Calcium nitrate: properties, production and applications
Calcium nitrate (nitrate of lime, calcium salt of nitric acid, Ca(NO₃)₂) is an inorganic salt that occupies a special position among mineral fertilizers and technical products. It is a colourless crystalline substance or white granules, readily soluble in water. Unlike most nitrogen fertilizers, calcium nitrate contains two nutrients simultaneously — nitrogen in nitrate form (14–15.5%) and calcium (26–27% calculated as CaO). This combination makes it indispensable for crops experiencing calcium deficiency, for greenhouse operations, hydroponic and fertigation systems, as well as a valuable raw material for the construction, chemical and water treatment industries.
Chemical Nature and Physicochemical Properties
The chemical formula of calcium nitrate is Ca(NO₃)₂, with a molecular mass of anhydrous salt of 164.09 g/mol. In nature, it occurs as the mineral nitrocalcite — the tetrahydrate Ca(NO₃)₂·4H₂O. Anhydrous calcium nitrate is a colourless hygroscopic crystalline substance with a melting point of 561 °C and a density of 2360 kg/m³. It is readily soluble in water: solubility is 128.8 g per 100 g of water at 20 °C and increases significantly with temperature. Aqueous solutions have a neutral or slightly alkaline reaction, which makes calcium nitrate a physiologically alkaline fertilizer — when applied to the soil, it does not acidify but, on the contrary, reduces acidity.
When heated above 500 °C, calcium nitrate decomposes to form oxygen and calcium nitrite, which then decomposes into calcium oxide and nitrogen dioxide. Calcium nitrate is non-flammable and explosion-proof, stable in the temperature range from minus 60 °C to plus 155 °C. However, it is highly hygroscopic, so it requires hermetic packaging and protection from moisture during storage.
Classification, Grades and Standards
Requirements for calcium nitrate in Russia and CIS countries are regulated by a system of standards. For technical calcium nitrate, GOST 4142-77 applies, which establishes requirements for the product obtained by neutralizing nitric acid with chalk or lime. For agricultural fertilizers, requirements are determined by manufacturers' technical specifications and agrochemical regulations.
Depending on the application, calcium nitrate is produced in several grades. Grade A (with a nitrogen content of at least 13.8% and CaO of at least 26.3%) is intended for industrial purposes and greenhouse operations. Grade B (similar composition but with the addition of boron up to 0.3%) is used for agricultural crops, especially those sensitive to boron deficiency (potatoes, sugar beet). Modern producers also offer specialized grades with increased calcium content (e.g., 17N:33CaO) and grades with magnesium and trace element additives for greenhouse complexes and fertigation systems.
Calcium nitrate is produced in granular and crystalline forms. The granular form (hemispherical granules of white or yellowish colour) is less hygroscopic, does not dust during application and stores better, making it the primary form for agricultural use. The crystalline form is used mainly for preparing solutions in hydroponics and laboratory practice.
Production Technology
The main industrial method for producing calcium nitrate is the neutralization of nitric acid with calcium carbonate (chalk or limestone). The process is carried out in acid-resistant towers, where coarsely ground calcium carbonate is treated with 40–48% nitric acid. The reaction proceeds according to the equation: CaCO₃ + 2HNO₃ → Ca(NO₃)₂ + CO₂ + H₂O. The resulting solution is filtered from impurities, evaporated under vacuum to a Ca(NO₃)₂ content of 75–82%, and then crystallized in a granulation tower or on cooling rolls.
To obtain a granular product, the calcium nitrate melt is sprayed through a nozzle in a tower cooled by air, which ensures the formation of spherical granules. An alternative method is the absorption of nitrous gases (mainly NO₂) with lime milk, which simultaneously allows the utilization of waste gases from production facilities. Modern technologies are aimed at increasing product purity and reducing energy consumption, as well as using by-products from other industries (e.g., sludge from titanium-magnesium production) as raw materials.
Agronomic Value and Applications
Nitrogen-calcium fertilizer. Calcium nitrate is one of the best fertilizers for crops requiring both nitrogen and calcium. Nitrogen in nitrate form is quickly involved in metabolic processes and is available to plants in the first days after application, ensuring a rapid start to vegetation. Calcium regulates the supply of nutrients to the plant, plays a key role in the formation of cell walls and membranes, increases resistance to stress and improves fruit quality. Calcium nitrate is especially effective for tomatoes, peppers, eggplants, cucumbers, cabbage, sugar beet, potatoes, apple trees and grapes.
Prevention of physiological disorders. Calcium nitrate is an effective means of preventing blossom-end rot in tomatoes, peppers and eggplants, as well as bitter pit in apples and other calcium deficiency-related disorders. Calcium nitrate solutions (typically 1–2% concentration) are used for foliar feeding during the growing season.
Greenhouses and hydroponics. Calcium nitrate is one of the basic water-soluble fertilizers for greenhouse complexes and hydroponic systems. It is fully soluble in water, contains no insoluble impurities and is compatible with most nutrient solution components. For fertigation, special high-purity grades with low ammonium nitrogen content (less than 1.1%) are used.
Acidic soils. Due to its physiologically alkaline reaction, calcium nitrate is the optimal choice for acidic soils. Calcium reduces the acidity of the soil solution and reduces the toxic effect of excess manganese and iron, which is characteristic of acidic soils.
Application rates. For root feeding of vegetable crops during the growing season, a solution of 20 g per 10 liters of water is used with an interval of 15–20 days, consuming 1–1.5 liters per 1 m². For foliar feeding, 10 g per 1 liter of water is used. For basic application in dry form before sowing — 10–20 g per 1 m².
Construction and Industry
In addition to agriculture, calcium nitrate finds wide application in the construction and chemical industries.
Concrete additive. Calcium nitrate is used as a setting and hardening accelerator for concrete, as well as an antifreeze additive for concreting in winter conditions. It densifies the concrete structure, increases its water resistance and does not cause corrosion of reinforcement. Application is most appropriate with Portland cement and low-aluminate cements.
Wastewater treatment. Calcium nitrate is used to prevent the formation of hydrogen sulfide in sewer systems. Calcium nitrate creates anoxic conditions under which sulfate-reducing bacteria stop producing H₂S, which eliminates unpleasant odours and corrosion of pipelines.
Other applications. Calcium nitrate is used to produce high-purity calcium oxide, in the production of reagents, in metallurgy, in the glass industry, as well as a component of cooling mixtures and in the production of latex coagulants.
Safety and Storage
Calcium nitrate belongs to moderately hazardous substances (hazard class 3). When working with the fertilizer, personal protective equipment (respirator, safety goggles, protective clothing) is recommended to prevent irritation of mucous membranes by dust. The product is non-flammable and explosion-proof.
Storage is carried out in closed, dry warehouse premises protecting the product from atmospheric precipitation and ground water. Calcium nitrate is highly hygroscopic, so when moistened it can cake and lose flowability. Mixing calcium nitrate with fertilizers containing phosphates and sulfates is not allowed, as this leads to the formation of insoluble precipitates and loss of nutrient availability. The product is supplied in 25 kg bags, in big bags of 500–1000 kg and in bulk. The guaranteed shelf life is 6 months from the date of manufacture.
Market and Trends
The global calcium nitrate market demonstrates steady growth, driven by the development of greenhouse vegetable production, the expansion of fertigation and hydroponics systems, and growing demand for calcium-containing fertilizers for the prevention of physiological plant disorders. The Asia-Pacific region is the largest producer and consumer, with China, India and European countries actively expanding capacity.
In Russia, calcium nitrate production is also actively developing. The Acron Group, at its Veliky Novgorod site, after commissioning the second unit, increased its total calcium nitrate production capacity to 300 thousand tonnes per year. The product is supplied both in granular form and as water-soluble grades for greenhouse operations. Key industry trends include the transition to granular forms with improved physical properties, the development of grades with boron and magnesium additives, and growing attention to calcium nutrition efficiency and loss reduction.
Conclusion
Calcium nitrate remains one of the key products of the global chemical industry and agriculture, combining the functions of a highly effective nitrogen-calcium fertilizer and a multifunctional technical raw material. Its unique properties — physiologically alkaline reaction, complete water solubility, the presence of two nutrients and compatibility with fertigation systems — make it indispensable for greenhouse operations, acidic soils and crops sensitive to calcium deficiency. Organising supplies of calcium nitrate, including grade selection (technical, agricultural, with boron, concentrated), quality confirmation and logistics, requires an individual approach that takes into account specific technological requirements and operating conditions.