Coal is a non-renewable energy source because it takes millions of years to form. That means what is in the ground now is all there is and we can’t realistically make more.The energy in coal comes from energy that was stored in giant plants that lived hundreds of millions of years ago in swamp forests, even before the dinosaurs! When these giant plants and ferns died, they formed layers at the bottom of the swamps.Water and dirt began to pile up on top of the dead plant remains. Over thousands of years pressure and heat would build up on top of the plant remains, undergoing chemical and physical changes and pushing out the oxygen, turning these remains into what we call coal.
A process for purification of coal comprises forming an aqueous leaching solution containing nitric and hydrofluric acid. Impurities are removed by contacting coal having a mesh size not greater than 8 (Tyler Series) with the leaching solution for a period of 15 to 120 minutes at a temperature of 20° to 100° C. During the contacting of coal with leaching solution, a gaseous material such as air can be bubbled therethrough to provide additional mixing action and oxidant material. Thereafter, the solution is removed and the leached coal washed with water.