Classifying – separating – and assorting solids – Fluid suspension – Liquid
Patent
1997-10-15
1999-08-31
Bollinger, David H.
Classifying, separating, and assorting solids
Fluid suspension
Liquid
209159, 210614, B03B 566, C02F 300
Patent
active
059441968
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a process for the recovery of mercury, or other heavy metals from a mercury or heavy metal contaminated material, and an apparatus suitable for use in such applications. In particular, the invention relates to a process for recovery of mercury from a mercury-contaminated soil in order to effect remediation of said soils, or for the recovery of mercury from a mercury-contaminated material such as a caustic sludge.
DESCRIPTION OF THE RELATED ART
Liquid mercury is used in a variety of industrial processes including its use as an electrode in some chlor-alkali plants for the production of gaseous chlorine and an aqueous solution of an alkali metal salt. The use of such mercury cells for this application is well known in the industry, and is commonly used for the electrochemical generation of chlorine and sodium hydroxide from a sodium chloride solution. The use of other alkali metal salts, such as potassium chloride to produce potassium hydroxide, is also known.
Occasionally, during operation of this type of chlor-alkali plant, some mercury may be lost to the environment where it contaminates the soil in the immediate vicinity of the cell. This contaminated soil is generally disposed of by, for example, sending the soil to a suitable landfill operation which is set up to handle this type of waste material. However, since the actual amount of mercury loss to the environment is relatively small, and the amount of soil which must be land-filled is generally large, the cost of such a land-filling operation can amount to a significant expense.
Further, during operation of this type of chlor-alkali plant, finely dispersed mercury droplets are suspended within the generated aqueous solution. These mercury droplets are typically removed from the aqueous solution by filtration through a suitable filtering medium. This medium is most commonly powdered or granular carbon, but can include other organic, polymeric or inorganic filtering medium. After the mercury has been removed from the aqueous solution, a mixture of mercury mixed with the filtering medium is generated. This mixture is termed in the industry as "caustic sludge" since typically, it is generated from an aqueous caustic (sodium hydroxide) solution.
However, in this document, the term "caustic sludge" will be used to refer to any mixture of mercury and a filtering medium wherein this mixture is generated during filtering of an alkali metal salt solution.
Caustic sludge is thus primarily a mixture of carbon and/or some other filtering medium, and mercury. The level of mercury is dependent on the operation of the plant, but may be as high as 70% (or more) mercury, by weight. However, typically, the level of mercury present is between 30% and 55%, by weight, of the content of the caustic sludge sample.
Disposal of this sludge is generally difficult and/or expensive because of its contamination with mercury. Thus, land-filling of the caustic sludge in an appropriate land-fill operation, as one disposal means, can be a significant expense. Further, loss of the mercury adds to the expense of the operation of the chlor-alkali facility.
A second method for disposal of the caustic sludge material is mixing the caustic sludge with a large excess of water while stirring in order to "wash" the mercury droplets from the caustic sludge amalgam. This approach has met with some success, but separation of the mercury from the sludge is not complete, and the method does not consistently provide the levels of mercury removal desired.
Accordingly, it would be desirable to provide an improved method for the removal of mercury from soils or from caustic sludge, and preferably, for the recovery of the mercury contained in the soil or sludge.
In the mining industry, it is known that ore particles containing precious metals, such as gold, can be separated from other particles of comminuted ores, by use of a hydraulic mineral separator. This type of device uses a upward flow of a liquid, which is preferably water, through an essenti
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Battikha Nabil Elias
Currie John Daniel
Kenno Richard Masaichi
Oram Peter Glen
Bollinger David H.
Bower Kenneth W.
Pioneer Licensing Inc.
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