Treatment of base metal concentrate by a two-step bioleaching process

Abstract

A method of recovering at least one base metal from a concentrate wherein a residue of a primary bioleach of the concentrate, under mesophilic and moderate themophilic conditions, is processed to recover at least one metal, and the base metal is recovered from a solution, produced by a secondary bioleach under thermophilic conditions, of a residue of the metal recovery process.

1 .- 21 . (canceled)  
   
   
       22 . A method of treating a concentrate containing at least one base metal which includes the steps of subjecting the concentrate to a primary mesophilic and moderate thermophilic bioleaching process to leach sulphides in the concentrate, processing a residue of the primary bioleach process to recover at least one metal from the primary bioleach residue, subjecting a residue from the metal recovery process to a thermophilic secondary bioleaching process to release the at least one base metal from the metal recovery residue into solution, and recovering the at least one base metal at least from the solution produced by the thermophilic secondary bioleaching process, and which is characterized in that it includes the step of preleaching the concentrate, before the primary bioleaching process, using leach solution from at least one of the bioleaching processes which increases ferric in the preleaching step thereby to increase the leaching of easily leachable base metal before the primary bioleaching process.  
   
   
       23 . The method according to  claim 22  wherein the primary bioleaching process is carried out at a temperature of from 35° C. to 50° C.  
   
   
       24 . The method according to  claim 22  wherein the at least one base metal is also recovered from a solution produced by the primary bioleach bioleaching process.  
   
   
       25 . The method according to  claim 22  wherein the leach solution is derived from the primary bioleaching process and the thermophilic secondary bioleaching process.  
   
   
       26 . The method according to  claim 22  wherein base metal which is leached during the preleaching step is removed from the concentrate before the primary bioleaching process.  
   
   
       27 . The method according to  claim 22  wherein elemental sulphur which accumulates during the preleach step due to rapid leaching of easily leachable sulphides is removed during the bioleaching stages.  
   
   
       28 . The method according to  claim 22  which includes the step of adjusting the pH of a solution produced in the preleaching step to maximize recovery of the at least one base metal using solvent extraction techniques.  
   
   
       29 . The method according to  claim 28  which includes the step of causing arsenic in the solution to precipitate as ferric arsenate by increasing the pH of the solution to at least 2.  
   
   
       30 . The method according to  claim 28  wherein the pH adjustment is carried out at a temperature of from 60° C. to 80° C.  
   
   
       31 . The method according to  claim 22  wherein the primary bioleaching process is carried out in a series of continuously stirred tank reactors which are operated at a temperature of from 35° C. to 50° C. in the presence of an active mixed culture of mesophilic and moderate thermophilic microorganisms.  
   
   
       32 . The method according to  claim 22  wherein a mixed culture of mesophile and moderate thermophile microorganisms are used to maximize sulphide bioleaching and sulphur biooxidation during the primary bioleaching process.  
   
   
       33 . The method according to  claim 32  wherein the mixed culture contains.  Leptospirillum ferrooxidans  and  Acidithiobacillus caldus.    
   
   
       34 . The method according to  claim 32  wherein the mixed culture of microorganims also contains thermophilic microorganims, which are not effectively active at the temperature range of 35° C. to 50° C.  
   
   
       35 . The method according to  claim 22  wherein the pH of the concentrate during the primary bioleaching processes is controlled at a value of from 1.2 to 1.7.  
   
   
       36 . The method according to  claim 22  which includes the step of supplying air with an oxygen content of from 95% to 98% to the concentrate during at least part of the bioleaching processes.  
   
   
       37 . The method according to  claim 22  which includes the step of removing toxic silver from the primary bioleaching residue.  
   
   
       38 . The method according to  claim 22  wherein the thermophilic secondary bioleaching process is carried out at a temperature of from 65° C. to 80° C. in the presence of active quantities of extreme thermophilic microorganims.  
   
   
       39 . The method according to  claim 22  which includes the step of controlling the pH of the concentrate during the secondary bioleaching process at a value of from 1.0 to 1.7.  
   
   
       40 . The method according to  claim 22  which includes the step of supplying air with a carbon dioxide content of from 1% to 5% to the concentrate during at least part of the bioleaching processes.  
   
   
       41 . The method according to  claim 22  wherein the at least one base metal is copper which is recovered by concentrating the copper and stripping, followed by cathode production by electrowinning.