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Natural Nanomaterials
Published in M. H. Fulekar, Bhawana Pathak, Environmental Nanotechnology, 2017
Zeolites are hydrated aluminosilicate minerals made of tetrahedral building blocks of AlO4 and SiO4 linked by rings. These units form a rigid, 3-D crystalline structure with a network of interconnected tunnels and cages. More than 40 naturally occurring zeolites are known. Natural zeolites are rock-forming, micro porous silicate minerals. An example is the mineral natrolite [Na2Al2Si3O10 ⋅ 2H2O]. In zeolite, the pore and channel sizes are nearly uniform, allowing the crystal to act as a nanoscale filter, or molecular sieve. Molecular sieves are materials that can be short molecules based on their size and chemical or electronic affinity. The size of the molecular or ionic species that can enter the pores of a zeolite is controlled by the diameters of the tunnels. The types of molecules that can pass through the pores are influenced by their electrical charges and chemical interaction with the sieve matrix. Due to the strong electron charge inside the pores and high surface energy, zeolites can act a catalyst. The nanoscale architecture of the silicate and alumina in zeolites gives them their remarkable properties. Because of their powerful properties as filters and catalysts, zeolites are invaluable scientific tools. Zeolites have an ‘open’ structure that can accommodate a wide variety of cations, such as Na+, K+, Ca2+, Mg2+ and others. These positive ions are rather loosely held and can readily be exchanged for others in a contact solution. Some of the more common mineral zeolites are analcime, chabazite, heulandite, natrolite, phillipsite and stilbite (Fuoco, 2012).
Microporous and Mesoporous Solids
Published in Elaine A. Moore, Lesley E. Smart, Solid State Chemistry, 2020
Elaine A. Moore, Lesley E. Smart
Over 60 naturally occurring zeolites have been characterised but only seven (analcime, chabazite, clinoptilolite, erionite, ferrierite, mordenite, and phillipsite) zeolites occur in large deposits, mostly in China and Cuba. However over 200 artificial zeolites have been synthesized. Before considering the structure of zeolites themselves, we look at silicates.
Carbon dioxide removal from biogas through sorption processes using natural and activated zeolite adsorbents
Published in Indian Chemical Engineer, 2022
Elshaday Mulu, Milton M. M’Arimi, Rose C. Ramkat, Elsabet Mulu
Natural zeolites occur in different forms, such as mordenite, clinoptilolite, chabazite, phillipsite and others. They contain inorganic and organic impurities that cover the pores of zeolite so that its adsorption ability is reduced. However, it can be improved by physical and chemical activation. Furthermore, artificial zeolites are commercially synthesised for applications such as adsorbent [10]. Some of the synthetic zeolites that are used as adsorbents include zeolites 5A and 13X, which are very effective in carbon dioxide uptake but are very expensive. Modified zeolite can be prepared from clay minerals, fly ash, sludge and waste porcelain under hydrothermal activation to enhance its adsorption capacity. This activation can help to clean the pore surface and increase its surface activity. Physical activation is done using around 300–400 °C [11]. Chemical activation can be done using either acids or bases, which remove impurities such as oxides, free silica and alumina, thereby, cleaning the surface of the pores [11].
Sodium adsorption by reusable zeolite adsorbents: integrated adsorption cycles for salinised groundwater treatment
Published in Environmental Technology, 2021
Ashley M. Siemens, James J. Dynes, Wonjae Chang
The unique sorption and selectivity properties of natural zeolites have led to their use as ion exchange media in many environmental applications. Zeolites have been considered for water and wastewater treatment, mine water reclamation, agronomy, horticulture, aquaculture, nuclear waste treatment, and multiple other applications [1–4]. Approximately 40 natural zeolites have been identified, with the most common types being clinoptilolite, erionite, chabazite, mordenite, and phillipsite, all of which are present in deposits in North America [5]. Chabazite and clinoptilolite deposits are mined in both the USA and Canada. Chabazite deposits are located in Nevada and Arizona, USA [6], as well as in Nova Scotia, Canada [7], and clinoptilolite is mined in British Columbia, Canada [8], as well as in five US states (California, Idaho, New Mexico, Oregon, and Texas) [6].
Assessment of the durability and environmental impact of seawater-activated portlandite-calcined clay binder
Published in Journal of Sustainable Cement-Based Materials, 2023
Adhora Tahsin, Salman Siddique, Warda Ashraf, Melanie Sattler
Portlandite was added to the RRC system as a calcium source to produce reaction products with binding properties. Figure 2(a–c) indicates that nearly all the portlandite in all the RRC mixes was consumed in seven days. In contrast, as shown in Figure 2(d), portlandite formed in the OPC mix’s hydration process over time. Phillipsite, a type of zeolite that leads to a heterogeneous microstructure formation, is another critical phase that was observed in the calcined clay mixes [52]. However, a previous research suggested that the formation of phillipsite leads to lower mechanical performance [53].