Water treatment - softening process
Let's start by saying why does pretreatment need a softening process? Has the city water been treated?
The final treatment equipment of the medical water system has higher requirements: the downstream pharmacopoeia water final treatment system is realized through membrane filtration, and the membrane filtration unit and EDI unit have requirements for the hardness of the influent water quality, which needs to meet the level of not higher than 3ppm, which can be called "soft water"; If the hardness continues to be too large, it can be called "hard water", and the consequences are scaling of the membrane system, which in turn leads to potential unplanned downtime. The hardness index needs to be stably controlled by the softening process, which is to achieve the softening of urban water through the softener. Softeners, also known as sodium ion exchangers, are mainly composed of resin, containers containing resin, valves and control systems.
So what is ion exchange?
Ion exchange is a chemical process that removes unwanted ions from water by exchanging them with ions with similar charges. This is achieved through resin beads, which attract and retain ions, often used for water softening. The main function of pharmaceutical water softeners is to exchange calcium and magnesium ions in urban water with the exchangeable sodium Na+ in nano resin, thereby reducing the hardness of water. The softening process mainly includes two process steps: "softening" and "regeneration".
1. Softening
Nano-strong acid cation exchange resin is usually used for softening pharmaceutical water treatment, which is the core medium of the softening process.
The nano-strong acid cation exchange resin bead polymer structure contains a permanently attached fixed negative ion that cannot be removed. In simple terms, resin beads have a fixed negative charge. Each negatively charged exchange site can accommodate a positively charged ion. In this case, sodium (positively charged) is attached to the exchange point (negative and positive charges are attracted to each other) So, the moving sodium ions attach to each fixed negative charge on the resin beads.
The principle of softening chemical reaction is as follows:
Calcium and magnesium ions suspended in water have a stronger positive charge than sodium bands. As hard water passes through the beads, the strong attraction of calcium and magnesium to the negatively charged beads "kicks" away the sodium ions, so that calcium and magnesium can take their place (and remain attached to the beads). Larger divalent calcium-magnesium ions require two exchange sites on the resin surface.
Eventually, the hardness of the resin beads becomes saturated, mainly calcium and magnesium, with no more exchange points producing demineralized water. The resin beads have been depleted and must be regenerated.
2. Regeneration
Softening is simple and widely used because the resin can be regenerated with a simple Nacl brine solution (usually 10%). After the saturation failure of the softening resin in the softener, Nacl is used for regeneration recovery. The ion exchange resin is soaked in a sodium chloride solution (brine), in which a large amount of brine precipitates the calcium and magnesium ions from the resin beads. Sodium in the saline solution adheres to the resin beads. After regeneration, the excess brine is rinsed off and the resin beads can be used again.
The principle of regeneration of the softening system is as follows:
During regeneration, an increase in the concentration of monovalent sodium ions forces the two charges of the calcium and magnesium ions to separate, essentially "loosening their control" at the exchange site. Due to the high concentration of sodium ions, it is now much easier to exchange monovalent sodium ions for divalent calcium and magnesium ions.
