How can I decrypt an encrypted SD card (HTC Evo 4G) on a different device? I encrypted both my phone and SD card upon purchasing my HTC Evo 4g LTE.  Recently the phone died (would get to the login screen and then reboot).

After a factory reset the SD card shows up as damaged.  I've tried mounting it in various ways, but neither the phone nor a computer will attempt to mount the drive - they just ask to format it.

Is there any hope of recovering the contents?
The simple answer is: You Can't

The volume is already encrypted and can only be read as random hex because the required key is stored in your phone in order to decipher it. Unfortunately there is no way for you to recover your sdcard contents because the key on your phone is also lost when you factory reset.

Just reformat it if you still want to use your sdcard.