Zeolite

Zeolita.

The zeolites or zeolites are microporous aluminosilicate minerals. They have the ability to hydrate and dehydrate reversibly. As of October 2012, 206 types of zeolites have been identified according to their structure, of which more than 40 are natural; the rest are synthetic. Natural zeolites are found in sedimentary, volcanic and metamorphic rocks.

They are often used and sold as commercial absorbents. Examples of their uses include petroleum refining, coloring of liquids and gases, and pollution control. This has led to commercial production. of artificial zeolites with particular characteristics.

Etymology

Andesita with amigdaloid vesicles filled with zeolite.

The term zeolite was originally coined in 1756 by Swedish mineralogist Axel Fredrik Cronstedt, who observed that rapidly heating stilbite produces large amounts of water vapor that had been absorbed by the material. Based on this, he named the material zeolite, where the Greek ζέω (zeo) means & # 34;boil & # 34; and λίθος (lithos), "stone".

Paragenesis

The main geological materials where zeolites lie are in sedimentary rocks and in various types of volcanic strata. Regarding geological environments, zeolites tend to form in specific environments that can be classified as follows: saline or alkaline lagoons, saline or alkaline surfaces and soils, ocean bottom sediments, areas where water percolates in open hydrological systems, areas of hydrothermal alteration and during sediment diagenesis.

Physical-chemical structure

Zeolites are composed of tetrahedrons formed by a cation and four oxygen atoms, that is, TO₄. The cation, T, can be silicon (Si), aluminum (Al) or even germanium (Ge), although silicon predominates. Since tetrahedrons are interconnected, their formula is TO₂ since tetrahedrons adjacent ones share oxygens. Because aluminum has lower charges than silicon, the inclusion of aluminum is chemically offset by the inclusion of K, Na, and Ca, or less frequently by Li, Mg, Sr, and Ba. These seven cations, although they are part of the zeolites, do not become part of the TO₂ framework. Zeolites are similar in structure and chemistry to feldspars with the difference that zeolites have larger cavities. large and usually hold water.

Types of mineral species

There are several types of natural zeolite, which arise in sedimentary rocks and are made up of aluminum, silicon, hydrogen, oxygen, and a variable number of water molecules. According to the IMA, the following zeolites are accepted as valid minerals:

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Uses

Zeolites have several uses:

• Agriculture
• Aquaculture
• The feeding of livestock
• As an ionic exchanger
• As a catalyst in the chemical industry
• As a filtering medium in water treatment

Agriculture

They are used as a soil and soil improver to increase the water and nutrient retention capacity in the growing area, improve soil permeability, and nitrogen conversion, and prevent soil nitrification. It is also used as an additive in physical mixtures of fertilizers and pesticides. The Reduction of the amount of irrigation stands out, it increases the efficiency of the fertilizers provided in the crops and reduces the volatilization of essential nutrients.

Aquaculture

It is mainly used to control ammonia levels in water. and slightly reduce the hardness of the water. It is also used as a nutritional supplement to sequester toxins and improve feed conversion.

Cattle Feeding

Currently it is used as a feed supplement for cattle, since it improves feed conversion. It has been shown that cattle can increase their weight with the use of zeolites due to a better use of nutrients, although the percentage of increase varies according to the species and the level of efficiency and productivity of each farm. It is ideal for diarrhea control, as it helps regulate acidity in the digestive tract and capture water and toxins. It is also used as a mycotoxin binder, especially AFBL1 aflatoxin and zearalenone, where it has proven to be more efficient than other clays.

Ion exchange

For a natural zeolite to be efficient in softening water, a chemical activation process is required to increase its surface area and its absorption capacity. Currently they are no longer used to soften water, since synthetic ion exchange resins have largely superseded them.

Catalyst in the chemical industry

They are very important for many petrochemical processes.

Zeolites, due to their highly crystalline pores, are considered as a molecular sieve, since their cavities are of molecular dimensions, so that when hard water passes, the larger molecules remain and the smaller ones continue their course, which allows a cleaner, softer and crystalline liquid to come out. Paul Weisz discovered in 1960 that some of these molecular sieves exhibit shape selectivity, making them highly specific for some catalytic applications.

But this screening capacity is limited. Due to the tiny size of the pores, the incoming water should have a very low amount of solids and turbidity; otherwise the resin will clog quickly, making the process economically unfeasible.

Its crystalline structure is formed by tetrahedrons that come together giving rise to a three-dimensional network, in which each oxygen atom is shared by two silicon atoms, thus forming part of the tectosilicate minerals.

As a filter medium in water treatment

It has been increasingly used as a filter medium as a substitute for silica sand, and multi-bed filters. For the following reasons:

• They have a surface area 10 times greater than sand and multilayer. Which allows you to retain smaller particles and achieve greater leakage of suspended solids
• Because they are 50% lighter than sand have greater permeability, which gives them greater solid load capacity, allowing them to provide longer filtration runs and provide substantial water and energy savings.

However, not all natural zeolites are suitable for this purpose, since many of them either have a quantity of clays and adherent soluble materials, which are released on contact with water, and do not allow it to be cleaned properly or they have heavy metals that are released during the filtration process.

An investigation led by Kenneth Tankersley, an archaeological geologist at the University of Cincinnati, reveals that, two millennia ago, the Mayans were pioneers in the use of zeolite to purify the water that the population drank in the metropolis of Tikal, in the northeast of present-day Guatemala.

Main producing countries

The main producer of zeolite is China. Its production of natural zeolites between 2011 and 2012 was 2 million tons.

In Latin America and the Caribbean, Cuba has extensive natural mineral reserves, grouped into 18 studied deposits. It came to be among the five largest zeolite producers worldwide, with an installed production capacity of 600,000 tons per year at the beginning of the 1990s XX. By 2017, production was only 20 thousand tons per year.

Other Latin American producers are Ecuador and Chile, with a production of 13,591 tons between 2000 and 2005.