Give the steps involved in the extraction

Extraction of Metals present low in the Activity series

Silver (Ag), gold (Au) and platinum (Pt) generally occur in the free or native state. This means that they can be isolated rather easily. Metals like

copper (Cu) and mercury (Hg) are comparitively more reactive and occur in combined states. For example, the ore of mercury is cinnabar (HgS)

while that of copper is copper glance (Cu2S). Both are converted into metallic form upon heating in air or oxygen.

Similarly,

Extraction of Metals present in the middle of the Activity series

The metals present in the middle of the series are zinc, iron, chromium, nickel, cobalt, lead etc. These are usually present as sulphides or

carbonares in nature. However, it is quite easy to obtain a metal from its oxide form which is then reduced to the metallic state. The various steps

involved in the process of extraction are briefly discussed.

(a) Calcination :

Calcination may be defined as the process of heating the ore below its melting point in the absence of air.

As a result of calcination, the following changes take place

- Moisture is driven out and the ore becomes dry.

- Some hydrated ores decompose and become anhydrous by losing molecules of water of crystallisation. For example, heat

(b) Roasting :

Roasting may be defined as the process of heating the ore below its melting point with excess of air.

As a result of roasting, the following changes occur :

- Any organic matter if present, gets destroyed.

- Impurities of non-metals such as sulphur, arsenic or phosphorus are converted into their volatile oxides which are removed. For example,

- Sulphides of the metals are converted into their oxides. For example,

- Small amounts of sulphides may also be converted into sulphates as a $^{5}$ result of roasting. For example,