First bring the disk out of the volume group, and clear the PVID:

[root@aix01]/root# lspv
hdisk3          000e583a618a3ca8                    testvg          active      
[root@aix01]/root# reducevg testvg hdisk3
[root@aix01]/root# chpv -C hdisk3

Format the disk, it will put 0 on each block:

[root@aix01]/root# dd if=/dev/zero of=/dev/hdisk3 bs=1024k count=$(bootinfo -s hdisk3)

Cleanup alternate disk

# alt_rootvg_op -X old_rootvg #remove the old vios installation
# chdev -l hdisk1 -a pv=clear # wipe out the PVID
# chpv -c hdisk1 #remove boot record
# dd if=/dev/zero of=/dev/hdisk1 bs=4092 count=12800 #erase hdisk1