The reaction path in the (Ba, Sr, Ca)SO-4 solid-solution aqueous-solution (SSAS) system was experimentally studied using a batch-reactor method. The effect of the impurities “fluorite” and “iron sulfides” admixed in a natural barite sample on the reaction path was followed by analyzing the aqueous solution continuously. The dissolution and precipitation of the impurity “fluorite” affected strongly the reaction path in the SSAS system, especially the Ca/Sr/Ba ratio in the aqueous solution. This influence became stronger with decreasing CaSO-4 in the solid solution. The dissolution and precipitation of fluorite could hinder the CaSO-4 component from dissolving into water, and reduce the release rate of SO{2-}-4 from the solid solution to the aqueous solution and the removing rate of Ba{2} from the aqueous solution. In the presence of fluorite and sulfides, the aqueous Ba{2} and Sr{2} concentrations were controlled by the dissolution-precipitation of the end-members BaSO-4 and SrSO-4, respectively; the aqueous F-, Ca{2} and SO{2-}-4 concentrations were controlled by the dissolution-precipitation of fluorite. The incongruent dissolution of the (Ba, Sr, Ca)SO-4 solid solution caused the solid phase to become progressively more enriched in the more insoluble component (BaSO-4), while the aqueous composition shifted towards the more soluble end-members (SrSO-4 and CaSO-4) as equilibrium was approached to. The reaction path in the (Ba, Sr, Ca) SO-4 solid-solution aqueous-solution (SSAS) system was experimentally studied using a batch-reactor method. The effect of the impurity “fluorite” and “iron sulfides ”admixed in a natural barite sample on the reaction path was followed by analyzing the aqueous solution continuously. The dissolution and precipitation of the impurity “ fluorite ”affected strongly the reaction path in the SSAS system, especially the Ca / Sr / Ba The dissolution and precipitation of fluorite could hinder the CaSO-4 component from dissolving into water, and reduce the release rate of SO {2 -} - 4 from the solid solution to the aqueous solution and the removing rate of Ba {2} from the aqueous solution. In the presence of fluorite and sulfides, the aqueous Ba {2} and Sr {2} concentrations were controlled by the dissolution- precipitation of the end-members BaSO-4 and SrSO- The incongruent dissolution of the (Ba, Sr, Ca) SO-4 solid solution caused by the dissolution of the aqueous F-, Ca {2} and SO { the solid phase to become progressively more enriched in the more insoluble component (BaSO-4), while the aqueous composition shifted toward the more soluble end-members (SrSO-4 and CaSO-4) as equilibrium was approached to.