GCSE OCR Gateway Chemistry C6.1b Refining copper by electrolysis

C6.1b  To be able to explain why and how electrolysis is used to extract some metals from their ores

Electrolysis of aqueous copper sulfate solution.

Refining copper using electrolysis.

Carbon reduction is an effective method for the extraction of metals below carbon in the reactivity series.

But two problems remain:

1: How to extract metals higher than carbon more reactive than carbon in the reactivity series?

2. How can a metal be refined to a greater level of purity?

Electrolysis is the answer to both these problems.

First, let’s look at how electrolysis is used to refine copper to a greater degree of purity than that obtained from the smelting of copper ores.

Here is a picture of what basic copper unrefined might look like:

A web site about copper extraction and refining has this to say:

A dc electric current, passed through the cells, dissolves the anodes and deposits the copper on cathodes. The final product of the refining process is electrolytic tough pitch (ETP) copper normally containing between 99.94 and 99.96% Cu. Cathodes are re-melted under controlled conditions and cast into forms suitable for further processing.

Here is a schematic diagram of the arrangement:

You can see from the diagram above basically what happens in the electrolysis process.  

There are two discharge equations to remember: one for the anode and one for the cathode.  

The end result is transfer of copper from anode to cathode.  

The mass of the anode decreases as it loses copper and other precious metals.  The mass of the cathode increases but not by the same amount since the precious metals and other unrefined products end up as anode sludge on the base of the electrolysis cell.

Here is a picture of a cathode being removed from an electrolytic cell after electrolysis.  You can see the bright copper colour indicating the fresh deposit of new copper transferred over from the anode.  Make a note too of how many cells you can see there are in this cell room!! 

The copper from the cathode is melted down and often cast into different products .  Here is a picture of the continuous casting of copper wire:

The picture below gives you some idea of the different uses we put copper to these days.  Particularly keep a look out in your area for green roofing material: it is copper slightly weathered down to green copper carbonate sometimes called verdigris.  Note in particular the green colour of the Statue of Liberty.