Physico-chemical characteristics of humic acids extracted from soils and phosphate rocks (Morocco)

Samples of humic acids (HAs) were extracted from two agricultural soils and one phosphate rock from Morocco. The materials were characterised by elemental analysis, acidity determination, gel permeability and I.R.spectroscopy. All results indicate that structures of humic acids extracted from phosphate rocks (HA(3)) were predominantly aliphatic and are poor in carboxylic groups, whereas humic acids extracted from soils (HA(1)+HA(2)) had structures preferentially aromatic containing large acid entities. Only HA(3) contained significant amounts of S (12.16%). By using the Electron Spin for Chemical Analysis (E.S.C.A.), the results show two forms of S. The first is incorporated in reduced (C-S-H) groups (74%), the second in oxidised (C-SO2) groups (26%).