Final disposal of Mercury
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The Swedish government has decided to phase out the use of mercury by the year 2000. Consequently, mercury will no longer be recycled and will be removed from the material cycle. There is therefore a requirement for a long-term solution to the problem of mercury storage/disposal. Following a government directive, the Swedish Environmental Protection Agency has made recommendations about the future disposal of mercury waste. Kemakta has played central part in the investigations, being responsible for questions concerning the waste inventory, waste characterisation, chemical processes, pre-treatment alternatives for the waste, geohydrological aspects of different disposal options, mechanisms of mercury dispersion, safety analysis, and disposal techniques. Mercury is a poisonous heavy metal and an environmental hazard. Widespread use of mercury has given rise to substantial environmental contamination. Mercury occurs naturally in the bedrock in insoluble, stable minerals. One underlying idea in the project is to return the waste-mercury to a stable form, as found in the geochemical cycle. The following disposal concepts have been investigated:
Kemaktas work has included the estimation of the release of mercury from different disposal alternatives. The release of mercury by advection as well as by diffusion has calculated; and consideration has been made of the following;
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Elemental mercury The calculations performed show that it is possible to design a final repository for mercury that gives rise to low emissions to the surroundings. The simulations show that in a short term, all the concepts studied can function acceptably and give small discharges. Discharges have been calculated for pre-treated and untreated waste for the different disposal concepts. Pre-treatment of the waste can include chemical stabilisation and reprocessing (concentration of the waste followed by chemical stabilisation). The use of buffering to improve repository function and reduce the discharge of mercury has been studied. The influence of time has also been investigated. Surface repositories are influenced by erosion and other degenerative processes, while the other disposal concepts are expected to maintain their function even in the long term. The next glaciation is expected in 5 000-10 0000 years, which is assumed to be time-limit for the integrity of surface repositories. The other repositories would be better able to withstand a glaciation. It is important to underline that a final repository has to be designed so that the interaction of different measures, such as waste pre-treatment, the use of buffer materials, and favourable hydraulic and chemical conditions, combine to give a low discharge. In practice, there are different methods of achieving low discharges, therefore, it is necessary to take a comprehensive approach to the assessment of the function of a final repository. |
