MALEIC HYDRAZIDE INTERACTION WITH SOIL CLAY SURFACES

The binding mechanism of the herbicide maleic hydrazide (MH) to mineral soil clay surfaces has been studied by adsorption isotherms at different pH, X-ray diffraction (XRD) and Fourier Transform Infrared spectroscopy (FT-IR). The results showed different mechanisms depending of the surface characteristics of the minerals. For hydroxylated (variable charge) surfaces such as lepidocrocite and sepiolite, the adsorption of MH occurred at external surfaces whereas for phyllosilicates of negative permanent charge, such as montmorillonite, MH penetrated also in the interlamellar spaces, as shown by XRD results. FT-IR spectra of MH-mineral complexes showed that MH was bonded to surface hydroxyl on lepidocrocite and sepiolite and to exchangeable cation, directly or through water-bridge, on montmorillonite by C = 0 groups of the herbicide molecule.