How can I mount an encrypted disk from the command line?
You want to run diskutil coreStorage unlockVolume &lt;UUID&gt;, where the UUID is the Logical Volume UUID associated with your encrypted disk, /dev/disk3.  You can get the lvUUID by running diskutil cs list in the terminal and looking for the output related to /dev/disk3.  The identifier is a long string that would look something like this 'B807C2A0-577F-3DB0-9002-F82B9137696C'.

It will prompt you for a password at that point and if it's correct, unlock the disk.