Liquid purification or separation – Processes – Ion exchange or selective sorption
Reexamination Certificate
2001-04-19
2003-04-22
Cintins, Ivars (Department: 1724)
Liquid purification or separation
Processes
Ion exchange or selective sorption
C210S679000, C210S687000, C210S688000, C502S401000, C502S402000, C502S407000, C502S415000
Reexamination Certificate
active
06551515
ABSTRACT:
BACKGROUND OF THE INVENTION
Effective methods for the recovery and/or separation of particular divalent metal ions, such as (a) Ca
2+
from source solutions containing Mg
2+
and/or other ions and (b) Cd
2+
from source solutions containing Zn
2+
and/or other ions, are of great importance in modern technology. It is particularly difficult to remove these particular metal ions in the presence of moderate to strong acids and soluble complexing or chelating agents, such as the halide ions, which have a high affinity for the desired metal ions. It is also difficult to remove the aforementioned divalent metal ions when they are present at low concentrations in solutions containing other metal ions at much greater concentrations. Hence, there is a real need for a process to selectively concentrate certain divalent metal ions when present at low concentrations and particularly when in the presence of acid solutions and other complexing agents.
Some methods for the recovery of divalent metal cations from solution are known in the art. However, the removal and/or separation of specific divalent metal cations is often complicated by a myriad of conditions including the presence of other divalent cations, the presence of other cations in very high concentrations and the presence of other chelating agents. It is also known that ligands present as solutes in a solvent have the ability to selectively form strong bonds with particular ions or groups of ions present as solutes in the same solvent according to size, donor atom-related properties and other known selectivity characteristics.
Ethyleneglycol-bis-(&bgr;-aminoethyl ether)-N,N,N,N′-tetraacetic acid and (ethylenediamine)tetraacetic acid, commonly referred to as EGTA and EDTA respectively, are both ligands that may be used as solutes to complex divalent ions. However, EGTA has a greater selective preference for larger divalent metal ions than EDTA. See
Critical Stability Constants, Volume
1
: Amino Acids
, A. E. Martell & R. M. Smith, Plenum Press, N.Y. & London, 1974. Therefore, EGTA is an important ligand for use in complexing larger divalent metal ions.
This being the case, researchers have not previously been able to incorporate EGTA into phase separation systems. This is significant because EGTA present in solution as a solute simply acts to complex selected ions, but does not provide a means for their separation. Specifically, never before has EGTA been successfully covalently bonded to inorganic and/or organic solid supports. As such, EGTA bonded to solid supports have not been used in phase separation processes for removing, separating and concentrating larger ionic radii or desired divalent ions from solutions, particularly where such desired ions are present in solutions with smaller and/or similar ions present at a much higher concentration.
As such, it would be useful to provide a composition and method for removing, separating, and/or concentrating certain desired divalent metal ions in solution from other ions, such as (a) Ca
2+
from Mg
2+
and/or (b) Cd
2+
from Zn
2+
, even when the desired ion is present at a low concentration.
SUMMARY OF THE INVENTION
The present invention is drawn to novel porous and/or non-porous particulate organic and/or inorganic solid supports containing EGTA ligands covalently bonded to the solid support through a spacer. When the particulate solid support is an organic resin or polymer, the EGTA ligand may be bonded directly to an activated polar group on the polymer. The invention is also drawn to methods for removing, separating, and/or concentrating certain desired divalent metal ions including (a) Ca
2+
from source solutions containing Mg
2+
and/or other ions and (b) Cd
2+
from source solutions containing Zn
2+
and/or other ions. In fact, the removal of these ions (Cd
2+
and/or Ca
2
)may occur when they are present at from very low to very high concentrations, i.e., from ppb to g/l levels of Cd
2+
and/or Ca
2+
.
The concentration of the desired ions is accomplished by forming a complex of the desired ions with an EGTA ligand bound solid support material by flowing a source solution containing the desired ions through a column or other separation device packed with EGTA ligand bound solid support material. This process enables the desired ions to complex with the EGTA ligand attached to the solid.support material. The metal ion and the EGTA ligand are then decoupled by flowing a receiving liquid through the column or other separation device (in much smaller volume than the volume of source solution passed through the column) to remove and concentrate the desired ions in the receiving liquid solution. The receiving liquid or recovery solution forms a stronger complex with the desired ions than does the EGTA, or alternatively, temporarily forms a stronger interaction with the EGTA ligand than do the desired metal ions, and thus, the desired metal ions are quantitatively stripped from the ligand in a concentrated form in the receiving solution. The recovery of desired ions from the receiving liquid may be accomplished by various methods commonly known in the art.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a composition and method for the removal and/or separation of particular divalent metal ions including Ca
2+
and Cd
2+
present in low concentrations from a solution utilizing an EGTA ligand attached to a solid support. The present invention is particularly adaptable to the removal of (a) Cd
2+
from source solutions containing Zn
2+
and/or other ions and (b) Ca
2+
from source solutions containing Mg
2+
and/or other ions. Further, the invention may be carried out in moderately acidic solutions, e.g., solutions with a pH greater than about 3.0. Furthermore, the desired selectivity and interaction strength is unexpectedly high despite the fact that one of the four carboxylic acid groups of the ligand is used to attach the ligand to the solid support.
The present invention requires that the EGTA ligand be covalently bonded to an organic polymeric or inorganic particulate solid support that can be porous or nonporous. If an inorganic solid support is used, a hydrophilic spacer is linked to a silicon, carbon, nitrogen, oxygen or sulfur atom and is further covalently bonded to the solid support. If an organic polymer or resin solid support is used, the ligand can contain a functional group reactive with a constituent of the polymer (such as an activated polar group). In either case, the structure may be represented by Formula 1, as follows:
SS—A—X—L Formula 1
where SS is a porous or non-porous particulate solid support, A is a covalent linkage mechanism, X is a hydrophilic spacer grouping and L is an EGTA ligand. If an organic resin or polymer is used for the solid support, the covalent linkage A and spacer X will then be integrated, and may actually be a single linkage, formed by the covalent bond formed by the reaction between the activated polar group from the polymer and the functional group from the ligand.
The SS—A—X— portion of Formula 1 is well known for use with ion binding ligands. Preferably, the solid support “SS” is an inorganic and/or organic particulate support material selected from the group consisting of sand, silicas, silicates, silica gel, glass, glass beads, glass fibers, alumina, zirconia, titania, nickel oxide, polyacrylate, polystyrene, polyphenol, combinations thereof, as well as any others described in U.S. Pat. Nos. 4,943,375, 4,952,321, 4,959,153, 4,960,882, 5,039,419, 5,071,819, 5,078,978, 5,084,430, 5,173,470, 5,179,213, 5,182,251, 5,190,661, 5,244,856, 5,273,660 and 5,393,892, which are herein incorporated by reference. However, other organic resins or any other hydrophilic organic and/or inorganic support materials meeting the above criteria can also be used.
The use of one or more ion binding ligands attached to an SS—A—X— solid support by a covalent linkage spacer group is illustrated in U.S. Pat. N
Bruening Ronald L.
Krakowiak Krzysztof E.
Cintins Ivars
IBC Advanced Technologies, Inc.
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