Q. Explain about Froth flotation process?

Froth flotation process is the most important method for beneficiation of ores. This process has made possible the beneficiation of low grade ores which could not be processed earlier. The process of froth flotation is extensively employed to concentrate sulphide ores. Thus, many oxide ores may also be concentrated by this process. It is based on the difference in wet ability of different minerals. In this process, the ore is finely ground to give a thick pulp containing 30-40% solids. A small amount of pine oil, cresylic acid or oleic acid, which causes frothing, is added to the pulp. A substance, which is capable of repelling water from the surface of mineral and therefore promotes attachment of mineral particles to air bubbles, is also added to pulp. This substance is known as collector. Sodium ethyl xanthate, C₂H₅OCS₂Na, is usually used as a collector in floating copper, lead and nickel sulphide ores. Another substance known as activator, which helps in the action of collector may also be added. The entire material, i.e. the mixture of pulp, collector and frother is taken in a container and hen air is blown. Air bubbles adhere to the mineral particles and make them float in the form of froth which is collected. The gangue is wetted by sinks and water.

Some ores have more than one mineral, so separation of one mineral from the other in addition to separation from the gangue is essential. To achieve this, a depressing agent or depressor, which suppresses the flotation of one of the minerals, is included. An important example is the concentration of lead-zinc ore. If the ore is concentrated without a depressor, both zinc and lead sulphides collect in the froth. If a small amount of zinc sup hate and sodium cyanide is added, zinc sulphide is depressed, permitting flotation of lead sulphide. After removing lead sulphide, copper sulphate is included to activate the depressed zinc sulphide and air is blown when zinc sulphide floats. This method is called as differential flotation.