Sludge from the harbour of Hamburg which was highly contaminated with heavy metals and organic toxicants has been stabilized by means of lime, calcium hydroxide, calcium carbonate, gypsum, trass, waste kiln dust, cement, coal fly ash and, red mud. Analysis of the solidification products by polarization microscope, electron microscope, X-ray diffraction, electron microprobe, and proton-induced X-ray emission microprobe (PIXE) indicates that new minerals have been formed. These new mineral formations stabilize the material and change, as confirmed by chemical extraction methods and different leaching tests, the phase specific bonding of heavy metals by incorporation into silicates, carbonates, sulfates, and hydroxides.