I've added "IRC Chat" as an item below "Home Site" on the main page. This takes you to KiwiIRC, and pre-fills the nickname field with your forum username. If you know this name is taken by someone else on Rizon, it isn't a valid name on IRC, or you simply want to use a different name, you can change it before you connect.
As always you're still encouraged to use a standalone IRC client like Hexchat
(requires Firefox), or AndChat
(for Android devices) instead of the web-based one.