Calcium sulfate

**Hydration States and Crystallographic Structures:**
– CaSO4 (anhydrite): anhydrous state
– CaSO4·2H2O (gypsum and selenite): dihydrate
– CaSO4·1/2H2O (bassanite): hemihydrate
– Specific hemihydrates: α-hemihydrate and β-hemihydrate

**Uses:**
– Production of plaster of Paris and stucco
– Forms moldable paste upon hydration
– Hardens as crystalline calcium sulfate dihydrate
– Poorly soluble in water
– Does not readily dissolve in water after solidification

**Hydration and Dehydration Reactions:**
– Gypsum converts to bassanite or plaster of Paris with heating
– Temperatures of 100-150°C needed for dehydration
– Dehydration equation: CaSO4·2H2O → CaSO4·1/2H2O + 1+1/2H2O
– Exothermic reaction for casting shapes and bone repair cement
– γ-anhydrite formed at 180°C, β-anhydrite at 250°C

**Applications:**
– **Food Industry:**
– Used as a coagulant in tofu
– FDA permits in various food products
– Known as E516 in the E number series
– Functions as a firming agent and leavening agent
– Used in cheese, bakery products, frozen desserts, and more
– **Dentistry:**
– Used in bone regeneration and graft materials
– Acts as a barrier in guided bone tissue regeneration
– Biocompatible and completely resorbed post-implantation
– Creates a calcium-rich milieu
– Does not evoke significant host response

**Production and Occurrence:**
– Main sources: naturally occurring gypsum and anhydrite
– Extraction methods: open-cast quarrying or deep mining
– World production: around 127 million tonnes per annum
– By-products: flue-gas desulfurization, phosphoric acid production, hydrogen fluoride production, zinc refining
– Recycling: calcium sulfate recovery from scrap drywall