By H. George Nowicki, Chris Brunning, Barbara Sherman, Henry Nowicki
This article provides some of the major definitions to help professionals working in the field of activated carbon. Using clear and precise words demonstrates your professional knowledge and enables you to make better decisions when purchasing activated carbon or using consultants and laboratory testing services. Vocabulary improvement and understanding of terms gives employees professional confidence, which will help them more effectively communicate with
A myriad of uses
A layperson may think of activated carbon as ‘that stuff’ in water-filter pitchers, but people in the field know that point of use (POU) devices are only one of many applications for activated carbon. From municipal drinking water treatments to waste water treatment for vapor-phase odor removal and water filtration and purification of effluent waters, activated carbon has many uses in addition to de-chlorinating water in pitcher devices.
Activated carbon’s main uses are in pollution and odor control, color removal, catalyst support and preparation of drinking water. In fact, activated carbon is used in many of our everyday typical tasks: the water used to prepare the morning coffee has been carbon filtered at a municipal plant and then through your POU residential device; the sugar used to sweeten that coffee was decolorized by carbon; the cigarette some smoke with that coffee has activated carbon in the filter for toxic chemical removal; even some automobiles and petrol filling stations have carbon filters to recover and use the gasoline vapors. Batteries contain activated carbon. The odor-control in cat litter boxes is endowed by a special de-dusted activated carbon. The gold and platinum jewelry industries use activated carbon in the processes of recovering precious metals and it is also used in renal dialysis units, as well as in a device to improve invitro fertilization of human ova.
Taken for granted for a long time because it was a low cost commodity, the prices of activated carbon have increased dramatically over the last year because of the five-year US tariff that began in January of 2007, which will probably be re-issued for another five years when it expires in 2012. The increased costs for activated carbon due to the US import tariffs against Chinese steam-activated, bituminous coal-based activated carbon have created an economic need to better understand the associated terminology within the industry so as to make more educated decisions about this commodity.
Wikipedia, the Internet encyclopedia, defines activated carbon as: “a general term which covers carbon material mostly derived from charcoal… It is a material with an exceptionally high surface area. Just one gram of activated carbon has a surface area of approximately 500 m², typically determined by nitrogen gas adsorption and includes a large amount of microporosity. Sufficient activation for useful applications may come solely from the high surface area, though often further chemical treatment is used to enhance the adsorbing properties of the material.”
The vocabulary and other important terms listed here are official definitions as defined by the American Society for Testing and Materials (ASTM), the American Water Works Association (AWWA) and NSF International.
Activated carbon glossary
Accelerated service life: the elapsed time unit the end point is reached in an accelerated adsorption test.
Activated carbon: a family of carbonaceous substances manufactured by processes that develop adsorptive properties.
Adsorbate: any substance that is or can be adsorbed.
Adsorption wave: see mass transfer zone.
Adsorption zone: see mass transfer zone.
Ash: residue after the combustion of a substance under specified conditions.
As is basis: as received.
Capacity: the rated service cycle, expressed as a function of time or volume of water treated by the system between manufacturer-specified servicings (cleaning, regeneration or replacement) of the medium (media).
Channeling: the flow of fluid through passages of lower resistance which can occur in fixed beds or columns of particles due to nonuniform packing, irregular sizes and shapes of the particles, gas pockets, wall effects and other causes.
Chemical adsorption: see chemisorption.
Coadsorption: the adsorption of two or more components on an adsorbent, each affecting the adsorbability of the other. Contact batch operation: an adsorption process in which an adsorbent is dispersed in a fluid to be treated and then separated when practical equilibrium is
Continuous moving bed: an adsorption process characterized by flow of a fluid through a continuously moving bed of granular adsorbent with continuous withdrawal of spent adsorbent and continuous addition of reprocessed or virgin adsorbent.
Crushing strength: the property of a particle to resist physical breakdown when contained and subjected to a slowly increasing, continuously applied force.
Degassing: removal of gases.
Density, absolute or true: the mass under specified conditions of a unit volume of a solid sorbent excluding its pore volume and inter-particle voids.
Density, apparent (density, bulk): the mass under specified conditions of a unit volume of a solid sorbent, including its pore volume and inter-particle voids.
Density, block: see density, particle.
Density, bulk: see density, apparent.
Density, particle (density, block): the mass under specified conditions of a unit volume of a solid sorbent including its pore volume but excluding inter-particle voids.
Dosage: the quantity of substance applied per unit weight or volume of the fluid being treated.
Dry basis: exclusive of any moisture which may be present.
Dust: an imprecise term referring to particulates capable of temporary suspension in air or other gases; also, particles smaller than an arbitrarily selected size.
Extractant water: water that has been in contact with a system or component(s) for a specified duration.
Filterability: the rate at which particles can be separated from a slurry by means of a permeable medium under specified conditions.
Freundlich adsorption isotherm: a logarithmic plot of quantity of component adsorbed per unit of adsorbent versus concentration of that component at equilibrium and at constant temperature, which approximates the straight line postulated by the Freundlich adsorption equation: X/M = kCn (where: X = quantity adsorbed; M = quantity of adsorbent; C = concentration; k and n = constants).
Heat of adsorption: the heat evolved during adsorpton.
Ignition temperature (kindling point): the lowest temperature at which combustion will occur spontaneously under specified conditions.
Impact strength: the property of a particle to resist physical breakdown when subjected to a rapidly increasing applied force.
Intermittent moving bed (pulse, slug): an adsorption process characterized by upward flow of a fluid through a fixed bed of granular adsorbent with periodic withdrawal of spent adsorbent from the bottom of the bed and additions of reprocessed or virgin adsorbent to the top of the bed.
Macropore: pores with widths exceeding 50 nanometers (500 angstrom units).
Mass transfer zone (adsorption wave, adsorption zone): the region in which the concentration of the adsorbate of interest in the fluid decreases from influent concentration to the lowest detectable concentration.
Mean particle diameter: the weighted average particle size, in millimeters, of a granular adsorbent computed by multiplying the percent retained in a size fraction by the respective mean sieve openings, summing these values and dividing by 100.
Mesopore: pores of widths between two and 50 nanometers (20 and 500 angstrom units).
Moisture content: the water content of a substance as measured under specified conditions.
Monomolecular layer: an adsorbed film, one molecule thick.
Multimolecular layer: an adsorbed film, more than one molecule thick.
Oven drying loss: the reduction in weight resulting when a substance is heated in an oven under specified conditions.
Pores: the complex network of channels in the interior of a particle of a sorbent.
Product water: water that has been treated by the system.
Revivification: see reactivation.
Service life (service time): the elapsed time until the end point is reached in an adsorption process.
Synthetic test solution: a solution of two or more components prepared under specified conditions for use in evaluation of adsorbents.
Uniformity coefficient: the ratio of the particle diameter corresponding to 60 percent finer on the cumulative particle size distribution curve to the particle diameter corresponding to 10 percent finer on the same distribution curve.
Unit volume: total water-holding volume without the medium (media) or components in place.
Water-extractable material: substances dissolved from other substances by water under specified conditions.
Wettability: the rate at which particles can be made wet under specified conditions.
Evolution of the activated carbon vocabulary
It is important that we all agree on the meanings of the words that we use to conduct day-to-day business. If you think there are any additional words that should be included in this list of important activated carbon terminology or if you have any other input about the content of this list, please let the authors know. We are open to additions and any other suggestions, which will be considered and may be incorporated into an updated version that we will be making available on the PACS website www.pacslabs.com approximately two months from this article’s publication date.
Any additional definitions that we may have overlooked can be emailed to George Nowicki: GeorgePACS@aol.com. Please include references for any suggested vocabulary, so that any new additions for the list can be properly verified before we add them to the future update.
About PACS Inc.
Professional Analytical and Consulting Services Inc. (PACS Inc.) is an independent promoter of the activated carbon industry. The firm has been awarded eight government grants to conduct R&D on new carbon products. PACS provides testing services to over 500 clients and has participated in over 40 legal proceedings as science advisors. It has developed the Activated Carbon School as a part of the 60 short courses available to scientists. This October 1-15, 2008 PACS will provide the 22nd International Activated Carbon Conference and Courses program near the Pittsburgh International Airport.
About the authors
Corresponding author H. George Nowicki III, B.S., B.A., is a Technician in the PACS laboratory and helps direct the day-to-day testing services. He can be reached by email at GeorgePACS@aol.com or by phone at (724) 457-6576. Chris Brunning, B.A., designs and maintains the PACS website www.pacslabs.com and works in the PACS mobile laboratory, where he performs asbestoses inspections and management plans for how companies should handle asbestoses. He can be reached by email at ChrisPACS@aol.com. Barbara Sherman, M.S., is the Manager of Operations and directs the day-to-day PACS Short Courses and Conferences services. She can be reached by email at BarbPACS@aol.com. Henry Nowicki, Ph.D., directs the research and development, is a Senior Consultant and is the new business developer for PACS. He can be reached by email at HNpacs@aol.com.