Abstract: The strengthening mechanism of ammonium chloride on activation of sphalerite by copper in low alkaline condition was studied using micro-flotation， measurement of zinc dissolved amount， copper-adsorption measurements and X-ray photoelectron spectroscopy. The flotation results show that ammonium chloride can enhance the copper activated flotation of sphalerite under weak alkaline condition. The results of zinc dissolution test show that ammonium chloride could promote the dissolution of zinc ions from the mineral surface. The measurement of copper adsorption showed that the adsorption amount and adsorption rate of copper on the mineral surface are both significantly increased after adding ammonium chloride. XPS analysis results show that the content of copper sulfide increases and the content of hydroxide decreases with the increase of added amount of ammonium chloride. The enhancement of ammonium chloride on copper activation of sphalerite is mainly achieved through the following ways: the storage and release of copper ions by cuprammonium complex ion maintains a higher concentration of copper ions in the solution and promotes copper-zinc ion exchange process； the ammonia molecule in the solution can promote the dissolution of zinc hydroxide on the mineral surface and promote the conversion process of copper hydroxide into the copper sulfide； zinc-ammonia complexation can promote copper-zinc ion exchange on mineral surface and increase surface copper adsorption.

Key words: Sphalerite, Activation, NH₄Cl, Cuprammonium complex ion, XPS, Solution chemistry analysis, Low alkaline condition