THE EFFECT OF METALLIC SALT ADDITIVES ON DIRECT SULFATION OF CALCIUM-CARBONATE AND ON DECOMPOSITION OF SULFATED SAMPLES

The effect of different types of metallic salt additives (Na2CO3, Li2C O3, K2CO3, Na2SO4, NaF, NaCl, ZnSO4, Ca(NO3)(2), Cs2CO3 and Al-2(SO4)( 3)) on direct sulfation of calcium carbonate is investigated. The expe riments were carried out in a thermogravimetric analyzer under isother mal conditions at temperatures between 700 and 875 degrees C. An ultra pure calcium carbonate sample with a mean size of 17 mu m and a specif ic 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 sam ple. All these additives correspond to alkaline compounds. The effect of additives on the decomposition of CaSO4 in sulfated samples was als o investigated. In this case nonisothermal experiments with a heating rate of 4 K min(-1) were performed in a CO2 atmosphere. The results in dicate that presence of some additives has a catalytic effect on sulfa te decomposition.