Sweden produces large amount of fly ash from waste combustion annually. Combustion the
waste generates two types of ashes, bottom ash/slag, and fly ash. Bottom ash is considered to
be more environmentally friendly and has a wide area of application such as road
constructions on landfills. While the fly ash has high level of heavy metals and for instance
dioxines which are harmful for the environment. This type of ash are deposited in a landfill
and gets classified as a hazardous waste which is expensive given that the deposit fee is high.
The fact that fly ash contains valuable metals as zinc, methods of recovering it are being
developed such as acid leaching. This is a promising method as the leachate used are acid
process water making the usage of the chemicals substantially lower which makes it
Waste incinerators in Sweden produce approximately 200 000 tons of fly ash annually and the
majority of it is transfered to Norway to get treated and put on a landfill. Some waste
management companies, e.g. Renova, are using another method called “the Bamberg method”
where fly ash is mixed with sludge to form a cake and put in the company’s own landfill.
The projects goal is to leach the fly ash by using acidic process water to obtain the metallic
substance particularly zinc making it easier and cheaper to landfill the ash and also to
optimize this method to get the most zinc out of the ash using minimum amount of the acidic
process water (5% HCI).
The laboratory work took place in the University of Borås. Fly ash and the acid process water
which were used under the laboratory work was obtained from RenovaAB.
The results shows that leaching the fly ash with acidic process water gave different release of
zinc but was 88% at most. The variation in the results depends on a few factors such as
amount of acidic process water, pH, time, blending time and the ashes content.
This project took environment and access to acidic water in consideration, which optimized
the method of using less amount of acid process water to get the most zinc as possible.
The results shows that leaching fly ash with acid process water is cost efficient and easy way
to recover zinc, which satisfy the goals of the project.