6, bipolar membrane technology
6.1 Introduction to bipolar film
Bipolar membrane (BPM) is a new film, usually by the anion exchange layer, cation exchange layer composite made of a composite ion exchange membrane, can also be in the film, the sun between the third layer of material to promote Water dissociation, as the anion exchange layer, cation exchange layer, the middle reaction layer composed of three-tier structure. Under the action of the DC electric field, the bipolar membrane can dissociate the water, and produce H + and OH- on both sides of the yang film and the film.
6.2 Application of bipolar membrane
6.2.1 Treatment of fluorine-containing waste liquid and recovery of valuable fluorine
In the production of fluorocarbon and uranium industry (UF6), the mass fraction of fluorine and organic acids contained in the effluent waste water is 50 to 500 x 10-6 and is usually required to be completely removed by KOH and the resulting KF solution contains many heavy metals (such as uranium, arsenic, etc.) and trace radioactive material, need to use Ca (OH) 2 and KF reaction regeneration KOH and generate insoluble waste. This method leads to the loss of valuable fluorine, and gives the user how to deal with radioactive material Ca (OH) 2 waste problem, if the use of bipolar membrane ionization dissociation technology can be directly KF into HF and KOH, not only can Recovery of high-value fluorine, and to avoid the use of lime, and reduce the amount of waste residue.
6.2.2 bipolar membrane for acid and alkali waste liquid purification and recovery
Industrial production will produce a lot of acid and alkali waste, such as ion exchange resin regeneration waste, pickling waste, lead storage battery waste, paper mill waste and so on. In order to reduce the pollution of the environment, these waste must be necessary to deal with the discharge, but the processing process is complex, the cost of money. The bipolar membrane electrodialysis process provides a good solution for the treatment of such waste streams. In 1986, China installed a set of electrodialysis and ion exchange joint equipment for the treatment of copper-containing wastewater in Zhejiang Province, and the treated copper content was 100mg / L and the pH value was 6 ~ 7. Emission standards.
6.2.3 Domestic sewage treatment
Domestic sewage is generally treated with biodegradation / chemical oxidation, but the amount of oxidant used too much, more residue. If a nanofiltration link is added between them, small molecules (relative molecular mass <100) that are degraded by microorganisms are allowed to pass through, and macromolecules (relative molecular mass> 100) that can not be degraded by microorganisms are retained. The macromolecule material is biodegraded by chemical oxidizer, which makes full use of biodegradability, saves oxidant and activated carbon, and reduces the final residue content.
6.2.4 Drinking water purification
With the increase in water pollution, people are increasingly concerned about the quality of drinking water. Experiments show that the bipolar membrane nanofiltration method can remove the micro-toxic by-products produced during the disinfection process, trace herbicides, insecticides, heavy metals, natural organic matter and hardness, sulfate and nitrate. At the same time with the treatment of good water quality and stability, the use of less chemicals, small footprint, energy saving, easy to manage and maintain the advantages.
6.2.5 Treatment of heavy metal wastewater
In the electroplating process and the production of alloys, often need to use a lot of water rinse, these cleaning water contains a very high concentration of heavy metals, nickel, iron, copper and zinc. In order to meet these emission requirements for these heavy metal-containing wastewater, the general measure is to treat these heavy metals as hydroxide precipitates. If the use of nanofiltration membrane technology, not only can recover more than 90% of the wastewater, so that purification, while the concentration of heavy metal ions concentrated 10 times, after the concentration of heavy metals with the value of recycling.
6.2.6 Wastewater treatment in food industry
N-P composite bipolar nanofiltration membrane on the monovalent salt and divalent salt has a significant separation, significantly reduce the COD content of wastewater to meet environmental requirements.
6.2.7 Bipolar Membrane Prospect
Bipolar film as a new type of film, with its unique advantages, to solve the environmental engineering has long been a number of technical problems to provide a lot of new ideas and solutions. The development of high-performance bipolar membrane, improve the preparation process of membrane, reduce the production cost of membrane, carry out research on the mechanism, study the mechanism of ion transport and water transfer in membrane, study high-performance bipolar membrane materials and preparation, broaden the application field , Has far-reaching significance.