A copper anode is a node that allows an electrical current to flow into an electrical device. It is usually, but not always, the positive terminal of an electrochemical cell where anions, negatively charged ions, are concentrated. There are many types of anodes, such as graphite anodes and aluminum anodes. Copper anodes differ from these in that they are used specifically for copper refining in a process referred to as copper smelting.
A copper anode is made from pulverizing a copper ore called chalcopyrite, CuFeS2, and mixing it with water, pine oil and amyl xanthate, a salt used to make the mixture water-repelling. After the mixture is made, compressed air is passed through it to allow further purification. Next, the chalcopyrite mixture is combined with limestone and sand and heated to approximately 2,300 degrees Fahrenheit (1,110 degrees Celsius) in an oxygen furnace.
As the mixture is being heated, the oxygen of the furnace reacts with the iron in the original chalcopyrite producing iron (II) oxide. The copper remains in the form of copper sulfide, an excellent conductor of electricity. Sulfur dioxide is also produced in this process as a byproduct.
Excess sulfur further reacts with copper sulfide to produce chalcocite (Cu2S) in a molten form that collects at the bottom of the furnace separated from other byproducts such as ferrosilite (FeSiO3) and wollastonite (CaSiO3). The remaining copper sulfide is processed even more by blowing heated oxygen into it. The gas then reacts with the sulfur to once again produce sulfur dioxide, leaving only copper.
The copper anode finally becomes useful during the final step of the copper purification process. The anode is used in electrolysis, a series of reactions that separate a chemical substance into its ions. In this case, electrolysis is used to convert the impure copper made from the previous process into pure copper. The impure copper is used to construct the copper anode in order for the pure copper to gather at the cathode.
Both the anode and the cathode are submerged in a solution comprised of sulfuric acid and copper (II) sulfate and connected to an outside power source. As an electrical current is run through the cell, impure copper metal is transformed into copper (II) ions at the anode, and these copper (II) ions are transformed back into pure copper metal at the cathode. The impurities, which might include otherwise precious metals such as gold and silver, fall to the bottom of the cell.