Ion exchange equilibrium is the limit state that ion exchange can achieve under certain conditions. In specific applications, it has always been expected that the reverse osmosis equipment and ion exchange machine equipment can operate under high water flow rates, so the response time is relatively limited and it is unlikely to achieve an equilibrium state of ion exchange. Therefore, scientific research on the factors that harm the ion exchange rate of reverse osmosis equipment is of practical significance in key practical activities.

The entire process of ion exchange is carried out between positive ions in water and exchangeable functional groups of ion exchange resins. The exchangeable functional groups of resin are irregularly distributed throughout every particle, not only on the surface of the resin particles, but also inside many of them. Therefore, the entire process of ion exchange in reverse osmosis equipment is very complex because it is not only a problem with the exchange site between positive ions, but also the entire process of positive ions diffusing into the particles in water. The rate of ion exchange chemical changes in reverse osmosis equipment belongs to the reflection between positive ions, which is generally rapid. Therefore, the ion exchange rate generally refers not only to such chemical changes, but also to the rate of change in ion concentration in the solution.

The challenge of how various operational standards can harm exchange speed has not been thoroughly understood, although many scientific studies have been conducted. Below is a brief description of some elements that can harm the ion exchange rate.

(1) Resin exchange functional groups. We know that the rate of chemical change between positive ions is rapid, so generally speaking, the difference in resin exchange functional groups does not harm the exchange rate. For example, sulfonic acid type cation exchange resin, regardless of its shape as H, Na or other, has a rapid exchange rate between various positive ions, and the difference between them is also very small. But for ion exchange resins that produce salt hydrolysis, the situation is different, and there will be a significant difference in exchange rates between H-type and salt type resins.

(2) The chemical crosslinking degree of the resin. The larger the chemical crosslinking value of the resin and the smaller the mesh, the slower the diffusion within its particles and the slower the exchange rate. When there are large positive ions in the water, the harm to the exchange rate becomes more obvious.

(3) Resin particles. The smaller the resin particles, the faster the exchange rate. This is because the smaller the particles of the resin, the smaller the distance between internal diffusion; In addition, the smaller the particles, the more they expand the diffusion area of the membrane, thereby accelerating the exchange rate. But resin particles are also not suitable for being very small, as they can expand the frictional resistance of water flow based on the resin layer, and are very easy to flow out during the operation of the softener.

(4) The concentration of the solution. The concentration of substances is a key factor in the diffusion rate of hazards, and the higher the concentration value, the faster the diffusion rate. Internal diffusion of ions in solution and membrane diffusion have different levels of harm. When the ion concentration in the solution is high, the diffusion rate of the membrane is rapid. At this time, the exchange rate is mainly controlled by internal diffusion, which is a crucial link. This is equivalent to the situation during resin regeneration in sewage treatment processes. If the concentration of electrolyte solution in the solution is small, the diffusion rate of the membrane becomes increasingly slow, so the exchange rate is controlled by membrane diffusion, which is equivalent to the situation when water becomes soft when using cation exchange resin. Naturally, when the ion concentration in aqueous solution changes, the resin may also cause internal diffusion due to swelling or contraction.

(5) Temperature. Raising the temperature can also accelerate internal diffusion and membrane diffusion, so when ion exchange equipment operates, the temperature is generally maintained at 20-40 ℃. But it cannot be too high, as excessive temperature can harm the heat resistance of the exchange agent, especially strong alkaline anion resins, which are not heat-resistant.

(6) Mixing or increasing water flow rate. The mixing or increasing water flow during the entire exchange process can only accelerate diffusion, but cannot harm internal diffusion.

(7) The nature of positive ions. It poses a great threat to the speed of internal diffusion, and the larger the hydration time of positive ions, the slower the internal diffusion; The more positive ion charge there is, the slower the internal diffusion. According to the experimental results, the positive ion increases by one positive charge, and the diffusion speed slows down to about 1/10 of the original. The factors that harm the speed of anion exchange are very similar to the situation of cation exchange. For anion exchange resins, there is still very little scientific research on the problem of membrane diffusion. However, it can be inferred that in very dilute aqueous solutions, membrane diffusion is crucial for strong alkaline resins; In concentrated solutions, intra particle diffusion is crucial. The chemical cross-linking degree of resin and the positive charge of positive ions pose much less harm to the diffusion rate of cations within resin particles compared to the harm of positive ions. For example, the harm level of positive ions to the diffusion rate is only 1/2 or 1/3 of that of positive ions for every positive charge increase in cations. When the chemical crosslinking degree of the resin is increased from 5% to 15%, the internal diffusion rate of monovalent cations decreases by about 1/10 of the original, while the internal diffusion rate of monovalent cations only decreases by 1/2. The diffusion rate of large pore resin is much faster than that of ordinary resin.

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