SD card corrupt after hot removal
Just setting up a new volume is pretty easy with:

diskutil eraseDisk ExFAT SD256 disk44


(I chose disk44 above for the example but you will need to choose your disk number after making sure you're not erasing the boot volume or other critical disks - check your backups and disconnect any external drives you aren't prepared to restore from backup)

See Cannot unmount disk0 resource busy and When erasing media in Disk Utility, how can I change the default format? for a little extra visual or other options of diskutil that work on a volume instead of destroying all data on the disk.