DE3829654A1 - Ion exchanger granules and use thereof for radio caesium decontamination of liquids - Google Patents

Abstract

Ion exchanger granules, which are characterised in that ammonium iron hexacyanoferrate, is bound to a plastic support, are outstandingly suitable for decontaminating liquids from radiocaesium.

Description

The present invention relates to an ion exchange granulate, which is characterized in that ammonium Iron hexacyanoferrate (AEHCF) on a plastic carrier is bound.

It is already known that AEHCF Cs⁺ is highly selective Ion exchange of the NH₄⁺ present in the lattice structure binds in the presence of other cations.

This fact was made possible by the very successful use of complex salt as feed additive for all important Pets (cows, calves, sheep, pigs, chickens) proven. In animals that are radio-cesium-contaminated Feed intake and smallest daily doses of AEHCF (1-3 g) received with the feed, the transition from Radiocesium from the intestine largely in meat, milk and eggs can be prevented (Transl. Animal Nutrition 15 113 (1987)).

For technical to large-scale cesium decontamination So far, however, the complex salt has been capable of liquids not be used because they are large enough Flow rates (l / h) are necessary which are the microcrystalline (⌀ 5-500 µm; DE-A 36 30 492) produced substance allows.

The object of the present invention is therefore to AEHCF in already in a form in which it is also for technical to industrial cesium decontamination from Liquids can be used.

This task is surprisingly accomplished by Solved ion exchanger granules according to the invention.  

The plastic carrier is preferably spherical. All basic plastic carriers are particularly preferred Cl⊖ or OH⊖ type ion exchanger used. Depending on the degree of networking (usually between 4-8% Divinylbenzene) a different mechanical strength, different pore structure and different Number of ionized groups per unit volume. The higher the degree of crosslinking, the more stable the carrier is against Shear forces. At the same time is its pore structure narrower and the number of binding groups larger. The number these groups are known to determine capacity (val / l), so that with a higher degree of crosslinking also higher ones Area loading densities (weight percent) of the complex salt can be achieved. But also straps with pronounced Coarse pore structure have been put into practical use already very well proven.

For the production of the ion exchanger granules according to the invention the plastic carrier is only with (NH₄) ₄Fe (CN) ₆ solution, then mixed with FeCl₃ solution and this process is repeated up to nine times.

In a preferred procedure, one is commercially available basic ion exchanger based on weight in relation 1: 3 mixed well with 0.5 molar (NH₄) ₄Fe (CN) ₆ solution and left for 1 hour. Then it is decanted and in the same ratio 1: 3 as often with Aqua least washed until the wash water is no (NH₄) ₄Fe (CN) ₆ contains more (FeCl₃ sample negative, if still blue in color arises).

The wash water is then sucked off via a suction filter and the carrier with three times the amount of 0.5 molar FeCl₃ solution mixed and left for 1 hour. Then it is decanted and with aqua dest. washed until the original blue supernatant is water clear.  

By repeating these operations up to nine times can be growing on the carrier according to an e-function Mass occupancy takes place. From a practical point of view, however 5 operations sufficient to 90% of those after 8 operations achievable maximum mass occupancy tie.

Depending on the application, due to the high binding capacity for Cs also a smaller number of operations made with smaller mass assignments of the carrier will.

The amount (weight percent) of AEHCF to be applied depends on the number of treatment steps of the wearer which ultimately also determines its color. Depending on the layer thickness, this varies between light blue over medium blue to a deep dark blue.

The granulate produced in this way has a high mechanical and thermal stability and can be in any grain size, mainly manufactured from 0.2-1.2 mm ⌀ will.

Due to the chemically strong bond between the carrier and Complex salt is a mechanical detachment at high flow rates and the washing away of fragments containing radio cesium excluded in the eluate.

Because the complex salt not only on the ball, but also bonded along the pores inside the sphere is the entire AEHCF spherical surface layer inside the carrier firmly anchored. In addition, these are internal Further binding sites for Cs ions are accessible on surfaces.  

The ion exchange granules according to the invention are suitable excellent for cesium decontamination of Liquids such as B. water, especially drinking water. It is particularly suitable for cesium decontamination of Whey permeate.

In practice, the finished product is moist, i. H. without prior drying, store.

When using in ion exchange columns is to avoid of column blockages a fluid throughput advantageous in the fluidized bed from bottom to top via pumps.

Depending on the size of the column, however, the optimal flow must first be found (l / h) can be determined. Rivers that are too low run over preferred ones Channels in the exchanger bed and thus use the exchanger volume not completely. In contrast, rivers are too high with strong swirling too quickly on the exchanger over, which negatively affect the degree of decontamination can.

The following test proves the excellent effectiveness of the granules according to the invention:

Two grams of one coated in 5 passes dry granules were in a glass column with constant temperature Weighed water jacket and then with 5 ml aqueous Cs solution or Cs-containing whey permeate following Composition overlaid:

Aqueous solution:
32.7 mg Cs / 100 ml + 7400 Bq Cs-134/100 ml
Whey permeate:
32.7284 mg Cs / 100 ml + 7400 Bq Cs-134/100 ml (100 ml whey permeate originally contains 0.284 μg Cs)
the whey permeate also contains:
2.44 g Na / l
4.54 g K / l
0.89 g Ca / l
0.24 g Mg / l

About an arrangement similar to a Mariotteschen bottle (here with a glass capillary in the liquid above the granulate and the column above sealing rubber plug was pulled out) the hydrostatic pressure in the column and thus the flow relative to 2 drops / min after a single setting kept constant.

The temperature was measured over a column water jacket Connection with a circulation pump constantly set at 20 ° C.

A dropper with fraction collector provided for fractions of 20 drops / 10 minutes, all in one borehole Gamma detector with respect to Cs-134 were measured.

The statistically assured increase above "0" Becquerel was evaluated as the beginning of the Cs breakthrough and the Cs retained on the column up to that point was determined from the liquid volume (ml) and the Cs concentration (mg / ml) which had been let through until then. The volume of liquid was determined after weighing the tubes from the accumulated net weight (curves) divided by the density of H₂O ( ρ H₂O = 0.99823 g / cm³) or whey permeate ( ρ whey = 1.014 g / cm³). For aqua dest. the binding capacity at 20 ° C was 17.84 mg Cs / g granules and for whey permeate 30.38 mg Cs / g granules. The higher binding capacity for Cs from whey permeate is due to the lower surface tension of the permeate compared to Aqua-dest. attributed. Larger surface tensions, e.g. B. in water, form micro-barriers for the diffusion of the Cs ions at the interfaces, so that the ion transition is slightly hindered thereby.

Nevertheless, also for aqueous solutions, for. B. for the Drinking water treatment, the Cs decontamination with 17.84 mg Cs / g granulate excellent.

Claims (5)

1. ion exchange granules, characterized in that ammonium iron hexacyanoferrate is bound to a plastic carrier. 2. Ion exchange granules according to claim 1, characterized characterized in that the plastic carrier is a basic Cl⊖ or OH⊖ type ion exchanger. 3. Process for the preparation of an ion exchange granulate of claims 1 and / or 2, characterized in that the plastic carrier only with (NH₄) ₄Fe (CN) ₆ solution and then mixed with FeCl₃ solution and this process is repeated up to nine times. 4. Use of an ion exchange granules Claims 1 and / or 2 for radiocesium decontamination of Liquids. 5. Use according to claim 4, characterized in that the liquid is whey permeate.