Concentration of ores (gravity separation, froth flotation, magnetic separation)

Concentration of ores is a crucial step in the extraction of metals. Metal ores generally exist as minerals. These minerals must be concentrated to increase the amount of metal for further processing. The three most commonly used methods are gravity separation, froth flotation, and magnetic separation.

Gravity separation

Gravity separation methods use the different relative densities of different minerals. This process separates heavier minerals from lighter particles. A common example of gravity separation is gold sieving in a stream.

In the picture above, the gold, which is denser, settles to the bottom while other lighter minerals and rocks are swept away. Historically, this method was very important during the gold rush.

Another example of gravity separation is the wet shaking table, where the table is usually tilted and along this inclination the material is introduced, usually in the form of a slurry. It is shaken to achieve separation between the minerals. The difference in density allows heavier particles to move to one side, while lighter particles remain on top or move to the other side.

Froth flotation

Froth flotation is a process for selectively separating hydrophobic substances from hydrophilic substances. It has been in use for over a century. This technique involves mixing powdered ore with water, forming a slurry, and then introducing air bubbles into this mixture.

In this process, the ore is first crushed and ground into a finer size and then ground into a pulp, and then treated with a detergent to help the ore bind with air bubbles. The mineral-rich froth is removed, leaving the unwanted material behind.

In froth flotation, various reagents are used to selectively separate the desired minerals. A collector such as xanthate may be added to attach the mineral particles to the froth and help them rise to the top of the container for collection.

Froth flotation is particularly useful for sulfide ores such as copper, lead, and zinc. The largest use of this method was in the mid-20th century with copper porphyry deposits.

Magnetic separation

Magnetic separation is based on the principle that minerals have magnetic properties and this property can be used to separate magnetic minerals from non-magnetic minerals. This method is used when the ore or impurities are of magnetic nature.

In the above scheme the ore is transported on a conveyor belt system. When the belt rotates over the magnetic roller, the magnetic particles stick to the belt and are separated from the non-magnetic particles, which follow a different trajectory due to inertia and gravity.

Magnetic separation has been widely used in metallurgical industries for the concentration of manganese ore, chromium ore, ilmenite in beach sand, and iron ores.

In short, the concentration of ores is a critical initial step in the appreciation, understanding, and implementation of metallurgical processes. Each method, whether it is gravity separation, froth flotation, or magnetic separation, uses the physical properties and chemistry of minerals to efficiently separate the desired materials.

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