Effect of sodium silicate on the flotation separation of chalcopyrite and galena using sodium sulfite and sulfonated lignin as depressant

•Exploring the inhibitory effect of combination depressant for galena.•Exploring the enhancement effect of Na2SiO3 on combination depressant.•Revealing the inhibition mechanism of combination depressant.•Revealing the enhancing mechanism of Na2SiO3 to combination depressant.