Recycling of Mineral Wool Waste
Authors: Katharina Grass, Victor Bartashov, Jurgen Sucker
IB Engineering GmbH, Vienna, Austria
The increase of volume of mineral wool waste and the need for its recycling is one of current priority issues in the manufacturing and use of mineral wool products. According to experts , the construction and demolition sector in EU countries only generates more than 2.5 million t/a of mineral wool waste.
Mineral wool waste in Europe accounts for 20 to 60% of the production volume. In practice, this means 160,000 to 480,000 tons of waste from 40 production lines, in average 20,000 t/a per line. . Considering that the yearly increase of industrial production, the volume of stored waste is constantly growing. Expenses for removal and disposal of industrial mineral waste are immensely high (on the average, 8–10% of the value of manufactured products ).
The major sources of mineral wool waste are listed below:
The production of mineral wool insulation accumulates a large amount of industrial waste at different stages of production process:
Fig. 1: Types and sources of mineral wool waste
Additionally, in accordance with the Commission Directive 97/69 / in EU, mineral wool is classified according to the degree of carcinogenic danger in the so-called "old" and "new" mineral wool.
Primarily, this concerns the return of used mineral wool products (construction and demolition sector, technical insulation, etc.). Since 2000, Europe has banned the production and use of biopersistent mineral fibers. Thus, for “old” mineral wool produced before 2000, stricter disposal rules are applied. Due to its carcinogenic effect, “old” mineral wool cannot be recycled in mineral wool production.
2. Handling of mineral wool waste
Currently three main directions of the subsequent use of mineral wool waste can be specified: landfill, recycling in mineral wool production and use in other industries.
Fig. 2: Main directions of mineral wool waste handling
Landfill is the easiest way in the practice of waste handling, though it has several disadvantages. For manufacturers of mineral wool products, these are, on the one hand, the loss of valuable raw materials that can be used in manufacturing a new insulating product, thus gaining profit (see Fig. 3).
Fig. 3: Material losses from waste in the production of mineral wool insulation materials
On the other hand, abstaining form waste recycling causes high additional costs for disposal and transport. The expenditures for the landfill of mineral wool waste in recent years has increased significantly in several countries. For example, the landfill fee, a few years ago in Germany amounted to 40 / 50 euros per ton. At present, the costs for waste disposal on landfills is approx. 225 euros / t .
Furthermore, inefficient use of non-renewable, easily accessible natural resources (basalt, dolomite, etc.) leads to their rapid depletion, as well as to accumulation of a large amount of waste. The latter, in turn, creates an environmental problem, having a negative impact on soil, surface- and underground water and occupying vacant land areas.
Depositing mineral wool waste is technically difficult due to its large volume, low bulk density, high elasticity, poor compressibility and, consequently, lack of stability at the landfill .
When solving the issue of disposal of "old" mineral wool, numerous attempts were made to use mineral wool waste in other industries. Existing research on this topic emphasizes the applications in which potentially carcinogenic fibers are destroyed or reliably bound. Scientific studies have been done on the use of mineral wool waste in following areas:
The difficulties in introducing these applications consist in the absence of proven technologies and the necessary equipment, as well as in the imperfection of the waste management system, including the organization of collection, sorting and preparation of waste.
2.3. Recycling of waste in mineral wool industry
From the point of view of a circular economy, the return of waste back to mineral wool production is the best solution, occupying the second place in waste management hierarchy after waste prevention . Remelting of mineral wool waste modifies such hazardous characteristics as morphology and chemistry during melting and solidification process . In addition, replacing primary raw materials with secondary ones reduces the energy consumption for smelting, thus making the process more economical.
One of the difficulties in reprocessing of mineral wool waste is, however, a high content of small waste, such as dust or shots. In the standard technology including cupola furnace, lump raw materials with a size of about 100 mm are used. Feeding a large amount of small waste can lead to blockage of air supply .
Therefore, the most common way to return small waste back to the cupola furnace is the preliminary formation of briquettes . When briquetting, the waste is ground to a homogeneous mass, mixed with cement and water, then formed into briquettes in a hydraulic press, dried in a drying chamber and reused in the process of producing mineral boards as one of the charge components .
Theis method, however, presents certain problems. At high temperature the briquettes bound with cement split into small pieces before the melting process starts, thereby making remelting in the cupola furnace impossible because of the interrupted feeding of air and gases .
Furthermore, the melting of briquettes containing cement causes more significant emissions of solid particles and sulfur oxides into the atmosphere than the melting of virgin rock . Hydraulic binders based on clay and liquid glass are also not optimal for briquetting, because the strength of such briquettes decreases at a temperature of about 500°C . Briquettes containing clay-based binder have poor moisture resistance and tend to absorb water and break down during storage .
From the industrial point of view, briquetting is a costly, intermediate process that requires additional material, energy, and human resources.
In the framework a research program one of European companies has developed a method for feeding mineral wool waste obtained in a centrifuge and crushed to a fraction of 0–6 mm directly into a cupola furnace . With this method, a maximum of 10% substitution of the virgin rock can be achieved.
Another known equipment for recycling of mineral wool waste is focusing exceptionally on waste from edge trimmings and manufacturing defect. Here the crushed waste is partially added to the product in the fiber collecting chamber . Same as in the previous method, the percentage of substitution of the primary raw material is limited, so this option cannot be used for a large amount of waste.
Summarizing the topic of recycling mineral wool waste and its use in manufacturing of mineral wool products, the following conclusions can be drawn:
Finally, it should be noted that all known methods of reusing the waste in production are currently applicable mainly to industrial waste, the chemical composition of which is known. Thus, a few mineral wool manufacturers recycle exclusively the used mineral wool insulation of own production . The composition and condition of mineral insulation waste removed during the demolition or renovation of buildings, are, in most cases, unknown . Therefore, due to strict requirements to chemical composition of mineral wool in the European Union, the reusing of such waste in production is currently considered unacceptable (see paragraph 1 and Fig. 2).
A few companies outside the European Union do not strictly divide mineral wool in "old" and "new", offering the disposal of old mineral wool from construction site .
3. Conclusion: the main reasons of irrational use of mineral wool waste
Regarding the above analysis, it can be concluded that one of the main reasons for the irrational use of industrial mineral wool waste is the lack of technologies and equipment that would allow to process a wide range of waste at minimal cost.
Our company has approached this challenge by developing an innovative technological solution. The technological line IBE13R designed by IB Engineering GmbH allows to recycle a wide range of mineral wool waste at minimal cost, while meeting the high requirements of resource efficiency and environmental protection (link: EQUIPMENT AND TECHNOLOGY FOR RECYCLING MINERAL WASTE)
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