Which kind of residues can be treated?
All inorganic residues including:
- dry air pollution control residues
- semidry air pollution control residues
- fly ash, and
- fly ash with sludge from a wet scrubber system, can be treated with the Ferrox®-process to avoid release of heavy metals and salts
The Ferrox®-process offers a solution to the problem of managing flue gas treatment products like fly ash and dry/semidry air pollution control residues (APC-residues) from municipal solid waste incineration (MSWI) and other inorganic combustion residues. These types of residues have been recognised as a potential threat towards the environment as high concentrations of heavy metals; especially lead and salts are leached out. This has made environmentally safe landfilling difficult, as fly ash and dry/semidry air pollution control residues from MSWI are produced in an amount of 10-50 kg per tonne MSW.
The principle of the Ferrox®-stabilisation
The Ferrox®-process is a simple technology. It is based on mixing the residue with a solution of ferrous iron into a suspension. This causes the ferrous iron to precipitate, whereby the heavy metals are bound to the solid phase. Subsequently the iron is oxidised into iron oxides, which, according to geochemistry, are known to be stable over a geological time scale and to be able to bind heavy metals.
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The principle of Ferrox®-stabilisation
The content of heavy metals in the stabilised residue is immobilised by the Ferrox®-process. During the process, salts dissolve and are removed with the wastewater. This results in low leachability of salts from the stabilised residue in addition to the low leachability of the heavy metals. The removal of salts during the process results in an overall mass reduction of the residue in the order of 10 % depending on the type.
The removal of salts can be further enhanced by washing the stabilised residue before transporting the stabilised residue to its final disposal site. The washing can be done in the filtration unit.
An additional step for stabilisation of Cr can be added. This step is integrated with the Ferrox®-process and can be applied if leachability of Cr is a particular problem.
