The effective cleaning of radioactive liquid wastes using the thermo-chemically modified natural zeolites of Armenia
Êàòåãîðèÿ: ÀÐÇÍÈ - 03.07.2005 |
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Proposal about the introduction of results of the project entitled:
“The effective cleaning of radioactive liquid wastes using the thermo-chemically modified natural zeolites of Armenia”
1. The urgency of problem
The natural resources including zeolites are the important component of economical and industrial progress, necessary for the development of society. At the atomic power stations (APS) during the working process liquid radioactive wastes (LRW) appear. These LRW include more than 200 different products of radioactive decay and isotopes. At present it is necessary to remove them into the environment after the cleaning for long-term storing. For this work rather rigid requirements concerning the content of radioactive touch are presented; that’s why the liquid wastes undergo for effective cleaning.
At present in atomic power engineering for the cleaning of APS drop water the work is going mainly in three directions: 1) extraction of radioactive elements from the drainage water of high activity; 2) disactivation (disinfection) of drainage water of low and average activity; 3) accumulation of radioactive drainage water for the long-term storage.
One of the main methods of cleaning of radioactive drainage water is the way of adsorption disactivation. For removing of isotopes one can use the minerals – “molecular sieves”. For this purpose the synthetic zeolites (3À, 4À, 5À, 13Õ), argillaceous minerals, silicagel, activated aluminium oxide, boron-silicate glasses and other materials are used.
Recently a great interest is shown to the possibility of application of zeolite-containing volcanic rocks – zeolitolites. It is caused by that the zeolitolites are characterized by high ion-changing selectivity to Cs137, Cs134, Sr90 , Co60,Mn54and other radioactive isotopes, as well as by a number of physical-technical indexes as chemical, thermal, radiation stability, mechanical firmness, irreversibility of sorption, rather high capacity and low cost.
2. The goal of investigations is the development of an effective technology of extraction of radioactive isotopes and heavy metals from LRW of Armenian APS using the mechanically, thermally, chemically and radiation modified natural zeolites.
3. Expected results:
- The complex modification: chemical, thermal and radiation modification aiming the improvement of ion-changing and sorption properties of natural zeolites for the application in technology of cleaning, division of gases and liquids.
- Establishment of dependences between the structure, dash composite compound and main properties of zeolites before- and after- complex modification.
- Assistance to solving of geoecological problems having also the commercial significance.
- The development and creation of pilot device of effective high-technological cleaning system on the basis of Armenian natural zeolites and its testing at Armenian APS.
4. Zeolites – the natural sorbents
Zeolites are hydro-aluminium-silicates of frame crystalline structure including cavities and channels engaged by Na+, K+, Ca+2, Mg+2 , etc. cations and water molecules. Cations and water molecules are characterized by high mobility; moreover, the ion change and dehydration usually pass reversibly. At zeolites heating the removal of water molecules takes place, and thin-porous active body turns out. The sizes of “entrance windows” in the porous structure are up to molecular (3 – 9 Angstrem). Generally the chemical composition of zeolites may be shown as:
(M2, M)O Al2O3 nSiO2 mH2O,
where M – one-valent cation (Na+, K+, Li+, :), M2 ¬– two-valent cation (Ca+2, Mg2+, Ba2+).
Armenian zeolite-containing tufas have volcanogenic-sedimentary origin and their general evaluated storage reach up to 500 mln ton.
Zeolites are discovered in following regions of Armenia:
1 Noemberyan region, near the village Nor Kohb
2 Alaverdi region – Lalvar river basin
3 Ashots region – Shirak mountain range
4 Tavoush – Ijevan region
5 Kotayk region, near Garni, Azat river basin
6 Vayk region – near the village Martiros
7 Kaphan region.
It is established mineralogically that the main rock-forming minerals of zeolitites of this group are: zeolites (clinoptilite, stilbite, mordenite, analcim, phillipsite), montmorillonite, celadonite, chlorite, chalcedony, christobalite, barite, pyrites, hydromicas of iron, new formations of calcite.
The content of main mineral of zeolites of Noemberyan layer (Nor Kohb region) – clinoptylolite (65-85%), and from other minerals are present quartz - 10-15%, montmorillonite - 5-10 %, the other – fieldspar, mica, etc.
5. The condition of radioactive wastes at Armenian APS
Radioactive wastes at Armenian APS are formed during the daily clearing up and deactivation of premises of controlled access zone, at deactivation and repair of equipment, at carrying out the building and repair works in the zone of controlled access and so on. Radioactive wastes include also some parts of equipment which cannot be deactivated or which are irradiated inside the reactor, as well as the control-measuring devices (CMD); the armature of pipelines or defense, - also protective clothing; filters of ventilation systems; spent sources of ionizing radiation; the devices; the water of special laundries, sanitary locks and passing blocks which are contaminated higher than permissible norms. There are storehouses at AAPS for solid (SRW) and liquid radioactive wastes (LRW).
6. The general volume of LRW storehouse
During the period 1983-2007 at AAPS for the processing of LRW an installation of deep steaming (IDS) was exploited. The salt melted substance obtained as a result of steaming has been placed in the metallic container and was kept in the storehouse of solid average-active wastes. At 2003 the containers (IDS) according to “the Program of Physical Inspection of Containers IDS” were withdrawn from storehouse solid average-active wastes and placed on the area of temporary storage of IDS containers.
7. The main results of work:
1. Among the zeolites of Nor Kohb region of Noemberyan layer the clinoptylolite differences (80-85 %) predominate, - especially in fractions 0,1-0,01 mm.
2. The thermal analysis shows that clinoptylolite have high thermal stability. The most optimal temperature of thermal treatment 350-4000Ñ may be considered.
3. The chemical processing of clinoptylolite in the solvents of sodium hypochloride brings to the maximal release of mineral from the present cations.
The most fully and fast the solvents’ cleaning takes place for the samples of clinoptylolite in sodium form processed by Na hypochloride. The chemically modified adsorbents in Na form are much more effective than natural – non-modified. The high salt-containing of LRW on other cations (K, Co), as well as the presence of ammonia and chlorine in it does not influence essentially at the extent of cleaning.
4. On the basis of results of laboratory investigations at YSU an experimental-pilot installation for the cleaning of real average- and weak-active LRW of AAPS is made.
Using this installation the ion-changing properties of natural and modified (Na form) clinoptylolite of Noemberyan layer (Nor Kohb region) have been investigated.
The chemically modified zeolite in Na form is at 5-7 orders more effective than natural. The content of radionuclides 137Cs è 134Cs in LRW after the cleaning decreases up to 2500 times.
Thus, on the basis of carried out investigations one can conclude that the most promising for further application for the purposes of geo-ecology – for cleaning of AAPS LRW are the zeolitolites of Nor Kohb region.
8. On the basis of results of investigations it may be recommended:
On the basis of results obtained during the laboratory investigations it has been developed and created an enlarged experimental-pilot four-column installation for cleaning of LRW at Armenian APS.
1. Using a large batch of modified and granulated zeolites the investigations of LRW cleaning process on the territory of Armenian APS have been carried out. After several cycles of cleaning it is established the decrease of radioactivity for isotopes Cs137 and Cs134 up to 2500 times in comparison with initial. It will allow to exclude the LRW, to decrease significantly the volumes of solid radioactive wastes (up to 2500 times) and to decrease the ecological risks.
2. A laboratory-production line for turning out the separate (first tens kilograms) lots of natural modified and granulated natural zeolite.
3. Besides, for the first time a micro-wave influence on the process of ion change is applied and positive interesting results are obtained.
4. The results obtained using the experimental-pilot 4-column installation may be a basis for composing of Technology Implementation Plan (TIP) and for patenting of developed technology of full cleaning of radioactive drainages.
9. It is proposed:
1. To make in installation consisting from four columns joint consistently and filled by zeolite sorbents of different modification. To use decationized CL-H and mono-cation CL-HCa forms for ion-changing sorption of strontium and CL – Na-form for ion-changing sorption of cesium.
2.. The average cost of modified zeolite for different radionuclides will be about 200 – 250 arm.dram (AMD) for one kg of sorbent.
3. The decrease of volume of weak-active LRW depending on salt-content will be on the average from 200 to 500 times.
4. For cleaning of 1000 litrs of low-active drainage waters at salt-formation up to 100 g/litre it is necessary about 6-8 kg of sorbent, and for average-active drainages – 10-12 kg of sorbent.
Prof. Dr. Rudolf Gevorgyan
the Department of Mineralogy, Petrology and Geochemistry
Yerevan State University.
1, Alex Manoogian St.,Yerevan- 25, Armenia
Tel:(+37410) 57-81-35; 22-74-04 home.; (+037407)77-555-71 mob.
Fax:(+37410) 55-46-41 ; E-mail: email@example.com