The present report deals with the treatment of flyash from a waste incineration plant in Neumnster, Germany. Normally suited for disposal on an open landfill, the ash is polluted with significant amounts of chromium. After elution with water highly soluble Cr(VI) can be found in the solution beyond the limiting values for open disposal. Affiliated with considerably higher costs, underground disposal is the only chance to despose of this material. In accordance with the approaches for producing chromium reduced cements the proposed treatment method works with reducing Cr(VI) to stable and insoluble Cr(III)-compounds. Besides the identification of an appropriate reducing agent, another focus lies on the reaction kinetics of metallic aluminium during mixing. The plant concept provides an EIRICH-mixer combined with a reaction bunker and subsequent drying of the ash mixture in a hot gas stream. Capability for storage and long time behavior under various circumstances were investigated to find out about the ability for landfill disposal. Results show that humid storage conditions favour the reoxidiation of Cr(III), leading to remobilisation and significant transgression of the critical values for Cr(VI). This can be traced back to the presence of manganese oxides, which act as oxidizing agents. Under these circumstances the proposed treatment method is not capable of producing a stable and inert ash mixture with reduced hazard potential to be disposed of at an open landfill.