Features of Obtaining and Properties of Fulvic Acid from the Peat of Nizhny Novgorod Region

Properties of fulvic acid (FA) extracted from the peat of the Nizhny Novgorod region of Russia by ultrasonic extraction with alkaline or ethanol solutions and further purification were studied in the paper. The purification of FA by the Lamar method was shown to possibly lead to the formation of FA polymorphs of the same composition but different structure (IR, solid-state 13С NMR, fluorescence, UV, energy-dispersive X-ray spectroscopy, SEM and optical microscopy, concentration of carboxyl and phenol groups). Aggregation of FA polymorphs in water led to the formation of nanoparticles with the average size of 8–10 nm and the zeta potential of –22 to –27 mV. The formation and properties of polymorphic supramolecular structures are greatly influenced by the drying mode. The solubility of the two FA polymorphs varied from freely soluble (3.3 mL of water per gram) after the FA solution freeze-drying to soluble (12 mL of water per gram) after the FA solution vacuum drying. The FA sample extracted by ethanol ultrasonic extraction from the peat, followed by convection drying, had a solubility of 666.7 mL of water per gram (Slightly soluble), a zeta potential of -6 mV, and a particle size of 15–20 nm.