Ion Exchange Process
Simply stated, Ion Exchange is the giving and receiving of ions between an ion exchange material and a process liquid. It takes place as the process liquid flows through the ion exchange material. Mobile ions on the ion exchange material are exchanged with ions in the process fluid. In La Habra Welding's Ion Exchange applications the ion exchange material is an activated copolymer matrix comprised of porous beads (resin) and the process fluid is finishing system wastewater.
Typical ion exchangers are ion exchange resins (functionalized porous or gel polymer), zeolites, montmorillonite, clay, and soil humus. Ion exchangers are either cation exchangers that exchange positively charged ions (cations) or anion exchangers that exchange negatively charged ions (anions). There are also amphoteric exchangers that are able to exchange both cations and anions simultaneously. However, the simultaneous exchange of cations and anions can be more efficiently performed in mixed beds that contain a mixture of anion and cation exchange resins, or passing the treated solution through several different ion exchange materials.
Ion exchangers can be unselective or have binding preferences for certain ions or classes of ions, depending on their chemical structure. This can be dependent on the size of the ions, their charge, or their structure. Typical examples of ions that can bind to ion exchangers are:
*H+ (proton) and OH? (hydroxide)；
*Single-charged monatomic ions like Na+, K+, and Cl?
*Double-charged monatomic ions like Ca2+ and Mg2+；
*Polyatomic inorganic ions like SO42? and PO43?；
*Organic bases, usually molecules containing the amino functional group -NR2H+；
*Organic acids, often molecules containing -COO? (carboxylic acid) functional groups;
*Biomolecules that can be ionized: amino acids, peptides, proteins, etc.
Ion exchange in metal separation
Ion-exchange processes are used to separate and purify metals, including separating uranium from plutonium and other actinides, including thorium; and lanthanum, neodymium, ytterbium, samarium, lutetium, from each other and the other lanthanides. There are two series of rare earth metals, the lanthanides and the actinides. Members of each family have very similar chemical and physical properties. Ion-exchange was for many years the only practical way to separate the rare earths in large quantities. This application was developed in the 1940s by Frank Spedding. Subsequently, solvent extraction has mostly supplanted use of ion exchange resins except for the highest purity products.
A very important case is the PUREX process (plutonium-uranium extraction process) which is used to separate the plutonium and the uranium from the spent fuel products from a nuclear reactor, and to be able to dispose of the waste products. Then, the plutonium and uranium are available for making nuclear-energy materials, such as new reactor fuel and nuclear weapons.
Ion-exchange beads are also an essential component in In-situ leach uranium mining. In-situ recovery involves the extraction of uranium-bearing water (grading as low as .05% U3O8) through boreholes. The extracted uranium solution is then filtered through the resin beads. Through an ion exchange process, the resin beads attract uranium from the solution. Uranium loaded resins are then transported to a processing plant, where U3O8 is separated from the resin beads and yellowcake is produced. The resin beads can then be returned to the ion exchange facility where they are reused.
The ion-exchange process is also used to separate other sets of very similar chemical elements, such as zirconium and hafnium, which incidentally is also very important for the nuclear industry. Zirconium is practically transparent to free neutrons, used in building reactors, but hafnium is a very strong absorber of neutrons, used in reactor control rods.
An ion-exchange resin or ion-exchange polymer is an insoluble matrix (or support structure) normally in the form of small (0.5-1 mm diameter) beads, usually white or yellowish, fabricated from an organic polymer substrate. The beads are typically porous, providing a high surface area. The trapping of ions occurs with concomitant releasing of other ions; thus the process is called ion-exchange. There are multiple types of ion-exchange resin. The most commercial resins are made of polystyrene sulfonate.
Ion-exchange resins are widely used in different separation, purification, and decontamination processes. The most common examples are water softening and water purification. In many cases ion-exchange resins were introduced in such processes as a more flexible alternative to the use of natural or artificial zeolites. Also, ion exchange resins are highly effective in the biodiesel filtration process.
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