The PARCOM-decision 90/3 from 14 June 1990 recommends that all chlorine-alkali electrolysis facilities in Western Europe using the amalgam process shall be phased out for reasons of environmental protection at the latest by 2010. For the treatment of the demolition material from decommissioned chlorine plants in particular soil and rubble soil washing should be considered as a treatment option as an alternative to thermal treatment or disposal. Owing to the different solubility of various mercuric sulphide species in aqueous systems such as in particular the sulfur mercuric ion, a flotation method was developed using organic sulphidisation agents and xanthates in the same process, which is applicable for solid high mercury wastes up to 1,000 mg/kg and at a particle size range of 500 µm and is capable to be implemented in existing or newly designed soil washing plants. All TCLP-tests performed with treated soil in laboratory scale were passing the leaching criteria for Hg < 0.2 mg/l. In the dry substance the target value Z2 according to the German LAGA: Hg < 10 mg/kg DW also could be achieved.