wordpress to cogigniter

So do you know PHP security then? A system just don't magically get secure by switching platform. There are a lot of things to make sure to look for when developing an application.

The easiest way are to use Wordpress Export function and generate XML, and built a custom importer based on that content. As it would be harder to make CodeIgniter to parse the Wordpress database itself.
https://wordpress.com/support/export/