Since the source of coal is an agglomeration of organisms and minerals accumulated over extended geological time periods, it contains most of the natural elements at concentrations that are characteristic of the environment of the deposit from which it was mined, including heavy metals and radioactive elements. In the combustion of coal, some of the elements evaporate and others concentrate in the mineral residue in the form of ash. The ash is composed mainly of the inorganic constituents of the coal: oxides of silicon, aluminum, iron and calcium, and also of some trace elements which are hazardous to the environment.
However, in general, the availability of the hazardous materials is quite low, both because of their level of solubility that is limited as a result of chemical bonds that are created in the ash at high temperatures of the combustion compartment and the glassy structure of the particles, and because of their low concentration in the ash as trace elements.
This is the reason that coal ash itself in not defined as a hazardous or toxic material in any country or by any environmental organization in the world. In Israel, as in all countries of the world, coal ash has been defined as “a returnable by-product of the energy production that requires environmental supervision for its uses”. This is due to the economic-social justification for preferring its beneficial utilization over its disposal as waste, and due to its contribution to the environment as a substitute for quarry materials, which prevents damage caused by quarrying and the air pollution that is inherent in converting them to industrial materials.
The environmental issues that must be addressed concerning the uses of coal ash concentrate on the following potential problems:
- Leaching of hazardous materials and the concern for pollution of water sources and land.
- Nuclear radiation and radon emissions in construction materials.
- Dust nuisances and exposure to free crystalline silica.
Israel is up to now, totally dependent on its groundwater and the Kineret for its water consumption. Under local hydro-geological conditions, the groundwater reservoirs are liable to be exposed to accumulated pollution of a few toxic elements, e.g. Cr, Se, whose availability in the coal fly ash is relatively high. However, since the exposure of the ash to the environment causes very rapid fixation processes to occur, the danger is lessened in a short period of time. Reducing direct contact of the coal ash with the environment minimizes the risk of pollutant leaching to a low level.
Nuclear radiation is liable to be a problem in construction materials that contain coal ash at very high levels (more than 50% by weight). Nevertheless, the physical structure of the raw ash particles and their being bound to the other construction materials, as well as the contribution of the ash to the compactness of the construction material, significantly reduce the amount of radon emission in construction materials, causing a reduction of the overall radiation from the materials to a level that has no risk of overexposure compared to radiation from natural raw materials and to the background radiation of the environment.
Coal ash dust is defined around the world as a nuisance, but in Israel it is included in the regulations concerning harmful dust. Although some of the silica that is in coal ash exists as Quartz, a crystalline substance that is liable to endanger those who are exposed to it in a consistent and prolonged manner, nevertheless, the means that are customarily used to prevent the dispersion of dust and for protection against exposure to the dust completely nullify this risk.
In any case, the presence of hazardous materials in coal ash requires an environmental examination of the ash itself and its uses. For this purpose, ash control mechanisms and characterization methods were developed in the developed countries of the world, as well as conditions and rules for usage that enable to exploit the economic benefits with reasonable environmental limitations. The Ministry of the Environment adopted the guidelines of the United States Environmental Protection Agency, which include a method for extraction of pollutants and a list of values that defines hazardous materials, and established a list of permitted maximum values in ash as a condition for use.
Israel Standard I.S. 5098 (Radioactive Elements in Construction Materials) defines the test methods and a maximum permitted value for nuclear radiation from construction materials, including products containing ash. Moistening of coal ash during infrastructure works, storage and transfer of dry coal fly ash in sealed vessels and use of means for personal protection of workers are sufficient to comply with workplace safety regulations for working with dust that is defined as harmful.
Within the framework of rules for preventing environmental nuisances, the uses of coal ash have been ranked according to three permitting levels:
- Uses exempt from limitations
- Uses that are minimally conditioned
- Uses that are limited