Some alkaline batteries may contain some amount of mercury in them but most alkaline batteries are made without mercury and so are mercury free.
Most alkaline batteries are made without the mercury and are made using common metals such as steel, zinc and manganese and do not pose a risk to health or the environment if they are used and disposed of appropriately.
Make sure you try and recycle the old alkaline batteries by finding a drop off place or a place you can mail them to and you might even be able to make some money off of recycling the old alkaline batteries.
You won't make much but you can make a little bit of money selling the old alkaline batteries or just drop them off at a recycling place that takes them.