Ash (analytical chemistry)

Ash is a solid residue from the combustion of organic material, ie fossil fuels, biofuels or organisms such as plants and animals. It arises from the inorganic part of the burned substance and therefore consists of minerals.

Chemical composition

Chemically, the ash content is considered a measure of the mineral content of the organisms. However, both values ​​are not identical, as in the combustion reacts the mineral substance, and thus can experience a weight gain or loss. Ash consists mainly of oxides and ( bi ) carbonates of various metals, such as CaO, Fe2O3, MgO, MnO, P2O5, K2O, SiO2, Na2CO3, NaHCO3, etc.

Determining the ash represents a purity test of organic substances, and is required in several of the Ph. Eur monographs. The flour type indicated on each baking flour packing, for example "Type 700 ", describes the ash content in milligrams per 100 grams of dry flour and is a measure of the extraction rate or amount of trash.

From the ash content can be closed in the analysis of food on the purity or dilution or extension of fruit juices, as ash contents are in undiluted juices known constant within limits.

If the temperature in the fire so high that the ash is soft and doughy, there arises during cooling by sintering a porous, but solid mass. This is also called slag. The ash softening, depending on the ingredients typically between 900 and 1200 ° C.

The bulk density of wood ash ( fresh from the oven, uncompressed) is about 0.3 kg / l

Use

Wood ash from the incineration of untreated, ie not chemically treated wood can be used as potassium fertilizer. As a guide for a needs-based application up to 3 liters of ash are per 10 m2 per year.

Because of atmospheric pollutants in the 1980s were in some German Länder " compensation " or " Bodenschutzkalkungen " large area performed (see liming ). In Austria remained such measures rather on research and pilot studies limited ( " Miracle Grow " against the destruction of forests ); significant large-scale operations there were hardly any. In Switzerland, the fertilization of the forest is prohibited by law and permitted only for research purposes.

Wood ash from untreated wood is also suitable for composting. You can influence the composting process and which should be in layers and incorporated in small amounts in the compost.

In many cases it is noted that it may occur during the combustion process in an accumulation of heavy metals. This effect is most relevant in the fire of tree wood due to the long service life. In short-lived woods of the heavy metal content is lower. Heavy metals are depending on the area in varying concentrations in forest soils. Ever since man smelted ores, metal particles were emitted with the resulting waste gases; they were distributed by winds and sank to the bottom and were brought rain to the ground. When wood is brought from the forest and burned ( and the ash is disposed of via domestic waste ), the biosphere heavy metal is withdrawn.

Ash is also used for scattering of icy sidewalks.

Wood ash can be used as natural toothpaste.

Wood ash was used as a cleaning agent ( lye ) for soapmaking and in the late Middle Ages as a flux for glass manufacture. The Incas used wood ashes to make corn for humans to digest. The tribe of the Huaorani in Ecuador used ash for body hair removal.

In construction, we used wood or coal ash ( ash extinguishing extinguishing or short ) as a non-flammable poured charge of cavities in wood-beamed ceilings for the purpose of thermal insulation and sound insulation as well as the flattening of Dippel tree ceilings.

No use is normal ashes on the dirt track, where volcanic ash will be used.

Environmental hazards

Stone, and lignite almost always contains traces of radioactive elements uranium, thorium and radium. The amount is generally depending on the deposit from a few ppm and 80 ppm, in European coal or lignite contains from about 80 to 135 ppm uranium. Since approximately 7.8 billion tons of coal per year is burned in coal-fired power plants around the world, one estimates the total output of 10,000 tons of uranium and 25,000 tonnes of thorium contained largely in the ashes.

Between 1960 and 1970, about 1100 tonnes of uranium was recovered from coal ash in the United States. 2007 commissioned the Chinese National Nuclear Corp., the Canadian company Sparton Resources, in collaboration with the Beijing No.. 5 Testing Institute to conduct experiments to obtain uranium from the ashes of the coal power plant Xiaolongtang in Yunnan Province. The uranium content of the ash from the power plant, with an average 210 ppm uranium ( 0.021% U) on the uranium content of some uranium ores.