Method for recovering valuable metals

Abstract

A method for recovering valuable metals, such as lead, silver and gold from the residue of an electrolytic zinc process, wherein the residue from the zinc process is suspended and sulfidized for converting the lead and silver compounds into sulfidic form, and further flotated for forming a flotation concentrate that contains valuable metals, wherein the sulfidizing and flotation processes are controlled electrochemically, so that the content of the sulfide ions fed in the sulfidizing stage is adjusted by means of the redox potential to a level where the grain size of the created valuable metal sulfides is sufficient for flotating them, and that the redox potential of the flotation stage is adjusted to be within a range where the collector chemical is adhered to the mineral to be flotated, but the sulfides are not oxidized.

1 . A method for recovering valuable metals, such as lead, silver and gold from the residue of an electrolytic zinc process, wherein the residue from the zinc process is suspended and sulfidized for converting the lead and silver compounds into sulfidic form, and further flotated for forming a flotation concentrate that contains valuable metals, wherein the sulfidizing and flotation processes are controlled electrochemically, so that the content of the sulfide ions fed in the sulfidizing stage is adjusted by means of the redox potential to a level where the grain size of the created valuable metal sulfides is sufficient for flotating them, and that the redox potential in the flotation stage is adjusted to be within a range where the collector chemical is adhered to the mineral to be flotated, but the sulfides are not oxidized. 
     
     
         2 . A method according to  claim 1 , wherein in the sulfidizing stage, the redox potential of the process is measured and adjusted at least in one stage. 
     
     
         3 . A method according to  claim 1 , wherein in the flotation stage, the redox potential is measured and adjusted in at least one stage. 
     
     
         4 . A method according to  claim 1 , wherein the redox potential of the slurry is measured by valuable metal or metal electrodes, glassy carbon or mineral electrodes, or by combinations thereof. 
     
     
         5 . A method according to  claim 1 , wherein in the flotation stage, a suitable reducing chemical is added in the slurry for adjusting the redox potential to a desired level. 
     
     
         6 . A method according to  claim 1 , wherein inert gas is fed in the flotation stage for adjusting the redox potential to a desired level. 
     
     
         7 . A method according to  claim 1 , wherein in the flotation stage, there is fed a gas mixture containing partly inert gas and partly air. 
     
     
         8 . A method according to  claim 1 , wherein at least part of the gas to be removed from the flotation stage is recirculated back to flotation. 
     
     
         9 . A method according to  claim 1 , wherein at least part of the metallic flotation concentrate created in the flotation stage is returned back to sulfidation. 
     
     
         10 . A method according to  claim 9 , wherein 10-30% of the metallic flotation concentrate created in the flotation stage is returned back to the sulfidizing stage. 
     
     
         11 . A method according to  claim 1 , wherein the flotation of valuable minerals is carried out in one single stage. 
     
     
         12 . A method according to  claim 1 , wherein the quantity of the sulfide ions to be fed in the sulfidizing stage is stoichiometric with respect to the quantity of the silver and lead contained in the slurry. 
     
     
         13 . A method according to  claim 12 , wherein the sulfide ions are conducted in the solution by using at least one chemical from the following group: Na 2 S, NaHS, Ca(HS) 2  and H 2 S. 
     
     
         14 . A method according to  claim 1 , wherein the pH is adjusted to be within the range 1-4. 
     
     
         15 . A method according to  claim 1 , wherein when using typical collector chemicals of sulfide minerals in the flotation, the redox potential is adjusted to be within the range −50-+350 mV vs. SHE. 
     
     
         16 . A method according to  claim 1 , wherein in sulfidizing, the redox potential is adjusted to be within the range −250-−0 mV vs. SHE. 
     
     
         17 . A method according to  claim 1 , wherein the sulfide ions are conducted in the solution by using at least one chemical from the following group: Na 2 S, NaHS, Ca(HS) 2  and H 2 S.