The principle of water purification using workshop ion exchange method is based on the exchangeability between various ions in resin and natural water. H-type cation exchange resin, in which the exchange groups can exchange with various cations in the raw water, allowing equal cations in natural water to bind to the resin and enter the water, thus removing metal cation impurities from the water. When the raw water passes through an anion exchange resin, the exchangeable groups in the exchange group will undergo a neutralization reaction, resulting in high-purity deionized water.
The process of treating raw water using ion exchange method can generally adopt a combination of cation bed, anion bed, and mixed bed. The mixed bed is composed of anion and cation resins mixed in a certain proportion. In order to reduce the burden of anion resin during large-scale production, a degassing tower is often added after the cation bed to remove carbon dioxide. After a period of use, the resin needs to be regenerated or replaced.
The electrodialysis method is designed by utilizing the directional migration of ions and the selective permeability of the exchange membrane under the action of an external electric field. Due to the negative charge on the cation membrane, it repels anions, allows cations in the solution to pass through, and causes them to move towards the cathode. The electrodialysis method is more economical and saves acid and alkali compared to the ion exchange method, but the purity of the water produced is not high and the specific resistance is low. Generally, when the salt content of the raw water reaches 3000mg/L, the resin will quickly age when using the ion exchange method to prepare purified water. Therefore, combining the electrodialysis method with the ion exchange method is more suitable for preparing purified water.
Reverse osmosis device is an operation that uses external pressure to make the water in the raw water pass through a semi permeable membrane, and impurities are blocked by the membrane to obtain purified water. The concentration of impurities in the raw water will increase. The structure of the reverse osmosis device in the workshop building is the same as that of ordinary microporous membrane filtration devices, but it requires high pressure (usually 2.5-7MPa), so the structural strength requirement is high. Due to the low rate of water penetration through the membrane, the membrane area per unit volume in general reverse osmosis devices is larger. The reverse osmosis devices commonly used in industrial production are spiral wound and hollow fiber.
When using reverse osmosis method for pure water, appropriate design can be adopted to strengthen the control function of the system, improve the reliability of the system, the quality of the effluent, and the processing capacity of the system. For example, using a "multi-stage series" design can improve the quality of the water; Adopting a "multi-level parallel" design can increase water production.