Weathered coal, commonly known as outcrop coal, generally refers to products formed by the infiltration and weathering of lignite, bituminous coal, anthracite, which are close to or exposed to the surface, through air, sunlight, rain, snow, sand, and ice. China’s weathered coal reserves are abundant, according to incomplete statistics, about 100 billion

. In most parts of the country, there are weathered coal, Shanxi, Xinjiang, Inner Mongolia, Heilongjiang, Yunnan, and the formation of weathered coal humic acid. The composition and characteristics of elements and molecules are large in parts of Henan. Weathered coal has high oxygen content and low calorific value, and has lost its value as a power fuel and coking coal. However, the generally weathered bituminous coal contains a large amount of regenerated humic acid (HA) and a variety of oxygen-containing reactive functional groups, such as carboxyl groups, phenolic hydroxyl groups, sulfhydryl groups, alcoholic hydroxyl groups, etc., generally good quality weathered coal humic acid content can reach more than 50% Therefore, it gives new value to the use of weathered coal.

Humic acid is an important organic part of most soils. At present, China’s soil quality is generally low, soil degradation is more serious, not only has a large degraded area, but also soil erosion, soil desertification, acidification and salinization continue to expand. With the intensification of industrial and urban pollution, soil heavy metal pollution and organic pollution have become increasingly serious. The application of weathered coal to soil improvement can not only turn waste into treasure, but also effectively improve soil degradation and pollution. At present, research in this direction has made great progress.

Weathered coal humic acid is a mixture of various condensed aromatic hydrocarbon groups and carboxylic acid-based compounds which can be dissolved in a dilute caustic alkali (KOH, NaOH) solution by complex action of biochemicals or by oxidation (including weathering). Its composition is not thermoplastic, nor elastic, neither melts nor crystallizes. It is an amorphous polymer colloid, mostly in a black or brown colloidal state. When dry, its appearance has a shell-like fracture, and both color and density increase as the degree of coalification of the coal deepens.

Observed under a 12 000-fold electron microscope, humic acid is a cluster of tiny spherical particles that form a cluster similar to grape bunches. The elemental composition of humic acid is similar to that of coal, which is mainly composed of carbon, hydrogen, oxygen, nitrogen, sulfur and other elements; its molecule is a macromolecule composed of several similar structural units. Each structural unit is composed of three main parts: an aromatic nucleus, a bridge bond and a reactive group. Aromatic nucleus: The nucleus of humic acid consists of 5 to 6 aromatic rings or heterocyclic rings, such as benzene, naphthalene, anthracene, pyrene, pyrrole, furan, thiophene, pyridine and the like.

Bridge key: There is a single bridge bond and a double bridge bond connecting the nucleus of humic acid. The bridge has -CH2-, -O-, -S- and the like. Reactive groups: The aromatic nucleus of humic acid has several reactive groups, mainly phenolic hydroxyl group, alcoholic hydroxyl group, carboxyl group, methoxy group and the like. Due to the presence of these groups, the humic acid has properties such as acidity, hydrophilicity, cation exchange performance, and complex metal ions.