Mercury Removal
from concentrated and diluted NaCl
In the production of chlorine and caustic soda, the diaphragm and mercury amalgam processes are increasingly being replaced by membrane technology which consumes less energy and is more environmentally benign. Nevertheless, about 35% of the world's chlor-alkali processes are still using the amalgam process. It is anticipated that the industry will gradually replace the amalgam processes with membrane processes over the next 10 years.
In general, the brine purification steps include: saturation, precipitation, clarification, filtration, selective ion exchange, electrolysis, and dechlorination . If the salt is already of high purity, such as vacuum salt, a primary purification with precipitation-filtration is not necessary and a secondary purification with ion exchange only is sufficient. After dechlorination, the loop is closed by sending the depleted brine back to saturation. If part of the circulating brine comes from a mercury cell plant, then the mercury should be removed from the brine prior to secondary treatment with Ambersep™ GT74.
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Some chlor-alkali plants are progressively moving from mercury to membrane cell technology. Both processes may co-exist for many years and will have to share the same brine feed circuit. The brine circuit of a mercury cell process contains mercury which is detrimental for membrane cell electrodes and also irreversibly fouls Amberlite™ IRC747. The use of Ambersep™ GT74 in front of Amberlite™ IRC747 is an excellent solution to both problems.
Fig. 1: Ambersep GT74 functionality
Its unique thiol functionality makes this resin an interesting building block for other functionalities and can be used for the selective removal of other metals. Ambersep™ GT74 is the only mercury-removal resin which can be efficiently regenerated and reactivated.
Fig. 2: Mercury removal process
The process generally uses 2-3 columns in a merry-go-round system. Typical mercury leakage levels are 1-2 ppb and the operating capacity is on the order of 60 g Hg per liter Ambersep™ GT74.
Fig. 3: Loading and regeneration process
Ambersep™ GT74 has been optimized for very low mercury leakage and low regenerant consumption. It is also very efficient for the recovery of precious metals, cadmium, and rhodium. Cadmium leakage as low as <2.2 ppb has been reported. For more information please consult our technical experts.
Recommended Product
Amberlite chelating resins for mercury
removal are approved by all major licensors and are in operation
throughout the world for many years.
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