Highly contaminated dredged harbour sludge has been mixed with lime, calcium carbonate, gypsum, waste kiln dust, cement, coal fly ash, and red mud for mechanical and/or chemical stabilization. Analyzing the products by electron microscope, microprobe and chemical extraction methods indicate, that new mineral formations fill the pores and stabilize the material. Heavy metals are incorporated into carbonates, sulfates and hydroxides; they show a shift in their phase specific bonding, but not always towards stronger fixation of metals than in the original material.