Process for recovery of metal values from materials containing arsenic and/or antimony

Abstract

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 such as sulphide ore or concentrate is disclosed. In one form the method comprises 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 concentration of free acid generated during the pressure oxidation step and promote the formation of pH-stable iron (III) sulphate products, thereby forming a slurry comprising a metal value-containing leach solution and a solid leach residue containing pH-stable iron (III) sulphate products and environmentally stable iron-arsenic and/or iron-antimony products; (c) separating the metal value-containing leach solution from the solid leach residue; (d) recovering the metal value (s) from the metal value-containing leach solution; and (e) recovering precious metal values, if present, in the solid leach residue by cyanide leaching.

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, the process 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 concentration of free acid generated during the pressure oxidation step and promote the formation of pH-stable iron(III) sulphate products, thereby forming a slurry comprising a metal value-containing leach solution and a solid leach residue containing pH-stable iron(III) sulphate products and environmentally stable iron-arsenic and/or iron-antimony products;   (c) separating the metal value-containing leach solution from the solid leach residue;   (d) recovering the metal value(s) from the metal value-containing leach solution; and   (e) recovering precious metal values, if present, in the solid leach residue by cyanide leaching.   
   
   
       2 . A 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 according to  claim 1 , wherein said metal value-bearing material is a copper-bearing material containing arsenic and/or antimony and a source of sulphate ions. 
   
   
       4 . A method according to  claim 1 , wherein said source of sulphate ions is a sulphide ore or ore concentrate. 
   
   
       5 . A method according to  claim 1 , wherein said at least one component selected to decrease the effective concentration of free acid generated during the pressure oxidation step and promote the formation of pH-stable iron(III) sulphate products includes an iron-containing component. 
   
   
       6 . A method according to  claim 1 , wherein said at least one component selected to decrease the effective concentration of free acid generated during the pressure oxidation step and/or promote the formation of pH-stable iron(III) sulphate products further includes a chemical agent. 
   
   
       7 . A method according to  claim 5 , wherein said iron-containing component provides a source of soluble iron and is added to the feed stream before pressure oxidation such that the molar ratio of iron to arsenic and/or antimony in the feed stream is greater than about 1:1, preferably greater than about 2:1 and more preferably greater than about 4:1. 
   
   
       8 . A method according to  claim 5 , wherein said iron-containing component includes at least one component selected from pyrite concentrate, calcined pyrite concentrate and any recovered iron-containing residues formed during a pressure oxidation process. 
   
   
       9 . A method according to  claim 8 , wherein said calcined pyrite concentrate is substantially free of alpha Fe 2 O 3  and contains one or more compounds selected from FeS, FeO, Fe 3 O 4  and gamma Fe 2 O 3 . 
   
   
       10 . A method according to  claim 1 , wherein said at least one component selected to decrease the effective concentration of free acid generated during the pressure oxidation step and promote the formation of pH-stable iron(III) sulphate products includes a chemical agent. 
   
   
       11 . A method according to  claim 6 , wherein said chemical agent includes at least one material sourced from limestone or lime, or one or more soluble salts containing magnesium, sodium, potassium and/or ammonium. 
   
   
       12 . A method according to  claim 11 , wherein said chemical agent is added in an amount sufficient to promote the formation of a jarosite phase containing sodium, potassium and/or ammonium and to limit the formation of any pH-unstable or meta-stable solid ferric sulphate products during pressure oxidation. 
   
   
       13 . A method according to  claim 11 , wherein said one or more soluble salts containing magnesium includes one or more compounds selected from magnesium oxide, magnesium hydroxide, magnesium carbonate (magnesite) and magnesium-calcium carbonate (dolomite). 
   
   
       14 . A method according to  claim 1 , wherein said at least one component is added to the feed stream prior to step (b). 
   
   
       15 . A method according to  claim 1 , wherein said feed stream is an ore or ore concentrate containing said metal values, and wherein said metal values include a base metal selected from the group consisting of copper, nickel, cobalt, zinc and platinum. 
   
   
       16 . A method according to  claim 1 , wherein said feed stream is an ore or ore concentrate containing said metal values, and wherein said metal values include a precious metal of gold and/or silver. 
   
   
       17 . 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 of metal value-containing material containing arsenic and/or antimony and a source of sulphate ions;   (b) subjecting the feed stream to acidic oxidative conditions under elevated temperature and pressure conditions in the presence of at least one iron-containing compound and/or at least one chemical agent, wherein the iron-containing compound and/or chemical agent is selected to decrease the effective free acid concentration generated during the pressure oxidation step and promote the formation of pH-stable iron(III) sulphate products, thereby forming a metal value-containing solution and a solid leach residue containing pH-stable iron(III) sulphate products and environmentally stable iron-arsenic and/or iron-antimony products;   (c) separating the metal value-containing solution from the solid leach residue;   (d) recovering the metal value(s), if desired, from the metal value-containing solution; and   (e) recovering precious metal values, if present, in the solid leach residue by cyanide leaching.   
   
   
       18 . A method according to  claim 17 , wherein the metal value-containing solution and solid leach residue obtained 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 step (c). 
   
   
       19 . A process for recovery of metal values from a metal value-bearing material containing arsenic and/or antimony and a source of sulphate ions, the process 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 iron-containing compound and/or at least one chemical agent, wherein the iron-containing compound and/or chemical agent is selected to decrease the effective concentration of free acid generated during the pressure oxidation step and promote the formation of pH-stable iron(III) sulphate products, thereby forming a slurry comprising a metal value-containing leach solution and a solid leach residue containing pH-stable iron(III) sulphate products and environmentally stable iron-arsenic and/or iron-antimony products;   (c) maintaining the slurry obtained from step (b) 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;   (d) separating the metal value-containing leach solution from the solid leach residue;   (e) recovering the metal value(s) from the metal value-containing leach solution; and   (f) recovering precious metal values, if present, in the solid leach residue by cyanide leaching.   
   
   
       20 . A method for recovering one or more metal values from a metal value-containing feed material containing arsenic and/or antimony, the method comprising the steps of:
 (a) providing the feed material to a pressure oxidation reactor;   (b) subjecting the feed material within the pressure oxidation reactor to pressure oxidation in the presence of at least one component selected to decrease the amount of free acid generated during the pressure oxidation and/or promote the formation of pH-stable iron(III) sulphate products, to form a slurry comprising:   (i) a metal value-containing solution; and   (ii) a solid leach residue comprising the pH-stable iron(III) sulphate products and environmentally stable iron-arsenic and/or iron-antimony products;   (c) separating the metal value-containing solution from the solid leach residue; and   (d) recovering the metal values from the metal value-containing solution.   
   
   
       21 . A 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 pH 2. 
   
   
       22 . A pressure oxidation process for recovering one or more metal values from a metal value-bearing material containing arsenic and/or antimony, comprising the step of providing to the process at least one component selected to promote the formation of solids that are sufficiently stable under pressure oxidation conditions such that the recovery of the one or more metal values is enhanced. 
   
   
       23 . A process according to  claim 22 , wherein said at least one component is selected to promote the formation of solids that do not significantly bind said one or more metal values. 
   
   
       24 . A process according to  claim 22 , wherein the at least one component is selected to promote the formation of solids capable of binding arsenic and/or antimony. 
   
   
       25 . A process according to  claim 22 , wherein said one or more metal values include a base metal and a precious metal and wherein said at least one component promotes the formation of solids that are stable under alkaline conditions of cyanidation processes used to recover precious metal values following the recovery of base metal values. 
   
   
       26 . A process according to  claim 22 , wherein said at least one component is an iron-containing compound. 
   
   
       27 . A process according to  claim 22 , wherein said at least one component further includes at least one chemical agent. 
   
   
       28 . A process according to  claim 22 , wherein said at least one component is a chemical agent. 
   
   
       29 . 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 of metal value-containing material containing arsenic and/or antimony and a source of sulphate ions;   (b) subjecting the feed stream to acidic oxidative conditions under elevated temperature and pressure conditions to form a metal value-containing solution and a solid leach residue;   (c) maintaining 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 step (d) to promote the formation of pH-stable iron(III) sulphate products;   (d) separating the metal value-containing solution from the solid leach residue;   (e) recovering the metal value(s), if desired, from the metal value-containing solution; and   (f) recovering precious metal values, if present, in the solid leach residue by cyanide leaching.