Process for high concentration cation exchanges metathesis
Provided is a method for high concentration cation exchange metathesis of divalent ions such as calcium with univalent ions such as sodium or potassium. Due to the difference between ionic valences between the exchanged ions, the provided process behavior is strongly dependent upon the selection of resin properties and to total solution normality. A combination of resin properties and solution normality is provided to achieve the cation exchange.
1. A method of cation exchange comprising:
contacting a divalent cation-feed solution with a strong acid cation ion exchange resin having a crosslinking of between 4 and 15% divinylbenzene (DVB) that has been initially loaded with a univalent charged counter ion, wherein the strong acid cation ion exchange resin has been loaded to greater than 90% of the resin capacity with the univalent charged counter ion, and wherein the univalent-loaded ion exchange resin has an initial ionic equivalent composition, the divalent cation-feed solution has a specified ionic equivalent composition, and the resin has a specified activity such that a separation coefficient K′ defined by the ion exchange reaction of divalent ion with univalent-loaded ion exchange resin is greater than or equal to 1.0;
exchanging the divalent cation with the univalent charged counter ion on the resin to produce a univalent counter ion-product solution and a divalent cation loaded resin, wherein the univalent counter ion-product solution has an ionic equivalent composition that is substantially the same as the initial ionic equivalent composition of the initial univalent-loaded ion exchange resin, and wherein before the last exchanging step, the divalent cation loaded resin is at least 90% divalent-ion form;
advancing the divalent cation loaded resin counter currently with respect to solution flow through a rinse zone wherein unreacted divalent cation-feed solution is recovered;
advancing the divalent cation loaded resin to a regeneration zone where the divalent cation loaded resin is contacted with a solution having a univalent exchangeable cation, wherein the divalent cation loaded resin has an initial ionic equivalent composition, the solution having a univalent exchangeable cation has a specified ionic equivalent composition, and the resin has a specified activity such that the separation coefficient, K′, is less than or equal to 1.0, where K′ is defined by the ion exchange reaction of divalent ion with univalent-loaded ion exchange resin, wherein the resin with capacity Q, in gram-equivalents-per-kg, resin bulk density ρ r , in kg-per-liter, resin mass action equilibrium constant K for the ion exchange equilibrium defined by absorption of the divalent ion on univalent-form ion exchange resin; and the total normality C 0 , in gram-equivalents-per-liter, of all cations in the divalent cation feed solution or the total solution normality of all cations in the univalent cation feed solution are given by:
K
′
=
K
Q
ρ
r
C
0
where
K
′
is
:
(
Eq
.
1
)
K
′
=
(
1
-
C
Ca
C
0
)
2
(
q
Ca
Q
)
(
C
Ca
C
0
)
(
1
-
q
Ca
Q
)
2
(
Eq
.
2
)
wherein C ca , in gram-equivalents-per-liter, is the solution normality of the divalent cation and q Ca , in gram-equivalents-per-kg, is the concentration of divalent species in the resin phase;
exchanging the divalent cation on the divalent cation loaded resin with the univalent exchangeable cation, producing a resin loaded with the univalent cation and a divalent cation product solution, wherein the divalent cation product solution has an ionic equivalent composition that is substantially the same as the initial ionic equivalent composition of the divalent cation loaded resin.
2. The method of claim 1 , wherein the strong acid cation ion exchange resin has been loaded to 100% of the resin capacity with the univalent charged counter ion.
3. The method of claim 1 , wherein the strong acid cation ion exchange resin has been loaded to greater than 98% of the resin capacity with the univalent charged counter ion.
4. The method of claim 1 , wherein the value of K′ in univalent ion loading onto divalent-form resin is greater than 0.85.
5. The method of claim 1 , wherein the value of K′ in univalent ion loading onto divalent-form resin is less than 1.2.
6. The method of claim 1 wherein the resin activity has a value that is within 10 percent of a calculated ideal value.
7. The method of claim 1 , wherein before the last exchanging step, the divalent cation loaded resin is at least 99% divalent-ion form.
8. The method of claim 1 , wherein the resin activity (A r =Qρ r ), is matched with the solution having a univalent exchangeable cation total normality C 0 , to provide the predetermined value of K′ as given in Equation 1.
9. The method of claim 1 , wherein
K′≧1.0 when exchanging divalent ions onto the resin and K′≦1.0 when exchanging univalent ions onto the resin.
10. The method of claim 1 wherein K′ is minimized when exchanging univalent ions onto divalent-loaded resin by maximizing the concentration of the univalent ions in the feed solution.
11. The method of claim 1 , wherein the resin activity (A r =Qρ r ) is provided by:
Q
=
K
′
C
0
K
ρ
r
(
gram
-
equivalents
/
kg
)
,
or
equivalently
,
(
Eq
.
3
)
A
r
=
K
′
C
0
K
(
gram
-
equivalents
/
L
)
(
Eq
.
4
)
where K′ is set to unity and K and ρ r (in kg-per-liter) are known, and C 0 (in gram-equivalents-per-liter) is set by the desired feed conditions.
12. The method of claim 1 , wherein shrinkage of the resin when placed in brine is not greater than 8% as compared after the rinse zone and after the regeneration zone.
13. The method of claim 1 , wherein the divalent cation feed solution is a cyanide solution where the concentration of the cyanide solution is 4-6.5 gram-equivalents per liter solution.
14. The method of claim 1 , wherein the resin is sulfonated polystyrene and has a divinylbenzene crosslinking of between 10 and 14%.
15. The method of claim 1 , wherein the resin is a gel resin.
16. The method of claim 1 , wherein the resin has a divinylbenzene crosslinking of between 8 and 12% and a volume change of 6-8% when immersed in concentrated brine as compared after the rinse zone and after the regeneration zone.
17. The method of claim 1 , wherein the resin has a divinylbenzene crosslinking of 12%±4%.
18. The method of claim 1 , wherein the resin is contained in a fixed volume column and the resin has a divinylbenzene crosslinking greater than 10%.
19. The method of claim 1 , wherein the resin is contained in a variable volume resin vessels that contracts the contained resin volume upon shrinkage of the resin, and expands the contained resin volume upon swelling of the resin.
20. The method of claim 1 , wherein the feed solution is heated to above 25 degrees C. and less than 120 degrees C.
21. The method of claim 1 , wherein the divalent cation in the divalent cation feed solution is calcium.
22. The method of claim 1 , wherein the univalent exchangeable cation in the solution having a univalent exchangeable cation is selected from sodium or potassium.
23. The method of claim 1 , wherein average bead diameter of the resin is less than 1200 microns.
24. The method of claim 1 , wherein average bead diameter of the resin is less than 750 microns.
25. The method of claim 1 wherein the divalent ion solution feed ion exchange with univalent-form resin is considered dilute, where K′>>1.0 and the univalent ion solution feed ion exchange with divalent-form resin is operated where K′ is within 10% of the ideal value as calculated by Equations 3 or 4.
26. The method of claim 1 , wherein the resin activity (A r =Qρ r ) is less than 2.4 gram-equivalents per liter.
27. The method of claim 26 , wherein the resin activity is matched with the divalent cation-feed solution having a total normality C 0 to provide the predetermined value of K′ as given in Equation 1 that is greater than or equal to 1.0.
28. The method of claim 1 , wherein the univalent cation feed solution is saturated or nearly saturated.
29. The method of claim 28 , wherein the solution having a univalent exchangeable cation is saturated sodium chloride.
30. The method of claim 1 , wherein average bead diameter of the resin is less than 650 microns.
31. The method of claim 30 , wherein average bead diameter of the resin is 325+/−25 microns.