Diuron adsorption on mechanically and thermally treated montmorillonite and sepiolite and characterization of adsorbents and complexes formed.

R. M. TORRES SÁNCHEZ; T. UNDABEYTIA; M. DOS SANTOS AFONSO; E. MORILLO; M. PÉREZ-SAYAGO; C. MAQUEDA

Antalya

Congreso; Euroclay 2011; 2011

Soc. turca de arcillas

The herbicide Diuron is widely used in agriculture, with the consequent increase of its occurrence in surface and groundwater. The adsorption in solid surfaces is an important factor controlling the presence of organic contaminants in water, and clay minerals have been proposed as adsorbents to remove hazardous compounds from polluted waters. Mechanical treatment of clay minerals usually generates materials of high specific surface area which improve its use as adsorbents of different contaminants. Besides, thermal treatments of clays remove the intra and inter particles water molecules causing changes in their pore size distribution and consequently in the external surface values. The objective of the present research was to evaluate the effectiveness of mechanical and thermal treatments of montmorillonite from Argentina and sepiolite from Spain in removing diuron from aqueous solution, and to characterize both the adsorbents and the complexes formed. The raw and ground samples (mill Herzog HS-100) for 60 and 180 seconds were further thermally treated at 500°C for 24 h. The samples were characterized by XRD, zeta potential and specific and total surface area using N2 (SN2) and water adsorption (Sw) methods. The ground treatment produced a Sw values decrease of around 50%, respect of the raw samples, for both montmorillonite and sepiolite samples. Further thermal treatment reduced more the Sw values until 70% of the respective raw samples. On the contrary the SN2 values for ground for montmorillonite and sepiolite samples showed an increase of 50% or a slight decrease respect of the raw samples and further thermal treatment reduced the SN2 values until 50% of the respective ground samples only for sepiolite samples. The X-ray patterns showed a decrease in crystallinity, with increase time of grinding and further thermal treatment, by decreasing the intensity of the peaks. While the d(001) reflexion peaks increases from 11.7 to 12.3Å, and remained constant for montmorillonite and sepiolite, respectively after grinding and further heating shift it from 9.25 to 9.7 Å and from 9.8 to 12.1 Å, for montmorillonite and sepiolite, respectively. The zeta potential showed an increase and no changes of the negative surface charge for montmorillonite and sepiolite ground samples, respectively. Further heating generated a slight decrease and a net increase of the negative surface charges for montmorillonite and sepiolite, respectively. The diuron adsorption produced a huge decrease of surface charge only on both raw samples while in samples mechanical treated changes are not noticeable. The diuron adsorption on samples mechanical and further thermal treated generated an opposite behavior on both clays. The negative surface charges for montmorillonite increased, while for sepiolite samples decreased. The adsorption of diuron on raw montmorillonite was small and decreased slightly after grinding for 60 and 180 seconds. However, the thermal activation showed a three times increased adsorption for 180s milled sample. Diuron adsorption on raw sepiolite was higher than on montmorillonite. Sepiolite grinding increased its adsorption capacity, and the thermal activation produced also an additional increase in all cases. Changes on the negative charge of raw adsorbents surfaces by the Diuron adsorption indicated their association to the surface and the d(001) shift to low values of 2q angles of montmorillonite indicated that an entrance of organic molecule on the interlayer space would occurred.