Silica sol ion exchange method

The ion exchange method is currently the most researched and most mature process, usually divided into the following two steps:

①Preparation of active silicic acid The ion exchange method is also known as the particle growth method. Generally, a strong acid type cation exchange resin is used to remove sodium ions in water glass, and a weak base type anion exchange resin is used to remove impurity anions in the system. The mass fraction of SiO2 contained in water glass is generally 2%~6%, and the pH value of active silicic acid is controlled at 2~4. Active silicic acid is unstable at room temperature and should be transferred to the next step as soon as possible, and stored at low temperature (4-10°C) if necessary. Regeneration of ion exchange resin: remove residual sodium silicate solution in the resin with water, and then rinse with sulfuric acid solution with a mass fraction of 3 until the leachate is neutral. ② Colloidal particle growth and concentration After the water glass is passed through the cation exchange resin to generate active silicic acid, one type is first stabilized with dilute alkali to control n(SiO2)/n(Na2O) at 80~100, and then carry out particle size growth and concentrate. There are two processes for particle size growth and concentration: one is that the particle size growth and concentration are carried out simultaneously in the same reactor; the other is that the particle size growth is performed first, and then the appropriate process is selected for concentration. The other is to add active silicic acid dropwise to the preheated dilute alkali solution made of water glass and alkali metal hydroxide, and control the pH value to increase the particle size. Similarly, the concentration process can be carried out simultaneously with the particle size increase, or the particle size can be increased first and then concentrated. Concentration methods include physical and chemical separation methods, such as heating evaporation concentration, ultrafiltration concentration, etc. are more effective concentration methods, and the concentration of SiO2 in the solution is increased to the concentration of silica sol. There are generally a small amount of impurities in the finished product, which need to be purified. An effective way to remove impurities is centrifugation.