Calcium carbonate is an essential raw material used in a wide range of everyday products, including chalk, toothpaste, rubber, and plastics, helping to reduce production costs and improve product properties. Calcium carbonate has also gained attention as an environmentally friendly carbon dioxide reduction technology and is likely to play an important role in future environmental industries.
What do chalk, newspaper, and toothpaste have in common? They’re all made from calcium carbonate. It’s what makes chalk white and smooth, newspaper smooth and printable, and toothpaste polished. Many of the products we use every day contain calcium carbonate, but its importance is often overlooked. Calcium carbonate doesn’t just improve the properties of products, it also contributes to reducing the cost of production and increasing the efficiency of these products. As such, calcium carbonate is a hidden ally in our daily lives.
The history of calcium carbonate, also known as limestone, begins more than a billion years ago when shellfish flourished on ancient Earth. Countless shells from the bottom of the ocean were deposited over time, buried under the ground by tectonic shifts, and formed into limestone under geothermal heat and pressure. The time and forces of nature have shaped limestone into the essential resource we have today. Because limestone is widely available in its natural state, it is easy and inexpensive to obtain. This is one of the reasons why limestone is used in so many different applications across industries.
Calcium carbonate is the main ingredient in cement, a basic building material, and is widely used in steel, agriculture, and chemicals. When used as the main ingredient in cement, it improves the durability of building structures through its strong binding power, and in the steel industry, it plays an important role in refining iron ore and removing impurities. In agriculture, it regulates the acidity of the soil to promote crop growth, making calcium carbonate an essential component of modern industry.
It also acts as a filler reinforcing agent to make rubber and plastics stronger. Calcium carbonate is added to rubber and plastic products to increase their strength and durability, while reducing production costs. Because it is used in so many different applications, it is important that the process of manufacturing calcium carbonate in its natural state is suitable for the industry that requires it. For this reason, the manufacturing process of calcium carbonate has been developed and optimized for each industry. In the following, we will explain how calcium carbonate is produced.
Calcium carbonate production methods are divided into two main categories: physical grinding and chemical synthesis. The first is the physical crushing method, which involves impacting large limestone particles to crush them. However, this doesn”t necessarily break them apart. When a crusher hits a calcium carbonate particle, some of the impact energy is used as kinetic energy, which causes the particle to move backward. The rest of the impact energy is absorbed inside the particles, which is called crushing energy and causes the particles to break apart. Since the goal is to crush the calcium carbonate, the kinetic energy is practically useless. As the size of the particles decreases with continued crushing, the percentage of impact energy used as kinetic energy increases, eventually reaching a crushing limit where 100% of the energy is used as kinetic energy and no further crushing occurs.
There are different methods of physical grinding: grinding calcium carbonate in air is called ‘dry grinding’ and grinding in water is called ‘wet grinding’. In the case of dry grinding, the grinding limitation is that the particles can only be broken down to a size of 1 to 46 microns. In the calcium carbonate industry, however, smaller particles are sometimes required. This is why a wet grinding process was developed. When calcium carbonate is crushed by dissolving it in water, the resistance of the water reduces the degree to which the particles recede. A smaller proportion of the impact energy is converted into kinetic energy, resulting in much smaller particles of 0.35 to 1.2 microns. The particles obtained by this physical grinding process are called heavy calcium carbonate.
Next, the principle of the chemical synthesis process can be easily understood from the molecular formula of calcium carbonate. When quicklime and carbon dioxide react, they form calcium carbonate. Since quicklime in its natural state does not react well with carbon dioxide, it is dissolved in water to form calcium hydroxide, which is then reacted with carbon dioxide. After the reaction, you get calcium carbonate and water, which is then used to dissolve the quicklime again. You may have seen icicle-like stalactites in limestone caves. The chemical synthesis process uses this recrystallization of calcium carbonate particles.
The first advantage of chemical synthesis is that the size of the particles can be freely controlled. As the calcium carbonate particles are recrystallized molecule by molecule, an inhibitor is added to stop the recrystallization when the required size particles are formed. This makes it possible to create very fine particles. The chemically synthesized calcium carbonate has a size of 0.03 to 0.08 microns, which is more than 10 times smaller than physical grinding. Hard calcium carbonate is also produced, which is between 0.08 and 3 microns.
A second advantage of the chemical synthesis process is that the desired particle shape can be induced. Calcium carbonate particles that have undergone physical grinding have been subjected to physical impacts from all directions, so they have no angles and are almost spherical in shape. The chemical synthesis process, however, can produce needle-like, cubic, or parallelepipedal structures depending on the direction in which the calcium carbonate is stacked, which has industrial applications. For example, needle-shaped calcium carbonate is used as a filler for lightweight paper. Spherical calcium carbonate made by physical grinding is dense when aggregated, but needle-shaped calcium carbonate is jagged when aggregated. For the same volume, needle-shaped calcium carbonate is much lighter, which is why it is used in lightweight paper.
However, the delicate process makes chemical synthesis expensive. For hard calcium carbonate, dry grinding is more than 10 times more expensive, and for crystalline calcium carbonate, the cost difference is more than 20 times greater, as it is a much more sophisticated process. Therefore, for general industry, where price is a major consideration, heavy calcium carbonate is used by physical grinding. If a specific shape or ultra-fine particles are required, chemical synthesis is used at a much higher cost.
Calcium carbonate has been one of the most popular raw materials on the planet for the past 5,000 years. You may not realize it, but it’s an important part of the materials industry, used in paper, toothpaste, rubber, plastics, and many other products we use every day. The chemical synthesis process also has the eco-friendly effect of reducing carbon dioxide emissions because it can capture carbon dioxide emitted from other processes to produce calcium carbonate. In recent years, as climate change and environmental issues have become a global topic, the calcium carbonate production process as a carbon dioxide reduction technology has gained attention. It is likely that calcium carbonate will play an important role in the environmental industry of the future.
