Through the conventional chlor-alkali production process, highly mercury (Hg) contaminated waste sludge is produced. Improper handling and disposal of this sludge may cause an environmental hazard. The leaching behaviour of Hg of land disposed mercurial sludge, originating from a chlor-alkali plant that still is in operation, was investigated using the German DIN 38414-S4 test. The total mercury content of the samples was above 1500 mg/kg, allowing the material to be classified as hazardous and high mercury waste. Concentrations of Hg in the leachates were higher than 0.02 mg/l stipulated by the 1991 EEC Landfill Directive Draft as a maximum limit for a waste that is to be landfilled. Total Hg contents and leachability differed markedly between the samples, pointing to a heterogeneity in the production of the sludge. The more limited release of Hg from one of the samples might reflect an ageing effect, or might reflect a better quality of the stabilization process at the time of production. Results indicate that the approach used to stabilize the sludge has not been sufficiently effective, and warrant caution about existing disposal sites and future management of these mercury containing waste materials.Key words: Mercury / Hazardous mercury waste / Chlor-alkali process / Heavy metal mobility / Leaching test
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