Process for leaching acid-consuming ores

Abstract

A process for leaching low sulphur content ores to release metal values employs two operational steps. In the first step fine, rod-milled elemental sulphur is preconditioned with sulphur oxidizing bacteria which may include Thiobacillus, in an agitated reactor with water. Sulphur produced by this preconditioning process is added to the ore heap during a typical agglomeration process used to adhere small ore particles to the large particles, which increases the permeability of the ore heap. The sulphuric acid produced during the sulphur preconditioning process can be added to the heap during agglomeration as well as by adding some of the acid to the leach solution reservoir. This process results in a homogeneous distribution of the sulphur in the heap so that acid will be produced at the reactive mineral sites and will be consumed immediately, thus maintaining a low acid concentration and a low driving force for the acid/gangue reactions resulting in overall lower acid consumption.

Having disclosed my invention I claim:  
     
         1 . A method of leaching low sulphur content ores to release metal values, comprising: 
 preconditioning finely ground elemental sulphur with bacteria, comprising  Thiobacillus thiooxidans , in a biological reactor so that the hydrophobic sulphur becomes wetted and the bacteria attach themselves to the sulphur surfaces; and    agglomerating the preconditioned sulphur particles throughout a leaching heap with the low sulphur content ores to release metal values.    
     
     
         2 . The method of  claim 1  wherein the bacteria further include  Thiobacillus ferrooxidans.    
     
     
         3 . The method of  claim 1  wherein said finely ground sulphur is produced by rod milling sulphur.  
     
     
         4 . The method of  claim 3  wherein the sulphur is rod milled such that 1.9 kilograms of sulphur in 1 liter of water for 15 minutes produces a product of approximately 50%-400 mesh.  
     
     
         5 . The method of  claim 1  further including adding a bacteria nutrient to the preconditioning process.  
     
     
         6 . The method of  claim 1  further including adding  Thiobacillus ferrooxidans  to the agglomerated leaching heap.  
     
     
         7 . The method of  claim 1  wherein the preconditioning process is conducted for 12-48 hours.  
     
     
         8 . The method of  claim 1  further including adding acidic bioleach solution produced during the preconditioning process to the ore during agglomeration to partially satisfy the acid demand of the ore.  
     
     
         9 . The method of  claim 1  further including adding acid bioleach solution produced during preconditioning to the leach solution reservoir to partially satisfy the acidic demand of the ore.  
     
     
         10 . The method of  claim 6  including controlling the pH in the heap in the range of 1.8-2.4 so that the  Thiobacillus ferrooxidans  can rapidly oxidize any metal sulphides present in the ore.