Search

The hydrothermal synthesis of nano-faujasite has been successfully performed and the effects of some crystallization parameters were investigated, along with the use of this material as a heavy-metal ion adsorbent. X-ray diffraction patterns have shown that the structure of the nano-faujasite is strongly dependent on both the crystallization time and the alkalinity of the synthesis medium. According to N 2 physisorption, X-ray fluorescence, SEM/EDS, and solid state 29 Si and 27 Al NMR data, the produced nano-faujasite consists of a solid with low molar Si/Al ratio (1.7), with high availability of ion exchange sites and high surface area/small particle size, allowing easy diffusion of metal ions to adsorbent active sites. As a consequence, an excellent performance on removal of Cd 2+ , Zn 2+ and Cu 2+ ions was found for this solid. The adsorption capacity followed the order Cd 2+ (133 mg·g -1 ) > Zn 2+ (115 mg·g -1 ) > Cu 2+ (99 mg·g -1 ), which agrees with the order of increasing absolute values of the hydration energy of the metal ions. Kinetic studies and adsorption isotherms showed that the metal ion removal takes place by ion exchange on the monolayer surface of the nano-faujasite. The electrochemical recovery of copper in metallic form exhibited an efficiency of 80.2% after 120 min, which suggests that this process can be adequately implemented for full-scale metal removal.

In this study β-zeolite, ferrierite and partially delaminated PREFER (precursor of ferrierite) zeolites with several chemical and textural properties were synthesized for the removal of zinc and lead ion metals from their respective solutions. Adsorption experiments involving the suspension of tiny amounts of these solids in aqueous solutions containing either Zn 2+ or Pb 2+ showed that the removal of these metals at a considerable extent may be attained. Among the studied materials, β-zeolite displayed the better performance in metal ion removal, which may be ascribed to its higher aluminum content, surface area and external surface area, that allows a greater density and availability of ion adsorption active sites. Kinetic data from a pseudo-second-order model indicate that the chemical interaction among metal ions and active sites is the rate-limiting step. Furthermore, the better performance of the β-zeolite displayed in reusability testing makes it a potential adsorbent for future applications in the treatment of effluents containing toxic metals.