In order to recycle valuable metals such as nickel and copper in nickel smelting slag,a nickel smelting slag in China is taken as the research object,the limitations of mineralogical characteristics of nickel smelting slag on the recovery of nickel and copper in flotation are deeply analyzed,and it is proposed to optimize the crystallization state of valuable metals nickel and copper by source roasting modification,so as to improve the recovery rate of nickel and copper flotation.The results show that,the grades of nickel and copper are 0.88% and 0.31%,respectively,accounting for about 20% of the oxidation state and residual state with poor floatability,and the nickel and copper with good floatability are mainly found in nickel pyrite,bornite and polydymite,but these three mineral phases are mostly scattered among the silicate minerals in the form of fine grains and irregularities,and it is difficult to achieve monomer dissociation,and the poor crystalline state of nickel and copper leads to the flotation recovery rate of only 24.61% and 38.77%,respectively.Optimizing the crystallization state of nickel?copper in the slag has become the key to improving the flotation recovery.After roasting modification,the proportion of nickel and copper in the metal state and sulfide state with good floatability is over 90%,and the flotation recovery rate is also increased by 41.55% and 41.23% respectively.