RESUMEN
Selenate and selenite are considered emerging contaminants and pose a risk to living organisms. Since selenium anion species are at low concentration in aquatic environments, materials for its retention are required to enable monitoring. Herein, hydrotalcite was calcined and characterised to investigate sorption and desorption of selenite and selenate in competition with nitrate, sulfate and phosphate. Sorption experiments were carried out in batch system and desorption by sequential dilution. Selenite and selenate concentration remaining after N desorption steps was determined by mass balance. The isotherms were adjusted to the dual-mode Langmuir-Freundlich model (R2 > 0.99). Maximum sorption capacity ranged from 494 to 563 meq kg-1 for selenite and from 609 to 659 meq kg-1 for selenate. Sulfate and phosphate ions showed greater competitive effect on the sorption of selenate and selenite, respectively. Low mobilization factors and high sorption efficiency (MF<3%; SE ≈ 100%) indicated that calcined hydrotalcite has the wanted characteristics for retention of relevant selenium anion species in aqueous media.
Asunto(s)
Monitoreo del Ambiente/métodos , Hidróxidos/química , Ácido Selénico/química , Ácido Selenioso/química , Absorción Fisicoquímica , Hidróxido de Aluminio/química , Magnesio/química , Hidróxido de Magnesio/química , Modelos Teóricos , Nitratos/química , Fosfatos/química , Ácido Selénico/análisis , Ácido Selénico/aislamiento & purificación , Ácido Selenioso/análisis , Ácido Selenioso/aislamiento & purificación , Compuestos de Selenio/química , Compuestos de Selenio/aislamiento & purificación , Sulfatos/química , Contaminantes del Agua/química , Contaminantes del Agua/aislamiento & purificaciónRESUMEN
Anthropogenic activities have increased the concentration of metal species in the environment. The toxicity of silver ions to aquatic and terrestrial organisms has required monitoring by analytical methods, besides actions to promote its control as pollutant. Sorption and desorption processes are directly related to the mobility and availability of metal ions in the environment. In this context, clay minerals can be used for pre-concentration, removal and recovery of silver ions from aqueous solution. Herein, two bentonite clays (BaVC-1 and SWy-2) were characterised and applied to investigate the sorption and desorption of silver ions. Isotherms were fitted to the dual-mode Langmuir-Freundlich model to qualify and quantify sorption sites and evaluate the mobilisation process. The maximum sorption capacity was 743 and 849 meq kg-1 for BaVC-1 and SWy-2, respectively. Hysteresis index (HI) and mobilisation factor (MF) suggest that the desorption of silver ions in BaVC-1 is about four times more conducive compared to that in SWy-2, although both materials have demonstrated a great potential for Ag+ pre-concentration from aqueous solutions.
Asunto(s)
Silicatos de Aluminio/química , Bentonita/química , Plata/química , Adsorción , Arcilla , Concentración de Iones de Hidrógeno , IonesRESUMEN
Analyses in chromatographic systems able to save mobile and stationary phases without reducing efficiency and resolution are of current interest. These advantages regarding savings have challenged us to develop a system dedicated to miniaturized liquid chromatography. This paper reports on the development of a high-pressure syringe-type pump, an oven able to perform isothermal and temperature programming and a software program to control these chromatographic devices. The experimental results show that the miniaturized system can generate reproducible and accurate temperature and flow rate. The system was applied to the separation of statins and tetracylines and showed excellent performance.