Estudo sobre a sorção de íons Cd2+ por hidrogenofosfato de cério (IV) em soluções aquosas

Abstract

The presence of cadmium in the environment requires attention, due to its carcinogenic and bioaccumulative power. To remediate water bodies contaminated with traces of this metal, different materials are reported in the literature. This work describes a method capable of removing 10-25% of Cd2+ from aqueous solutions through cerium IV hydrogen phosphate (CeP), a lamellar material that acts as a cation exchanger. In the present study, CeP was obtained in three times of hydrothermal treatment (4h, 16h and 24h). Powder X-ray diffraction confirmed the lamellar characteristic of all synthesized CePs and that this space increases as the synthesis time increases, as well as the crystallinity of the material. The sorption of Cd2+ in CeP 24h was superficial in contrast to CeP 4h, which in turn has a less pronounced fibrillar morphology compared to other CeP. IR and Raman spectroscopies showed, respectively, that sorption occurs via ion exchange and that the symmetry of phosphates after sorption is maintained. 31P nuclear magnetic resonance (31P NMR) delimited the molecular formula of CeP and thermogravimetric analysis demonstrated that Cd2+ ions can be adsorbed solely or in the form of aquocomplexes. In addition, the mode of Cd sorption by each material was studied by applying agitation (dynamic) or not (static). In this general consideration, the best results were obtained for Cd adsorption using CeP 24h in dynamic mode according to the ion adsorption capacity values (%). In all cases studied, sorption occurred using the pseudo-second order kinetic model and the Langmuir isotherm; which provided qmax values. (maximum adsorption capacity), where all CePs and sorption modes performed better than other materials of different classes, with emphasis on the Cd2+ sorption with agitation for CeP 4h. Therefore, it is concluded that sorption with agitation is the best procedure, with the 24h CeP being more suitable for punctual use and the 4h CeP for prolonged use.