Hydrochloric acid: properties, production and applications
Hydrochloric acid (muriatic acid, HCl) is an aqueous solution of hydrogen chloride, a strong monobasic inorganic acid, and one of the most important and large-tonnage products of the modern chemical industry. Anhydrous hydrogen chloride is a colourless gas with a pungent odour, heavier than air, readily soluble in water. Hydrochloric acid is a colourless, transparent liquid with a pungent odour that "fumes" in air due to the release of gaseous HCl. Technical acid may have a yellowish colour due to impurities of chlorine and iron salts. The density of concentrated acid (37% HCl) is about 1.19 g/cm³. Hydrochloric acid is miscible with water, benzene and ether in all proportions. The boiling point of the azeotropic mixture (20.2% HCl) is 108.6 °C, and the melting point of 37% acid is minus 28 °C. The molecular mass of HCl is 36.46.
Chemical Properties
Hydrochloric acid is a strong acid; in aqueous solutions, it almost completely dissociates into hydronium ions H₃O⁺ and chloride ions Cl⁻. It reacts with metals located to the left of hydrogen in the electrochemical series, releasing hydrogen and forming chlorides. The acid reacts with metal oxides and hydroxides, salts, and ammonia. Hydrochloric acid is a non-oxidising acid, meaning it does not oxidise metals but dissolves them through the reduction of hydrogen ions. A mixture of hydrochloric and nitric acids in a 3:1 volume ratio is known as "aqua regia" and is capable of dissolving gold and platinum metals.
Production Technology
Modern industrial hydrochloric acid production is based on several methods. The main method for producing synthetic hydrochloric acid is the synthesis of hydrogen chloride by the reaction of hydrogen and chlorine, followed by absorption of HCl by water. The reaction proceeds via a chain mechanism and is exothermic: H₂ + Cl₂ = 2HCl + 184.7 kJ/mol. In production conditions, synthesis is carried out in special furnaces where hydrogen continuously burns in a chlorine stream. The resulting hydrogen chloride is absorbed by demineralised or technical water in absorbers, forming hydrochloric acid with a mass fraction of HCl from 31 to 35%.
A second important source is by-product hydrochloric acid, formed as a by-product during the chlorination of organic compounds, the production of organochlorine products and the electrolysis of sodium chloride solutions. Historically, hydrochloric acid was produced from common salt and sulfuric acid (the sulfate method), but this method is now of limited use. Another method is the electrolysis of metal salt solutions with the release of HCl.
Regulatory Framework
In Russia and CIS countries, requirements for hydrochloric acid are regulated by a system of state standards. Technical synthetic hydrochloric acid complies with GOST 857-95, which applies to acid with a mass fraction of HCl of at least 35%. For reagent-grade hydrochloric acid, GOST 3118-77 applies (density 1.15–1.19 g/cm³). Hydrochloric acid belongs to hazard class III substances according to GOST 12.1.007-76. The maximum allowable concentration of hydrogen chloride in the working area air is 5 mg/m³.
Applications
Hydrochloric acid finds wide application in various industries. In metallurgy, the acid is used for pickling ferrous and non-ferrous metals — removing rust, scale and oxide layers from the surface of steel and other metals. Pickling with hydrochloric acid is the most widespread chemical process for removing iron oxides from metal surfaces without significantly affecting the metal itself. Solutions with concentrations up to 200 g HCl per litre at a temperature of about 60 °C are typically used.
In the oil and gas industry, hydrochloric acid is used for acid treatment of oil and gas wells to enhance oil recovery. Solutions of 15–28% HCl dissolve carbonate rocks (limestone, dolomite), increasing reservoir permeability and well flow rates. Special inhibitors are added to the acid to protect equipment from corrosion.
In the chemical industry, hydrochloric acid serves as a feedstock for the production of various metal chlorides, organochlorine compounds, vinyl chloride (a PVC precursor), dyes and pharmaceuticals. It is used for pH control and neutralisation in industrial processes. In the food industry, hydrochloric acid is used for the production of gelatin and other food additives. In water treatment — for pH adjustment and regeneration of ion-exchange resins. In electronics — for cleaning and etching semiconductor materials. Hydrochloric acid is also used for cleaning boilers and heat exchange equipment from deposits, in synthetic rubber production and in the leather industry.
Global Production and Market
The global hydrochloric acid market demonstrates steady growth. According to Research and Markets, the market was valued at USD 2.18 billion in 2025 and is projected to reach USD 2.33 billion in 2026 at a CAGR of 7%. By 2030, the market may reach USD 2.98 billion at a CAGR of 6.4%. According to Fortune Business Insights, the market was valued at USD 2.04 billion in 2025, with a projected growth to USD 3.21 billion by 2034 (CAGR 5.2%). In physical terms, the market volume in 2025 was 7.29 million tonnes, and by 2031 it is projected to grow to 9.99 million tonnes (CAGR 5.39%).
The Asia-Pacific region is the largest hydrochloric acid market, driven by large-scale steel, chemical and electronics production in China and India. North America accounts for about 40.68% of the global market. Europe demonstrates stable demand, supported by strict environmental regulations and a developed chemical industry. Key market growth drivers are the expansion of steel production, development of the oil and gas industry, growth in water treatment and increasing demand for chemical intermediates.
Production in Russia
The Russian hydrochloric acid market demonstrates steady growth. In 2024, Russian enterprises produced more than 1,223 thousand tonnes of hydrochloric acid. In the first quarter of 2025, according to operational data from Rosstat, production volume amounted to 322 thousand tonnes, which is 12.3% more than in the same period of 2024. In monetary terms, hydrochloric acid output in 2024 is estimated at almost RUB 11.5 billion. The compound annual growth rate of producer prices in 2021–2024 was 34.4%.
The largest hydrochloric acid producers in Russia are JSC KAUSTIK (leading positions in synthetic hydrochloric acid output), JSC BSK, PJSC Khimprom, LLC GaloPolimer Kirovo-Chepetsk and others. Production in the Volga Federal District accounts for more than 48% of the all-Russian volume. A project is being implemented in Tatarstan to build a new hydrochloric acid production facility with a capacity of 26,300 tonnes per year with investments of RUB 3 billion. In the Irkutsk region, a Sayan enterprise has started producing synthetic hydrochloric acid — the first in Eastern Siberia and the Far East.
Safety and Storage
Hydrochloric acid is a corrosive and hazardous substance of hazard class III. Concentrated acid causes severe chemical burns to the skin and mucous membranes; HCl vapours irritate the respiratory tract and eyes. When working with the acid, personal protective equipment must be used: acid-resistant gloves, protective goggles or face shields, and protective clothing. Premises must be equipped with supply and exhaust ventilation; analysis should be carried out in a fume hood. Hydrochloric acid is stored in hermetically sealed containers made of acid-resistant materials (glass, polyethylene, ceramics). Steel containers may only be used with an internal coating. The acid is non-flammable and non-combustible. When mixing with water, the acid must be added to the water, not vice versa.
Conclusion
Hydrochloric acid remains one of the key products of the global chemical industry, providing metal pickling, acid well treatment, chloride production, water treatment and many other processes. The growth of steel production, development of the oil and gas industry and expansion of the chemical industry create sustained demand for this essential chemical. Russia, possessing significant production capacities and implementing expansion projects, maintains its position as one of the leading players in the hydrochloric acid market.