Delete Query from codeigniter

[eluser]xtremer360[/eluser]
I'm trying to figure out how I need to do this query. I'm trying to delete all the users who have registered but not activated witin a certain time limit.

Code:

function purgeNA($expirePeriod)
{
    $this->db->where('usersStatusesID', 1);
    $this->db->where('UNIX_TIMESTAMP(registrationDate) <', time() - $expirePeriod);
    $this->db->delete($this->usersRegistrationsTable);
}

Here's my db structure:

Code:

usersRegistrationsTable - userID, registrationDate
usersTable              - userID, usersStatusesID