The Hoopes process is a metallurgical process, used to obtain the aluminium metal of very high purity(about 99.9% pure). The process was patented by William Hoopes, a chemist of the

Aluminum Company of America Alcoa Corporation (an acronym for Aluminum Company of America) is a Pittsburgh-based industrial corporation. It is the world's eighth-largest producer of aluminum. Alcoa conducts operations in 10 countries. Alcoa is a major producer of primary ...

(ALCOA) in 1925.

Introduction

It is a method used to obtain

aluminium Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...

of very high purity. The metal obtained in the

Hall–Héroult process The Hall–Héroult process is the major industrial process for smelting aluminium. It involves dissolving aluminium oxide (alumina) (obtained most often from bauxite, aluminium's chief ore, through the Bayer process) in molten cryolite, and el ...

is about 99% pure, and for most purposes it is taken as pure metal. However, further purification of aluminium can be carried out by the Hoopes process. This is an

electrolytic process An electrolytic process is the use of electrolysis industrially to refine metals or compounds at a high purity and low cost. Some examples are the Hall-Héroult process used for aluminium, or the production of hydrogen from water. Electrolysis i ...

The process

The cell used in this process consists of an iron tank lined with carbon at the bottom. A molten alloy of

copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...

, crude aluminium and

silicon Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic ta ...

is used as the anode. It forms the lowermost layer in the cell. The middle layer consists of molten mixture of

fluorides Fluoride (). According to this source, is a possible pronunciation in British English. is an inorganic, monatomic anion of fluorine, with the chemical formula (also written ), whose salts are typically white or colorless. Fluoride salts typi ...

sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable ...

, aluminium and barium (

cryolite Cryolite ( Na3 Al F6, sodium hexafluoroaluminate) is an uncommon mineral identified with the once-large deposit at Ivittuut on the west coast of Greenland, mined commercially until 1987. History Cryolite was first described in 1798 by Danish vete ...

+ BaF₂). The uppermost layer consists of molten aluminium. A set of

graphite Graphite () is a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on lar ...

rods dipped in molten aluminium serve as the cathode. During electrolysis, Al³⁺ ions from the middle layer migrate to the upper layer, where they are reduced to aluminum by gaining 3 electrons. Equal numbers of Al³⁺ ions are produced in the lower layer. These ions migrate to the middle layer. Pure aluminium is tapped off from time to time. The Hoopes process gives about 99.99% pure aluminium.

Introduction

The process

References

Further reading