What is the principle behind softening water through series hydrogen-sodium ion exchange?

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The hydrogen ion-sodium ion combined system can be divided into the integrated hydrogen-sodium ion softening method, the hydrogen ion-sodium ion parallel softening method, and the hydrogen ion-sodium ion series softening method. The comprehensive hydrogen-sodium ion softening method features an ion exchanger that contains both a hydrogen ion exchanger layer and a sodium ion exchanger layer, also known as a dual-layer ion exchanger. The water first passes through the upper layer of hydrogen ion exchangers, making the water acidic. It then passes through the lower sodium ion exchanger, which absorbs the hydrogen ions in the acidic water. The reaction equations are as follows: H2SO4 + 2NaR → 2HR + Na2SO4; HCl + 2NaR → 2HR + NaCl. In this way, the acidity in the water is eliminated, and the remaining calcium and magnesium ions that have not been absorbed by the hydrogen ions in the upper layer are also absorbed by the sodium ion exchanger. Since there is still some carbonate hardness in the ten water, the softened water after treatment retains a certain level of alkalinity. The hydrogen-sodium ion parallel softening method involves softening the incoming water in both hydrogen ion and sodium ion exchangers, followed by mixing the acidic water produced by the hydrogen ion exchanger with the alkaline water produced by the sodium ion exchanger. Finally, it enters the CO2 remover to remove free CO2. When the parallel method is used, the ratio of water flow entering the hydrogen ion and sodium ion exchangers can be adjusted according to the quality of the incoming water, in order to control the alkalinity of the softened water. Series hydrogen-sodium ion softening system. Part of the water enters the hydrogen ion exchanger first to be softened, and then it is mixed with the remaining untreated water. After the mixed water has had its free CO2 removed by a CO2 remover, it enters the intermediate water tank. Finally, it is pumped into a sodium ion exchanger for softening. This system is suitable for use when the alkalinity of the incoming water is high, with the residual alkalinity not exceeding 0.35 irunol/L. The residual alkalinity of the water produced by the comprehensive hydrogen-sodium ion softening method is approximately 1.0–1.5 mmol/L, while that in a series-connected system is about 0.7 mmol/L