Reuses of wood ash: a review
Résumé
Wood ashes come from different industries. They are the residue, left after combustion of wood in biomass boilers. Compositions depend on the type of the input, nature of the wood, the temperature of burning, the treatment cycle and the duration. They are rich in Ca, K, Mg and Si elements (pH=9-13.5) and despite their composition with the nutrient content and sometimes with heavy metals, they are considered as waste. The disposal inlandfills has been a common method for removal for a long time but it became a growing problem with new environmental regulations and landfill sites are less available and more expensive. To find potential recovery for recycling wood ash is necessary and a challenge. Considering circular economy and zero waste option, alternative materials with wood ashes should constitute a new way to reuse them and put them back into natural cycle. Physicochemical characterization and mineralogical properties of wood ash are important in the development and implementation of new materials with addition of byproducts so as to obtain eco-materials. But these properties are not much studied or reported in literature. More data are needed to develop and propose formulations for materials. First physical properties as bulk density and particle distribution are of interest. XRD and IR analysis are necessary for identifying the compounds and oxides that inform on the mineralogy. Images obtained by scanning electron microscope are useful to analyse microstructure: type of wood ash particles, their shape, the porosity network (shape and size)…. As chemical properties, alkalinity or neutralizing capacity of wood ash and leaching behaviour are required as well. Considering wood ash properties, needs of some industries (ceramics, agriculture, road and construction engineering) and circular economy concept, it is possible to conduct research works on the feasibility to mix eco-binders, ashes, industrial by-products and waste, so as to implement formulations and to develop industrial process for manufacturing ecomaterials.