Which of the following is not a method of concentration?

Concentration of ore means physically removing the unwanted gangue (impurities such as sand, clay, or rock) from the ore before the metal is chemically extracted. Physical concentration methods exploit a measurable physical-property difference between the ore particles and the gangue -- particle density (gravitational separation), surface wettability (froth flotation), or magnetic response (magnetic separation).

Applying this to the given options: the Froth Flotation Method uses a collector chemical to coat the surface of ore particles so they become water-repellent (hydrophobic), while a frothing agent stabilises air bubbles that carry these coated particles up into a froth layer, leaving the gangue in the slurry below; the Magnetic Method passes the crushed ore over a magnetic separator so a magnetically susceptible mineral (e.g., magnetite) is deflected away from non-magnetic gangue; the Gravitational Separation Method uses flowing water or a shaking table so denser ore particles settle out while lighter gangue is carried away. All three physically separate ore particles from gangue and are therefore concentration methods. Calcination, by contrast, is a thermal treatment applied AFTER concentration: the already-concentrated ore is strongly heated (usually with limited air access, below its melting point) to drive off volatile matter such as water of crystallisation and carbon dioxide, converting a hydrated or carbonate ore into its oxide. It does not separate ore particles from gangue at all, so it is not a method of concentration.

• Froth Flotation Method -- a collector renders ore particles hydrophobic and a frother stabilises air bubbles that lift them into a froth, separating them from gangue; a concentration method.

• Magnetic Method -- a magnetic field deflects a magnetically susceptible mineral away from non-magnetic gangue; a concentration method.

• Gravitational Separation Method -- flowing water or a shaking table lets denser ore particles settle while lighter gangue washes away; a concentration method.

• Calcination -- heats the already-concentrated ore to drive off volatile impurities such as water of crystallisation and carbon dioxide; does not separate ore from gangue, so NOT a concentration method.

Since Froth Flotation, the Magnetic Method, and Gravitational Separation are all physical concentration techniques while Calcination is a later thermal-treatment step, Calcination is the one that is not a method of concentration.