CHEMICAL BENEFICIATION OF LIGNITE COALS FOR REDUCING ASH AND MINERAL IMPURITIES

Аннотация

In Uzbekistan, the effective utilization of low-grade coal extracted from the Angren coal deposit—initially considered unsuitable as fuel—is of critical importance. By processing and upgrading the quality of this coal, it becomes possible to supply high-quality solid fuel for both the population and various industrial sectors. This approach ensures the efficient use of coal resources, which are among the country’s valuable mineral assets. To obtain clean and efficient fuel from lignite—a natural energy source and a key factor in the development of the nation’s industry and living standards—it is essential to develop waste-free coal beneficiation technologies. Key words: lignite (brown coal), fuel, coal ash, mineral substances, calorific value, chemical reagent. Introduction: Until now, coal has been used directly as fuel without any processing, which resulted in high ash content and a large amount of waste. To minimize such waste, coal is now being processed and recognized as one of the most promising sources for the production of solid fuels. Moreover, it serves as a key raw material for obtaining various chemical compounds and composite materials [1]. In the national economy, the processing of coal to produce synthetic fuel has become a strategic priority, especially for countries without their own oil reserves. In this regard, the development of new technologies for converting domestic coal resources into alternative fuels has become a necessity [2]. As a result, within a short period, coal has turned into one of the most vital energy sources required for industrial and transportation development tomeet the energy demands ofsociety. Literature review: Lignite coal, also known as brown coal, is an abundant but low-quality energy resource due to its high ash content, moisture, and non-combustible mineral impurities. These properties limit its direct application as an efficient fuel and contribute to increased www.wordlyknowledge.uz ILMIYMETODIK JURNAL JOURNAL OFIQRO –ЖУРНАЛ ИҚРО –IQRO JURNALI –volume 16,issue01,2025 ISSN:2181-4341, IMPACT FACTOR( RESEARCH BIB )–7,245,SJIF–5,431 environmental pollution during combustion, especially through the release of sulfur oxides (SO₂), which are responsible for acid rain formation. Therefore, the chemical beneficiation of lignite has gained increasing attention as a promising method for improving its fuel quality and environmental performance. Numerous studies have explored various techniques for the chemical treatment of coal, including acid leaching using hydrochloric acid (HCl), sulfuric acid (H₂SO₄), nitric acid (HNO₃), and phosphoric acid (H₃PO₄). Among these, dilute hydrochloric acid (e.g., 0.1 M and 1 M concentrations) has demonstrated high efficiency in removing acid-soluble mineral compounds such as calcium (Ca), magnesium (Mg), sodium (Na), potassium (K), and partially iron (Fe) and aluminum (Al)oxides from coal ash.This selective leaching significantly reduces theash content and improves theoverall calorific valueof lignite. Earlier research by industrial laboratories and GOST-regulated studies (e.g., GOST 11022-95, GOST 26148) has confirmed that treating coal with HCl not only reduces ash by 12–13% but also facilitates partial desulfurization through the dissolution of compounds like FeS₂, CaSO₄, and FeSO₄. In addition, water washing prior to acid treatment helps eliminate water-soluble salts such as carbonates, chlorides, and sulfates, thus reducing acid consumption and improving process efficiency. Investigations on lignite samples from Angren, Shargun, and Baysun deposits in Uzbekistan have revealed that mineral content in raw coal ash may reach up to 60%, severely affecting the combustion performance. Chemical beneficiation of these coals has shown substantial improvement in reducing both ash and sulfur content, with the optimized use of 0.1 M HCl yielding the best results. Moreover, the treated coal exhibits a higher heating value (HHV) due to theremoval ofnon-combustiblemineral matter. Overall, the literature suggests that chemical beneficiation, especially using dilute hydrochloric acid, is a viable method for enhancing the fuel characteristics of lignite coals and reducing their environmental impact. However, further work is needed to optimize reagent concentration, process temperature, and treatment timeto achieve industrial-scale applicability. Methodology: Lignite coal samples of the brands 2BPK, 2BR-B2, 2BOM, and 2BR were collected from the Angren, Shargun, and Baysun coal deposits in Uzbekistan. Each sample was air-dried, homogenized, and ground to a particle size below 0.2 mm for laboratory analysis. Prior to acid leaching, each coal sample underwent water washing to remove water-soluble mineral impurities. Approximately 10 g of each coal sample was mixed with 100 mL of distilled water and stirred for 30 minutes at room temperature. The suspension was filtered, and the solid residue was dried at 105°C. The pre-washed samples were then subject