In the production of ion-exchange membrane caustic soda, the content of calcium and magnesium ions in the brine entering the tank is required to be lower than 20 wtppb. The common chemical refining method can only reduce the content of calcium and magnesium ions in the brine to about 10 wtppm. If the content of calcium and magnesium ions is reduced to the level of 20 wtppb, it must be treated with chelating resin.

D408 and D409 are macroporous styrene ion exchange resins containing iminodiacetic acid chelate group, which can form multi coordination complexes with metal ions. In the first and second order metal ion solutions, it only forms stable complexes with the second order metal ions, showing high selectivity and high affinity for divalent metal ions. The selectivity for metal ions is similar to EDTA, and the selectivity order is: Hg>Cu>Pb>Ni>Cd>Zn>Co>Mn>Ca>Mg>Ba>Sr>Na. It has a very firm structure, good chemical stability, high mesh size and large chelating capacity, and is used for removing calcium and magnesium impurities from salt water used in chlor alkali industrial ion-exchange membrane caustic soda production. It is also widely used in the wastewater field (copper and nickel wastewater).