Dichromates are effective inhibitors of galena and are mainly used for lead suppression and copper flotation in the separation of copper-lead mixed concentrates. Potassium dichromate and sodium dichromate are commonly used, with potassium dichromate being the most widely used. When using dichromates to suppress galena, the following points should be noted:
(1) Dichromates have poor inhibitory power on galena activated by copper ions. When the copper-lead mixed concentrate contains secondary easily oxidizable copper sulfide minerals (such as chalcocite, bornite, and covellite), dichromates cannot be used for lead suppression and copper flotation separation. This is because these secondary copper sulfide minerals are easily oxidized, and after oxidation, they will dissolve copper ions into the slurry, activating galena and affecting the inhibitory power of dichromates on galena. In this case, cyanide can be used instead to suppress copper and float lead, achieving copper-lead separation.
(2) The stirring time should be long. Because dichromates only inhibit the oxidation of galena on its surface, the stirring time must be long (more than 30 minutes, sometimes more than 1 hour) when using dichromates to inhibit galena to promote surface oxidation and effectively inhibit it.
(3) When using dichromates to inhibit galena for the separation of copper-lead mixed concentrates, because dichromates cannot desorb the xanthate on the surface of galena, the mixed concentrate is generally de-treated (using activated carbon) before separation, and then dichromates are added to inhibit galena and improve the inhibition effect.
(4) The suitable pH value for inhibiting galena with dichromates is generally 7.4–8.
(5) Because dichromates have a strong inhibitory effect on galena, once galena is inhibited, it is difficult to reactivate.