Modelling the humification process and the humic acid molecule

The structural origin of the properties of humic acids (HA) is of great importance. Natural humic acids (HA) consist of several major functional groups, predominantly carboxylic (R-COOH) and phenolic (R-OH), as well as carbonyl (C=O) and quinoid. Carboxylic and phenolic functionalities determine the H-binding, metal binding and charge properties of HA. In addition, all HA of diverse geographic and climatic origins contain stable organic radicals which are considered to play a key-role on the transformation of humic acid itself. Presently, the oxidative polymerization of polyphenols in soils is thought to be among the major processes of formation of natural humic substances. Given the acknowledged structural complexity and heterogeneity of natural HA, an approach adopted by various groups was the production of ‘‘synthetic HA”. Recently we have presented a method for performing a Humic Acid Like Polymer (HALP) at significant yields with no use of a catalyst. Herein we present a detailed study off the mechanism of the polymerization in conjunction with S.E.C. data of the evolution of the molecular size of the HALP. Finally the relation of the structures with physicochemical properties is discussed.