EP3807223A1

EP3807223A1 - Method for removing radioactive iodide from wastewater

Info

Publication number: EP3807223A1
Application number: EP19733436.0A
Authority: EP
Inventors: Robert N. Grass
Original assignee: Turbobeads GmbH
Current assignee: Turbobeads GmbH
Priority date: 2018-06-18
Filing date: 2019-06-18
Publication date: 2021-04-21
Also published as: WO2019243338A1; CH715104A2

Abstract

The invention relates to a method for reducing the iodide content in aqueous systems, particularly to a method for purifying hospital wastewater created in connection with radiochemistry, diagnostics and therapy. Radioactive iodide is removed from wastewater in that it is precipitated by an excess of silver or copper ions. The remaining heavy metal ions are removed from the wastewater in a second step by precipitation using a halide salt. The treated wastewater thus contains reduced radioactive contamination and a low content of heavy metals and can be discharged to public wastewater systems.

Description

Method of removing radioactive iodide from waste water

The present invention relates to methods for reducing the iodide content in aqueous systems; in particular processes for cleaning with hospital wastewater which arise in connection with radiochemistry, diagnosis and therapy. The present invention further relates to systems which can be used in these processes. The present invention further relates to kits of chemicals which are suitable for these processes and / or can be used in these plants.

In radiochemistry, radioactive sodium iodide preparations are used to treat thyroid carcinomas; these contain 131J. Since the excretions (faeces, urine, sweat) of the patients radiate radioactively over the treatment period, the wastewater of the patients in clinics must be collected separately in decay tanks. The wastewater is stored in these decay tanks until it falls below a limit value (emission of permitted radiation in MBq per week) specified by the Federal Office of Public Health (in Switzerland, in other countries). Due to the half-life of 131J, the radioactive sodium iodide doses administered to the patients, and the permitted delivery limits, the required storage time of the waste water in the decay tank is determined (typically 1-2 months). The size of the decay tanks that a given clinic has available (permanently installed in the space provided) limits the number of patients who can be treated with radioactive iodine. Thus, in order to be able to treat more patients, a hospital has to do a great deal of construction work (increase the decay tank volume). Other radioactive iodide compounds are also used in hospitals and other facilities. The term radioactive iodide therefore includes the isotopes 131J, 123J and 125J, with 131J being of special importance.

In order to reduce the radioactivity in the corresponding hospital wastewater, the radioactive iodide must be removed from the water.

There are several methods for removing iodide from water that can be found in a standard chemistry textbook, such as binding iodide using starch, precipitating iodide using silver to form insoluble silver iodide, and precipitating iodide using Cu (l) to form CuJ. Due to the low iodine concentrations in the wastewater, the starch method has proven to be unusable. The precipitation of iodide using silver ions has been described for the treatment of radioactive water from nuclear power plants (US5352367). Alternatively, the removal of iodine using copper has been described (Tachikawa et al. Int. J. Appl. Radiation Isotopes, 1975, 26, 758). Copper (l) ions are of particular interest here, since the salt cul also has a low solubility. However, these two methods of precipitation for the removal of radioactive iodide cannot be used for the treatment of hospital wastewater due to the following problem-specific disadvantages (restrictions):

- In addition to iodine, hospital wastewater also contains high chlorine loads (as chloride), whereby the chloride concentration is usually considerably higher than the iodine concentration. If an lx-4x excess of silver or copper is added to iodine as in US5352367, the amount of metal is not sufficient to bind the entire iodide and chloride. Even if significantly more metal is added, a large part of the metal ions is bound by the chloride, so that only a small part remains for the reaction with the iodide. As a result, the precipitation of the iodide is only incomplete.

- An excess of the metal salt must be used, with metal ions remaining in the solution after the precipitation of iodide and chloride. This heavy metal-containing water, like the iodide-contaminated hospital wastewater, must not be disposed of as wastewater.

- When iodide and chloride are precipitated using silver or copper (l) ions, a very fine precipitate results from precipitated silver iodide and silver chloride particles in the waste water. This cannot be filtered in a reasonable time, since the small particles clog the filter pores.

The object of the present invention is therefore to provide methods for removing the radioactivity from the decay tanks so that the water can be drained off more quickly. In a broader context, the task is to provide methods for removing iodide, especially radioactive iodide, from aqueous systems. Furthermore, there is the task of providing plants and kits that are suitable for these processes. The tasks outlined above are solved according to the independent claims. The dependent claims represent advantageous embodiments. Further advantageous embodiments can be found in the description and the figures. The general, preferred and particularly preferred embodiments, ranges etc. given in connection with the present invention can be combined with one another as desired. Likewise, individual definitions, embodiments, etc. can be omitted or not relevant.

The present invention is described in detail below, advantageous methods being described in a first aspect and advantageous systems in a second aspect. It goes without saying that the various embodiments, preferences and ranges disclosed and described below can be combined with one another as desired. In addition, depending on the embodiment, individual definitions, preferences and areas cannot be used. Furthermore, the term "comprising" includes the meanings "containing" and "consisting of".

The terms used in the present invention are used in the generally customary sense familiar to those skilled in the art. Unless there is any other meaning from the direct context, the following terms in particular have the meaning given here

/ Definitions.

Wastewater: The term is well known and includes aqueous systems that arise when used in the past. Such aqueous systems are contaminated by their previous use, that is to say they have changed in properties or composition. The term wastewater thus includes the radioactive contaminated hospital wastewater as well as gray water (according to EN12056-1), black water (according to EN6107-7: 1997), wastewater from industrial processing processes and wastewater from nuclear power plants. In connection with the present invention, the term wastewater describes in particular those aqueous systems which, in addition to iodide (in particular 131J), also contain chloride. Radionucleotide decay system, especially in a hospital or clinic: The term refers to a system that collects and retains waste water until the radioactive level falls below a specified limit. Accordingly, such systems comprise a container (also referred to as a decay tank) which is at least provided with an inlet and an outlet. The inlet enables a connection to the sewage network of the hospital; the process is a connection to the municipal water disposal.

As will be explained in detail below, it is possible with the method according to the invention to remove radioactive iodine by precipitation with silver or copper ions from water without silver or copper ions remaining in the water and in a way that the metal chloride can be carried out / Metal iodide particles can be separated easily and quickly. This enables the process to use significantly smaller decay tanks.

According to a first aspect, the task outlined above is carried out in a multi-stage process, i.e. in a multi-step process. According to the present invention, chemicals are added to the radioactive water in a predetermined sequence. Each step fulfills a specific part of the task:

1. Add non-radioactive iodide (as iodide-containing salt, e.g. Nal) to the waste water. In order to promote the precipitation of radioactive iodide, non-radioactive iodide is added to the water. Since the precipitation process (in step 2) is given by the solubility product of the metal iodide (for silver iodide K = 8.52 E-17), a residual concentration of iodide always remains in solution after the precipitation of iodide with heavy metal ions. The greater the non-radioactive portion of the original iodide concentration, the greater the portion of the non-radioactive iodide that remains in solution after precipitation, and the more radioactive iodide is precipitated.

2. Precipitation of iodide and chloride by adding copper (l) ions (in excess). Since copper (I) ions are difficult to dissolve in water without the addition of appropriate complexing agents, it is advantageous to introduce the copper as copper (II) salt and by a suitable one Conversion of reducing agents (eg ascorbic acid, reducing sugars) into copper (l). Alternatively, metallic copper shavings can be converted into copper (I) ions using a suitable oxidizing agent (eg Cu (II) by disproportionation, air). Precipitation of iodide and chloride by adding silver ions (in excess). Since the initial concentrations of iodide and chloride in the wastewater are not constant and cannot be determined with sufficient accuracy, an excess of silver or copper ions (eg as silver nitrate, copper nitrate) must be added. An increase in the metal ion concentration during the precipitation process also favors the deposition of the iodide concentration remaining in solution after the precipitation (via solubility product). Precipitation of the excess heavy metal ions by adding another salt. Water-soluble chloride, iodide and bromide salts are suitable for this, since these form poorly water-soluble salts with the silver and copper ions. For this purpose, an excess of the soluble salt must be used again, and it is therefore important to ensure that the salt is not harmful to health, is inexpensive and is not regulated / limited in the local wastewater regulation. The use of table salt (aCI) is particularly suitable for this, but KCl, Nal, Kl can also be used. This process increases the salinity of the wastewater, which favors the easier flocculation of the precipitated substances and thus also significantly simplifies the separability of the precipitated particles. It is also possible to use a salt that can be removed by a further flocculation step. An example of this is iron (III) chloride and subsequent flocculation of the iron ions as hydroxides by increasing the pH. In this variant, the flocculation of the iron hydroxides helps the separation of the previously precipitated salts by aggregation with copper iodide, copper chloride, silver iodide and silver chloride particles. Optionally, a polymeric flocculant can be added after the excess heavy metal has been precipitated. Anionic polymers such as eg polyacrylic acids, cellulose derivatives, polysaccharides, polyamines, polyvinyl alcohol, and soaps.

6. The precipitated substances, which largely consist of silver iodide, copper iodide (radioactive and non-radioactive), silver chloride, copper iodide and optionally iron hydroxides, are separated by a suitable solid / liquid process (eg by filtration, sedimentation in a tank and / or via a Flydrocyclone) removed from the waste water. As a result, the radioactive content of the wastewater is significantly reduced and the water does not contain any further ions or solids that limit the direct release of the water to the public wastewater network. This means that the wastewater can be disposed of more quickly (with a significantly shorter decay time, ideally without further decay in tanks). From an experimental point of view, the use of methods in which the viscosity of the liquid media is low has proven itself. In practice this is especially important during the separation process, preferred viscosity values are <0.01 Pa s. Methods with viscosity values below 0.002 Pa s are particularly preferred.

7. The solid (which is radioactive by containing 1-131) is stored for decay.

After the radioactive iodide has completely subsided, the silver is purified from the solid (e.g. by dissolving the Agl and AgCI in acid and chemically reducing the silver with glucose). The silver can now be used again (e.g. as water-soluble nitrate) in step 2.

In a preferred embodiment, the hospital waste water is treated in several steps and the radioactivity of the waste water is gradually reduced. In the first step, at least 90% of the available halide ions (CI-, I.) Is generated by generating Cu (l) ions immediately before, or in the wastewater, and with the optional addition of non-radioactive halide ions (depending on the specific composition of the hospital wastewater) -, Br-) precipitated in the water. In a further step, silver ions are added to the water, which leads to a majority (> 80%) of the halide ions remaining after the 1st treatment step being precipitated. In other preferred embodiments, the temperature before or after the addition of the metal salts and / or additional halide ions is reduced or raised by at least 10 ° C. by heating or cooling the waste water. Suitable methods for this are well known to the person skilled in the art and include the use of immersion heaters, instantaneous water heaters, heat exchangers or the addition of ice.

Hospital wastewater is stored for weeks now in order to ensure that radioactivity decays, which naturally requires large tanks with residence times of weeks to months. In a preferred embodiment, the hospital wastewater is therefore treated continuously or semi-continuously. This is characterized by the fact that the residence time of the water in the purification process is less than 24 hours and the untreated, radioactive hospital wastewater is stored for less than 3 days. This can drastically reduce the space required for the storage of radioactive waste water for a typical hospital.

The metering of the metal ions and / or optional halide ions to the hospital wastewater is preferably carried out via a T-piece, followed (in the direction of flow) by a static mixer, e.g. commercially available from Sulzer-Chemtech, followed by a solid / liquid separation process. Corresponding separation processes are well known to the person skilled in the art and include how they are used in traditional wastewater treatment. Filtration is the preferred method. Optionally, the filter load can be reduced using a hydrocyclone or an upstream sedimentation basin. One-way filtration elements of compact construction are preferably used, e.g. commercially available from PALL or 3M.

In a preferred embodiment, at least one ion-selective electrode or an overall conductance electrode is used for process monitoring in the process described above. Corresponding electrodes are commercially available from Mettler-Toledo.

Since the process means that the water does not have to be stored in the tanks as long, larger volumes of wastewater can be processed with the tank volume remaining the same, and thus more patients with thyroid carcinoma can be treated with radioactive iodine therapy. The present invention furthermore relates to a kit comprising various chemical components. This kit provides the chemicals suitable for the inventive method and is therefore suitable for carrying out the method as described here and also suitable for operating a system as described below. One of the kits mentioned below is preferred: kit A, kit B and kit C.

Kit A:

aqueous solution of copper (II) sulfate, preferably 0.5-1 mol / l, preferably buffered in the pH range 5-9;

- aqueous solution of sodium iodide, preferably 0.5-1 mol / l, preferably buffered in the pH range 5-9;

- aqueous solution of ascorbic acid, optionally in combination with its Na salt, preferably 0.5-2 mol / l, preferably buffered in the range pH 4-9.

Kit B:

- aqueous solution of ascorbic acid, optionally in combination with its Na salt, preferably 0.5-2 mol / l, preferably buffered in the range pH 4-9;

one or more of the solutions containing a flocculant, preferably chitosan,

Kit C:

- aqueous solution of sodium iodide, preferably 0.5-1 mol / l, preferably buffered in the pH range 5-

9;

- Flocculant, preferably chitosan, preferably as a solution. According to a second aspect, an improved radionucleotide decay system is provided.

The known radionucleotide decay systems essentially comprise one or more storage containers which are connected to the sewage system, e.g. a hospital. The volume of the storage tanks is dimensioned so that a sufficient dwell time is ensured before the wastewater is discharged into the public network.

The inventive decay system enables the addition of various chemicals, in particular copper (II) salts and suitable reducing agents (e.g. ascorbic acid) and non-radioactive halide solutions (e.g. Nal, NaCl, NaBr, Kl, KCl), in order to carry out the process described in the first aspect. In one embodiment, the inventive decay system comprises, in addition to the storage container, means for adding liquid components, in particular

- Means suitable for addition

a water-soluble salt containing iodide;

a soluble silver salt;

a soluble Cu (II) salt;

a reducing agent;

a water-soluble, halide salt;

Acids, bases, buffers,

- if necessary, means for adding solid components, in particular a flocculant;

- if necessary, means for determining characteristic parameters of an aqueous composition, in particular

for determining the pH value;

Radioactivity determination means;

to determine the temperature;

to determine the viscosity;

- If necessary, means for separating a solid.

- If necessary, means for mixing the storage container of the system. The examples below serve to further explain the invention; they are not intended to limit the invention in any way:

Example 1: Reference example according to ÜS5352367 with excess AgN0 ₃ :

One liter of water with a radiation level of 190 kBc / l was taken from a hospital decay pool. 1g of silver nitrate was added to this solution, after which a milky precipitate could be observed. This precipitation could only be separated with great difficulty (and after a waiting time of more than one hour) by means of a pleated filter. However, the entire precipitate could not be separated off, so the water remained cloudy and had a radiation exposure of over 50 kBc / l. After the filtered water was left standing in a glass overnight, it was further observed that a metal mirror film formed on the glass wall, which shows that the silver ion concentration in the water was high (and the water cannot be disposed of in the waste water).

Example 2: without addition of Nal, with precipitation of silver ions

One liter of water with a radiation level of 190 l <Bc / l was taken from a hospital decay pool. 1 g / l of silver nitrate was first added to this solution, after which a milky precipitate could be observed. After a reaction time of 10 minutes, 400 mg of NaCl was added to the water, after which the precipitate was compacted (precipitation of Ag as AgCl). The precipitate was quickly removed from the water using a pleated filter. The clear, remaining water had a radiation exposure of 6.7 kBc / l. No silver film was observed even after the water was left standing in a glass for a long time.

Example 3: with addition of Nal with precipitation of silver ions

One liter of water with a radiation level of 190 kBc / l was taken from a hospital decay pool. 0.02 g of sodium iodide was first added to this solution (without any visible effect). Then 1 g / l silver nitrate was added, after which a milky precipitate could be observed (precipitation of iodide and chloride as Agl and AgCl). After a reaction time of 10 minutes 400 mg of NaCl was added to the water, after which the precipitate condensed (precipitation of Ag as AgCl). The precipitate was quickly removed from the water using a pleated filter. The clear, remaining water had a radiation load of 3.4 kBc / l and could therefore be disposed of as waste water without further decay. The solid was stored for decay.

Example 4: Precipitation of sodium iodide with copper ions

A 100 ml of a solution with 1 mg / ml sodium iodide in drinking water was treated with 1.06 mg / ml copper (II) sulfate. The resulting slightly cloudy solution immediately became milky white by adding ascorbic acid (reduction of Cu (il) to Cu (l)). The white solid (1.22 mg / ml) was able to be filtered off from the solution and could be identified by X-ray diffraction as a lupfer (l) iodide. The stoichiometry of the reaction Cu ⁺ + I -> Cul can be used to calculate that at least 96% of the originally dissolved iodide has been precipitated.

Example 5: Removal of radioactive iodide from hospital wastewater with copper ions

100 liters of radioactive hospital wastewater with a radiation exposure of 29900 Bq / L were collected in a 120 liter tank (from a radio iodine therapy station). Then 0.8 liters of a 0.66 molar sodium iodide (non-radioactive) solution was added and mixed with the tank contents. Then 1 liter of a 0.66 M copper (II) sulfate solution was added and mixed with the tank contents. Then 1 liter of a 0.66 M ascorbic acid solution was added, whereupon a white radioactive precipitate was formed, which contains Cu (l). After mixing the tank contents, it was left to stand for 4 days so that the precipitation could settle completely. The water in the supernatant then had a radiation level of 171 Bq / L. This corresponds to a> 99% reduction in the original radioactive exposure to water.

The supernatant could simply be drained off (98% of the original volume). The remaining sediment (2% of the original volume of the above precipitation) was placed in a decay basin.

Claims

Expectations

1. A method for removing iodide, especially radioactive iodide, from wastewater, comprising the following steps:

a. Provision of waste water which is contaminated with iodide and possibly with chloride; b. optionally adding a water-soluble, halogen-containing salt, in particular one

Salt containing iodide;

cl. addition of a soluble Cu (II) salt in excess to the expected chloride and iodide loading of the water;

c2. Addition of a reducing agent to reduce Cu (II) to Cu (I);

c3. optionally adding a water-soluble silver salt;

d. if necessary, adding a water-soluble, halide-containing salt, in excess to the copper and silver salts used beforehand, to the waste water obtained in this way;

e. if necessary adding a flocculant to the waste water obtained in this way;

f. if necessary, adjusting the pH of the waste water obtained in this way, preferably in the range pH 5-9;

G. Separating the solid obtained, in particular the radioactive solid, from the treated waste water.

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

• it comprises steps a, cl, c2 and g or consists of steps a, cl, c2 and g; or

• it comprises steps a, cl, c2, d and g or consists of steps a, cl, c2, d and g; or

® it comprises steps a, b, cl, c2, d and g or consists of steps a, b, cl, c2, d and g; or

• it comprises steps a to g or consists of steps a to g.

B. The method according to any one of claims 1-2, characterized in that the copper

concentration in the water after the treatment is less than 1 mg / l and the silver concentration, if present, in the water after the treatment is less than 1 mg / l.

4. A method for removing iodide, especially radioactive iodide, from waste water, comprising the following steps:

a. Provision of waste water which is contaminated with iodide and possibly with chloride;

b. if necessary, adding a water-soluble salt containing iodide;

c. Addition of a soluble silver salt in excess of the expected chloride and iodide loading of the water to this waste water;

d. Add a water-soluble, halide salt in excess to the previous one

silver salt used for the waste water thus obtained;

e. if necessary adding a flocculant to the waste water obtained in this way;

f. if necessary, adjusting the pH of the waste water obtained, preferably pH 5-9;

5. The method according to claim 4, characterized in that

• it comprises steps a, c, d and g or from the steps a, c, d and g

consists; or

• it comprises steps a, b, c, d and g or consists of steps a, b, c, d and g; or

• it comprises steps a, c, d, e, f and g or consists of steps a, c, d, e, f and g; or

• it comprises steps a to g or consists of steps a to g.

6. The method according to any one of claims 4-5, characterized in that the silver

concentration of the water after the treatment is less than 5 mg / l, is preferably less than 50 pg / l, particularly preferably is less than 1 pg / l.

7. The method according to any one of the preceding claims, characterized in that the waste water contains radioactive iodide and the radioactivity of the water after the treatment has less than 10% of the initial activity and / or. less than 10 kBc / l.

8. The method according to any one of the preceding claims, characterized in that the viscosity of the waste water in step g is less than 0.01 Pa s, preferably less than 0.002 Pa s.

9. The method according to any one of claims 1-8, characterized in that the solid, in particular the radioactive solid after decay, is worked up thermally and / or chemically (step h.).

10. The method according to claim 9, characterized in that the silver contained therein is recovered by working up the solid.

11. A method for increasing the capacity of a radionucleotide decay system, in particular in a hospital or clinic, characterized in that steps a, c, d and g according to claims 1-10 are carried out in said radionucleotide decay system.

12. The method according to claim 11, characterized in that the originally radioactive hospital wastewater is disposed of in the public wastewater network within 10 days, preferably within 1 day.

13. Kit, in particular for carrying out the method according to one of claims 1-12, comprising the following components in separate containers according to kit A, B or C:

Kit A:

• aqueous solution of copper (II) sulfate, preferably 0.5-1 mol / l, preferably buffered in the pH range 5-9;

• aqueous solution of sodium iodide, preferably 0.5-1 mol / l, preferably buffered in the pH range 5-9;

• aqueous solution of ascorbic acid, optionally in combination with its Na salt, preferably 0.5-2 mol / l, preferably buffered in the pH range 4-9;

Kit B:

• aqueous solution of ascorbic acid, optionally in combination with its Na salt, preferably 0.5-2 mol / l, preferably buffered in the pH range 4-9; one or more of the solutions containing a flocculant, preferably chitosan;

Kit C:

• Flocculant, preferably chitosan, preferably as a solution.

14. Radionucleotide decay system, in particular in a hospital or clinic

characterized in that the originally radioactive (hospital) waste water can be disposed of in the public waste water network within one day.

15. Plant according to claim 14, comprising

• Means for adding liquid components, particularly suitable for adding

• a water-soluble salt containing iodide;

• a soluble silver salt;

• a soluble Cu (II) salt;

• a reducing agent;

• a water-soluble, halide salt;

• acids, bases, buffers,

• if necessary, means for adding solid components, in particular a flocculant;

• Means for determining characteristic parameters of an aqueous

Composition, in particular

«To determine the pH value;

• means for determining radioactivity;

• to determine the temperature;

• to determine the viscosity;

• Means for burning off a solid if necessary.

• if necessary, means for mixing the storage container of the system.