Electrochemical removal of dissociable cyanides
The method of the invention provides means of destroying highly stable metal cyanide ions found in a solution, and converting the cyanide to harmless by-products. Contrary to conventional methods which merely complex the cyanide into a mechanically or physically removable complex, the present method destroys the cyanide found in the sample. The invention is directed to a method of destroying cyanide comprising providing a highly alkaline solution containing a metal cyanide ions; and subjecting the solution to electro-oxidation.
1. A method of destroying cyanide comprising:
providing a solution containing metal cyanide ions, said solution being at a pH between 9 and 11.5; and
subjecting the solution to electro-oxidation in an electrolysis cell thereby destroying the metal cyanide ions and forming non-cyanidric compounds,
said cell comprising a metal anode and a metal cathode, wherein said metal anode comprises copper, and wherein the electro-oxidation is performed under conditions to provide the formation of a Cu containing passivation layer on the copper of the metal anode.
2. The method according to claim 1 , wherein said Cu containing passivation layer is a compound or complex selected from one or more of a compound or complex of Cu and oxygen; or a compound or complex of Cu and the anion of a weak acid.
3. The method according to claim 1 , wherein the electro-oxidation is performed at an applied anode current density of from between 1.0 and 7.5 mA/cm 2 .
4. The method according to claim 3 , wherein the electro-oxidation is performed at an applied anode current density of from between 1.0 and 7 mA/cm 2 .
5. The method according to claim 1 , wherein the metal anode is selected from the group consisting of a solid Cu electrode, an electrode comprising Cu in the form of a wire mesh, an electrode comprising Cu in the form of a reticulated foam, and a metal comprising a Cu laminate or Cu layer.
6. The method according to claim 1 , wherein the metal cathode is selected from the group consisting of a metal or conductive material which is not soluble in alkaline solutions.
7. The method according to claim 6 , wherein the metal cathode is selected from the group consisting of iron, steel, stainless steel, titanium, copper, and carbon/graphite.
8. The method according to claim 7 , wherein the metal cathode is iron.
9. The method according to claim 1 , wherein prior to subjecting the solution to electro-oxidation, said method comprises an intermediate step comprising adjusting the pH of the solution to a pH between 9 and 11.5 by adding an acid or a base to said solution.
10. The method according to claim 8 , wherein the pH of the solution is adjusted to from about 10 to about 11.
11. The method according to claim 9 , wherein the pH of the solution is adjusted from a lower pH by addition of a weak acid selected from the group of phosphoric acid or an organic acid.
12. The method according to claim 1 , wherein the metal cyanide is ferro-cyanide.