Overview
Desulfurization gypsum is a synthetic calcium sulfate dihydrate produced as a byproduct of flue gas desulfurization (FGD) systems in coal-fired power plants. When SO2 emissions are scrubbed from exhaust gases using limestone slurry, the resulting chemical reaction produces this high-purity gypsum material. Approximately 150-200 million tons are produced globally each year, making it one of the most abundant industrial byproducts. Unlike mined natural gypsum, FGD gypsum typically has higher purity (90-98% CaSO4·2H2O) and more consistent chemical composition, though it may contain trace elements from coal combustion.
Physical and Chemical Properties
Desulfurization gypsum shares the same chemical formula (CaSO4·2H2O) as natural gypsum but differs in crystal structure and morphology. FGD gypsum forms as fine, homogeneous crystals with average particle sizes of 30-60 microns, compared to natural gypsum's larger, more irregular particles. The material begins losing water of crystallization at 60-80°C, converting to hemihydrate (CaSO4·½H2O) at 120-180°C. Complete dehydration to anhydrite occurs above 200°C. Its pH is neutral (6.5-7.5), and it exhibits low thermal conductivity (0.25 W/m·K) and good fire resistance.
Main Applications
Over 80% of desulfurization gypsum is used in construction materials. In cement production, it serves as a setting time regulator, typically added at 3-5% of clinker weight. For gypsum board manufacturing, FGD gypsum can directly replace mined gypsum after calcination. Agricultural applications include soil conditioning for sodic soils and as a calcium/sulfur fertilizer. Emerging uses include road base stabilization and filler in plastics/paints. In Japan, nearly 100% of FGD gypsum is recycled, while global utilization rates average 60-70%.
Safety and Storage
As a non-hazardous material, desulfurization gypsum requires standard industrial hygiene practices. Dust control measures are recommended during handling to prevent respiratory irritation. Bulk storage should be under roof or covered with tarpaulins to prevent moisture absorption and hardening. Long-term stockpiles require proper drainage to prevent leachate, though studies show FGD gypsum leachates typically meet drinking water standards for heavy metals. Some regional regulations may classify it as an industrial byproduct requiring specific handling documentation.
B2B Procurement Guide
When sourcing desulfurization gypsum, verify the supplier's power plant source and quality control processes. Key specifications include: moisture content (<10% for most applications), CaSO4·2H2O purity (>90%), chloride content (<100 ppm for wallboard), and unburned carbon content (<0.5%). Bulk shipments typically move by rail or barge, with truck delivery for regional buyers. Consider proximity to source - transportation costs often exceed material costs. Some suppliers offer processed (dried, ground) versus raw FGD gypsum at different price points. Contracts may include quality guarantees and volume discounts.
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