CETMIC   05378
CENTRO DE TECNOLOGIA DE RECURSOS MINERALES Y CERAMICA
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Glyphosate and its metabolites adsorption on clays
Autor/es:
M. DOS SANTOS AFONSO; M. GENET; R. M. TORRES SÁNCHEZ
Lugar:
Aveiro, Portugal
Reunión:
Congreso; Euroclay 2007; 2007
Institución organizadora:
Potuguese Clay Group, Industrial Mineral and Clays Centre
Resumen:
Glyphosate, (PMG) is the most employed herbicide around the world. After application a significant amount reaches the soil due to the different treatment methods and weather conditions. PMG is adsorbed onto the soil components such as clays, organic matter, oxides and humic substances. PMG metabolites are aminomethylphosphonic acid (AMPA), methylphosphonic acid (MPA) and sarcosine (SAR). Montmorillonite (M), develops high specific surface and a net surface charge having at least two available types of adsorption surface. PMG forms inner-sphere complexes with several metals such as Al+3 and Fe+3 and iron oxides surfaces. Both, PMG and M have negative net charge at all pH evaluated, so no electrostatic attractive phenomena is associated with PMG-M interaction. Some parameters as particle morphology (SEM), pzc, size particle, TG and specific surface area were measured to characterize the clay. Electrophoretic mobility and size particle of a treated sample with PMG was evaluated due to the enormous changes in M stability suspension in presence of PMG. Multisite isotherms were found for adsorption indicating that almost two types of specific adsorption sites are present in clay surface. DRX and XPS analysis of PMG, AMPA, MPA and SAR adsorbed onto M were made to determine the interlayer role and the structure of surface complexes formed during the adsorption processes. In all the cases the d(001) parameter shifted to lower values of 2è which indicate the clay expansion due to ligand incoming into the interlayer space. The =NH2 +, =NH and P2p surface speciation were calculated from XPS results. Physicochemical parameters related with adsorption process are reported for all sample at all measured conditions.After application a significant amount reaches the soil due to the different treatment methods and weather conditions. PMG is adsorbed onto the soil components such as clays, organic matter, oxides and humic substances. PMG metabolites are aminomethylphosphonic acid (AMPA), methylphosphonic acid (MPA) and sarcosine (SAR). Montmorillonite (M), develops high specific surface and a net surface charge having at least two available types of adsorption surface. PMG forms inner-sphere complexes with several metals such as Al+3 and Fe+3 and iron oxides surfaces. Both, PMG and M have negative net charge at all pH evaluated, so no electrostatic attractive phenomena is associated with PMG-M interaction. Some parameters as particle morphology (SEM), pzc, size particle, TG and specific surface area were measured to characterize the clay. Electrophoretic mobility and size particle of a treated sample with PMG was evaluated due to the enormous changes in M stability suspension in presence of PMG. Multisite isotherms were found for adsorption indicating that almost two types of specific adsorption sites are present in clay surface. DRX and XPS analysis of PMG, AMPA, MPA and SAR adsorbed onto M were made to determine the interlayer role and the structure of surface complexes formed during the adsorption processes. In all the cases the d(001) parameter shifted to lower values of 2è which indicate the clay expansion due to ligand incoming into the interlayer space. The =NH2 +, =NH and P2p surface speciation were calculated from XPS results. Physicochemical parameters related with adsorption process are reported for all sample at all measured conditions.