Titanium anode electrodialysis electrolysis and its application in seawater desalination

Desalination of seawater by electrodialysis is achieved by means of an electrodialysis desalinator. Desalinizer desalinization principle, under the action of external direct current electric field, when the raw water containing salt flows through the Yin, cation exchange membrane and partition composed of the chamber, the Yin and Yang ions in the water began to move, anion to the anode direction migration, cation to the cathode direction migration. Due to the selective permeability of the ion exchange membrane, the fixed exchange group of the cation exchange membrane (referred to as positive membrane) is negatively charged, thus allowing the passage of cations in water and blocking anions. Anion exchange membrane (referred to as the negative film) of the fixed exchange group with positive charge, so allow the water through the anion and block cations, resulting in the freshwater compartment in the ion migration to the concentrated water compartment, so as to achieve the purpose of desalination.

Seawater and brackish water desalination, salt content of up to 60g/L brackish water desalination into drinking water, to solve the problem of drinking water in desert areas. Electrodialysis desalination is widely used in food, light industry and other industries to produce pure water; Pre-treatment of high purity water produced by electronic, pharmaceutical, chemical and other industries; Primary softening and desalting of boiler feed water; Seawater desalination for drinking water and some chemical products desalination treatment.

Electrode material is one of the key components of electrodialysis desalinator. This electrode material is required to be able to withstand both oxidation and reduction, that is, can be used as both anode and cathode, but the general electrode material can not meet this requirement. Graphite electrodes, for example, are quickly corroded and have a shorter working life. At present, the ideal electrode is multi-component metal anode containing iridium, which can not only meet the requirements of electrode reversal, but also has low overpotential, electric saving performance, and longer service life than common ruthenium-titanium coated metal anode.

Preparation of tetramethylammonium hydroxide by electrodialysis

Tetramethylammonium hydroxide is a kind of polymerization catalyst commonly used in the synthesis of silicone rubber and silicone oil. In the past preparation process, tetramethylammonium iodide solution and silver oxide reaction; Tetramethylammonium chloride, potassium hydroxide reaction in methanol solution; Ion exchange resin technology, etc., these processes are complex, there are more impurity ions into the product, raw materials (such as silver oxide) expensive, difficult to achieve industrialization. High purity tetramethylammonium hydroxide can be directly prepared by electrodialysis, which has the advantages of low raw material cost, small equipment, large production capacity and simple process.

The electrodialysis tank is divided into two chambers by perfluorinated cation exchange membrane. The anode uses active coated titanium electrode and the cathode is stainless steel. The anode chamber was injected with 30% tetramethylammonium chloride solution, and the cathode chamber was injected with 2% tetramethylammonium hydroxide solution. When direct current is switched on, an electrochemical reaction occurs on the two plates. Current density 11A/d square meters, groove voltage 10V current efficiency about 80%. Ammonium hydroxide with a concentration of about 15% was prepared. The product pentahydrate and ammonium hydroxide crystals can be obtained by decompression concentration.

Recovery of nickel from nickel plating wastewater by electrodialysis electrolysis

For a long time, ion exchange, electrodialysis and other methods have been used in the treatment of nickel plating wastewater. The essence of these methods is to concentrate the wastewater and reuse it. However, due to the concentration process, the impurities in the wastewater are also concentrated, which brings great inconvenience or can not be reused at all. Many electrochemists try to recover nickel from nickel wastewater by electrolysis. For nickel-containing wastewater, nickel's standard electrode potential is already more negative (-0.25V). During electrolysis in dilute solution, nickel's precipitation potential becomes more negative due to concentration polarization. Hydrogen is prefertively precipitated in large quantities, and the cathode current efficiency of nickel precipitated is extremely low, or even no nickel precipitated. Therefore, it is impossible to obtain good results from electrolytic nickel recovery from nickel plating wastewater with low concentration by increasing the surface area of the cathode and reducing the current density. Only by trying to improve the concentration of nickel ions near the cathode surface, can the current efficiency of electrolytic nickel recovery be effectively improved, and can the electrolytic method be used to recover nickel from nickel plating wastewater successfully.

A method combining electrodialysis and electrolysis is used to recover nickel from nickel containing wastewater. The basic principle of this method is that the ion exchange membrane has the function of selective ion transmission of different electrical properties, that is, in the electrolyte solution, the anion exchange membrane allows the cation to pass through and block anions; Cation exchange membranes allow anions to pass through and block cations. Therefore, under the action of electric field, the solution action can effectively make nickel ions in wastewater to migrate to the cathode chamber, the middle chamber sulfate ions and other anions through the cation exchange membrane into the anode chamber, nickel ions and other cations through the anion-exchange membrane into the cathode chamber, so that if the cathode chamber solution can maintain a high concentration of nickel ions, Nickel ions can then be deposited as metals on the cathode with higher current efficiency. The concentration of nickel ions in the middle chamber is gradually reduced to achieve the purpose of wastewater treatment and nickel recovery.

The electrodialysis unit consists of three cathode chambers, four anode chambers and six circulation chambers. Stainless steel plate is used for the cathode, and insoluble titanium anode is used for the anode. When the PH value of the wastewater is about 5, the control of the appropriate current density, can be highly efficient recovery of metal nickel, nickel containing ions about 1g/L nickel plating wastewater treatment to about 50mg/L, the average current efficiency can reach more than 60%, the purity of recovered nickel up to 99.7%.