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 underground mine or mono dump disposal. Physical-chemical soil washing plants have proven to be suitable for the treatment of contaminated soils during the last 25 years. The first soil washing plants were based on the principle that soil was liberated by mechanical energy input and the contaminant-soil separation took place by applying subsequent combinations of classifying and separation processes. Because of the concentration of contaminants in the fine particle fraction, flotation becomes a significant separation process in the particle-size-fraction below 500 µm. In the past the successful application of soil flotation was mostly related to the treatment of organic contaminants such as Petrol Hydrocarbons (PHC) and Polycyclic Aromatic Hydrocarbons (PAH). Previous investigations regarding the flotation of heavy-metal contaminated soils were performed with material from a former steel works and rolling mills inner city site in Berlin. A recovery of maximum 75 % lead and 44 % zinc was obtained for a one step flotation. The recovery of the cleaned soil amounted to 92 % . Preliminary tests performed with mercury-contaminated soil in a range of 1,000 mg/kg have shown that a removal of mercury from the soil under the given laboratory conditions in a particle size range of 25 500 µm is possible. The best results were received with KAX as a collecting agent at a pH of 8. In order to provide the best treatment for different soils from various chlorine-alkali electrolysis plants and acetaldehyde factories a categorization based on various samples selected from former and currently ongoing mercury remediation cases worldwide could be made, showing that the silt and clay fraction in very cohesive soils from chlorine-alkali plants have a much lower mercury content than sandy soils up to a concentration of fine in a range of 20 mass-%. Next to the positive effect of attrition for the enrichment of mercury in the fin particle range the importance of the removal of other with mercury closely linked soil components in chlorine-alkali soils such as carbon (mostly as graphite from the electrodes) was highlighted in this thesis. Owing to the different solubility of various mercuric sulphide species in aqueous systems such as in particular the sulfur mercuric ion HgS22- a flotation method was developed using organic sulphidisation agents and xanthates in the same process. Performing tests rows with different mercury concentrations have proven that this process is applicable for solid high mercury wastes up to 1,000 mg/kg up to 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 “Zuordnungswert 2 (Z2)” of the German LAGA: Hg <10 mg/kg DW could be reached. The thesis includes also experience made with other treatment options than soil washing such as in particular stabilization/solidification and thermal desorption.