RESUMO
The rice hull ash is composed by 94% of SiO2, an agricultural waste that can be recovered and purified by a depolymerization reaction yielding an organo-silicic gel. The purpose of this paper is to show that this silica can be used to fix Cd2+ from aqueous solution. The pH of hydrolysis of the organo-silicic gel is the main factor modifying the distribution between the solid and the solution. The contact time between the Cd2+ solution and the solid was studied to optimize the sorption conditions. The equilibrium measurements were performed after 40 hours at room temperature. The competition with Ca2+ ions in the solutions was also studied in order to evaluate the selectivity of the Cd2+ fixation. It was found that the rice hull ash has a higher capacity to fix Cd2+ than the rice hull derivatives.
Assuntos
Cádmio/química , Cálcio/química , Oryza/química , Dióxido de Silício/química , Adsorção , Concentração de Íons de Hidrogênio , Hidrólise , Fatores de Tempo , Eliminação de Resíduos Líquidos , Água/química , Poluentes Químicos da Água/químicaRESUMO
The present study discusses the effect of gamma-irradiation on Cs+-exchanged X and A zeolites. The incorporation of Cs+ ions into A and X zeolites was performed using three different cesium salts (chloride, nitrate or acetate). Cs+ ions immobilized into the vitrified zeolites by thermal treatment are located in different sites of the zeolite networks. It is found that gamma-irradiation favors cesium retention depending on the cesium precursor salt used in the cationic exchange step.
Assuntos
Césio/química , Raios gama , Zeolitas/química , Zeolitas/efeitos da radiação , Alumínio/análise , Cristalização , Vidro , Temperatura Alta , Concentração de Íons de Hidrogênio , Troca Iônica , Espectroscopia de Ressonância Magnética , Análise de Ativação de Nêutrons , Espectrometria por Raios X , Difração de Raios XRESUMO
Cobalt exchanged X zeolites were gamma irradiated and heated until the zeolite structure collapsed. Heating destroys the zeolite network as found by X-ray-diffraction and 29Si, 27Al MAS NMR spectroscopy. Gamma irradiation treatment diminished the collapsing temperature of zeolite. Cobalt leaching from crystalline and amorphized zeolites was verified by ion exchange with NaCl solution. Results show that cobalt is not released from the amorphous materials. Furthermore adsorption of xenon and 129Xe NMR spectroscopy reveal that cobalt ions are heterogeneously distributed in the non irradiated amorphous materials. Gamma irradiation causes the mobility of cobalt in the amorphous materials resulting then in a more homogeneous distribution. Cobalt is, thus, retained safely in the amorphous materials.