Treatment process of gas containing zero-valent mercury and mercury separation system

Patent metadata

Field	Value
Publication number	US-9884288-B2
Application number	US-201515312044-A
Country	US
Kind code	B2
Filing date	May 18, 2015
Priority date	May 21, 2014
Publication date	Feb 6, 2018
Grant date	Feb 6, 2018

Abstract

A treatment process of a gas containing zero-valent mercury and a mercury separation system, by which the amount of an iodine compound used can be reduced when the zero-valent mercury is separated from the gas containing the zero-valent mercury by using the iodine compound. The process has a step of oxidizing the zero-valent mercury contained in the gas with a first liquid phase containing an alkali metal iodide, thereby obtaining a second liquid phase containing a divalent mercury ion and an iodide ion; a step of separating the divalent mercury ion as mercury sulfide by adjusting the pH of the second liquid phase; and a step of circulating a third liquid phase which is obtained by separating the mercury sulfide in the mercury separation step to use the third liquid phase as the first liquid phase in the mercury oxidation step.

First claim

The invention claimed is:

1. A treatment process of a gas containing zero-valent mercury, comprising
a mercury oxidation step of oxidizing the zero-valent mercury contained in the gas containing the zero-valent mercury with a first liquid phase containing an alkali metal iodide to take the zero-valent mercury into the first liquid phase, thereby obtaining a second liquid phase containing a divalent mercury ion and an iodide ion;
a mercury separation step of separating the divalent mercury ion as mercury sulfide by adjusting the pH of the second liquid phase obtained in the mercury oxidation step with a pH adjustor and adding an alkali metal sulfide; and
a first circulation step of circulating a third liquid phase which is obtained by separating the mercury sulfide in the mercury separation step and contains an alkali metal ion and the iodide ion to use the third liquid phase as the first liquid phase in the mercury oxidation step.

2. The treatment process according to claim 1 , wherein the alkali metal of the alkali metal iodide used in the mercury oxidation step is the same alkali metal as the alkali metal of the alkali metal sulfide used in the mercury separation step.

3. The treatment process according to claim 1 , wherein in the mercury oxidation step, the gas containing the zero-valent mercury is brought into contact with the first liquid phase on a mercury adsorbing and oxidizing material composed of a carbon-based material.

4. The treatment process according to claim 3 , wherein the carbon-based material is subjected to a water-repellent treatment.

5. The treatment process according to claim 1 , wherein the gas containing the zero-valent mercury contains sulfur oxide.

6. The treatment process according to claim 1 , wherein the gas containing the zero-valent mercury contains oxygen.

7. The treatment process according to claim 1 , wherein the mercury oxidation step has a second circulation step of collecting the second liquid phase and circulating the collected second liquid phase to use the second liquid phase as the first liquid phase.

8. The treatment process according to claim 1 , wherein the alkali metal iodide is at least one selected from potassium iodide, lithium iodide and sodium iodide, and the iodine ion concentration in the first liquid phase is 0.01 to 10% by weight.

9. The treatment process according to claim 1 , wherein in the mercury separation step, the pH adjustor is at least one selected from lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium hydrogencarbonate, sodium hydrogencarbonate, potassium hydrogencarbonate, lithium carbonate, sodium carbonate and potassium carbonate, and the pH of the second liquid phase is adjusted to 1.7 to 7.

10. The treatment process according to claim 1 , wherein in the mercury separation step, the alkali metal sulfide is at least one selected from lithium sulfide, sodium sulfide and potassium sulfide, and the amount of sulfur contained in the alkali metal sulfide is 0.6 to 1.2 times in terms of molar ratio with respect to the divalent mercury contained in the second liquid phase to which the alkali metal sulfide is added.

11. The treatment process according to claim 1 , wherein in the mercury separation step, the addition of the alkali metal sulfide is controlled on the basis of the oxidation-reduction potential of the second liquid phase to Which the alkali metal sulfide is added.

12. The treatment process according to claim 1 , which has an iodine gas, recovery step of bringing an alkali metal hydroxide into contact with an iodine gas generated in the mercury oxidation step to absorb the iodine gas.

13. The treatment process according to claim 12 , wherein a solution in which the iodine gas obtained in the iodine gas recovery step is absorbed is circulated to the mercury separation step.

14. A mercury separation system comprising:
a mercury oxidation unit into which a gas containing zero-valent mercury is introduced and which is configured to oxidize the zero-valent mercury with a first liquid phase containing an alkali metal iodide to take the zero-valent mercury into the first liquid phase, thereby obtaining a second liquid phase containing a divalent mercury ion and an iodide ion;
a mercury separation unit configured to separate the divalent mercury ion as mercury sulfide by adjusting the pH of the second liquid phase discharged from the mercury oxidation unit with a pH adjustor and adding an alkali metal sulfide; and
a first circulation unit configured to circulate a third liquid phase which is obtained by separating the mercury sulfide in the mercury separation unit and contains an alkali metal ion and the iodide ion to use the third liquid phase as the first liquid phase in the mercury oxidation unit.

15. The mercury separation system according to claim 14 , wherein the mercury oxidation unit has a mercury oxidation portion configured to oxidize the zero-valent mercury with the first liquid phase to take it into the first liquid phase and a liquid tank portion which communicates with the mercury oxidation portion and is configured to store the second liquid phase, and also has
a second circulation unit configured to circulate the second liquid phase stored in the liquid tank portion to the mercury oxidation portion to use the second liquid phase as the first liquid phase.

16. The mercury separation system according to claim 15 , wherein the iodine ion concentration in the liquid tank portion is 0.01 to 10% by weight.

17. The mercury separation system according to claim 15 , which has an alkali metal iodide addition unit configured to add an alkali metal iodide into the liquid tank portion.

18. The mercury separation system according to claim 14 , wherein the mercury separation unit has an oxidation-reduction potential measuring unit configured to measure the oxidation-reduction potential of the second liquid phase to which the alkali metal sulfide is added, and an addition controlling unit configured to control the addition of the alkali metal sulfide on the basis of the oxidation-reduction potential measured by the oxidation-reduction potential measuring unit.

19. The mercury separation system according to claim 14 , which has an iodine gas recovery unit configured to bring an alkali metal hydroxide into contact with an iodine gas generated in the mercury oxidation unit to absorb the iodine gas.

20. The mercury separation system according to claim 19 , which has a third circulation unit configured to circulate a solution in which the iodine gas emitted from the iodine gas recovery unit is absorbed to the mercury sulfide separation unit.

21. A mercury separation system comprising:
a mercury oxidation device having a mercury oxidation portion filled with a mercury adsorbing and oxidizing material composed of a carbon-based material, a gas introduction unit configured to introduce a gas containing zero-valent mercury into the mercury oxidation portion to circulate it, an alkali metal iodide supplying unit configured to introduce a liquid containing an alkali metal iodide into the mercury oxidation portion to cause the liquid to flow down along a surface of the mercury adsorbing and oxidizing material and a liquid tank portion configured to store the liquid having flowed down;
a mercury separation device having a pH adjusting unit configured to add a pH adjustor to the liquid taken out of the liquid tank portion, a mercury sulfide generation unit configured to add an alkali metal sulfide to the liquid taken out to generate mercury

Assignees

• Chiyoda Corp

Inventors

• Takeda Dai
• Awai Eiji
• Matsumoto Jun
• Uemura Masataka
• Marukawa Hironobu

Classifications

• B01D53/96

  Regeneration, reactivation or recycling of reactants · CPC title

• B01D2251/30

  Alkali metal compounds · CPC title

• F23J2215/60

  Heavy metals; Compounds thereof · CPC title

• B01D2257/602

  Mercury or mercury compounds · CPC title

• B01D2251/108

  Halogens or halogen compounds · CPC title