I know of no reason you couldn't put citrus in compost. My gardening encyclopedia says you may use any plant material that will rot fairly quickly, as long as it is not diseased. Be advised, this is for a "compost HEAP" and may not apply to a "Bin" for some reason. All my references do say to not use fats or meats of any kind in compost. I have had good luck by processing large pieces of kitchen veggie waste,( ie: cabbage stalks, carrots, turnips, etc.) in my food processor. Composting as small a piece as possible speeds up the job!
Bonnie W.
November 2007