MECHANISM OF FORMATION OF HUMUS COATINGS ON MINERAL SURFACES .3. COMPOSITION OF ADSORBED ORGANIC-ACIDS FROM COMPOST LEACHATE ON ALUMINA BY SOLID-STATE (13)CNMR

The adsorption of compost leachate DOC on alumina is used as a model f or elucidation of the mechanism of formation of natural organic coatin gs on hydrous metal oxide surfaces in soils and sediments. Compost lea chate DOC is composed mainly of organic acid molecules. The solid-stat e C-13 NMR spectra of these organic acids indicate that they are very similar in composition to aquatic humic substances. Changes in the sol id-state C-13 NMR spectra of compost leachate DOC fractions adsorbed o n alumina indicate that the DOC molecules are most likely adsorbed on metal oxide surfaces through a combination of polar and hydrophobic in teraction mechanisms. This combination of polar and hydrophobic mechan ism leads to the formation of bilayer coatings of the leachate molecul es on the oxide surfaces.