If your good with the terminal you can attempt to eject it with diskutil command
first type diskutil list this will bring up everything that is mounted you will see something like this
/dev/disk0
#: TYPE NAME SIZE IDENTIFIER
0: Apple_partition_scheme *111.8 Gi disk0
1: Apple_partition_map 31.5 Ki disk0s1
2: Apple_HFS Gren 111.7 Gi disk0s3