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metallurgical
Metallurgy is a domain of materials science and engineering that studies the physical and chemical behavior of metallic elements, their inter-metallic compounds, and their mixtures, which are known as alloys.
Metallurgy encompasses both the sc ...
method employed in the purification 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 ...
which contains
copper oxide Copper oxide is a compound from the two elements copper and oxygen.
Copper oxide may refer to:
* Copper(I) oxide (cuprous oxide, Cu2O)
* Copper(II) oxide
Copper(II) oxide or cupric oxide is an inorganic compound with the formula CuO. A black so ...
as an impurity and also in the purification of tin which contains tin oxide (stannic oxide or "SnO
2") as an impurity. The impure metal, usually in the form of molten blister copper, is placed in an anode furnace for two stages of refining. In the first stage, sulphur and iron are removed by gently blowing air through the molten metal to form
iron oxides and
sulfur dioxide.
[J J Oudiz, "Poling processes for copper refining," ''Journal of Metals'', December 1973, 35–38.] The iron oxides are skimmed or poured off the top of the copper and the gaseous sulfur dioxide exits the furnace via the off-gas system. Once the first ''
oxidation
Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...
'' stage is complete, the second stage (''reduction'' or ''poling'') begins. This involves using a reducing agent, normally
natural gas
Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...
or
diesel
Diesel may refer to:
* Diesel engine, an internal combustion engine where ignition is caused by compression
* Diesel fuel, a liquid fuel used in diesel engines
* Diesel locomotive, a railway locomotive in which the prime mover is a diesel engin ...
(but
ammonia
Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wa ...
,
liquid petroleum gas,
and naphtha can also be used), to react with the
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...
in the copper oxide to form copper . In the past, freshly cut ("green") trees were used as wooden poles.
[John B Huttl, "'Poling' becomes ancient history at Phelps Dodge smelters," ''E&MJ'' Volume 162, No. 7, July 1961, 82–85.] The sap in these poles acted as the reducing agent. The heat of the copper makes the pole emit wood gas(CO
2 and H
2) that reduces the cuprous oxide to copper.
It was the use of these greenwood poles gave rise to the term "poling."
Care must be taken to avoid removing too much of the oxygen from the anode copper, as this will cause other impurities to change from their oxide to metallic states and they will remain in solid solution in the copper, reduce its conductivity and change its physical properties. Also upper surface can be covered with coke to prevent reoxidation of metal.
References
;Sources
''The Canadian Encyclopedia''
Metallurgical processes
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