If you use
/ban -k <nick> <reason>
that will kick & ban <nick> giving <reason> as the reason. This is a permanent ban until it's manually removed. If you want it to unset the ban after a certain amount of time, then use
/ban -ku<time> <nick> <reason>
where <time> is the amount of time the ban is to be in effect for measured in seconds
Appears that SladeKraven & I have differing opinions as to just exactly what you were looking for.