Ion exchange of zeolite Na-P-c with Pb2+, Zn2+, and Ni2+ ions

Summarization: This paper examines the ion-exchange properties of synthetic zeolite Na-P0, which was pro- duced from perlite-waste fines and has a SiO2:A1203 ratio of 4.45:1 and a cation-exchange capacity (CEC) of 3.95 meq g ~. Although equilibrium is attained rapidly for all three metals, exchange is incomplete, with At(max) (maximum equilibrium fraction of the metal in the zeolite) being 0.95 for Pb, 0.76 for Zn, and 0.27 for Ni. In both Na ~ ␣89 and Na --* ␣89 exchange, the normalized selectivity coefficient is virtually constant for :~A~(normalized equilibrium fraction of the metal in the zeolite) values of --<0.6, suggesting a pronounced homogeneity of the available exchange sites. The Gibbs standard free energy, AG~ of the Na ---)␣89 exchange calculated from the normalized selectivity coefficient is -3.11 kJ eq and, for the Na ~ 1/2Znexchange, it is 2.75 kJ eq ~. Examination of the solid exchange products with X-ray diffraction (XRD) revealed a possible decrease in crystallinity of zeolite Pb-Pc as suggested by the significant broadening and disappearance of diffraction lines. This decrease is associated with a reduction of pore opening, as indicated from Fourier-transform infrared analysis (FTIR), which in turn results in a decrease of the amount of zeolitic water. Thermogra- vimetric-differential thermogravimetric (TG-DTG) analysis showed that water loss occurs in three steps, the relative significance of which depends on the type of exchangeable cation and subsequently on the type of complex formed with the cation and/or the zeolite channels. Zeolite Na-Pc might be utilized in environmental applications, such as the treatment of acid-mine drainage and electroplating effluents.Presented on: Clays and Clay Mineral

Chemical signature of two Permian volcanic ash deposits within a bentonite bed from Melo, Uruguay

A Permian bentonite deposit at Melo, Uruguay is composed of a calcite-cemented sandstone containing clay pseudomorphs of glass shards (0-0.50 m) overlying a pink massive clay deposit (0.50-2.10m). The massive bed is composed of two layers containing quartz and smectite or pure smectite respectively. The smectite is remarkably homogeneous throughout the profile: it is a complex mixed layer composed of three layer types whose expandability with ethylene glycol (2EG 1EG or 0EG sheets in the interlayer zone which correspond to low-, medium- and high-charge layers respectively) varies with the cation saturating the interlayer zone. The smectite homogeneity through the profile is the signature of an early alteration process in a lagoonal water which was over saturated with respect to calcite. Compaction during burial has made the bentonite bed a K-depleted closed system in which diagenetic illitization was inhibited. Variations in major, REE and minor element abundances throughout the massive clay deposit suggest that it originated from two successive ash falls. The incompatible element abundances are consistent with that of a volcanic glass fractionated from a rhyolite magma formed in a subduction/collision geological context.<br>Um depósito Permiano de bentonita em Melo, Uruguai,é composto por um arenito com cimento calcítico contendo pseudomorfos de argila sobre detritos vítreos(0-0.50 m) superpostos a um deposito maciço de argila rosado (0.50-2.10 m). A camada maciça é composta por dois níveis contendo quartzo e esmectita ou esmectita pura, respectivamente. A homogeneidade de esmectita ao longo do perfil é notável: trata-se de um interestratificado composto de três tipos de camadas, cuja expansibilidade com etileno-glicol (folhas 2EG, 1EG ou 0EG na zona interfoliar correspondentes a camadas com baixa, média e alta carga, respectivamente) variam com o tipo de cátion que satura a zona interfoliar. A homogeneidade da esmectita ao longo do perfil é a assinatura de um processo de alteração precoce em uma água lagunar supersaturada em calcita. A compactação durante o soterramento tornou a camada de bentonita um sistema fechado empobrecido em K no qual a ilitização diagenética foi inibida. Variações nas abundâncias de elementos maiores, menores e ETR no depósito maciço de argila sugere que este foi originado a partir de duas quedas sucessivas de cinza. A abundância de elementos incompatíveis é consistente com a de um vidro vulcânico fracionado a partir de um magma riolitico formado em um ambiente geológico de subducção/colisão