In Germany we accumulate 5 million tonnes of municipal solid waste incinerator bottom ash and 50 to 100 million tonnes of construction waste a year. These contain valuable metals and raw materials for the production of asphalt, concrete and cement. Dr. Franz-Georg Simon, Head of the Contaminant Transport and Environmental Technologies Division, discusses in this interview how BAM research can guarantee safe, cost-effective and environmentally-friendly resource recovery and re-use of materials.
Experts predict a serious shortage of raw materials in respect of metals. Your research is contributing to the recycling economy of metals. What exactly are you working on?
When domestic waste is incinerated, ashes are produced which contain valuable metals like iron, copper and aluminium. We are researching preparation techniques that increase the recovery of these metals, because the production of such metals from ore requires very high energy usage. For example, in the case of aluminium we can save 90 percent of the energy if it is reclaimed from waste sources. In contrast to plastics, the qualities of metal do not change through the process of recycling. That means that metal can survive at the same quality for a relatively long time in a cycle of re-use. This is an enormous advantage.
However, metals do adhere to minerals that are released during the incineration and extraction process. These deposits are disrupted during the remelting of the metals in metallurgy and this increases the energy consumption. At BAM we have examined a further procedural step that minimises the mineral deposits.
The products of this recycling process are still regarded as waste, though. How can you ensure that the environment is not damaged by these?
Metals do not have any pollution potential, they can be processed further immediately. But 90 percent of the ashes are minerals and should be processed into substitute construction materials. We are particularly concerned about their environmental sustainability. We have tested and further developed realistic washing and thermal processes to reduce the level of pollutants. Our goal was to create a price-effective construction material out of the ashes that was also very environmentally sustainable. BAM also tested partially automated analytical processes that could be carried out around the clock without monitoring. These are today being applied to the quality control of construction materials.
What do you think are the biggest challenges in this area of research?
In Germany 5 million tonnes of solid waste incineration ash are produced each year, and around ten to twenty times as much from construction waste. At BAM we are therefore researching processes that work well and are also cost effective. Handling costs of more than €2 to €3 per tonne would hardly be acceptable for this mineral material, as it costs that much to produce the construction materials from natural sources. We need automated processes so that industry can examine a high number of samples around the clock. The quality assurance of substitute building materials must also be ensured, since otherwise their environmental sustainability is not guaranteed.
The Federal Government wants to use the Ersatzbaustoffverordnung (substitute building materials ordinance) to create a nationwide regulation for the exploitation of such materials. We are supporting this process with our results and are participating in the establishment of sensible limits.
What is your next research project?
In our current extension project with medium-sized companies we are primarily investigating the mineral content of municipal solid waste incinerator bottom ash. Amongst other things we are looking at applications for the cement industry, which uses a lot of energy. If we could make use of waste materials there we would be able to save a significant amount of energy.