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 Zeolite

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Femminile Serpente
Numero di messaggi : 1826
Data d'iscrizione : 22.03.10
Età : 39
Località : Prov. CN

MessaggioOggetto: Zeolite   Sab 6 Ago 2011 - 14:25

Viene usata principalmente per trasformare l'energia, il suo potere è la combinazione delle due forze elementali Terra e Fuoco, aiuta ad abbattere le negatività e le emozioni nocive.

FONTE: http://www.snazzdragon.com/main/az/stones/zeo.php

Zeolites

Zeolites are a family of rare and beautiful volcanic minerals made up of silicon and aluminium, which have complex crystal structures and unique properties. They form in the cracks and cavities of volcanic rocks where heat and pressure compress and transform the minerals present into strange crystalline forms.

Zeolites are mainly used in magic to transform energy and are very effective healing stones. They harness the combined power of elemental Earth and Fire, breaking down negativity, harmful emotions and illness and transforming the energy that is released so that it can be used for positive purposes. Zeolites are good crystals to work with if you face difficult decisions or doubt your ability to keep going in the face of adversity. Just keeping a Zeolite near you during these times can help -- whisper your troubles to the crystal before sleeping and it can transform despair into hope and show solutions to your problems in your dreams.



FONTE: http://it.wikipedia.org/wiki/Zeolite

Zeolite
Da Wikipedia, l'enciclopedia libera.

Le zeoliti (dal greco zein, "bollire" e lithos, "pietra" per il motivo che se le zeoliti vengono riscaldate si rigonfiano[1]) sono minerali con una struttura cristallina regolare e microporosa caratterizzati da una enorme quantità di volumi vuoti interni ai cristalli[2]. La parola zeolite (pietra che bolle) fu coniata dallo studioso svedese Axel Fredrik Cronstedt che osservò il liberarsi di vapore acqueo (dovuto all'acqua intrappolata nelle cavità) scaldando uno di questi minerali.

Caratteristiche chimico-fisiche

La chimica dello stato solido ha permesso di ricavare approfondite informazioni riguardo alla struttura e alle proprietà delle zeoliti. Questi minerali presentano una intelaiatura strutturale a base di alluminosilicato con cationi intrappolati all'interno di cavità a "tunnel" o a "gabbia". Una classe cospicua ed importante di zeoliti possiede una struttura a gabbia sodalite, consistente in un ottaedro tronco ottenuto asportando con il taglio tutti i vertici. Dato che le gabbie possiedono simmetria cristallina, le zeoliti rappresentano una classe di setacci molecolari con selettività maggiore rispetto, ad esempio, alla silice o al carbone attivo, che possiedono vuoti irregolari. Altra peculiarità consiste nello scambio ionico, processo chimico-fisico consistente nello scambio del catione contenuto all'interno della struttura cristallina con ioni presenti in soluzione e che possiedono dimensioni e proprietà elettrostatiche compatibili con la struttura entro la quale vanno ad inserirsi. Ad esempio, zeoliti naturali contenenti cationi Na+ o K+ sono in grado di scambiare specie ioniche quali Ca2+ e Mg2+.

Dal punto di vista della loro struttura le zeoliti sono dei tettosilicati: il silicio o l'alluminio sono siti al centro di un tetraedro ai cui vertici sono disposti gli atomi di ossigeno. L'impalcatura così creata lascia all'interno dei cristalli varie cavità che possono essere riempite da acqua (che il minerale può perdere con l'esposizione all'aria o se è riscaldato) e gli altri metalli presenti.[1]

Le zeoliti possono scambiare i metalli siti nei loro canali con altri metalli, ad esempio se una zeolite di sodio viene immersa in una soluzione di potassio concentrata tale zeolite diverrà una zeolite di potassio.[1]

La dimensione dei pori è importante in quanto ad essi è legata l'azione catalitica: le molecole entrano in questi pori selettivamente e subiscono ad esempio le reazioni di cracking e di isomerizzazione. Inoltre il tipo di catione presente all'interno della struttura zeolitica influenza la cinetica di scambio ionico.


FONTE IMMAGINE: http://it.wikipedia.org/wiki/File:ZeolitesUSGOV.jpg

Utilizzi

Esistono numerosissime zeoliti, sia naturali che di sintesi, molte delle quali hanno proprietà utili nell'industria: sono ad esempio utilizzate nell'industria petrolchimica come catalizzatori eterogenei, nei detergenti in sostituzione dei polifosfati, in agricoltura, in edilizia e nell'addolcimento delle acque. Un utilizzo importante in sintesi inorganica permette di ottenere complessi facendo reagire cationi metallici, intrappolati all'interno della struttura zeolitica, con opportuni reagenti complessanti; il composto di coordinazione ottenuto resta intrappolato all'interno della gabbia, essendo troppo grande per potervi uscire. Vengono inoltre utilizzate in alcune pompe da vuoto preliminare poiché, alle temperature dell'azoto liquido, sono in grado di accumulare sulle enormi superfici interne un gran numero di molecole di gas.

Anticamente le zeoliti venivano utilizzate come scambiatori di ioni, disidratanti e setacci molecolari. Tuttavia per questi scopi vengono prodotte le zeoliti sintetiche pertanto, attualmente le zeoliti vengono usate per scopi scientifici e collezionistici.[1]

Le zeoliti sintetiche

Le zeoliti sintetiche vengono frequentemente sintetizzate lavorando ad alte pressioni con l'ausilio di autoclavi. Ad esempio, è possibile effettuarne una sintesi scaldando in autoclave a 100-200 °C una soluzione di idrossido di tetrapropilammonio, che fa da templante, con silice colloidale e allumina microporosa. Le permutiti sono una classe di zeoliti sintetiche ottenute fondendo miscele di quarzo, caolino e carbonato di sodio; molte di loro hanno proprietà meccaniche e di scambio ionico migliori rispetto alle zeoliti naturali.

Note

^ a b c d Autori Vari, Scheda Zeoliti in "Il magico mondo di minerali & gemme, De Agostini (1993-1996), Novara
^ "Le zeoliti e i materiali microporosi", di Costanza Pazé, pubbl. su "Le Scienze quaderni", mum.115, settembre 2000, pag.39


FONTE: http://en.wikipedia.org/wiki/Zeolite

Zeolite
From Wikipedia, the free encyclopedia

Zeolites are microporous, aluminosilicate minerals commonly used as commercial adsorbents.[1] The term zeolite was originally coined in 1756 by Swedish mineralogist Axel Fredrik Cronstedt, who observed that upon rapidly heating the material stilbite, it produced large amounts of steam from water that had been adsorbed by the material. Based on this, he called the material zeolite, from the Greek ζέω (zeō), meaning "boil" and λίθος (lithos), meaning "stone".[2]

As of November 2010, 194 unique zeolite frameworks have been identified, and over 40 naturally occurring zeolite frameworks are known.[3][4]

Zeolites are widely used in industry for water purification, as catalysts, and in nuclear reprocessing. Their biggest use is in the production of laundry detergents. They are also used in medicine and in agriculture.

Properties

Zeolites have a porous 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, clinoptilolite, heulandite, natrolite, phillipsite, and stilbite. An example mineral formula is: Na2Al2Si3O10·2H2O, the formula for natrolite.

Natural zeolites form where volcanic rocks and ash layers react with alkaline groundwater. Zeolites also crystallize in post-depositional environments over periods ranging from thousands to millions of years in shallow marine basins. Naturally occurring zeolites are rarely pure and are contaminated to varying degrees by other minerals, metals, quartz, or other zeolites. For this reason, naturally occurring zeolites are excluded from many important commercial applications where uniformity and purity are essential.

Zeolites are the aluminosilicate members of the family of microporous solids known as "molecular sieves." The term molecular sieve refers to a particular property of these materials, i.e., the ability to selectively sort molecules based primarily on a size exclusion process. This is due to a very regular pore structure of molecular dimensions. The maximum size of the molecular or ionic species that can enter the pores of a zeolite is controlled by the dimensions of the channels. These are conventionally defined by the ring size of the aperture, where, for example, the term "8-ring" refers to a closed loop that is built from 8 tetrahedrally coordinated silicon (or aluminum) atoms and 8 oxygen atoms. These rings are not always perfectly symmetrical due to a variety of effects, including strain induced by the bonding between units that are needed to produce the overall structure, or coordination of some of the oxygen atoms of the rings to cations within the structure. Therefore, the pores in many zeolites are not cylindrical.


A form of thomsonite (one of the rarest zeolites) from India
Attribution: Rob Lavinsky, iRocks.com – CC-BY-SA-3.0
FONTE IMMAGINE: http://en.wikipedia.org/wiki/File:Thomsonite-61017.jpg

Sources

Conventional open pit mining techniques are used to mine natural zeolites. The overburden is removed to allow access to the ore. The ore may be blasted or stripped for processing by using tractors equipped with ripper blades and front-end loaders. In processing, the ore is crushed, dried, and milled. The milled ore may be air-classified as to particle size and shipped in bags or bulk. The crushed product may be screened to remove fine material when a granular product is required, and some pelletized products are produced from fine material.

Currently, the world’s annual production of natural zeolite is about 3 million tonnes. The major producers in 2010 were China (2 million tonnes), South Korea (210,000 t), Japan (150,000 t), Jordan (140,000 t), Turkey (100,000 t) Slovakia (85,000 t) and United States (59,000 t).[5] The ready availability of zeolite-rich rock at low cost and the shortage of competing minerals and rocks are probably the most important factors for its large-scale use. According to the United States Geological Survey, it is likely that a significant percentage of the material sold as zeolites in some countries is ground or sawn volcanic tuff that contains only a small amount of zeolites. Some examples of such usage are dimension stone (as an altered volcanic tuff), lightweight aggregate, pozzolanic cement, and soil conditioners.[6]

There are several types of synthetic zeolites that form by a process of slow crystallization of a silica-alumina gel in the presence of alkalis and organic templates. One of the important processes used to carry out zeolite synthesis is sol-gel processing. The product properties depend on reaction mixture composition, pH of the system, operating temperature, pre-reaction 'seeding' time, reaction time as well as the templates used. In sol-gel process, other elements (metals, metal oxides) can be easily incorporated. The silicalite sol formed by the hydrothermal method is very stable. Also the ease of scaling up this process makes it a favorite route for zeolite synthesis.

Synthetic zeolites hold some key advantages over their natural analogs. The synthetics can, of course, be manufactured in a uniform, phase-pure state. It is also possible to manufacture desirable zeolite structures which do not appear in nature. Zeolite A is a well-known example. Since the principal raw materials used to manufacture zeolites are silica and alumina, which are among the most abundant mineral components on earth, the potential to supply zeolites is virtually unlimited. Finally, zeolite manufacturing processes engineered by man require significantly less time than the 50 to 50,000 years prescribed by nature. Disadvantages include the inability to create crystals with dimensions of a comparable size to their natural counterparts.

Uses

Commercial and domestic

Zeolites are widely used as ion-exchange beds in domestic and commercial water purification, softening, and other applications. In chemistry, zeolites are used to separate molecules (only molecules of certain sizes and shapes can pass through), and as traps for molecules so they can be analyzed.

Zeolites have the potential of providing precise and specific separation of gases including the removal of H2O, CO2 and SO2 from low-grade natural gas streams. Other separations include noble gases, N2, O2, freon and formaldehyde. However, at present, the true potential to improve the handling of such gases in this manner remains unknown.

On-Board Oxygen Generating Systems (OBOGS) use zeolites to remove nitrogen from compressed air in order to supply oxygen for aircrews at high altitudes.[7]

Gemstones

Thomsonites, one of the rarer zeolite minerals, have been collected as gemstones from a series of lava flows along Lake Superior in Minnesota and to a lesser degree in Michigan, U.S.A. Thomsonite nodules from these areas have eroded from basalt lava flows and are collected on beaches and by scuba divers in Lake Superior.

These thomsonite nodules have concentric rings in combinations of colors: black, white, orange, pink, red, and many shades of green. Some nodules have copper inclusions and rarely will be found with copper "eyes." When polished by a lapidary the thomsonites sometimes display chatoyancy.[10]

Medical

Research into and development of the many biochemical and biomedical applications of zeolites, particularly the naturally occurring species heulandite, clinoptilolite and chabazite has been ongoing.[11]

Zeolite-based oxygen concentrator systems are widely used to produce medical-grade oxygen. The zeolite is used as a molecular sieve to create purified oxygen from air using its ability to trap impurities, in a process involving the adsorption of nitrogen, leaving highly purified oxygen and up to 5% argon.

QuikClot brand hemostatic agent, which is used to stop severe bleeding,[12] contains a calcium-loaded form of zeolite.

Use as nutritional supplements

Some clinoptilolite-based dietary supplements may have demonstrated antioxidant activity in humans. This has not been confirmed or repeated by any other group. There is no scientific or medical support for its use in immunotherapy.[13]

Agriculture

In agriculture, clinoptilolite (a naturally occurring zeolite) is used as a soil treatment. It provides a source of slowly released potassium. If previously loaded with ammonium, the zeolite can serve a similar function in the slow release of nitrogen. Zeolites can also act as water moderators, in which they will adsorb up to 55% of their weight in water and slowly release it under plant demand. This property can prevent root rot and moderate drought cycles.

Animal husbandry

"Both natural and synthetic zeolites have been used in animal nutrition mainly to improve performance traits and, based on their fundamental physicochemical properties, they were also tested and found to be efficacious in the prevention of ammonia and heavy metal toxicities, poisonings as well as radioactive elements uptake and metabolic skeletal defects."[14]

In concentrated animal growing facilities, the addition of as little as 1% of a very low sodium clinoptiloite was shown to improve feed conversion, reduce airborne ammonia up to 80%, act as a mycotoxin binder, and improve bone density.[15] It can be used in general odor elimination for all animal odors.[6]

Domestic pet care

Aquarium keeping

Zeolites are marketed by pet stores for use as a filter additive in aquariums.[6] In aquariums, zeolites can be used to adsorb ammonia and other nitrogenous compounds. However, due to the high affinity of some zeolites for calcium, they may be less effective in hard water and may deplete calcium. Zeolite filtration is used in some marine aquaria to keep nutrient concentrations low for the benefit of corals adapted to nutrient-depleted waters.

Where and how the zeolite was formed is an important consideration for aquariums. Most Northern hemisphere natural zeolites were formed when molten lava came in contact with sea water, thereby 'loading' the zeolite with Na (sodium) sacrificial ions. These sodium ions will speciate with other ions in solution, thus the takeup of nitrogen in ammonia, with the release of the sodium. One deposit in southern Idaho near Bear River is a fresh water variety ( Na<.05%) In southern hemisphere zeolites, such as found in Australia, which were formed with fresh water, thus the calcium uptake on formation.

Zeolite is an effective ammonia filter, but must be used with some care, especially with delicate tropical corals that are sensitive to water chemistry
and temperature.


Cat litter

Non-clumping cat litter is often made of zeolite or diatomite.
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