Zeolites (minerals)
Zeolites are a group of naturally occurring minerals formed from volcanic rock and ash interacting with alkaline groundwater. Classified as microporous aluminosilicates, they possess a unique crystalline structure that allows them to function as "molecular sieves," capturing specific molecules based on size and shape. There are approximately 175 known zeolite frameworks, with 40 being naturally occurring, and they can be mined in various locations worldwide, including the United States.
The absorbent properties of zeolites make them valuable in numerous applications. They are widely used in laundry detergents to trap dirt and impurities during the wash cycle. Additionally, zeolites find utility in aquarium filters and cat litter, as well as in medical settings for purifying air and producing medical-grade oxygen. Their resistance to heat and chemicals allows them to be effective in nuclear reactors and oil filtration systems. In agriculture, zeolites like clinoptilolite can enhance soil quality by retaining essential nutrients and moisture. Overall, zeolites are versatile minerals with significant roles in household, industrial, and agricultural contexts.
Zeolites (minerals)
Where Found
Zeolites are found naturally wherever volcanic rock and ash interact with alkaline groundwater. They are mined extensively in many parts of the world. Zeolites are also easily produced through artificial means; often artificial zeolites are purer and therefore preferable to the organic variety. As of 2008, 175 cataloged unique zeolite frameworks had been identified, 40 of which are naturally occurring.
Primary Uses
The primary use for zeolites is in laundry detergents. The mineral’s porous nature allows particles of dirt and contaminants to be captured in the wash cycle and then rinsed away in the rinse cycle. Other common uses are as aquarium filters and cat litter. Zeolites are also used extensively within the medical profession as molecular sieves to filter and purify air to make medical grade oxygen.
Technical Definition
Zeolite is a crystalline mineral most commonly used as an absorbent in commercial settings. Zeolites are microporous aluminosilicates with well-defined structures that act as “molecular sieves,” capturing oxygen, minerals, and water and holding them within their many and variable-sized pores. Zeolites generally contain silicon, aluminum, and oxygen in their frame and water or other molecules within their pores. Their defining feature is a framework made up of four connected networks of atoms. They are tetrahedrous in nature, with a silicon atom in the middle and oxygen atoms in the corners. They can link together by their corners and form beautiful structures that contain cavities and channels in which other molecules can become trapped. Because of this property, Zeolites are excellent means of filtering out impurities in many things.
Description, Distribution, and Forms
Zeolites are aluminosilicates. They are more commonly referred to as “molecular sieves” because of a particular ability within the substance to sort molecules by their sizes and shapes. The size of a pore within the zeolite controls what molecules can flow into it. These pores are generally noncylindrical in nature. An “eight-ring” refers to a closed loop consisting of eight silicon or aluminum atoms and eight oxygen atoms. These atoms are tetrahedral in nature but not always symmetrical because of the bonding restraints within the zeolite, which are often often based on the positioning of the oxygen atoms within the structure.
Zeolite products are many and varied. Found in both natural and human-made forms, they are capable of absorbing and filtering out impurities in water and other liquids. They are resistant to heat and chemicals, which makes them excellent filtration devices in nuclear reactors and oil filtration systems.
History
Zeolite was given its name by Swedish mineralogist Axel Fredrik Cronstedt. Cronstedt heated a material then referred to as stilbite and observed that a small piece of the substance produced a large amount of steam. Cronstedt, pulling from the Greek words zeo, which means “boil,” and lithos, which means “stone,” named the material zeolite.
Obtaining Zeolites
Zeolites are formed when volcanic rock and layers of ash are subjected to groundwater containing alkaline. These types of zeolites are seldom pure, often containing contaminates from other minerals and substances. Open-pit zeolite mines can be found in Arkansas, Idaho, and New Mexico. topsoil is removed from the site, making access to the zeolite possible. The zeolite can be blasted free, cut free with ripper blades, or scraped from the ground with a bulldozer or top loader. Once removed from the ground, the zeolite is crushed, dried, and milled. Once processed, the substance is ready to use.
Uses of Zeolites
Zeolites can be found in many places. Their adaptability as a natural and human-made filter makes them useful in both household and industrial settings.
Oxygen concentrators containing zeolite are commonly used to produce medical-grade oxygen. The zeolite is able to filter impurities out of the air. Zeolites are also commonly used in water filtration systems for the same reason; they capture impurities in the water when water is filtered through them.
Zeolites are resistant to radiation, making them quite useful in nuclear reactions. They capture debris and waste products inside nuclear reactors. These waste products can be removed easily and disposed of without inhibiting the reactor’s capabilities. Once filled with fission by-products, the zeolite can be hard-pressed. This seals in the fission waste, making the by-product more easily disposable than the by-products of more conventional radioactive waste disposal methods.
In agriculture, a naturally occurring zeolite called clinoptilolite is used in the treatment of soil. The absorbent nature of this particular zeolite allows for vital minerals to be time-released into the soil. Potassium and nitrogen, in particular, are substances that can be released in this manner. Also, because zeolites are absorbent, water can be introduced into arid soil. In regions where water is overly abundant in the soil, introducing zeolites can help prevent root rot and improve harvests. Zeolites introduced into waterlogged soil can capture and retain up to 55 percent of their weight.
Zeolites are also commonly used in the heating and refrigerating industry. Zeolite’s ability to absorb heat makes it useful in the capture and collection of heat and moisture that would escape otherwise. The introduction of zeolite into such environments improves the efficiency of both tasks.
This ability of zeolites to capture impurities in water and other liquids is not overlooked in the pet supply industry. Zeolite is an ingredient in many aquarium filters. It captures and filters ammonia and other nitrogenous compounds in aquariums, keeping the water from becoming toxic to fish and other aquatic creatures.
Another common use for zeolites is in cat litter. The nonclumping variety of cat litter is commonly made of zeolite or diatomite. This porous litter captures liquid, and is easily removed from the litter box.
Zeolites introduced into the food supply of animals can improve the animal’s ability to process the food and help to improve the animal’s bone density. Additionally, zeolites can reduce the airborne ammonia in holding pens by up to 80 percent.
Zeolite is also used in the petrochemical industry, filtering out impurities in crude oil and other petroleum products. Zeolite is hydrogenized and turned into powerful acid via ion exchange. Once zeolite is acidified, processes such as isomerization (a process that converts one compound into another with the same number of atoms, only rearranged), alkylation (which transfers the alkyle group of one atom to another), and catalytic cracking can be carried out. Catalytic cracking is a process that requires a furnace and a reactor. Crude oil is heated in the furnace, then sent to the reactor, where it is introduced to the acidic zeolite. It is run through the zeolite three times; each time it is filtered through a cooler version of the acidified zeolite. The next step is the separation of hydrogen from the crude oil. It is sent to a fractionator (yet another separation process that divides components of a compound by their physical qualities) in the final step and becomes the end product.
Bibliography
Auerbach, Scott M., Kathleen A. Carrado, and Prabir K. Dutta. Handbook of Zeolite Science and Technology. Boca Raton, Fla.: CRC Press, 2003.
Peiper, Howard. Zeolite: Nature’s Heavy Metal Detoxifier. Sheffield, Mass.: Safe Goods, 2006.
Xu, Ruren, et al. Chemistry of Zeolites and Related Porous Materials: Synthesis and Structure. New York: Wiley-Interscience, 2007.
U.S. Geological Survey.