Compendium of the most significant studies with reference to properties, intake, effects.

Lagosz, A., Malolepszy, J. and Garrault, S., 2006. Hydration of tricalcium aluminate in the presence of various amounts of calcium sulphite hemihydrate: Conductivity tests. Cement and concrete research, 36(6), pp.1016-1022.

Abstract. Hydration of calcium aluminate C3A (3CaO·Al2O3) in the presence of calcium sulphite hemihydrate (CaSO3·0.5H2O), with the molar ratio of substrates close to 1, produces the C3A·CaSO3·11H2O calcium monosulphite aluminate phase. Small amounts of calcium sulphite added to calcium aluminate (the ratio of CaSO3·0.5H2O / C3A equalling 0 : 1) change the rate of C3A hydration and influence the whole reaction. Reaction processes for various ratios of the C3A–CaSO3·0.5H2O mixture were examined in pure distilled water with a considerable amount of liquid W / S = 38–50 (constant W / C3A). Processes in the liquid phase were monitored with conductivity equipment, and the XRD analysis was used to identify the phases precipitated during the examined reactions.

Cai M, Quan S, Li J, Wu F, Mailhot G. Calcium Sulfite Solids Activated by Iron for Enhancing As(III) Oxidation in Water. Molecules. 2021 Feb 21;26(4):1154. doi: 10.3390/molecules26041154.

Abstract. Desulfurized gypsum (DG) as a soil modifier imparts it with bulk solid sulfite. The Fe(III)-sulfite process in the liquid phase has shown great potential for the rapid removal of As(III), but the performance and mechanism of this process using DG as a sulfite source in aqueous solution remains unclear. In this work, employing solid CaSO3 as a source of SO32-, we have studied the effects of different conditions (e.g., pH, Fe dosage, sulfite dosage) on As(III) oxidation in the Fe(III)-CaSO3 system. The results show that 72.1% of As(III) was removed from solution by centrifugal treatment for 60 min at near-neutral pH. Quenching experiments have indicated that oxidation efficiencies of As(III) are due at 67.5% to HO•, 17.5% to SO5•- and 15% to SO4•-. This finding may have promising implications in developing a new cost-effective technology for the treatment of arsenic-containing water using DG.

Dam-Johansen, K. and Østergaard, K., 1991. High-temperature reaction between sulphur dioxide and limestone—IV. A discussion of chemical reaction mechanisms and kinetics. Chemical Engineering Science, 46(3), pp.855-859.

Abstract. A model describing the chemical kinetics of the sulphation of calcium oxide has been developed in terms of elementary chemical reaction mechanisms. The model predicts that the rate-determining reaction at low tempeatures is the disproportionation of calcium sulphite and that the rate-determining reaction at high temperatures is the direct oxidation of calcium sulphite and/or the reaction between calcium oxide and sulphur trioxide. The model is in good agreement with the limited amount of experimental measurements of initial rates of the sulphation reaction available in the literature.

Kaplan, N., & Maxwell, M. A. (1981). Nonregenerable flue gas desulfurization systems in the United States.

Abstract. In June 1980, 65 of the 73 flue gas desulphurization (FGD) systems operational at utility plants in the United States were nonregenerable systems, representing 23,000 MW or 93.5 percent of all FGD-controlled generating capacity. An additional 89 nonregenerable units were under construction or planned, representing about 45,000 MW, an increase of about 200 percent of controlled capacity. It is projected that by 1990, the contribution of nonregenerable systems to total controlled capacity will drop slightly from 93.5 percent to 92.1 percent, based on known commitments. The four processes discussed in the paper - wet lime, limestone, sodium alkali and dual alkali - are all in commercial use at one or more full-scale utility plants. The wastes from three of these processes - lime, limestone and dual alkali - are principally mixtures of calcium sulphite, calcium sulphate and varying amounts of fly ash. At a few plants, the calcium sulphite is converted to calcium sulphate by means of forced oxidation. The thickened, filtered and treated wastes from these three processes are generally placed in ponds or landfill sites. Currently, the FGD systems installed at utilities are primarily lime and limestone scrubbing processes. These account for more than 80 percent of the FGD-controlled capacity. The lower initial cost and the lower sensitivity to boiler load changes has made the sodium alkali process attractive for use with industrial boilers, although its operating cost is higher than some of the other systems. The capital costs for the type of FGD systems considered in the paper range from $88.81 per installed kW for the sodium alkali process to $106.50 for the dual-alkali process (1979 dollars). The range for total annual operating costs is 4.88 mills/kWh for the limestone process to 6.79 mills/kWh for the sodium alkali system.

Malaga-Starzec, K., Panas, I., & Lindqvist, O. (2004). Model study of initial adsorption of SO2 on calcite and dolomite. Applied Surface Science, 222(1-4), 82-88.

Abstract. The rate of calcareous stone degradation is to a significant extent controlled by their surface chemistry with SO2. Initial surface sulphite is converted to a harmful gypsum upon, e.g. NO2 catalysed oxidation. However, it has been observed by scanning electron microscopy that the lateral distributions of gypsum crystals differ between calcitic and dolomitic marbles. The first-principles density functional theory is employed to understand the origin of these fundamentally different morphologies. Here, the stability differences of surface sulphite at calcite CaCO3 (s) and dolomite CaxMg1−xCO3 (s) are determined. A qualitative difference in surface sulphite stability, favouring the former, is reported. This is taken to imply that calcitic micro-crystals embedded in a dolomitic matrix act as sinks in the surface sulphation process, controlled by SO2 diffusion. The subsequent formation of gypsum under such conditions will not require SO42− (aq) ion transport. This explains the homogeneous distribution of gypsum observed on the calcitic micro-crystals in dolomite. In contrast, sulphation on purely calcitic marbles never reaches such high SO2 coverage. Rather, upon oxidation, SO42− (aq) transport to nucleation centres, such as grain boundaries, is required for the growth of gypsum crystals.