Considerable effort has been devoted in recent years to upgrading high-sulfur coals by both physical and chemical methods. Some methods are mild, selectively removing mineral components without significantly altering the organic matter. The more drastic methods break down the coal structure, separating it into an inorganic sludge and an organic product essentially not coal. As a recently publicized example, high gradient magnetic separation has been proposed as a technique for removing pyrite and other weakly paramagnetic minerals for slurried coal. The Bureau of Mines froth flotation process removes pyrite and other minerals by taking advantage of differences in density and wettability of these undesirable substances and organic material. A method known as Meyer's Process involves up to six leaches of pulverized coal with ferried salt solution at about 100 C, converting pyrite to surface and elemental sulfur. A more vigorous chemical method requires leaching finely pulverized coal with aqueous alkali at about 225 C in a closed system under or inert atmosphere, followed by treatment with strong acid and leaching with water. The still more vigorous PAMCO process involves dissolution of coal in solvent at elevated temperature, hydrogen treatment, physical separation of undissolved matter, and vacuum distillation of the dissolved products.