Reduction by heat:
Metals that are unreactive, like Hg, can be reduced from their ores by heating them. Mercury ore cinnabar is actually mercury sulphide. This can be heated at 300°C so that S is removed as SO2 and HgO is obtained. Hg is a very unreactive metal. HgO dissociates into Hg and oxygen soon.
The reaction is shown below.
Reduction by electrolysis:
Highly reactive metal – oxides and metal – chlorides are not easy to be reduced by chemical reactions. Metals such as Na, K, Mn, Ca have to be freed from their ores by electrolytic processes. These metals are so reactive that they themselves are powerful reducing agents. Molten metal – oxides or chlorides form the electrolyte in an electrochemical cell. The cathode of the cell provides the electrons needed for the metal to free itself from the metal – oxide or metal – chloride bonds. In the electrolysis, metals atoms get deposited on the cathode electrodes, which then have to carefully removed and stored.