How can I do a redirect with CodeIgniter?

I had a wordpress site before I built my site with codeigniter. I was getting a fair amount of traffic to those wordpress pages but replaced the site with a totally different layout and codeigniter instead of wordpress.

I have a lot of pages cached by Google in the form of www.website.com/category/post. I have a 1 page style site now. I'm not sue how to do the redirects from the old pages to the new page. Any help you can give is appreciated