Ion membrane electrolysis technology is a high-efficiency and new type of sewage treatment technology. With the continuous expansion of its application range, it has penetrated into many industries, bringing new changes to my country’s water resources treatment.
Overview of ionic membrane electrolysis
Ion membrane electrolysis technology, also known as membrane cell electrolysis, is a method of using cation exchange membrane to separate the unit electrolysis cell into anode chamber and cathode chamber to separate electrolysis products. Ion membrane electrolysis is a new technology developed on the basis of ion exchange resin.
The use of ion exchange membranes has the characteristics of selectively permeating anions and cations, allowing ions with one charge to pass through and restricting the passage of ions with opposite charges, so as to achieve the purpose of concentration, desalination, purification, purification and electrochemical synthesis. This technology has been used For the production of chlor-alkali, desalination of seawater and brackish water.
The preparation of industrial water and ultrapure water, the purification of enzymes, vitamins and amino acids and other pharmaceuticals, the recovery of electroplating waste liquid, the treatment of radioactive wastewater, etc., among which the most widely used and most effective is the chlor-alkali industry. In the chlor-alkali industry, cation-exchange membrane electrolyzers are used to electrolyze salt or potassium chloride aqueous solutions to produce chlorine gas, hydrogen gas, and high-purity caustic soda or potassium hydroxide.
Ion membrane electrolysis process
After two times of purification, the concentrated brine solution enters the anode chamber continuously, and the sodium ions move to the cathode chamber through the cation exchange membrane under the action of the electric field. , while releasing hydrogen at the cathode.
Chloride ions in the brine solution are restricted by the membrane and basically cannot enter the cathode chamber and are oxidized to chlorine gas on the anode.
After partial sodium chloride electrolysis, the remaining brackish water flows out of the electrolytic cell to remove dissolved chlorine, and after the solid salt is re-saturated and refined, it returns to the anode chamber to form a brine loop similar to the mercury method.
Part of the sodium hydroxide solution leaving the cathode chamber is used as a product, and a part is returned to the cathode chamber after adding pure water. The circulation of the lye helps to precisely control the amount of water added and also removes the heat generated inside the electrolyzer.
Application of ionic membrane electrolysis technology in wastewater treatment
3.1 Alkaline wastewater treatment
For many alkaline wastewater, the ion membrane electrolysis method is used to treat it without adding any chemical substances, which can greatly reduce the COD of the wastewater, recover the alkali in the wastewater, quickly reduce the pH value of the wastewater, and play a good role in the subsequent biochemical units. The pretreatment effect of papermaking black liquor is an application in this regard.
Some researchers used a heterophasic single-cation membrane electrodialyzer, with a titanium-based lead-coated plate as the anode and a polyethylene heterophase membrane as the ion exchange membrane, studied the influence of operating conditions such as current density, temperature and other factors, and obtained the current density. 350A/m, the current efficiency is 85%~99%, the alkali recovery rate is 70%~75%, and the power consumption is 5000~6000kW/t. A series of studies have been done on the basic theory, technical characteristics and influencing factors of pulp black liquor treatment, and the optimal process conditions for using this technology to treat grass pulping black liquor have been studied, and the Na+ balance in the process has been studied, and lignin has been preliminarily discussed. , Electrochemical oxidation of hemicellulose.
The State Key Laboratory of Pollution Control and Recycling Research has carried out research on the treatment of propylene oxide chlorohydrin tail gas alkali washing wastewater by ion membrane electrolysis. When the electrolysis voltage is 5.0V, the COD removal rate of wastewater can reach 78% after circulating treatment for 3 hours. , the recovery rate of alkali in wastewater can reach 73.55%, which plays a good pretreatment role for subsequent biochemical units.
3.2 Organic acid wastewater treatment
In the process of producing organic acid by fermentation, the extraction and separation of organic acid is a weak link, which often produces a large amount of waste water. The extraction and separation of organic acids by ionic membrane method can not only improve the yield, but also greatly reduce the discharge of wastewater as a cleaning process.
In recent years, the application of this method in the treatment of tartaric acid, citric acid, alanine and other organic acid wastewater has been extensively studied. The ion membrane electrolysis method is used to pretreat high-concentration ammonia nitrogen organic wastewater in monosodium glutamate production. Several factors for ammonia nitrogen removal were investigated.
The removed ammonia nitrogen is recovered in the form of concentrated ammonia water to realize waste recycling; the effluent is basically colorless after deamination of the wastewater, and the COD is also reduced to a certain extent. After comprehensively considering the energy consumption, for wastewater with a concentration of ammonia nitrogen up to 7500mg/L, under the operating conditions of 4V, 11L/h, and 60°C, the average removal rate of ammonia nitrogen can be stabilized at about 72.66% after electrolysis for 1.5h.
3.3 Electroplating wastewater treatment
The wastewater discharged from the electroplating industry generally contains a large amount of heavy metal ions. Most of these metal ions are relatively precious metals and have extremely high recycling value.
Ion membrane electrolysis technology utilizes the redox characteristics of metal ions to replace or partially replace the hydrogen evolution and oxygen evolution reaction that occurs at the cathode and anode, so that some metals can be precipitated and recovered on the cathode, and some reduced metal ions can also be processed on the anode as required. oxidation.
Some researchers made their own ion-exchange membrane electrolyzers to study the feasibility of the passivation solution in the copper production process, which can not only recover copper and zinc, but also oxidize Cr3+ to Cr6+; the researchers took the galvanizing passivation solution as the treatment object The research was also carried out, and the optimal process conditions of temperature 30～40℃ and voltage 4.0V were determined. Under these conditions, the current efficiency of Cr3+ with mass concentration of 29.06g/L in the passivation solution oxidized to Cr2O72- can reach 50% ～60%, and the zinc removal amount is 0.2～0.3g/h.
3.4 Metallurgical Wastewater Treatment
The COMAT method is an ideal closed-loop process for leaching low-grade copper by using an acidic sulfate medium, but this method still produces ammonium sulfate waste liquid, which can only be discharged after being treated with lime according to the traditional method. The ammonium is electrochemically decomposed into sulfuric acid and ammonia, and the cathode compartment is separated from the anode compartment by the cathode membrane.
After electrification, sulfuric acid is enriched in the anode chamber, and ammonia water is generated in the cathode chamber.
Some researchers began to study the recovery of free alkali in sodium tungstate solution by ion-exchange membrane electrolysis technology in the early 1980s, and began to apply it in industry; some researchers also carried out a series of in-depth studies.
After the success of the exploratory experiment, the electrolytic anode, electrolytic cell structure, and electrolytic cell combination mode of the electrolytic system were deeply studied, and certain results were obtained. On this basis, an industrial expansion test was carried out using sodium tungstate feedstock , indicating that the continuous operation mode is beneficial to the stable operation of the sodium tungstate solution membrane electrolytic dealkalization process. Under the current density of 60~65℃ and 1000A/m2, the mass concentration of free alkali in the raw material solution is 63.5g/L, and the removal rate can reach 63.5g/L. 80%, and the current efficiency can reach 88%, which has industrial practical value; some researchers have systematically studied the influence of various process parameters on the electrolysis effect when the ion membrane electrolysis of tungsten extraction process wastewater is carried out in a small electrolyzer, and The application effects of some domestic ion membranes are compared.
The metallurgical industry often needs to deal with waste lye, and use cationic membrane electrolysis to recover the waste caustic. After electrification, the anions (Cl-) in the industrial waste lye are trapped in the anode chamber, and K+ or Na+ passes through the cationic membrane and is in the cathode chamber. Produces highly concentrated lye.
4 Conclusion
In summary, the ion membrane electrolysis technology has achieved industrial application in some fields, especially in industries such as chlor-alkali. Although there are still many problems to be solved in the application of wastewater treatment, its unique performance and laboratory research results have been Shows its huge potential and prospects. With the deepening of research, this technology will definitely become a general technical method for wastewater treatment. Therefore, it is necessary to increase human and material resources, study unique processes and establish experimental plants, so that the application and research of ion membranes can promote each other.