Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Group iib metal
Patent
1998-05-15
2000-02-15
Bos, Steven
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Group iib metal
423108, 588234, 588223, C01G 1300, C22B 4300
Patent
active
060249315
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process for removing mercury from organic, mineral and/or metallic materials contaminated with mercury, using a thermal treatment in a kiln, wherein the mercury components evaporate, are subsequently washed out of the combustion gases and are separated.
2. Description of Prior Art
Enormous amounts of mercury-contaminated old scrap are known to be all over the world. In part, this scrap comes from electrolysis installations for producing alkaline metals or chlorine, from old waste dumps and from disposal companies which are inappropriately run. Due to a great danger of the spread of mercury, not only are the actual production facilities contaminated, but in most cases so are all the buildings, the surrounding ground, furniture, cables, etc. Added to this is greatly contaminated waste, such as reject production batches, and waste from dentistry. Correspondingly the materials to be decontaminated include mineral and/or metallic materials. Added to this are organic components, such as paper, wood, plastics, which can also be contaminated by mercury.
An important cost item when removing mercury is the determination of the extent of contamination. The analysis to be carried out is time-consuming and correspondingly expensive and, in particular in connection with buildings and installations, must take place in a surface-covering pattern. If the costs of mercury removal can be considerably lowered, it is less expensive to reduce the number of measurements and instead to decontaminate in a surface-covering manner.
SUMMARY OF THE INVENTION
It is therefore one object of this invention to provide a particularly cost-efficient process for mercury removal, which in addition results in a particularly high degree of mercury removal.
This object is attained by a process as described in the specification and in the claims.
Besides the thermal treatment processes for mercury removal, chemical extraction installations for mercury removal are known. These known installations are extremely expensive and are mostly only suitable for small amounts of materials to be decontaminated. If the initial materials to be decontaminated are a mixture, it is difficult to realize a product purity of less than 20 ppm Hg.
Various thermal mercury removal installations are known. These known installations operate by indirectly heated electric or gas kilns, wherein heating takes place from an exterior source. The evaporated mercury must be evacuated from the kiln. Thus the kiln is flushed with nitrogen or air in several cycles and afterwards evacuated again. Depending on the number of the alternatingly performed evacuations and flushings, a purity of less than 1 ppm can be achieved. The decontamination costs run to approximately 10 to 20,000 DM/t.
It would be possible in principle to perform a mercury removal process with a multiple-hearth kiln. However, tests performed by the inventor have shown that such a kiln is less suitable for this purpose, since the diffusion paths in a multiple-hearth kiln are relatively long. The process takes place at relatively high temperatures of more than 800.degree. C., and the retention time in the kiln of the materials to be decontaminated must be very long, at least several hours. The construction and maintenance of multiple-hearth kilns is very expensive.
Some attempts for mercury removal in rotating kilns have been made, but the results were not convincing and accordingly a large industrial installation has not yet been realized. Known rotating kilns, which are lined with fire-resistant mineral materials, were employed in these attempts. A great amount of abrasion took place at the mineral lining, which correspondingly burdens the end products. This is a particular problem if the basic materials to be decontaminated are free of mineral materials. The end product obtained by the process then is accordingly greatly burdened with mineral materials. The rotating kilns lined with minerals lead to making the process inflexible, be
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Bos Steven
Deco-Hanulik AG
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