DD283276A7 - PROCESS FOR PREPARING AN ADSORPTION AGENT FOR THE DEPOSITION OF RADIOACTIVE GASES AND DUST - Google Patents

Abstract

The invention relates to a method for producing an adsorbent for the separation of radioactive gases and evaporation from the exhaust air of nuclear power plants. The object and the object of the invention is to develop a process according to which an adsorbent with high adsorption capacity, effectiveness and abrasion resistance for use for the adsorption or separation of radioactive iodine compounds, in particular vaporous iodine and methyl iodide, as well as of krypton and xenon isotopes the exhaust air can be produced. According to the invention, a clay mineral and / or alumina pretreated and comminuted with caustic soda is thoroughly milled after addition of an imprecating agent from the inorganic iodine compound series, mixed with pulverulent activated carbon in a ratio of at least 20:80 *, shaped by extrusion and after drying in the inert gas atmosphere Gentle at intervals, also sintered in an inert gas stream to achieve a high abrasion resistance {adsorbents; manufacture; gases; Daempfe, radioactive; deposition; iodine compound; Abrasion resistance}

Description

Field of application of the invention

The invention relates to a method for producing an adsorbent for the elimination of radioactive iodine compounds, such as methyl iodide and vaporous iodine and radioactive noble gases such as krypton and xenoisotopes from the exhaust air of nuclear power plants.

Characteristic of the known technical solutions

Nuclear fission, which occurs in nuclear reactors, produces radioactive iodine isotopes, which must be separated by suitable filter devices.

It occur as pollutants elemental iodine in vapor form and methyl iodide.

It is known that damp elementary iodine easily and methyl iodide due to its high vapor pressure, however, can hardly be separated by adsorption from wet air.

The deposition of iodine takes place via the use of fine-pore activated carbons, of methyl iodide with the help of impregnated activated carbon by isotope exchange or by salt formation (DACollins, IRTaylor: Atomic Energy Authority: "The Development of impregnated charcoals for trapping methyl iodide at high humidity "1967) In the isotope exchange, an activated carbon impregnated with inactive inorganic iodine compounds (eg KJ) is used.

During the short residence time of the radioactive methyl iodide on the coal bed, an exchange of the iodine isotopes occurs on the adsorbent.

The disadvantage of this method is that the Acsorptionkapazität the impregnated coal is still too low, and it can therefore come by adsorption of organic vapors from the room air to the spontaneous drop in performance (JG Wilhelm: Jodfilter in nuclear power plants: Commission of the EEC, Report Nr.075 , 75.5 PSTD). The impregnation of the activated carbon with tertiary amines allows the binding of methyl iodide by formation of quaternary ammonium salts. However, the amines reduce the ignition point of the activated carbon and are volatile, so such impregnations find little industrial use.

The exhaust air from reactors is cleaned by using deceleration systems. In this case, radioactive krypton and xenon isotopes passed through mitformed activated carbon adsorber and deposited as a solid on the coal due to their short half-life (H.J. Schroeder, H. Queiser, W. Reim: Kerntechnik 13 (1971), p 205). The difficult noble gas adsorption is impaired by too low adsorption capacity of the activated carbon, by strongly polar surface groups and moist exhaust air as well as by carbon abrasion.

Object of the invention

The object of the invention is to develop a process for the preparation of an improved highly effective adsorbent for the separation of radioactive gases and vapors.

Explanation of the essence of the invention The invention has for its object to develop a method for producing an adsorbent whose use

In nuclear power plants once the more effective direct adsorption of radioactive iodine compounds, in particular methyl iodide, allows, and on the other hand is able to separate radioactive noble gas isotopes. The adsorbent must be extremely resistant to abrasion and have a high adsorption capacity which is an uncontrollable spontaneous

Performance loss of the activated carbon, z. B. by adsorption of organic vapors and wet Li, ft, counteracts. According to the invention, the adsorbent from a mixture of powdered activated carbon, powdered! clay mineral

and or alumina and an impregnating agent.

The inventive method for producing this adsorbent is such that a clay mineral and or alumina

crushed to a grain size of 100% if possible below 0.05 mm, with a 5 to 30% strength alkali, preferably 10%

Potassium hydroxide, with stirring for 1 to 5 hours, preferably 2 hours pretreated and then at temperatures

from 70 to 100 ⁰ C, preferably 80 to 90 ⁰ C, is dried.

The alkali hydroxide causes a widening of the lattice structure up to 700 to 80 OmVg and a fixation of this structure by Exchange of divalent cations for alkali ions, which is retained even after drying. After the pretreatment, the impregnation of the clay mineral and / or the alumina with an aqueous solution of a

inorganic iodine compound, preferably potassium iodide, wherein the proportion of impregnating agent, based on

Dry substance, 10 to 90Ma .-%, preferably 40Ma .-%, is. For this purpose, the pretreated clay mineral and / or the alumina with an aqueous solution of an inorganic iodine compound

thoroughly mashed for at least 30 minutes in the kneader and then for 10 to 20 hours, preferably 15 to 16 hours

Achieve optimal impregnation left. The impregnated clay mineral and or clay is mixed with a powdered activated carbon, their specific internal surface

is above 10000Vg and that over pore distribution maxima in the range of 10 to 100A, preferably 15 to 30A and 250 to

1000 A, preferably 400 to 600 A, mixed, pressed in extruders to formations, then at

Temperatures of 80 ⁰ C to 150 ° C, preferably 80 to 9O ⁰ C, dried in an inert gas atmosphere and in an inert gas in Sintered intervals of 30 minutes at 500 to 55O ⁰ C, 600 to 650 ° C and 750 to 85O ⁰ C. The lower limit for the proportion of impregnated clay mineral and or clay to the total adsorbent is included Through the use of iodine-impregnated clay mineral and or clay and activated carbon in a defined ratio is achieved

that the isotope exchange in the elimination of radioactive iodine and methyl iodide within the lattice structure of the

Clay minerals and / or the clay around the adsorptive binding of the resulting in extremely low concentrations Edelgasisotope takes place in the activated carbon. The adsorption capacity and thus the effectiveness of this adsorbent is so

high, that once the said radioactive substances are completely separated and also the possible adsorption of organic vapors and moist air does not lead to a spontaneous and uncontrollable drop in performance.

The drying and sintering in an inert gas atmosphere prevents the formation of highly polar surface groups. Due to the high strength obtained by the sintering, no carbon abrasion occurs. embodiment The starting materials clay mineral and activated carbon have the following quality characteristics: clay mineral Species: montmorillonite clay mineral

specific surface: 175m ² / g

Rig density: 735g / l Grain: 100% less than 0.05 mm activated carbon Type: Steam-activated charcoal based on charcoal Ash content: 3.2%

specific surface area: 132OmVg

Pore distribution maxima at: 20-30Ä and 450-550A Iodine number: 1260 mg / g Grain: 100% smaller 0.071 mm

480g of crushed clay mineral are at 11 of a 10% potassium hydroxide solution under continuous stirring for 2 hours at 8O ⁰ C then vorbehandeltund dried.

The pretreated clay mineral is obtained after addition of an aqueous potassium iodide solution containing 320 g KJ. Dry substance, contains, 30 minutes intensively mashed in a kneader. The exposure time for the impregnation ... (el is

15 hours.

The impregnated clay mineral is mixed with 1200g powdered activated carbon, by extrusion at a pressure of

100at pressed into molds, then dried in a nitrogen atmosphere at 9O ⁰ C and by stepwise sintering in a nitrogen stream of 200l / h at intervals of 30 minutes at temperatures of 500 b'.c 55O ⁰ C, 600 to 65O ⁰ C and 740 bis 850 ⁰ C solidifies.

For the adsorbent, the following quality and application-specific properties are achieved:

specific surface: 1050 mVg

Rig density: 480g / l Content of potassium iodide: 16Ma .-% Ratio of impregnated clay mineral to activated carbon: 40: 60Ma .-% When using the adsorbent to eliminate the iodine isotopes 131 j, 133 j, methylene iodide CH ₃ 131 j and Krypton- and Xenonisotopeausd ^{<3rAbluftvonKemenergieanlagenwerdenmiteinerSchichtdickevon20cmAbscheidungsgradevons>} 99% errcicht.

Claims (5)

1. A process for the preparation of an adsorbent for the separation of radioactive gases and vapors, in particular of iodine, methyl iodide and krypton and xenoisotopes from the exhaust air of nuclear power plants, characterized in that a comminuted to a particle size of 100% below 0.05 mm and pretreated with alkali lye clay mineral and / or clay with the addition of an impregnating agent for at least 30 minutes in the kneader, after a contact time of 10 to 20 hours, preferably 15 to 16 hours and then mixing with a powdered activated carbon by extrusion presses to formations, which then at temperatures from 80 to 150 ⁰ C, preferably 80 to 90 ⁰ C, dried in an inert gas atmosphere and gently sintered in inert gas at intervals of 30 minutes at 500 to 550 ⁰ C, 600 to 650 ⁰ C and 750 to 850 ⁰ C. 2. The method according to claim 1, characterized in that the pretreatment of the comminuted 1 onminerales and or the alumina with a 5 to 30% strength alkali, preferably 10% potassium hydroxide, with constant stirring for 1 to 5 hours, preferably 2 hours, and then the clay mineral and or alumina at temperatures from 70 to 100 ⁰ C, preferably 80 to 90 ⁰ C, dried. 3. The method according to claim 1, characterized in that for the impregnation, an aqueous solution of an inorganic iodine compound, preferably potassium iodide, is used, wherein the proportion of impregnating agent, based on dry matter, 10 to 90Ma .-%, preferably 40 wt .-%, is. 4. The method according to claim 1, characterized gekennzeichi. > t that the pulverulent activated carbon has a specific internal surface area of more than 1000 m ² / g and pore distribution maxima in the range of 10 to 100 Å, preferably 15 to 30 Å and 250 to 1000 Å, preferably 400 to 600 Å. 5. The method according to claim 1-3, characterized in that the proportion of the impregnated clay mineral and or alumina on the adsorbent is at least 20Ma .-%.