Combustion of waste is used to recover energy from waste that is not suitable for material recycling. At the same time the volume of waste that needs to be landfilled decreases significantly. The ashes formed have different properties and contain different types of chemical compounds. At the bottom of the combustion chamber the bottom slag or bottom ash is taken out. This ash flow consists of solidified ash melt, pieces of metal and other non-combustible materials. The gas flow from the combustion, i.e. the flue gas, is treated with chemicals to absorb acid gases, volatile metals or metal compounds and dioxins. After that the particles carried by the flue gas are collected in filters. This ash flow is called fly ash or filter ash. The chemical components of the fuel are transformed chemically during the combustion and the flue gas treatment. Knowledge about which chemical products are formed during these reactions is important when landfilling or utilization of the ash in some application is planned. Examples are utilization of bottom slag as construction material like a filling material in a road or as replacement for cement in concrete.
Knowledge about the chemical nature of the ash components is also valuable for the development of methods for recovery of valuable metals from waste combustion ash.
Our research in ash chemistry includes 3 tracks:
1. Identification of the chemical compounds of important metals in the fly ash
2. Development of methods for recovery of valuable metals from waste combustion ash
3. Development of environmentally sound ways to utilize the waste combustion bottom ash in construction materials
A fly ash from combustion of waste can contain valuable metals like copper and zinc in concentrations of 0.5-several weight percent which is comparable to the ores that are considered worth mining. Unfortunately, there are only very few analytical methods that can show the identity of the chemical compounds of metals in such concentrations. One of those is X-ray Absorption Spectroscopy (XAS) based on synchrotron generated radiation. We have used XAS to study the speciation of Cd, Cu, Zn och Sb in ashes from combustion of bio fuels and municipal waste. The measurements have been made at the European Synchrotron Radiation Facility (ESRF) in Grenoble (http://www.esrf.eu/ ), at MaxLab in Lund and during 2019 at the new synchrotron facility MAXIV in Lund.
Our results show that it is possible to recover Cu and Zn from waste combustion fly ash with a good yield with hydrometallurgical methods at the same time as Pb and Cd are removed from the ash. We have also found that several of the metals are bound in ferrites and similar compounds which have low solubility. This explains why the leaching yield for those metals did not reach 100%.
Since the bottom ash contains slag that has chemical properties that are close to those of cement, we are investigating if it can be used as replacement for cement in some applications or as raw material for manufacturing of geopolymers.
The research is funded by Formas, Vinnova, Energimyndigheten och SIP Re:Source
Direct determination of cadmium speciation in municipal solid waste fly ashes by synchrotron radiation induced is-X-ray fluorescence and µ-X-ray absorption spectroscopy
X-ray Fluorescence Tomography of Individual Waste Fly Ash Particles
X-ray fluorescence tomography of individual municipal solid waste and biomass fly ash particles
Determination of the cd-bearing phases in municipal solid waste and Biomass single fly ash particles using SR-mu XRF Spectroscopy
Assessment of copper and zinc recovery from MSWI fly ash in Guangzhou based on a hydrometallurgical process
Henric Lassessons licentiatavhandling
Karin Karlfeldts avhandling
Jinfeng Tangs avhandling
Professor Britt-Marie Steenari