Liquid purification or separation – Processes – Liquid/liquid solvent or colloidal extraction or diffusing...
Reexamination Certificate
2002-10-03
2004-04-13
Fortuna, Ana (Department: 1723)
Liquid purification or separation
Processes
Liquid/liquid solvent or colloidal extraction or diffusing...
C210S651000, C210S653000, C210S490000, C210S656000, C210S502100
Reexamination Certificate
active
06719905
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 & P. 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 a membrane support. As such, EGTA bonded membranes 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 a novel composition comprising an EGTA ligand covalently bonded to a membrane. 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 (Ca
3+
and/or Cd
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 membrane. The separation is effected in a separation device, such as a membrane cartridge, through which the source solution is flowed. This process enables the desired ions to complex with the EGTA ligand attached to the membrane. The metal ion and the EGTA ligand are then decoupled by flowing a receiving liquid through the 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/or Cd
2+
present in low concentrations from a solution utilizing an EGTA ligand attached to a membrane. The present invention is particularly adaptable to the removal of (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. The invention may also 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 membrane support.
The present invention requires that the ligand be covalently bonded to a membrane which acts as a support to the EGTA ligand. Specifically, the composition of the present invention comprises an EGTA ligand that is covalently bonded to a membrane as represented Ad Formula 1, as follows:
M—B—L Formula 1
where M is any membrane or composite membrane derivatized to have a hydrophilic surface and which contains polar functional groups, L is an EGTA ligand and B is the covalent linkage joining the ligand (L) to the membrane (M) surface. Typically, the EGTA ligand (L) is joined to the membrane surface by the reaction of ligand precursor XL where X is a functional group which reacts with an activated polar group on the membrane surface, thereby forming covalent linkage B. Representative of B linkages are members selected from the group consisting of amide (—NHC(O)—, ester (—C(O)C—), thioester (—C(O)S—), carbonyl (—C(O)—), ether (—O—), thioether (—S—), sulfonate (—S(O)
2
O—) and sulfonamide (—SO
2
NH—), though amide bonds are often preferred.
More specifically, the membrane (M) may be inherently hydrophilic, partially hydrophilic or a composite comprising a porous polymer membrane substrate having an insoluble cross-linked hydrophilic coating deposited thereon. Membranes that are inherently hydrophilic or partially hydrophilic and contain moieties appropriate for forming covalent bonds with the ligand (L) have particular utility. Such membranes include polyamides such as nylon, and cellulosic materials such as cellulose, regenerated cellulose, cellulose acetate and nitrocellulose. If the membrane used does not contain reactive groups, it may be modified or derivatized appropriately.
Composite membranes are also preferred. A composite membrane comprises a porous polymer or copolymer membrane core and an insoluble coating deposited thereon. The substrate and the coating may be joined by crosslinking, grafting or by other known procedures. Representative suitable polymers forming the membrane core substrate include fluorinated polymers including poly (tetrafluoroethylene) (“TEFLON”), polyvinylidene fluoride (PVDF), and the like; polyolefins such as polyethylene, ultra-high molecular weight polyethylene (UPE), polypropylene, polymethylpentene, and the like; polystyrene or substituted polystyrenes; polysulfones such as polysu
Bruening Ronald L.
DiLeo Anthony J.
Jiang Tongbo
Krakowiak Krzysztof E.
Fortuna Ana
IBC Advanced Technologies, Inc.
Thorpe North & Western LLP
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