Research of the replacement of dichromate with depressants mixture in the separation of copper-lead sulfides by flotation

•Humic substance and hydrogen peroxide are promising depressants on galena.•The hydrogen peroxide can accelerate dissolution of galena lattice.•An adsorption model is finally obtained. To reduce the environmental impact caused by highly toxic dichromate in flotation separation of copper-lead sulfide, the replacement of dichromate with depressants mixture (humic substance and hydrogen peroxide) was investigated in this paper. The single mineral flotation and the mixed binary minerals experiment at pH 6.5 showed that combined depressants could be efficient in separating galena from chalcopyrite and achieve a lead concentrate comparable to conventional method using dichromate as typical depressant. The contact angle measurement and atomic force microscopy (AFM) imaging indicated that, for the same concentration of sodium humate, the treatment by hydrogen peroxide could increase surface wettability and largely enhance chemical adsorption of humate on galena surface. Ion dissolution tests and adsorption tests indicated that the hydrogen peroxide can accelerate dissolution of galena lattice and the hydrogen peroxide or Pb2+ could promote the adsorption of NaHA on the surface of galena.