Froth Flotation

CSF Science - Earth & Beyond, Level 6
Describe the processes and issues associated with the extraction and use of minerals and fossil fuels.

CSF Science - Natural & Processed Materials, Level 5
Devise and demonstrate methods of separating mixtures and solutions.

Developed by Peter Nisbet, Fairhills High School.

Froth Floatation

Mining companies use special chemicals to 'float' sulphide minerals away from the crushed rock particles. The froth flotation process using bubbles to float out metallic ore was invented by Graeme Jameson, an Australian scientist working at Mount Isa. A simplified version of this flotation method can be carried out using basic chemicals and equipment found in the science classroom.
(Information about Graeme Jameson and his work with bubbles can be obtained from the Minerals Education Centre Victoria using the information request form.)

A sample of ore to be separated can be made by mixing iron filings with sand. A ratio of 1:4 should be satisfactory. This ratio can be increased if there does not appear to be enough iron filings in the mixture.

Students add two spatulas of the ore sample to a large test tube and then add 3cm of water. A rubber stopper is placed in the tube which should then be shaken for ten seconds.

Students should observe no bubbles or separation of the sand and iron filings. As the mixture sinks in the test tube, the iron filings may settle to the bottom.

2 cm of kerosene and 5 drops of a good quality detergent should now be added, the stopper replaced and the test tube shaken again for ten seconds.

Observation should now show white bubbles moving up the inside of the test tube, carrying the iron filings with them. The sand remains at the bottom of the test tube.

Note:

• Students should hold their thumbs over the stoppers and point the top of the test tubes away from other students. The stopper should not fly off as no gas is generated.
• Different detergents should be tested to select the most appropriate.

Why does it work?

The kerosene coats the iron filings and makes them become water repellent (collector). When each comes in contact with an air bubble produced by the detergent (frother), it is attracted to the air and repelled by the water so it sticks to the bubble. The filings then move up with the bubbles into the froth and can be skimmed off.

For more information contact MEV