Bacterial leaching of copper and zinc without iron leaching

Abstract

Thiobacillus ferrooxidans and Thiobacillus thiooxidans play major roles in bacterial leaching of metals from ores and tailings through their oxidative action on ferrous iron (Fe 2+ ) and sulfide or sulfur (S 0 ). We have studied the effects of various inhibitors such as cyanide, azide and anions (phosphate, nitrate, chloride) on Fe 2+ or S 0 oxidation by resting cells, on Fe 2+ or S 0 as an energy source for growth and finally on leaching of Fe or Zn from a sample containing pyrite (FeS 2 ) and sphalerite (ZnS). All of these inhibitors inhibited Fe 2+ oxidation more strongly than S 0 oxidation and generally stopped the growth on Fe 2+ at lower concentrations than on S 0 . All three anions inhibited the leaching of Fe more strongly than Zn leaching, but potassium phosphate was the most selective. In the leaching experiments with T. ferrooxidans and T. thiooxidans either singly or combined, phosphate at 10-100 mM reduced the Fe leaching almost completely (by 90-over 95%) without affecting the Zn leaching (0-40%). Furthermore, the method can be used for recovery of other minerals from other sulfide ores.

1 . A method of leaching zinc from ore comprising: 
 providing a quantity of ore including pyrite (FeS 2 ) and sphalerite (ZnS);    providing iron-oxidizing or sulfur-oxidizing bacteria, said bacteria being capable of bacterial solubilization of pyrite and sphalerite to iron and zinc respectively;    providing a bacterial growth medium capable of supporting growth of the iron-oxidizing or sulfur-oxidizing bacteria;    supplementing the growth medium with an inhibitor that inhibits pyrite solubilization but does not inhibit sphalerite solubilization or inhibits sphalerite solubilization to a lesser extent than pyrite solubilization;    placing the ore and the iron-oxidizing or sulfur-oxidizing bacteria in the growth medium; and    incubating the bacteria and the ore under conditions permitting solubilization of the sphalerite to zinc.    
     
     
         2 . The method according to  claim 1  wherein the inhibitor is an anion.  
     
     
         3 . The method according to  claim 2  wherein the anion is selected from the group consisting of: phosphate; nitrate; chloride; and mixtures thereof.  
     
     
         4 . The method according to  claim 1  wherein the inhibitor is a respiratory inhibitor.  
     
     
         5 . The method according to  claim 4  wherein the respiratory inhibitor is selected from the group consisting of: azide; cyanide; and mixtures thereof.  
     
     
         6 . The method according to  claim 1  wherein the inhibitor is selected from the group consisting of phosphate, nitrate, chloride, azide, cyanide and combinations thereof.  
     
     
         7 . The method according to  claim 1  wherein the ore is composed of tailings.  
     
     
         8 . The method according to  claim 1  wherein the iron or sulfur-oxidizing bacteria are selected from the group consisting of:  Thiobacillus ferrooxidans; Thiobacillus thiooxidans;  and a mixture thereof.  
     
     
         9 . The method according to  claim 1  wherein the inhibitor is phosphate or chloride.  
     
     
         10 . The method according to  claim 9  wherein the phosphate or chloride is in the bacterial growth medium at a concentration of 10-100 mM.  
     
     
         11 . The method according to  claim 9  wherein the phosphate or chloride is a potassium salt.  
     
     
         12 . The method according to  claim 11  wherein the potassium salt is in the bacterial growth medium at a concentration of 10-100 mM.  
     
     
         13 . The method according to  claim 1  wherein the bacterial growth medium comprises: 
 0.4 g/L (NH 4 ) 2 SO 4 ;  
 0.1 g/L K 2 HPO 4 ;  
 0.4 g/L MgSO 4 .7H 2 O; and  
 10-100 mM phosphate or chloride,  
 adjusted to pH 2.3 with H 2 SO 4 .  
 
     
     
         14 . A growth media for iron-oxidizing or sulfur-oxidizing bacteria for bacterial leaching of a mineral from ore without iron leaching comprising: 
 0.4 g/L (NH 4 ) 2 SO 4 ;    0.1 g/L K 2 HPO 4 ;    0.4 g/L MgSO 4 .7H 2 O; and    10-100 mM phosphate or chloride,    adjusted to pH 2.3 with H 2 SO 4 .    
     
     
         15 . A method of leaching a mineral from ore comprising: 
 providing a quantity of ore including an iron ore and a sulfide mineral of a metal;    providing iron-oxidizing or sulfur-oxidizing bacteria, said bacteria being capable of bacterial solubilization of the iron ore and the sulfide mineral to iron and the metal respectively;    providing a bacterial growth medium capable of supporting growth of the iron or sulfur-oxidizing bacteria;    supplementing the growth medium with an inhibitor that inhibits iron solubilization but does not inhibit solubilization of the sulfide mineral or inhibits solubilization of the sulfide mineral to a lesser extent than iron solubilization;    placing the ore and the iron or sulfur-oxidizing bacteria in the growth medium; and    incubating the ore and the bacteria under conditions permitting solubilization of the sulfide mineral to the metal.    
     
     
         16 . The method according to  claim 15  wherein the ore comprises pyrite, sphalerite, chalcopyrite, covellite (CuS), chalcocite (Cu 2 S), millerite (NiS), pentlandite ((Ni or Co)Fe) 9 S 8  or mixtures thereof.  
     
     
         17 . The method according to  claim 15  wherein the metal is selected from the group consisting of zinc, copper and mixtures thereof.  
     
     
         18 . The method according to  claim 15  wherein the inhibitor is selected from the group consisting of phosphate, nitrate, chloride and mixtures thereof.  
     
     
         19 . The method according to  claim 15  wherein the inhibitor stimulates solubilization of the sulfide mineral.  
     
     
         20 . The method according to  claim 15  wherein the solubilization of metals occurs at different times, permitting the separate recovery of each metal.