WO2013066189A1

WO2013066189A1 - Continuous method for concentration of iodide

Info

Publication number: WO2013066189A1
Application number: PCT/NO2012/050211
Authority: WO
Inventors: Thorstein Dyrstad; Odd Henning Sirnes; Tom Sirnes
Original assignee: Individual
Current assignee: Individual
Priority date: 2011-10-31
Filing date: 2012-10-30
Publication date: 2013-05-10
Anticipated expiration: 2014-04-30
Also published as: NO20121266A1; NO336304B1

Abstract

Method for concentration of iodide from a first aqueous, iodidic solution (2) and to a second aqueous, iodidic solution (92), the method comprising the steps: a) to acidify the first solution (2;32) with a mineral acid; b) to add an oxidizing agent to an acidic solution (2'; 32') from step a) in order to oxidize iodide to elementary iodine; c) to add an amylose-containing material to a solution (2";32") from step b) such that an iodine-amylose-complex is formed; d) to substantially separate the iodine-amylose-complex formed in step c) from a fluid (36); e) to add a reducing agent to an iodine-amylose-complex fraction (80) containing the iodine-amylose-complex from step d) in order to reduce elementary iodine to iodide in order to separate iodide from amylose; and f) to separate the mixture (80') from step e) in a second aqueous, iodidic fraction (92) and an amylose-containing fraction (90), where step d) comprises using at least one separation device (70) comprising a filter.

Description

CONTINUOUS METHOD FOR CONCENTRATION OF IODIDE

The present invention relates to a method for concentration of iodide from a first aqueous, iodidic solution and to a second aqueous, iodidic solution. The concentrated aqueous, iodidic solution may be used for further production of elementary iodine. More specifically the present invention relates to using an amylose-containing material in a continuous concentration process and a method for continuous downstream processing of iodine-amylose-complex.

Iodine is an element that does not exist in nature in a pure condition, but in ionized condition, most often in the form of iodide ( ). The metallic form of iodine (I₂) is called elementary iodine. Iodine may also occur as iodate (I0₃ ^~). In the following iodine will be used for elementary iodine, iodide and iodate, and iodic will be used to describe a solution that may contain elementary iodine, iodide or iodate.

It is known to produce elementary iodine from saline water pumped up from wells in the ground. Such wells may be gas-producing wells or oil-producing wells. The water from gas-producing and oil-producing wells is also named produced water. Produced water may contain hydrocarbons. Such saline water may contain various amounts of iodine. The salt in the salt water is substantially in the form of NaCI.

The saline, produced water will in the following be described as feed water. The feed water will contain small amounts of iodine. Commercial extraction may take place at a start concentration of iodide of 5-150 ppm, but the iodide contents are most often in the range 7-30 ppm. Good sources may contain 50-70 ppm of iodide. It is known to commercially exploit salt water from the Japanese Minami Kanto gas field where the iodide contents are 100-300 ppm and from the Anakardo Basin gas field in Oklahoma, USA, where the iodide contents may be as high as 1500 ppm.

A known method is first to cleanse the feed water of hydrocarbons and thereafter acidify the feed water with a mineral acid, as for example sulphuric acid (H₂S0₄). Iodine will then be available as HI in the acidified feed water. Thereafter an oxidizing agent as for example chorine (Cl₂) is added and elementary iodine is formed according to the reaction :

2HI + Cl₂ = I₂ + 2HCI

This solution contains low concentrations of iodine. Concentration may be done by blowing air through the solution, possibly after heating of the solution. Iodine then will evaporate and be brought into an absorption tower. This tower is called a "blow out tower". The tower has an acidic environment and sulphur dioxide is added in order to reduce iodine to iodide:

I₂ + 2H₂0 + S0₂ = 2HI + H₂S0₄

Thereafter chlorine is added in order to oxidize the iodide such that it is deposited as iodine:

2HI + Cl₂ = I₂ + 2HCI

Thereafter the iodine is filtered and cleansed before packing.

Recent techniques comprise process steps where iodine in the acidified feed water is captured by ion exchange in an anion-exchange resin as described in US patent No. 3,346,331. When the anion-exchange resin is saturated, the anion-exchange resin is treated with a NaOH-solution followed by a NaCI-solution in order to elude iodine from the anion-exchange resin in the form of iodide and iodate. Iodine in the elusion is recovered by adding mineral acid such that iodide and iodate are converted to elementary iodine which then crystallizes. US patent No. 4,131,645 discloses to lead feed water directly over an anion-exchange resin without any preceding acidification and oxidation.

Patent specification WO 2010/056864 Al discloses to oxidize iodide by means of hypochlorite produced in situ from the chlorine contents of the produced water. The produced water is preferably filtered in order to remove particles and other filterable impurities before the water is acidified. Elementary iodine is captured in the subsequent step by an anion-exchange resin or by an adsorption unit comprising activated carbon. Iodine is separated from the anion-exchange resin by a NaOH- solution. Thereafter the solution is acidified to a pH between 0.5 and 3 with HCI. Then sodium-hypochlorite (NaOCI) is added in order to oxidize iodide and iodine is deposited. Iodine is separated from activated carbon by leading sulphur dioxide gas (S0₂) and water therethrough. The solution will contain hydrogen-iodide (HI) and sulphuric acid (H₂S0₄). The iodide may be oxidized by adding hydrogen-peroxide (H₂0₂) and elementary iodine is deposited.

It is known that anion-exchange resins become ineffective as they are overgrown by hydrocarbons that may be present in the feed water.

From WO 2010/033945 Al it is known to adsorb elementary iodine to a column of activated carbon. Here also, the oil components in the produced water must be removed before the separation of iodine commences. The feed is acidified with for example sulphuric acid (H₂S0₄) or with hydrochloric acid (HCI). Thereafter an oxidizing element as for example sodium-hypochlorite (NaOCI) or chlorine (Cl₂) is added, or it can be an electrochemical process. The solution is led over activated carbon which captures the iodine. Iodine may also be regenerated from the activated carbon as described above. The patent specification also describes that hydrocarbons are separated from the feed water before the first oxidizing step. This may be done with a hydro cyclone and there may also be emulsifiers added to the feed water.

The patent specification SU827376 discloses a method for extracting iodine from produced water from oil wells and ground water where the steps comprise of acidifying the iodic feed water, adding starch to the acidic feed water and letting the iodine- starch-solution sediment. In order to accelerate the process of sedimentation a flocculating agent constituting a salt of the polymer 2-methyl-5-vinylpyridin dimethyl sulfate is added. After sedimentation the fluid phase is tapped off and the iodine- starch slurry is filtered and washed with water. The washed iodine-starch slurry is treated with acidic sulfite solution in order to isolate iodine from the starch. The iodine solution, which may contain 0.4-0.5% iodine, is made alkaline and is treated further in order to extract iodine in a per se known way. A continuous process is not described.

The patent specification FR945359 discloses a method for extracting iodine from marine algae. The extract from marine algae is acidified with sulphuric acid. Sodium nitrite is added to the acidic solution as an oxidizing agent. Starch is added to the solution for the formation of starch-iodide. The starch-iodide is deposited and clear iodine-free residual fluid is decanted. The starch-iodide is brought into suspension with water and sodium-bisulfite-solution or potassium-bisulfite-solution is added as a reducing agent. After some time the iodic supernatant is decanted. The deposited starch is washed and the wash water is added to the iodic supernatant. Thereafter the iodine or iodide is extracted according to known methods. No continuous process is described. The patent specification FR897641 discloses a method for extracting iodine from marine algae. The extract from marine algae is acidified with sulphuric acid. An oxidizing agent as for example sodium nitrite is added to the acidic solution. The solution is mixed with starch or amylose-material. Starch-iodide is separated from the iodine-depleted medium. Several possible methods for processing of the starch-iodide are described. One method is to wash the starch-iodide with a concentrated solution of a sulfite and an alkali-hyposulfite and thereafter separate by decanting the starch material from the iodidic fluid. No continuous process is described.

The invention has for its object to remedy or to reduce at least one of the drawbacks of the prior art, or at least to obtain a useful alternative to prior art.

The object is attained through features described in the description given below and in the following patent claims.

The present invention provides a method for extraction of an aqueous, iodidic concentrate which thereafter may be processed to elementary iodine. The basis for the process is water which comes from underground, geological formations, as the water may appear alone as a fluid in the formation or comes from hydrocarbon formations.

The present invention relates to a continuous process for extraction of an aqueous, iodidic concentrate. A continuous process is preferable compared to known processes using sedimentation, possibly also flocculation, and decanting in one or more process steps.

The present invention relates to a method for concentration of iodide from a first aqueous, iodidic solution and to a second aqueous, iodidic solution, the method comprising the steps:

a) to acidify the first solution with a mineral acid;

b) to add an oxidizing agent to an acidic solution from step a) in order to oxidize iodide to elementary iodine;

c) to add an amylose-containing material to a solution from step b) such that an iodine-amylose-complex is formed;

d) to substantially separate the iodine-amylose-complex formed in step c) from the fluid;

e) to add a reducing agent to an iodine-amylose-complex fraction containing the iodine-amylose-complex from step d) in order to reduce elementary iodine to iodide to separate iodide from amylose; and

f) to separate a mixture from step e) into a second aqueous, iodidic solution and an amylose-containing fraction,

where step d) comprise to use a continuous operable device comprising a filter.

Produced water from a gas-producing well or from an oil-producing well may constitute the first iodidic solution. The first iodidic solution may also come from a well which is in connection with groundwater that does not contain hydrocarbons.

Step f) may comprise using a continuously operable separation device comprising a filter. Step b) may comprise adding an oxidizing agent chosen from a group

comprising chlorine (Cl₂) and a hypochlorite-compound (Oc ). Step b) may comprise adding hydrogen peroxide (H₂0₂) as an oxidizing agent. Step e) may comprise adding a reducing agent chosen from a group comprising reducing sulphur-compounds, tocopherols and reducing acids.

The method may further comprise filtering the first iodidic solution previous to step a) in order to remove impurities from the first iodidic fluid. The solution may be filtered through a continuously operable filter chosen from a group comprising continuously operable ceramic membrane filters, continuously operable ceramic ultra-membrane filters and continuously operable polymer membrane filters. The filter may have a pore size from and including 0.01 μηη to and including 2 μιτι.

The filter in step d) may be chosen from a group comprising continuously operable ceramic membrane filters, continuously operable ceramic ultra-membrane filters and continuously operable polymer membrane filters. The filter may have a pore size from and including 0.01 pm to and including 2 pm.

The filter in step f) may be chosen from a group comprising continuously operable ceramic membrane filters, continuously operable ceramic ultra-membrane filters and continuously operable polymer membrane filters. The filter may have a pore size from and including 0.01 pm to and including 2 pm.

Said filters may be the same type of filter in the different steps of the process, or they may be different types of filters. The pore size may be the same in the different steps of the process, or it may be different and adapted to the actual step of the process.

The method may further comprise that step d) comprises to use a separation device that may be operated such that the concentration between iodide in the first, aqueous, iodidic solution and iodine in the iodine-amylose-complex fraction is at least 1 : 150. The separation device may be operated such that the concentration between iodide in the first, aqueous, iodidic solution and iodine in the iodine-amylose-complex fraction is at least 1 : 250. The separation device may be further operated such that the concentration between iodide in the first aqueous, iodidic solution and iodine in the iodine-amylose-complex fraction is at least 1 : 500. The separation device may be further operated such that the concentration between iodide in the first aqueous, iodidic solution and iodine in the iodine-amylose-complex fraction is at least 1 : 750. The separation device may be further operated such that the concentration between iodide in the first aqueous iodidic solution and iodine in the iodine-amylose-complex fraction is at least 1 : 1000.

In the following an example of a preferred embodiment which is illustrated in the enclosed drawing, is described, where:

Fig. 1 shows a flow chart for one embodiment of the invention. Step 1

In the figure the reference numeral 1 denotes a process according to the invention. Organic components in a feed water 2 are removed by means of filtering in a filter 3. Particularly feed water 2 from geological formations containing hydrocarbons could comprise organic components that may have an interruptive effect on the subsequent steps of the process. A membrane filter 3 with a pore size from 0.01 pm to 2 pm is suitable for the purpose. A ceramic membrane filter 3 with a pore size from 0.01 pm to 2 pm is particularly suitable for the purpose. Further a ceramic ultra-filtering membrane filter 3 with a pore size from 0.01 pm to 0.05 pm is particularly suitable for the purpose. Alternatively a polymer membrane with pore size from 0.01 pm to 0.05 pm may be used in the filter 3, Said membrane filter 3, ceramic membrane filter 3 and ceramic ultra-filtering membrane filter 3 may be arranged for continuous operation. Required negative or positive pressure relative to the ambient pressure in order to drive the feed water 2 through the filter 3 is dependent on the chosen type of filter and pore size and the person skilled in the art will know how to calculate this.

Construction and running of such filters 3 are known within the art and will not be discussed any further herein.

Two fluid flows will stream out from the filter 3: an iodidic, cleansed permeate 32 and a retentate 34 containing impurities. The retentate 34 may for example contain 1-5% hydrocarbons depending on the concentration of these in the feed water 2. The retentate 34 may be led to an outlet, led back to the geological structure or be processed for extraction of the hydrocarbons. The retentate 34 will not be discussed any further herein. Step 2

Step 2A

An acidifying agent is added to the iodic permeate 32 from step 1. The acidifying agent may be a mineral acid, as for example sulphuric acid (H₂S0₄) or hydrochloric acid (HCI). The acidifying agent is dosed to the permeate 32 by means of a per se known dosing device 4 which may comprise a first holding tank 40 for the acidifying agent, a first metering pump 41 and a pH-meter (not shown). The permeate 32 may be acidified to a pH between 6.5 and 0.5. It is skillful to choose a proper concentration for the acidifying agent based on the pH of the permeate 32 and the pH desired to be achieved in this step, the desired volume ratio between the permeate 32 and the acidifying agent and how the permeate 32 and the acidifying agent are to be mixed.

In an alternative method, especially where the feed water 2 comes from a

groundwater that does not contain any hydrocarbons, step 1 may be left out. The acidifying agent is in this method added to the feed water 2.

Step 2B

An oxidizing agent is added to the acidified permeate 32' from step 2A or to the acidified feed water 2'. The oxidizing agent may for example be chlorine, a

hypochlorite compound (OCI-), as for example sodium-hypochlorite (NaOCI), or hydrogen-peroxide (H₂0₂). The oxidizing agent is dosed to the acidified permeate 32' or the acidified feed water 2' by means of a per se known dosing device 4 which may comprise a second holding tank 42 for the oxidizing agent and a second metering pump 43. It is skillful to choose a proper concentration for the oxidizing agent based on the desired volume ratio between acidic permeate 32' or acidic feed water 2', and oxidizing agent, and how the acidic permeate 32' or the acidic feed water 2' and the acidifying agent are to be mixed. Iodide in the acidic permeate 32' or in the acidic feed water 2' will oxidize to elementary iodine in and after step 2B.

Step 2C

An amylose-containing fluid is added to the permeate 32" or to the feed water 2" from step 2B. The amylose-containing fluid may for example be an aqueous starch solution. In an alternative embodiment the starch may be added to the permeate 32" or the feed water 2" from step 2B in dry condition and suspended in the permeate 32" or the feed water 2". Known starches have different ratios between amylopectin and amylose. Amylose may make up from 20% to 30% of the total amount of starch. By breeding or genetic modification of plants, this ratio may be changed such that the amylose-portion of the starch increases beyond 30% in the plant's starch-containing organ or organs.

The amylose-containing fluid is dosed to the permeate 32" or the feed water 2" by means of a per se known dosing device 4 which may comprise a third holding tank 44 for the amylose-containing fluid and a third metering pump 45. It is skillful to choose a proper concentration for the amylose-containing fluid based on the desired volume ratio between permeate 32" or feed water 2", and amylose-containing fluid, and how the permeate 32" or the feed water 2" from step 2B and the amylose-containing fluid are to be mixed.

In order to avoid a gelling reaction starting in the amylose-containing fluid, the temperature of the fluid may be held lower than 55 °C in the third holding tank 44. If necessary the temperature in the permeate 32" or the feed water 2" is reduced to less than 55 °C before the permeate 32" or the feed water 2" is mixed with the amylose- containing fluid or alternatively with the dry starch. This may be done in a per se known way in for example a countercurrent plate heat exchanger (not shown) and is not discussed any further herein. The temperature in the feed water 2 may be adjusted prior to the membrane filter 3 of step 1, just after the membrane filter 3 in step 1, just after step 2A or just after step 2B.

The mixture of permeate 32" or feed water 2" and the amylose-containing fluid is mixed further in a proper, first mixing apparatus 50. Particularly a mixing apparatus 50 of the flow-through type is suitable for this purpose, for example a static mixer of per se known type.

Step 2D

The mixture 36 of permeate 32" or feed water 2" and the amylose-containing fluid from step 2C is led to a reaction tank 60 in order for iodine in the mixture 36 to have time to form complex with the amylose. The iodine-amylose-complex is coloured bluish-black to black. The detention time of the mixture 36 in the reaction tank 60 is decided based on the amount of iodine in the feed water 2 and the concentration of amylose in the amylose-containing fluid, among other things.

The reaction tank 60 may be arranged to batch-fill and batch-tap. In an alternative embodiment the reaction tank 60 may be arranged for continuously filling and tapping .

Step 3

From the reaction tank 60 from step 2D the mixture 36 with the iodine-amylose- complex is brought to a first separation device 70 arranged to be able to separate the iodine-amylose-complex from the essential of the fluid . Such a first separation device 70 may comprise a filter. The filter 70 may comprise a ceramic membrane filter. The ceramic membrane filter 70 may comprise a ceramic ultra-membrane filter. The filter 70 may comprise a polymer membrane filter, or it may comprise a combination of two or more filters 70. The filter 70 may be a membrane filter with a pore size from and including 0.01 pm to and including 2 pm. The filter 70 may be arranged for continuous operation.

Out from the first separation device 70 two material flows will stream : a concentrated iodine-amylose-complex fraction 80 and a separated fluid 82 comprising any excess iodine and other dissolved matters as for example salts and saccharides. The separated fluid 82 may be led to outlet and will not be discussed any further herein. It is essential to the invention that the separation device 70 is chosen in such a way or is operated in such a way that the material flow containing the iodine-amylose fraction 80, constitute a slurry or at least shows a pumpable consistency. The separation device 70 may be operated such that the concentration between iodide in the feed water 2 and iodine in the iodine-amylose-complex fraction 80 is at least 1 : 150. The separation device 70 may be operated such that the concentration between iodide in the feed water 2 and iodine in the iodine-amylose-complex fraction 80 is at least 1 : 250. The separation device 70 may be fu rther operated such that the concentration between iodide in the feed water 2 and iodine in the iodine-amylose-complex fraction 80 is at least 1 : 500. The separation device 70 may be operated such that the concentration between iodide in the feed water 2 and iodine in the iodine-amylose- complex fraction 80 is at least 1 : 750. The separation device 70 may be operated such that the concentration between iodide in the feed water 2 and iodine in the iodine- amylose-complex fraction 80 is at least 1 : 1000.

Step 4

The iodine-amylose-complex fraction 80 from step 3 is possibly added water to a proper consistency in a per se known way (not shown), for example such that the ratio between the iodine-amylose-complex fraction 80 and added water is 1 : 1.

Thereafter a reducing agent is dosed to the aqueous iodine-amylose-complex fraction 80 by means of per se known dosing device 4 which may comprise a fourth holding tank 46 for the reducing agent and a fourth metering pump 47. It is skillful to choose a proper concentration for the reducing agent based on the desired volume ratio between aqueous iodine-amylose-complex 80 and reducing agent, and how iodine- amylose-complex 80 and the reducing agent are to be mixed . The reducing agent may for example be a reducing sulphur compound, a tocopherol or a reducing acid. The reducing sulphur compound may for example comprise thiosulphate (S₂0₂ ^2-). The reducing sulphur compound may comprise a sulfite, where the sulfite may comprise for example bisulfite (HS0₃ ^") such as for example sodium bisulfite (NaHS0₃) or metasulfite (S₂0₅ ~), such as for example sodium metasulfite (Na₂S₂0₅), also known as sodium pyrosuifite. The reducing acid may for example be ascorbic acid (C₆H₈0₆) or oxalic acid (H₂C₂0₄).

Iodine quickly reduces to iodide and separates from the amylose on adding of the reducing agent. For further ensuring separation from amylose the mixture 80' of iodine-amylose-complex fraction 80 and the reducing agent may be led through a second mixing apparatus 52 as for example a static mixer of per se known type.

Step 5

The mixture 80' of amylose and separated iodide from step 4 is brought to a second separation device 72 arranged to be able to separate amylose from the iodic fluid. Such a second separation device 72 may comprise a filter. The filter 72 may comprise a ceramic membrane filter. The ceramic membrane filter may comprise a polymer membrane filter, or it may comprise a combination of two or more filters 72. The filter 72 may be a membrane filter with a pore size from and including 0.01 pm to and including. 2 pm. The filter 72 may be arranged for continuous operation.

Two material flows will stream out from the second separation device 72: an aqueous amylose-containing fluid 90 and an iodidic, aqueous fluid 92. The amylose-containing fluid 90 may be led back to the third holding tank 44 for amylose-containing fluid. It is essential to the invention that the separation device 72 is chosen or operated such that the material flow containing the amylose-containing fluid 90, constitutes a slurry or at least shows a pumpable consistency.

The second aqueous, iodidic solution 92 may in addition to iodide also contain residues of the reducing agent. The second aqueous, iodidic solution 92 is a concentrate of iodide and contains substantially more iodide than the feed water 2 per unit of space. The second aqueous, iodide concentrate 92 may be further treated on-site with per se known techniques, as for example the "blow out" method, to produce elementary iodine, or the second aqueous, iodide concentrate 92 may be transported to another location for further processing.

Claims

P a t e n t c l a i m s

1. Method for concentration of iodide from a first aqueous, iodidic solution (2) and to a second aqueous, iodidic solution (92), the method comprising the steps:

a) to acidify the first solution (2; 32) with a mineral acid;

b) to add an oxidizing agent to an acidic solution (2'; 32') from step a) in order to oxidize iodide to elementary iodine;

c) to add an amylose-containing material to the solution (2"; 32") from step b) such that a iodine-amyiose-complex is formed;

d) to substantially separate the iodine-amyiose-complex formed in step c) from the fluid (36);

e) to add a reducing agent to an iodine-amyiose-complex fraction (80) containing the iodine-amyiose-complex from step d) in order to reduce elementary iodine to iodide in order to separate iodide from amylose; and f) to separate a mixture (80') from step e) in a second aqueous, iodidic solution (92) and an amylose-containing fraction (90),

c h a r a c t e r i z e d i n that

step d) comprises using a continuously operable separation device (70) comprising a filter.

2. Method for concentration of iodide in accordance with claim 1,

c h a r a c t e r i z e d i n that step f) comprises using a continuously operable separation device (72) comprising a filter.

3. Method for concentration of iodide in accordance with claim 1,

c h a r a c t e r i z e d i n that step b) comprises adding an oxidizing agent chosen from a group comprising chlorine (Cl₂) and a hypochlorite-compound (OCI^").

4. Method for concentration of iodide in accordance with claim 1,

c h a r a c t e r i z e d i n that step b) comprises adding hydrogen peroxide (H₂0₂) as an oxidizing agent.

5. Method for concentration of iodide in accordance with claim 1,

c h a r a c t e r i z e d i n that step e) comprises adding a reducing agent chosen from a group comprising reducing sulphur- compounds, tocopherols and reducing acids.

6. Method for concentration of iodide in accordance with claim 1,

c h a r a c t e r i z e d i n that the method further comprises filtering the first iodidic solution (2) previous to step a) in order to remove impurities from the first iodidic solution (2).

7. Method for concentration of iodide in accordance with claim 6,

c h a r a c t e r i z e d i n that the solution (2) is filtered through a continuously operable filter (3) chosen from a group comprising continuously operable ceramic membrane filters, continuously operable ceramic ultra-membrane filters and continuously operable polymer membrane filters.

8. Method for concentration of iodide in accordance with claim 7,

c h a r a c t e r i z e d i n that the filter (3) has a pore size from and including 0.01 μιτι to and including 2 μιτι.

9. Method for concentration of iodide in accordance with claim 1,

c h a r a c t e r i z e d i n that the filter (70) is chosen from a group comprising continuously operable ceramic membrane filters, continuously operable ceramic ultra-membrane filters and continuously operable polymer membrane filters.

10. Method for concentration of iodide in accordance with claim 9,

c h a r a c t e r i z e d i n that the filter (70) has a pore size from and including 0.01 μητι to and including 2 pm.

11. Method for concentration of iodide in accordance with claim 2,

c h a r a c t e r i z e d i n that the filter (72) is chosen from a group comprising continuously operable ceramic membrane filters, continuously operable ceramic ultra-membrane filters and continuously operable polymer membrane filters.

12. Method for concentration of iodide in accordance with claim 11,

c h a r a c t e r i z e d i n that the filter (72) has a pore size from and including 0.01 pm to and including 2 pm.

13. Method for concentration of iodide in accordance with claim 1,

c h a r a c t e r i z e d i n that step d) comprises using a separation device (70) that is operated such that the concentration between iodide in the first aqueous, iodidic solution (2) and iodine in the iodine- amylose-complex fraction (80) is at least 1:150.

14. Method for concentration of iodide in accordance with claim 13,

c h a r a c t e r i z e d i n that step d) comprises using a separation device (70) that is operated such that the concentration between iodide in the first aqueous, iodidic solution (2) and iodine in the iodine- amylose-complex fraction (80) is at least 1:250.

15. Method for concentration of iodide in accordance with claim 14,

c h a r a c t e r i z e d i n that step d) comprises using a separation device (70) that is operated such that the concentration between iodide in the first aqueous, iodidic solution (2) and iodine in the iodine- amylose-complex fraction (80) is at least 1:500.

16. Method for concentration of iodide in accordance with claim 15,

c h a r a c t e r i z e d i n that step d) comprises using a separation device (70) that is operated such that the concentration between iodide in the first aqueous, iodidic solution (2) and iodine in the iodine- amylose-complex fraction (80) is at least 1:750.

17. Method for concentration of iodide in accordance with claim 16,

c h a r a c t e r i z e d i n that step d) comprises using a separation device (70) that is operated such that the concentration between iodide in the first aqueous, iodidic solution (2) and iodine in the iodine- amylose-complex fraction (80) is at least 1:1000.