RESUMO
Grape stalk is an organic waste produced in great amounts in the industrialization processes of grape. This work presents the results of studies carried out to use this waste as raw material to prepare activated carbon through the physical and chemical route. The physicochemical characterization of this material suggests the presence of unusually high levels of ashes. Metal content was determined and high levels of potassium, sodium, iron, calcium and magnesium in carbonized and raw grape stalk were exhibited. This characteristic made difficult physical activation at high temperatures. A leaching step was included before the activation with steam, and adsorbents with surface areas between 700 and 900 m(2)/g were obtained. Physical activation was also performed at lower temperatures using carbonized grape stalk without leaching, leading to the development of some grade of porosity, with an area of 412 m(2)/g. These results would indicate the catalytic effect of the minerals present in this raw material. Chemical activation using phosphoric acid as activating agent seemed to be a very efficient method as final products with BET areas between 1000 and 1500 m(2)/g were obtained.
Assuntos
Agricultura/métodos , Carbono/química , Carvão Vegetal/química , Adsorção , Cálcio/análise , Celulose/química , Ferro/análise , Lignina/química , Magnésio/análise , Ácidos Fosfóricos/química , Potássio/análise , Eliminação de Resíduos/métodos , Sódio/análise , Vitis , Eliminação de Resíduos Líquidos/métodosRESUMO
Highly reactive carbon/Fe composites were prepared from tar used as a carbon source, and hematite (alpha-Fe(2)O(3)), a widespread naturally available iron oxide. Tar was impregnated on hematite and thermally treated under N(2) atmosphere. Mössbauer, powder X-ray diffraction and magnetization data suggested that treatment at 400 and 600 degrees C produced only magnetite (Fe(3)O(4)) whereas at 800 degrees C mainly metallic iron (Fe(0)) was produced. Raman, TG and XRD analyses of the different composites revealed the presence of amorphous and graphitic carbon highly dispersed on the iron oxide surface. The composites obtained at 800 degrees C were very efficient in reducing aqueous Cr(VI), as CrO(4)(2-), even compared to finely ground commercial Fe(0). XPS and Mössbauer data showed that after five consecutive reuses, the composites deactivated, due to the surface oxidation of Fe(0). A simple treatment at 800 degrees C completely regenerated the composite by reducing Fe(3+) species allowing several reuses.