Process and apparatus for recovery of cyanide and metals

Abstract

Disclosed is a process for recovery of cyanide and metals from a liquor containing complexes of cyanide and metal typically generated by a metallurgical or industrial process. The process involves electrochemical dissociation of the metal-cyanide complex and electrowinning of the metal while free cyanide generated in the process is recovered in a membrane treatment step for re-use in a metallurgical process utilising it. An electrochemical apparatus, which may be used in the process, forms a further aspect of the invention. A membrane process alone, for separation of cyanide, from liquors containing cyanide complexes is a further aspect of the invention.

The claims defining the invention are as follows:  
     
         1 . A process for recovery of cyanide and metals from a liquor containing a compound or complex of cyanide and metal generated by a metallurgical process including the steps of: 
 (a) electrochemical treatment of said liquor in an electrochemical cell for electrochemically dissociating said compound or complex present in an electrolyte steam;    (b) recovering the metal by electrowinning;    (c) passing electrolyte through a membrane treatment step for recovering a free cyanide stream; and, optionally, (d) recycling the free cyanide stream for recovery or re use.    
     
     
         2 . The process of  claim 1 , wherein said complex of cyanide and metal is a base metal-cyanide complex.  
     
     
         3 . The process of  claim 2 , wherein said complex of cyanide and metal is a copper-cyanide complex.  
     
     
         4 . The process of  claim 1 , wherein said complex of cyanide and metal is a precious metal-cyanide complex.  
     
     
         5 . The process of  claim 1 , wherein said membrane treatment step is pressure or diffusion driven for the separation of free cyanide from cyanide complexes and metal ions.  
     
     
         6 . The process of any one of the preceding claims wherein thiocyanide is present in said liquor and is oxidised to form free cyanide at an anode during electrochemical treatment of said liquor in said electrochemical cell.  
     
     
         7 . The process of any one of the preceding claims in which metal powder formed at the cathode is recovered by solid-liquid separation.  
     
     
         8 . The process of  claim 6 , wherein solid-liquid separation is conducted in a hydrocyclone.  
     
     
         9 . The process of any one of the preceding claims further including the step of concentrating cyanide permeate for recycling or re-use.  
     
     
         10 . The process of  claim 9 , including a membrane process for concentrating cyanide.  
     
     
         11 . The process of any one of the preceding claims wherein said membrane treatment step for recovering free cyanide is conducted within said electrochemical cell.  
     
     
         12 . The process of any one of  claims 1  to  10  wherein said membrane treatment step for recovering free cyanide is conducted externally of said electrochemical cell.  
     
     
         13 . An electrochemical apparatus for recovering metals by electrowinning from a low concentration metal containing solution, said apparatus including: 
 (a) a housing including at least one electrochemical cell and having inlet and outlet means to enable electrolyte to pass through each cell;    (b) an anode for each cell;    (c) a cathode for each cell;    (d) flow circulating means for circulating a high velocity turbulent flow of electrolyte through each cell; and    (e) an electrical connection between anode and cathode of each cell for completing an electrical circuit between them.    
     
     
         14 . The electrochemical apparatus of  claim 13 , wherein a baffle means is located between the electrodes of each cell.  
     
     
         15 . The electrochemical apparatus of  claim 13  wherein said baffle means is an electrode, preferably the anode.  
     
     
         16 . The electrochemical apparatus of any one of  claims 13  to  15 , wherein said inlet means includes one or more inlet port means located to create a flow of electrolyte past the electrodes.  
     
     
         17 . The electrochemical apparatus of any one of  claims 13  to  16 , wherein said outlet means includes one or more outlet port means.  
     
     
         18 . The electrochemical apparatus of any one of  claims 14  to  16 , wherein said port means are offset from a centre axis of each cell.  
     
     
         19 . The electrochemical apparatus of any one of  claims 13  to  17 , wherein said anode and cathode of each cell are supported by a supporting frame having opposed frame members provided with respective inlet and outlet port means communicating each cell with inlet and outlet manifolds, said supporting frame members having internal curved walls forming part of each cell.  
     
     
         20 . The electrochemical apparatus of any one of  claims 13  to  19  wherein each cell includes a membrane for separation of species formed during electrowinning.  
     
     
         21 . A process for treatment of an aqueous cyanide or thiocyanide bearing stream including a membrane treatment step for separating free cyanide, a cyanide complex or a thiocyanide from said stream.  
     
     
         22 . A process for recovery of cyanide and metals from a liquor containing a compound or complex of cyanide and metal comprising the step of electrochemically treating said liquor in an electrochemical cell for electrochemically dissociating said complex to form free cyanide.