Lignite Fulvic Acids: Analysis by Dynamic Light Scattering

Humic and fulvic acids derived from South Ural lignite are studied. The composition of the coal, humic acids, and fulvic acids are characterized by technical and elemental analysis, Fourier transform infrared (FTIR) spectroscopy, and CP/MAS 13 C NMR spectroscopy. A method is proposed for extracting fulvic acids from lignite.by means of an aqueous hydrochloric-acid solution of n -butanol. It is established that fulvic acids are characterized by higher content of oxygen-bearing aliphatic groups with a predominance of carboxylic acids and complex esters, while humic acids have a higher content of carbon, hydrogen, and aromatic fragments. Dynamic light scattering shows that colloidal aggregations of fulvic acids in water are disperse systems with bimodal (at low concentrations) and monomodal (at higher concentrations) size distributions of nanoparticles and submicroparticles. The low negative values of the zeta potential for aqueous fulvic acid colloids indicate instability and a tendency to complex formation.