Despite many technological possibilities, proper sanitation of sludge creates problems to their natural use. Thus, new solutions are still being looked for. Liming is one of the methods for sludge sanitation, however, rather expensive one. Seeking the substitute of high calcium content and non-toxic for environment has led to investigations on the application of mineral wastes - ashes from semi-dry sulfur removal from flue gases in the "Opole" power plant for sludge sanitation purposes. Ash was mixed with sludge in various proportions. After 3 days, the microbiological exams of the mixtures were carried out. The investigation data proved the performed sanitation effective and confirmed microbiological usability of the sludge for a natural use. The total contents of heavy metals and their distribution between particular fractions were determined in the sludge mixtures with mineral waste and in reference samples (i.e. sludge and mineral waste). No significant changes of metals proportion bound with biogenie fractions (fractions I- II) after addition of the mineral wastes to sludge were observed. Cadmium, zinc and partially chrome are bound with the iron and manganese oxides fraction (fraction III) which is sensitive to the redox potential changes. No significant change of contents was observed with the increase in a contribution of sludge or mineral waste. In all samples of the organic fraction (fraction IV) chrome and copper are bound in the highest amounts, and in the residue fraction (fraction V) cadmium, nickel and lead are bound, mainly. The investigation has showed that addition of optional proportions of sludge and mineral wastes mixtures into soil did not result in increase in heavy metals hazard. The investigation of the metals speciation in sludge and their mixtures with the mineral wastes showed similar metals distribution in individual fractions. The most hazardous elements for soil, water and plants such as lead, chrome, nickel, cadmium and zinc are bound in slightly soluble fractions and thus are hardly available to the ecosystem.