There is a difference between ash and charcoal. Ash is completely burnt wood and charcoal is partially burnt wood. The charcoal from your fire will work to remove toxins. Just not as well as activated charcoal. Activated charcoal is charcoal taken to to a completely different level. To activate charcoal is usually heated with steam to something like 900 degrees centigrade. Very, Very hot. This breaks down the charcoal so that it has a tremendous surface area. The more surface area the more it absorbs. So to do the same job it requires much more plain charcoal. Most commercial activated charcoal is made from coconut hulls.