Engineering - Metallurgy

Metallurgy is taken to mean the extraction of metals from their various ores, the heat treatment of metals and the production of alloys.


Metallic minerals are usually found in nature in the form of ores. An ore is a solid, naturally occurring mineral compound from which at least one metal can be obtained. These ores are mined and then the extraction of the metal occurs.

Mining Methods

There are four main mining methods :

  1. Open Cast Mining
  2. Underground Mining
  3. Open Pit Mining
  4. Dredging
1. Open Cast Mining

Used to gather ores that are in fairly horizontal layers near to the surface. Overburden may need to be removed first in order to get at the ore. If the mineral is in rock explosives may be used.

2. Underground Mining

Underground Mining is the most expensive type of mining, and so there must be enough ore to make the process worthwhile. The ore is to be found deep beneath the surface and deep shafts are sunk. A series of tunnels are dug from the main shaft. The ore is blasted and drilled, then usually crushed, transferred to Transport Cars, which carry the ore to a Hoist Bucket, which in turn carries the ore to the surface. There the ore is treated and the metal mineral extracted.

3. Open Pit Mining

Used when the ore is in deep wide layers. This is a relatively cheep form of mining as a lot of mechanisation can be used. The ore is blasted, then moved to truck which take it to the refining plant. This process is similar to quarrying.

4. Dredging

Dredging occurs in shallow waters in rivers or in the sea. The overburden is stripped first and then the Dredge Barge removes the ore, which is separated on the ship. The waste product is then returned to the water in an area that has already been dredged. The Dredge Barge then gives its cargo to a larger Carrier Ship for transportation to shore.

Mining Methods Compared

Type of Mining Advantages Disadvantages
Open Cast Mining Cheap, Quick Overburden, Environmentally unfriendly
Underground Mining Deep access, Environmentally friendly, No overburden Very expensive, Dangerous
Open Pit Mining Lots of mechanisation possible, Quick Environmentally unfriendly, Overburden
Dredging Also increases depth of waterway Only in shallow water, Can change currents, Overburden

Concentration Of Ores

As it is bad business to transport waste material the ore that is removed from the earth is concentrated as much as possible before transportation. The ore is first mined, then crushed, then ground into fine particles and then concentrated.

Methods of Concentration :

  1. Gravity or Wet Mill : Because the ore and the waste will have different densities, shaking the combination while wet will result in the denser material sinking to the bottom of the container, thus separating the ore and the waste.

  2. Flotation : This method is often used to separate two ores which may be in a mixture. Air is blown through the ore in a vat of water which has special chemical floating agents in it. The result is that one of the ore type particles stick to the bubbles as they rise creating a froth at the top of the vat, and the other ore sinks to the bottom.

  3. Magnetic Separation : Used for magnetic ores. The ore is poured over a rotating drum which contains a fixed magnet. The magnetic ore is held to the drum until the waste has fallen off.

Metal Extraction

Now the metal has to be extracted from the ore. There are three main methods :

  1. Pyrometallurgy : Used where the metal ore occurs as an oxide. When the mixture is heated molten metal, slag and gases are produced. The gas is left to escape, the slag is removed leaving the desired molten metal.

  2. Thermo - Electrometallurgy : This process is similar to electroplating where an anode, (-), and a cathode, (+), attract, depending on the mineral, either the metal or the waste.

  3. Hydrometallurgy : The ore is dissolved in a solvent to make a solution which through electrolysis separates the metal from the waste.