RU2113024C1 - Inorganic spherically granulated composite zirconium hydroxide-based sorbent and method of preparation thereof - Google Patents

Abstract

FIELD: sorbents. SUBSTANCE: invention focuses on sorbents used when cleaning liquid media in dynamic mode to remove radionuclides. Sorbent of invention contains mixed metal hexacyanoferrate with general formula M(I)_xM(II)_(4-x)/2[Fe(CN)₆], where M(I) is lithium, sodium, potassium, and ammonium cations, or their mixture; M(II) manganese, ferric, cobalt, nickel, cupric, zinc, and cadmium cations, or their mixture; x=0-3.6, in amount 5-54 wt % and 0-48 wt % water. The latter is determined under drying sorbent at 110 C. Sorbent is prepared via consecutive chemical treatment of gel spheres of zirconium hydroxide containing 15-75 wt % water by aqueous solution of M(II) salt and then M(I) hexacyanoferrate followed by drying at 18 to 300 C. EFFECT: increased selectivity to cesium radionuclides and sorption capacity as well as stability under prolonged use. 6 cl, 6 tbl

Description

The invention relates to an inorganic composite spherogranulated ion exchanger (sorbent) based on an inorganic carrier — zirconium hydroxide and transition metal hexacyanoferrate, as well as to a method for producing it. The sorbent is effective in the continuous purification of liquid media (process, drinking and waste waters) from various radionuclides, in particular ¹³⁷ Cs and ¹³⁴ Cs. It can find application in the extraction of valuable microcomponents, such as silver, rubidium, cesium, from water flows.

 Despite significant progress in the development of new ion-exchange materials, especially those that are selective for metal ions, there is a certain drawback in ion exchangers, which have increased selectivity for heavy alkali metal ions, in particular cesium cations. Organic cation exchange resins, although they are chemically and mechanically stable materials, exhibit much lower selectivity in this regard than inorganic sorbents based on sparingly soluble transition metal hexacyanoferrates [1. Tananaev I.V., Seifer G.B., Kharitonov Yu.Ya. and others. Chemistry of ferrocyanides. -M.: Science, 1971; 2. Loewenschuss H. Metal-ferrocyanide complexes for the decontamination of cesium from agueous radioactive waste // Radioact. Waste Manage., 1982, v. 2, No. 4, p. 327; 3. Milyutin V.V., Gelis V.M., Penzin R.A. Sorption-selective characteristics of inorganic sorbents and ion-exchange resins with respect to cesium and strontium // Radiochemistry, 1993, v. 35, No. 3, p. 76].

Inorganic sorbents based on mixed transition metal ferrocyanides (e.g. nickel and cobalt) obtained by precipitation are known. For example, a sorbent of the composition K ₂ Co [Fe (CN ₆ )] is used to remove radioactive cesium from aqueous solutions having a pH of 1-14 [4. U.S. Patent No. 3,296,123, cl. 210-38, 1967]; the sorbent is prepared by adding an aqueous solution of K ₄ [Fe (CN ₆ )] to an aqueous solution of cobalt salt — Co (NO ₃ ) ₂ , CoSO ₄ and CoCl ₂ to form a precipitate that is separated, washed and dried at a temperature of not more than 150 ^o C. A sorbent of the composition K _n Ni _m [Fe (CN ₆ )] (where n = 0.92-1.00, m = 1.50-1.54), which is used to extract rubidium from solutions [5. Auth. St. USSR N 552105, class B 01 J 1/22, C 01 D 17/00, 1977]; the sorbent is obtained by reducing the gel-like precipitate Ni _1,5 [Fe (CN ₆ )] to hexacyanoferrate (II), followed by granulation of the obtained product by freezing.

 Despite the good sorption-selective properties of such ion exchangers, their use in the column mode of sorption is inefficient, since the sorbents obtained by the gel method are characterized by low strength and, during the filtration process, the charge material is quickly caked and destroyed. In addition, these inorganic ion exchangers have an irregular grain shape, which creates a significant pressure drop when filtering the solution through a sorbent.

To overcome these shortcomings, composite sorbents based on an organic spherical granular carrier and mixed transition metal hexacyanoferrates have been proposed: on anion exchange resin [6. UK patent N 1115258, CL B 01 D 15/04, 1968; 7. US patent N 3453214, CL. G 21 F 9/12, B 01 D 15/04, C 01 D 11/04, 1969; 8. German patent N 4009651, cl. B 01 J 45/00, 39/04, A 23 C 21/00, G 21 F 9/06, 1991], on cation exchange resin [9. Auth. St. N 778780, cells, B 01 J 19/04, C 01 D 17/00, 1980; 10. European patent N 217143, CL B 01 J 39/02, 39/16, 1987], on porous coal or granular cellulose [11. RF patent N 2021009, cl. B 01 J 20/02, 20/30, 1994]. Sorbents are used mainly for the decontamination of solutions from radioactive cesium (except [9], which is intended for hydrometallurgy and chemical technology). Sorbents are obtained by alternately treating the organic base with concentrated solutions of transition metal salts and alkali metal hexacyanoferrate (II); in this way receive:
- hexacyanoferrates of the formula A _z M _y [Fe (CN ₆ )], where A is Li, Na, K, Rb, M is Sc, Ti, Cr, Mn, Fe, Co, Ni, Cu [6];
- A _z M _y [Fe (CN) ₆ ], where A is an alkali metal, M is Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn [7];
- mixed hexacyanoferrate of ammonium and copper [8];
- mixed hexacyanoferrate of alkali metal and copper [9].

Inorganic composite sorbents are also obtained by introducing an inorganic powdery sorbent into the reaction mixture during the polycondensation synthesis of an organic cation exchanger [10]; in this case, hexacyanoferrates of metals such as Co, Fe, Ni, Cu, Mn, Zn, Ti, Cd, Zr, Cr, V, Pb, Mo, which are introduced in an amount of 1-80 wt.% from total mass. Finally, sorbents can also be obtained by treating the porous organic support with an aqueous suspension obtained by mixing salts of the transition metal, alkali metal hexacyanoferrate and water-soluble phosphate, the transition metal salt containing this metal in different oxidation states [II]; the composition of the crystalline phase formed in the carrier is compound M $\genfrac{}{}{0ex}{}{\text{1}}{\text{x}}$ M $\genfrac{}{}{0ex}{}{\text{2}}{\text{y}}$ [Fe (CN) ₆ ], where M ¹ is Fe, Ni, Cu, Co, Cr, Ti, and M ² is Li, K, Na, NH ₄ , and the sorbent contains up to 25-30 wt.% Of the active component .

 The disadvantages of the known sorbents according to patents [6-11] are that in conditions of prolonged use during the decontamination of highly active solutions or when working in strong radiation fields, the destruction of the organic base (carrier) and the destruction of the sorbent occurs; as a result, this reduces the useful time of the download.

Therefore, the most preferred from the point of view of radiation resistance are composite hexacyanoferrate sorbents on an inorganic carrier, which is usually used as:
- alumogel [12. Auth. St. USSR N 801871, class B 01 J 19/04, 1981], and the active component is mixed hexacyanoferrates (II) of potassium and Mg, Zn, Mn or Fe in an amount of 26.9-57.4 wt.%;
- zeolites, or aluminosilicates [13. German patent N 3045921, class B 01 J 20/16, 1981; 14. Auth. St. USSR N 1115792, class B 01 J 20/00, 1984], the active component according to [13] is mixed alkali metal and calcium hexafyanoferrates (II), according to [4] mixed alkali metal hexafyanoferrates (II) and Cu, Ni, Co, Mn or Zr;
silica gel [15. Auth. St. Czechoslovakia N 179541, class B 01 J 13/00, 1979], the active component is potassium hexafyanoferrates (II) and Zn, Cd or Ni;
- fiberglass [6], the active component, as described above, mixed hexacyanoferrate (II) of an alkali metal and a transition metal in an amount of 20 wt.%.

 All of these composite sorbents, except sorbent [14], used in chemical technology for the separation of rubidium and cesium from technological and natural waters, are intended for the selective separation of radioactive cesium from technological and waste solutions of the nuclear industry.

 The main disadvantage of the known hexacyanoferrate composite sorbents on an inorganic carrier [65, 12-15] is associated with their unsatisfactory chemical resistance in alkaline media (especially at pH values> 9-10), which is due to the natural inorganic matrix. In addition, in order to form a high concentration of the crystalline phase in the carrier (both inorganic and organic), the base is usually treated with saturated solutions of reagents and repeatedly, which complicates the synthesis and increases the volumes of the generated wastewater.

 The closest in technical essence to the claimed sorbent and the method of its production is an inorganic spherical granular sorbent based on zirconium hydroxide obtained using the sol-gel method, in which the hardening of the material is combined with the formation of granules (Kalinin N.F., Zilberan M.V. and etc. On the production technology of inorganic sorbents // Abstract of the XIII All-Russian seminar "Chemistry and technology of inorganic sorbents". Minsk, 1991, p. 29). In the known technical solution, the method for producing the sorbent is based on a sol-gel process and granulation with a binder, which includes hardening a suspension of an inorganic sorbent, for example zirconium hydroxide, in a solution of an organic polymer capable of forming a stable sol. The obtained composite sorbent has high hydromechanical strength, uniformity of particle size distribution and can be used as a chemically stable cation-exchange loading of columns in the treatment of aqueous streams having an alkaline environment.

 A disadvantage of the known technical solution is the low sorption capacity for heavy alkali metals and low selectivity for cesium radionuclides in the presence of a salt background and high alkalinity (pH> 8-9). In addition, the use of a polymer binder in the known sorbent limits its scope for technological solutions with a high level of activity and high temperature due to radiation and thermal degradation of the organic base and destruction of the material.

 The basis of the invention is the task of creating a spherical granular inorganic composite sorbent on an inorganic carrier - hydrated zirconia containing mixed transition metal hexacyanoferrate as a selective sorption medium and characterized by increased stability in water flows (especially in the alkaline region) under conditions of its long-term operation, and also develop a method for producing this sorbent, providing the formation in an inorganic basis of the specified crystalline phases s and creation of the necessary complex of physicochemical properties and characteristics in the composite (spherical grain shape, high sorption capacity, increased selectivity to cesium radionuclides from highly concentrated salt solutions, including those having a pH of more than 8, satisfactory mechanical strength of grain, increased chemical resistance sorbent), which ultimately will ensure the effective use of the material in dynamic conditions and increase the working resource of the load.

где
M^I - Li⁺, Na⁺, K⁺, NH $\genfrac{}{}{0ex}{}{\text{+}}{\text{4}}$ или смесь,
M^II - Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺ или их смесь,
x=0-3,6,
в количестве 5-54 мас.% и воду в количестве 0-48 мас.%, определяемую с помощью высушивания при 110^oC.The problem is solved in that it offers a spherical granular inorganic composite sorbent based on hydrated zirconia containing mixed metal hexacyanoferrate of the composition as active component

Where
M ^I - Li ⁺ , Na ⁺ , K ⁺ , NH $\genfrac{}{}{0ex}{}{\text{+}}{\text{4}}$ or a mixture
M ^II - Mn ²⁺ , Fe ²⁺ , Co ²⁺ , Ni ²⁺ , Cu ²⁺ , Zn ²⁺ , Cd ²⁺ or a mixture thereof,
x = 0-3.6,
in an amount of 5-54 wt.% and water in an amount of 0-48 wt.%, determined by drying at 110 ^o C.

 The proposed composite sorbent based on hydrated zirconia containing the crystalline phase of hexacyanoferrates of the claimed composition as an active component has enhanced chemical resistance, as well as capacity and selectivity for cesium, which ensures an increase in its working life in liquid streams as a load. An increase in the content of the crystalline phase in the sorbent over 54 wt.% Leads to a deterioration in the strength properties of the material, and a decrease in its content is less than 5 wt. % - to a significant decrease in sorption capacity.

According to the above formula, the composition of the crystalline phase at x = 0-3.6 varies from simple transition metal hexacyanoferrate (II) M $\genfrac{}{}{0ex}{}{\text{II}}{\text{2}}$ [Fe (CN) ₆ ] to mixed alkali metal and transition metal hexacyanoferrate M $\genfrac{}{}{0ex}{}{\text{I}}{\text{3.6}}$ M $\genfrac{}{}{0ex}{}{\text{II}}{\text{0.2}}$ [Fe (CN) ₆ ]. The increase in the alkali metal content in the claimed composition above the specified limit (x> 3.6) leads to a significant decrease in the sorption ability of the inorganic ion exchanger.

The problem is also solved by the proposed method for producing the aforementioned material, including the treatment of gel spheres of zirconium hydroxide containing 15-75 wt.% Water, an aqueous solution of a transition metal salt of Mn, Fe, Co, Ni, Cu, Zn and / or Cd, washing with water then processing with an aqueous solution of alkali metal hexacyanoferrate (II) salt of Li, Na, K and / or ammonium, washing with water and drying to a moisture content of 0-48 wt.%. In this case, the gel spheres of zirconium hydroxide are treated with an aqueous solution of a transition metal to a metal content of 50-800 mmol / l, and solutions of chlorides, nitrates or sulfates with a concentration of 0.1 mol / l to saturated are used as transition metal salts, and during further processing of the gel spheres, solutions of hexacyanoferrate salts with a concentration of 0.1 mol / l to saturated are used. However, at the final stage, the drying and heat treatment of the gel spheres is carried out at 18-300 ^o C to a moisture content of 0-48 wt.%, Obtaining granules of the target product.

In accordance with the claimed method, gel spheres of hydrated zirconium dioxide (GDC) obtained by any known methods (for example, sol-gel methods: [16. Application 94028672/26 from 08/15/94, for which positive decision dated 5.06.95 g] either [17. Auth. St. USSR N 1491561, CL B 01 J 20/06, 1989]). The gel spheres of HDC with a moisture content of 15-75 wt.% Are treated in an appropriate container with stirring or in a column with an aqueous solution of a salt of a transition divalent metal Mn, Fe, Co, Ni, Cu, Zn, Cd. The upper limit of humidity is due to technological limitations in the synthesis of spherical gel particles of HDC. The lower value of humidity is associated with a change in the porous structure of HDC particles during thermal dehydration: the specific volume and pore size are greatly reduced, as a result of which diffusion of large Fe (CN) is difficult at the second processing stage $\genfrac{}{}{0ex}{}{\text{-}}{\text{6}}$ - -ions in the matrix, which affects the decrease in the content of the crystalline phase and, accordingly, the capacity of the final product. Use solutions of nitrates, chlorides or sulfates of these salts with a concentration of from 0.1 mol / l to saturated. The conditions and mode of chemical treatment (contact time, mixing speed, etc.), as well as the ratio of solid to liquid T: W, are chosen over a wide range so that at this stage, after sorption, the content of the transition metal in the gel spheres of the HDC is 50-800 mmol / l. Here, the lower level of the transition metal content is due to a decrease in the concentration of the crystalline phase in the sorbent and, accordingly, a decrease in sorption ability, and the upper level is due to a noticeable decrease in the strength of the final product. Then the gel sphere is washed with water from the reaction products.

Next, the washed gel spheres are treated with an aqueous solution of alkali metal hexacyanoferrate (II) salts of Li, Na, K and / or ammonium at an initial concentration in the solution of 0.1 mol / L to saturated. The conditions and processing conditions are supported, as in the first stage. The finished granules are washed with water and dried in air at 18-300 ^o C to a moisture content of 0-48 wt.%. Heat treatment of the finished product above 300 ^o C is impractical, because contributes to the thermal decomposition of the formed crystalline phase, as a result of which the sorption-selective properties of the sorbent are worsened.

где M^I - Li⁺, Na⁺, K⁺, NH $\genfrac{}{}{0ex}{}{\text{+}}{\text{4}}$ или их смесь,
M^II - Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺ или их смесь,
x=0-3,6,
в количестве 5-54 мас.% и воду в количестве 0-48 мас.%, определяемую с помощью высушивания при 110^oC.The final result is a durable, spherical granular material based on HDC, containing mixed metal hexacyanoferrate (II) type

where M ^I - Li ⁺ , Na ⁺ , K ⁺ , NH $\genfrac{}{}{0ex}{}{\text{+}}{\text{4}}$ or a mixture thereof,
M ^II - Mn ²⁺ , Fe ²⁺ , Co ²⁺ , Ni ²⁺ , Cu ²⁺ , Zn ²⁺ , Cd ²⁺ or a mixture thereof,
x = 0-3.6,
in an amount of 5-54 wt.% and water in an amount of 0-48 wt.%, determined by drying at 110 ^o C.

 The method of producing the sorbent is technologically advanced and quite simple, since it allows to exclude lengthy operations of deposition, filtering of the gel and its grinding. The washing of gel particles at all stages of the process occurs at a significantly lower consumption of wash water. The method does not require multiple alternating operations for processing an inorganic base, as is the case with organic ion exchangers.

Example 1. Received spherical granular particles of zirconium hydroxide by the electrochemical method according to the method [16]. For this, an aqueous solution of zirconium oxychloride with a concentration of 1.4 mol / L was fed into a single chamber electrolyzer with a capacity of 100 l made of titanium. The casing itself served as the cathode, and platinum was used as the anode. Electrolysis was carried out in two stages. At the first stage, the mode was maintained at a cathodic current density of 640 A / m ² and a temperature of 35-40 ^° C until the atomic ratio Cl / Zr of 0.92 was reached in the working solution. In the second stage, electrolysis was carried out at 70-80 ^o C until the atomic ratio Cl / Zr in the electrolyte solution reached 0.70.

The obtained zirconium hydroxide gel (GDC) was dispersed dropwise through a metal capillary with an inner diameter of 0.25 mm into a concentrated ammonia solution. The gel particles of HDC obtained as spheres were separated from the mother liquor and washed with deionized water. The result was spherical granules of the original HDC, containing in their composition water in an amount of 75.1 wt. %, estimated by weight loss of the sorbent by drying at 110 ^o C. These same granules of HDC were used to obtain the inventive inorganic sorbent in example 2 and according to table 1 (examples 3-8), table 2 (examples 12) and table 4 (examples 26-33).

As a prototype used granules HDC with a moisture content of 29.8 wt.% (Gross formula ZrO ₂ • 16.5 H ₂ O).

 In addition, to obtain granules of HDC with a different water content (Examples 13-15 of Table 2 and Examples 16-25 of Table 3), the initial spherical-granulated material was sprayed with a thin layer on a tray before processing and dried in air to a certain degree of humidity.

 Example 2. The best embodiment of the invention.

0.5 l of a 0.69 mol / l solution of Ni (NO ₃ ) _{2 was} added to 1.0 l of spherogranulated particles of HDC with a moisture content of 75.1 wt.%, Obtained according to example 1 and transferred to a conical glass flask, the solution was stirred in for 2 hours (first stage). The mother liquor was discarded and the solid phase was washed with deionized water.

48,6, C_крист 39,8,

11,6. Кристаллическая фаза, составляющая 39,8 мас% в общей массе продукта, соответствовала эмпирической формуле K_1,72Ni_1,14[Fe(CN)₆]. Сорбент имел статическую обменную емкость по цезию 0,65 моль/кг и коэффициент распределения ¹³⁷Cs в 2 моль/л растворе хлориде натрия 4,5 • 10³ л/кг.The washed granules were poured with 0.6 L of a 0.43 mol / L K ₄ Fe (CN) ₆ solution, the solution was stirred for 4 hours (second stage). The mother liquor was discarded and the solid phase was washed with deionized water. The granules were scattered in a thin layer on a tray and dried in air, and then in a thermostat at 110 ^° C. The granules were dispersed and a 0.4-1.0 mm fraction was used. The resulting material had the following chemical composition, wt.%:

48.6, C _crest 39.8,

11.6. The crystalline phase, constituting 39.8 wt% in the total mass of the product, corresponded to the empirical formula K _1.72 Ni _1.14 [Fe (CN) ₆ ]. The sorbent had a static cesium exchange capacity of 0.65 mol / kg and a distribution coefficient of ¹³⁷ Cs in a 2 mol / L solution of sodium chloride 4.5 • 10 ³ L / kg.

In a similar way, samples 3-8 of the table were synthesized. 1, however, the target products were dried in air to a different degree of humidity or thermally dehydrated at 110-500 ^o C. For testing, a fraction of 0.4-1.0 mm was used everywhere. As can be seen from the data, the best properties for the proposed solution show samples 4-7, having a moisture content of 0-48 wt.%. Higher humidity leads to a deterioration in strength properties (example 3), annealing of the final product at temperatures above 300 ^o C is impractical, as it contributes to a significant decrease in sorbability and selectivity of the sorbent (example 8).

In the same way, but using a solution of NiSO ₄ , received samples of different composition of the inventive sorbent (examples 9-11).

 In addition, in table. 2 (samples 12-15) presents the conditions of chemical treatment in the second stage of granules obtained when using water as a starting material (DDC) with a lower water content than in example 2, provided that a constant amount of nickel ions was introduced in the first stage .

 Table 3 shows the synthesis conditions and properties of the target product according to the proposed method based on a mixed potassium hexacyanoferrate and copper as a crystalline phase. As follows from examples 16–20, the optimal concentration of the transition metal in the HDC during chemical treatment at the first stage is 50–800 mmol / L of the initial gel spheres: with a lower content of the transition metal, the sorption capacity decreases noticeably, and with a higher content, the granules of the target product become fragile and crumble. In addition, in table. Figure 3 shows the effect of dehydration and heat treatment of the target product after the second stage of synthesis on its sorption-selective properties and substantiates the ranges of the proposed solution for the content of the crystalline phase in the composite sorbent and for the water content.

 In the table. 4 shows data on the properties and conditions of the synthesis of sorbents with other compositions of the crystalline phase and humidity obtained in example 2 by varying the concentration of reagents and the type of salts used at both stages of the synthesis, and in some cases also the ratio T: G.

Chemical analysis of the composition of the proposed composite material was performed as follows. After chemical dissolution, a portion of the sorbent in concentrated sulfuric acid upon heating, the solution was diluted with water and analyzed for the following macrocomponents:
- the content of ZrO ₂ - direct titration of zirconium with a solution of complexone III in the presence of an xylenol orange indicator against a background of 0.3-0.5 mol / l H ₂ SO ₄ ;
- content of Fe (CN) $\genfrac{}{}{0ex}{}{\text{4-}}{\text{6}}$ - direct titration with a solution of KMnO ₄ against a background of 0.1-0.3 mol / l H ₂ SO ₄ ;
- the content of transition metals (Mn, Fe, Co, Ni, Cu, Zn, Cd) - direct titration with a solution of complexone III in the presence of appropriate indicators according to "GOST 10398-76. Reagents. Complexometric method for determining the content of the basic substance.";
- the content of alkali metals (Li, Na, K) - flame photometrically using a flame analyzer fluid PAJ-2;
- ammonium content - gravimetrically in the form of ammonium tetraphenyl borate precipitated in an alkaline medium.

The moisture content of the sorbent (water content) was determined by the weight loss during drying of the sample at 110 ^o C for 5 hours

 The static exchange capacity (COE) of the samples was evaluated by the absorption of cesium ions from a 0.1 mol / L CsCl solution at a ratio of T: W = 100 g / ml, a contact time of 6 days, and periodic stirring.

The sorbent selectivity was evaluated by the distribution coefficient of the ¹³⁷ Cs (Kd) radionuclide in two salt media: 2 mol / L NaCl solution and simulated solution (content, g / L: H ₃ BO ₃ 100; NaNO ₃ 100; Na ₂ CO ₃ 10; NaCl 10; NaOH ≈ 100 to a pH value of 11.5) at a ratio of T: W = 1: 200 g / ml, a contact time of 6 days and periodic stirring.

 The degree of peptization of the sorbents was determined as follows. A portion of the sorbent 10 g was transferred into a glass flask and poured into 500 ml of deionized water, the solution was stirred periodically for 5 days. The sorbent was separated by filtration through an ashless blue ribbon filter. The metal hexacyanoferrate content was determined in the solution and its loss from peptization per 1 g of sorbent was calculated as a percentage of the initial amount. Data on the degree of peptization of the proposed sorbents and their comparative characteristics are given in table. 5.

Example 34. Received a sorbent based on mixed potassium hexacyanoferrate and cobalt by a gel method according to the known technical solution [4]. For this, 100 ml of a 0.5 mol / L K ₄ Fe (CN) ₆ solution was added slowly (over 30 min) to 240 ml of a 0.3 mol / L CoCl ₂ solution. The precipitate formed was left to stand for 1 h, then it was centrifuged, washed several times with water and dried at 115 ^° C. Insufficiently strong granules of irregular shape of dark red color with a bulk density of 0.46 kg / dm ^{3 were} obtained. The sorbent had a composition of K _1.12 Co _1.44 [Fe (CN) ₆ ], a static cesium exchange capacity of 0.63 mol / kg and a cesium distribution coefficient in a 2 mol / L NaCl solution equal to 2.0 • 10 ³ L / kg

 As can be seen from the table. 1-5, all inorganic spherogranulated sorbents obtained according to the proposed technical solution are characterized by high sorption ability and selectivity to cesium, as well as increased chemical resistance in aqueous media (more than 30 times compared to the analogue [4] according to Table 5).

 The usefulness of the proposed sorbents for the decontamination of technological aqueous solutions of nuclear power plants in dynamic mode follows from examples 35 and 36.

Example 35. A real solution from the tank of the liquid radioactive waste storage facility of a nuclear power plant, taken from a depth of 2 m, was passed through a glass sorption column with a diameter of 0.7 cm, loaded with 2.0 cm ^{3 of the} sorbent obtained in Example 30 (sorbent composition — Na _0.46 K _1.12 Co _1.21 [Fe (CN) ₆ ]. Fractional composition of the sorbent 0.4-0.63 mm. The solution was filtered at a volume rate of 10 column volumes per hour. The composition of the solution from the storage tank is shown in Table 6 .

After passing through 2125 column volumes of the solution, the ¹³⁷ Cs filtrate activity was at the level of 2.0 • 10 ^-7 Ci / L, which corresponded to a purification coefficient of 1025. The purification coefficient of ⁶⁰ Co was 1.5.

Example 36. An aqueous solution of Na ₂ SO ₄ with a concentration of 100 g / l, a pH of 9.2 and an activity of ¹³⁷ Cs 2.36 • 10 ^-8 Ci / l, which is a simulated regenerate of a block desalting plant of a nuclear power plant, was passed through a glass sorption column with a diameter of 0.9 cm, loaded with 1.5 cm ^{3 of} sorbent obtained according to example 2 (crystalline phase composition K _1.72 Ni _1.14 [Fe (CN) ₆ ]). The fractional composition of the sorbent is 0.4-0.63 mm. Filtration was carried out with a space velocity of 20 column volumes per hour.

After a continuous working resource of 3080 column volumes, the ¹³⁷ Cs filtrate activity was lower than 2 • 10 ^-11 Ci / L, which corresponded to a purification coefficient of more than 1000.

Claims (6)

1. Inorganic spherogranulated composite sorbent based on zirconium hydroxide, characterized in that it contains a mixed metal hexacyanoferrate (II) type

where M ^I - Li ⁺ , Na ⁺ , K ⁺ , NH $\genfrac{}{}{0ex}{}{\text{+}}{\text{4}}$ or a mixture thereof;
M ^II - Mn ²⁺ , Fe ²⁺ , Co ²⁺ , Ni ²⁺ , Cu ²⁺ , Zn ²⁺ , Cd ²⁺ or a mixture thereof;
x = 0 - 3.6,
in an amount of 5 to 54 wt.% and water in an amount of 0 to 48 wt.%, determined by drying at 110 ^o C.  2. A method of obtaining an inorganic spherogranular sorbent based on zirconium hydroxide, characterized in that the gel sphere of zirconium hydroxide with a water content of 15 to 75 wt.% Is treated with an aqueous solution of a transition metal salt of Mn, Fe, Co, Ni, Cu, Zn and / or Cd, washed with water, then treated with an aqueous solution of alkali metal hexacyanoferrate salts of Li, Na, K and / or ammonium, washed with water and dried to a moisture content of 0 - 48 wt.%.  3. The method according to claim 2, characterized in that the treatment of the gel spheres with a solution of a salt of a transition metal is carried out to a metal content of 50 - 800 mmol / L.  4. The method according to claim 2 or 3, characterized in that as the transition metal salts are used solutions of chlorides, nitrates or sulfates with a concentration of from 0.1 mol / l to saturated.  5. The method according to claims 2 to 4, characterized in that the gel spheres are treated with solutions of hexacyanoferrate salts at a concentration of from 0.1 mol / l to saturated. 6. The method according to PP.2 to 5, characterized in that the gel sphere of the final product is dried at 18 - 300 ^o C.

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