Influence of clay minerals and exchangeable cations on the formation of humic-like substances (melanoidins) from D-glucose and L-tyrosine

The ability to produce humic-like polymeric compounds, with D-glucose and L-tyrosine as starting materials, was evaluated in different mineral systems: (1) Ca-, Al- and Cu(II)-saturated montmorillonite; (2) Ca-, Al- and Cu(II)-saturated kaolinite; (3) quartz in the presence of two different amounts of the same cations (according to the cation exchange capacity of the clays); and (4) untreated quartz (as control). All systems proved to be effective in the formation of humic-like compounds, particularly quartz, in the presence of cations. The effectiveness in promoting humification reactions was strictly related to the amounts of added cations. In the reaction conditions considered, the humification appears to be due more to the cations than to the type of clay minerals. The clayey systems synthesized more complex (aromatic) substances than the quartz ones.