Modeling sulfur dioxide deposition on calcium carbonate

Sulfur dioxide is the main decay factor of carbonate-based stones (limestones, marble, etc.) in polluted environments, with crust formation and solubilization of the stone being the main components. The deposition and presence of airborne particles can accelerate and enhance the decay processes due to sulfur dioxide. Different laboratory tests have been carried out to study the deposition and reaction of sulfur dioxide with calcium carbonate. The rate and extension of reactions is strongly influenced by the relative humidity and the presence of foreign substances. It has been found that the evolution of the concentration of the involved species (CaCO3, CaSO3. (1)/2H2O, and CaSO(4)(.)2H(2)O) can be represented by a mathematical model of the form X = k(1)[1 - exp(k(2)t)], where X is the concentration expressed as a molar fraction, t is time, k(1) is the concentration as t tends to infinity, and k(2) can be associated with a pseudo-first-order rate constant. The effect of different metallic oxides and salts, silica gel, and activated carbon has been tested.