Process for Leaching Lateritic Ore at Atmospheric Pressure

Abstract

An atmospheric leaching process in the recovery of nickel and cobalt from a lateritic ore, the lateritic ore including a low magnesium ore fraction and a high magnesium ore fraction, the process including the steps of: (a) forming an aqueous pulp of the lateritic ore, (b) leaching the aqueous pulp with a concentrated mineral acid at atmospheric pressure to produce a slutty containing a pregnant leach liquor and a leach residue, (c) treating the pregnant leach liquor either separately or as part of the slurry to recover dissolved nickel and cobalt therefrom, leaving a magnesium barren solution, (d) treating the magnesium containing solution to recover a magnesium containing salt therefrom.

1 . An atmospheric leaching process in the recovery of nickel and cobalt from a lateritic ore, said lateritic ore including a low magnesium ore fraction and a high magnesium ore fraction, said process comprising:
 (a) forming an aqueous pulp of said lateritic ore;   (b) leaching said aqueous pulp in a single process stage with concentrated sulphuric acid at atmospheric pressure to produce a slurry containing a pregnant leach liquor and a leach residue;   (c) treating the pregnant leach liquor either separately or as part of said slurry to recover dissolved nickel and cobalt therefrom, leaving a magnesium containing barren solution;   (d) treating said magnesium containing barren solution to recover a magnesium sulphate therefrom;   (e) treating said magnesium sulphate to recover SO 2  gas and a magnesium compound selected from MgO, Mg(OH) 2  and MgCO 3 , said magnesium compound being recyclable as a neutralising agent for treatment of at least one of the pregnant leach liquor and the barren solution; and   (f) forming sulphuric acid from said SO 2  gas for recycling to said leaching step (b).   
     
     
         2 . The process of  claim 1  further including the step of increasing the pH of at least one of the pregnant leach liquor and the barren solution to produce an iron containing precipitate. 
     
     
         3 . The process of  claim 1 , wherein both the low and high magnesium fractions are leached simultaneously during said leaching step (b). 
     
     
         4 . The process of  claim 1 , wherein the low and high magnesium fractions are leached sequentially during said leaching step (b). 
     
     
         5 . The process of  claim 1 , wherein the leaching step (b) is conducted at a temperature above about 60° C. 
     
     
         6 . The process of  claim 5 , wherein the temperature is at least about 80° C. 
     
     
         7 . The process of  claim 1 , wherein the ratio of high magnesium ore to low magnesium ore is in a dry ratio of from about 0.5 to about 1.3. 
     
     
         8 . The process of  claim 2 , wherein the step of increasing pH further comprises adding a neutralising agent to the at least one of the pregnant leach liquor and the barren solution to increase the pH to a value of approximately 3 or above. 
     
     
         9 . The process of  claim 2  wherein the step of increasing pH further comprises adding an oxidising agent in order to oxidise any residual Fe 2+  to Fe 3+  and cause its precipitation as a hydroxide. 
     
     
         10 . The process of  claim 9 , wherein the oxidising agent is air. 
     
     
         11 . The process of  claim 1 , wherein the pregnant leach liquor is treated to recover at least one of nickel and cobalt using at least one of ion exchange, resin-in-pulp, direct recovery by solvent extraction, mixed hydroxide precipitation and mixed sulphide precipitation. 
     
     
         12 . The process of  claim 11 , wherein the pregnant leach liquor is treated to recover nickel and cobalt using mixed hydroxide precipitation or mixed sulphide precipitation. 
     
     
         13 . The process of  claim 1 , wherein the magnesium sulphate is treated to recover magnesium. 
     
     
         14 . The process of  claim 1 , wherein the magnesium sulphate is subjected to calcination to produce SO 2  gas and at least one of MgO and MgCO 3 . 
     
     
         15 . The process of  claim 1 , wherein the magnesium compound is used as a neutralising agent in step (c). 
     
     
         16 . The process of  claim 1 , wherein the magnesium compound is used to precipitate at least one of iron, aluminium, and manganese from at least one of the pregnant leach liquor from (b) and the barren solution from (c).