Decomposition of Metal Nitrates
Most metal nitrates decompose on heating to give metal oxides. Decomposition of silver nitrate is different as it yields elemental silver.
$$\ce{2AgNO3 -&gt; 2Ag + O2 + 2NO2}$$
Usually the metals which lie very low in the activity series decompose to give their elemental form.
I don't think it's possible to extract metals from just any nitrate by strong heating. They will yield their respective oxide which won't give the element rather they'll just fuse (melt) just like stable metal oxides like $\ce{Al2O3}$ does.