How Do I Eject A Card From The SD Card Slot In OS X?
Before ejecting the SD card, be sure that any transferring between the card and your computer has been completed. Then find the icon on your desktop for the SD card and drag it to the trash. Once the icon is no longer visible on your computer it is safe to remove the SD from its slot. You can follow the same steps for CD/DVDs and external hard drives.
If you can't see the SD card icon on your desktop, go to Finder > Finder Preferences and click the General tab. Check the box labeled "External disks" so that the SD card will show on your desktop.