Natural bitumens are solid hydrocarbon materials that exist naturally in the shallow layers of the earth’s crust, and in some parts of the earth’s crust, they protrude from the soil and have caused the discovery of these materials by humans.
In fact, natural bitumens are surface crude oils whose light components evaporate over time and turn into solid or liquid bitumen with high viscosity due to weathering, sulfurization, polymerization, and condensation.
This type of bitumen is divided into the following groups based on the method of formation, physical properties, solubility (in carbon disulfide and trichloroethylene) and chemical composition:
These groups themselves are divided into other categories. For example, asphaltites are divided into the following three groups:
Gilsonite is the most famous type of natural bitumen and it is soluble in aromatic and aliphatic solvents. It is brittle and can be crushed into a dark brown powder. When Gilsonite is added to asphalt cement or hot mix asphalt in production, it helps produce pavement mixes with remarkable stability.
Depending on the type of reactions performed and the duration of the reactions, natural bitumen in liquid, semi-solid and solid states with different chemical qualities have been formed in mines and lakes, which are called rock bitumen and lake bitumen, respectively.
Rock bitumens are mainly limestone and sand rocks in which crude oil has penetrated and with the passage of time its volatile substances evaporate and bitumen remains in the rocks.
When crude oil naturally rises through the broken layers of the earth and its volatile substances evaporate, natural bitumen is formed on the ground, which is called lake bitumen such as Behbahan Lake Bitumen in Iran and Trinidad Lake in southwest Trinidad