The Importance of Calcium Carbonate
Calcium carbonate (CaCO3) comprises more than 4% of the earth’s crust and is found worldwide. Its most common natural forms are chalk, limestone, and marble (produced by the sedimentation of small fossilized shellfish, snails, and coral over millions of years). Chalk occurs as a microcrystalline material and has been used to draw and write for over ten thousand years. Limestone is more compact and durable than chalk (limestone blocks were used to construct the ancient Egyptian pyramids!). One of limestone’s other iterations, travertine was used since ancient times as a building material and was a key component for the Roman aqueducts. A metamorphic rock made up of coarse crystalline particles, marble has been used in construction, building, and art throughout history. The ancient Greeks used it for friezes, relief sculptures, and freestanding statues, and those later created by Michelangelo during the Renaissance.
Applications of Calcium Carbonate
One of the most versatile materials, calcium carbonate, now has hundreds of other uses. Many of these applications require crushing the rocks that contain calcium carbonate. Manufacturing processes used to fabricate this concentrated powder allow numerous industries to utilize it to fabricate a wide array of products.
Beyond being used as a standalone building material, the construction industry uses calcium carbonate as an ingredient in cement. As such, it’s employed as a binder to make asphalt for roadways, concrete, and mortar after being classified according to particulate size.
Agriculture & Aquaculture
Agricultural lime uses calcium carbonate as its active ingredient to inexpensively neutralize acidic soil and make it suitable for planting. Livestock farmers often use vitamins and premixed feed containing calcium carbonate as a supplement, adding bulk to feed while keeping it free of dust. In aquaculture, it regulates pH in the soil in ponds before aquatic organisms are introduced. Calcium carbonate is the active ingredient in agricultural lime and is used in animal feed.
Plastics & Sealants
Products such as vinyl siding and fencing use rigid polyvinyl chloride, with improved impact strength resulting from the addition of calcium carbonate. Manufacturing processes allow it to replace more expensive impact modifying substances. Processed calcium carbonate is also used in various sealants and adhesives used within the automotive and construction industries.
Valued for its brightness and ability to scatter light, paper manufacturers use it as an inexpensive filler when making colored opaque paper. With this filler made from calcium carbonate, manufacturing processes used at the wet end of paper-making equipment give the paper a glossier and brighter look. Its use in the paper industry improves the productivity of paper-making machines, enhances optical properties, and reduces costs by replacing more expensive agents used for brightening and pulp fiber.
Paints & Coatings
Also used as a filler in coating pigments and paints, calcium carbonate is valued for its unique white color. In some cases, up to 30 percent of the weight of certain paints is made up of calcium carbonate. Manufacturing processes that create distinctive particle shapes also allow paint manufacturers to reduce titanium dioxide levels and improve the product’s ability to obscure contrasting colors.
Healthcare & Cosmetics
Calcium carbonate can also be used as a means to regulate and improve human health.
It is used in:
- Antacid tablets or liquids
- Calcium dietary supplements
- Filler for tablets
- Multi-vitamin and mineral tablets
Calcium carbonate is also used in kidney dialysis treatment, specifically hyperphosphatemia, to normalize phosphate concentrations for patients with chronic kidney disease. Combining with dietary phosphate, calcium carbonate forms calcium phosphate, which is insoluble in water.
Calcium carbonate is also used as a filler in cosmetics, especially colored ones. Its powdered form also helps absorb excess oil from the skin.
Cosmetics that often use calcium carbonate include:
- Body powders
- Eye shadows
- Face powders
- Makeup bases
Cosmetic grade calcium carbonate is also used in antiperspirant deodorants.
Commonly used as a food preservative, calcium carbonate is in several food products found in supermarkets.
- Baking powder
- Dry-mix dessert mixes
With unique particle shapes and smaller-sized particles resulting from calcium carbonate manufacturing, processed food and beverages can be easily and effectively fortified with calcium while maintaining the flavor.
The way in which minerals separate when processed is referred to as cleavage, and calcite’s cleavage is rated as perfect in three directions. The term “calcite” refers to the crystalline structures that make up calcium carbonate. Manufacturing processes break these crystals along three planes, resulting in block-like fragments. This and another feature of calcite, referred to as double refraction, enables calcite crystals to diffuse light at two different angles. This feature makes it valuable for numerous optical applications, such as fabricating light detectors and monochromators.
Calcium carbonate helps treat wastewater by neutralizing microorganisms like algae, bacteria, and fungi within the water. The mineral’s surface serves as a means by which microorganisms are immobilized, with calcium carbonate acting as a carrier on which these microorganisms gather. This treatment method reduces the chemicals needed, making it more environmentally friendly.
The Calcium Carbonate Manufacturing Process
Natural mineral sources are necessary to make commercially usable calcium carbonate. Manufacturing processes are used to improve specific properties and reduce the size of particles within the material. Calcium carbonate is mined from open pits or underground, then drilled, blasted, and crushed. After this, the crushed stone is sized and washed, removing much of the colored impurities within the material.
From there, calcium carbonate goes through either dry or wet processing. The wet process involves a chemical synthesis that uses carbon dioxide, with wet processing often following dry processing to increase purity. This method also works in reverse, as when calcium carbonate reacts with acids, it produces carbon dioxide. This enables geologists to reliably test a mineral to determine whether it contains calcium carbonate.
Dry Calcium Carbonate Processing
Dry processing requires a series of reduction procedures involving grinding and otherwise physically reducing material into smaller and smaller particles. Typically, the ground material is then classified by repeated screening for coarse particles – resulting in a “screen grade” material – or via air classifying to separate out finer particles. Screened grade material usually falls within 6-40 mesh (400-3360 microns) on average. When using marble for calcium carbonate manufacturing, processing results in an even purer mineral form. However, limestone is generally used due to its lower cost. The resulting ground calcium carbonate is then graded according to its specific properties, used for various uses, or processed further via wet processing.
Processing of Precipitated Calcium Carbonate
Commonly, calcium carbonate goes through a process by which it is precipitated chemically into a purer form so that the mineral is contained within a suspended solution. This is referred to as wet processing and generally results in finer particles and a purer material. Derived from lime, precipitated calcium carbonate manufacturing processes involve hydrating quicklime (calcium oxide) to initiate a chemical reaction between the quicklime and water to make a slurry consisting of calcium hydroxide. This essentially makes a water-based suspension, of which half or more can be solid matter.
This process entails using carbon dioxide and heat in a process called calcination, which results in what is called “milk-of-lime” because of its extreme whiteness. After treating it with carbon dioxide, it precipitates into calcium carbonate salt. The subsequent material features a narrow and uniform particle size distribution, with particles around two microns in diameter. The precipitated calcium carbonate can be made with crystals of diverse shapes and sizes, which are adjusted to make the resulting material perform optimally for specific applications. This purified form of calcium carbonate is used within the paper, plastic, healthcare sectors, and various cosmetics and skin products.
Machines Used for Processing Calcium Carbonate
Heavy machinery is primarily used during the dry processing phase, when calcium carbonate manufacturing processes focus on reduction through milling, crushing, and screening, whereas air classification is generally used in later reduction phases. The equipment used during processing calcium carbonate powder affects grain types and particle size distribution.
Prater Equipment for Calcium Carbonate Manufacturing Processes
Prater Industries makes a number of machines well-suited for breaking apart aggregates like limestone, chalk, or marble to make calcium carbonate. Manufacturing processes used depend largely on the application for which the calcium carbonate will be used.
Prater Mega Mills
Prater’s Mega Mill is essentially a hammermill that works to crush particles through impact, acting as a secondary piece of reduction equipment. The Mega Mill uses a high-speed rotor with hammers affixed to support pins at the point where they pivot. These are equally spaced in a pattern that surrounds the grinding chamber. Precision bearings support the rotor, which allows the hammers to operate close to any screens within the frame at a very close tolerance. Repeated impacts by the Mega Mill reduce particle size as the particles collide and accelerate into each other, interrupter plates, and screen surfaces. Prater’s Mega Mill can be customized for calcium carbonate manufacturing by regulating clearance between screens and hammers, changing the number and size of screen holes, amending the number of hammers used, adjusting hammer tip speed, and modifying hammer thickness.
Prater Air Classifying Mills
Prater’s air classifying mill combines dual-stage grinding and milling operations operating inside a closed circuit with an air classifier. It first reduces the size of the material with a high-speed grinding rotor that reduces via impact force. When used in calcium carbonate manufacturing, the air classifying mill uses serrated jaws and screens to provide additional shear to reduce accelerated particles. The independently controlled air classifier within the mill separates calcium carbonate particles that do not meet specifications, recirculating them for further reduction. They are very useful when processing precipitated calcium carbonate, which requires a tight particle distribution.
Prater Air Classifiers
Prater’s air classifiers are used within systems designed for calcium carbonate manufacturing. Processing the powdered calcium carbonate by separating differently sized particles via centrifugal force, it works within pneumatic circuits by conveying raw material through its primary air inlet. The classifier uses aerodynamic drag forces to act upon the particles, with the variability of the force used determining density and diameter of the particles.