Help mounting rw

Hello, fairly new to the Linux world. I work for a public school and would really appreciate any help, i'm trying to help search a student device with CAINE. I'm trying to pull an image of the drive for analysis, first I'm trying to mount an external USB hard drive 'sdb' with read and write privileges so I can write to it and copy the image with Guymager tool. If i just try to mount with CAINE it automatically write protects anything.

I'm tried first as root user: mkdir /media/forensicA
Then: mount -o rw /dev/sdb /media/forensicA

but i get this error:
"wrong fs type, bad option, bad superblock on /dev/sdb/, missing codepage or helper program, or other error"

i've googled around but nothing specific that helps.