Calcium Sulfate

Product Overview

Calcium sulfate is a stable inorganic calcium‑salt compound. Commercially, it is mainly available in three forms: dihydrate calcium sulfate (gypsum rock), hemihydrate calcium sulfate (plaster of Paris), and anhydrous calcium sulfate (anhydrite). As a green inorganic gelling and filling raw material, it boasts the world's largest reserves and widest range of applications. It normally appears as an odorless, non‑toxic white crystalline powder or granule with sound physicochemical stability. It features excellent gelling, flame‑retardant, filling and weather‑resistance properties, and is widely used in construction building materials, industrial filling, food processing, medical care, soil improvement for agriculture, mold manufacturing and many other fields.

The three forms show prominent property differences. Dihydrate calcium sulfate has the highest stability and hardly deteriorates, serving as the primary basic raw material. Hemihydrate calcium sulfate rapidly sets and hardens upon contact with water, acting as the core raw material for gypsum building materials, molds and medical bandages. Anhydrous calcium sulfate features high hardness and good temperature resistance, and is mostly used for high‑end filling and drying auxiliary agent scenarios. None of these products are hazardous chemicals; they are safe and eco‑friendly with no risk of combustion, explosion or poisoning. Benefiting from abundant natural gypsum ore resources and mature industrial purification technology for desulfurized gypsum, China takes the global lead in production capacity. Stable bulk supply and customized specifications are available, which thoroughly addresses key customer pain points of high import prices, long lead times and unstable batch quality.

Basic Parameters

Production Processes of Calcium Sulfate

(1) Natural Gypsum Calcination

Heat is applied to remove crystal water from dihydrate calcium sulfate (CaSO₄·2H₂O) and convert it into gelling hemihydrate calcium sulfate (CaSO₄·0.5H₂O). Using natural gypsum (dihydrate calcium sulfate) as feedstock, heating is performed in calcination equipment. At about 100 °C, water molecules start migrating from lattice vacancies; stable crystal nuclei form at 120 °C. Above 160 °C, diffusion and crystal growth complete to yield β‑hemihydrate calcium sulfate. This low‑temperature calcination generally runs at 107‑170 °C.

Under high‑temperature calcination (800‑1000 °C), dihydrate calcium sulfate is fully dehydrated into anhydrous calcium sulfate. Partial calcium sulfate decomposes into calcium oxide, which acts as an activator during hydration‑hardening and endows materials with new properties.

(2) By‑Product Recovery from Chemical Industry

The core principle is to convert calcium‑ or sulfur‑containing industrial waste into sparingly‑soluble calcium‑sulfate precipitate via acid‑base neutralization or double‑decomposition reactions.

Neutralization Method: Waste sulfuric acid from chemical plants reacts with slaked lime (calcium hydroxide) to generate calcium‑sulfate precipitate and water.
Reaction Equation：

Oxidation Method: Sulfur dioxide from coal‑fired flue gas is first absorbed by limestone slurry to form calcium bisulfite, which is further oxidized by oxygen to produce calcium sulfate.
Reaction Equation：

Double‑Decomposition Method: Phosphate rock is decomposed by sulfuric acid, generating large volumes of phosphogypsum mainly composed of calcium sulfate. It can be recovered through washing and purification. This represents the primary source of by‑product calcium sulfate from domestic phosphorus‑chemical enterprises in China.

Precipitation Method: Calcium chloride, a by‑product of the ammonia‑soda alkali‑making process, reacts with sodium sulfate to produce calcium‑sulfate precipitate and sodium chloride.
Reaction Equation：

Grade Classification of Calcium Sulfate

(1) Food‑Grade Calcium Sulfate

In food applications, calcium sulfate serves as a nutrient supplement, yeast activator, dough modifier, firming agent, chelating agent, gelling agent, baking‑powder ingredient, carrier, filler, pH regulator and grinding agent. It is largely applied in baked goods. As a firming agent, it is used in canned potatoes, tomatoes, carrots, kidney beans and chili peppers. It is also an ingredient in confectionery, ice‑cream and other frozen desserts. In beer brewing, it is added during malt processing to raise calcium‑ion content in water. It functions as an abrasive in food‑contact cleaners, and is also used in cosmetics and toothpaste.

(2) Pharmaceutical‑Grade Calcium Sulfate

In medical practice, calcium sulfate is mainly used for fracture immobilization and bone‑defect repair. Its key benefits include promoting bone healing, providing mechanical support, good biocompatibility and degradable absorbability. Acting as a bone‑graft substitute, it releases calcium ions to stimulate osteoblast activity and accelerate new‑bone formation, and is commonly applied to fill non‑weight‑bearing bone defects. After setting, it delivers certain compressive strength to supply temporary structural support for fracture sites, preventing soft‑tissue collapse and maintaining bone anatomical morphology. It shows no tissue rejection and triggers minimal inflammatory response after implantation, complying with ISO 10993 biocompatibility standards. In‑vivo, it is gradually decomposed and absorbed by osteoclasts at a rate matching new‑bone growth, and is eventually fully replaced by autologous bone tissue.

(3) Industrial‑Grade Calcium Sulfate

Calcium sulfate is an important set‑retarding agent for cement, normally dosed at 3‑5 %. It effectively regulates cement setting time, prevents flash‑set and ensures smooth construction operations. In the building sector, high‑strength gypsum boards, blocks and plastering materials heavily rely on calcium sulfate. Thanks to its fire‑proof, sound‑insulating and humidity‑modulating characteristics, it is widely adopted for indoor partition walls, suspended ceilings and decorative projects.

Industrial Chain

Upstream Core Raw Materials: Natural gypsum ore, limestone, desulfurization mother liquor, purified water, refined impurity‑removing additives. China possesses abundant natural‑gypsum reserves and mature mining systems. It ranks first globally in output of desulfurized by‑product gypsum with 100 % raw‑material self‑sufficiency, eliminating import dependence and enabling strict source control over cost and quality.

Downstream Application Fields: Construction & infrastructure, paper‑making & coatings, rubber‑plastic filling, food processing, medical devices, agricultural soil remediation, metallurgy & chemical engineering, precision mold‑making, advanced‑material whisker preparation, etc.

Safety, Storage and Transportation

Calcium sulfate is a non‑toxic, harmless, non‑flammable, non‑explosive, non‑strong‑corrosive green inorganic salt. It is not classified as a hazardous chemical, and shall be stored and transported as general chemical or building‑material cargo with extremely low operational risks. Only powder dust may mildly irritate respiratory tracts and eye mucous membranes; no severe poisoning, explosion or corrosion hazards exist.

Storage Specifications

Store in dry, cool, ventilated and dedicated clean chemical warehouses with fully sealed packaging to isolate humid air, rainwater and water vapor. Special humidity control is required for hemihydrate calcium sulfate: it is highly hygroscopic and pre‑hydrates in the presence of moisture, leading to performance failure. All grades shall be kept away from high‑temperature heat sources and open flames; prolonged high‑temperature stacking is forbidden to avoid dehydration and property deterioration. Store separately by zone. Do not co‑store with strong acids, strong bases or strong oxidants to prevent chemical reactions, contamination and material degradation. Ventilation and dehumidification equipment shall be available for warehouses in high‑humidity southern regions to guarantee storage stability and service performance.

Transportation Specifications

Follow general‑cargo transportation standards. Implement full protection against rain, moisture, sunlight exposure and package damage, and keep packages intact and sealed. Do not co‑transport with toxic, odorous or corrosive goods to avoid odor adsorption and contamination. LTL, full‑truck, sea and land freight are all supported. Export shipments require no hazardous‑chemical filing or hazardous‑containers; documentation is simple with fast customs clearance and low logistics costs.

Safety Protection

For routine operations, wear dust‑proof respirators, work gloves and safety goggles. Keep work zones ventilated to minimize dust accumulation and fugitive dust. In case of powder contact with eyes or respiratory tracts, flush immediately with plenty of running water. No major safety risks occur during ambient‑temperature storage, handling and usage; operational safety is high.

Frequently Asked Questions (FAQ)

Q: Why does plaster of Paris cake and lose efficacy? How to prevent it?

A: Caking and failure of hemihydrate plaster of Paris stem mainly from moisture‑induced pre‑hydration. Upon exposure to atmospheric moisture, premature hydration and setting occur, causing powder caking, disordered initial‑/final‑setting time, sharp drop in mechanical strength, and even complete scrappage in severe cases. Effective preventive measures: adopt fully sealed moisture‑proof packaging; maintain constant temperature and controlled humidity in warehouses; prohibit open‑air stacking and rain exposure. Shorten inventory turnover cycles in hot‑humid seasons. For large‑volume project procurement, customized double‑layer moisture‑proof packaging is available to maximize product activity and service performance.

Q: What advantages does Chinese calcium sulfate have versus imported supplies?

A: ① Reliable supply: Dual capacity from mineral ore and industrial by‑products eliminates supply‑disruption risks; large‑volume long‑term orders can be reliably fulfilled.
② Cost‑effective: Full domestic industrial‑chain self‑sufficiency removes import premiums, delivering prominent cost benefits for bulk purchases.
③ Flexible customization: Particle size, whiteness, purity, setting time and packaging specifications can be tailored; both small trial batches and mass production are supported.
④ Efficient service: Near‑source shipment within China and fast after‑sales response; simple and convenient export logistics.
⑤ Quality assurance: Stable batches and controllable impurities, avoiding large batch‑to‑batch variations and difficult after‑sales claims associated with imported goods.

Q: Does calcium sulfate pose corrosion risks to equipment?

A: Calcium sulfate is chemically neutral, stable and inert with no corrosive properties. Conventional industrial and building‑material equipment made of carbon steel, 304/316 stainless steel, PP, PE and fiberglass‑reinforced plastic are compatible without special anti‑corrosion retrofits, resulting in low equipment‑maintenance costs. Only under long‑term high‑humidity and high‑salinity conditions shall ordinary carbon‑steel equipment receive routine anti‑rust treatment; no risk of severe equipment corrosion and damage exists.