Press shortcut key [K] to open this interface, and click on the disassembly icon. All of your equipment can be disassembled from the Skill interface.
You will have a chance to obtain either an [Essence Stone] or [Useless Dust] after disassembling the equipment you no longer need.
[Essence Stone] can be used for equipment-remaking or for task purposes.
[Useless Dust] is actually not as useless as you may think. You can use the alchemy skill to reform it into an essence stone.
1) Higher level equipment has a higher possibility to obtain materials
2) Your equipment will not be able to be disassembled if it has already been reinforced to +9.