This paper, describes the researches completed on the purification of the Slovak coals intended for the production of electric power, with a view to solve the ecological problems created by these coals. Both gravimetric concentration processes (tables and spirals) and physico-chemical and chemical processes were investigated; also, a comparison was made with Spanish coals. The results obtained confirm that by treating the Slovak energetic coals in Humphrey＇s spirals, it is possible to decrease their ash content below 30 % wt, with a sulphur content similar to the initial ones, but with a much higher thermal power. This makes that the quantity of sulphur reaching combustion per power unit produced, becomes substantially lower, with the resulting ecological advantage. As to the nitric acid leaching processes studied is concerned, these result in a substantial sulphur decrease, but also in an excessive attack to the organic matter in the case of the Slovak coals, which does not occur in the comparable Spanish coal, and by that reason the process does not seem to be a feasible one.