RU2262383C1 - Method of preparing microspherical sorbent for treating liquid wastes to remove radionuclides, nonferrous and heavy metal ions - Google Patents

Abstract

FIELD: sorbents.

SUBSTANCE: invention relates to sorbents prepared from microspherical components of fly ashes from heat-and-power stations. For synthesis of microspherical sorbent, cenospheres isolated from coal combustion fly ashes are used, which are stabilized with respect to their composition by granulometric classification, gravitational and magnetic separation. Cenospheres are preliminarily perforated by treatment with etching solution based on mineral acid, after which active component is precipitated in internal space of microspherical carrier. Active components is selected from inorganic ion-exchange materials (ammonium molybdophosphate, transition metal ferrocyanides and sulfides, magnesium phosphate, magnesium carbonate, and the like) and organic extractants (trioctylphosphine oxide, triisobutylphosphine sulfide, and the like). Precipitation of is effected from supersaturated organic solutions or via synthesis directly in internal space of microspherical hollow carrier.

EFFECT: enhanced metal sorption efficiency.

6 cl, 2 dwg, 1 tbl, 6 ex

Description

The invention relates to sorbents obtained from industrial raw materials, in particular from the microspherical components of volatile ashes of thermal power plants, and can be used in nuclear energy and the chemical and metallurgical industry for the purification of liquid radioactive waste and wastewater from hydrometallurgical industries from radionuclides, non-ferrous and heavy metal ions , as well as for the additional extraction of platinum group metals, mainly palladium, from waste solutions and pulps.

Sorption technology, including the use of solid extractants (TWEX), is considered more effective than liquid extraction in the case of the separation of metals from very dilute solutions (less than 1 mg / l). Inorganic ion-exchange materials are known (sulfides, oxides, hydroxides, phosphates, ferrocyanides, heteropoly compounds, etc.) [V.V. Volkhin Selective inorganic sorbents and their use // Chemistry and technology of inorganic sorbents. Interuniversity collection of scientific papers. Perm Polytechnic Institute, 1980, pp. 3-19] and organic extractants specific for metal cations of a certain type [Mazurenko EA Extraction Guide. Kiev: Technique, 1972, 448 pp.], Which are used for the purification of liquid wastes from radiochemical and hydrometallurgical industries from radionuclides, non-ferrous and heavy metal cations, and platinum group metals. Mechanically strong forms of solid sorbents based on inorganic ion exchangers (composite sorbents) and organic extractants (TVEX) can be obtained by applying the active component to porous inorganic or organic polymer carriers.

Thus, solid extractants for extraction from solutions of palladium, silver and mercury in the extraction chromatography mode are obtained by applying triisobutylphosphine sulfide and extractants of a similar nature to an organic carrier based on copolymers of styrene and divinylbenzene [Dakshinamoorthy A., Kumar T., Nandy K.K., et al . Separation of palladium by extraction chromatographic technique using Cyanex 471X (tri isobutyl phosphine sulphide) on Chromosorb-102 // Journal of Radioanal and Nucl. Chemistry, 2000, Vol.245, No.3, p.595-598], kizilgur, porous glass beads [Pat. US No. 4623522, 1986] or silica gel [Singh R., Khwaja A.R., Gupta B., et al. Uptake and extraction chromatographic separation of mercury (II) by triisobutylphosphine sulfide (TIBPS) sorbed on silica gel and decontamination of mercury containing effluent // Talanta, 1999, V.48, p.527-535}. Such TWEXs effectively extract silver and palladium from aqueous solutions, however, cannot be used to extract these components from heterogeneous media containing suspended solids.

Composite sorbents based on inorganic ion exchangers for extracting ¹³⁷ Cs radionuclide from liquid radioactive waste (LRW) are obtained by applying transition metal hexacyanoferrates (II) onto a fibrous or granular cellulose carrier {Pat. RF №2111050, 1998], as well as on silica gel [Pat. US No. 6046131, 2000]. Abroad, a composite selective ^137Cs sorbent based on the ammonium salt of molybdophosphoric heteropoly acid introduced into a polyacrylonitrile (AMP-PAN) polymer matrix has been developed [Tranter T.J., Herbsta RS, Todd T.A., et al. Evaluation of ammonium molybdophosphate-polyacrylonitrile (AMP-PAN) as a cesium selective sorbent for the removal of ¹³⁷ Cs from acidic nuclear waste solutions // Advances in Environmental Research, 2002, V.6, p. 107-121]. However, despite the high efficiency of organomineral sorbents at the sorption stage, at the final stage of conditioning of radioactive waste, the problem arises of converting a sorbent saturated with radionuclides into a mineral-like stable form suitable for long-term burial. When using traditional inorganic carriers (silica gel, aluminum gel), it is highly likely that the finely dispersed phase of the inorganic active component will be carried away from the surface of the sorbent in contact with solutions of radioactive and other toxic elements.

Closest to the claimed invention is a microspherical zeolite sorbent for the purification of liquid waste from radionuclides, non-ferrous and heavy metal ions (US Pat. RF No. 2214858, 2003), which contains one or more zeolites of the type NaX, NaA or NaP1, localized in a microspherical matrix hollow media with a diameter of up to 400 microns. The sorbent is obtained by hydrothermal treatment of hollow aluminosilicate microspheres of energy ashes (cenospheres) in the presence of an activating solution, while the synthesis of zeolites proceeds both on the outer and inner surfaces of the hollow microspheres. The exchange capacity of the sorbent for cesium and strontium is 2 mEq / g sorbent, and for cations Ni, Cu, Cr, Co, Cd, Hg, Zn - about 1 mEq / g. Despite the wide range of recoverable cations, the zeolite sorbent provides high degrees of purification only in a narrow region of acidity (pH 3-7) and with a low salt content (not more than 0.1 g-equiv Na ⁺ / L). Sorbent selected for the prototype.

The aim of the invention are sorbents in the form of hollow spherical granules up to 400 microns in size with a porous glass-crystalline shell and an active component localized in the internal free volume. Another objective of the invention is to obtain microspherical sorbents based on cenospheres of energy ashes, the active components of which are inorganic ion exchangers and organic extractants.

This goal is achieved by the fact that the cenospheres are pre-perforated by treatment with an etching reagent based on mineral acid, and the active component is introduced into the internal volume by its synthesis directly in the cavity of the cenospheres or by precipitation from supersaturated organic solutions.

The essence of the claimed invention is as follows. Cenospheres of fly ash are an affordable and relatively cheap aluminosilicate material obtained as a by-product from coal combustion in thermal power plants. Cenospheres of fly ash of Kuznetsk coal are characterized by the following chemical composition (wt.%): SiO ₂ - 63.1-65.2; Al ₃ O ₃ - 20-26.4; Fe ₂ O ₃ - 4.2-5.1; Ca - 0.9-2.1; MgO - 1.0-2.6; K ₂ O - 2.3-4.0; Na ₂ O - 0.5-1.2. Further stabilization of the composition of the cenospheres can be carried out by dividing the cenospheres by size, density and magnetic properties [Pat. RF №2212276, 2003].

Peculiarities of the morphology and mineral-phase composition of the cenospheres make this material a promising raw material for the production of microspherical carriers and sorbents. Due to the presence of an internal cavity, high strength of the glass crystal shell, thermal stability and acid resistance of the cenosphere, microcontainers can be considered mechanically strong and stable in aggressive environments for encapsulating the active component in the internal volume of the carrier. This design of the microspherical sorbent most meets the requirements of the treatment of especially hazardous waste, since the aluminosilicate shell of the carrier with a given through porosity prevents the uncontrolled removal of the dispersed active component and can serve as a matrix for the burial of radionuclides in stable mineral-like compounds.

Along with this, in terms of their mineral phase composition, the cenospheres are glass-crystalline material based on aluminosilicate glass with inclusions of nanosized iron-containing phases of spinel structure, which determine the magnetic properties of a microspherical hollow carrier [Vereshchagina TA, Anshits NN, Maksimov NG et al. The nature and properties of iron-containing nanoparticles dispersed in the aluminosilicate matrix of cenospheres // Physics and Chemistry of Glass, 2004, No. 3 - in print}. This allows you to create processes of sorption extraction of precious metals from liquid wastes containing finely dispersed suspensions of solid components (for example, from the pulp of the tailings of sulfur-sulfide flotation), based on the possibility of magnetic concentration of the sorbent and its separation from a heterogeneous medium.

The open porosity of the cenosphere shell (perforation) and thereby the accessibility of the internal volume is achieved by the action of acidic reagents on areas of glass inhomogeneous in chemical and phase composition associated with fine impregnation of ore minerals (quartz, hematite, magnetite, mullite). In particular, etching of the cenospheres with a hydrofluoric acid reagent (for example, NH ₄ F-HCI-H ₂ O) makes it possible to obtain regular through pores of rounded shape in the cenosphere shell with a diameter of 2-20 μm, ensuring the availability of the inner volume of the globules to fill it with the active component. Depending on the composition of the cenospheres and the type of reagent used, it is possible to obtain a microspherical hollow carrier with a given through porosity of the shell.

Known methods for applying active components to porous carriers, including impregnation with salt solutions with intermediate drying of a saturated carrier, are not applicable in this case due to the extremely low solubility of inorganic ion exchangers in water and most organic solvents. When applying compounds that are soluble in organic solvents but not soluble in water (for example, organic extractants), the solvent removal step should also be avoided by evaporation, since the active component is carried out to the outer surface of the microspherical carrier. In this regard, the filling of the internal cavity of the cenospheres is carried out by synthesis of a substance directly in the internal volume of the carrier or its deposition from a supersaturated solution.

Depending on the problem to be solved, microspherical sorbents with various active components can be obtained, including inorganic ion exchangers (ammonium molybdophosphate (AMP), transition metal ferrocyanides and sulfides (Zn, Cu, Ni, etc.), Mg and ammonium phosphates), and organic extractants (triisobutylphosphine sulfide (TIBPS), trioctylphosphine oxide (TOFO), etc.). The list of selective sorbents is not limited to the given examples.

Figure 1 shows a granule of a microspherical hollow carrier obtained by etching cenospheres with a particle size of 0.4-0.315 mm reagent NH ₄ F-HCI-H ₂ O (according to scanning electron microscopy).

Figure 2 shows a granule of a microspherical sorbent with a particle size of 0.16-0.1 mm with ammonium molybdophosphate localized in the internal volume (according to optical microscopy).

The invention is demonstrated by the following examples.

EXAMPLE 1. To obtain a microspherical sorbent using a stabilized cenosphere with an iron content of 3.1 wt.% Calculated on Fe ₂ About ₃ , a particle size of 0.16-0.1 mm and a bulk density of 0.37 g / cm ³ obtained in the separation of the concentrate of cenospheres of fly ash of Kuznetsk coal by the method of particle size classification, hydrodynamic separation and magnetic separation.

A portion of cenospheres is placed in a polypropylene glass and treated with an etching solution of the following composition:

NH ₄ F - 3.7 g

HCI (12 M) - 10 ml

H ₂ O (dist) - up to 100 ml.

Processing time 15 minutes, the ratio of solid phase: liquid = 1: 10.

At the end of processing, the cenospheres are divided into floating (non-perforated cenospheres) and drowned (perforated cenospheres) layers. Both layers are collected and dried separately in a ventilated chamber at 100-110 ° C. To obtain the sorbent use perforated cenospheres.

Perforated cenospheres are placed in a separatory funnel, which is pumped out with a water-jet pump to a residual pressure of 8.0 kPa and maintained at this vacuum for 30-40 minutes. After that, a hot (60-80 ° C) solution of the following composition is fed into the funnel from below from below:

(NH ₄ ) ₆ Mo ₇ O ₂₄ · 4H ₂ O - 160 g

NH ₄ H ₂ PO ₄ - 8 g

H ₂ O (dist) - 500 ml.

The ratio of cenosphere: solution = 1: 2.

At the end of this procedure, the funnel with cenospheres and hot solution is held for 20-30 minutes, and then through the lower valve the funnel is connected to the atmosphere, as a result of which the solution fills the internal cavities of the perforated cenospheres.

Cenospheres filled with a solution are filtered off from the excess liquid phase and placed in an installation for treating with gaseous hydrogen chloride under static or dynamic conditions with continuous rotation of the vessel with cenospheres. During the processing time, which is 24 hours, a yellow precipitate of ammonium molybdophosphate forms directly in the inner cavity of the perforated cenospheres.

The resulting product is washed with distilled water and dried in a ventilated chamber at 100-120 ° C. Table 1 shows the characteristics of the obtained sorbent.

EXAMPLE 2. To obtain a microspherical sorbent, stabilized cenospheres with an iron content of 3.1 wt.% Calculated on Fe ₂ O ₃ , fineness of 0.315-0.2 mm and bulk density of 0.34 g / cm ^{3 are used} . The etching solution is carried out as in example 1. The perforated cenospheres are isolated as in example 1, placed in a separatory funnel and, under vacuum, as described in example 1, they are filled with a hot (60-80 ° C) solution of the following composition (stage 1 of filling the cenospheres):

K ₄ Fe [(CN) ₆ ] · 3H ₂ O - 40 g

H ₂ O (dist) - 100 ml.

Cenospheres filled with a solution are filtered off from the excess liquid phase and dried in a ventilated chamber at 100-120 ° C.

The resulting product is again evacuated and filled with a hot solution of the following composition (2 stage of filling the cenospheres):

CuSO ₄ · 5H ₂ O - 55 g

H ₂ O (dist) - 100 ml.

The cenospheres are left in the solution for 24 hours to crystallize the copper ferrocyanide, then they are filtered off from the excess liquid, washed with distilled water and dried in a ventilated chamber at 100-120 ° C (Table 1).

EXAMPLE 3. To obtain a microspherical sorbent, the cenospheres are used as in example 2. The etching solution and the extraction of perforated cenospheres are carried out as in example 1. A portion of the perforated cenospheres is sequentially in two stages, as described in example 2, filled with solutions of the following composition:

Stage 1 of filling the cenospheres: 2 stage of filling cenospheres: MgSO ₄ · 7H ₂ O - 45 g Na ₃ PO ₄ · 12H ₂ O - 80 g H ₂ O (dist) - 100 ml H ₂ O (dist) - 100 ml.

Cenospheres are left in solution for 24 hours to crystallize magnesium phosphate, then filtered off from excess fluid, washed with distilled water and dried in a ventilated chamber at 100-120 ° C (Table 1).

EXAMPLE 4. To obtain a microspherical sorbent, the cenospheres are used as in example 2. The etching solution and the extraction of perforated cenospheres are carried out as in example 1. A sample of perforated cenospheres is sequentially in two stages, as described in example 2, filled with solutions of the following composition:

Stage 1 of filling the cenospheres: 2 stage of filling cenospheres: Na ₂ S - 42 g NiNO ₃ · 6H ₂ O - 96 g H ₂ O (dist) - 100 ml H ₂ O (dist) - 100 ml.

The cenospheres are left in the solution for 24 hours to crystallize nickel sulfide, then they are filtered off from the excess liquid, washed with distilled water and dried in a ventilated chamber at 100-120 ° С (Table 1).

EXAMPLE 5. To obtain a microspherical sorbent, stabilized cenospheres with an iron content of 3.1 wt.% Calculated on Fe ₂ O ₃ , particle size 0.4-0.315 mm and bulk density 0.33 g / cm ^{3 are used} . Processing the etching solution and the selection of perforated cenospheres is carried out as in example 1. A portion of the perforated cenospheres in succession in two stages, as described in example 2, is filled with solutions of the following composition:

Stage 1 of filling the cenospheres: 2 stage of filling cenospheres: Na ₂ CO ₃ - 45 g MgSO ₄ · 7H ₂ O - 45 g H ₂ O (dist) - 100 ml H ₂ O (dist) - 100 ml.

The cenospheres are left in the solution for 24 hours to crystallize magnesium carbonate, then they are filtered off from excess fluid, washed with distilled water and dried in a ventilated chamber at 100-120 ° C.

EXAMPLES 6, 7. To obtain microspherical sorbents of the type of solid extractants, stabilized cenospheres with an iron content of 3.3 wt.% Calculated on Fe ₂ O ₃ , fineness of 0.16-0.125 mm and bulk density of 0.38 g / cm ^{3 are used} . The etching solution and the selection of perforated cenospheres are carried out as in example 1. Samples of perforated cenospheres are placed in a separatory funnel and, under vacuum, as described in example 1, they are filled with a hot (50 ° C) solution of the following composition:

Example 6 Example 7 trioctylphosphine oxide - 102.6 g triisobutylphosphine sulfide - 40 g C ₂ H ₅ OH - 100 ml. With ₂ H ₅ OH - 100 ml.

The resulting products are left in solution for 24 hours, after which they are filtered off from excess fluid, washed with distilled water and dried in air at 20-25 ° C for a day.

For the obtained sorbents, equilibrium ion-exchange capacities were measured for Cs, Pd cations and some non-ferrous metals. The sorption results are presented in table 1.

Thus, the above examples confirm the possibility of reproducibly producing microspherical sorbents based on cenospheres of energy ashes, the active components of which are inorganic ion exchangers and organic extractants.

Table 1
Characteristics of microspherical sorbents based on cenospheres Example Perforated cenosphere Perforated Cenosphere Sorbent Sorption Results Fraction size, mm Bulk weight, g / cm ³ Specific surface, m ² / g Active component The content of the active component, wt.% Bulk weight, g / cm ³ Specific surface, m ² / g Sorbed ion Sorbent capacity, mg / g Solution composition 1 0.16-0.1 0.25 1,5 Ammonium Molybdic Phosphate 23.0 0.33 47 Cs 6.4 Cs - 68 mg / l NaNO ₃ - 350 g / l HNO ₃ - 1 mol / L 2 0.315-0.2 0.35 0.6 Copper ferrocyanide 41.3 0.59 1.9 Cs 6.0 Cs - 63 mg / L 3 0.315-0.2 0.27 0.8 Magnesium Phosphate 21.8 0.35 8.8 Ni 10,4 Ni - 100 mg / L 4 0.315-0.2 0.27 0.8 Nickel sulfide 19.3 0.34 12.1 Pd 25.0 Pd - 45 mg / L Cu 1.9 Cu - 19 mg / L 5 0.4-0.315 0.27 0.7 Magnesium carbonate 40.8 0.46 1.9 Co 1,0 Co - 10 mg / g 6 0.16-0.125 0.30 1.8 Trioctyl phosphine oxide 19.8 0.51 0.7 Pd 20.8 Pd - 340 mg / L 7 0.16-0.125 0.30 1.8 Triisobutyl phosphine sulfide 21,2 0.40 0.7 Pd 33.7 Pd-340 mg / L

Claims (6)

1. A method of producing a microspherical sorbent for cleaning liquid wastes from radionuclides, non-ferrous and heavy metal ions, comprising introducing the active component into the inner volume of the cenospheres with a diameter of up to 400 microns with a porous glass-crystal shell, characterized in that the cenospheres are pre-perforated by treatment with etching reagent based on mineral acid and the introduction of the active component into the internal volume is carried out by its deposition directly in the cavity of the cenospheres. 2. The method according to claim 1, characterized in that ion-exchange materials or organic extractants are used as the active component. 3. The method according to claim 2, characterized in that the active component is selected from the range including ammonium molybdophosphate, transition metal ferrocyanides and sulfides, magnesium phosphate, magnesium carbonate, trioctyl phosphine oxide or triisobutyl phosphine sulfide. 4. The method according to claim 1, characterized in that the deposition of the active component is carried out in the process of its synthesis. 5. The method according to claim 1, characterized in that the deposition of the active component is carried out from its supersaturated organic solutions. 6. The method according to claim 1, characterized in that as the etching reagent use a solution of the composition NF ₄ F-HCI-H ₂ O with a content of F ^- 1 g-ion / l with a molar ratio F ^- / Cl ^- = 1,0 .

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