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Sodium sulfate accumulation in the water system is a common problem in the production of primary metals from sulfide minerals. In flash smelting-flash converting copper smelters, when molten copper matte quenched in industrial water to produce matte granules, Na2SO4 precipitated and entered the system, which had negative influence on the matte converting process. The reaction behaviors of copper matte powder containing Na2SO4 have been studied through thermodynamic calculation and single-particle experiments. Calculated results showed that a liquid sulfate phase, Na2S containing copper matte, and Cu–Na alloy may form in the processing conditions of the converting process. The influence of the Na2SO4 dosage, fluxing conditions, and processing temperature has been systematically studied, and the results obtained showed that: (1); Na2SO4 physically precipitated on matte particles, and the Cu–Na alloy phase was found within copper phase in reacted particles; (2); Na2SO4 contamination hindered oxygen transfer by forming a low melting sulfate phase, and the de-sulfuration rate of matte powder changed dramatically along with the variation in Na2SO4 amount; (3); CaO flux was able to promote the converting reactions and Na2SO4 transformation; (4); Na2SO4 melt and formed a sulphate layer on matte particles at 1000 °C, Cu–Na alloy phase was found in samples collected at 1200 °C, and Cu–Na–O phase was detected in blister copper at 1600 °C. [ABSTRACT FROM AUTHOR]