Refining of Metals: Zone Refining, Distillation and Chromatographic Method

Refining can be defined as the process of purification of metals to remove the impurities from the metals so that at last, the product is purer in form. There are also other purification methods like metal reduction but in the metal reduction method, the metal is not changed in a 100% pure form while in the refining technique we get 100 % pure form metal. However, the techniques vary from metal to metal and there are some metals that are also exceptions. Let’s now understand the different types of refining methods.

Key Terms : Refining process, types of distillation, Zone refining, Poling

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Refining Methods of Metals

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There are various methods used in the refining process of metals. They are listed below-

• Distillation
• Liquidation
• Poling
• Oxidation
• Electrolytic refining
• Zone refining
• Vapour phase refining
• Van-Arkel method
• Chromatographic method

Distillation 

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It is the process of separating the components from a mixture based on their boiling points. In metal refining, this method helps to retrieve the low boiling point metals like Zinc, Arsenic, etc. In this procedure, the metal is heated beyond its boiling point until it is converted into vapor. Hence, the impurities flees in form of vapor and pure metals will stay.

Read more : Metallurgy

The distillation refining process is further classified into three subcategories which are listed below.

• Simple distillation
• Steam distillation
• Fractional distillation

Liquidation

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This method extracts the components of ore metal or alloys by performing partial melting. In this method, we have to pass some amount of heat. Therefore, the low melting point metals will melt and change in liquid form and the impurities, which have high boiling points, will remain same in the solid form. So, this is a little bit easier than the distillation process of refining. One more thing we have to remember is that the whole process is conducted in a sloped container so that the pure metals in the liquid form can be collected easily.

Poling

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Poling method is used for refining the metals that contain the oxidized impurities. This process is divided into two steps in which firstly the copper is kept in the anode furnace for refining it two times. And then iron or sulphur will get released in form of iron oxide or sulphur oxide through air blowing.

Oxidation

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Oxidation is basically the process of removing the impurities from silver and gold. In this process, metals like gold and silver are kept in a special heated furnace, and then hot air is passed through it. So, the impurities like lead, copper, tin will be oxidized and we will get the metal in the pure form.

Electrolytic refining

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 This is the most widely used method in the refining process of metals. Most of the metals like gold, silver, copper, and zinc are oxidized using an electrolytic refining method in which refining is done through the process of electrolysis. Here, the impure metal is placed at the anode and the cathode has a thin strip of the pure metal, and an electrolyte, a metal salt, is used for refining. The impure metal dissolves from the anode to electrolytes and pure metal deposits on the cathode.

Zone refining: 

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The great scientist W.G.Pfann invented the zone refining method against impurities. In this, the metals are purified with the help of other metals by melting and crystallization processes. The reason behind this is that the impurities have the highest solubility in the molten metal as compared to the solid metals.

Chapter Related Topics: 

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Sample Questions

Ques: What is the green coating that develops on copper when it loses shine -
A)Copper carbonate
B)Basic copper carbonate
C)Copper oxide
D)Copper hydroxide (1 mark)

Ques:Amalgam is an alloy of which metals?
A)Copper and zinc
B)Mercury
C)Lead
D)Tin and zinc (1 mark)

Ques:Reaction between X and Y forms the compound Z. Now X loses an electron and Y gets the electron. Which of the given properties is not shown by Z?
A)Conducts electricity in a molten state
B)High melting points
C)Behave as solid
D)Low melting point (1 mark)

Ques: An element X is soft and can be cut by a knife. It’s can’t be kept open as it’s very reactive in air and it reacts vigorously with the water. Identify element X.
A)Na
B)Ca
C)P
D)Mg (1 mark)

Ques: In the method of galvanization, iron is protected from which of the following metal?
A)Aluminium
B)Gallium
C)Silver
D)Zinc (1 mark)

Ques: Oxides of moderately reactive metals like zinc, iron, nickel, copper is reduced using which of the following technique?
A)Carbon as reducing agent
B)Sodium as reducing agent
C)Ca as reducing agent
D)Al as reducing agent (1 mark)

Ques: The process in which carbonate ore is heated strongly in the absence of air to convert it into metal oxide is called as-
A)reduction
B)Smelting
C)Calcination
D)Roasting (1 mark)

Ques: The highly reactive metals like Na, Mg, etc. are extracted by-
A)reduction of carbon
B)Electrolysis of molten oxides
C)reduction of Aluminium
D)Electrolysis of molten Chlorides (1 mark)

Ques: Non-metals form covalent chlorides because-
A)They can give electrons to chlorine
B)They can share electrons with chlorine
C)They can give electrons to chlorine atoms to form the chloride irons.
D)they cannot share electrons with chlorine irons (1 mark)

Ques: Which of the following is the correct arrangement of the given metals in the ascending order of their reactivity?
A)Zinc > iron > Magnesium > Sodium
B)Sodium > magnesium > Iron > Zinc
C)Sodium > Zinc > Magnesium > Iron
D)Sodium > Magnesium > Zinc > Iron (1 mark)

Ques: Which property of metals is used for the making bells and strings of musical instruments like sitar?
A)Ductility
B)Conductivity
C)Sonorousness
D)Malleability (1 mark)

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