We explain what filtration is and the types that exist. Also, some examples and methods for separating mixtures.
What is filtration?
Filtration is known as a technique to separate solid in suspension within a fluidliquid or gas), using a filter medium consisting of a porous material called a sieve, filter or screen. This filter retains the larger solids and allows the fluid to pass, along with the particles undersized.
The filtration process is thus very similar to that of the sifted, except that the latter is used to separate solid materials of different thickness or size. Filtration is one of the most used methods for separating mixtures in the daily life of the human being. It is also a method widely used in different types of industriesTherefore, there are different mechanical devices capable of carrying it out with a varied range of precision.
Commonly, we speak of leaks in everyday life when we refer to the excesses of humidity that soften cement and other building materials, allowing water to flood into the pores of walls, ceilings and soils, breaking through and deteriorating them. In that case, it is the Water the one that filters through the cement, and colloquially it is often said "there are leaks in the walls or the ceiling."
Filtration types
In the filtration process, what is left in the filter is called “residue”, and what passes through it is called “filtrate”. The filter material that makes up the filter is essential to ensure that the filtration works properly for specific purposes. There are various types of porous materials used as filter media, eg cloth, porous or perforated solids, polymeric fibers. On the other hand, depending on the size of the pores of the filter material used, the filtration process can be classified into different types:
- Ordinary filtering. It is the process that is carried out with membranes or sieves whose pores are equal to or greater than one millimeter (mm).
- Microfiltration. It is the type of filtration that is carried out with sieves whose pores range between 0.1 and 10 microns (1 mm = 1000 microns).
- Ultrafiltration. It is the filtration process that retains molecules whose weight exceeds 103 Dalton / gmol, allowing to separate protein or disinfect water with bacteria. Thus, this type of filtration allows filtering particles with a diameter of up to 0.01 micron.
- Nanofiltration. This process allows the retention of molecules without electrical charge that have a weight greater than 200 Dalton / gmol in the filtering membrane, and is applied in the chemical industry mainly to concentrate organic compounds.
Examples of filtration
When finished boiling pasta we separate it through a strainer.
Some everyday examples of filtration can be:
- Prepare coffee. To make coffee or other infusions, the substance (tea, coffee, etc.) is put in contact with boiling or very hot water, to force it to release its content into the water. Then they must be separated, and for that the mixture in a filter, made of cloth or paper, which retains the coarser particles of the infusion (the so-called "erasure" of the coffee) and the liquid is allowed to pass through.
- Leaks from broken pipes. Water from a broken pipe can accumulate and seep through the concrete of which buildings are made, softening its consistency and working its way downward through the work of the gravity, or upwards due to Pressure. In both cases, the water seeps through the cement, leaving any particles on the other side of the wall.
- Water purifiers. Water filters for centuries have operated by sifting drinking water, either by means of particularly porous stones (such as in jars or jars) or by means of papers, corks and other solids that serve to retain the particles that the water brings with it. In this way, the water is as clean as possible.
- Strain the pasta. When we make pasta or spaghetti, we boil the food in water and then we separate it through a strainer, which is nothing more than a coarse filter. Thus, it is possible to retain the cooked pasta and discard the hot water.
Water filtration
Water filtration is a process necessary to guarantee its minimum potability, that is, it does not contain stones, earth, metals or other waste materials that may have dragged its way into our homes.
For this, filtering devices or mechanisms installed in the pipe itself are used, which retain dirt and solid materials, allowing water to pass through their porous bodies. This mechanism does not prevent against microorganisms, so it only guarantees a first sanitary measure for water consumption.
Mixture separation methods
Filtering is just one of the methods for separating mixtures, that is, one of the procedures that we have when separating two or more mixed substances. Other methods of separating mixtures are:
- Decantation. It is a physical method of separation that consists of waiting for gravity to act on the solids present in a fluid, allowing them to settle and be mechanically removed. It can also be used to separate a mixture of two liquids that have different densities, that is, they are immiscible with each other. In this case, the mixture contained in a separating system (for example, a separating funnel) is allowed to settle, where the densest liquid passes to the bottom, and the least dense remains at the top, making it possible to separate both.
- Magnetic separation. To separate metals or magnetic particles of a liquid or other solid, a magnet since it will attract only metallic particles, and will leave intact diamagnetic particles (particles that repel magnetic fields, that is, they are not attracted by the magnetic field generated by a magnet).
- Distillation. It is a procedure that consists of separating the components of a liquid mixture using the difference between their boiling points and condensation. Thus, heat is supplied to the mixture, until the lower-boiling component passes into the vapor phase. Then this steam it condenses in another container, and the liquid with the highest boiling point remains in the original container. In this way, both liquids are separated.
- Evaporation. It is a process similar to distillation. It allows to separate mixtures of solids in liquids. In this case, the liquid in which the solid is dissolved is evaporated, and thus the solid can be recovered at the bottom of the container. This process is used in the salt flats to separate the salt that we later use in our meals (NaCl), from the sea water.