I am not sure Fasting will clean out the Mercury, but it will help you with many other ailments that are resulted from Mercury.
Good idea to fast without any supplements. After you complete your fast please try Cilantro regimen and Iodine protocol, both are metal removal vehicles and cleans all small amounts deposited in tissues. The problem with these metals is the deposits also allows bacteria to grow around it and people are immune to Antibiotics . Not that I advocate taking Antibiotics .
While doing Cilantro and Iodine detox please continue with Bentonite clay and coffee enemas. I also don't suggest enemas during a long fast, first days it is ok after that I is enervating.
Another thing you can add to your diet is Turmeric, a few tablespoons a day. It will help with swollen glands and tongue.