Marshmallow SD card internal memory

I'm using lenovo A7000 and recently updated marshmallow and chosen 32GB SD card as internal memory. It was worked as internal memory perfectly quite some time, all of sudden I got message that SD corrupted and doesn't show data stored in the card, it shows zero files, I lost all media files!! However USB storage option in settings SD card shows 6.5GB used out of 28GB. Since it's treated as internal memory I'm not able to read the card as drive in other devices/computer. I have important media files and documents in SD card and I didn't backup them. I'm bit worried!!! How to recover the data from SD card. I assume if SD card changed back to portable, it will format and lose data!!! Please support