An equilibrium solubility model for the accurate prediction of the end point of semibatch hydroxide precipitation reactions in high ionic strength aqueous solutions is presented. We are interested in end-point and solution-pH predictions to determine the amount of base addition necessary to exactly achieve the base hydroxide solubility limit for the removal of heavy metals without excess base addition. Experimental verification of the model predictions is carried out using a chloride, iron, and magnesium system that is a model of the industrial system of interest. As shown by the experimental results, very good end-point predictions are possible even with the incorporation of a number of simplifying assumptions in the activity coefficient models.