe the present invention more clearly, the present invention is further described in detail below using embodiments in conjunction with the accompanying drawings.

[0028] A method for preparing high-purity cesium carbonate comprises the following steps: using cesium garnet as a raw material, adding 20-40% sulfuric acid at a liquid-solid volume mass ratio of sulfuric acid to cesium garnet of 4:1-7:1, controlling the temperature to be 100-120°C for leaching for 4-12h, filtering while hot to obtain a leachate and a leach residue; cooling the leachate to 10-50°C for crystallization, and performing solid-liquid separation to obtain crude cesium alum and a first crystallization mother liquor; adding a solvent at a liquid-solid mass ratio of the solvent to the crude cesium alum of 4:1-7:1 for dissolution and heating to 90-105°C, wherein the solvent is at least one of pure water, the slag washing water 1 described in step S4, the slag washing water 2 described in step S5, and a cesium sulfate solution from which aluminum has been removed. At least one of cesium salts or cesium solutions in which the molar amount of cesium is greater than the molar amount of aluminum in the production process is added, and the added amount is calculated as the molar amount of cesium, and the molar amount of aluminum is subtracted from the molar amount of cesium added, which is 1-50 times the total molar amount of rubidium and potassium in the solution (there is no cesium salt or solution in the above production process during the first preparation, and cesium sulfate, cesium chloride, cesium nitrate, etc. are used instead); then cooled to 10-50°C for recrystallization to obtain high-purity cesium alum and recrystallization mother liquor; dissolving the high-purity cesium alum, adding an aluminum removal agent to remove aluminum, controlling the endpoint pH to 8-10, filtering and washing to obtain a cesium sulfate solution, aluminum removal slag and slag washing water; adding Ba(OH)2 to the obtained cesium sulfate solution for conversion, filtering to obtain a cesium hydroxide solution and a barium sulfate precipitate, washing the barium sulfate The second slag washing water is obtained by precipitation, and dilute sulfuric acid is added during washing to control the pH value of the washing water to 1-6; CO2 gas is introduced into the cesium hydroxide solution to purify and remove impurities, and the end point pH is controlled to be 10-12, and the cesium hydroxide is converted into cesium carbonate, and impurities of calcium and barium are removed, and high-purity cesium carbonate and purified slag are obtained by solid-liquid separation; the obtained high-purity cesium carbonate solution is evaporated and concentrated, and CO2 is introduced into the concentrated high-purity cesium carbonate solution under stirring and the end point pH value is controlled to be in the range of 7-9 for carbonization and crystallization, and high-purity cesium bicarbonate and a second crystallization mother liquor are separated; the obtained high-purity cesium bicarbonate is vacuum dried at 60-90°C for 4-48h, and then the temperature is increased to 250-300°C and kept warm for 4-24h for decomposition, and finally a high-purity cesium carbonate product is obtained.

[0029] When testing high-purity cesium carbonate products, the total amount of impurities Li, Na, K, Rb, Ca, Mg, Al, Fe, SiO2 and heavy metals (in terms of Pb) is ≤0.001%wt; specifically, Li ≤0.00005%wt, Na ≤0.00005%wt, K ≤0.00005%wt, Rb ≤0.0001%wt, Ca ≤0.00005%wt, Mg ≤0.00005%wt, Fe ≤0.00005%, heavy metals (in terms of Pb) ≤0.00005%wt, Al ≤0.0001%wt, SiO2 ≤0.0004%wt, and the cesium carbonate content minus the sum of the above impurities is ≥99.999%wt, calculated as Cs2CO3.

[0030] Comparative Example 1

[0031] Take 1.0 kg of cesium garnet (Cs2O=30.5%), add 6 liters of 40% sulfuric acid, control the temperature to 100°C for leaching for 12 hours, filter while hot to obtain a leachate and a leach residue; cool the leachate to 30°C for crystallization, separate the solid and liquid to obtain crude cesium alum and the first crystallization mother liquor; add water to the crude cesium alum at a liquid-solid mass ratio of 7:1 and dissolve at 100°C, then cool to 50°C for recrystallization to obtain refined cesium alum and a recrystallization mother liquor; dissolve high-purity cesium alum, stir and add aluminum removal agent CaO to remove aluminum, control the end point pH to 10, filter and wash to obtain cesium sulfate solution and aluminum removal residue; the obtained sulfur The cesium acid solution is converted by adding Ba(OH)2 at a molar amount of 1.5 times of the sulfate radical, and filtered to obtain a cesium hydroxide solution and a barium sulfate precipitate; CO2 gas is introduced into the obtained cesium hydroxide solution to purify and remove impurities, and the end point pH is controlled to be 10, and solid-liquid separation is performed to obtain cesium carbonate and purified slag; the cesium carbonate solution is evaporated and concentrated, and CO2 is introduced into the solution under stirring and the end point pH is controlled to be 9 for carbonization crystallization, and cesium bicarbonate and a second crystallization mother liquor are separated; the cesium bicarbonate is vacuum dried at 80°C for 24 hours, and then the temperature is increased to 280°C and kept warm for 24 hours to finally obtain a cesium carbonate product. The cesium carbonate content and impurities were tested, and the results showed that: Li≤0.0001%wt, Na≤0.0005%wt, K≤0.001%wt, Rb≤0.001%wt, Ca≤0.001%wt, Mg≤0.0001%wt, Fe≤0.0001%, heavy metals (as Pb)≤0.0005%wt, Al≤0.0002%wt, SiO2≤0.005%wt, and the cesium carbonate content as Cs2CO3 was ≥99.99%wt.

[0032] Example 1

[0033] Take 1.0kg of cesium garnet (Cs2O=25.5%), add 7 liters of 40% sulfuric acid, control the temperature to 120°C for leaching for 12h, filter while hot to obtain a leachate and a leach residue; cool the leachate to 30°C for crystallization, separate the solid and liquid to obtain crude cesium alum and the first crystallization mother liquor; add water to the crude cesium alum at a liquid-solid mass ratio of 4:1 and dissolve it at 105°C; take samples to detect the content of rubidium, potassium and aluminum ions, and add cesium sulfate when the cesium molar amount is 25 times the total molar amount of rubidium and potassium in the solution after deducting the aluminum molar amount, and then cool to 20°C for recrystallization, and recrystallize twice under the same conditions to obtain high-purity cesium alum and recrystallization mother liquor; add pure water to dissolve the high-purity cesium alum, stir and add aluminum removal agent CaO to remove aluminum, control the endpoint pH to 10, filter and wash to obtain sulfur The invention discloses a cesium acid solution, aluminum-removing slag and a slag washing water; Ba(OH)2 is added to the obtained cesium sulfate solution according to 2.0 times of the molar amount of sulfate root for conversion, and cesium hydroxide solution and barium sulfate precipitate are obtained by filtration, and the barium sulfate precipitate is washed with dilute sulfuric acid to obtain a slag washing water II, and the pH value of the washing water is controlled to be 6; CO2 gas is introduced into the obtained cesium hydroxide solution for purification and impurity removal, and the end point pH is controlled to be 10, and high-purity cesium carbonate and purified slag are obtained by solid-liquid separation; the high-purity cesium carbonate solution is evaporated and concentrated, and CO2 is introduced into the solution under stirring and the end point pH is controlled to be 9 for carbonization crystallization, and high-purity cesium bicarbonate and a second crystallization mother liquor are separated; the high-purity cesium bicarbonate is vacuum dried at 90°C for 4h, and then the temperature is raised to 250°C and kept warm for 24h to finally obtain a high-purity cesium carbonate product.

[0034] Example 2

[0035] Take 1.0kg of cesium garnet (Cs2O=16.2%), add 4.0 liters of 20% sulfuric acid, control the temperature to 110°C for leaching for 4h, filter while hot to obtain a leachate and a leach residue; cool the leachate to 50°C for crystallization, separate the solid and liquid to obtain crude cesium alum and the first crystallization mother liquor; add pure water to the solvent and crude cesium alum according to a liquid-solid mass ratio of 7:1, and heat to 90°C for dissolution; take samples to detect the content of rubidium, potassium and aluminum ions, and add the high-purity cesium bicarbonate solution obtained in Example 1 according to the cesium molar amount, and then cool to 40°C for recrystallization, and recrystallize again under the same conditions to obtain high-purity cesium alum and recrystallization mother liquor; dissolve the high-purity cesium alum in pure water, stir and add aluminum removal agent Ca(OH)2 for aluminum removal, control the final The pH value is 8, filtered and washed to obtain cesium sulfate solution, aluminum-removing slag and slag washing water one; Ba(OH)2 is added to the obtained cesium sulfate solution according to 1.5 times the molar amount of sulfate root for conversion, filtered to obtain cesium hydroxide solution and barium sulfate precipitate, and the barium sulfate precipitate is washed with dilute sulfuric acid to obtain slag washing water two, and the pH value of the washing water is controlled to be 1; CO2 gas is introduced into the obtained cesium hydroxide solution to purify and remove impurities, and the end point pH is controlled to be 8, and high-purity cesium carbonate and purified slag are obtained by solid-liquid separation; the high-purity cesium carbonate solution is evaporated and concentrated, CO2 is introduced into the solution under stirring and the end point pH is controlled to be 7 for carbonization crystallization, and high-purity cesium bicarbonate and the second crystallization mother liquor are separated; the high-purity cesium bicarbonate is vacuum dried at 60°C for 24h, and then the temperature is raised to 300°C and kept warm for 4h to finally obtain a high-purity cesium carbonate product.

[0036] Example 3

[0037] Take 1.0kg of cesium garnet (Cs2O=18.8%), add 5.0 liters of 30% sulfuric acid, control the temperature to 100°C and leach for 8h, filter while hot to obtain a leachate and a leach residue; cool the leachate to 40°C for crystallization, separate the solid and liquid to obtain crude cesium alum and a first crystallization mother liquor; add the solvent and crude cesium alum to the slag washing water in Example 1 at a liquid-solid mass ratio of 6:1, heat to 95°C to dissolve, take samples to detect the content of rubidium, potassium and aluminum ions, and add the high-purity cesium carbonate obtained in Example 1 after deducting the aluminum molar amount according to the cesium molar amount, which is 15 times the total molar amount of rubidium and potassium in the solution, and then cool to 30°C for recrystallization, and recrystallize again under the same conditions to obtain high-purity cesium alum and a recrystallization mother liquor; dissolve the high-purity cesium alum in pure water, stir and add aluminum removal agent Ba(OH)2 to remove aluminum, control The end point pH is set to 9, filtered and washed to obtain cesium sulfate solution, aluminum-removing slag and slag washing water one; Ba(OH)2 is added to the obtained cesium sulfate solution according to 1.05 times the molar amount of sulfate root for conversion, filtered to obtain cesium hydroxide solution and barium sulfate precipitate, the barium sulfate precipitate is washed with dilute sulfuric acid to obtain slag washing water two, and the washing water pH is controlled to be 3; CO2 gas is introduced into the obtained cesium hydroxide solution to purify and remove impurities, the end point pH is controlled to be 9, and high-purity cesium carbonate and purified slag are obtained by solid-liquid separation; the high-purity cesium carbonate solution is evaporated and concentrated, CO2 is introduced into the solution under stirring and the end point pH is controlled to be 8 for carbonization crystallization, and high-purity cesium bicarbonate and a second crystallization mother liquor are separated; the high-purity cesium bicarbonate is vacuum dried at 80°C for 6h, and then the temperature is raised to 270°C and kept warm for 12h, and finally a high-purity cesium carbonate product is obtained.

[0038] Example 4

[0039] Take 1.0 kg of cesium garnet (Cs2O=22.5%), add 6.0 kg of 40% sulfuric acid, control the temperature to 110°C for leaching for 6 hours, filter while hot to obtain a leachate and a leach residue; the leachate is cooled to 30°C for crystallization, and solid-liquid separation is performed to obtain crude cesium alum and a first crystallization mother liquor; the solvent and crude cesium alum are added to the slag washing water II described in Example 3 at a liquid-solid mass ratio of 5:1, heated to 100°C for dissolution, and samples are taken to detect the content of rubidium, potassium and aluminum ions. According to the cesium molar amount, cesium is 1 times the total molar amount of rubidium and potassium in the solution after deducting the aluminum molar amount. Add the cesium sulfate solution obtained in Example 2, then cool to 50°C for recrystallization, and recrystallize twice under the same conditions to obtain high-purity cesium alum and recrystallization mother liquor; dissolve the high-purity cesium alum in pure water, stir and add aluminum removal agents Ca(OH)2 and Ba(OH)2 (any The method comprises the following steps: removing aluminum by using a cesium sulfate solution (meaning caesium hydroxide solution), controlling the end point pH to be 10, filtering and washing to obtain a cesium sulfate solution, aluminum removal slag and slag washing water one; adding Ba(OH)2 at 1.2 times the molar amount of sulfate to the obtained cesium sulfate solution for conversion, filtering to obtain a cesium hydroxide solution and a barium sulfate precipitate, washing the barium sulfate precipitate with dilute sulfuric acid to obtain a slag washing water two, and controlling the washing water pH to be 5; introducing CO2 gas into the obtained cesium hydroxide solution for purification and impurity removal, controlling the end point pH to be 8, and performing solid-liquid separation to obtain high-purity cesium carbonate and purification slag; evaporating and concentrating the high-purity cesium carbonate solution, introducing CO2 into the solution under stirring and controlling the end point pH to be 8 for carbonization crystallization, and separating to obtain high-purity cesium bicarbonate and a second crystallization mother liquor; vacuum drying the high-purity cesium bicarbonate at 90°C for 10 hours, and then heating to 260°C for 10 hours to finally obtain a high-purity cesium carbonate product.

[0040] Example 5

[0041] Take 1.0 kg of cesium garnet (Cs2O=16.2%), add 5.0 liters of 20% sulfuric acid, control the temperature to 120°C, leach for 10 hours, filter while hot to obtain a leachate and a leach residue; cool the leachate to 35°C for crystallization, separate the solid and liquid to obtain crude cesium alum and the first crystallization mother liquor; add the cesium sulfate solution from which aluminum has been removed in Example 4 to the solvent and crude cesium alum at a liquid-solid mass ratio of 7:1, heat to 90°C to dissolve, take samples to detect the content of rubidium, potassium and aluminum ions, and add the cesium hydroxide solution obtained in Example 2 after subtracting the aluminum molar amount based on the cesium molar amount, which is 40 times the total molar amount of rubidium and potassium in the solution, and then cool to 40°C for recrystallization, and recrystallize again under the same conditions to obtain high-purity cesium alum and recrystallization mother liquor; dissolve the high-purity cesium alum in pure water, stir and add aluminum removal agent CaO to remove aluminum, The end point pH is controlled to be 9, and cesium sulfate solution, aluminum removal slag and slag washing water 1 are obtained by filtering and washing; Ba(OH)2 is added to the obtained cesium sulfate solution according to 1.8 times the molar amount of sulfate root for conversion, and cesium hydroxide solution and barium sulfate precipitate are obtained by filtering, and the barium sulfate precipitate is washed with dilute sulfuric acid to obtain slag washing water 2, and the washing water pH is controlled to be 3; CO2 gas is introduced into the obtained cesium hydroxide solution for purification and impurity removal, and the end point pH is controlled to be 8, and high-purity cesium carbonate and purification slag are obtained by solid-liquid separation; the high-purity cesium carbonate solution is evaporated and concentrated, and CO2 is introduced into the solution under stirring and the end point pH is controlled to be 7 for carbonization and crystallization, and high-purity cesium bicarbonate and a second crystallization mother liquor are separated; the high-purity cesium bicarbonate is vacuum dried at 70°C for 18 hours, and then the temperature is increased to 280°C and kept warm for 8 hours, and finally a high-purity cesium carbonate product is obtained.

[0042] Example 6

[0043] Take 1.0kg of cesium garnet (Cs2O=25.5%), add 7 liters of 40% sulfuric acid, control the temperature to 120°C, leach for 12h, filter while hot to obtain a leachate and a leach residue; cool the leachate to 30°C for crystallization, separate the solid and liquid to obtain crude cesium alum and the first crystallization mother liquor; add the solvent and crude cesium alum to the slag washing water one and slag washing water two (any ratio) in Example 5 at a liquid-solid mass ratio of 4:1, and heat to 105°C for dissolution; take samples to detect the content of rubidium, potassium and aluminum ions, and add the cesium sulfate solution in Example 5 from which aluminum has been removed after deducting the aluminum molar amount according to the cesium molar amount, and then cool to 50°C for recrystallization to obtain high-purity cesium alum and a recrystallization mother liquor; dissolve the high-purity cesium alum, stir and add aluminum removal agents CaO and Ba(OH)2 (any ratio) to remove Aluminum, control the end point pH to 10, filter and wash to obtain cesium sulfate solution, aluminum removal slag and slag washing water one; add Ba(OH)2 according to 1.1 times the molar amount of sulfate root to the obtained cesium sulfate solution for conversion, filter to obtain cesium hydroxide solution and barium sulfate precipitate, wash the barium sulfate precipitate with dilute sulfuric acid to obtain slag washing water two, and control the pH of the washing water to be 6; introduce CO2 gas into the obtained cesium hydroxide solution for purification and impurity removal, control the end point pH to 10, and separate the solid and liquid to obtain high-purity cesium carbonate and purification slag; evaporate and concentrate the high-purity cesium carbonate solution, introduce CO2 into it under stirring and control the end point pH to 9 for carbonization crystallization, separate and obtain high-purity cesium bicarbonate and the second crystallization mother liquor; vacuum dry the high-purity cesium bicarbonate at 90°C for 4h, then heat it to 260°C and keep it warm for 20h, and finally obtain a high-purity cesium carbonate product.

[0044] Example 7

[0045] Take 1.0kg of cesium garnet (Cs2O=16.2%), add 4 liters of 30% sulfuric acid, control the temperature to 110°C, leach for 10h, filter while hot to obtain a leachate and a leach residue; the leachate is cooled to 30°C for crystallization, and solid-liquid separation is performed to obtain crude cesium alum and a first crystallization mother liquor; the solvent and crude cesium alum are added to the second slag washing water in Example 6 at a liquid-solid mass ratio of 6:1, and heated to 100°C for dissolution; sampling is performed to detect the content of rubidium, potassium and aluminum ions, and cesium is 30 times the total molar amount of rubidium and potassium in the solution after deducting the molar amount of aluminum according to the molar amount of cesium, and the second crystallization mother liquor obtained in Example 6 is added, and then cooled to 30°C for recrystallization, and recrystallized again under the same conditions to obtain high-purity cesium alum and recrystallization mother liquor; the high-purity cesium alum is dissolved, stirred and aluminum removal agents CaO, Ca(OH)2 and Ba(OH)2 (any The method comprises the following steps: removing aluminum by using 1% tantalum (about 0.1%), controlling the endpoint pH to be 10, filtering and washing to obtain a cesium sulfate solution, aluminum removal slag and slag washing water one; adding Ba(OH)2 at 1.05 times the molar amount of sulfate to the obtained cesium sulfate solution for conversion, filtering to obtain a cesium hydroxide solution and a barium sulfate precipitate, washing the barium sulfate precipitate with dilute sulfuric acid to obtain a slag washing water two, and controlling the washing water pH to be 4; introducing CO2 gas into the obtained cesium hydroxide solution for purification and impurity removal, controlling the endpoint pH to be 9, and performing solid-liquid separation to obtain high-purity cesium carbonate and purification slag; evaporating and concentrating the high-purity cesium carbonate solution, introducing CO2 into the solution under stirring and controlling the endpoint pH to be 9 for carbonization and crystallization, separating to obtain high-purity cesium bicarbonate and a second crystallization mother liquor; vacuum drying the high-purity cesium bicarbonate at 90°C for 20h, then heating to 270°C and keeping warm for 18h, and finally obtaining a high-purity cesium carbonate product.

[0046] Example 8

[0047] Take 1.0 kg of cesium garnet (Cs2O=22.5%), add 6 liters of 20% sulfuric acid, control the temperature to 100°C and leach for 12 hours, filter while hot to obtain a leachate and a leach residue; cool the leachate to 35°C for crystallization, separate the solid and liquid to obtain crude cesium alum and the first crystallization mother liquor; add pure water to the solvent and crude cesium alum at a liquid-solid mass ratio of 5:1, and heat to 95°C to dissolve; take samples to detect the content of rubidium, potassium and aluminum ions, and add the high-purity cesium carbonate solution obtained in Example 7 after subtracting the aluminum molar amount of cesium, which is 20 times the total molar amount of rubidium and potassium in the solution, and then cool to 20°C for recrystallization, and recrystallize again under the same conditions to obtain high-purity cesium alum and recrystallization mother liquor; dissolve the high-purity cesium alum, stir and add aluminum removal agents CaO and Ca(OH)2 (any ratio) to remove aluminum, control The end point pH is 8, and cesium sulfate solution, aluminum-removing slag and slag washing water 1 are obtained by filtering and washing; Ba(OH)2 is added to the obtained cesium sulfate solution according to 1.5 times the molar amount of sulfate root for conversion, and cesium hydroxide solution and barium sulfate precipitate are obtained by filtering, and the barium sulfate precipitate is washed with dilute sulfuric acid to obtain slag washing water 2, and the pH of the washing water is controlled to be 5; CO2 gas is introduced into the obtained cesium hydroxide solution for purification and impurity removal, and the end point pH is controlled to be 10, and high-purity cesium carbonate and purified slag are obtained by solid-liquid separation; the high-purity cesium carbonate solution is evaporated and concentrated, CO2 is introduced into the solution under stirring and the end point pH is controlled to be 9 for carbonization crystallization, and high-purity cesium bicarbonate and a second crystallization mother liquor are separated; the high-purity cesium bicarbonate is vacuum dried at 80°C for 16 hours, and then the temperature is increased to 280°C and kept warm for 16 hours, and finally a high-purity cesium carbonate product is obtained.

[0048] The high-purity cesium carbonate obtained in the above Examples 1-8 was tested according to the industry standard YS / T 756-2011. The test items were Li, Na, K, Rb, Ca, Mg, Al, Fe, SiO2 and heavy metal (Pb) total amount ≤ 0.001%wt, and the Cs2CO3 content was 100% minus the remainder of the sum of the measured values ​​of the impurities listed above. The test results of 8 samples all showed: Li≤0.00005%wt, Na≤0.00005%wt, K≤0.00005%wt, Rb≤0.0001%wt, Ca≤0.00005%wt, Mg≤0.00005%wt, Fe≤0.00005%, heavy metal (as Pb)≤0.00005%wt, Al≤0.0001%wt, SiO2≤0.0003%wt, cesium carbonate content as Cs2CO3≥99.999%wt, the quality is significantly better than the current market products and the product of Comparative Example 1.

[0049] Obviously, the above embodiments are only examples for clearly explaining the present invention, and are not intended to limit the implementation methods. It is not necessary and impossible to list all the implementation methods exhaustively. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description, and the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A method for preparing high-purity cesium carbonate, comprising the following steps: S1 leaching: using cesium garnet as raw material, leaching with sulfuric acid to obtain leaching solution and leaching residue; S2 cooling and crystallizing: cooling and crystallizing the leachate described in S1 to obtain crude cesium alum and the first crystallization mother liquor; S3 recrystallization: dissolving the crude cesium alum described in S2 and performing recrystallization to obtain high-purity cesium alum and a recrystallization mother liquor; S4 aluminum removal: dissolving the high-purity cesium alum described in S3 with pure water, adding an aluminum removal agent to remove aluminum, filtering and washing to obtain a cesium sulfate solution, aluminum removal slag and slag washing water; S5 conversion: adding Ba(OH)2 to the cesium sulfate solution described in S4 for conversion, filtering to obtain a cesium hydroxide solution and a barium sulfate precipitate, washing the barium sulfate precipitate to obtain slag washing water II; S6 purification and impurity removal: purifying and impurity removal of the cesium hydroxide solution described in S5, washing and filtering to obtain a high-purity cesium carbonate solution and purified slag; S7 concentration and carbonization crystallization: evaporating and concentrating the high-purity cesium carbonate solution described in S6, carbonizing and crystallizing the concentrated high-purity cesium carbonate solution, and separating the solid from the liquid to obtain high-purity cesium bicarbonate and a second crystallization mother liquor; S8 drying and decomposition: drying and decomposing the high-purity cesium bicarbonate described in S7 to obtain a high-purity cesium carbonate product; The method is characterized in that, when the recrystallized crude cesium alum is dissolved in step S3, at least one of the cesium salts or cesium solutions in which the cesium molar amount is greater than the aluminum molar amount in the production process is added, and the added amount is calculated based on the cesium molar amount, and the added cesium molar amount minus the aluminum molar amount is 1-50 times the total molar amount of rubidium and potassium in the cesium alum.

2. The preparation method according to claim 1, characterized in that: The cesium salt in which the molar amount of cesium is greater than the molar amount of aluminum in the production process includes the high-purity cesium bicarbonate obtained in step S7 and the high-purity cesium carbonate obtained in step S8.

3. The preparation method according to claim 1, characterized in that: The cesium solution in which the molar amount of cesium is greater than the molar amount of aluminum in the production process includes the cesium sulfate solution in step S4, the slag washing water 1 in step S4, the cesium hydroxide solution in step S5, the slag washing water 2 in step S5, the high-purity cesium carbonate solution in step S6 and the second crystallization mother liquor in step S5.

4. The preparation method according to any one of claims 1 to 3, characterized in that: The step S3 is performed by recrystallization for more than two times.

5. The preparation method according to claim 4, characterized in that: The sulfuric acid concentration in step S1 is 20-40%, the liquid-solid mass ratio of sulfuric acid to cesium garnet is 4:1-7:1, and the leaching temperature is 100-120°C.

6. The preparation method according to claim 4, characterized in that: The temperature of the cooling crystallization in step S2 is 10-50°C, preferably 30-50°C.

7. The preparation method according to claim 4, characterized in that: The dissolution temperature of the recrystallization in step S3 is 90-105°C, the liquid-solid mass ratio of the solvent to the crude cesium alum is 4:1-7:1, and the crystallization temperature is 10-50°C, preferably 30-50°C.

8. The preparation method according to claim 4, characterized in that: The aluminum removal in step S4 refers to adding an aluminum removal agent until the end point pH is 8-10, and the aluminum removal agent is at least one of CaO, Ca(OH)2 and Ba(OH)2.

9. The preparation method according to claim 7, characterized in that: The solvent is at least one of pure water, the slag washing water 1 in step S4, the slag washing water 2 in step S5, and a cesium sulfate solution from which aluminum has been removed.

10. The preparation method according to claim 4, characterized in that: The amount of Ba(OH)2 added in step S5 is 1.05-2.0 times the molar amount of sulfate in the cesium sulfate solution.

11. The preparation method according to claim 10, characterized in that: The Ba(OH)2 is purified by recrystallization.

12. The preparation method according to claim 4, characterized in that: In step S5, dilute sulfuric acid is added when washing the barium sulfate precipitate, and the pH of the washing water is controlled to be 1-6.

13. The preparation method according to claim 4, characterized in that: The purification and impurity removal in step S6 refers to introducing CO2 gas into the cesium hydroxide solution until the pH value is 8-10.

14. The preparation method according to claim 4, characterized in that: In step S7, the carbonization crystallization is carried out by introducing CO2 into the concentrated high-purity cesium carbonate solution under stirring until the pH value is 7-9.

15. The preparation method according to claim 4, characterized in that: The drying and decomposition conditions in step S8 are vacuum drying at 60-90° C. for 4-48 hours, and then heating to 250-300° C. and keeping warm for 4-24 hours.

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