Zeolites The stones that boil-a natural way of cleaning up nature (original) (raw)
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Natural Zeolites as Sustainable and Environmental Inorganic Resources over the History to Present
General chemistry, 2019
Zeolites synthetic as well as natural, based on their beneficial properties and economic value, represent for a long time recognized industrial commodities. Natural zeolites are highly porous, hydrated aluminosilicates with a rigid crystalline structure and a network of interconnected tunnels and cages (such as honeycomb). Total pore volume of some natural zeolites reaches up to 35%. Their structures consist of a three dimensional framework, having a negatively charged lattice. The negative charge is balanced by cations, which are exchangeable with certain cations from aqueous or gaseous media. Based upon these facts and according to a new definition, zeolites are also clathrates or inclusion compounds, able to host various guest substances in their versatile structures and thus enhance their adsorption potential to broaden range of pollutants.
Mineral Commodity Report 23 - Zeolites
2002
Zeolites are crystalline, porous 3-dimensional aluminosilicates of the alkali (mainly Na and K) and alkaline-earth (mainly Ca) metals. Their crystal structure is based on a three dimensional framework of (SiAl)O4 tetrahedra with all four oxygens shared by adjacent tetrahedra (see illustrations in Armbruster and Gunter, 2001). This results in a channel structure with molecular dimensions of 3 to 10 Å. Because some of the Si4+ is substituted by Al3+, there is a net negative charge which is balanced by extra-framework exchangeable cations, mainly Na+, K+, Ca2+ or Mg2+. These cations are loosely held within the central cavities and surrounded by water molecules. The water molecules are loosely held in the pores and most zeolites can be reversibly dehydrated, and their cations readily exchanged. Zeolites have an empirical formula of: (M2,M )Al2O3gSiO2.zH2O, where M + is usually Na or K, M2+ is Mg, Ca, or Fe, and g and z are variable multipliers. Rarely Li, Sr, or Ba may substitute for M+...
A comparative study of three closely related unsolved zeolite structures
Studies in Surface Science and Catalysis, 2007
In this report we discuss the synthesis and physicochemical characterizations of three zeolites with unsolved crystal structures: SSZ-57, SSZ-74, and IM-5. The diffraction data of SSZ-57 are similar to, but distinct from, the data for ZSM-5, ZSM-11, or ZSM-5/11 intergrowths. The powder diffraction data of SSZ-74 can be indexed in a unit cell with dimensions similar to those found in ZSM-5 and ZSM-11. The organic structure directing agents (SDA) used to prepare SSZ-74 and IM-5 are similar to SDA molecules that often yield multidimensional 10-ring zeolites. The micropore volumes, adsorption uptake rates of 2,2dimethylbutane, and the constraint index tests of these three unknown materials are also consistent with those expected for multidimensional 10-ring zeolites.
Potential uses of natural zeolites for the development of new materials: short review
MATEC Web of Conferences, 2016
Zeolites stand apart among the many families of porous materials. Due to their structure, they have a number of important practical properties such as a high adsorption capacity and the ability to cation exchange. However, the main feature distinguishing them from other porous bodies and inherent only for zeolites is the ordering of the pores in their size, orientation, and mutual locations. Pore diameters for the crystalline structures of various zeolites may vary from 0.25 to about 15 nanometers. The crystalline arrangement of these pores in space converts zeolites in the naturally existing nanostructured materials, possessing the unique property to present ordered location of stabilized nanoparticles. 2 Available reserves of zeolites 2.1 Estimates of World reserves Although, there are no certain figures on the total amount of zeolites in the world, it is well known that they are present on all the continents with varying mineral contents and kinds. World production of natural zeolites was estimated in the year 2004 to be between 2.5 and 3 million metric tons (Mt) based on reported production by some countries [5]. Three years later world production of natural zeolites was estimated to be approximately the same [6]. Last year (2015) situation [7] is shown in Figure 1. 2.2 Availability of natural zeolites in Russia Less than ten deposits are exploited at present in Russia, between others the Holinsk deposit (clinoptilolite) and Mukhor-Tala deposit (mordenite) in the Republic of Buryatia, and "Priargunskoe" Mining and Chemical Association [8]. Evaluation of the Mukhor-Tala deposit was reported in Ref. [9]. Such a small amount of produced zeolite
Zeolites and Their Potential Uses in Agriculture
Advances in Agronomy, 2011
Zeolites are natural crystalline aluminosilicates. They are among the most common minerals present in sedimentary rocks. Zeolites occur in rocks of diverse age, lithology, and geologic setting, and represent valuable indicators of the depositional and postdepositional (diagenetic) environments of the host rocks. It was reported that, of the 40 naturally occurring zeolites studied by research groups, the most well-known ones are clinoptilolite, erionite, chabazite, heulandite, mordenite, stilbite, and phillipsite. Structurally, zeolites are tectosilicates exhibiting an open three-dimensional structure containing cations needed to balance the electrostatic charge of the framework of silica and alumina tetrahedral units. Pores and voids are the key characteristics of zeolite
In this review zeolites are presented as one product for environmental protection control, separation science and technology. Due to their unique porous properties they have attracted the attention of many researchers. Special attention is given to clinoptilolite gaining an increasing interest in preserving and improving the environment. Major uses of clinoptilolite in the field of catalysts, gas separation and ion exchange are reviewed, though its increasing applications in various areas such as environmental protection, industry, agriculture, food additives and medicine are also considered. The scope of the work is to present the zeolite science, focusing on natural zeolite structures and properties as well as to summarize clinoptilolite applications and its role in solving environmental problems.
In the attempt to explain why there are so many hypothetical zeolites and so few observed, a model of assembling zeolite-type frameworks as a packing of natural building units (smallest cages) and/or essential rings (smallest windows) is proposed. The packing units have no common T atoms, hence the model takes into account the process of polycondensation of T 4+ (OH) 4 or [T 3+ (OH) 4 ] − complex groups resulting in oligomeric T n O m (OH) k units, eliminating water molecules, and forming T−O−T bridges. The packings were modeled for all zeolite minerals and most of the synthetic zeolite-type frameworks accounting for 163 zeolites of the 201 known. It is shown that the extra-framework cations can play a role of templates for the packing units. Application of the model to 1220 hypothetical zeolites shows that only a small set could be explained as packing of tiles, suggesting a possible ranking of feasibility that may help to unravel the zeolite conundrum.
Zeolites: A Theoretical and Practical Approach with Uses in (Bio)Chemical Processes
Applied Sciences
This review provides a state-of-the-art summary of distributed zeolite technology, as well as identifying strategies to further promote the absorption of these materials in various areas of study. Zeolites are materials that can be synthesized or found in natural rock deposits a with a basic composition consisting in Al, Si, and O. Zeolite’s consideration as a future material is due to many facile synthesis methods to obtain different structures with variations in pore size, surface area, pore volume and physical properties. These methods are developed using the control of relevant synthesis parameters that influences structure formation, such as crystallization temperature, time of aging and/or crystallization, stoichiometric relationships between components of synthesis gel, pH of the medium, and in some cases the type of structure-directing agent. Each method will lead to geometric changes in the framework formation, making possible the formation of typical chemical bonds that ar...