General Principles and Processes of Isolation of Elements

Extraction of Crude Metal from Concentrated Ore


Metals are incredibly useful substances. It is well accepted that our technologically advance lives would not be possible without metals. Their physical properties such as electric conductivity, density, malleability etc make them perfect for industrial use. Now let us take a look at extraction of metals from their ores.

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Extraction of Metals

Now we already saw how the ore of a metal is concentrated to remove impurities known as gangue. After concentration of ores, we must now extract metal from in it. This step will give us metal in its pure form i.e. the native form of metal.

First, we must convert the ore to a suitable form. The metals need to be in an oxide form for the reduction process to be easier. Hence the ores are converted to oxides, so it is ideal for reduction. After doing so the ores will undergo reduction, to give us metal. Therefore the two main steps of extraction of metals are,

  • Convert Ores to form oxides
  • Reduction of Metal Oxides

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Convert Ores to Oxides

It is easier to reduce oxides than say sulphides. Oxygen is more electronegative than other elements. So it is easier for oxides to accept an electron pair and get reduced. There are various ways to carry out this step. Let us take a look at them

1] Calcination

This is the process of heating a substance in a limited supply of air or oxygen. We subject the ore to thermal energy (heat) so we can change their chemical state and turn them into oxides. Although we must ensure that we keep the temperatures below the melting point of the metal. Hydroxides and carbonates are usually converted to oxides via this process. Here is how an iron ore is converted to iron oxide, to then later enable reduction

Fe2O3.xH2O → Fe2O3 (solid) + H2O (gas)

2] Roasting

Roasting is another way to convert compounds to oxides.  It is a metallurgical process involving gas-solid reactions at elevated temperatures with the goal of purifying the metal component. In roasting the ore is heated up in the furnace in a regular supply of air. Again we ensure that the temperatures are within the melting point of the metal.

Here the oxygen in the air reacts with the sulphide ores to give us oxides. The sulphur in the ore forms sulphur dioxide and separates out. Here is a Zinc Sulphide chemical reaction

2ZnS + 3O2 → 2ZnO + 2SO2

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 Extractions of Crude Metal

Reduction of Metal Oxides

This is the second step in the extraction of metals from their respective ores. Now once we obtain metal oxides from the ores, they must now reduce them. Again in this reduction process, we heat the metal oxide. But this time we add a reducing agent. This reducing ageing is usually Carbon or a carbon compound. This is because they react best with oxygen and are readily and cheaply available.

Now when the carbon reacts with the metal oxide reduction takes place, This is when electron gain or electronation occurs. This means the carbon combines with the oxygen, leaving us with a pure metal. The general reaction for reduction is as follow

MxOy + yC → xM + CO

Extraction of Metals

To chose the ideal reducing agent for a certain ore, and to also find out the correct amount of thermal energy requirement we must depend on Giggs Energy interpretations. We represent these graphically using an Ellingham Diagram.

Solved Question for You

Q: In the extraction of copper from its sulphide ore, the metal forms by reduction of Cu2O with which of the following?

  1. ZnS
  2. CO
  3. Cu2S
  4. None of the above

Ans: The correct option is “C”. Compounds of certain metals reduce to metals without using any additional reducing agent ores of Cu, Pb, Hg etc. Their sulphide ores are partially roasted to give some oxide. This oxide is now reduced to the metal by the remaining sulphide ore at elevated temperatures in the absence of air. This process is what we call self-reduction.

Cu2S + 2Cu2O →6Cu + SO2

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