Replying to Corrupted SD recovery help

Looking for help recovering photos.

My SD card in my Samsung s4 decided to shit the bed and my phone now tells me it is corrupted and can't access anything.

I saw online that there is some sort of chkdsk thing you can do on windows. I have a macbook though. I ran it through disk utility repair and it says it Can't unmount disk.

I know nothing about this except I can't access all my photos. Is there any decent software out there that is free? What's the recommended way forward?

Thanks. xoxo