Process to recover base metals

Abstract

A hydrometallurgical process to leach at least one base metal from one or more base metal sulphide feeds comprising the steps of providing a base metal sulphide feed; processing at least a portion of the feed by roasting to reduce the content of sulphur therein to a predetermined sulphur content level; directing some or all of the processed feed with or without some of the unprocessed feed to an oxidative leach step to carry out an oxidative leach step under conditions sufficient to recover at least a portion of the base metal from the feed, the predetermined sulphur content level being selected so as not to exceed that which is required to provide a source of heat for the oxidative leach step and to provide sufficient sulphate to complex the portion of the base metal being recovered

1 . A hydrometallurgical process to leach at least one base metal from one or more base metal sulphide feeds comprising the steps of: 
 providing a base metal sulphide feed;    processing at least a portion of the feed by roasting to reduce the content of sulphur therein to a predetermined sulphur content level;    directing some or all of the processed feed with or without some of the unprocessed feed to an oxidative leach step to carry out an oxidative leach step under conditions sufficient to recover at least a portion of the base metal from the feed, the predetermined sulphur content level being selected so as not to exceed that which is required to provide a source of heat for the oxidative leach step and to provide sufficient sulphate to complex the portion of the base metal being recovered.    
     
     
         2 . A process as defined in  claim 1  wherein the directing step is carried out to recover substantially all of the recoverable base metals from the feed.  
     
     
         3 . A process as defined in  claim 2  wherein the roasting step occurs under auto thermal conditions.  
     
     
         4 . A process as defined in  claim 1  wherein the processing step includes the step of dividing the base metal sulphide feed into a first portion and a second portion, the first portion being subjected to the roasting step to form a roasted first portion.  
     
     
         5 . A process as defined in  claim 4  wherein the second portion is directed to the oxidative leach step together with at least a portion of the roasted first portion.  
     
     
         6 . A process as defined in  claim 1  wherein the oxidative leach step is carried out in one or more reaction vessels.  
     
     
         7 . A process as defined in  claim 1 , further comprising the step of recovering sulphur dioxide from the roasting step and converting the sulphur dioxide to sulphuric acid.  
     
     
         8 . A process as defined in  claim 4  wherein the roasted first portion is at least partially depleted of sulphide.  
     
     
         9 . A process as defined in  claim 5  wherein the roasted first portion is totally or partially blended with the second portion prior to delivery to the one or more reaction vessels.  
     
     
         10 . A process as defined in  claim 5  wherein the step of directing the feed includes injecting the roasted first portion at different locations in the one or more reaction vessels.  
     
     
         11 . A process as defined in  claim 6  wherein the one or more reaction vessels includes one or more autoclaves and/or one or more agitation tanks.  
     
     
         12 . A process as defined in  claim 6  wherein one or more of the reaction vessels form one or more flow paths, which themselves may be in series or parallel relationship.  
     
     
         13 . A process as defined in  claim 12  wherein one or more of the reaction vessels includes a number of compartments in series along one or more of the flow paths.  
     
     
         14 . A process as defined in  claim 1  wherein the oxidative leach step is carried out in a heap.  
     
     
         15 . A process as defined in  claim 4  further comprising the steps of: 
 collecting a pressure leach slurry from the autoclave; and thereafter    directing an additional portion of the roasted first portion to the pressure leach slurry, after it has been discharged from the autoclave.    
     
     
         16 . A process as defined in  claim 1  wherein the feed includes gold, or platinum group metals and the oxidative leach step generates a slurry temperature within the autoclave ranging from about 190 to about 230 degrees Celsius.  
     
     
         17 . A process as defined in  claim 16  wherein the gold, or platinum group metals are recovered using either a subsequent cyanidation step or a PLATSOL step.  
     
     
         18 . A process as defined in  claim 1  wherein the oxidative leach step generates a slurry temperature within the reaction vessel ranging from about 40 to about 250 degrees Celsius.  
     
     
         19 . A process as defined in  claim 1  wherein the pulp density in the feed to the oxidative leach step ranges from about 5 to about 30 percent.  
     
     
         20 . A process as defined in  claim 4  wherein the first portion ranges from about 5 percent to about 100 percent of the feed.  
     
     
         21 . A process as defined in  claim 1  wherein the one or more base metal sulphide feeds includes a concentrate formed from a flotation step, a gravity concentration step or a gravity/flotation concentration step.  
     
     
         22 . A process as defined in  claim 21  wherein the first and second portions originate from different concentrates.  
     
     
         23 . A process as defined in  claim 16  wherein the oxidative leach step occurs in the presence of sulphuric acid at a concentration not exceeding 80 g/L.