Displacement chromatographic method for separating uranium isotopes

Claim 3

In the method of separating 235U isotope from 238U isotope by opportunity for exchange between uranium on solid ion exchange sites and uranium in an adjacent aqueous solution during oxidation-reduction equilibria involving tetravalent and hexavalent uranium, and wherein the various ion exchange sites and solutions involve at least five species of cations consisting of a reductant metal cation, the oxidized form of the reductant metal cation, tetravalent uranium cation, hexavalent uranium cation, an oxidant metal cation, the reduced form of the oxidant metal cation, and a cheap cation for elutriating the oxidant metal from the cation exchange sites, the improvement which consists of: providing a fixed bed comprising solid particles of ion exhange material, the liquid treatment solutions being fed at an initial portion and the solutions being withdrawn at a terminal portion, said bed having a great length relative to its average cross sectional dimension, and feeding a solution containing the cheap cation to elutriate other cations so that throughout the entire length of said bed, the cation exchange sites are occupied predominantly by such cheap cations and to provide a cheap cation region extending the entire length of the bed; treating said bed with a batch of a solution of a reducing metal cation to provide a reducing metal region extending the entire length of the bed, the cation sites after such treatment being occupied predominantly by the reducing metal cations said reducing metal cations being capable of reducing dissolved hexavalent uranium to sorbed tetravalent uranium; treating said bed having the reducing metal region throughout its full length with a controlled batch of a solution of hexavalent uranium susceptible of enrichment to provide at the initial portion of the bed a uranium zone, the remaining reducing metal region havinG a length which is several times the length of the uranium region, and the total bed length being several times the length of the uranium region to provide a bed length/uranium region length ratio which is significantly greater than one, and withdrawing a solution containing the oxidized form of the reducing metal; treating said bed with a first controlled-size batch of a solution of an oxidizing metal cation to form an oxidizing metal region which grows from the initial portion and has a front boundary at the rear boundary of the uranium region, whereby the reducing metal region is shortened to extinction as the oxidized form of the reducing metal ion is elutriated from the bed, and as the uranium region moves along the bed by chromatographic displacement from the initial position with its rear boundary at the initial portion of the bed to its elutriation position with its front boundary at the terminal portion of the bed, such displacement occurring without significantly modifying the bed length/uranium region length ratio; treating said bed with a second controlled-size batch of a solution of an oxidizing metal cation for elutriating uranium from the bed during an initial elutriation period to recover a solution of hexavalent uranium containing an enriched concentration of 235U; treating said bed with a third controlled-size batch of a solution of an oxidizing metal cation for elutriating uranium from the bed during the principal elutriation period to recover a batch of solution of hexavalent uranium containing an isotope distribution resembling that of the feed, whereby the rear boundary of the uranium region is moved to adjacent the terminal portion of the bed, said principal batch of solution of recovered hexavalent uranium being many times larger than the recovered batch of enriched uranium; treating said bed with a fourth controlled-size batch of a solution of an oxidizing metal cation for elutriating uranium from the bed during the final elutriation period to recover a solution of hexavalent uranium having an isotopic distribution different from that occurring during the middle of the uranium elutriation, whereby throughout the entire length of the bed, the cation exchange sites are predominantly occupied by oxidizing metal cations; and elutriating the oxidizing metal from the bed by repeating the treatment with a solution of a cheap cation so that throughout the entire length of the fixed bed the cation exchange sites are predominantly occupied by such cheap cations and to provide a cheap cation region suitable for repetition of the steps of the process.

Claim 4

In the method of separating 235U isotope from 238U isotope by opportunity for exchange between uranium on solid ion exchange sites and uranium in an adjacent aqueous solution during oxidation-reduction equilibria involving tetravalent and hexavalent uranium, and wherein the various ion exchange sites and solutions involve at least five species of cations consisting of a reductant metal cation, the oxidized form of the reductant metal cation, tetravalent uranium cation, hexavalent uranium cation, an oxidant metal cation, the reduced form of the oxidant metal cation, and a cheap cation for elutriating the oxidant metal from the cation exchange sites, the improvement which consists of: providing a fixed bed comprising solid particles of ion exhange material, the liquid treatment solutions being fed at an initial portion and the solutions being withdrawn at a terminal portion, said bed having a great length relative to its average cross sectional dimension, and feeding a solution containing the cheap cation to elutriate other cations so that throughout the entire length of said bed, the cation exchange sites are occupied predominantly by such cheap cations and to provide a cheap cation region extending the entire length of the bed; treating said bed with a batch of a solution of a reducing metal cation to provide a reducing metal region extending the entire length of the bed, the cation sites after such treatment being occupied predominantly by the reducing metal cations said reducing metal cations being capable of reducing dissolved hexavalent uranium to sorbed tetravalent uranium; treating said bed having the reducing metal region throughout its full length with a controlled batch of a solution of hexavalent uranium susceptible of enrichment to provide at the initial portion of the bed a uranium zone, the remaining reducing metal region havinG a length which is several times the length of the uranium region, and the total bed length being several times the length of the uranium region to provide a bed length/uranium region length ratio which is significantly greater than one, and withdrawing a solution containing the oxidized form of the reducing metal; treating said bed with a first controlled-size batch of a solution of an oxidizing metal cation to form an oxidizing metal region which grows from the initial portion and has a front boundary at the rear boundary of the uranium region, whereby the reducing metal region is shortened to extinction as the oxidized form of the reducing metal ion is elutriated from the bed, and as the uranium region moves along the bed by chromatographic displacement from the initial position with its rear boundary at the initial portion of the bed to its elutriation position with its front boundary at the terminal portion of the bed, such displacement occurring without significantly modifying the bed length/uranium region length ratio; treating said bed with a second controlled-size batch of a solution of an oxidizing metal cation for elutriating uranium from the bed during an initial elutriation period to recover a solution of hexavalent uranium containing an enriched concentration of 235U; treating said bed with a third controlled-size batch of a solution of an oxidizing metal cation for elutriating uranium from the bed during the principal elutriation period to recover a batch of solution of hexavalent uranium containing an isotope distribution resembling that of the feed, whereby the rear boundary of the uranium region is moved to adjacent the terminal portion of the bed, said principal batch of solution of recovered hexavalent uranium being many times larger than the recovered batch of enriched uranium; treating said bed with a fourth controlled-size batch of a solution of an oxidizing metal cation for elutriating uranium from the bed during the final elutriation period to recover a solution of hexavalent uranium having an isotopic distribution different from that occurring during the middle of the uranium elutriation, whereby throughout the entire length of the bed, the cation exchange sites are predominantly occupied by oxidizing metal cations; and elutriating the oxidizing metal from the bed by repeating the treatment with a solution of a cheap cation so that throughout the entire length of the fixed bed the cation exchange sites are predominantly occupied by such cheap cations and to provide a cheap cation region suitable for repetition of the steps of the process.

Claim 5

A chromatographic displacement method for separating a fraction enriched in 235U isotope from a feed material containing both 235U and 238U isotopes comprising at some time conducting each of the following steps: loading a controlled size batch of tetravalent uranium feed material to establish a uranium region having a front boundary and a rear boundary on a prescribed initial segment of a fixed bed cation-exchange system having a prescribed overall length which is several times longer than the length of the uranium region, said system having an initial portion to which solutions are fed and a terminal portion from which effluent solutions are withdrawn; loading the rest of said system length fully with a prescribed reducing cation to provide a reducing cation region in front of the uranium region and extending substantially to the terminal portion of the system, said prescribed reducing cation being a metal cation capable of reducing dissolved hexavalent uranium to sorbed tetravalent uranium; percolating a first controlled size batch of a solution containing a prescribed oxidizing agent through the column length containing said combination of a reducing region in front of a uranium region, thereby moving the uranium region along the cation exchange system while shortening the reducing cation region until the front boundary of the urAnium region is at the terminal portion of the cation exchange sytem, the reducing cation region having been shortened to extinction by the percolation of said first controlled size batch of solution of oxidizing agent; and recovering a solution containing hexavalent uranium enriched in 235U isotope from the effluent during the percolation of a second controlled size batch of solution containing said prescribed oxidizing agent through the column length, containing said combination of an uranium region in front of an oxidizing region, the enrichment factor for the fractional concentration of 235U isotope being greater than during the percolation of a third controlled size batch of solution containing said oxidizing agent for withdrawing an effluent containing the principle portion of the uranium, said third controlled size batch being significantly larger than said second controlled size batch of solution of oxidizing agent.

Claim 6

A chromatographic displacement method for separating a fraction enriched in 235U isotope from a feed material containing both 235U and 238U isotopes comprising at some time conducting each of the following steps: loading a controlled size batch of tetravalent uranium feed material to establish a uranium region having a front boundary and a rear boundary on a prescribed initial segment of a fixed bed cation-exchange system having a prescribed overall length which is several times longer than the length of the uranium region, said system having an initial portion to which solutions are fed and a terminal portion from which effluent solutions are withdrawn; loading the rest of said system length fully with a prescribed reducing cation to provide a reducing cation region in front of the uranium region and extending substantially to the terminal portion of the system, said prescribed reducing cation being a metal cation capable of reducing dissolved hexavalent uranium to sorbed tetravalent uranium; percolating a first controlled size batch of a solution containing a prescribed oxidizing agent through the column length containing said combination of a reducing region in front of a uranium region, thereby moving the uranium region along the cation exchange system while shortening the reducing cation region until the front boundary of the urAnium region is at the terminal portion of the cation exchange sytem, the reducing cation region having been shortened to extinction by the percolation of said first controlled size batch of solution of oxidizing agent; and recovering a solution containing hexavalent uranium enriched in 235U isotope from the effluent during the percolation of a second controlled size batch of solution containing said prescribed oxidizing agent through the column length, containing said combination of an uranium region in front of an oxidizing region, the enrichment factor for the fractional concentration of 235U isotope being greater than during the percolation of a third controlled size batch of solution containing said oxidizing agent for withdrawing an effluent containing the principle portion of the uranium, said third controlled size batch being significantly larger than said second controlled size batch of solution of oxidizing agent.

Claim 7

A chromotographic displacement method for separating a fraction enriched in 235U isotope from a feed material containing both 235U and 238U isotopes comprising: first, feeding a solution containing trivalent titanium to a column system containing cation-exchange material to provide a titanium region extending substantially the full length of the column, said column having an initial portion to which solutions are fed and a terminal portion from which effluent solutions are withdrawn; second, feeding a controlled size batch of a solution containing hexavalent uranium to provide a uranium region near the initial portion of the column and recovering an effluent solution containing tetravalent titanium from the terminal portion of the column, the length of the resulting titanium region being several times the length of the resulting uranium region; third, feeding a first controlled-size batch of solution containing trivalent iron to form an iron region behind the uranium region and to move the uranium region along the length of the column while shortening the titanium region until the boundary between the uranium region and the titanium region is at the terminal portion of the column and thereafter feeding a second controlled-size batch of solution containing trivalent iron during an initial portion of the uranium elutriation for recovering a relatively small batch of solution containing hexavalent uranium enriched in 235U isotope; fourth, feeding a third controlled-size batch of solution containing trivalent iron for recovering a solution containing hexavalent uranium during the elutriation of the principal portion of the uranium region, such third batch being much larger than the second batch of solution containing trivalent iron; and provided, however, that the feeding of said first controlled batch of solution containing trivalent iron is initiated before the trivalent titanium, sorbed on the resin, is completely replaced by uranium by reason of control of the size of the batch of the solution of uranium to load uranium onto a shorter length of the column than the length of column loaded with titanium.

Claim 8

A chromotographic displacement method for separating a fraction enriched in 235U isotope from a feed material containing both 235U and 238U isotopes comprising: first, feeding a solution containing trivalent titanium to a column system containing cation-exchange material to provide a titanium region extending substantially the full length of the column, said column having an initial portion to which solutions are fed and a terminal portion from which effluent solutions are withdrawn; second, feeding a controlled size batch of a solution containing hexavalent uranium to provide a uranium region near the initial portion of the column and recovering an effluent solution containing tetravalent titanium from the terminal portion of the column, the length of the resulting titanium region being several times the length of the resulting uranium region; third, feeding a first controlled-size batch of solution containing trivalent iron to form an iron region behind the uranium region and to move the uranium region along the length of the column while shortening the titanium region until the boundary between the uranium region and the titanium region is at the terminal portion of the column and thereafter feeding a second controlled-size batch of solution containing trivalent iron during an initial portion of the uranium elutriation for recovering a relatively small batch of solution containing hexavalent uranium enriched in 235U isotope; fourth, feeding a third controlled-size batch of solution containing trivalent iron for recovering a solution containing hexavalent uranium during the elutriation of the principal portion of the uranium region, such third batch being much larger than the second batch of solution containing trivalent iron; and provided, however, that the feeding of said first controlled batch of solution containing trivalent iron is initiated before the trivalent titanium, sorbed on the resin, is completely replaced by uranium by reason of control of the size of the batch of the solution of uranium to load uranium onto a shorter length of the column than the length of column loaded with titanium.

Claim 9

In a method of preparing compositions having isotopic distributions of 235U isotope and 238U isotope different from the isotopic distributions of uranium feedstock compositions by providing for exchange between tetravalent uranium sorbed on ion exchange sites in a uranium region of a bed of ion exchange solids and a flowing adjacent aqueous solution of hexavalent uranium, said methos including a step of treating the uranium region of the bed with an aqueous solution of a salt of an oxidizing metal cation, whereby the sorbed tetravalent uranium is oxidized to form a solution comprising both the lower valent form of the oxidizing metal cation and hexavalent uranium, such treatment forming an oxidizing metal sorbed to provide an oxidizing metal region in which the ion exchange sites are occupied predominantly by sorbed oxidizing metal cations, said region having a front boundary at the rear boundary of the advancing uranium region, the improvement of reductive chromatographic displacement which consists of: providing a porous bed of ion exchange solid material, which bed remains in a predominantly fixed position relative to solution flow, the liquid treatment solutions being supplied at at least one feed zone and the solutions being withdrawn at at least one effluent zone, there being a large ratio of the length of the bed to the cross section dimension of the bed, thereby promoting substantially plug flow of aqueous solutions, the cross sectional characteristics of such flow not being adversely affected as the solutions advance along the length of the bed, there being at least sometimes a plurality of displaceable regions along the length of the bed, some of the chemical reactions occurring at the boundaries between adjacent regions of the bed, the front boundary of an advancing region being distinguished from the rear boundary and from the principal portion of an advancing region: feeding a solution of a metal cation to provide a region of the bed in which the ion exchange sites are occupied predominantly by sorbed reducing metal cations capable of reducing dissolved hexavalent uranium to sorbed tetravalent uranium, such reducing metal region extending ahead of the uranium region so that the rear boundary of the reducing metal region is at the front boundary of the uranium region, said feeding being stoichiometrically equivalent to the hereinafter designated feeding of the oxidizing metal cation and being many times the stoichiometric equivalent of the tetravalent uranium sorbed on the ion exchange sites in the uranium region; feeding a solution of an oxidizing metal cation to provide an oxidizing metal region having a front boundary at the rear boundary of the uranium region, such feeding being a driving force for advancing the combination of the front boundary of the oxidizing metal region, the uranium region, and the rear boundary of the reducing metal region along the length of the bed by reductive chromatographic displacement, such displacement predominantly occuring without significantly modifying the ratio of bed length to uranium region length, the rate of feeding of the oxidizing metal solution being controlled to promote said plug flow of aqueous solutions through the bed and the feeding of the oxidizing metal being continued for many hours, the feeding of the oxidizing metal ion being many times the stoichiometric equivalent of the tetravalent uranium sorbed in the uranium region, said feeding of the oxidizing metal cation being substantially stoichiometrically equal to the feeding of the reducing metal cation; withdrawing from the bed an aqueous solution containing a quantity of an oxidized form of the reducing metal cation corresponding to the amount of reducing metal cation fed to the bed; withdrawing from the bed an aqueous solution containing a quantity of a reduced form of the oxidizing metal cation, such reduced form being a lower valent form of the oxidizing metal cation corresponding to the amount of oxidizing metal cation fed to the bed; feeding a solution of hexavalent uranium compound susceptible of enrichment to provide a uranium region having a front boundary at the rear boundary of the reducing metal region, said uranium region having a rear boundary at the front boundary of the oxidizing metal region, the combination of the rear boundary of the reducing metal region, the uranium region, and the front boundary of the oxidizing metal region being adapted to advance by reductive chromatographic displacement along the length of the bed, the thus fed hexavalent uranium solution being subjected to reduction to tetravalent uranium absorbed on the ion exchange sites, such uranium reduction occurring at the boundary between the front of the uranium region and the rear of the reducing metal region, and the tetravalent uranium absorbed on the ion exchange sites being subJected to oxidation to hexavalent uranium cation in solution, such uranium oxidation occurring at the boundary between the rear of the uranium region and the front of the oxidizing metal region, such aqueous solution of hexavalent uranium generated within the ion exchange bed flowing from the rear boundary through the body to the front of the uranium region, and after the uranium region has advanced a length many times the cross sectional dimension of the bed; withdrawing from the front and rear boundaries of the uranium region solutions of uranium compounds having an isotopic distribution different from that in the uranium solution fed to the bed.

Claim 10

In a method of preparing compositions having isotopic distributions of 235U isotope and 238U isotope different from the isotopic distributions of uranium feedstock compositions by providing for exchange between tetravalent uranium sorbed on ion exchange sites in a uranium region of a bed of ion exchange solids and a flowing adjacent aqueous solution of hexavalent uranium, said methos including a step of treating the uranium region of the bed with an aqueous solution of a salt of an oxidizing metal cation, whereby the sorbed tetravalent uranium is oxidized to form a solution comprising both the lower valent form of the oxidizing metal cation and hexavalent uranium, such treatment forming an oxidizing metal sorbed to provide an oxidizing metal region in which the ion exchange sites are occupied predominantly by sorbed oxidizing metal cations, said region having a front boundary at the rear boundary of the advancing uranium region, the improvement of reductive chromatographic displacement which consists of: providing a porous bed of ion exchange solid material, which bed remains in a predominantly fixed position relative to solution flow, the liquid treatment solutions being supplied at at least one feed zone and the solutions being withdrawn at at least one effluent zone, there being a large ratio of the length of the bed to the cross section dimension of the bed, thereby promoting substantially plug flow of aqueous solutions, the cross sectional characteristics of such flow not being adversely affected as the solutions advance along the length of the bed, there being at least sometimes a plurality of displaceable regions along the length of the bed, some of the chemical reactions occurring at the boundaries between adjacent regions of the bed, the front boundary of an advancing region being distinguished from the rear boundary and from the principal portion of an advancing region: feeding a solution of a metal cation to provide a region of the bed in which the ion exchange sites are occupied predominantly by sorbed reducing metal cations capable of reducing dissolved hexavalent uranium to sorbed tetravalent uranium, such reducing metal region extending ahead of the uranium region so that the rear boundary of the reducing metal region is at the front boundary of the uranium region, said feeding being stoichiometrically equivalent to the hereinafter designated feeding of the oxidizing metal cation and being many times the stoichiometric equivalent of the tetravalent uranium sorbed on the ion exchange sites in the uranium region; feeding a solution of an oxidizing metal cation to provide an oxidizing metal region having a front boundary at the rear boundary of the uranium region, such feeding being a driving force for advancing the combination of the front boundary of the oxidizing metal region, the uranium region, and the rear boundary of the reducing metal region along the length of the bed by reductive chromatographic displacement, such displacement predominantly occuring without significantly modifying the ratio of bed length to uranium region length, the rate of feeding of the oxidizing metal solution being controlled to promote said plug flow of aqueous solutions through the bed and the feeding of the oxidizing metal being continued for many hours, the feeding of the oxidizing metal ion being many times the stoichiometric equivalent of the tetravalent uranium sorbed in the uranium region, said feeding of the oxidizing metal cation being substantially stoichiometrically equal to the feeding of the reducing metal cation; withdrawing from the bed an aqueous solution containing a quantity of an oxidized form of the reducing metal cation corresponding to the amount of reducing metal cation fed to the bed; withdrawing from the bed an aqueous solution containing a quantity of a reduced form of the oxidizing metal cation, such reduced form being a lower valent form of the oxidizing metal cation corresponding to the amount of oxidizing metal cation fed to the bed; feeding a solution of hexavalent uranium compound susceptible of enrichment to provide a uranium region having a front boundary at the rear boundary of the reducing metal region, said uranium region having a rear boundary at the front boundary of the oxidizing metal region, the combination of the rear boundary of the reducing metal region, the uranium region, and the front boundary of the oxidizing metal region being adapted to advance by reductive chromatographic displacement along the length of the bed, the thus fed hexavalent uranium solution being subjected to reduction to tetravalent uranium absorbed on the ion exchange sites, such uranium reduction occurring at the boundary between the front of the uranium region and the rear of the reducing metal region, and the tetravalent uranium absorbed on the ion exchange sites being subJected to oxidation to hexavalent uranium cation in solution, such uranium oxidation occurring at the boundary between the rear of the uranium region and the front of the oxidizing metal region, such aqueous solution of hexavalent uranium generated within the ion exchange bed flowing from the rear boundary through the body to the front of the uranium region, and after the uranium region has advanced a length many times the cross sectional dimension of the bed; withdrawing from the front and rear boundaries of the uranium region solutions of uranium compounds having an isotopic distribution different from that in the uranium solution fed to the bed.

Claim 11

The method of claim 5 in which the reducing metal ion region ahead of the uranium region is a region in which most of the cation sites are occupied by trivalent titanium cations attributable to the feeding of a titanous salt solution.