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DEACWATION OF RADfOACTIVE ELEMENTS

The nuclear industry and nuclear energy programs require solution of problems associated with the development of effective and cheap methods for the purification of radioactive waste. Approximate calculations show that in the near future the total activity of radioactive waste products throughout the world will be 4-6 x 1011 Ci

In 1986 a dramatic accident occurred in Cernobyl and it was observed that metabolic similarity to K favors cesium's uptake by plants after radiocontamination of agricultural lands. Intake of radiocontaminated food, tea and milk is one of the main pathways for radiation exposure. In recent years, studies on natural zeolites as potential, low cost countermeasure amendments in an attempt to reduce transfer of radionuclides including ^Cs from soil to plant in radio contaminated soils are gaming importance.

At present research is concentrated in three directions: extraction of radioactive elements from effluents of high activity, deactivation (decontamination) of low and medium activity effluents and the concentration of radioactive effluents for long-term storage.

One of the main methods of purification of radioactive waste is adsorption deactivation. Many synthetic and natural materials have been used as adsorbents, but recently great interest has been shown in the use of zeolite-containing rocks; this material, particularly clinoptilolite-containing tuffs, are characterized by high ion-exchange selectivity for ^Cs, ^Sr and other radioactive elements. They also possess chemical, thermal and radiation stability, mechanical strength, show irreversibility of sorption, and are of sufficiently high capacity and low initial cost.

Experiment earned out to eliminate liquid radioactive wastes is given in [20J. The activity of LRW (liquid radioactive wastes) should not exceed 3 X 10'10 Ci/L. Taking this into account, a system was prepared and it was shown that the dinoptilolite having grain size 0.25 - 1.0 mm is recommended to use to eliminate the LRW of low activity containing ^Cs and """Sr.

^Cs has a relatively long half-life of about 30 years and is considered as one of the most hazardous radiotoxic elements for the environment [21]. One of the most effective methods for the treatment and disposal of radioactive wastes has been based on ion-exchange using inorganic ion-exchangers. The desirable characteristics of high exchange capacity and favorable selectivity for some radioisotopes have made certain zeolites quite useful for the treatment of radioactive wastes. Thermal, mechanical and radiation stability are further advantages of these materials. A zeolite

can also be incorporated into a cement matrix and easily stored in stainless drum which a common practice for long term storage of radioactive waste. Radioactive waste treatment processes utilizing zeolites have been developed and used successfully since the introduction of atomic energy installations. The most effective and abundant natural zeolite which have been considered for radioactive waste-treatment is clinoptilolite [20]. Among these, clinoptilolite has received much attention due to its widespread occurrence and high selectivity for ^Cs and ^Sr and was demonstrated to be effective in removing these radioisotopes from process waste waters.

All these applications which involve zeolites require a better understanding of behavior of different cationic forms of zeolites for sorption of trace concentration of radioisotopes. Since zeolites can be important sources and sinks of thermal energy during dehydration / rehydration when exposed to thermal effects of radiation, sorption measurements at different temperatures may also be appropriate
"SGW"
"Hiz"
Brightness, %
78.5
84.2
Content of Water, %
5.0
12.9
Abrasion Resistance (mg)
70.5
85.2
Granulation, microns %10
16.45
14.7
PH
9.6
4.5
When zeolite (clinoptilotite) is used in paper making, more porous paper is produced. This kind of paper has lower density compared to conventional paper; is less smooth but more opaque. Paper brightness which depends on the filler is almost same for both conventional and zeolite added paper. As the surface of zeolite added paper is less smooth (in micron size), it is less susceptible to ink blotting than those filled with clay

Hayakawa and Kobayashi (1973) patented a lightweight paper made from a mixture of 7% pulp, 25% chemically ground pulp, 28% bleached raft, 1% sizing, 1% aluminium suifate, and 28% zeolite powder
 
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