# Alkaline Extraction of Organomineral Potassium Humate from Coal Mining Waste
## 1 Introduction  
Currently, the use of environmentally friendly and safe substances in agriculture is becoming relevant. One of the directions of the future is the use of humic substances. Humic substances are high-molecular compounds of natural origin, which are formed as a result of the oxidation of coal or changes in dead biomass, and are shapeless formations with a chaotic structure of dark brown color, which can dissolve or swell in water. [1]. These compounds do not have a single chemical formula, but it is known that their main structures are aromatic rings and functional groups (hydroxyl, carboxyl, carbonyl, alkyl and methoxyl) [2]. In addition to aromatic rings, the substance may contain polypeptide and polysaccharide fragments. Even simple compounds, such as fulvic acids, have a complex chemical structure. Since the structure of the humic substances molecule cannot be quantitatively described by traditional methods, researchers have developed a classification method based on solubility in alkalis and acids. Thus, humic substances are classified into three categories: humins--substances insoluble neither in acids nor in alkalis; humic acids--substances insoluble in acids, but soluble in alkalis; fulvic acids--substances soluble in acids and alkalis [3]. Humic acids are fractions of humic substances that are soluble in an alkaline medium, semi-soluble in water, and insoluble in an acidic medium. This classification parameter may vary depending on the content of humic acids, pH and ionic bonds. Due to their amphiphilic nature, humic acids form micelle-like structures called false micelles in a neutral and acidic environment. This property is used for use in water treatment plants and to increase the solubility of hydrophobic preparations in water [4, 5]. Humic substances contain various functional groups, the number of which depends on the origin, timing, climate and environmental conditions during the extraction and production of humic substances [6]. The various functions of humic substances mainly relate to the functional groups of phenols and carboxylic acid. These properties provide humic substances with many positive properties, such as improved plant growth and complex formation with heavy and variable metals, which means that they can remove heavy metals from the body and form chelated compounds. In addition, their antiviral and anti-inflammatory activity has been proven [7]. It has been proven that the presence of phenols, carboxylic acids and quinones in the structure of humic substances is associated with their antioxidant, fungicidal and bactericidal activity [8]. In the literature, a number of authors have a common opinion about the chemical composition of humic substances obtained from various sources [9; 10]. Thus, substances prepared on the basis of humic substances contain 50% carbon, 35% oxygen and 5% hydrogen, and the remaining percentage is nitrogen and sulfur [11]. The largest amount of carbon is contained in hard and brown coal, and its content can reach 60-65%. The ability of humic substances to bind cationic metals and complexes makes them useful in various fields. Thus, they ensure the transfer of micronutrients from soil to plants and from feed additives to the body of farm animals [12]. In addition, humic substances reduce the content of heavy metals in soil, water and living organisms [13]. The main source of humic substances is brown coal. Its reserves in Kazakhstan amount to 34 billion tons [14]. It was found that brown coal differs in chemical composition compared to other sources of humic substances. It contains various trace elements that can be used in the production of animal feed additives [15]. The main methods of isolation of humic substances include alkaline extraction with ammonia solutions or potassium/sodium hydroxides. Such methods convert humic substances into water-soluble salts, that is, potassium or sodium humates with high biological activity. This method is practically waste-free, therefore it is widely used in many countries [16; 17].