Refining Definition
Refining is defined as the process of reducing the impurities of a substance. Metals that are extracted from its ore are usually impure in nature. The extracted impure metal is called crude metal. Refining of metals is the final process. After the extraction process the metal is free from impurities. The refining method to be chosen will depend on the physical and chemical properties of a particular metal. There are different methods of making a metal pure :
Distillation
Liquation
Poling
Electrolysis
Zone refining
Vapour Phase refining
Chromatographic Method
Distillation
Metals such as Zinc and Mercury consist of a very low boiling point. So zinc and mercury readily vaporise while heating them, leaving behind their impurities. The leftover impure of metal is heated beyond its melting point in a furnace and the vapours are reconverted to metals once the impurities are separated.
Liquidation
Liquidation is suitable for metals having low melting points like tin. In Liquidation process, the impure metal is heated and then it flows on a sloped surface. While flowing, the impurities will remain behind and the pure metal will collect at the bottom of the slope.
Poling
Poling is a method used for metals that have oxidised impurities to purify them. Poling is mainly used to purify metals that are in the impure form like copper or tin of copper oxide or tin oxide. In the poling method a log of wood is taken that is still green and then used to stir the liquid metal. The hydrocarbons of the green wood reduce the metal, and the oxygen leaves as CO2 gas.
Electrolytic Refining
Electrolytic Refining is the most common and widely used method because it is applicable to most metals. In Electrolytic Refining, different electrochemical properties of the metals and the impurities are used. In Electrolytic Refining, the impure metal is the anode and the pure metal is cathode. The electrolyte is the type of the salt solution of the same metal through which an electric current is passed. The pure metal extracted from the anode will dissolve in the electrolyte bath and then collect at the anode. The impurities found will either dissolve or be found in a heap at the base of the anode.
Vapour-Phase Refining
In Vapour-phase refining, For releasing a metal from impurities, it is first converted into a suitable volatile compound by heating it. And the heating requirements are:
The metal used for this process should form a volatile compound with a suitable reagent.
The volatile compound that is to be used should be easily decomposable so that the recovery is easy.
Ni + 4CO Ni(CO)4 Ni + 4CO.
Zone Refining
It is a special method used to purify metals. In this method, metals are purified to a very high degree. Impure metal rod is placed in a container filled with inert gas. Then a circular heater is placed around the rod at the top for heating the impure metal. And when the heater shifts to the next zone, the pure metal cools and crystallises. The impurities that are melted will move along with the movement of the heater and shift to the next zone. All these impurities are then collected to the last zone and then it can be separated.
Chromatographic Method
This method depends on the chromatography. Chromatography mainly deals with the movements of components at different rates in a mixture and/or differential absorption of an absorbent. In the chromatographic method, impure metal is put in either liquid or a gas medium. Then the medium is moved through an absorbent. Different components will absorb the impure metal at different levels. And then those components are removed by using a suitable solvent. There are different forms of chromatographic methods, like Column Chromatography, Thin Layer Chromatography, Gas-liquid chromatography etc.
Did You Know?
The distillation using a terracotta apparatus was prevalent in Indus valley civilization since 3000 B.C. Also, Babylonians practised this method in Mesopotamian civilisation.
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FAQs on Refining
1. Define the Van Arkel method for zirconium?
Van Arkel method is used for preparing pure metals by removing all the oxygen and nitrogen present in the form of impurity in certain metals like Zr and Ti which are used in space technology.
It’s chemical reaction can be defined as:
Zr(s) + 2I2(g) → ZrI4(g) → Zr(s) + 2I2
Same chemical reaction is for Ti.
2. What is the refining process?
Refining plays an important part in metallurgy. Metals that are extracted from its ore are usually impure in nature and these impure metals which are extracted are called crude metals. Refining is defined as a method of removing impurities in order to obtain metals of high purity. The impurities are then removed from crude metal by different types of methods based on the properties of the metal and the properties of impurities. The methods involved in the purification are:
Distillation
Liquation
Poling
Electrolysis
Zone refining
Vapour phase refining
Chromatographic methods
3. What are the different forms of impurities?
Different forms of impurities include:
Impurities caused from unreduced oxides of metal
Impurities caused by Non-metals like C, Si, P, As, S, etc.
Impurities caused by foreign metals.
Impurities caused by slags and flux.
4. What are the types of distillation methods?
The distillation method is further divided into three types :
Simple Distillation:
In this method, liquids are separated from solids or other non-volatile substances.
Steam Distillation:
In this method, essential oils from flowers are extracted.
Fractional Distillation:
In this process, cadmium is separated from zinc. Zinc containing cadmium is mixed with powdered coke and then it is heated. The first batch of condensate contains cadmium, whereas pure zinc is obtained from subsequent steps.
5. Where can students find useful information regarding refining methods?
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6. What kind of metals are purified using the zone refining method?
Zone refining method is used to refine metalloids like silicon, germanium, boron, etc. Likewise, some metals such as tantalum and gallium are refined too.
7. Where does the impurity of impure metals go after refining?
After passing the electric current, the impure metals disintegrate from the anode and mix with the electrolytic solution. Only the soluble impurities dissolve into the solution. On the other hand, the insoluble impurities are collected as anode mud at the bottom of it.
8. What is the fundamental difference between smelting and refining?
Smelting refers to the extraction of metals from ores using pyrometallurgy (heating and melting). Refining refers to the process of extracting valuable metals from ores and different raw materials. More specifically, refining denotes the processes of acquiring a purer version of metal.
9. Which method is used to refine copper?
Electrolysis is the process generally used to refine copper.