The hard drive is mostly aluminum casing and the 'discs' are also usually aluminum. Take it apart and sell the metal. The discs will punch off the spindle and then you can melt them down and then sell them. Some HD discs can be alloys as well. If you really want to destroy the data and not recycle, throw the discs into a camp fire or your fire pit. The miniscule pollution will have no impact to the earth.
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