The use of slag in the context of the circular economy is a common and long-standing practice in many European countries (e.g. Denmark, the Netherlands, Germany, France, etc.). In other countries, legislative changes have recently been made to support this use (e.g. Finland, Poland, Lithuania). Research results and technological developments over the last 20-30 years show that slag is a secondary raw material for a range of materials (ferrous, non-ferrous and precious metals) and, in parallel, the mineral fraction after separation can be used in construction applications, subject to several conditions that significantly minimise the negative impact on the environment. Gravel is suitable for use as a protective or base uncemented layer in the construction of roadways or other linear structures, where it replaces traditional gravel layers. This use in the waste regime, under precisely defined technical conditions (e.g. layer thickness, distance from groundwater level, limitation of the amount of infiltrating precipitation, distance from drinking water sources) and environmental conditions (dry matter content and leachability limits), is also safe in terms of potential environmental impacts. These technical conditions guaranteeing environmental safety must be verified and established during the preparation of the construction as part of the construction procedure.
- Gravel is suitable for use as a protective or underlying uncemented layer in the construction of roadways or other linear structures, where it replaces traditional layers of gravel. This use in the waste regime, under precisely defined technical conditions (e.g. layer thickness, distance from groundwater levels, limitation of the amount of infiltrating precipitation, distance from drinking water sources) and environmental conditions (dry matter content and leachability limits), is also safe in terms of potential environmental impacts.
- This is not the often confused use as a primary raw material in non-insulated applications or "backfilling" where the material is freely accessible and directly exposed to the weather.
- Only technologically treated slag that has undergone the process of separation of ferrous and non-ferrous metals, the maturation process and other treatments that lead to volumetric stabilization of slag, improvement of geotechnical properties and improvement of environmental properties (decrease in leachability of heavy metals) can be used for construction.
- Building use is only allowed - subject to the conditions below - for narrowly defined applications (in layman's terms "under the surface of an impermeable layer") where there is limited contact with the environment:
o Cinder does not exhibit any of the hazardous properties HP1-HP15 and has a valid Hazardous Properties Exclusion (including HP14 Ecotoxic). In the acute toxicity tests carried out by ecotoxicology, the requirements of the currently applicable Waste Act Implementing Regulations must be met.
o The starch shall comply with the limit values for dry matter content and leachability derived specifically for the above defined applications. The levels of pollutants in the dry solids of the waste will not exceed the maximum permissible levels of inorganic and organic pollutants specified in the current legislation in force.
o The quality parameters of the slag are regularly verified to ensure compliance with strict environmental criteria, it is a waste of the other category, i.e. hazardous properties are excluded.
The use of slag in compliance with these points is based on long-term practice in a number of European countries supported by a large amount of data focused on both the construction and environmental part of this issue. (For example, for the needs of the Czech ZEVO, this practice was clearly summarized in several expert studies prepared by the consortium of the Institute of Environmental Protection of the CAS and Danish Waste Solutions between 2018-2020)
The above-mentioned use of slag is fully in the spirit of the principles of circular economy and contributes to increased recycling, reduction ofCO2 emissions and saving of valuable primary raw materials and applies the principles of the best available techniques for slag management according to the BREF 2019.
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