6.2 What is the role of depressant in froth floatation process?

 In the froth floatation process, the role of the depressants is to separate two sulphide ores by selectively preventing one ore from forming froth. For example, to separate two sulphide ores (ZnS and PbS), NaCN is used as a depressant which selectively allows PbS to come with froth, but prevents ZnS from coming to froth. This happens because NaCN reacts with ZnS to form Na2[Zn(CN)4]. 

                                             4 NaCN + ZnS       Na2Zn(CN)4 + Na2S