Filtration in the context of Passive diffusion

Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolinite, Al₂Si₂O₅(OH)₄). Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impurities, such as a reddish or brownish colour from small amounts of iron oxide.

Clays develop plasticity when wet but can be hardened through firing. Clay is the longest-known ceramic material. Prehistoric humans discovered the useful properties of clay and used it for making pottery. Some of the earliest pottery shards have been dated to around 14,000 BCE, and clay tablets were the first known writing medium. Clay is used in many modern industrial processes, such as paper making, cement production, and chemical filtering. Between one-half and two-thirds of the world's population live or work in buildings made with clay, often baked into brick, as an essential part of its load-bearing structure. In agriculture, clay content is a major factor in determining land arability. Clay soils are generally less suitable for crops due to poor natural drainage; however, clay soils are more fertile, due to higher cation-exchange capacity.

Drying is a mass transfer process consisting of the removal of water or another solvent by evaporation from a solid, semi-solid or liquid. This process is often used as a final production step before selling or packaging products. To be considered "dried", the final product must be solid, in the form of a continuous sheet (e.g., paper), long pieces (e.g., wood), particles (e.g., cereal grains or corn flakes) or powder (e.g., sand, salt, washing powder, milk powder). A source of heat and an agent to remove the vapor produced by the process are often involved. In bioproducts like food, grains, and pharmaceuticals like vaccines, the solvent to be removed is almost invariably water. Desiccation may be synonymous with drying or considered an extreme form of drying.

In the most common case, a gas stream, e.g., air, applies the heat by convection and carries away the vapor as humidity. Other possibilities are vacuum drying, where heat is supplied by conduction or radiation (or microwaves), while the vapor thus produced is removed by the vacuum system. Another indirect technique is drum drying (used, for instance, for manufacturing potato flakes), where a heated surface is used to provide the energy, and aspirators draw the vapor outside the room. In contrast, the mechanical extraction of the solvent, e.g., water, by filtration or centrifugation, is not considered "drying" but rather "draining".

Mineral wool is any fibrous material formed by spinning or drawing molten mineral or rock materials such as slag and ceramics. It was first manufactured in the 19th century. Applications include thermal insulation (as both structural insulation and pipe insulation), filtration, soundproofing, and hydroponic growth medium. Mineral wool can cause irritation to the eyes, skin and lungs, especially during its manufacture and installation.

Suspended solids refers to small solid particles which remain in suspension in water as a colloid or due to motion of the water. Suspended solids can be removed by sedimentation if their size or density is comparatively large, or by filtration. It is used as one indicator of water quality and of the strength of sewage, or wastewater in general. It is an important design parameter for sewage treatment processes.

It is sometimes abbreviated SS, but is not to be confused with settleable solids, also abbreviated SS, which contribute to the blocking of sewer pipes.

Water purification is the process of removing undesirable chemicals, biological contaminants, suspended solids, and gases from water. The goal is to produce water that is fit for specific purposes. Most water is purified and disinfected for human consumption (drinking water), but water purification may also be carried out for a variety of other purposes, including medical, pharmacological, chemical, and industrial applications. The history of water purification includes a wide variety of methods. The methods used include physical processes such as filtration, sedimentation, and distillation; biological processes such as slow sand filters or biologically active carbon; chemical processes such as flocculation and chlorination; and the use of electromagnetic radiation such as ultraviolet light.

Water purification can reduce the concentration of particulate matter including suspended particles, parasites, bacteria, algae, viruses, and fungi as well as reduce the concentration of a range of dissolved and particulate matter.

A sieve (/ˈsɪv/), fine mesh strainer, or sift is a tool used for separating wanted elements from unwanted material or for controlling the particle size distribution of a sample, using a screen such as a woven mesh or net or perforated sheet material. The word sift derives from sieve.

In cooking, a sifter is used to separate and break up clumps in dry ingredients such as flour, as well as to aerate and combine them. A strainer (see colander), meanwhile, is a form of sieve used to separate suspended solids from a liquid by filtration.

The urinary system, also known as the urinary tract or renal system, is a part of the excretory system of vertebrates. In humans and placental mammals, it consists of the kidneys, ureters, bladder, and the urethra. The purpose of the urinary system is to eliminate urine from the body, regulate blood volume and blood pressure, control levels of electrolytes and metabolites, and regulate blood pH. The kidneys have an extensive blood supply via the renal arteries which leave the kidneys via the renal vein. Each kidney consists of functional units called nephrons. Following filtration of blood and further processing, the ureters carry urine from the kidneys into the urinary bladder. The urethra carries urine from the bladder through the penis or vulva during urination. The female and male urinary system are very similar, differing only in the length of the urethra.

800–2,000 milliliters (mL) of urine are normally produced every day in a healthy human. This amount varies according to fluid intake and kidney function.

Filter feeders are aquatic animals that acquire nutrients by feeding on organic matter, food particles or smaller organisms (bacteria, microalgae and zooplanktons) suspended in water, typically by having the water pass over or through a specialized filtering organ that sieves out and/or traps solids. Filter feeders can play an important role in condensing biomass and removing excess nutrients (such as nitrogen and phosphate) from the local waterbody, and are therefore considered water-cleaning ecosystem engineers. They are also important in bioaccumulation and, as a result, as indicator organisms.

Filter feeders can be sessile, planktonic, nektonic or even neustonic (in the case of the buoy barnacle) depending on the species and the niches they have evolved to occupy. Extant species that rely on such method of feeding encompass numerous phyla, including poriferans (sponges), cnidarians (jellyfish, sea pens and corals), arthropods (krill, mysids and barnacles), molluscs (bivalves, such as clams, scallops and oysters), echinoderms (sea lilies) and chordates (lancelets, sea squirts and salps, as well as many marine vertebrates such as most species of forage fish, American paddlefish, silver and bighead carps, baleen whales, manta ray and three species of sharks—the whale shark, basking shark and megamouth shark). Some water birds such as flamingos and certain duck species, though predominantly terrestrial, are also filter feeders when foraging.

Diatomaceous earth (/ˌdaɪ.ətəˈmeɪʃəs/ DY-ə-tə-MAY-shəs), also known as diatomite (/daɪˈætəmaɪt/ dy-AT-ə-myte), celite, or kieselguhr, is a naturally occurring, soft, siliceous sedimentary rock that can be crumbled into a fine white to off-white powder. It has a particle size ranging from more than 3 mm to less than 1 μm, but typically 10 to 200 μm. Depending on the granularity, this powder can have an abrasive feel, similar to pumice powder, and has a low density as a result of its high porosity. The typical chemical composition of oven-dried diatomaceous earth is 80–90% silica, with 2–4% alumina (attributed mostly to clay minerals), and 0.5–2% iron oxide.

Diatomaceous earth consists of the fossilized remains of diatoms, a type of hard-shelled microalgae, that have accumulated over millions of years. It is used as a filtration aid, mild abrasive in products including metal polishes and toothpaste, mechanical insecticide, absorbent for liquids, matting agent for coatings, reinforcing filler in plastics and rubber, anti-block in plastic films, porous support for chemical catalysts, cat litter, activator in coagulation studies, a stabilizing component of dynamite, a thermal insulator, and a soil for potted plants and trees as in the art of bonsai. It is also used in gas chromatography packed columns made with glass or metal as stationary phase.

A fireplace or hearth is a structure made of brick, stone or metal designed to contain a fire. Fireplaces are used for the relaxing ambiance they create and for heating a room. Modern fireplaces vary in heat efficiency, depending on the design.

Historically, they were used for heating a dwelling, cooking, and heating water for laundry and domestic uses. A fire is contained in a firebox or fire pit; a chimney or other flue allows exhaust gas to escape. A fireplace may have the following: a foundation, a hearth, a firebox, a mantel, a chimney crane (used in kitchen and laundry fireplaces), a grate, a lintel, a lintel bar, an overmantel, a damper, a smoke chamber, a throat, a flue, and a chimney filter or afterburner.

In chemistry, work-up refers to the series of manipulations required to isolate and purify the product(s) of a chemical reaction. The term is used colloquially to refer to these manipulations, which may include:

• deactivating any unreacted reagents by quenching a reaction.
• cooling the reaction mixture or adding an antisolvent to induce precipitation, and collecting or removing the solids by filtration, decantation, or centrifugation.
• changing the protonation state of the products or impurities by adding an acid or base.
• separating the reaction mixture into organic and aqueous layers by liquid-liquid extraction.
• removal of solvents by evaporation.
• purification by chromatography, distillation or recrystallization.

The work-up steps required for a given chemical reaction may require one or more of these manipulations. Work-up steps are not always explicitly shown in reaction schemes. Written experimental procedures will describe work-up steps but will usually not formally refer to them as a work-up.

Purification in a chemical context is the physical separation of a chemical substance of interest from foreign or contaminating substances. Pure results of a successful purification process are termed isolate. The following list of chemical purification methods should not be considered exhaustive.

• Affinity purification purifies proteins by retaining them on a column through their affinity to antibodies, enzymes, or receptors that have been immobilised on the column.
• Filtration is a mechanical method to separate solids from liquids or gases by passing the feed stream through a porous sheet such as a cloth or membrane, which retains the solids and allows the liquid to pass through.
• Centrifugation is a process that uses an electric motor to spin a vessel of fluid at high speed to make heavier components settle to the bottom of the vessel.
• Evaporation removes volatile liquids from non-volatile solutes, which cannot be done through filtration due to the small size of the substances.
• Liquid–liquid extraction removes an impurity or recovers a desired product by dissolving the crude material in a solvent in which other components of the feed material are soluble.
• Crystallization separates a product from a liquid feed stream, often in extremely pure form, by cooling the feed stream or adding precipitants that lower the solubility of the desired product so that it forms crystals. The pure solid crystals are then separated from the remaining liquor by filtration or centrifugation.
• Recrystallization: In analytical and synthetic chemistry work, purchased reagents of doubtful purity may be recrystallised, e.g. dissolved in a very pure solvent, and then crystallized, and the crystals recovered, in order to improve and/or verify their purity.
• Trituration removes highly soluble impurities from usually solid insoluble material by rinsing it with an appropriate solvent.
• Adsorption removes a soluble impurity from a feed stream by trapping it on the surface of a solid material, such as activated carbon, that forms strong non-covalent chemical bonds with the impurity.
• Chromatography employs continuous adsorption and desorption on a packed bed of a solid to purify multiple components of a single feed stream. In a laboratory setting, mixture of dissolved materials are typically fed using a solvent into a column packed with an appropriate adsorbent, and due to different affinities for solvent (moving phase) versus adsorbent (stationary phase) the components in the original mixture pass through the column in the moving phase at different rates, which thus allows to selectively collect desired materials out of the initial mixture.
• Smelting produces metals from raw ore, and involves adding chemicals to the ore and heating it up to the melting point of the metal.
• Refining is used primarily in the petroleum industry, whereby crude oil is heated and separated into stages according to the condensation points of the various elements.
• Distillation, widely used in petroleum refining and in purification of ethanol separates volatile liquids on the basis of their relative volatilities. There are several type of distillation: simple distillation, steam distillation etc.
• Water purification combines a number of methods to produce potable or drinking water.
• Downstream processing refers to purification of chemicals, pharmaceuticals and food ingredients produced by fermentation or synthesized by plant and animal tissues, for example antibiotics, citric acid, vitamin E, and insulin.
• Fractionation refers to a purification strategy in which some relatively inefficient purification method is repeatedly applied to isolate the desired substance in progressively greater purity.
• Electrolysis refers to the breakdown of substances using an electric current. This removes impurities in a substance that an electric current is run through
• Sublimation is the process of changing of any substance (usually on heating) from a solid to a gas (or from gas to a solid) without passing through liquid phase. In terms of purification - material is heated, often under vacuum, and the vapors of the material are then condensed back to a solid on a cooler surface. The process thus in its essence is similar to distillation, however the material which is condensed on the cooler surface then has to be removed mechanically, thus requiring different laboratory equipment.
• Bioleaching is the extraction of metals from their ores through the use of living organisms.

Separation process

A filter cake is formed by the substances that are retained on a filter. Filter aids, such as diatomaceous earth or activated carbon are usually used to form the filter cake. The purpose is to increase flow rate or achieve a smaller micron filtration. The filter cake grows in the course of filtration, becoming "thicker" as particulate matter and filter aid is retained on the filter.

With increasing layer thickness, the flow resistance of the filter cake increases. After a time, the filter cake has to be removed from the filter, e.g. by backflushing. If this is not accomplished, the filtration is disrupted because the resistance of the filter cake gets too high; hence, too little of the mixture to be filtered can pass through the filter cake, and the filter becomes plugged or clogged. The specifications of the filter cake dictate the filtration method of choice.

A cigarette filter, also known as a filter tip, is a component of a cigarette, along with tobacco, cigarette paper, capsules and adhesives. Modern filters were introduced in the early 1950s.

Filters may be made from plastic cellulose acetate fiber, paper or activated charcoal (either as a cavity filter or embedded into the plastic cellulose acetate fibers). Macroporous phenol-formaldehyde resins and asbestos have also been used. The plastic cellulose acetate filter and paper modify the particulate smoke phase by particle retention (filtration), and finely divided carbon modifies the gaseous phase (adsorption).

An artificial membrane, or synthetic membrane, is a synthetically created membrane which is usually intended for separation purposes in laboratory or in industry. Synthetic membranes have been successfully used for small and large-scale industrial processes since the middle of the twentieth century. A wide variety of synthetic membranes is known. They can be produced from organic materials such as polymers and liquids, as well as inorganic materials. Most commercially utilized synthetic membranes in industry are made of polymeric structures. They can be classified based on their surface chemistry, bulk structure, morphology, and production method. The chemical and physical properties of synthetic membranes and separated particles as well as separation driving force define a particular membrane separation process. The most commonly used driving forces of a membrane process in industry are pressure and concentration gradient. The respective membrane process is therefore known as filtration. Synthetic membranes utilized in a separation process can be of different geometry and flow configurations. They can also be categorized based on their application and separation regime. The best known synthetic membrane separation processes include water purification, reverse osmosis, dehydrogenation of natural gas, removal of cell particles by microfiltration and ultrafiltration, removal of microorganisms from dairy products, and dialysis.

Microfiltration is a type of physical filtration process where a contaminated fluid is passed through a special pore-sized membrane filter to separate microorganisms and suspended particles from process liquid. It is commonly used in conjunction with various other separation processes such as ultrafiltration and reverse osmosis to provide a product stream which is free of undesired contaminants.