PHYSICAL/CHEMICAL TREATMENT OF MERCURYCONTAMINATED WASTES FROM FORMER CHLORINE-ALKALI ELECTROLYSIS PLANTS –APPLICATION OF FLOTATION TECHNOLOGIES IN SOIL WASHING PLANTS

摘要

Physical-chemical soil washing plants have proven to be suitable for the treatment of contaminated soils during the last 20 years. The principle is based on the fact that soil is liberated by mechanical energy input. The contaminant-soil separation takes place by applying a sequence of classifying and separation processes. Owing to 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 Petroleum Hydrocarbons (PHC) and Polycyclic Aromatic Hydrocarbons (PAH) (Richter and Schmidt, 1997). Investigations into the flotation of heavy metal-contaminated soils were performed with material from a former steel works and rolling mills at an inner-city site in Berlin. Recovery of maximum 75 per cent lead and 44 per cent zinc was obtained for single-stage flotation. The recovery of cleaned soil amounted to 92 per cent (Stapelfeldt and Richter, 2002). The OSPARCOM decision 90/3 of 14 June 1990 recommends that all chlorine-alkali electrolysis facilities in Western Europe using the amalgam procedure be decommissioned by 2010 for reasons of environmental protection. For the treatment of demolition material from chlorine plants in particular, soil and rubble soil washing should be considered as a treatment option. Tests with increasing particle size ranges indicate that under given laboratory conditions selective separation in the size range 25 - 500 μm is possible. Studies of cleaned soil involving sequential extraction show above all that moveable heavy metal fractions are floated. Considering the reuse of soil, this is of significant importance. The flotation kinetic can be described by a first-order two-class mathematical model.