Applications and Electrorefining

Most metals found in nature exist as ores in combination with other elements such as oxygen and sulfur. Electrolysis can be used to separate metals from their ores and remove impurities from the metals. The general process is known as electrorefining. Other electrolytic processes are used to obtain a number of important chemicals. 

The anode and cathode sides of the cell are separated by a membrane that allows the sodium ions to migrate from the anode side of the cell to the cathode side. 

Electrorefining can be used to purify a metal by using alternate electrodes of a pure and impure metal. Impurities oxidized at the anode, which is made of the impure metal, travel into solution. By arranging the cell appropriately, the ion of the metal to be purified is reduced on the pure metal cathode. For example, copper metal that contains lead and iron may be used as one electrode and pure copper as the other electrode in a cell. When the proper voltage is applied, copper, lead, and zinc will be oxidized and move into the electrolyte. Because copper is more easily reduced compared to zinc and lead, it will be plated out at the pure copper cathode. Therefore, this process effectively removes the zinc and lead impurities from the copper. 

The electrolysis of aqueous sodium chloride is used to prepare chlorine, sodium, and hydrogen. 

The production of aluminum actually involves several steps. Bauxite is the ore that contains aluminum oxide (Al Oj) used to produce aluminum. Impurities of iron, sulfur, silicon and other elements are removed from bauxite using the Bayer process to produce purified alumina. The Bayer process, patented in 1887 by Austrian Karl Josef Bayer (1847-1904), involves pulverizing bauxite and treating it with a hot sodium hydroxide solution to produce sodium alu-minate (NaA102). Sodium aluminate is then placed in a reactor in which temperature and pressure can be varied to precipitate out impurities. The sodium aluminate solution is then hydrolyzed to produce purified alumina  

---