The desulfurization gypsum produced can be processed into marketable products and sold directly to cement plants or gypsum board manufacturers.
Heavy calcium carbonate, often referred to as “medium-grade calcium carbonate,” is a colorless, odorless white powder that is sparingly soluble in water and insoluble in alcohol. In dilute acetic acid, dilute hydrochloric acid, or dilute nitric acid, it dissolves upon effervescence and boiling. When heated to 898°C, it begins to decompose into calcium oxide and carbon dioxide.
Manufacturers of heavy calcium carbonate contend that it is produced by grinding natural carbonate minerals such as calcite, marble, and limestone. It boasts high chemical purity, strong chemical inertness, limited reactivity, excellent thermal stability—remaining undecomposed below 400°C—high whiteness, low oil absorption, low refractive index, a soft texture, dryness, the absence of water of crystallization, low hardness, minimal abrasion, non-toxicity, and an unpalatable taste.
Heavy calcium carbonate manufacturers believe that heavy calcium carbonate is widely used in various daily chemical industries, including artificial floor tiles, rubber, plastics, papermaking, coatings, inks, cables, construction materials, food, pharmaceuticals, textiles, animal feed, toothpaste, and more. As a filler, it increases product volume, thereby reducing production costs. When used in rubber, it can increase the rubber’s bulk, improve its processability, provide partial reinforcement or strengthening, and help adjust the rubber’s hardness.
In the coal-fired power generation industry, medium-calcium pulverized-coal power plants use heavy-grade calcium carbonate powder for flue-gas desulfurization. During this process, the heavy-grade calcium carbonate reacts with sulfur dioxide produced during coal combustion to form calcium sulfite, which then oxidizes in the presence of air to yield gypsum (calcium sulfate), thereby effectively reducing sulfur dioxide emissions from coal-fired power plants by up to 90%. The resulting desulfurization gypsum can be processed into marketable products and sold directly to cement plants or gypsum-board manufacturers. The amount of calcium carbonate desulfurization powder required depends on the sulfur content of the coal; typically, a 300,000-kilowatt coal-fired power plant consumes about 40,000 metric tons of desulfurization powder annually.
Medium-calcium heavy calcium carbonate is one of the most commonly used fillers in the rubber industry. By incorporating large amounts of medium-calcium into rubber, product volume can be increased while reducing the consumption of expensive natural rubber, thereby significantly lowering production costs. Moreover, when medium-calcium is used as a filler in rubber, the resulting vulcanizates exhibit higher tear strength and superior abrasion resistance compared with those made from pure rubber.
The plastics industry specifies that heavy-grade calcium carbonate powder used in calcium-based plastic masterbatches and color masterbatches must have a particle size of 400 mesh, with no change in whiteness after high-temperature heating. The ore structure is required to exhibit high crystallinity, with a calcium carbonate content of 99% and a whiteness of 95%. Medium-grade calcium carbonate serves as a skeletal filler in plastic products, significantly enhancing dimensional stability. According to manufacturers of heavy-grade calcium carbonate, it can also improve product hardness, surface gloss, and surface smoothness.
In the coatings industry, heavy-grade calcium carbonate powder is used in medium-calcium latex paints at dosages of 800 or 1,000 parts per hundred, with a whiteness of 95% and a calcium carbonate content of 96%. Medium-calcium calcium carbonate is even more widely used in the coatings sector—for example, it accounts for more than 30% of the formulation in thick-bodied paints.
In the waterborne coatings industry, medium-grade calcium carbonate powder for waterborne coatings is typically 800 or 1,000 mesh, with a whiteness of 95% and a calcium carbonate content of 96%. Medium-grade calcium carbonate plays a significant role in waterborne coatings: it prevents paint settling, ensures easy dispersion, delivers excellent gloss, and can be used at levels of 20–60% in the formulation. In the paper-making industry, medium-grade calcium carbonate powder for paper production is usually 325 mesh, with a required whiteness of 95% and a calcium carbonate content of 98%. Manufacturers of heavy-grade calcium carbonate emphasize that calcium plays a crucial role in the paper industry by enhancing paper strength and whiteness while keeping costs low.
In the feed and fertilizer industries, medium-calcium powder is used as a calcium supplement to replace traditional shell powder, thereby reducing costs. In the fertilizer sector, medium-calcium powder with varying degrees of whiteness can enhance granule formation and adjust color.
Medium-calcium powder for the construction industry (dry-mix mortar, concrete)
For dry-mix mortar, the heavy-grade calcium carbonate powder shall be 325 mesh, with a whiteness of at least 95% and a calcium carbonate content of 98%. Medium-grade calcium carbonate plays an important role in concrete applications in the construction industry, as it not only reduces production costs but also enhances the toughness and strength of the final product.
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