Mixture separation

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Under mixture separation understands Technical Chemistry a separation method for human under natural given conditions or actions Human Interest. It is sorted, dismantled or divided in such a way that the original fractions are again separated.

Mixtures

Segregation, also segregation, or mixture separation, presupposes the presence of mixtures . They can be natural or have arisen through human influence. The segregation can also be brought about by nature itself or it is recognized as an economically sensible activity, which then mostly uses physical or chemical methods that are also operated commercially as a separation process (not every separation requires a separation process and separation processes require the existence of a Mixture not in advance), but then also require precise knowledge of what should or must be separated. Inspection, sampling and analysis help you choose the segregation process or develop new techniques.

Separation, separation, separation

Liquid mixtures, also called emulsions , tend to separate themselves if there are differences in density between the components. This is also known as phase separation . This applies to many products of daily use, hence the frequent pack Note "Shake well before use!" The glass production is both known. The still heterogeneous mixture of quartz and various additives put together according to the recipe is subject to "batch melting" in a first stage, followed by "Lauterschmelzen" ( refining by removing unwanted gas contents), which then leads to a homogeneous mixture.

Insofar as the type of mixture that is to be separated is determined according to the given structure, or - occasionally undesirable - takes place without further action, an appropriate separation process can be used.

Separation of solids

With the keywords waste and material recycling, a traditional form of segregation of solids is already indicated. The classic " rag collector " with his cart took everything in the so-called waste that could be of interest to his client, a private recycling company. “Bones, rags, paper!” Was the exclamation with which he announced his arrival. Today he has modernized himself and no longer takes everything with him in his truck, but mainly metals that promise the highest collective proceeds, especially non-ferrous metals . A time when everything was collected and used was that of the Nazi four-year plans , which were determined by the scarcity of many things and the pursuit of self-sufficiency. This can be referred to as the first stage of segregation. The things that were still fairly mixed up by the collectors were sorted at the recycler's yard and stored in separate boxes. In the past, as now, special attention was paid to metallic groupage. Trained workers further contributed to the segregation by separating iron and non-ferrous metals, steel, cast iron, copper and copper-containing zinc, light metal, lead and tin (bottle caps) from one another. At this stage it was also possible - according to what was said in the introduction - to analyze a collected batch for the average content of the substances it contains and, on this basis, to send it to a smelting facility, at the end of which valuable pure copper could be available, for example.

A basically related, but more complex way of tracing mixtures or mixtures back to the substances they contain is metallurgy, with its various processes for extracting primary metal from ore-bearing rocks, starting with the separation (segregation) of gangue and ore or the recycling of presorted metallic waste. At the beginning of the process, there is always an examination of the composition, before individual substances can be isolated from the mixture using methods that have been tried and tested or that have yet to be developed. Without knowledge of the formation of mixtures that contain elements that are important for technology, a process as important as demixing or material separation through electrolysis is not possible. Regardless of the language used, electrolysis is an indispensable technique for separating naturally occurring mixtures, tracing them back to their prehistoric, intermingled individual components. One of the most important processes in inorganic chemistry is chlor-alkali electrolysis, which supplies both the chemical raw material chlorine and metallic sodium.

One of the easier-to-use methods of demixing solids is the use of an existing difference in density or different grain sizes. Shaking, sieving, wind sifting, seigern , floating flotation can be classified here.

Separation of liquid mixtures

Since many types of liquid mixtures are conceivable, a restriction to examples is necessary, which are required by the technical requirements and economic efficiency.

In the case of carbonated mineral water, the "pearling out" of the water when the bottle is opened is also a separation. The same applies to alcoholic beverages with a high percentage of alcohol in their original state that are "reduced to drinking strength" with the addition of water. If the seal is not airtight, the rectified alcohol, which in turn comes from the segregation of a fermentation product by means of distillation, leaves the water-alcohol mixture due to its lower vapor pressure over time. Self-segregation of this kind finds its parallel in fractional distillation, as an acceleration of an often natural process ("evaporation") through an increase in temperature. The Cuveés, high-quality wines made from different grape varieties, cannot be separated. The same applies to paints in which the basic component is colored with various additives.

The separation of waste water through to separation by centrifugation is technically interesting. Wastewater, even with a high degree of pollution, is now separated by water treatment plants to such an extent that drinking water is produced at the end of the process stages, whereas the impurities that form the undrinkable part of the mixture and are separated in a multi-stage process as solids, such as organic fats, nitrogen-rich filtrates (faeces) or basic detergent residues can be recycled.

Crude oil that emerges from the pump is a mixture of components with different boiling points, which also lead to different uses. The refinery, which is basically a distillation plant, separates the different fractions due to different boiling points. This principle of fractional distillation makes it possible to separate the majority of all liquid mixtures that occur. Alternatively, separation by centrifugation is also possible. Well-known examples here are butter production and, conversely, milk defatting or honey production by centrifuging the honeycombs. Furthermore, liquid mixtures can also be brought about by utilizing differences in density (allowing them to stand) or chemical reactions which promote such differences and are therefore intentionally initiated. The component of the mixture, which has been artificially brought to a higher density, precipitates and can be filtered off. In principle, a large proportion of the wet analytical methods of inorganic chemistry are based on this.

The segregation of a molten, that is to say liquefied, metallic alloy composed of constituents of different densities can take place automatically or by using a method that promotes segregation. The simplest type of segregation is by increasing the force of gravity. Alloy components with a high density, such as lead in a bronze alloy, sink to the bottom, while lighter ones, such as silicon primary crystals in an AlSi alloy, accumulate in the upper area of ​​the melt.

There are many ways of separating a melt through deliberately induced chemical reactions. For example, components to be removed from the “mixture” can first be converted into their oxides , then separated from the liquid base and fed for further use with or without processing ( melt treatment ).

Separation (separation into individual components) of gaseous mixtures

A gas mixture is air, which - expressed as a volume percentage - is made up of 78.07% nitrogen , with 20.95% oxygen , further 0.94% noble gases (mostly argon ) and "only" 0.03% carbon dioxide . A separation of these components, a demixing, was impossible until Carl von Linde was able to liquefy the air using cryotechnical measures, in order to then break it down into its constituent parts by fractional distillation. Almost all methods of breaking down gas mixtures into their constituent parts, identifying useful and harmful ones, utilizing or disposing of them, are based on Linde's invention. This applies in particular to the field of chemical warfare (chemical weapons , warfare agents ), imaginary toxic gases or liquids of organic origin ( green cross , yellow cross , sarin ), their controlled separation (in the case of binary warfare agents ), decomposition or combustion to carbon dioxide and water to be preferred to risky separation attempts is.

Individual evidence

  1. ↑ Representation and processing of glasses. In: Egon Wiberg, Arnold F. Holleman, Nils Wiberg: Textbook of inorganic chemistry. Walter de Gruyter & Co, Berlin.
  2. ↑ Entry on warfare agents. In: Römpp Online . Georg Thieme Verlag, accessed on June 20, 2014.

Literature used