RESUMO
The adsorption of fluoride and arsenic ions by modified natural materials may have an impact on the removal of F- and As(V) from waters. In this work, a zeolitic material and pozzolan (commonly known as pumicite) were modified with aluminium an iron by an electrochemical method and chemical precipitation, respectively. The adsorbents were characterized by X-ray diffraction, scanning electron microscopy with energy X-ray disperse spectroscopy analysis and the point of zero charge (pHzpc). F- and As(V) adsorption properties of both materials were investigated. Adsorption kinetic data were best fitted to pseudo-second-order model and equilibrium data to the Langmuir isotherm model. The highest F- and As(V) sorption capacities were obtained for modified zeolitic (0.866â mg/g) and pozzolan (3.35â mg/g) materials, respectively, with initial F- or As(V) concentrations of 10â mg/L. It was found that the unmodified materials did not show either adsorption of F- ions or As(V), which indicated that Al and Fe in the adsorbents are responsible for the adsorption of these ions. In general, both modified materials show similar capacities for the adsorption of F- and As(V).
Assuntos
Alumínio/química , Arsênio/química , Técnicas Eletroquímicas , Fluoretos/química , Ferro/química , Poluentes Químicos da Água/química , Purificação da Água/métodos , Adsorção , Precipitação QuímicaRESUMO
The removal behaviors of fluoride ions from aqueous solutions and drinking water by aluminum modified hematite, zeolitic tuff and calcite were determined. Drinking water containing naturally 8.29 mg of fluoride ions per liter was characterized. The hematite, zeolitic tuff and calcite were aluminum modified by an electrochemical method. The effects of contact time and the dose of adsorbent were determined. The PZC (point of zero charge) values for aluminum modified hematite, zeolitic tuff and calcite were 6.2, 5.8 and 8.4, respectively. Adsorption kinetic data were best fitted to pseudo-second-order and Elovich models and equilibrium data to Langmuir-Freundlich isotherm model. The highest fluoride sorption capacities (10.25 and 1.16 mg/g for aqueous solutions and drinking water respectively) were obtained for aluminum modified zeolite with an adsorbent dosage of 10 g/L and an initial F(-) concentration of 9 and 8.29 mg/L for aqueous solutions and drinking water respectively (the final concentrations were 0.08 and 0.7 mg/L respectively). The main mechanism involved in the adsorption of fluoride ions is chemisorption on heterogeneous materials according to the results obtained by fitting the data to kinetic and isotherm models respectively. Aluminum modified zeolitic tuff showed the best characteristics for the removal of fluoride ions from water.
RESUMO
The purpose of this work was to evaluate the potential of aluminum modified iron oxides, in a continuous flow for removal of fluoride ions from aqueous solutions and drinking water. The breakthrough curves obtained for fluoride ions adsorption from aqueous solutions and drinking water were fitted to Thomas, Bohart-Adams, and bed depth service time model (BDST). Adsorption capacities at the breakthroughs, Thomas model constant, kinetic constant and the saturation concentration were determined. The results show that in general, the adsorption efficiency decreases as the bed depth increases, and this behavior shows that the adsorption is controlled by the mass transport resistance. The adsorption capacity for fluoride ions by CP-Al is higher for fluoride aqueous solutions than drinking water.
Assuntos
Alumínio/química , Água Potável/química , Compostos Férricos/química , Fluoretos/isolamento & purificação , Adsorção , SoluçõesRESUMO
Corrosion problems having to do with drinking water distribution systems are related to many processes and factors and two of them are ionic acidity and carbon dioxide, which were considered in this work. The corrosion character of water is determined by the corrosion indexes of Langelier, Ryznar, Larson, and Mojmir. The results show that pipes made of different materials, such as plastics or metals, are affected by corrosion, causing manganese to be deposited on materials and dissolved in water. The deterioration of the materials, the degree of corrosion, and the deposited corrosion products were determined by X-ray diffraction and Scanning Electron Microscopy. High levels of manganese and nitrate ions in water may cause serious damage to the health of consumers of water. Three wells were examined, one of them presented a high content of manganese; the others had high levels of nitrate ions, which increased the acidity of the water and, therefore, the amount of corrosion of the materials in the distribution systems.