Refining of metal is one of the processes which involves separation of impurities like sand particles, other metals etc. from the metal of choice. Therefore, refining of metal comes under the science of study physical and chemical properties of the metal which refers as Metallurgy.
The process of refining of metal is done after the extraction of metal. Thus, the process of metal refining removes the gangue particles or matrix from the metals and gives a pure or refined metal.
Content: Refining of Metal
What are the metals?
Metal can define as the elements which are solid, hard, lustrous and are having good conductance overheat and electricity. The metals are having the following properties like:
Physical appearance: Metals are hard, crystalline and opaque. Some metals are coloured while some are not.
Malleability: Metals are malleable i.e. it can mould into various shapes.
Ductility: Metals are ductile i.e. it can transform into thin wires.
Lustrous: Metals are shiny in appearance.
Conductivity: Metals acts as a good conductor of heat and electricity.
Types of metals
According to the periodic table, the metals can be categorized into:
Alkali metals: These belong to the element in column 1 of the periodic table. These metals comprise six elements namely Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Cesium (Cs) and Francium (Fr). These metals strongly react with water to produce “Alkali” and that’s why it refers as Alkali metals.
Alkaline earth metals: These belong to the elements in column 2 of the periodic table. Alkaline metals comprise six elements namely Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba) and Radium (Ra). These metals react with the molecular oxygen and form an alkaline compound or we can say compounds with basic nature.
Transition metals: These belong to the elements from column 3 to column 12 of the periodic table. Transition metals comprise of fourty elements from column 3- 12 refers to “d-block elements” and comprises of twenty elements in the lanthanide and actinide series, refers to “Inner transition metals” or “f-block elements”.
Rare earth metals: It comprises of fifteen elements. As from the name it is clear, that these kinds of metals rarely occurs in nature. Rare earth metals contain elements from Lanthanum to Lutetium plus Scandium and Yttrium.
Poor metals: These metals comprises of fourteen elements.
Semimetals: It also refers as “Metalloids”. The property of Semimetals interlinks between the property of metals and non-metals. Semi-metal comprises of nine elements namely Boron (B), Silicon (Si), Germanium (Ge), Arsenic (As), Antimony (Sb), Tellurium (Te), Polonium (Po), Iodine (I) and Astatine.
Occurrence of metals
In nature, the metals can occur in both Free State and Combined state. Metals occur in a free state: Metals that occur in free- state are having least chemical reactivity like gold, silver, mercury etc. refers as “Noble metals”.
Metals occur in a combined state: The metals which occur in a combined state can combine with air, moisture, CO2, non-metals etc. and forms compounds like oxides, carbonates, halides etc.
Therefore, a metal can define as an element that is present in a mineral of the ore, from which it can be further extracted and refined.
Methods for Refining of metal
The refining of crude metal can perform by many methods where the impurities can present in the form of other metals, non-metals, an unreduced oxide of a metal, flux, slag etc.
There are the following methods which employe in the refining of the metal:
- Electrolytic refining
- Zone refining
In the process of liquation, the easily fusible and the metals which are having a low melting point for example Tin, Lead etc. are employed. The process mainly involves the following steps which can be summarized into:
- Pouring of impure metal: In this step, pass the impure metals over the sloping hearth of the reverberatory furnace.
- Heating: Then, heat the metal at a temperature little above the melting point.
- Drain off: Drain out the refined or pure metal by leaving the infusible impurities.
In the process of polling, stir the impure molten metal with the help of bamboo. The hydrocarbons will reduce the metal oxide present as an impurity. This method can refine metals like Copper (Cu) and Tin (Sn).
By the process of distillation, volatile metals like Zinc (Zn) and Mercury (Hg). The metals which are having very low boiling point vaporizes, by leaving behind the impurities. In this, heat the impure metal at a temperature above its melting point in a reverberatory furnace. Then, reconvert the vapours into the metal after the separation of gangue particles.
It is the most widely used method, as it can be used for the refining of many metals. It works on the principle of electrochemical properties of the metals. The impure metal is of an anode, pure metal is of a cathode and the electrolytic solution contains the salt of the same metal that is used.
When we pass an electric current, the impure metal from the anode will dissolve by which the anode becomes thinner by which the impure metal gets deposited in the pure cathode which becomes thicker. The impurities will either dissolve or be found at the base of the anode as Sludge or Anode mud.
This method was first given by William pfann. Some inert gases are filled in the container where the impure metal is placed inside it. Then around the rod, place a circular heater at the top.
Then the impure metal heats up due to the circular heater. The pure metal crystallizes and cools when the heater shifts to the next zone. The molten impurities will then move to the next zone along with the heater, which we can collect or separate from the last zone.