Bone char (Latin:carbo animalis) is a porous, black, granular material produced bycharring animalbones. Its composition varies depending on how it is made; however, it consists mainly oftricalcium phosphate (orhydroxyapatite) 57–80%,calcium carbonate 6–10% andcarbon 7–10%.[1] It is primarily used for filtration and decolorisation.
Bone char is primarily made from cattle and pig bones; however, to prevent the spread ofCreutzfeldt–Jakob disease, theskull andspine are no longer used.[2] The bones are heated in a sealed vessel at up to 700 °C (1,292 °F); the oxygen concentration must be kept low while doing this, as it affects the quality of the product, particularly itsadsorption capacity. Most of theorganic material in the bones is driven off by heat, and was historically collected asDippel's oil; that which is not driven off remains asactivated carbon in the final product. Heating bones in an oxygen-rich atmosphere givesbone ash, which is chemically quite different.[clarification needed][citation needed]
Used bone char can be regenerated by washing with hot water to remove impurities, followed by heating to 500 °C (932 °F) in akiln with a controlled amount of air.
Thetricalcium phosphate in bone char can be used to removefluoride[3] and metal ions from water, making it useful for the treatment of drinking supplies.Bone charcoal is the oldest known water defluoridation agent and was widely used in the United States from the 1940s through to the 1960s.[4] As it can be generated cheaply and locally it is still used in certain developing countries, such asTanzania.[5]Bone chars usually have lowersurface areas thanactivated carbons, but present high adsorptive capacities for certain metals, particularly those fromgroup 12 (copper,zinc, andcadmium).[6] Other highly toxic metal ions, such as those ofarsenic[7] andlead[8] may also be removed.The practical example of the use of bone char in water purification is demonstrated by use ofnanofiltration in Tanzania.[9]
Sugars (clockwise from top-left): white refined, unrefined, unprocessed cane, brown
Historically, bone char was often used insugar refining as a decolorizing and deashing agent, particularly in cane sugar as this contains more colored impurities.
Bone char possesses a low decoloration capacity and must be used in large quantities,[10] however, it is also able to remove various inorganic impurities, most importantlysulfates and the ions of magnesium and calcium. The removal of these is beneficial, as it reduces the level ofscaling later in the refining process, when the sugar solution is concentrated.[11] Modern alternatives to bone char includeactivated carbon andion-exchange resins. However, a small number of companies remain completely or partially dependent on bone char for sugar refinement.
Bone char is also used as a blackpigment forartist's paint, printmaking, calligraphic and drawing inks as well as other artistic applications because of its deepness of color and excellent tinting strength.Bone black and ivory black are artists' pigments which have been in use since historic times—by both old masters likeRembrandt andVelázquez and more modern painters such asManet andPicasso. The black dresses and high hats of the gentlemen in Manet'sMusic in the Tuileries are painted in ivory black.[12][13]
Ivory black was formerly made by grinding charredivory inoil. Nowadays ivory black is considered a synonym for bone black. Actual ivory is no longer used because of the expense and because animals that are natural sources of ivory are subject to international control asendangered species.
In the 18th and 19th centuries, bone char mixed with tallow or wax (or both) was used by soldiers in the field to impregnate military leather equipment, both to increase its lifespan and as the simplest way to obtain pigment for black leatherware. Military and civilians used it as shoe polish and preservative, including on shoes with the "rough" side out. In period reference materials, it is referred to as "black ball".
The ESA-NASASolar Orbiter satellite uses a refined form of bone char applied to its titanium heatshield. This protects it against the glare and heat of the sun. Irish company Embio developed the coating and uses its 'CoBlast' technique, originally developed to coat titanium medical implants.[14]
This photo shows the Solar Orbiter with its black, bone char coated heatshield.
The production of bone char was featured on theDiscovery Channel's TV seriesDirty Jobs, on episode 19 of season 5, "Bone Black", originally broadcast on 9 February 2010.[2]
Human bone char, referred to as "bone charcoal", is mentioned inThomas Pynchon's novelThe Crying of Lot 49. The bones come from US soldiers who died in combat during WWII and were buried in a lake in Italy, and the char is used for filters in cigarettes.
Human bone char is mentioned inJaroslav Hašek's novelThe Good Soldier Švejk. The work contains a reference to soldiers not dying in vain because their bones will be used to make bone charcoal ("spodium") for sugar refineries, the protagonist getting disciplined by his commander for wondering whether the coal from officers' bones is sold to the refineries at a higher price than that made from ordinary privates' bones.
^Medellin-Castillo, Nahum A.; Leyva-Ramos, Roberto; Ocampo-Perez, Raul; Garcia de la Cruz, Ramon F.; Aragon-Piña, Antonio; Martinez-Rosales, Jose M.; Guerrero-Coronado, Rosa M.; Fuentes-Rubio, Laura (December 2007). "Adsorption of Fluoride from Water Solution on Bone Char".Industrial & Engineering Chemistry Research.46 (26):9205–9212.doi:10.1021/ie070023n.
^Mjengera, H.; Mkongo, G. (January 2003). "Appropriate deflouridation technology for use in flourotic areas in Tanzania".Physics and Chemistry of the Earth, Parts A/B/C.28 (20–27):1097–1104.Bibcode:2003PCE....28.1097M.doi:10.1016/j.pce.2003.08.030.
^Ko, Danny C.K.; Porter, John F.; McKay, Gordon (December 2000). "Optimised correlations for the fixed-bed adsorption of metal ions on bone char".Chemical Engineering Science.55 (23):5819–5829.Bibcode:2000ChEnS..55.5819K.doi:10.1016/S0009-2509(00)00416-4.
^Deydier, Eric; Guilet, Richard; Sharrock, Patrick (July 2003). "Beneficial use of meat and bone meal combustion residue: "an efficient low cost material to remove lead from aqueous effluent"".Journal of Hazardous Materials.101 (1):55–64.Bibcode:2003JHzM..101...55D.doi:10.1016/S0304-3894(03)00137-7.PMID12850320.
^Asadi, Mosen (2006).Beet-Sugar Handbook. Hoboken: John Wiley & Sons. p. 333.ISBN9780471790983.
^Chung Chi Chou, ed. (2000).Handbook of sugar refining: a manual for the design and operation of sugar refining facilities. New York: Wiley. pp. 368–369.ISBN9780471183570.
^Bomford D, Kirby J, Leighton, J., Roy A.,Art in the Making: Impressionism. National Gallery Publications, London, 1990, pp. 112-119
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