• It reveals the difference in flotation effect between Cu2+ activated sphalerite and germanium-bearing sphalerite. • Finding the higher the content of germanium in sphalerite, the worse the activation effect of copper ion. • The mechanism difference between copper ion activated sphalerite and germanium-bearing sphalerite was explained in this paper. Although numerous studies on the flotation activation of sphalerite by copper ion have been reported, but there are still some important problems to be studied further. Previous research works did not comprehensively investigate the effect of germanium content on the floatability of germanium-bearing sphalerite, and did not obtain direct evidence of the activation difference of copper ions on sphalerite and germanium-bearing sphalerite. In this paper, the effect of germanium content in sphalerite on the floatability of sphalerite was studied using micro flotation test. The difference mechanism between copper ion activated sphalerite and germanium-bearing sphalerite was studied using surface adsorption amount measurements, Zeta potential measurements, local electrochemical impedance spectroscopy analysis, and time-of-flight secondary ion mass spectrometry. The results show that the increase of germanium content reduces the floatability of sphalerite and reduces the adsorption of copper and xanthate. Especially after activation by copper ions, the downward trend is more obvious. The reason for the less adsorption of copper and xanthate on the surface of germanium-bearing sphalerite is that Ge occupies the exchange site of Cu and Zn. [ABSTRACT FROM AUTHOR]