Processing of Metal Values from Concentrates

Abstract

The present invention relates to an improved method for the recovery of metal values, in particular copper and gold, from a metal value-bearing material containing arsenic and/or antimony and a source of sulphate ions, by means of a high temperature pressure oxidation process followed by cyanidation of the resultant high temperature pressure oxidation residue.

1 . A method for the recovery of metal values from a metal value-bearing material containing arsenic and/or antimony and a source of sulphate ions, comprising the steps of:
 (a) providing a feed stream comprising a metal value-bearing material containing arsenic and/or antimony and a source of sulphate ions;   (b) subjecting the feed stream to oxidative conditions under elevated temperature and pressure conditions thereby forming a slurry comprising a metal value-containing leach solution and a solid residue;   (c) separating the metal value-bearing leach solution from the solid leach residue;   (d) recovering the metal value(s) from the metal value-bearing leach solution; and   (e) recovering any precious metal values in the solid leach residue by cyanide leaching.   
   
   
       2 . The method according to  claim 1 , wherein the slurry from step (b) is maintained at a temperature in the range of from about 70° C. to about 100° C. for a period in the range of from about 15 minutes to about 4 hours prior to separating the metal value-containing solution from the solid leach residue. 
   
   
       3 . A method for the recovery of metal values from a metal value-bearing material containing arsenic and/or antimony and a source of sulphate ions, comprising the steps of:
 (a) providing a feed stream comprising a metal value-bearing material containing arsenic and/or antimony and a source of sulphate ions;   (b) subjecting the feed stream to oxidative conditions under elevated temperature and pressure conditions in the presence of at least one component selected to decrease the effective free acid concentration during the pressure oxidation step and promote the formation of pH-stable iron(IH) sulphate products, thereby forming a slurry comprising:   (i) a metal value-containing leach solution and a solid residue containing pH-stable iron (Ill) sulphate products; and   (ii) environmentally stable iron-arsenic and iron-antimony products,   (c) separating the metal value-bearing leach solution from the solid leach residue;   (d) recovering the metal value(s) from the metal value-containing leach solution; and   (e) recovering any precious metals in the solid leach residue by cyanide leaching.   
   
   
       4 . The method according to  claim 3 , wherein the oxidation conditions in the vessel used in step (b) provide the slurry, in at least a first part of the vessel, with an Oxygen Reduction Potential (ORP) of below about 425 mV, when measured with a standard platinum (Pt) electrode against a standard silver/silver chloride (Ag/AgCl) electrode, and a soluble ferric to ferrous molar ratio of below about 1:1, and wherein the oxidation conditions provide the slurry, in at least a second part of the vessel, with an OPR of above about 425 mV and the soluble ferric to ferrous molar ratio of above about 1:1, to facilitate the precipitation of the pH-stable iran(HI) products and oxidation of the sulphide sulphur to sulphate. 
   
   
       5 . The method according to  claim 4 , wherein the ORP in the reaction slurry in said first part of the vessel is below about 400 mV. 
   
   
       6 . The method according to  claim 4 , wherein said first part of the vessel encompasses up to about 50% of the total volume of the vessel used in step (b). 
   
   
       7 . The method according to  claim 4 , wherein said second part of the vessel encompasses up to about 50% of the total volume of the vessel used in step (b). 
   
   
       8 . The method according to  claim 4 , wherein the oxidation conditions are controlled by limiting the rate of oxygen injection into the first and/or second part of the vessel. 
   
   
       9 . The method according to  claim 4 , wherein the vessel of step (b) is a pressure vessel, preferably an autoclave, and more preferably, a substantially continuously operated autoclave. 
   
   
       10 . The method according to  claim 3 , wherein the slurry from step (b) is maintained at a temperature in the range of from about 70° C. to about 100° C. for a period in the range of from about 15 minutes to about 4 hours prior to separating the metal value-containing solution from the solid leach residue. 
   
   
       11 . A method for the recovery of metal values from a metal value-containing feed material containing arsenic and/or antimony and a source of sulphate ions, the method comprising the steps of:
 (a) providing a feed stream comprising a metal value-bearing material containing arsenic and/or antimony and a source of sulphate ions;   (b) subjecting the feed stream to oxidative conditions under elevated temperature and pressure conditions in the presence of certain iron-containing compounds and/or other chemical agents selected to decrease the effective free acid concentration during the pressure oxidation step and promote the formation of pH-stable iron(III) sulphate products, thereby forming a slurry comprising:
 (i) a metal value-containing leach solution and a solid residue containing pH-stable iron (III) sulphate products; and 
 (ii) environmentally stable iron-arsenic and iron-antimony products; 
   (c) separating the metal value-bearing leach solution from the solid leach residue;   (d) recovering the metal value (s) from the metal value-containing leach solution; and   (e) recovering any precious metal values in the solid leach residue by cyanide leaching.   
   
   
       12 . The method according to  claim 11 , wherein the oxidation conditions in the vessel used in step (b) provide the slurry, in at least a first part of the vessel, with an Oxygen Reduction Potential (ORP) of below about 425 mV, when measured with a standard platinum (Pt) electrode against a standard silver/silver chloride (Ag/AgCl) electrode, and a soluble ferric to ferrous molar ratio of below about 1:1, and wherein the oxidation conditions provide the slurry, in at least a second part of the vessel, with an OPR of above about 425 mV and the soluble ferric to ferrous molar ratio of above about 1:1, to facilitate the precipitation of the pH-stable iron(III) products and oxidation of the sulphide sulphur to sulphate. 
   
   
       13 . The method according to  claim 12 , wherein the ORP in the reaction slurry in said first part of the vessel is below about 400 mV. 
   
   
       14 . The method according to  claim 12 , wherein said first part of the vessel encompasses up to about 50% of the total volume of the vessel used in step (b). 
   
   
       15 . The method according to  claim 12 , wherein said second part of the vessel encompasses up to about 50% of the total volume of the vessel used in step (b). 
   
   
       16 . The method according to  claim 12 , wherein the oxidation conditions are controlled by limiting the rate of oxygen injection into the first and/or second part of the vessel. 
   
   
       17 . The method according to  claim 12 , wherein the vessel of step (b) is a pressure vessel, preferably an autoclave, and more preferably, a substantially continuously operated autoclave. 
   
   
       18 . The method according to  claim 11 , wherein the slurry from step (b) is maintained at a temperature in the range of from about 70° C. to about 100° C. for a period in the range of from about 15 minutes to about 4 hours prior to separating the metal value-containing solution from the solid leach residue. 
   
   
       19 . The method according to  claim 11 , wherein the chemical agents added to the material in the feed stream include metal salts, preferably soluble alkali metal ion salts, more preferably sodium, potassium and ammonium salts. 
   
   
       20 . The method according to  claim 11 , wherein the chemical agents added to the material in the feed stream include a source of soluble sulphate salts, preferably magnesium and/or zinc sulphate. 
   
   
       21 . The method according to  claim 20 , wherein the source of soluble sulphate salts include carbonate and/or hydroxide salts of magnesium and/or zinc formed in situ under the oxidative conditions of step (b) or by the leaching of zinc sulphide minerals present in the material in the feed stream. 
   
   
       22 . The method according to  claim 11 , wherein the chemical agents added to the material in the feed stream include a base and/or carbonate, preferably limestone or lime. 
   
   
       23 . The method according to  claim 3 , wherein the pH stable iron(IH) sulphate products formed are composed of one or more jarosite-type minerals including hydronium, sodium, potassium or ammonium jarosite, preferably hydronium and/or sodium jarosite. 
   
   
       24 . The method according to  claim 1 , wherein the metal value-bearing material containing arsenic and/or antimony is a copper-bearing material containing arsenic and/or antimony, preferably a copper sulphide containing arsenic and/or antimony, and more preferably a mixed copper-gold sulphide containing arsenic and/or antimony. 
   
   
       25 . The method according to  claim 1 , wherein the metal value-containing material is an ore or ore concentrate that contains arsenic and/or antimony, and includes one or more recoverable metals selected from the group consisting of copper, nickel, cobalt, zinc, palladium and platinum. 
   
   
       26 . The method according to  claim 1 , wherein the metal value-containing material is an ore or ore concentrate that includes one or more recoverable precious metals, preferably gold and silver. 
   
   
       27 . The method according to  claim 1 , wherein die material in the feed stream includes iron compounds, preferably iron (IU) compounds. 
   
   
       28 . The method according to  claim 27 , wherein the molar ratio of Fe:(As+Sb) in the material in the feed stream in step (b) is greater than about 1:1, and preferably greater than about 2:1. 
   
   
       29 . The method according to  claim 27 , wherein the iron compounds are derived from pyrite, preferably calcined pyrite produced under conditions that favour the formation of more solubilzable forms of iron compounds including FeS, FeO, Fe 3 O 4  or gamma-Fe 2 O j  over the formation of alpha-Fe 2 O 3 . 
   
   
       30 . The method according to  claim 1 , wherein prior to the step of recovering the metal value(s) from the metal value-containing leach solution, the pH is reduced to a pH of less than about pH2.