Evaluation of the simplified method of fulvic fractions extraction from peat and lignite

Abstract

Due to numerous and valuable properties of humic substances, preparations produced from alternative organic materials have been widely used in agriculture, bioremediations, dietary supplements and others. In addition to well-known humic acids, fulvic acids (FA) are a valuable product with a wide range of applications. The aim of performed examinations was to assess the thermal and physicochemical properties of FA obtained from lignite and peat using simplified conventional and ultrasound-assisted methods. DSC coupled with TG and MS, 13C NMR, FTIR spectroscopy and differential pulse voltammetry has been used to examine extracted FA. Depending on the source of FA and the extraction method applied, their structure and properties differ. Obtained FA fractions varied for both tested raw materials in terms of analyzed carbon structures, and the highest discrepancy was observed for carbonyl groups (20.2 pp) in fractions obtained by conventional extraction. The use of the ultrasound-assisted extraction (UAE), in comparison with the traditional method, lowered the ratio of carbon in carbonyl groups by 8.4 pp and increased the ratio of aromatic and aliphatic carbon by 3.5 and 4.9 pp, respectively, for FA obtained from lignite. As for FA obtained from peat, the UAE effect appeared to be less impactful in terms of structural changes. Thermal analysis showed that the products were thermally stable up to 100 °C, and the simplified extraction resulted in the creation of mineral-organic structures that decomposed at unusually high temperatures. Simplifying the extraction process, by excluding inorganic purification and protonation of obtained FA fractions, greatly affects product quality and limits its possible application.

Preparation and Molecular Structural Characterization of Fulvic Acid Extracted from Different Types of Peat

“…The lack of a peak at approximately 1700 cm −1 for other samples may be due to the C=O vibration caused by the blockage of aliphatic chains, which dominate the HPO samples analyzed. Huculak-M ączka et al [20] used simplified conventional and ultrasound-assisted methods to evaluate the fulvic acid components extracted from peat and lignite. They determined that the fulvic acid obtained from peat had a more aliphatic structure, higher aromatic carbon ratio, and lower carbonyl carbon ratio than that obtained from lignite.…”

Application of Alkaline Deep Eutectic Solvents as a Green Alternative to the Traditional Extractants for the Isolation of Humic Substances

“…Peat is referred to as a source of HSs with a lower degree of humification, resulting in greater participation of heteroatoms and reduction of aromatic structures, compared to HSs isolated from lignite. It also results in the higher amount of oxygen-containing functional groups, e.g., COOH. , …”

“…It also results in the higher amount of oxygen-containing functional groups, e.g., COOH. 30,31 Spectroscopic Analysis. The quality assessment of the obtained humic extracts, based on spectroscopic methods, allowed a description of the influence of ADESs and the type of raw material used on the chemical structure of isolated products.…”