Which of the following ores are concentrated by froth flotation?

Copper pyrites

The correct answer is option 1. Copper pyrites.

Froth flotation is a widely used process for selectively separating valuable minerals from their ores. It works based on the principle that different minerals have different surface properties, particularly their affinity for water (hydrophobicity) and air (aerophilicity). Here is a detailed explanation:

Principle of Froth Flotation:

Froth flotation exploits the differences in the surface properties of minerals by making use of specific reagents called collectors and frothers.  Collectors are molecules that selectively bind to the surface of the target mineral, rendering it hydrophobic, or water-repellent. This process is essential for separating valuable minerals from gangue minerals (unwanted minerals). Frothers are chemicals that stabilize the froth and create a stable foam layer on the surface of the flotation cell. This foam contains the floated minerals and can be mechanically separated from the aqueous solution.

Process Overview:

The ore is ground into fine particles and mixed with water to form a slurry. Collectors, such as xanthates, sulfides, or fatty acids, are added to the slurry. These collectors selectively adsorb onto the surface of the desired minerals, rendering them hydrophobic. Air is bubbled through the slurry, and the hydrophobic mineral particles attach to the air bubbles, forming a froth on the surface of the flotation cell. The froth containing the floated minerals is then skimmed off from the surface and collected, while the gangue minerals remain in the aqueous solution.

Application to Copper Pyrites (Chalcopyrite):

Chalcopyrite \((CuFeS_2)\), commonly known as copper pyrites, is a sulfide mineral and an important copper ore. In froth flotation, collectors such as xanthates or dithiophosphates are typically used to selectively bind to the surface of chalcopyrite particles, rendering them hydrophobic. When air is bubbled through the slurry, the hydrophobic chalcopyrite particles attach to the air bubbles and rise to the surface to form a froth. The froth containing the chalcopyrite particles is then collected, while the gangue minerals, which are hydrophilic, remain in the aqueous solution and are discharged.

Why Haematite, Magnetite, and Aluminium are not Concentrated by Froth Flotation:

Haematite \((Fe_2O_3)\) and magnetite \((Fe_3O_4)\) are iron ores, but they are oxides rather than sulfides. These minerals do not exhibit sufficient hydrophobicity for effective separation using froth flotation. Instead, they are typically concentrated using magnetic separation methods. Aluminium ores, such as bauxite \((Al_2O_3·nH2O)\), primarily consist of aluminum oxide minerals along with various impurities. Froth flotation is not suitable for concentrating aluminium ores because aluminum oxide minerals are generally hydrophilic and do not adhere well to air bubbles.

In summary, froth flotation is a highly effective method for concentrating sulfide ores like copper pyrites by selectively separating them from gangue minerals based on their surface properties. However, it is not suitable for concentrating oxide ores like haematite and magnetite or aluminum ores like bauxite, which are typically concentrated using alternative methods such as magnetic separation.