How does Samsung implement SD card encryption?
Samsung uses its own solutions for sdcard encryption in android device at file level.
Only device which encrypted the sdcard can decrypt it because when sdcard is encrypted an encryption policy file is saved into device and sdcard.
If you insert encrypted sdcard into other device then you will only will able to see the encrypted contents of those files.

So,if you have the same device which encrypted the sdcard and you know the lockscreen which was used to encrypt it then you can easily decrypt the sdcard by navigating as below :

Settings -> Security -> Encrypt External Sdcard -> Disable/Turn off

A notification pop up will appear for decrypting sdcard on your device