Why Copper Electrolysis?
Copper is a good conductor of electricity, and is used extensively to make electrical wiring and components. The purification of copper is a form of recycling. Copper is purified further using electrolysis and we call it Copper Electrorefining (electrolytic refining).
In industry this is carried out on a massive scale. The electrolytic copper production is processed in the huge copper electrolytic tank fulfilled with copper electrolytic solution. Even the best chemical method cannot remove all the impurities from the copper, but with electrolytic refining it is possible to produce 99.99% pure copper (whatever method is used to manufacture copper from its ore, its final purification is by electrolysis).
Process for the Electrolytic Refining of Copper
Raw material: Blister Copper
It is extracted from copper mine in smelting furnace, contains 98.5% copper. It is the raw material of electrolytic copper production. While the final electrolytic copper product contains 99.99% copper in it.
How does it work: Copper electrorefining produces copper essentially free of impurities, and separates valuable impurities such as gold and silver from copper for recover as by products. The process for electrorefining copper is typical of those carried out in aqueous solution.
In this process, the positive electrode (the anode) is made of the impure copper which is to be purified. The negative electrode (the cathode) is a bar of pure copper. The two electrodes are placed in a solution of sulfuric acid and copper(II) sulfate (CuSO4) (electrolyte–solution the ions travel through), and selectively electroplating pure copper from this electrolyte without the anode impurities.
Copper Electrolytic Refining Plant
|Copper Electrolysis Machines||Electrolytic copper refining tank||Copper anodes casting machine||Pure copper cathode sheets||Off-gas treatment system|
◆ Electrolytic copper refining tanks
Anode plates are hung by their “handles” in electrolytic copper refining tank. Pure copper cathode sheets suspended on solid copper bars are inserted into the same tank, one sheet between each anode. When an electric current is passed from the anodes through the electrolyte to the cathodes, copper from the anodes moves into the solution and is plated onto the starter sheet. Impurities from the anodes settle to the bottom of the tank.
◆ Copper anodes (plates) casting machine
The copper anode will be casting into anode plates in molds semi-automatically. After pretreatment removing of tin, lead, iron, aluminum starts charging of the copper material into the furnace which is followed by smelting process. When the impurities are removed follows the slag removal and phase of reduction with natural gas. Reduction is aimed to remove the free oxygen. After the reduction the process is ended by casting, where the final product is casted into the form of copper anodes.
The same machine can be used for casting copper anodes during copper recycling or for recasting of scrap anodes at an electrolytic copper refinery.
◆ Pure copper cathode sheets
The refining anodes taken out from the refining furnace is changed into electrolytic copper with purity of 99.99% through an electrolysis process: During electrolysis, copper (II) ions leave the impure copper anode and since they are positive, migrating to the negative cathode. From time to time, the pure copper is scraped off the cathode. Impurities from the copper anode, such as gold, silver, platinum and tin, collect at the bottom of the electrolyte solution, deposited as anode slime.
More details on the impurities here:
–Ag, Au, tin and Pt are more noble than copper, insoluble in this electrolyte and so do not deposit on the cathode. They will be found as metals in the anode slime;
–Soluble impurities of iron and nickel dissolve in the electrolyte, which has to be continually purified to prevent excessive deposition onto the cathodes, which would reduce the purity of the copper;
–Sn, Bi and Sb dissolve anodically but will precipitate in the electrolyte as oxide or hydroxide compounds which will be found in the anode slime;
–Pb is oxidized anodically but will form insoluble lead sulfate in this electrolyte again, this will fall to the slime in the base of the cell.
Hence, the impurities accumulate in either the electrolyte or the cell slime and these can be processed further to recover the significant metal.
Pure copper cathode sheets are removed from tanks in the electrolytic refining plant
◆ Off-gas treatment system – Spray Tower
Off-gases from whole process are filtered and the dust collected returned to the furnace.
|Impure copper powder||500kg/day||1000kg/day||2000kg/day||5000kg/day|
|Copper electrolysis cycle||15 days/48 hour||15 days/48 hour||15 days/48 hour||15 days/48 hour|
|Production capacity of pure copper||370kg||750kg||1500kg||3750kg|