Cannot mount USB after unsafe eject
Depending on what you want to do, you have a few options.
You can erase the content of the device and start again:
sudo mkfs.vfat -I /dev/sdb
sudo hdparm -z /dev/sdb
mkdir /tmp/x
sudo mount /dev/sdb /tmp/x
You can try checking the file system on /dev/sdb1, but based on comments from the op, it looks like it's a cdrom image, so it's read-only.