The effect of different types of metallic salt additives (Na2CO3, Li2CO3, K2CO3, Na2SO4, NaF, NaCl, ZnSO4, Ca(NO3)(2), Cs2CO3 and Al-2(SO4)(3)) on direct sulfation of calcium carbonate is investigated. The experiments were carried out in a thermogravimetric analyzer under isothermal conditions at temperatures between 700 and 875 degrees C. An ultrapure calcium carbonate sample with a mean size of 17 mu m and a specific surface area of 0.43 m(2) g(-1) was used. From the sulfation tests some additives (Na2CO3, Li2CO3, K2CO3, Na2SO4, NaF, NaCl) enhanced the sulfation capacity and sulfation rate with respect to the undoped sample. All these additives correspond to alkaline compounds. The effect of additives on the decomposition of CaSO4 in sulfated samples was also investigated. In this case nonisothermal experiments with a heating rate of 4 K min(-1) were performed in a CO2 atmosphere. The results indicate that presence of some additives has a catalytic effect on sulfate decomposition.