RU2172297C2 - Method of treatment of sewage - Google Patents

Abstract

FIELD: treatment of sewage in atomic and radiochemical industries; cleaning natural water from radioactive isotopes for radiation protection of attending personnel and environment. SUBSTANCE: method includes loading iron-containing sorbent on base of highly-dispersed hematite modified by sodium polyaluminoethylsiliconate at ratio of Ai/Al = 2.8 to 3.2 followed by heat treatment at temperature of 150 to 150 C continued for 60 to 70 min at the following ratio of compoents, % mass (in terms of dry residual): hematite, 90,79 to 95.86; sodium polyaluminoethylsiliconate, 4.14 to 9.21 sorption is performed at temperature of sewage ranging from 20 to 60 C irrespective of pH of medium and rate of filtration of 2 to 5 m/h. EFFECT: enhanced efficiency of cleaning sewage and enhanced radioactive safety of used sorbents on base of iron-containing systems. 5 tbl

Description

 The invention relates to materials for wastewater treatment of the nuclear and radiochemical industries, as well as natural aqueous media from radioactive isotopes and to ensure radiation safety of staff and the environment.

The most widely used sorbent is high-iron slurry of 0.1 mm fraction with an iron content of up to 85 wt.% For water purification from strontium ions Sr ²⁺ [1]. Sorption is carried out under static conditions at pH 3-8 of the medium. The equilibrium sorption value is 20-24 hours. The maximum sorption of Sr ^{2+ ions is} 0.37 mmol / t (the degree of wastewater treatment is 31%).

The disadvantage of this method of purifying water from Sr ^{2+ ions} is the low degree of purification, the use of acidic aggressive environments, the high time for establishing sorption equilibrium, and a narrow pH range for use.

 The closest in technical essence and the achieved result is a method of purifying water from heavy metal ions, including the introduction of magnetite-based sorbent into water and passing it through a magnetic filter with loading from permanently magnetized elements regenerated by reverse water-air washing. After reaching the maximum dirt capacity of the filter before its regeneration, the pH is reduced to 3-3.5. Activation of the spent suspension is carried out electrochemically [2].

 The disadvantage of this method is the low degree of wastewater treatment from divalent radioactive isotopes, the use of acidic aggressive environments and the complexity of the treatment cycle.

 The invention is aimed at increasing the degree of wastewater treatment and radiation safety of spent sorbents based on iron oxide systems.

This is achieved by the fact that in the known method of wastewater treatment, including mixing an iron-containing sorbent with purified water, sorption until the sorption equilibrium is established, according to the proposed solution, highly dispersed hematite modified with sodium polyaluminoethylsiliconate with a ratio of Si / Al = 2.8-3 is used as the sorbent , 2, followed by heat treatment of the modified sorbent at a temperature of 150-160 ^o C for 60-70 min with the following ratio of components, wt.% (In terms of dry residue):
Hematite - 90.79 - 95.86
Sodium polyaluminoethylsiliconate - 4.14-9.21,
moreover, the treatment is carried out at a temperature of wastewater of 20-60 ^o C, and the filtration rate is 2-5 m / h, in addition, sorption is carried out at independent pH values of the medium.

Comparative analysis with the prototype shows that the claimed purification method is characterized by the use of hematite as a sorbent, the presence of a surface modified with sodium polyaluminoethylsiliconate on the sorbent, with a ratio of Si / Al = 2.8 - 3.2, heat treatment of the modified sorbent at a temperature of 150 - 160 ^o C in within 60-70 minutes, the cleaning is carried out at a temperature of wastewater 20-60 ^o C, and the filtration rate is 2-5 m / h In addition, sorption is carried out at independent pH values. Thus, the inventive cleaning method meets the criteria of the invention of "novelty."

 Comparison of the claimed technical solution not only with the prototype, but also with other technical solutions in this field, namely the treatment of hematite with alkalis, in particular sodium polyaluminoethylsiliconate, was not found, which allows us to conclude that the claimed solution meets the criterion of "inventive step".

As iron-containing raw materials, finely dispersed hematite concentrate of the Yakovlevsky KMA deposit with a density of 5500 kg / m ^{3 of a} fraction of 20-30 microns, having the chemical composition shown in Table 1, is used. 1.

 The sodium polyaluminoethylsiliconate modifier is obtained by treating an aqueous solution of sodium ethylsiliconate (GKZh-10, TU 6-02-696-76), widely used in construction, with aluminum powder grade PAP-1 at a Si / Al ratio of 2.8 - 3.2. As a result of the chemical interaction of these components, the formation of a spatial metal oligomer with an increased molecular weight occurs. In the process of obtaining a metal oligomer, it was established for the first time that, with an increase in molecular weight, its sorption ability increases.

As divalent radioactive isotopes, aqueous solutions containing radioactive strontium isotopes Sr-90 (half-life T _1/2 = 28.1 years, specific activity A = 152 kBq / kg) are widely used not only in the nuclear and radiochemical industries, but also in natural waters (especially after the accident at the Chernobyl nuclear power plant).

 The quantitative content of the components of the proposed and known sorbents are given in table. 2.

Example 2. 69.99 g (93.31 wt.%) Of hematite with a particle size of less than 50 μm was modified by thorough grinding with 17.47 ml (6.69 wt.%) Of sodium polyaluminoethylsiliconate (PAESP-3.2) for 5 min . The resulting mixture was subjected to heat treatment at a temperature of 150 ^o C for 60 minutes As a result of the modification, 75 g of sorbent is formed. Next, the sorbent was ground to dispersion of the particles of the initial hematite.

The sorbent was loaded into an adsorption column with a diameter of 40 mm. A 1.5 L solution of 40 ^° C and pH 2 containing the Sr-90 radioisotope and having an activity of 152 kBq / L was passed through the column from the bottom up. The specific activity of the purified solution is 0.76 kBq / L. The degree of purification at a filtration rate of 2 m / h was 99.5%.

Example 2. 69.99 g (93.31 wt.%) Of hematite with a fineness of less than 50 microns were modified by thorough grinding with 17.47 ml (6.69 wt.%) Of sodium polyaluminoethylsiliconate (PAESN-3.2) for 5 min . The resulting mixture was subjected to heat treatment at a temperature of 150 ^o C for 60 minutes As a result of the modification, 75 g of sorbent is formed. Next, the sorbent was ground to dispersion of the particles of the initial hematite.

The sorbent was loaded into an adsorption column with a diameter of 40 mm. A 1.5 L solution with a temperature of 40 ^° C. and a pH of 12 containing the Sr-90 radioisotope and having an activity of 152 kBq / L was passed through the column from top to bottom. The specific activity of the purified solution is 0.76 kBq / L. The degree of purification at a filtration rate of 2 m / h was 99.5%.

 To obtain comparative data, similar experiments were conducted in parallel on other sorbent compositions. The test results of the sorption properties of the composition of the sorbents are presented in table. 3 and 4 (the initial activity of the Sr-90 radionuclide in the aqueous solution was 152 kBq / l).

From the table. 3-4 shows that the proposed method of wastewater treatment from radioactive strontium Sr-90 at an aqueous solution temperature of 20-60 ^o C and a filtration rate of 2 m / h, allows to increase the degree of water purification 2.2-2.3 times in comparison with a known method.

 The dependence of the degree of purification of an aqueous solution from radioactive Sr-90 at a Si / Al ratio in the modifier is given in table. 5 (with an activity of Sr-90 152 kBq / l).

 From the table. Figure 5 shows that the highest degree of water purification from radioactive strontium Sr-90 is achieved when the Si / Al ratio in sodium polyaluminoethylsiliconate is 3.2.

 The activity of used water systems containing radioactive strontium Sr-90 was measured before and after purification using the gamma-ray spectral method based on a multichannel analyzer with Progress software in the Spektr radiation monitoring laboratory accredited to the State Standard of the Russian Federation (accreditation certificate N 41143-96 )

 After cleaning the water systems with the proposed sorbent, the concentration of radioactive strontium Sr-90 did not exceed 45 Bq / kg, which corresponds to the radiation safety standards NRB-96. In addition, the spent sorbent has a specific effective activity of not more than 370 Bq / kg, which corresponds to class 1 radiation safety and can be used in all types of construction according to GOST 30108-94 ("Building materials and products. Determination of specific effective activity of natural radionuclides").

Sources of information
1. V.N. Pak, N.G. Obukhov. Sorption of Sr ²⁺ and Cu ²⁺ cations from aqueous solutions with iron-containing sludge / J. Applied Chemistry. - 1995. - 68, N 2. - S. 214-217.

 2. RF patent N 1836299. The method of wastewater treatment. MKI C 02 F 1/48, 1/28, / A. N. Kuchina, I.A. Zabulonsky, G.N. Kochetov, B.M. Emelyanov; Kiev Ing. -builds. institute - N 4939904/26; Claim 05/29/1991; Publ. 08/23/1993, Blvd. N 31 (prototype).

Claims (1)

A method of wastewater treatment, including loading an iron-containing sorbent in the water to be purified, sorption to establish sorption equilibrium, characterized in that highly dispersed hematite modified with sodium polyaluminoethylsiliconate with a ratio of Si / Al = 2.8 - 3.2 is used as a sorbent, followed by heat treatment at a temperature of 150 - 160 ^o C for 60 - 70 min with the following ratio of components, wt.% (in terms of dry residue):
Hematite - 90.79 - 95.86
Sodium polyaluminoethylsiliconate - 4.14 - 9.21,
moreover, sorption is carried out at a temperature of wastewater of 20-60 ^° C, independent pH values and a filtration rate of 2-5 m / h.

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