RESUMO
Magnetic-clay (MtMag) and magnetic-organoclay (O100MtMag) nanocomposites were synthesized, characterized and evaluated for arsenic adsorption. Batch arsenic adsorption experiments were performed varying pH conditions and initial As(V) concentration, while successive adsorption cycles were made in order to evaluate the materials reuse. The highest As(V) removal efficiency (9 ± 1 mg g-1 and 7.8 ± 0.8 mg g-1 for MtMag and O100MtMag, respectively) was found at pH 4.0, decreasing at neutral and alkaline conditions. From As(V) adsorption isotherm, two adsorption processes or two different surface sites were distinguished. Nanocomposites resulted composed by montmorillonite or organo-montmorillonite and magnetite as the principal iron oxide, with saturation magnetization of 8.5 ± 0.5 Am2 Kg-1 (MtMag) and 20.3 ± 0.5 Am2 Kg-1 (O100MtMag). Thus, both materials could be separated and recovered from aqueous solutions using external magnetic fields. Both materials allowed achieving arsenic concentrations lower than the World Health Organization (WHO) recommended concentration limit after two consecutive adsorption cycles (2.25 and 4.5 µg L-1 for MtMag and O100MtMag, respectively).
Assuntos
Poluentes Químicos da Água , Purificação da Água , Adsorção , Arseniatos , Bentonita , Concentração de Íons de Hidrogênio , Cinética , Fenômenos Magnéticos , Poluentes Químicos da Água/análiseRESUMO
Pyrimethanil (2-aniline-4, 6-dimethylpyrimidine, PRM) is used in fruit packing plants to control fungal infections and diseases. The effluents greatly polluted with this fungicide, as a point source contamination, need to be technologically treated for their regeneration before they reach water bodies. This work evaluates the use of organo-montmorillonites, synthetized in our laboratory, for their application in adsorption and coagulation/flocculation processes for the removal of PRM from water. The adsorption-desorption performance of PRM in a raw montmorillonite (Mt) and several organo-montmorillonites (organo-Mt) obtained by different amounts and types of exchanged surfactants (octadecyltrimethylammonium (ODTMA) and didodecyldimethylammonium (DDAB) bromides and benzyltrimethylammonium chloride (BTMA)) was studied. The PRM adsorption on raw Mt was assigned mainly to an interlayer occupancy, while hydrophobic interactions between PRM and the surfactants in the exchanged samples increased PRM adsorption, which was correlated with the surfactant loading. PRM desorption showed irreversible behavior in raw Mt, which changed to reversible for organo-Mt samples, and was also correlated with the increase of surfactant loading.Two of the organo-Mt with high surfactant loading (twice the CEC) were assayed for the removal of commercial PRM in coagulation/flocculation tests, and their performance was compared to that of the native clay (Mt). The use of the organo-Mt produced flocculation at a very low ratio (0.5 g L-1), whereas no flocculation was observed with Mt. These results proved the feasibility of the use of organo-Mt for the treatment of wastewater contaminated with PRM using a low organo-Mt/liquid ratio.
Assuntos
Bentonita/química , Pirimidinas/química , Purificação da Água , Adsorção , Floculação , ÁguaRESUMO
The 4-chloro-2-methylphenoxy acid (MCPA) is an herbicide widely used in agriculture, which generates a great concern about contamination of surface water and serious consequences for human health and the environment. In this work, the adsorption of MCPA on an Argentine montmorillonite (MMT) and its organo-montmorillonite product (OMMT) with different dodecyl trimethyl ammonium loading was investigated. MCPA adsorption on OMMT increases at least 3 times, with respect to the amount determined for MMT. X-ray diffraction and zeta potential analyses indicated the inner (interlayer) and outer surface participate as adsorption sites. Changes in surface electric charge and also interlayer expansion suggest that dimethyl amine (MCPA counterion) was also surface-adsorbed. The larger aggregates of OMMT, without and with MCPA, obtained compared to those of MMT samples, generate an improvement in the coagulation efficiency. This property, particularly after MCPA retention, allows an easier separation of the solids from the solution and enables a simple technological process application.