Acid Recovery

Abstract

Nickel is recovered from a nickeliferous ore, where the ore includes impurities in the form of metals other than nickel and cobalt. The ore is subjected to atmospheric leaching using sulphuric acid to dissolve nickel and cobalt from the ore and produce a leach liquor. The sulphuric acid is regenerated by rapidly heating the leach liquor to a temperature in excess of 120° C. to produce a slurry including sulphuric acid and precipitated oxides of impurities present in the leach liquor, and separating the precipitated oxides from the slurry to produce a clarified acid rich liquor stream for recycle to leaching.

1 . In a method of recovering nickel from a nickeliferous ore, wherein the ore includes impurities in the form of metals other than nickel and cobalt, and wherein the ore is subjected to atmospheric leaching using sulphuric acid to dissolve nickel and cobalt from the ore and produce a leach liquor, the sulphuric acid is regenerated using a method comprising:
 a) rapidly heating the leach liquor to a temperature in excess of 120° C. to produce a slurry comprising sulphuric acid and precipitated oxides of impurities present in the leach liquor; and,   b) separating the precipitated oxides from the slurry of step a) to produce a clarified acid rich liquor stream for recycle to leaching.   
     
     
         2 . The method of regenerating sulphuric acid of  claim 1 , wherein step a) is conducted at a temperature in the range of 120° C. to 220° C. to initiate the precipitation of oxides of impurities by hydrolysis. 
     
     
         3 . The method of regenerating sulphuric acid of  claim 1 , wherein step a) is conducted at a temperature in the range of 180° C. to 220° C. to initiate the precipitation of oxides of impurities by hydrolysis. 
     
     
         4 . The method of regenerating sulphuric acid of  claim 1 , wherein the leach liquor of step a) has at least 10 g/L of dissolved iron. 
     
     
         5 . The method of regenerating sulphuric acid of  claim 1 , wherein the leach liquor of step a) has at least 25 g/L of dissolved iron. 
     
     
         6 . The method of regenerating sulphuric acid of  claim 1 , wherein the precipitated oxides are hematite or alunite. 
     
     
         7 . The method of regenerating sulphuric acid of  claim 1 , wherein the leach liquor of step a) has an initial free acid concentration of at least 10 g/L free acid. 
     
     
         8 . The method of regenerating sulphuric acid of  claim 1 , wherein step a) is conducted using an autoclave which operates in combination with one or more pre-heating stages arranged to receive steam that is generated from cooling or “flashing” when the slurry discharged from the autoclave is depressurized. 
     
     
         9 . The method of regenerating sulphuric acid of  claim 8 , wherein the autoclave includes one or more steam injection points arranged received fresh steam to control the temperature within the autoclave in use. 
     
     
         10 . The method of regenerating sulphuric acid of  claim 1 , wherein the leach liquor of step a) is a pregnant leach liquor. 
     
     
         11 . The method of regenerating sulphuric acid of  claim 10 , wherein the pregnant leach liquor is subjected to a metals recovery process to recover nickel and cobalt from the pregnant leach liquor and form a barren leach liquor. 
     
     
         12 . The method of regenerating sulphuric acid of  claim 11 , wherein the metals recovery process is selected from the group consisting of sulphide precipitation with hydrogen sulphide gas, solvent extraction, ion exchange, and combinations thereof. 
     
     
         13 . The method of regenerating sulphuric acid of  claim 11 , wherein the metals recovery process is sulphide precipitation conducted on a pregnant leach liquor having a level of acidity of less than 10 g/L free acid at a temperature in the range of 80° C. to 120° C. 
     
     
         14 . The method of regenerating sulphuric acid of  claim 10 , wherein a neutralizing agent is added to a bypass stream of the clarified acid-rich liquor stream of step b) to achieve a target free acid content in a neutralized pregnant liquor stream within the range of 1 g/L to 10 g/L of free acid. 
     
     
         15 . The method of regenerating sulphuric acid of  claim 14 , wherein the neutralized pregnant liquor stream is directed to a metals recovery process. 
     
     
         16 . The method of regenerating sulphuric acid of  claim 14 , wherein the neutralizing agent is calcium carbonate. 
     
     
         17 . The method of regenerating sulphuric acid of  claim 14 , wherein the portion of clarified acid-rich leach liquor of step b) which forms the bypass stream is determined by ensuring that the target amount of nickel recovered using the metals recovery process is equal to the amount of nickel being leached per pass during atmospheric leaching. 
     
     
         18 . The method of regenerating sulphuric acid of  claim 1 , wherein the leach liquor of step a) is a barren leach liquor. 
     
     
         19 . The method of regenerating sulphuric acid of  claim 1 , wherein atmospheric leaching is conducted using a heap leaching process.