This page consists of screenshots from Security Settings – Block/Unblock IP Ranges Screen in Captcha Bank WordPress Plugin.
This gives an idea about how to Block/Unblock IP Ranges and view the comments related to it. You can easily block IP Range by providing Starting and Ending Range. You can also choose Time Duration to block the IPs for specific time period or to permanently block it from the site.
Using this, you can view list of Blocked IP Ranges and if needed delete them from the list.