PICLORAM ADSORPTION ON PILLARED CLAY

JOSE LUIS MARCO BROWN; C. MARTÍN BARBOSA LEMA; ROSA M. TORRES SÁNCHEZ; MARÍA DOS SANTOS AFONSO

Castellaneta Marina, Italy

Conferencia; XIV International Clay Conference; 2009

ASSOCIAZIONE ITALIANA PER LO STUDIO DELLE ARGILLE

Picloram acid, 4-amino-3,5,6-trichloropicolinic acid, is a herbicide commonly used in agriculture in Argentina and Brazil. A significant amount of applied pesticide can reach soil and groundwater and / or surface water bodies through the drainage and/or lixiviation processes due to different application methods and environmental conditions. Pillared clays (PILCS) are interesting material to be used as catalysts and adsorbents, due to its multi-charged centers, large area, high interlayer space and thermal stability. PILCS synthesized with oxide pillars of Cr, Zr, Al, Ti, and Fe have been used in studies of adsorption of organic compounds as well as toxic metals such as As, Cd, Cr, Co, Cu Adsorption of Picloram on iron oxides PILCS could be the basis for the development of adsorbent materials for the remediation of polluted environments and to design materials for controlled release of herbicides. Fe Oxide Pillared Clays (Fe-PILCS) were synthesized from the montmorillonite clay (Wyo, USA) and Fe(NO3)3 as was previously reported (Belkhadem et al, 2008; Cañizares et al, 1999). PILCS were characterized by XRD, elemental analysis, DTA, TGA and by N2 adsorption (BET). Adsorption studies on Fe-picloram PILCS were made after 48hs equilibration of PILCS with an aqueous solution of Picloram at known concentration, pH and ionic strength were kept constant during the whole experiment. Picloram-Fe-PILCS were characterized using the same techniques as for PILCS. The adsorption results were compared with those obtained previously for the picloram adsorption on un-modified Wyo (Marco Brown et al, 2008). Surface area and interlayer space of Fe-PILCS were bigger than Wyo. An analysis of the adsorption isotherms of picloram on the Fe-PILCS showed that picloram adsorption increases with decreasing pH. The adsorption of picloram was over 90% at pH=3, this value is much higher than the adsorption on Wyo over similar conditions, 20%. However, at pH 7 adsorption on Fe-PILCS was lower than these obtained on Wyo. Picloram adsorption on Fe-PILCS is heavily greater to pHs below 7 showing a significant increase in the efficiency of the process which makes them susceptible to be used for dosing or remediation of pesticides.