LT5124B - Method for obtaining zeolite sorbent - Google Patents

Abstract

The present invention conserns a method of making zeotite sorbent which can be used for removing of radionuclides from water solutions, deactivation of objects and equipment, with further fixation of radionuclides. A raw material containing zeoliteis saturated with KOH solution and then is hetaed at 350-550 C temperature. Jf the raw material is saturated with 4-5 weight % of KOH solution, it is heated during 0,5-1 h at 140-150 C, than is washed with water having pH 10-11. The raw material saturated with KOH and having 0,5-2 weigt % of organic compounds (re-counted on pure carbon) is heated 0,5-1,5 h at 350-550 C temperature with providing of hot air.

Description

The present invention relates to the field of chemical technology, specifically to the preparation of zeolitic sorbents, and can be applied to the removal of radionuclides from aqueous solutions by deactivating objects and equipment and subsequently fixing the radionuclides.

A known method of preparing zeolitic sorbents having a cubic 12.24 + 12.27A lattice (zeolital group A) (See 5pex fl. UeonnTHbie MoneKynapHbie cma - M.: Mvip, 1976, - c.731-764). Zeolite sorbents are obtained from the aluminosilicate raw material by heat treatment (crystallization step) followed by granulation of the resulting powder product together with a binder (usually about 10-20% by weight of clay) and heating at 450 + 600 ° C. The major disadvantage of these sorbents is the relatively low selectivity of cesium and strontium radionuclides.

The closest embodiment of the present invention is a method of obtaining a zeolitic sorbent type (A) having a cubic 12.24 + 12.27A lattice (see RU2057582, B01J20 / 18). The zeolite sorbent type (A) thus obtained is heated at a temperature of 450-600 [deg.] C. with a zeolite containing up to 0.2% fine dispersible carbon.

The disadvantage of this process is that the long production process and the desired result are achieved only if the feedstock contains fine dispersible carbon.

The object of the present invention is to improve the sorption-selective properties of the sorbent and to widen the spectrum of the radionuclides to be sorbed.

The objective is achieved by saturating the raw material containing zeolite with an alkali solution and then heating it at 350-550 ° C. In addition, the raw material is saturated with 5-8% potassium alkali solution. After saturating the stock with 4-5% potassium alkaline solution, heat for 0.5-1 h at 140-150 ° C and then wash with water at pH = 10-11. Potassium-alkali-saturated feedstock containing 0.5-2% organic compounds (expressed as pure carbon), heated for 0.5-1.5h at 350-550 ° C while simultaneously supplying hot air.

i

Zeolites are a group of minerals of the silicate class. They are mainly aluminosilicates of the formula M2 / nOAI ₂ O ₃ xSiO2yH2O; where M is the alkali or alkaline earth metal, n is the degree of oxidation. Zeolites have a tight and regular pore structure. These pores are filled with water molecules under normal temperature conditions. If water is removed from the pores of the zeolite, the pores may be refilled with water or other substances.

Synthetic zeolites are obtained by crystallization of a mixture of silicates and Na aluminate at 80 + 100 ° C. The resulting crystals (1 + 15μτη) are mixed with 15 + 20% ductile clay and form a mixture of 2 + 4mm diameter granules. For cation exchange e.g. In CaCl ₂ solution, the zeolites take the Ca form from the Na-form. The bulk density of the granulated zeolite is 0.62 + 0.78 kg / m ³ , the pressure resistance limit is 8 + 15 mPa, the dynamic moisture capacity is 90 + 160 mg / cm ³ . General purpose zeolite mole ratio SiO2 / AI ₂ O ₃ - 1 to 2 and acid resistant

- 6 to 10. The starting material contains 80 + 85% zeolite. The final product (after demineralization) contains 78 + 81% zeolite.

Experiments have shown that upon alkali saturation of the zeolite feedstock, the aluminum and silicon in the zeolite lattice dissolve during heat treatment (heating) to convert to KAIO ₂ and K ₂ SiO ₃ salts, which are highly effective sorbents.

- Radionuclide multicomponent ionic phocculants.

In addition, during the alkaline treatment, a system of transport pores (tubules) is formed in the sorbent matrix. At the same time, the kinetic parameters of the ion exchange of the target solution with sorbent potassium are significantly improved. In a zeolite lattice, the ion-exchange cation contains a potassium ion whose ionic radius is closest to that of the cesium and strontium ions. This is one of the factors that determine the good exchange rates of cesium and strontium absorption ions - diffusion coefficients, distribution constants and, ultimately, the volume of dynamic exchange of cesium and strontium radionuclides. ΚΑΙΟ ₂ and K2SiO ₃ salts (aluminate and potassium silicate) are effective absorbers of radionuclides in colloidal or semi-nuclear complexes.

The following are examples of methods for obtaining a zeolite sorbent.

example. 100g of zeolite is saturated with 5-8% KOH solution, heated for 0.5-1.5h at 350550 ° C. The compressive strength of 92-95 g (A) zeolite currant, density 0.8-0.85 g / cm ³ , is 7.5 N / granule.

example. 100g of zeolite is saturated with 4-5% KOH solution, heated for 0.5-1.0h at 140150 ° C, then washed with water at pH = 10-11. 8892 g of sorbent having characteristics similar to those of Example 1 are obtained.

example. 100g of treated zeolite containing organic matter (about 0.5-2% expressed as pure carbon) saturated with 5-8% KOH solution heated for 0.5-1 h at 350-550 ° C while also supplying hot air to the furnace. 90-92 g of sorbent having the above parameters is obtained.

The results of the study are presented in the table. The sorption-selective properties of the resulting zeolitic sorbents are compared with those of the prototype. The comparison is made under conditions close to those in which the sorbents were tested using the technology described in the prototype description.

Sorbent Distribution constant, Kd Cr Thu 1. Prototype 1250 3300 Example 2.1 1340 2900 Example 3.2 1210 3450 4. Example 3 1380 3570

The data in the table show that the sorbents obtained by the proposed process exhibit better sorption-selective properties for cesium and strontium radionuclides than the sorbents obtained by the prototype method.

Claims (4)

DEFINITION OF INVENTION A process for the preparation of a zeolite sorbent comprising heating a zeolite-containing raw material at high temperature, wherein the zeolite-containing raw material is first saturated with an alkali solution and then heated at 350-550 ° C. 2. A process according to claim 1, wherein the raw material is saturated with 5-8% potassium alkali solution. 3. A process according to claims 1 and 2, wherein the starting raw material is saturated with 4-5% potassium alkali solution, heated for 0.5-1 h at 140-150 ° C and washed with water at pH-10-11. 4. A process as claimed in claims 1-3, wherein the alkali-saturated feedstock containing 0.5-2% of organic compounds (expressed as pure carbon) is heated at a temperature of 350-550 ° C for 0.5-1.5h. supplying hot air at the same time.