Wood ash is the residue powder left after the combustion of wood, such as burning wood in a home fireplace or an industrial power plant. It is used traditionally by gardeners as a good source of potash for domestic gardens or any garden.
Contents
Composition[edit]
Variability in assessment[edit]
Many studies have been conducted regarding the chemical composition of wood ash, with widely varying results. Some quote calcium carbonate (CaCO3) as the major constituent,[1] others find no carbonate at all, but calcium oxide (CaO) instead.[2] Some show as much as twelve percent iron oxide[2] while others show none,[3] though iron oxide is often introduced through contamination with soil. A comprehensive set of analyses of wood ash composition from many tree species has been carried out by Emil Wolff,[4] among others.
There are several factors which have a major impact on the composition:
- Fly ash: some studies include the solids escaping via the flue during combustion, others do not.
- Temperature of combustion[5] carries two direct effects:
- Dissociation: conversion of carbonates, sulfides, etc. to oxides results in no carbon, sulfur, carbonates, or sulfides. Some metallic oxides (e.g. mercuric oxide) even dissociate to elemental state and/or vaporize completely at wood fire temperatures.
- Volatilization: in studies where the fly ash is not measured, some combustion products may not be present at all.
- Experimental process: If the ashes are exposed to the environment between combustion and the analysis, oxides may convert back to carbonates via carbon dioxide in the air.
- Type, age, and growing environment of the wood stock impact the composition of the wood, and thus the ash.
Measurements[edit]
Typically between 0.43 and 1.82 percent of the mass of burned wood (dry basis) results in ash.[5] Also the conditions of the combustion affect the composition and amount of the residue ash, thus higher temperature will reduce ash yield.[3]
Much wood ash contains calcium carbonate as its major component, representing 25[6] or even 45 percent[1] Less than 10 percent is potash, and less than 1 percent phosphate; there are trace elements of iron, manganese, zinc, copper and some heavy metals.[6] However, these numbers vary, as combustion temperature is an important variable in determining wood ash composition.[5] All of these are, primarily, in the form of oxides.[5]
Uses[edit]
Wood ash is commonly disposed of in landfills, but with rising disposal costs, ecologically friendly alternatives are becoming more popular.[7]
For a long time, wood ash has been used in agricultural soil applications, as it recycles nutrients back to the land. Wood ash has some value as a fertilizer, but does not contain nitrogen. Because of the presence of calcium carbonate, it acts as a liming agent and will deacidify the soil by increasing its pH.[6]
Wood ash has a very long history of being used in ceramic glazes, particularly in the Chinese, Japanese and Korean traditions, though now used by many craft potters. It acts as a flux, reducing the melting point of the glaze.[8]
Potassium hydroxide can be made directly from wood ash[9] and in this form, is known as caustic potash or lye. Because of this property, wood ash has also traditionally been used to make wood-ash soap.
Wood ash with a high char content has also proven to be effective as an odor control agent, especially in composting operations.[10]
Bio-leaching[edit]
The ectomycorrhizal fungi Suillus granulatus and Paxillus involutus can release elements from wood ash.[11]
See also[edit]
References[edit]
- ^ a b Hume E (11 April 2006). "Wood Ashes: How to use them in the Garden". Ed Hume Seeds.
- ^ a b Tarun R. Naik, Rudolph N. Kraus, and Rakesh Kumar (2001), Wood Ash: A New Source of Pozzolanic Material, Department of Civil Engineering and Mechanics, College of Engineering and Applied Science, The University of Wisconsin – Milwaukee
- ^ a b Etiegni L, Campbell AG (1991). "Physical and chemical characteristics of wood ash". Bioresource Technology 37 (2): 173. doi:10.1016/0960-8524(91)90207-Z.
- ^ Wolff, Emil (1871). Aschen-Analysen. Berlin: Wiegandt und Hempel.
- ^ a b c d Misra MK, Ragland KW, Baker AJ (1993). "Wood Ash Composition as a Function of Furnace Temperature" (PDF). Biomass and Bioenergy 4 (2): 103. doi:10.1016/0961-9534(93)90032-Y.
- ^ a b c "Wood Ash in the Garden". Purdue University, Department of Horticulture and Landscape Architecture. 16 November 2000. Retrieved 2008-10-01.
- ^ Demeyer A, Voundi Nkana JC, Verloo MG (2001). "Characteristics of wood ash and influence on soil properties and nutrient uptake: an overview". Bioresource Technology 77 (3): 287–95. doi:10.1016/S0960-8524(00)00043-2. PMID 11272014.
- ^ Rogers, Phil (2003). Ash Glazes (2nd ed.). London: A&C Black. ISBN 0-7136-57820.
- ^ "Making lye from wood ash". Journey to Forever. 14 May 2009. Retrieved 2008-10-01.
- ^ Rosenfeld, P. and Henry, C. (2001). "Activated Carbon and Wood Ash Sorption of Wastewater, Compost and Biosolids Odorants". Water Environment Research 7 (4): 388–393.
- ^ Geoffrey Michael Gadd (March 2010). "Metals, minerals and microbes: geomicrobiology and bioremediation". Microbiology 156. pp. 609–643.
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