What Are The Indicators To Measure The Quality Of Ion Exchange Resin

Generally, the performance quality of ionic resin can be measured according to the following indicators.

(1) Selectivity and selection coefficient of resin resin has different affinity for different ions, preferentially select ions with strong affinity, and its binding force makes it not easy to leak. However, due to the strong binding, it is difficult to replace the ion when it is regenerated. The difference in resin's ionic affinity depends on two aspects: first, the performance of the resin itself, especially its own crosslinking degree. The greater the degree of cross-linking, the greater the selectivity of ions, and the stronger its affinity. Otherwise, the weaker it is. The second is related to the properties, composition and concentration of ions in the solution. In normal temperature and low concentration solution, the selectivity of various resins to different ions is roughly as follows.

① Strong acid cation exchange resin This resin for the more valence ions in the solution, the stronger the affinity. In the same number ion, the greater the atomic number, the stronger the affinity, and the selectivity order is as follows:

Fe. +>Co2+>Al. +>Ca2+> : Mg. +>Ag+>K+>Na+>Li+

② Weak acid cation exchange resin This resin has a particularly strong ability to select hydrogen ions, and its ability to select polyvalent ions is also better than that of low-cost ions, and the selectivity order is as follows:

H+>Fe2+>Al. +>Ca2+>Mg2+>K+>Na+>Li+

③ Strong base anion exchange resin In general, the selectivity of strong base negative resin increases with the increase of the valence number of anions in the solution, and its affinity law is as follows:

cr2 O; One >sOi >CrO: one >NOf>cl >OH >F >HcOf

The selection law of weak base anion exchange resin depends on the ion valence state, hydrated ion radius and ion structure in the solution. But weak alkali negative resin has stronger selectivity to OH 1. The order of ion selection of weak alkali negative resin is as follows:

OH > cr2O; One >soi one >NOf>cl one >}tC()

The selectivity of ion is not only related to itself and resin, but also to temperature, concentration and pH value. The selection rule of the above resin is only suitable for low concentration aqueous solution. In concentrated aqueous solutions (generally ion concentrations above 3mol/L), the situation is more complicated, and even the opposite selection order will occur. The regeneration of resin is achieved by using the concentration of acids, bases and salts.

(2) Moisture content Due to the hydrophilicity of the ion exchange resin, it always contains a certain amount of hydrated water (or combined water), called moisture content. The moisture content is usually? The percentage of moisture contained in the gram wet resin (after removing the surface water) is expressed (generally about 5%), and can also be converted to the following: Expressed in grams as a percentage of dried resin.

(3) Density Resin density is an important index for the design of exchange columns and the determination of backwash strength, and it is also the main factor affecting the stratification of resin. Resin density is divided into dry density and wet density. Dry density is the density after vacuum drying at a temperature of 105 ° C. Wet density is divided into wet true density and wet apparent density.

① Wet true density refers to the ratio of the mass of the resin fully expanded in water to the true volume (excluding the particle pore volume) (g/mL), generally 1.04 ~ 1.30g/mL. Different types of resin, wet true density is different. Even if the same type of positive resin or negative resin, due to the different types of exchange ions contained, the wet true density is not the same. Order of their magnitude

As follows:

Positive resin R-H

Negative resin R-OH

Wet apparent density, also known as bulk density, refers to the mass of the resin after it fully expands in water, and the value is generally 0.60 ~ 0.85g/mI. The wet apparent density can be used to calculate the amount of resin required to fill the ion exchange column.