Bone char
.jpg) Pills of bone char
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Other names
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| ECHA InfoCard | 100.029.470 |
| EC Number | 232-421-2 |
| Properties | |
| Appearance | black powder |
| Density | 0.7 - 0.8 g/cm3 |
| insoluble | |
| Acidity (pKa) | 8.5 - 10.0 |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Bone char (Latin: carbo animalis) is a porous, black, granular material produced by charring animal bones. Its composition varies depending on how it is made; however, it consists mainly of tricalcium phosphate (or hydroxylapatite) 57–80%, calcium carbonate 6–10% and carbon 7–10%. It is primarily used for filtration and decolorization.
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); a low concentration of oxygen must be maintained while doing this, as it affects the quality of the product, particularly its adsorption capacity. Most of the organic material in the bones is driven off by heat, and was historically collected as Dippel's oil; that which is not driven off remains as activated carbon in the final product. Heating bones in an oxygen-rich atmosphere gives bone ash, which is chemically quite different.
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 tricalcium phosphate in bone char can be used to remove fluoride 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. As it can be generated cheaply and locally it is still used in certain developing countries, such as Tanzania. Bone chars usually have lower surface areas than activated carbons, but present high adsorptive capacities for certain metals, particularly those from group 12 (copper, zinc, and cadmium). Other highly toxic metal ions, such as those of arsenic and lead may also be removed.
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