Pills of bone char
|Solubility in water||insoluble|
|Acidity (pKa)||8.5 - 10.0|
|Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)|
Bone char (Latin: carbo animalis) is a porous, black, granular material produced by charring animal bones. It's composition varies depending on how its made, however it consists mainly of tricalcium phosphate (or hydroxylapatite) 57-80%, calcium carbonate 6-10% and activated carbon 7-10%. It is primarily used for filtration and decolourisation.
Bone char is primarily made from cow bones, however to prevent the spread of Creutzfeldt–Jakob disease the skull and spine are never used. The bones are heated in a sealed vessel at up to 700 °C (1,292 °F), the concentration of oxygen must be very carefully controlled while doing this, as it effects the quality of the product; particularly its adsorption capacity.
Used bone char can be regenerated by washing with hot water to remove impurities, followed by heating to 500 °C (932 °F) in a kiln with a controlled amount of air.
The calcium triphosphate in bone char can be used to remove fluoride and metal ions from water. Bone chars usually have lower surface areas than activated carbons, but present high adsorptive capacities for copper, zinc, and cadmium.
- It is used to refine crude oil in the production of petroleum jelly.
- In the 18th and 19th century, bone char mixed with tallow or wax (or both) were 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 leatherwares.
- Bone char is also used as a black pigment. It is sometimes used for artist's paint, printmaking, calligraphic and drawing inks as well as other artistic applications because of its deepness. Ivory black is an artists' pigment formerly made by grinding charred ivory in oil. Today it is considered a synonym for bone char. Actual ivory is no longer used because of the expense and because animals who are natural sources of ivory are subject to international control as endangered species.
In popular culture
- The production of bone char was featured on the Discovery Channel's TV series Dirty Jobs, on episode 24 of season 4, "Bone Black", originally broadcast on 9 February 2010.
- Human bone char, referred to as "bone charcoal," is mentioned in Thomas Pynchon's novel The 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.
- Fawell, John (2006). Fluoride in drinking-water (1st published. ed.). Geneva: WHO. p. 47. ISBN 9241563192.
- "Dirty Jobs: Episode Guide"
- Huan Jing Ke Xue (February 2007). Chemical fixation of metals in soil using bone char and assessment of the soil genotoxicity (in Chinese) 28 (2). pp. 232–7. PMID 17489175.
- Wilson, J.A., Pulford, I.D. and Thomas, S. (2003). Sorption of Cu and Zn by bone charcoal 25. Environmental Geochemistry and Health. pp. 51–56.
- Choy, K.K.H. and McKay, G. (2005). Sorption of metal ions from aqueous solution using bone char 31. Environment International. pp. 845–854.