Metal extraction with focus on Zn from fly ash by means of using acid process waters

Every year over 5 000 000 ton of solid waste are combusted in Sweden. In addition to the production of heat and electricity, this also results in large quantities of ash. The bed ash, or slag, is used as construction material on landfills, while the fine fly ash is deposited. The reasons to this deposition are the content of potential hazardous metal compounds and easily leached chlorides. Several metals as for example Cu and Zn can be found in concentrations of the same level or even higher in the ash compared to metal ores used for mining. Thus, there is a large interest to develop methods for metal extraction from ash.

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The aim of this project is to

  • optimize the leaching of metals, with focus on Zn, from ash by means of using acid industrial waste products.
  • evaluate different methods to extract Zn and possibly other metals from the leachate and study the most promising method like bio-electrochemical systems more thoroughly.

The project will be performed by laboratory experiments and can be divided in three main parts;

  1. Optimized leaching- different leaching parameters such as time, L/S-quote and different solvents are studied.
  2. Recovery of interesting metals from the leachate- different recovery methods as solid phase extraction and bio electrolyze will be studied to determine their suitability for specific metal recovery and the most suitable method, based on technical, environmental and economic aspects, will be investigated by lab work.
  3. Verification of the developed recovery method- the developed method will be tested, verified and evaluated on different fly ashes derived from Waste to Energy plants in Sweden. The developed and tested method will be briefly evaluated according to environmental and economic aspects.


The overall goal of the project is to obtain results that can be the basis for the construction of a pilot plant, where Zn (and possibly other metals) can be extracted from fly ash in an environmentally and economically sustainable manner. A full scale plant for Zn recovery is under construction in Switzerland. However, there are several important differences between Sweden and Switzerland, which means that if a similar plant were built in Sweden it might not be economically viable. Thus we needs studies starting from the Swiss process but adapted to Swedish conditions to be able to develop effective and sustainable recovery methods.