What is the normal range for calcium and magnesium ions in the rear column of the resin column?

I’m not sure what the original poster intends to convey; when resin towers are connected in series, it is still to further ensure the high quality of the brine.

Finally, if the total amount of calcium and magnesium ions in the water is less than or equal to 20 PPb, it is considered qualified

Ensure that the quality of the saltwater is even better – it must not exceed 20

At current densities below 4 KA/M2, a level not exceeding 30 PPb is acceptable.

The combined content of calcium and magnesium in the brine at the outlet of the secondary tower of the resin tower is considered acceptable if it is less than 20 ppb

For Tower 1, the required concentration is less than 30 PPb; Tower 2 serves as a guarantee tower, meaning it acts as a double safety measure

This question is a bit misleading; the sum of calcium and magnesium levels is less than 20 PPb.

Strictly speaking, modern high-current-density electrolyzers require calcium levels to be less than or equal to 15 PPb, and magnesium levels to be less than or equal to 5 PPb.

Regarding the original poster’s question, I think we first need to clarify the concept of a “back tower”. Woody process: Two towers in operation (Tower A and Tower B) ； “The concept of the \"rear tower\" is either A or B; therefore, the calcium and magnesium levels in the rear tower must be below 20 PPB to ensure the safety of the ion exchange membrane. Kasuga Chemical and other processes: operation with three towers in series (ABC three-tower system) ； All three ABC towers can be in the “rear tower” position; therefore, their calcium and magnesium levels in the effluent must also be below 20 PPB in order to effectively protect the ion exchange membrane. Of course, the lower the PPB value, the better. However, calcium and magnesium levels within 20 PPB fully meet the safety requirements for ion exchange membranes without affecting current efficiency.