Often times I've had need to reuse Linux boot disk as back drives for my Mac. It should be possible to format the disk, however, when using Disk Utility it's not possible to partition and format the disk by just selecting it because only the free partition shows up by default. To partition and format the entire disk, you must enable the "Show all Devices" View in Disk Utility. Use Command-2 or the View menu. At this point the full disk will show up in the device tree and the partitions will be listed underneath. Select the entire disk, then partition and erase it.