Stoichiometric ratio 𝑆𝑡 0.2 0.5 1 Leaching time t / h In addition to modeling the leaching, the determination of the ion concentration is necessary for control. Due to the kinetics of anhydrite, Ca 2+ ion determination via chromatography with a measuring time of 30 minutes is not feasible for control purposes. Here, using an ion selective electrode (ISE) coupled with ion chromatography offers a possible solution to decrease measurement time and allows inline prediction of Ca 2+ ion concentration. Coupling the ISE with chromatography or titration is essential, as calcium and magnesium influence each other during the carbonate precipitation as discussed in the Section (Anhydrite Carbonate precipitation).