The normal Grindstone lacks this capability, and the only way to remove curses is to combine same-items in a crafting grid- that is very expensive and rarely ever has a use for doing so.

Currently, the Diamond Grindstone's only use is a progression limiting based one. The ability to grind Curses away with your enchantments, and get some extra XP from that as well, would add another nice rewarding use to the Diamond Grindstone.

Good suggestion, I'd had this idea myself and tried it but gave up when i saw how complicated the grindstone code it. However, seeing this suggestion made me give it another attempt and it has been implemented for the next version