Having a couple to toss I checked with Iowa DNR and online. You can drive way out to Bondurant to the recycling center there or, better yet, go to Home Depot and dispose of them there:
At each The Home Depot store, customers can simply bring in any expired,unbroken CFL bulbs, place them in a plastic bag and deposit them both into a collectionunit. The bulbs will then be managed responsibly by an environmental managementcompany who will coordinate CFL packaging, transportation and recycling to maximizesafety and ensure environmental compliance. Customers will be able to locate the CFLreceptacle on the front end of the store near the entrance, by the Returns desk or near theexit doors inside the store.
Go to the Home Depot Eco Options page for further information.