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.

Calcium sulphite is a fairly common chemical compound formed by the reaction between Ca(OH)2 and SO2. It belongs to the sulphite group, sulphur-based components that release sulphur dioxide SO2, an active preservative compound. It can be in an anhydrous or hydrated form.

It appears in the form of a white powder.

The sulphite group includes:

What it is used for and where

Food

Ingredient listed in the European food additives list as E226, synthetic preservative. Also acts as a bleaching agent. Fermentation bactericide.

Other uses

• water treatment for chlorine removal (NH₂CL, NHCL₂, NCL₃) in swimming pools, showers.
• analytical reagent
• bleaching agent for plastic products
• production of calcium plastics

Safety

Symptoms related to sulphite sensitivity can be of varying nature and importance. The most common are headache and generalised itching or swelling, but cases of nausea, bronchoconstriction, diarrhoea, hypotension and shock have also occurred (1).

EFSA's Scientific Panel on Food Additives and Flavourings assessed the risk for toxic elements in sulphur dioxide (E 220-228), based on data submitted by stakeholders, and concluded that the EU specification maximum limits for arsenic, lead and mercury should be lowered and a maximum limit for cadmium should be introduced (2).

Sodium sulfite studies

Molecular Formula     CaSO₃     CaO₃S    CaO₄S

Molecular Weight      120.14

CAS  10257-55-3

UNII    7078964UQP

EC Number   233-596-8

DSSTox ID  DTXSID10883104

IUPAC  calcium;sulfite

InChl=1S/Ca.H2O3S/c;1-4(2)3/h;(H2,1,2,3)/q+2;/p-2

InChl Key      GBAOBIBJACZTNA-UHFFFAOYSA-L

SMILES  [O-]S(=O)[O-].[Ca+2]

MDL number  MFCD00040663 

Nikkaji      J43.737I

Synonyms:

• Calcium sulfite hydrate (1:1:1)
• Sulfurous acid calcium salt (1:1)

References_____________________________________________________________

(1) Gunnison AF, Jacobsen DW. Sulfite hypersensitivity. A critical review. CRC Crit Rev Toxicol. 1987;17(3):185-214. doi: 10.3109/10408448709071208.

Abstract. Sulfiting agents (sulfur dioxide and the sodium and potassium salts of bisulfite, sulfite, and metabisulfite) are widely used as preservatives in foods, beverages, and pharmaceuticals. Within the past 5 years, there have been numerous reports of adverse reactions to sulfiting agents. This review presents a comprehensive compilation and discussion of reports describing reactions to ingested, inhaled, and parenterally administered sulfite. Sulfite hypersensitivity is usually, but not exclusively, found within the chronic asthmatic population. Although there is some disagreement on its prevalence, a number of studies have indicated that 5 to 10% of all chronic asthmatics are sulfite hypersensitive. This review also describes respiratory sulfur dioxide sensitivity which essentially all asthmatics experience. Possible mechanisms of sulfite hypersensitivity and sulfur dioxide sensitivity are discussed in detail. Sulfite metabolism and the role of sulfite oxidase in the detoxification of exogenous sulfite are reviewed in relationship to the etiology of sulfite hypersensitivity.

(2) EFSA Panel on Food Additives and Flavourings (FAF); Younes M, Aquilina G, Castle L, Engel KH, Fowler PJ, Frutos Fernandez MJ, Fürst P, Gundert-Remy U, Gürtler R, Husøy T, Manco M, Mennes W, Moldeus P, Passamonti S, Shah R, Waalkens-Berendsen I, Boon P, Cheyns K, Crebelli R, FitzGerald R, Lambré C, Mirat M, Ulbrich B, Vleminckx C, Mech A, Rincon AM, Tard A, Horvath Z, Wright M. Follow-up of the re-evaluation of sulfur dioxide (E 220), sodium sulfite (E 221), sodium bisulfite (E 222), sodium metabisulfite (E 223), potassium metabisulfite (E 224), calcium sulfite (E 226), calcium bisulfite (E 227) and potassium bisulfite (E 228). EFSA J. 2022 Nov 24;20(11):e07594. doi: 10.2903/j.efsa.2022.7594. 

Abstract. Sulfur dioxide-sulfites (E 220-228) were re-evaluated in 2016, resulting in the setting of a temporary ADI of 0.7 mg SO2 equivalents/kg bw per day. Following a European Commission call for data, the present follow-up opinion assesses data provided by interested business operators (IBOs) and additional evidence identified in the publicly available literature. No new biological or toxicological data addressing the data gaps described in the re-evaluation were submitted by IBOs. Taking into account data identified from the literature search, the Panel concluded that there was no substantial reduction in the uncertainties previously identified in the re-evaluation. Therefore, the Panel considered that the available toxicity database was inadequate to derive an ADI and withdrew the current temporary group acceptable daily intake (ADI). A margin of exposure (MOE) approach was considered appropriate to assess the risk for these food additives. A lower confidence limit of the benchmark dose of 38 mg SO2 equivalents/kg bw per day, which is lower than the previous reference point of 70 mg SO2 equivalents/kg bw per day, was estimated based on prolonged visual evoked potential latency. An assessment factor of 80 was applied for the assessment of the MoE. At the estimated dietary exposures, when using a refined exposure scenario (Data set D), MOEs at the maximum of 95th percentile ranges were below 80 for all population groups except for adolescents. The dietary exposures estimated using the maximum permitted levels would result in MOEs below 80 in all population groups at the maximum of the ranges of the mean, and for most of the population groups at both minimum and maximum of the ranges at the 95th percentile. The Panel concluded that this raises a safety concern for both dietary exposure scenarios. The Panel also performed a risk assessment for toxic elements present in sulfur dioxide-sulfites (E 220-228), based on data submitted by IBOs, and concluded that the maximum limits in the EU specifications for arsenic, lead and mercury should be lowered and a maximum limit for cadmium should be introduced.