There are also electric regeneration and thermal regeneration processes. Electro-regeneration is a technology that the fresh water chamber of electrodialyzer is filled with cation and anion resins, and the cation and anion resins are regenerated simultaneously by using H+ and OH- generated by polarization. Thermal regeneration is based on the sensitivity of easily regenerated weak acid or weak base resin to temperature: low temperature (25℃) is beneficial to exchange, and high temperature (85℃) is beneficial to regeneration due to the increase of H+ and OH- ion concentration in water, so the water temperature can be adjusted without regenerant.
The application of ion exchange in wastewater treatment can recover useful substances, such as chromium-containing wastewater. Firstly, the chromium-containing wastewater is exchanged with H-type cation resin to remove cations such as Cr3+ and Fe3+;
Cr6+ in water mainly exists in the form of H2Cr2O7 under acidic conditions and is exchanged by OH anion resin;
After the wastewater was exchanged by anion-cation resin, chromium was adsorbed on the resin and the wastewater was purified. When the cationic resin fails, it can be regenerated with acid to restore the resin to its original form:
Similarly, anion resin can be regenerated with alkali after failure:
(á NH)2Cr2O7+4NaOH。
Na _ 2cro _ 4 obtained from 2nhoh+2n2cro _ 4+H2O can be exchanged with H-type cation bed for sodium removal.
4R—SO3H+2Na2CrO4？
4R—SO3Na+H2Cr2O7+H2O
Because anion exchange resin has the highest selectivity to Cr2O, when anion exchange reaches equilibrium, the resin is basically (R [N] 2cR2O7 type, so the obtained chromic acid has high concentration and purity, and can be reused in production. After sodium removal, the resin becomes Na type, which can be transformed by acid regeneration.
Sodium bisulfate+hydrochloric acid+sodium bisulfate+sodium chloride
The above principle can be used to treat other kinds of metal surface processing wastewater, such as wastewater containing gold, nickel, cadmium and copper. In addition, ion exchange method can also be used to recover and remove radioactive substances from wastewater of nuclear reactors, hospitals and laboratories.