Inocente Rodríguez-Iznaga

Natural clinoptilolite as an exchanger of Ni2+ and NH4+ ions under hydrothermal conditions and high ammonia concentration

Natural clinoptilolite from Caimanes deposit (Moa-Cuba) has been used for the nickel removal from aqueous solution by ion exchange. The Ni2+ elution, using ammonia-rich solution, has been also studied in form of a nickel removal–elution ion-exchange cyclic process. The stability of clinoptilolite as an exchanger of Ni2+ and NH4+ cations under hydrothermal conditions and high ammonia concentrations is analyzed. No loss in the clinoptilolite exchange capacity of Ni2+ and NH4+ ions during the Ni2+ removal–elution cycles was found. The treatment of the clinoptilolite with NH4OH concentrated solutions provokes not only the Ni2+ elution by ion exchange, but also a substantial increase of the Ni2+ ions removal capacity of the zeolite. This is explained by OH− anions adsorption (or occlusion) on the zeolitic phase particles and the consequent nickel hydroxide precipitation.

The role of carbonate ions in the ion-exchange Ni2+=2NH4+ in natural clinoptilolite

The removal and recuperation of nickel and other heavy metals, from the ammoniacal-carbonate residual liquors of the Cuban Nickel Industry, by ion exchange have been studied using natural clinoptilolite from Caimanes deposit (Moa, Cuba). The present study was conducted to analyze the influence of carbonate anions during the NH4+ and Ni2+ exchange in clinoptilolite. The main ion-exchange kinetic parameters were determined on the basis of the Barrer theory and other criteria. The analysis of the results obtained by kinetic study, infrared spectrometry and X-ray diffraction led to the conclusion that, in addition to ion exchange, the Ni precipitates in the form of low soluble phases.

Effect of the zeolitic matrix on the reduction process of Cu 2+ cations in clinoptilolite, mordenite and erionite

Three different zeolites (erionite, mordenite and natural clinoptilolite) were used to study influence of zeolite topology on the state of copper during ion-exchange and following reduction in hydrogen flow. This comparative study clearly demonstrates the influence of used zeolite matrices on the process of implantation of copper nanospecies. Starting from the ion-exchange, the alterations in the state of Cu2+ ions start to be evident due to variations of the intensity of charge transfer band. Copper ions start to reduce at specific temperatures depending on the type of zeolite matrix. Copper plasma resonance band change its shape and position for different zeolites. In the case of Cu-CLI samples this band change both the shape and position for different temperature of reduction. These observations permit to suggest that the mechanism of copper ion reduction and agglomeration to form copper nanoparticles noticeably depend on the type of zeolite matrix. This mechanism is more complex for the Cu CLI than for the Cu-MOR and Cu-ERI systems. Copper nanoparticles formed at low temperatures in the case of Cu-CLI samples undergo changes while temperature of reduction grow.

Thermal analysis and porosimetry of natural zeolites from mexican and cuban deposits

Irina Zvereva, Roman Kremnev, Vasiliy Sirotov, Saint-Petersburg State University, 7/9 Universitetskaya nab., St. Petersburg 199034, Russia Inocente Rodríguez-Iznaga, Instituto de Ciencias y Tecnologнa de Materiales (IMRE) – Universidad de La Habana, Zapata y G, s/n, La Habana 10400, Cuba Miguel-Angel Hernández, Departamento de Investigaciуn en Zeolitas, BUAP, Puebla, México Vitalii Petranovskii, Centro de Nanociencias y Nanotecnologнa, Universidad Nacional Autуnoma de México, Km 107 Carretera Tijuana-Ensenada, AP 14, Ensenada 22860, Baja California, México E-mail: irinazvereva@yandex.ru (Irina Zvereva*)

Use of natural mordenite to remove chromium (III) and to neutralize pH of alkaline waste waters.

ABSTRACT The natural mordenite from Palmarito de Cauto deposit (PZ), Cuba, was studied in this work as an ion exchanger to remove Cr3+ cations from alkaline aqueous solutions at different pH and chromium concentrations. The mordenite stability under cyclic treatment processes with alkaline solutions and its capacity to decrease the pH of the solutions was also analyzed. It was shown that PZ removes Cr3+ ions from alkaline solutions, and it happens independently of the starting chromium concentration and the pH of the exchange solution used. This material has an important neutralizing effect on alkaline solutions, expressed in a significant pH decrease from the early stages of the treatments. For solutions with initial pH equal to 11, it decreases to a value of around seven. The stability of this material is not affected significantly after continuous cyclic treatment with NaOH solution, which shows that mordenite, in particular from Palmarito de Cauto deposit, has high stability in alkaline solutions. The results are important as they suggest that natural zeolites may be of interest in treatments of alkaline industrial waste effluents.

Reduction of Cu2+in exchanged Ag+natural clinoptilolite: structural study

Modified zeolites with cations, clusters and metallic nanoparticles are of interest due to the possibility to develop materials with new properties [1]. A study concerning the thermal reduction under hydrogen flow of mixed bimetallic system Cu2+ and Ag+ exchanged natural clinoptilolite Tasajeras deposit, Cuba is presented. The influence of silver in the reduction of Cu2+ was studied. X-Ray diffraction experiments on natural clinoptilolite, as well as on ion-exchanged monometallic and bimetallic samples were performed. The peak intensities of the exchanged samples, are changed as a result of the ion exchange, and they are fundamentally associated with differences in nature, amount and position of the extra-framework ions in the channels of the natural zeolites [2, 3]. The fig 1 shows the magnitude of the Fourier Transform (FT) for the EXAFS signals of the natural clinoptilolite exchanged with Cu2+ and of the natural clinoptilolite exchanged with both Cu2+ and Ag+ and reduced at 150 oC . The TF of the experimental EXAFS signal of metallic Cu, has been also added. The amplitude of the peak at 1.82 Å, associated with the coordination of Cu2+ with 4 oxygen atoms, decreases upon Cu was added. A detailed analysis of the graph reveals also that for the exchanged and reduced samples a peak at 2.58 Å begins to emerge. This maximum coincides with the first maximum of the metallic Cu and may be associated with the formation of small clusters of Cu. The addition of Ag+ favors the decrease of the reduction temperature of Cu2+. The reduction of Cu2+ and Ag+ cations shows existence of notable interinfluence between both cations during this process. The Cu2+ reduction is favored by the presence of Ag+. The aggregation of the reduced highly dispersed species both for copper and silver is limited in this bimetallic system. The introduction of Ag+ as the second cation in the copper exchanged zeolites appears to be an efficient tool for the control of the size of the resultant reduced nanoparticles.