The process of ion exchange has found practical use in wastewater treatment and water preparation systems, specifically for demineralization, desalination, correction of the chemical composition of water, removal of toxic or valuable substances in processing natural or industrial wastewater.
Despite the abundance of the chemical properties of electroplating wastewater contaminants, both organic and inorganic, the specific chemical interaction of ions, which exchange ionites (forming complex functional groups, weakly ionized form of ionites) becomes important.
Ion exchange is the most environmentally dangerous technology for deep purification of water and using it as a part of combined water treatment systems requires research of the interconnected processes: the exchange of ions between phases and the transfer of solvent.
The end result of the balanced distribution in these system is the result of the Donnan distribution of components and the chemical reactions of ion exchange.
This can be explained by the structural changes in the system of ionite-solution, since we know that wastewater treatment begins with the cationic exchange of cation exchanger with a sulfate group. The sulfate group in this is an ionogenic group and has the highest affinity with multicharged ions, which are the primary contaminant in electroplating wastewater. This is due to the following processes:
- strong electrostatic interaction of multicharged counter-ions with fixed ions;
- strengthening of hydrogen bonds between the molecules of hydrate water;
- strengthening of bonds with counter-ions and fixed ions.
Complete regeneration of cationite requires a 2.5 excess of acid, while desorption of double-charged ion from the cationite, even larger acid exceed is required. The result is that a significant excess of acid exists in wastewater after cationic exchange filters, along with the salts of copper, nickel, calcium etc. This limits the use of eluate (regeneration solutions) for their recycling.
The process of anionic exchange is performed consecutively first in low-basic and then in highly basic anion exchangers. The need to used low-basic anion exchangers is due to their easy regeneration, but the low-basic anion exchangers absorb practically no weak acids. It is important that highly basic anion exchangers function in any pH range. At the same time, highly basic anion exchangers are more difficult to regenerate.
At present, the degree of wastewater mineralization and reduction of its volume occurs. Therefore it is reasonable to consider combined batch or semi-batch systems with complete purification and final polishing to reuse the water in the production process.
