Wood charcoal: properties, grades and applications

Wood charcoal is a macroporous high-carbon solid product obtained by pyrolysis (thermal decomposition) of wood without access to oxygen. It is one of the oldest materials known to mankind: its use for metal smelting began as early as the 4th–3rd centuries BC. Industrial production of wood charcoal began in the mid-19th century with the development of metallurgy. Despite being displaced by cheaper coal coke in the 20th century, wood charcoal retains strategic importance for several industries and remains in demand in household and agricultural applications. Global production of wood charcoal exceeds 6 million tonnes per year.

Chemical Nature and Physicochemical Properties

Wood charcoal is a product of deep thermal decomposition of wood. Its structure and properties are determined by the pyrolysis temperature. Industrial charcoal obtained at 450–550 °C contains (by mass): carbon — 80–92%, hydrogen — 4.0–4.8%, oxygen — 5–15%, mineral impurities — 1–3%. The yield of the finished product is 25–35% of the mass of absolutely dry wood.

The key physical characteristics of wood charcoal determine its industrial value:

• High porosity (75–80%) and low apparent density (260–380 kg/m³). It is the developed porous structure that ensures high adsorption capacity and the ability to retain moisture and nutrients.

• Calorific value (30–34 MJ/kg). Wood charcoal is a high-calorie fuel.

• Low ash content (1–3%). This is especially important for metallurgical processes where impurities are undesirable.

• Chemical resistance and reducing ability. The carbon in wood charcoal actively participates in reduction reactions.

Wood charcoal contains high-molecular structures of aliphatic and aromatic series. By calcining it to various temperatures and using additives, materials with specified dielectric properties can be obtained.

Classification, Grades and Standards

In Russia and CIS countries, requirements for wood charcoal are established by GOST 7657-84 "Charcoal. Specifications". The standard applies to wood charcoal obtained by pyrolysis and carbonization of wood in industrial-type apparatuses. Depending on the wood species and production method, three grades are established:

• Grade A — charcoal obtained by pyrolysis of wood of group 1 species (hardwood: oak, birch, etc.). This is the highest quality charcoal with maximum density and strength. It is intended, among other things, for the production of activated carbons.

• Grade B — charcoal obtained by pyrolysis of a mixture of wood of groups 1 and 2. It is used for the production of carbon disulfide.

• Grade V — charcoal obtained by carbonization of a mixture of wood of groups 1, 2 and 3. This is a lower quality charcoal used primarily as fuel.

Each grade is divided into classes. For grade A of the highest class, the following are standardized: apparent density not less than 0.37 g/cm³, ash mass fraction not more than 2.5%, non-volatile carbon mass fraction not less than 90%, water mass fraction not more than 6%. For grades B and V, the tolerances for these indicators are wider. By agreement with the consumer, a water mass fraction in charcoal (except grade A of the highest class) of up to 20% is allowed, with recalculation of the actual mass to 6% moisture content.

In addition to GOST, there is a classification by type of firing:

• Black charcoal — produced at temperatures of 400–800 °C with subsequent cutting off of air access. It is softer, has a developed porous structure and a higher specific surface area (350–400 m²/g). Carbon content — 65–90%.

• White charcoal — fired at higher temperatures (1000–1200 °C) and quenched outside the kiln with a mixture of ash and sand. It is harder and denser, carbon content — 90–95%, but the specific surface area is smaller (200–250 m²/g).

Production Technology

Wood charcoal production is based on pyrolysis — heating wood without access to oxygen. The process includes several stages:

1. Raw material preparation. Wood (preferably hardwoods — birch, oak) is dried and crushed.

2. Pyrolysis (carbonization). The raw material is heated in sealed retorts or kilns at a temperature of 450–550 °C (for black charcoal) or up to 1000–1200 °C (for white). This decomposes complex organic substances, releasing volatile compounds (pyrogases) and forming a solid carbonaceous residue.

3. Calcination (optional). To increase density and purity, the charcoal may be subjected to additional calcination.

4. Cooling and stabilization. The finished charcoal is cooled in an oxygen-free environment to prevent spontaneous combustion.

5. Screening and packaging. The charcoal is screened into fractions and packaged in bags or paper sacks.

Modern technologies allow the pyrogas generated during pyrolysis to be utilized for heating the retorts, making production more energy-efficient and environmentally friendly.

Applications

Metallurgy and reduction processes. Wood charcoal is used as a reducing agent for the production of crystalline silicon and siliceous ferroalloys in submerged arc furnaces. It is also used for the recovery of non-ferrous metals (gold, copper, nickel, etc.) from solutions and as fuel in metallurgy.

Chemical industry. Wood charcoal serves as a raw material for the production of activated carbon (after additional activation) and carbon-graphite products. It is also used as a reagent for the production of carbon disulfide, calcium carbide and other chemical products.

Production and filtration. Wood charcoal is used as a sorbent for water and air purification, although its adsorption capacity is lower than that of activated carbon. It is used in filters for water treatment and industrial wastewater purification.

Agriculture. Wood charcoal is applied to the soil as a meliorant (biochar). It improves soil structure, increases its water-holding capacity, adsorbs toxic substances and gradually releases nutrients to plants. It is used for mulching lawns and restoring weakened trees.

Household and food industry. Wood charcoal (especially birch) is widely used for cooking on grills, barbecues and mangals. It provides high combustion temperatures, does not produce open flames and gives food a characteristic aroma. It is also used for heating residential premises, fireplaces and stoves.

Other applications. Wood charcoal is used in the production of gunpowder, as a pigment (black pigment), in medicine (as an enterosorbent in tablet form), in veterinary medicine and for purifying moonshine.

Safety and Storage

Wood charcoal is fire-hazardous, especially in a finely divided state, due to its tendency to spontaneous combustion upon contact with moisture and oxidizers. Storage is carried out in dry, well-ventilated areas, in hermetic packaging, away from ignition sources and oxidizers. Storage of charcoal together with food products is not allowed, as it easily adsorbs foreign odors. When working with charcoal dust, a respirator is recommended.

Market and Trends

The global wood charcoal market demonstrates steady growth, driven by the development of metallurgy, the chemical industry and demand for eco-friendly fuel. The largest producers are countries with rich forest resources, including Russia, Brazil, Indonesia and African countries.

In Russia, in 2025, wood charcoal production reached 108,100 tonnes, an increase of 19.4% compared to 2024 and 36% compared to 2022. The growth is driven by both domestic demand and export supplies. Russian charcoal is exported to European countries (France, Germany) and the Asia-Pacific region (including China). Key industry trends include the transition to more environmentally friendly production technologies (utilization of pyrogases, use of renewable raw materials), as well as growing demand for wood charcoal as an alternative fuel in the context of economic decarbonization. A promising direction is the production of premium-quality charcoal briquettes for grills and barbecues.

Conclusion

Wood charcoal remains an important product combining the functions of a high-calorie fuel, reducing agent and adsorbent. Its unique properties — high porosity, low ash content and reducing ability — make it indispensable in metallurgy, the chemical industry, agriculture and household use. Understanding the grade composition according to GOST 7657-84, production technologies and applications is the basis for competent material selection and the organization of efficient supplies.