Bone char

Bone char

Pills of bone char
Names
Other names bone charcoal bone black ivory black animal charcoal abaiser Pigment black 9 CI 77267
Identifiers
CAS Registry Number	8021-99-6
ChemSpider
EC number	232-421-2
Properties
Appearance	black powder
Density	0.7 - 0.8 g/cm3
Solubility in water	insoluble
Acidity (pKa)	8.5 - 10.0
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references

Bone char (Latin: carbo animalis) is a porous, black, granular material produced by charring animal bones. Its composition varies depending on how it's made; however, it consists mainly of tricalcium phosphate (or hydroxylapatite) 57-80%, calcium carbonate 6-10% and activated carbon 7-10%.^[1] It is primarily used for filtration and decolourisation.

Production

Bone char is primarily made from cow bones; however, to prevent the spread of Creutzfeldt–Jakob disease, the skull and spine are never used.^[2] 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.

Uses

Water treatment

The tricalcium phosphate in bone char can be used to remove fluoride^[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 USA 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 as Tanzania.^[5] 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).^[6] Other highly toxic metal ions, such as those of arsenic^[7] and lead^[8] may also be removed.

Sugar refining

Sugars (clockwise from top-left): white refined, unrefined, brown, unprocessed cane

Bone char is often used in sugar refining as a decolourising and deashing agent. This practice is of concern to vegetarians and vegans (animal use), and the bone char does come into contact with the sugar-solution, even if does not become part of it (insoluble). Additionally, it is used as part of the refining process for cane sugar but not beet sugar. Bone char possesses a lower decolouration capacity than activated carbon, however unlike carbon it is able to remove inorganic impurities; most importantly sulfate and the ions of magnesium and calcium. The removal of these is beneficial, as it reduces the level of scaling later in the refining process, when the sugar solution is evaporated to dryness.^[9] Alternatives to bone char have long been proposed,^[10] however the only current alternatives are ion-exchange resins, which are more expensive.

Niche uses

• 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.^[2]

• 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.

See also

• Pot ash
• Carbon black
• Activated carbon

References

External links

•  "Blacks". Encyclopedia Americana. 1920.