RU2165284C2 - Method of conducting continuous countercurrent sorption process - Google Patents

Abstract

FIELD: radiochemistry, particularly, purification of liquid radioactive wastes. SUBSTANCE: method includes separation of solid and liquid phases in cascade of single-stage centrifugal sorbent devices installed horizontally. In this case, supplied from one side of cascade is sorbent suspension and from the other side of cascade, solution to be treated. Intensive forced mixing serves to increase sorption rate and as a result productivity of sorbing device. EFFECT: higher efficiency due to intensified mixing, raised rate of phase separation, provided use of finely divided sorbent and improved radiation safety. 3 cl, 2 dwg, 1 tbl, 2 ex

Description

 The invention relates to methods for implementing sorption processes, in particular, to a number of methods for implementing a continuous countercurrent process using a solid sorbent for extraction from solutions of trace amounts of heavy metals, radionuclides, oil products, or other impurities. The invention can be used in radiochemical and hydrometallurgical, food and other industries, as well as in solving environmental problems of liquid industrial waste treatment.

There are various ways of conducting sorption processes:
semi-continuous processes with a fixed bed of sorbent;
continuous, countercurrent processes with a moving sorbent bed using columns and mixing-settling sorbers (Galkin, Tikhomirov. Main processes and apparatuses of uranium technology. M., Atomizdat, 1981. S. M. Korpacheva, E. I. Zakharov. Fundamentals of theory and calculation of pulsed column reactors, M., Atomizdat, 1990. EI Zakharov, B. E. Ryabchikov, V. S. Dyakov. Ion-exchange equipment of the nuclear industry, M. Energoatomizdat, 1987, p. 92).

 A countercurrent process using mixing settling sorbers is known (Auth. St. N 258898, 1970, Development and use of pulsation equipment, edited by S. M. Karpacheva, Atomizdat 1974, p. 161.).

The main disadvantages of columns and mixing-settling sorbers are:
- low speed of phase separation under the influence of gravitational forces and the need to load large volumes of sorption materials;
- weak phase mixing during pulsation;
- the need to use large granules of sorbent in industrial apparatus.

The closest in technical essence and the achieved result is a method that is a continuous, countercurrent sorption process with the separation of liquid and solid phases in a cascade of single-stage sorption apparatuses installed horizontally by feeding on one side of the cascade a suspension of the sorbent, and on the other, the solution to be processed (RU 2034056 C1, 1995, 4 l.)
However, when working with radioactive solutions, significant amounts of radioactive materials are accumulated on the sorbent, which can be a radiation and nuclear hazard. With a decrease in the volume of sorption columns, productivity decreases sharply.

 The objective of the present invention is to provide a high-performance continuous countercurrent process with a solid-phase sorbent for use in radiochemical, hydrometallurgical, food and other industries for the extraction of valuable products in low concentrations, as well as in solving environmental problems of the treatment of liquid wastes containing heavy metals, radionuclides, petroleum products and other pollution. The invention is also aimed at improving nuclear and radiation safety when working with radioactive materials.

 The problem is solved by the described method of conducting a continuous sorption countercurrent process with separation of liquid and solid phases in a cascade of sorption apparatuses installed horizontally, when a sorbent slurry is fed from one side of the cascade, and a solution is processed on the other side of the cascade, each of which is equipped with a mixing and separation chambers, and in each of the apparatuses, the phases are first mixed, and then separated by centrifugal forces.

 Preferably, when mixing the phases produce forced mixing.

 Preferably, the use of a sorbent with a particle size of less than 1 mm in the method.

 To implement the inventive method, you can use the known types of centrifugal apparatuses, for example, the type of ECT (Chemical industry N 2, 1996, p. 63). The centrifugal apparatus consists of a housing and a rotor with a drive. A mixing chamber and collectors are located in the housing for collecting flows exiting the rotor. A sorbent suspension and a solution to be purified are fed into the mixing chamber, where both solutions are mixed with a mixer mounted on the rotor. The resulting suspension enters the rotor and after separation under the action of centrifugal forces on the suspension of the sorbent and the purified solution is removed from the rotor.

EXAMPLE 1
The method of conducting a multi-stage countercurrent sorption process using centrifugal sorbers is schematically presented in figure 1. To carry out the process, several centrifugal sorbers are connected in series to the cascade. On one side of the cascade, a solution, for example liquid radioactive waste, from which it is necessary to extract radionuclides or other heavy metals, is supplied to the centrifugal sorber (1). On the other side of the cascade, a suspension of pure sorbent is fed into the centrifugal sorber (7). Sorbers are connected in a cascade in such a way as to provide a counterflow of solid and liquid phases. The solution to be cleaned enters the mixing chamber of the first sorber, then it is fed through the rotor to the mixing chamber of the second sorber and in the same way to the third sorber, etc. Similarly, the suspension of the sorbent is fed into the mixing chamber of the last sorber, with the help of a rotor it is separated from the liquid phase and fed into the mixing chamber of the neighboring apparatus. In the mixing chamber of each sorbent, the sorbent contacts the liquid phase, as a result of which the sorbent extracts radionuclides and heavy metals from the solution. Ultimately, the saturated sorbent is discharged from the first sorber, and the purified solution from the last apparatus.

 With high productivity, centrifugal sorbers have small volumes of the mixing chamber and separation chamber. Therefore, a small volume of radioactive liquid and a small mass of sorbent are simultaneously located in the cascade. Due to this, the radiation and nuclear hazard of the processes of extracting radioactive materials from aqueous solutions is sharply reduced. A comparative analysis of the continuous sorption method for the purification of liquid radioactive waste containing uranium and plutonium on pulsating columns and centrifugal sorbers is presented in the table.

 From the table it follows that the centrifugal system is approximately 20 times smaller than the equivalent column in terms of capacity in the volume of LRW filling. Therefore, with equal activity of the processed LRW, a pulsating column is 4000 times more dangerous in radiation and nuclear terms and should have powerful biological protection of personnel from gamma radiation, while a system of centrifugal devices will not pose a serious radiation hazard.

 In FIG. 2 shows an installation with a capacity of 400 l / h, consisting of 3 series-connected centrifugal sorbers mounted horizontally.

Each of the sorbers in FIG. 2 contains:
1 - mixing chamber,
2 - mixer
3 - conveying device (auger),
4 - separation chamber (rotor).

 In Fig. 2, the solid arrow indicates the supply of the sorbent suspension, and the dashed line indicates the supply of the solution to be processed. The solution to be cleaned enters the mixing chamber of the first sorber, then it is fed into the rotor by the conveying device (screw) and then to the mixing chamber of the second sorber, and in the same way it enters the third sorber, etc. Similarly, the suspension of the sorbent is fed into the mixing chamber of the last sorber, with the help of a rotor it is separated from the liquid phase and fed into the mixing chamber of the neighboring apparatus. In the mixing chamber of each sorbent, the sorbent contacts the liquid phase, as a result of which the sorbent extracts radionuclides and heavy metals from the solution. Ultimately, the saturated sorbent is discharged from the first sorber, and the purified solution from the last sorber.

 Example 2

Sorption of ¹³⁷ Cs from liquid radioactive waste (LRW) of a low level of activity. For decontamination of LRW with an initial activity of 2 · 10 ^-6 Ci / l (according to Cs), a 400 l / h installation consisting of 3 sequential centrifugal sorbers is used (Fig. 2). The ratio of liquid and solid phases W: T = 1000: 1. The distribution coefficient of Cesium on the sorbent "Mokoton-Cs" is 5 · 10 ³ . The degree of purification from 137 cesium at three stages is 200. The activity of LRW at the output will be 1 · 10 ^-8 Ci / l. In this case, the volume of LRW and the mass of the sorbent that are constantly in the installation will be 36 L and 36 g, respectively, and the total β, γ-activity of the suspension, which is constantly in the installation, will be 7.2 · 10 ^-5 Ci. For comparison, in the case of using a pulsating column (sorber) of the same productivity and efficiency, the volume of LRW and the mass of the sorbent in the column are 200 l and 50 kg, respectively, and the β, γ-activity of the column is more than 0.1 Ci.

Claims (3)

 1. A method of conducting a continuous, countercurrent, sorption process with separation of liquid and solid phases in a cascade of sorption apparatuses installed horizontally, when a suspension of sorbent is fed from one side of the cascade, and a solution is processed on the other hand, characterized in that each of the sorption apparatuses equipped with a mixing and separation chambers, while in each of the devices, the phases are first mixed, and then separated by centrifugal forces.  2. The method according to p. 1, characterized in that when mixing the phases produce forced mixing.  3. The method according to claim 1, characterized in that a sorbent with a particle size of less than 1 mm is used.

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