Formatting mac and encrypted memory Currently I have a 128GB SD for data in my macbook, but is encrypted using utility. If I format my mac, the stored key will be gone.

How can I do this safely? Is there any way to do this without losing access to my SD?

Thank you
I'm a little unclear what your configuration is...
If your "128GB SD" is an external drive: Unencrypt the data, reformat macbook, encrypt data again.

If your "128GB SD" is the drive that you wish to reformat: 
Copy the data to another external drive unencrypted, reformat your drive, copy the data back onto it and encrypt it over again.

Is there anything keeping you from doing either of these?