Also known as activated charcoal or activated coal, activated carbon has been used by humans since antiquity. Virginia Tech notes that references to its use as a purification agent were found in Egypt as early as 1500 BC. In ancient India, charcoal was used for drinking water filtration.
In modern times, commercially available powdered activated carbon was first introduced in Europe during the early 20th century, and its use spread rapidly through the sugar refining industry. Not long afterwards, it was discovered that activated carbon could remove noxious tastes and smells from drinking water.
Today, it is a reasonably inexpensive, easy to obtain product that is highly useful in both large-scale commercial operations and individual home applications.
What Is Activated Carbon?
Activated carbon is a very porous material with a strong ability to attract and hold various compounds. This property makes it highly useful in applications that require purification or cleansing, from treating food poisoning to purifying contaminated water supplies. It can be created from any natural material that contains a high concentration of carbon such as coal, wood, or peat.
The material is heated slowly in a low- or no-oxygen environment to remove water and other substances without causing combustion, resulting in a product known as char. The char then undergoes extensive chemical or physical processing that dramatically increases its surface area and creates a network of submicroscopic pores. After processing, a pound of activated carbon has roughly the same surface area as six football fields.
How Does Activated Carbon Work?
Activated carbon primarily works through physical adsorption. Although the difference between adsorption and absorption is subtle, it is very important. As Chromatography Today explains, in absorption, the absorbed material is evenly distributed throughout the entire volume of the absorbent product. In adsorption, the material binds only to the surface molecules, creating a sort of film.
Carbon’s surface molecules are attractive by nature, and they seek out other molecules with which they can bind. The vast surface area of activated carbon provides a tremendous number of individual molecules seeking bonds. Activated carbon’s highly porous nature permits the adsorbed compounds to freely penetrate the material, finding all available surface spots for bonding. Activated carbon binds with not only liquid impurities, but also some gas impurities.
In addition, activated carbon creates chemical reactions with some substances such as chlorine. These can create a less volatile, and often less objectionable, compound. For example, the chemical reaction with chlorine creates chloride, removing the strong odor and taste from chlorine-treated drinking water.
Activated carbon is best at adsorbing organic compounds with low water solubility and high molecular weight. It does not bind well to all materials. In particular, it is relatively ineffective at adsorbing alcohols, strong acids or bases, metals, and most inorganic materials. However, it can be treated with a variety of chemicals to improve its adsorption of those compounds.
Forms of Activated Carbon
Activated carbon is available in several forms including powdered, granular, and extruded. Each is ideally suited to certain applications. Each form of activated carbon can also be impregnated, or treated with other chemicals to improve its use in a specific application.
Powdered activated carbon, or PAC, consists of fine particles that can pass through an 80-mesh sieve. Because it is so fine, PAC is not normally used alone. Instead, it is generally used in processing equipment such as gravity filters or clarifiers.
Granular activated carbon, or GAC, consists of larger particles than PAC. Because GAC particles are larger than PAC, they have a smaller external surface area per unit of volume. Therefore, GAC particles are especially useful in adsorbing materials with a high diffusion rate such as vapors and gases.
Extruded activated carbon, or EAC, is a type of carbon that is mixed with a binder and shaped into cylindrical pellets. EAC is generally used in gas phase applications due to its high mechanical strength, low dust output, and minimal pressure drop.
Activated carbon is used in a stunning array of applications including the medical and pharmaceutical fields, personal protective devices, air and water treatment at both the municipal and individual levels, food and beverage product preparation, and even heavy industry.
• Medical Uses
Generally known in the medical field as activated charcoal, WebMD notes that activated carbon is particularly useful in fighting poisonings. It is also under investigation for use in reducing intestinal gas, lowering cholesterol, treating pregnancy-related bile flow problems, and even combating hangovers. However, activated carbon does not bind well to alcohol, so its efficacy against hangovers seems doubtful.
Activated carbon’s medical usefulness stems from its ability to trap chemicals. It binds the toxins to prevent their absorption by the stomach and intestines, as well as their circulation throughout the bloodstream. It does not bind to all chemicals, so it is not a cure-all, but for poisonings it is effective. Activated carbon has largely replaced stomach pumping and induced vomiting as the first-line treatment of choice.
Polymer-coated activated carbon is used in hemoperfusion, a treatment that removes toxins and waste products from the blood by removing it from the body and passing it over an adsorbent material before returning it to the patient.
Activated carbon can also be formed into cloth and used for wound dressings and ostomy applications. This cloth helps to draw out bacteria and other toxins, assisting the healing process.
• Personal Protective Devices
Medical cloth made from activated carbon can be specially formed, cut, and laminated to create a variety of customized personal protective devices. Masks that contain activated carbon filters serve an important role for first responders and military members facing chemical threats. Military use of activated carbon respirators and filters dates to World War I, when these devices were invented to counter the threat posed by chlorine and other gas weapons. Today, impregnated activated carbon filters are available to meet specific threats.
• Air Purification
Activated carbon is heavily used in air purification, including biogas treatment. The toxic materials found in this gas, as well as hydrogen sulfide and other compounds that create noxious odors, are easily removed by activated carbon.
Biogases are created by the anaerobic digestion of organic materials, and tend to form around landfills, cow pastures, and municipal waste treatment facilities. Activated carbon lowers VOCs, or Volatile Organic Compounds, from biogases, as well as those emitted by other products such as paint and construction materials.
Impregnated activated carbon is used to remove inorganic materials from gas streams before they reach the atmosphere. The specific compounds that are mixed with the carbon depend on the materials that are being removed.
• Water Treatment
As a water treatment product, activated carbon is used to purify both drinking water and contaminated water from industrial processes. For potable drinking water, it can be used at both the municipal and individual home levels. At both levels, activated carbon removes such contaminants as pesticides, algae breakdown products, VOCs and micro pollutants. It can also improve the color, smell, and taste of drinking water by removing the compounds that affect those qualities.
When treating effluent water from industrial processing, activated carbon is used to remove both toxic and noxious compounds, returning the water to a safe state. Activated carbon is sometimes used alone, but is more often used to bind specific chemicals as one part of a multi-prong approach to wastewater treatment.
In many cases, activated carbon from water treatment applications can be reactivated and reused. This normally occurs at the municipal level, with the spent carbon collected in large tankers and moved to dedicated reactivation centers. The carbon from potable water applications is kept entirely separate from that used in wastewater treatment.
• Food and Beverage Preparations
Activated carbon has many uses in the preparation of food and beverage products. It is used primarily to improve taste and smell, as well as appearance. For example, activated carbon can decolorize sugar syrups, remove unwanted flavor compounds from beer and other alcoholic beverages, remove bitterness from certain foods, and even decaffeinate tea and coffee. It is also used to enhance fruit juices and oils by removing unwanted compounds, and even to purify the carbon dioxide that is added to soft drinks.
• Pharmaceutical Industry
The pharmaceutical industry is strictly regulated to ensure that products are safe, effective, and free from contaminants. Activated carbon is used at every stage of processing to ensure the purity of each component. It can not only remove impurities and naturally occurring color variations, but also proteins and other unwanted organic compounds. This is particularly important in the processing of such biomedical products as enzymes and amino acids.
• Industrial Processing
Activated carbon plays a very important role across a wide range of industrial processes. Its ability to bind chemicals makes it useful in industries ranging from battery making to gold recovery. Activated carbon is an ideal addition to many liquid chemicals. It can purify recirculating solvents by removing corrosive compounds and dissolved impurities, remove unwanted organic compounds from naturally occurring minerals, and alter the natural color of various chemical compounds.
As a catalyst, activated carbon can produce a wide range of chemical reactions. This property is used in the creation of numerous products including dry cell batteries, petroleum distillates, and even herbicides.
Precious metal recovery is the process of removing gold and other valuable metals from waste streams. Special activated carbon can be used to adsorb the desired metal during processing and hold it for later recovery.
• Gas Storage and Delivery
Activated carbon is nontoxic and environmentally friendly. It also has a tremendous capacity for gas storage due to its highly porous nature.
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