Study of the acid–base properties of fulvic acid-like substances extracted from senescent leaves of eucalyptus and oak

Abstract

The acid-base properties of two fulvic acids (FA) extracted from senescent leaves of eucalyptus and oak were characterized by carrying out potentiometric titrations at two FA concentrations and four ionic strengths (0.005 M <[KNO(3)] <1.0 M). Experimental data were analyzed by means of the master curve approach, which includes an electrostatic spherical double layer model, and the Langmuir-Freundlich isotherm was used to fit the data. The contribution of the electrostatic effect to the proton binding reaction was lower than that observed for soil fulvic acids. The chemical heterogeneity of both samples was described by two acid sites with p Ks of about 4 and 7.5, the most abundant being the carboxylic site of p K = 4.

An experimental and modeling study of humic acid concentration effect on H+ binding: Application of the NICA–Donnan model

“…1 it is apparent that the negative charge on humic acid increased as pH increased due to the dissociation of the acidic functional groups of humic acid and this is in agreement with relative results already reported in the literature [27,28,[35][36][37][38][39]. The negative charge on GHA (200, 100, and 50 mg L À1 ) at pH 3.5 was equal to 1 = 4 of the developed negative charge at pH 10.…”

Acid properties of fulvic and humic acids isolated from two acid forest soils under different vegetation cover and soil depth

“…Comparison of the different types of vegetation shows that in the FA extracted from the surface horizon of both AM and GR soils, the lowest values of the C/N atomic ratio correspond to Eucalyptus spp., in accordance with Antelo et al (2003), who found a greater content of N in the fulvic-like acids extracted from senescent leaves of Quercus robur than in fulvic-like acids extracted from senescent leaves of Eucalyptus globulus.…”