Thanks to their properties, REEs are extensively used in many daily commodities. Unfortunately, the REEs resources are finite and the access to the supplies is uncertain. For this reason, it is necessary produce and use the REEs in a sustainable manner [1]. Moreover, the widespread use of these elements has resulted in an increasing of REEs contamination in environmental matrices, creating problems to humans and ecosystems due to their bioavailability [2]. Despite of vast efforts in research about rare earth elements recycling a very low percent of these elements was recycled during the last years. This is mainly due to inefficient collection, technological problems and, especially, a lack of incentives. As a matter of fact that the most of conventional methods nowadays used for the extraction, recovery and separation of REEs have need a high consumption of energy and often given rise to secondary pollutants [3]. An eco-friendly and low cost effective alternative to recycle REE is the adsorption [4,5,6] process using zeolites [7]. Indeed, the properties of these sorbent materials to capture and concentrate significant quantities of species make them ideal candidates not only for the development of recycling but also for remediation processes, separation, environmental monitoring and resource recovery processes. However, at the best of the Authors’ knowledge, the adsorption mechanism and selectivity of REEs on zeolites has not been extensively treated in literature. To fully understand the adsorption mechanism and selectivity of zeolites a key aspect is to implement studies on adsorption capacities and on the distribution of different cations on adsorbent materials. In fact, the partitioning of ions and the distribution of bulk phase at the interface between minerals and aqueous solution, involves a complex interplay of chemical, electrostatic and crystallographic factors. For this reason, in this work NaX zeolite ion exchanged with Y and Nd (from liquid solutions) were studied by X-ray diffraction in order to locate the Rare Earth cations in the zeolite framework and the resulting changes in its structural properties. The Nd-exchanged NaX-XRD pattern has clearly showed the occurrence of a new diffraction peaks, which are absent in the Y-exchanged NaX. Moreover, Rietveld refinement also has indicated variations in the unit cell parameters, suggested the incorporation of REEs in the structure. According to the literature [7] the analysis of the difference Fourier map has allowed us to recognize a maximum three-fold coordinated to framework oxygen which can be assigned to Al extraframework ion. [1] C. Zhanheng (2011). Global rare earth resources and scenarios of future rare earth industry. Journal of Rare Earths, 1-6. [2] H. Ichihashi, H. Morita & R. Tatsukawa (1992). Rare earth elements (REEs) in naturally grown plants in relation to their variation in soils. Environmental Pollution, 157-162. [3] S. Massari, M. Rubert (2013). Rare earth elements as critical raw materials: Focus on international markets and future strategies. Resources Policy, 36–43. [4] C. Qing (2010). Study on the adsorption of lanthanum(III) from aqueous solution by bamboo charcoal. Journal of Rare Earths, 125-131. [5] S. Xu, Z. Wang, Y. Gao, S. Zhang, and K. Wu (2015). Adsorption of Rare Earths(III) Using an Efficient Sodium Alginate Hydrogel Cross-Linked with Poly-γ-Glutamate. Plos one, 1-12. [6] B. E. Johnson, P. H. Santschi, C.Y. Chuang, and S. Otosaka (2012). Collection of Lanthanides and Actinides from Natural Waters with Conventional and Nanoporous Sorbents. Environmental Science & Technology, 11251−11258. [7] J. G. Nery, M. V. Giotto, Y. P. Mascarenhas, D. Cardoso, F. M. Zanon Zotin, E. F. Sousa-Aguiar (2000). Rietveld refinement and solid state NMR study of Nd-, Sm-,Gd-, and Dy-containing Y zeolites. Microporous and Mesoporous Materials, 281-293.
STRUCTURAL CHARACTERIZATION OF NaX ZEOLITE EXCHANGED WITH Y AND Nd ELEMENTS
ELISA RODEGHERO
;ANNALISA MARTUCCI;ROBERTA GUZZINATI;LUISA PASTI
2017
Abstract
Thanks to their properties, REEs are extensively used in many daily commodities. Unfortunately, the REEs resources are finite and the access to the supplies is uncertain. For this reason, it is necessary produce and use the REEs in a sustainable manner [1]. Moreover, the widespread use of these elements has resulted in an increasing of REEs contamination in environmental matrices, creating problems to humans and ecosystems due to their bioavailability [2]. Despite of vast efforts in research about rare earth elements recycling a very low percent of these elements was recycled during the last years. This is mainly due to inefficient collection, technological problems and, especially, a lack of incentives. As a matter of fact that the most of conventional methods nowadays used for the extraction, recovery and separation of REEs have need a high consumption of energy and often given rise to secondary pollutants [3]. An eco-friendly and low cost effective alternative to recycle REE is the adsorption [4,5,6] process using zeolites [7]. Indeed, the properties of these sorbent materials to capture and concentrate significant quantities of species make them ideal candidates not only for the development of recycling but also for remediation processes, separation, environmental monitoring and resource recovery processes. However, at the best of the Authors’ knowledge, the adsorption mechanism and selectivity of REEs on zeolites has not been extensively treated in literature. To fully understand the adsorption mechanism and selectivity of zeolites a key aspect is to implement studies on adsorption capacities and on the distribution of different cations on adsorbent materials. In fact, the partitioning of ions and the distribution of bulk phase at the interface between minerals and aqueous solution, involves a complex interplay of chemical, electrostatic and crystallographic factors. For this reason, in this work NaX zeolite ion exchanged with Y and Nd (from liquid solutions) were studied by X-ray diffraction in order to locate the Rare Earth cations in the zeolite framework and the resulting changes in its structural properties. The Nd-exchanged NaX-XRD pattern has clearly showed the occurrence of a new diffraction peaks, which are absent in the Y-exchanged NaX. Moreover, Rietveld refinement also has indicated variations in the unit cell parameters, suggested the incorporation of REEs in the structure. According to the literature [7] the analysis of the difference Fourier map has allowed us to recognize a maximum three-fold coordinated to framework oxygen which can be assigned to Al extraframework ion. [1] C. Zhanheng (2011). Global rare earth resources and scenarios of future rare earth industry. Journal of Rare Earths, 1-6. [2] H. Ichihashi, H. Morita & R. Tatsukawa (1992). Rare earth elements (REEs) in naturally grown plants in relation to their variation in soils. Environmental Pollution, 157-162. [3] S. Massari, M. Rubert (2013). Rare earth elements as critical raw materials: Focus on international markets and future strategies. Resources Policy, 36–43. [4] C. Qing (2010). Study on the adsorption of lanthanum(III) from aqueous solution by bamboo charcoal. Journal of Rare Earths, 125-131. [5] S. Xu, Z. Wang, Y. Gao, S. Zhang, and K. Wu (2015). Adsorption of Rare Earths(III) Using an Efficient Sodium Alginate Hydrogel Cross-Linked with Poly-γ-Glutamate. Plos one, 1-12. [6] B. E. Johnson, P. H. Santschi, C.Y. Chuang, and S. Otosaka (2012). Collection of Lanthanides and Actinides from Natural Waters with Conventional and Nanoporous Sorbents. Environmental Science & Technology, 11251−11258. [7] J. G. Nery, M. V. Giotto, Y. P. Mascarenhas, D. Cardoso, F. M. Zanon Zotin, E. F. Sousa-Aguiar (2000). Rietveld refinement and solid state NMR study of Nd-, Sm-,Gd-, and Dy-containing Y zeolites. Microporous and Mesoporous Materials, 281-293.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
