Calling all myrmecologists (cool word I found on the internet)!
You see them on the sidewalk from time to time. An ant struggling with a fallen comrade hurrying toward somewhere. Is it dragging them back to the anthill for a proper interment or perhaps a meal. Do ants engage in cannibalism? Hurry please, I must know.
Soylent Green is made of AAAANNNNTSSS!!!
Many species of ant create refuse piles away from their main nest. A dead ant in the nest will start to rot and may harbor bacteria or fungus that could affect the other ants in the nest.
Here’s a nice forum that covers lots of ant topics! 
(both silly and serious)
Some ants “recycle” their dead by eating them, and as Dog Wonder mentions, other ants remove their dead (and other refuse) by placing them on a rubbish heap far away from the nest. Source: Ants by Wilson and Holldobler, the absolute definitive research book on the little buggers (it won the Pulitzer, no less). It’s huge, but endlessly fascinating; I recommend it highly. I plowed through it cover-to-cover while researching a screenplay.
Oh, and one more thing:
I have another question related to this. Every once and while I will see an ant hill where it looks like every ant in the place has come out and they are literally climbing on top of on another in a giant mess. What in the world are they doing?
I think the ants climbing on top of each other are participating in an event similar to the grad ceremony at the Naval Academy where the Plebes get to climb the dildo-like thingy and get the hat off the top.