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Calcium sulfite is an inorganic compound with the chemical formula CaSO₃.
Calcium sulfite consists of calcium ions (Ca²⁺) and sulfite ions (SO₃²⁻) arranged in an ionic solid structure.
Calcium sulfite is commonly encountered as a white to off-white solid.
CAS Number: 10257-55-3
Molecular Formula: CaH4O3S
Molecular Weight: 124.17
EINECS Number: 233-596-8
Synonyms: Calcium sulfite, Sulfurous acid, calcium salt (1:1), Calcium sulphite, UNII-7078964UQP, Sulfurous acid calcium salt (1:1), EINECS 233-596-8, 7078964UQP, CALCIUM SULFITE [MI], INS No. 226, CALCIUM SULFITE (CaSO₃), CALCIUM SULFITE (1:1), DTXSID10883104, INS-226, EC 233-596-8, CALCIUM SULFITE (E 226), E-226, RefChem:122913, DTXCID701022682, 10257-55-3, Calciumsulfite, calcium;sulfite, MFCD00040663, 15091-91-5, SULFUROUS ACID, CALCIUM SALT (1:1), HYDRATE (8CI,9CI), Calciumsulfit, CaO₃S, SCHEMBL62796, AKOS015856584, NS00086811, Q899410, Sulfurous acid, calcium salt;calcium sulphite;sulfurous acid, calcium salt (1:1);Calciumsulfit;CalciumSulfitePowder
Calcium sulfite does not occur widely as a natural mineral but is mainly produced as an industrial by-product.
Calcium sulfite is formed during flue gas desulfurization (FGD) processes, where sulfur dioxide (SO₂) is removed from exhaust gases using calcium-based sorbents.
In many cases, calcium sulfite is further oxidized to calcium sulfate.
Physically, calcium sulfite is a fine powder with low solubility in water.
Calcium sulfite is more soluble than calcium sulfate but still considered sparingly soluble.
Its solubility and stability depend on pH, oxygen availability, and temperature.
Calcium sulfite is a reducing agent and can be oxidized to calcium sulfate in the presence of oxygen.
This oxidation process is often intentional in industrial systems.
The sulfite ion is less stable than sulfate and readily participates in redox reactions.
Calcium sulfite is relatively stable under dry conditions but can slowly oxidize when exposed to air and moisture.
In aqueous environments, it may react with acids to release sulfur dioxide gas.
This behavior distinguishes it from more stable sulfate salts.
Calcium sulfite is mainly of interest in environmental engineering, industrial chemistry, and materials processing.
Calcium sulfites formation and transformation are important in pollution control technologies.
Calcium sulfite is also studied in waste management and recycling of desulfurization by-products.
Calcium sulfite can remove residual chlorine from water, including combined residual chlorine (NH2Cl, NHCl2, and NCl3) and free residual chlorine (ClO-, HOCl, and Cl2).
Compared with traditional activated carbon, it has a more efficient chlorine removal effect, is safer, more resistant to high temperatures, and does not breed bacteria.
Calcium sulfite is widely used in various water treatments for residual chlorine removal in Southeast Asian countries and regions such as Japan, South Korea, Malaysia, and Taiwan.
Calcium sulfite, or calcium sulphite, is a chemical compound, the calcium salt of sulfite with the formula CaSO3·x(H2O).
Two crystalline forms are known, the hemihydrate and the tetrahydrate, respectively CaSO3·½(H2O) and CaSO3·4(H2O).
Calcium sulfite is most notable as the product of flue-gas desulfurization.
Calcium sulfite commonly exists in hydrated forms, such as calcium sulfite hemihydrate (CaSO₃·½H₂O).
The hydration state affects particle size, reactivity, and handling characteristics.
Hydrated forms are especially common in industrial by-products from flue gas treatment.
In aqueous systems, calcium sulfite establishes an equilibrium with dissolved sulfite and bisulfite species.
This equilibrium is strongly influenced by pH and dissolved oxygen concentration.
Under alkaline and oxygen-rich conditions, oxidation to calcium sulfate is favored.
From a materials perspective, calcium sulfite particles are generally fine and porous.
This morphology increases surface area and enhances reactivity.
These properties are relevant in gas–solid and solid–liquid reaction systems.
Calcium sulfite plays an important transitional role in desulfurization chemistry.
It represents an intermediate product between sulfur dioxide capture and final sulfate formation.
Understanding its stability is critical for optimizing pollution control processes.
Thermally, calcium sulfite decomposes at elevated temperatures.
Decomposition may release sulfur dioxide and form calcium oxide or sulfate depending on conditions.
This limits its use in high-temperature environments without further treatment.
In environmental systems, calcium sulfite can influence oxygen demand in water.
Oxidation of sulfite consumes dissolved oxygen.
This property is considered when managing waste streams containing sulfite compounds.
Calcium sulfite is chemically less stable than calcium sulfate.
Its tendency to oxidize gives it different storage, handling, and disposal considerations.
This distinction is important in industrial safety and environmental compliance.
Melting point: 600°C
Density: 33.3[at 20℃]
solubility: slightly soluble in ethanol; soluble in acid solutions
form: solid (rough estimate)
color: white
Water Solubility: 0.0043g/100mL (18°C), 0.001g/100mL (100°C) H2O; slightly soluble alcohol; soluble in acid solutions with SO2 evolution [MER06] [CRC10]
Calcium sulfite is produced on a large scale by flue gas desulfurization (FGD).
When coal or other fossil fuel is burned, the byproduct is known as flue gas. Flue gas often contains SO2, whose emission is often regulated to prevent acid rain.
Sulfur dioxide is scrubbed before the remaining gases are emitted through the chimney stack.
An economical way of scrubbing SO2 from flue gases is by treating the effluent with Ca(OH)2 hydrated lime or CaCO3 limestone.
Calcium sulfite shows pH-dependent chemical behavior in aqueous environments.
Under acidic conditions, sulfite ions can be protonated to bisulfite and sulfurous acid, which may release sulfur dioxide gas.
This sensitivity to pH is important in both industrial handling and environmental impact assessments.
In flue gas desulfurization systems, calcium sulfite formation is often an intermediate step rather than the final product.
Many systems intentionally oxidize calcium sulfite to calcium sulfate to obtain a more stable and reusable material (synthetic gypsum).
Control of oxidation conditions directly affects product quality and by-product management.
Calcium sulfite particles tend to have high surface reactivity due to their fine particle size.
This makes them more chemically active than calcium sulfate in wet systems.
However, it also increases their tendency to undergo unwanted oxidation during storage.
From a crystallographic standpoint, calcium sulfite has less well-defined and less stable crystal structures than sulfate salts.
This contributes to its lower thermodynamic stability.
As a result, it is rarely found as a persistent mineral in natural environments.
In waste management, calcium sulfite requires controlled disposal or conversion.
If left untreated, it can generate sulfur dioxide under certain conditions.
Therefore, stabilization or oxidation to calcium sulfate is often preferred.
In environmental chemistry, calcium sulfite is relevant to oxygen balance and redox processes.
Its oxidation consumes dissolved oxygen, which can affect aquatic systems if released improperly.
This makes monitoring important in industrial effluents.
Calcium sulfite is best described as a reactive, transitional inorganic compound.
Its importance lies more in its role within industrial and environmental processes than in direct end-use applications.
Calcium sulfite is a white, crystalline inorganic compound with several industrial and niche uses driven by its reducing properties, ability to bind sulfur dioxide, and role as an intermediate or byproduct in various chemical processes.
Uses:
Calcium sulfite is primarily used in flue gas desulfurization (FGD) systems as an intermediate product.
Calcium sulfite forms when sulfur dioxide reacts with calcium-based sorbents during air pollution control.
In many systems, it is subsequently oxidized to calcium sulfate for stabilization and reuse.
In environmental engineering, calcium sulfite is used in research and process optimization of sulfur dioxide removal technologies.
Studying its formation and oxidation behavior helps improve efficiency of emission control systems.
This is important for reducing industrial air pollution.
Calcium sulfite is applied in waste management and by-product recycling.
FGD by-products containing calcium sulfite are treated or converted into more stable materials such as synthetic gypsum.
This supports waste minimization and resource recovery.
In chemical and materials research, calcium sulfite is used as a model compound for studying sulfite oxidation and redox reactions.
Its behavior helps researchers understand sulfur chemistry in aqueous and solid systems.
These studies are relevant to both industrial chemistry and environmental processes.
Calcium sulfite has limited industrial direct-use applications due to its lower stability.
However, it plays a crucial functional role as a transitional compound in sulfur control technologies.
Its value lies mainly in process chemistry rather than as a final commercial product.
Calcium sulfite is used in laboratory and pilot-scale studies related to air pollution control.
It helps simulate and evaluate sulfur dioxide capture efficiency under different operating conditions.
These studies support the design and scaling of desulfurization systems.
In water and wastewater treatment research, calcium sulfite is examined for its reducing properties.
Calcium sulfite can act as an oxygen scavenger in controlled environments.
This application is mainly experimental rather than widespread industrial use.
Calcium sulfite is applied in cement and construction research as a minor additive or intermediate.
When oxidized to calcium sulfate, it can influence setting behavior and material properties.
This is relevant in studies involving industrial by-products in building materials.
In environmental chemistry studies, calcium sulfite is used to model sulfite behavior in soils and sediments.
Calcium sulfite helps researchers understand sulfur cycling and redox transformations.
These insights are important for assessing environmental impact of industrial emissions.
Calcium sulfite is also used in educational and academic research.
Calcium sulfite serves as an example of an unstable inorganic salt undergoing oxidation and acid–base reactions.
This makes it useful for teaching concepts in industrial chemistry and environmental engineering.
Safety Profile:
Calcium sulfite sulfite is considered to have low to moderate toxicity under normal handling conditions.
It is not classified as highly hazardous, but its chemical reactivity requires appropriate precautions.
Most risks arise from its potential to release sulfur dioxide.
Exposure to dust or fine particles can cause irritation of the eyes, skin, and respiratory tract.
Inhalation may lead to coughing, throat irritation, or shortness of breath.
Adequate ventilation and dust control are recommended in occupational settings.
In acidic or moist environments, calcium sulfite can release sulfur dioxide gas.
Sulfur dioxide is a respiratory irritant and can cause eye irritation and breathing difficulties.
This risk is particularly relevant during storage, handling, or disposal under improper conditions.
Skin contact may cause mild irritation, especially with prolonged exposure.
Eye contact with dust can result in redness and discomfort.
Protective gloves and eye protection should be used during handling.
Calcium sulfite is non-flammable and does not pose a fire or explosion hazard.
However, thermal decomposition at high temperatures may release sulfur oxides.
Standard fire safety procedures for inorganic solids are sufficient.
From an environmental standpoint, calcium sulfite can contribute to oxygen depletion when oxidized in water.
This may negatively affect aquatic organisms if released untreated.
Proper stabilization and disposal according to environmental regulations are necessary.
