Dependence on molecular weight of acid-base properties of humic and fulvic acids

Abstract

The organic matter of Irish peat of Sphagnum was extracted with 0.1 M NaOH and separated into humic (HA) and fulvic (FA) acids. Afterwards, HA and FA fractions were obtained at different nominal molecular weight using a tangential ultrafiltration system. The behaviour of such fractions has been studied both in acid and alkaline solutions. Solutions at different ionic strength have been titrated under different conditions and the resulting curves have been elaborated through a computer program based on a bimodal Gaussian distribution. The typical parameters (pK(A) mean value and dispersion degree) of the two main groups of HA and FA acidic functionalities have been determined.