Flotation is a common process in sulfide ore beneficiation. Due to the restrictions and lack of access to high-quality water sources for industrial purposes, recycled water plays an important role in the flotation processes. Due to the existence of various organic and inorganic substances in the process, water influences the flotation performance. In this work, the effect of accumulation of sulfate ion in processed water on galena flotation was investigated. Flotation experiments using processed water without sulfate ion led to a concentrate containing 40.7% of lead and a maximum recovery of 58.9%. The presence of higher sulfate ion levels (2000 M) in processed water caused a significant decrease in the grade and recovery of the lead concentrate. With 2000 mg/L of sulfate ion, the grade and recovery of lead decreased from 40.7 to 24.3% and from 58.9 to 32.1 %, respectively. Thermodynamic calculations showed that when the sulfate ion concentration was increased from 300 to 2000 ppm, it was more likely that lead sulfate (solid) was formed. With increase in the xanthate ion concentration from 10-6 to 10-4 M, could be substituted by . On the basis of the results obtained, it was concluded that in order to reduce the negative effects of sulfate ion accumulation in water and increase the efficiency of the galena flotation process, higher dosages of xanthates should be added to the system.