WO1990009026A1

WO1990009026A1 - Process for decontaminating materials that have been attacked by metallic ions or by radioactive substances

Info

Publication number: WO1990009026A1
Application number: PCT/EP1990/000173
Authority: WO
Inventors: Franz Roiner
Original assignee: Franz Roiner
Priority date: 1989-01-31
Filing date: 1990-01-31
Publication date: 1990-08-09
Also published as: DE3912702C1; DE3912702C2

Abstract

Decontamination process for materials which have been attacked by or exposed to metallic ions and/or radioactive substances. The attacked or exposed substances are introduced into a dissociative liquid. Then whatever coarsely-dispersed, colloidaly-dispersed and/or molecularly-dispersed substances this dissociative liquid contains are removed from it, after which the dissociative liquid, which now only contains ionically-dispersed and in some cases molecularly dispersed substances, is guided over an ion-exchange material in such a manner that an ion-selecting exchange takes place. To ensure that solids and semisolids, even those that are already in a colloidaly-dispersed state, are also decontaminated, the attacked substances are sprayed in a selective manner with the dissociative liquid. The pH, temperature and/or content of the dissociative liquid is regulated in such a manner that it is primarily the unwanted ions that are dissociated. The ion-exchange material comprises a matrix carrying ion-selecting substances.

Description

Process for the decontamination of substances contaminated with metal ions and / or radioactive substances

The invention relates to a method for the decontamination of substances infested or contaminated with metal ions and / or radioactive substances according to the preamble of claim 1.

Solids or semi-solid substances, even if they are in colloidally disperse form, are often associated with harmful metal ions, in particular also with radioactive metal isotopes. These solids or semi-solid substances can arise or occur, for example, through use in chemical plants, in the manufacture of electrical or cooling devices, through use and use in nuclear power plants, or due to environmental damage. In addition, substances are known, such as certain fertilizers, which are carriers of harmful metal ions and / or radioactive metal ions.

Process engineering therefore tries to find suitable methods to disinfect the contaminated substances. Thus, from DE-PS 37 04 046 a method according to the preamble of claim 1 is known, in which radioactive metal isotopes are removed from liquid food or animal feed, using Berlin blue and possibly prior separation of silt and solids by Pre-filtering or centrifuging from the liquid. Methods are also known from the literature for selectively removing cesium from liquids which contain cesiu and other salts but do not contain any molecularly disperse or colloidally disperse or coarsely disperse substances using a floating bed column which contains ammonium molybdate phosphate.

The first-mentioned method has the disadvantage that a salt with a defined grain size is used which has to be flowed through, the vessel containing the salt having to have appropriate sieving devices. However, both requirements reduce an economically necessary flow rate. In addition, the liquid is only freed from coarsely dispersed substances. It has been shown that this cleaning is not sufficient, since the colloidally dispersed substances in particular significantly interfere with the ion exchange. In addition, there is a high irreversible risk of bacteriological contamination, which can no longer be eliminated simply by using disinfectant. Solids and semi-solids cannot be disinfected at all using this process.

The same applies to the second method mentioned. With this method, pre-filtering is not provided at all.

Both methods together have the major disadvantage that ke cleaning or washing process is provided by continuously recycling the decontaminated liquid. Only by means of appropriate recycling, however, can the ions still adhering and being connected to the contaminated material after only once connecting contaminated substances and liquid be so far removed that their content reaches the value N or approximately zero, so that tolerable final salaries can be achieved.

From DE-OS 36 34 180 a method for the recovery of reusable in nuclear power plants boric acid solutions au in nuclear power plants radioactive waste and solutions gene is known, in which already cleaned liquid is returned to the starting solution. The concentrate is removed from the first stage (first reverse osmosis device). Because concentrate from the third stage. third reverse osmosis device) is recycled, but not the permeate.

In the process described in DE-OS 36 34 180 al permeate is led to permeate.

DE-OS 31 48 228 discloses a process for the recovery of uranium-containing aqueous solutions, in which the pH of the aqueous solution is first adjusted to a basic value above about 8. The insoluble substances including the precipitation caused by the pH adjustment are then removed. Then the basic solution with its content of remaining soluble substances is acidified to a pH below about 6. The acidified solution and its content are brought together with an ion exchange material with at least one idoxime group therein to remove and retain ions containing uranium from the acidified solution. Finally, the uranium is obtained from the ion exchange material by combining this material with an acid.

EP-OS 252 166 discloses a process for the continuous or quasi-continuous separation of cesium ions from aqueous solutions by ion exchange on ammonium molybdate phosphate. Salts are used for decontamination used.

The prior publication "Süddeutsche Zeitung, No. 41, dated January 19, 1987, page 11" discloses a method for decontaminating whey powder heavily contaminated with cesium, which essentially corresponds to the method of DE-PS 37 04 046.

The object of the invention is to propose a method according to the Oberbegri of claim 1, with which the disadvantages described above can be remedied and with which, above all, solids and semi-solid substances, even if they are already in the form of a colloid, can be detoxified.

According to the invention this object is achieved by the features specified in the characterizing part of claim 1. The infested substances can optionally be sprayed with the dissociation liquid. As a result of this or by introducing the infested or contaminated substances into a dissociation solution, the harmful mole ions and / or radioactive substances (isotopes) attached to the infested or contaminated substance are induced to dissociate. This also applies if the infested or contaminated substance is already a liquid. The pH of the dissociation liquid is adjusted in terms of pH, temperature and / or ingredients so that primarily the undesirable ions dissociate. As a result, the dissociation equilibria are shifted so sustainably from the ion connection towards the ion solution that an economical ion selection can then take place. The pH of the dissociation liquid is adjusted in terms of pH, temperature and / or content so that certain undesirable ions dissolve, while others, for example non-harmful ions, remain in the substances to be treated. It has been shown that the degree of decontamination and the selective ion separation of contaminated substances can be considerably increased if the dissociation liquid contains certain sugars, salts, alcohols, acids or alkalis, that is to say substances which influence the dielectric constant.

In addition, it is particularly advantageous in the treatment of foods if, for example, calcium or magnesium, but also so-called trace elements such as iron or the like, of substances such as, for example, open-chain globular protein substances, are bonded so tightly that they do not or hardly dissociate despite introduction into a dissociation liquid.

For some substances it is quite advantageous to force polyvalent ions, including those of a radioactive type, to dissociate by suitable selection of the dissociation liquid, inter alia by setting a suitable pH value.

Another advantage of the invention lies in the fact that ion-selecting material is not used in salt form, but the ion-selecting substances are applied to a basic structure (carrier substance, matrix) which contains an ion-exchange base material, e.g. a resin that can be. The ion-selective substances can also be applied to membranes or other filters or the like as a basic structure (carrier substance).

As already known per se, the liquid which has flowed through the ion-selective material can again be brought into contact with the starting material as a so-called rinsing and / or washing liquid, in which case liquid substances and / or liquids can be added or removed. This The process continues until the content of harmful metal ions and / or isotopes of the source material to be disinfected has reached a tolerable value or a value of zero or close to zero. The liquid freed of unwanted ions, especially radioactive ions, can be returned to the starting solution in such a way that, due to new dissociation equilibria created by ion selection, further unwanted ions still adhering to the contaminated substances dissociate so that they are brought into the ion-dispersed form and this Solution, which is again enriched with undesirable ions, mainly radioactive isotopes, is freed from the substances preventing d ion exchange after process step b and is again passed over ion exchange material, which is coated with ion-selective substances, according to feature c2. This cleaning and / or washing process can be continued until the substances infested with undesired metal ions and / or radioactive substances have a content of these undesirable substances of zero or close to Nu.

As is known per se, the separation of coarsely disperse substances by separation, the separation of colloidally disperse substances by membrane filtration and / or, if necessary, the separation of molecularly disperse substances by membrane filtration b pressures equal to or higher than 20 bar.

The ion exchanger base material (matrix) can consist, for example, of a polystyrene ball. As is known in the prior art, terminal ionizable substances are not applied to these, but preferably a salt complex, for example ammonium copper cyanoferrate. In conventional ion exchangers known from the prior art, ion bonds are formed terminal ionic behavior solved and other ions placed here. In contrast to the present invention, the microstructural exact fit is never taken into account. Therefore, the previously known ion exchangers can be regenerated relatively easily. In the invention, the ion exchangers can hardly or only with difficulty be regenerated. However, this is also not necessary in the case of harmful metal ions or radioactive ions to be removed, since their proportion in the contaminated product is so small that regeneration is not necessary. Here too, there is a further considerable advantage over the known methods. According to the prior art, either a salt (Berlin blue) or ammonium molybdate phosphate is used as such, since it is not applied to an ion exchanger base material (Matarix), or ion exchangers according to the prior art, consisting of a matrix, are used in the ion-forming Anchor groups are installed. In contrast, a new type of ion exchange is used in the invention, which could also be referred to as "ion trapping". According to the invention, no ion-forming anchor groups act on a matrix. Rather, according to the invention, a salt complex with a special lattice structure (= microstructural spatial configuration of the salt body) applied to a matrix acts as an ion scavenger.

Exemplary embodiments are explained below with reference to the accompanying drawings.

Figure 1 shows a selective ion exchange according to the prior art. After general dissolution of the powder, heating of the solution and before stacking of the solution, a three-stage ion exchange takes place, the polyvalent ions in the ion exchanger I and monovalent ions in the ion exchanger II (except radioactive ions) and the radioactive ions are removed in the ion exchanger III. This prior art scheme has significant disadvantages. On the one hand, not only are harmful ions such as cesium ions removed, but also calcium, magnesium, potassium, sodium and others, and when using anion exchangers also phosphates, sulphates, chloride ions and others. On the other hand, these ion exchangers often have to be regenerated, so that regeneration salt (brine) that is difficult to dispose of arises.

Another considerable disadvantage is that the solution flowing over the ion exchangers is virtually completely demineralized. This in turn is extremely disadvantageous for the dissociation behavior of the liquid stream retained in the filter station during a washing process to be carried out. If, for example, calcium should not dissociate or if it should dissociate poorly, for example cesium after remixing, then it is understandable that this process can be carried out if the washing liquid contains calcium in certain proportions but is free of cesium.

Fig. 2 shows the scheme on which the invention is based, since the disadvantages just mentioned are eliminated. For example, contaminated whey powder is introduced into a liquid adjusted in its osmolality, so that only the ions or salts to be removed, for example cesium salts, really go into solution during the dissolution process.

Coarsely disperse and colloidally disperse substances are then separated from this solution. This process means that the dissociation behavior of, for example, cesium is further promoted, since this increases the water supply in the permeate. Since the shift of the equilibrium towards the ion-disperse side is unfavorable for all other ions (since these are already present in the solution liquid), the ions to be removed again pass into the perme in increased ion form (see also Figs. 5 and 6).

The permeate now contains the salts present in the solution (without mixing with, for example, whey powder) and the cesium derived from the whey powder (the other salts contained in whey powder remain largely in the retentate due to the unfavorable solution situation).

Without the necessary pre-stacking, this permeate is then passed at a temperature of 60 ° C. over an ion exchanger which is designed in such a way that only the cesium ions dissolved in the permeate are captured. The ion exchanger composition consists of a base resin composition with anchor groups (prior art). According to the invention, a further salt complex is applied to this ion exchange material corresponding to the prior art in such a way that it cannot be detached. This salt complex is designed so that its lattice structure acts as a cesium scavenger, for example. An ion exchange with respect to, for example, cesium ions takes place on this applied salt complex vol. This type of ion exchange now allows all other ions to pass unhindered and removes from the liquid (permeae only the cesium ions, for example. Of course, depending on the salt complex used, other radioactive or interfering metal ions can also be used.

After removal of, for example, cesium ions from the permeate, the original solution is without cesium ions available again. It can be returned to the retentate as a so-called washing solution. This washing solution is particularly well suited for recycling, since only the cesium ions, for example, have been removed from it, so that there is a very favorable gradient for recycling with respect to cesium. When recycling, any cesium ions still present are washed out in the liquid retained by the filter.

Washing processes are always advantageous when the liquid that has been reunited has to be largely decontaminated to near zero Bq.

Fig. 3 shows an optimization scheme.

Fig. 4 shows a selective (dashed) ion exchange and the sequence according to the invention. The whey powder is delivered with the freight wagon 1. It passes into the sack emptying machine 3 through the unloading lock 2. After passing through the sack conditioning 4, it reaches the weighing container 5. After passing through the powder mixer 6, it is fed to the dissolving tank 10. There is also a bag filter 7, a fine filter and a fan 9. The batch tank 12 follows after the dissolving tank 10 and pasteu 11. The ultrafiltrate 13 is then carried out. The material arrives from the ultrafiltration 13 into the storage tank I 14. The ion exchanger I is provided with the reference symbol 15, the ion exchanger II with the reference symbol 17 and the ion exchanger II with the reference symbol 18. The storage tank II has the reference symbol 16. At the end of the process there are the resin discharge container 19 and the hard transport container 20 and the storage tank III with the reference number 21

Fig. 5 shows the course of the activity concentration in Dependence on the time for different material flows. In the example shown, the temperature was 60 ° C +/- 5 K, the volume flow V 800 +/- 200 liters / hour, the dry matter content was 20 +/- 1 _ and the pH of the whey powder solution was 5.0 +/- 0 , 1 and the pH value in the permeate 4.9 +/- 0.1. An activity concentration close to zero Bq could be achieved.

Fig. 6 shows the course of the activity concentration of the whey powder solution in the batch tank as a function of the time of the decontamination process. The temperature of the permeate was 58 ° C +/- 10 K, the volume flow V 1,000 +/- 50 liters / hour, the dry matter content K 20 +/- 1 I, the pH value 5.0 +/- 0.2 . The measured values are shown in the drawing legend.

The ion exchange base material can be a resin. The ion-selecting material can also be applied to membranes or other filters as a carrier substance.

According to an advantageous development of the invention, after passing through the ion exchange material applied to a basic framework, the dissociation liquid freed from harmful metal ions, in particular radioactive ions, is continuously fed back into the process in such a way that no concentration takes place due to a necessary separation process according to feature b of the claims.

Claims

1. Process for the decontamination of substances infested or contaminated with metal ions and / or radioactive substances in which

al) the infested or contaminated substances are introduced into a dissociation liquid,

b) then coarsely disperse, colloidally dispersed and / or molecularly disperse substances, if any, are separated from this dissociation liquid, and

cl) this dissociation liquid, which only contains ion-disperse and possibly molecularly disperse substances, is then passed over ion exchange material in such a way that an ion-selective exchange takes place,

characterized,

a2) that the infested substances are optionally sprayed with the dissociation liquid,

a3) that the dissociation liquid is adjusted in terms of pH, temperature and / or ingredients so that primarily the undesirable ions dissociate, and >2>

c2) that the ion exchange material consists of a basic structure and ion-selective substances applied thereon.

2. The method according to claim 1, characterized in that

d) that the dissociation liquid has a pH of 5.4 or less than 5.4 in the case of the dissociation of polyvalent ions.

3 .. The method according to claim 1, characterized in

e) that the dissociation liquid has a pH greater than 5.4 in the case of promoting the dissociation behavior of monovalent ions.

4. The method according to any one of the preceding claims, characterized by dadurc,

f) that the dissociation liquid contains substances which prevent desired ions from dissociating, so that a pre-ion selection takes place and at the same time the dissociation behavior of the interfering metal ions and / or radioactive ions is promoted.

5. The method according to any one of the preceding claims, dadurc

_ marked,

g) that the ion exchange material with the applied ion-selecting substances is attached in an ion exchange device in such a way that ion selection in a given order.

6. The method according to any one of the preceding claims,

h) in which the liquid freed from undesired metal ions and / or radioactive substances, primarily radioactive ions, is then returned to the starting solution,

i) and in which this cleaning and / or washing process is continued until the substances infested or contaminated with undesired metal ions and / or radioactive substances have a content of these undesired substances of zero or close to zero,

characterized,

k) that the liquid freed from undesired metal ions and / or radioactive substances, primarily radioactive ions, mixes after deionization and before remixing or during remixing with the still contaminated starting material with substances and / or liquids which influence the dissociation behavior of ions becomes.

7. The method according to any one of the preceding claims, characterized dadurc, o

1) that the substances applied to the basic structure are substances whose lattice structure is such that the ions to be selected are taken up by these structures with a precise fit.

8. The method according to any one of the preceding claims, characterized in

m) that after passing through the ion exchange material applied to a backbone, the dissociation liquid freed from harmful metal ions, in particular radioactive ions, is continuously fed back to the process in such a way that no concentration takes place due to a necessary separation process according to b.