Physical Adsorption:
Activated carbon captures mercury (particularly gaseous mercury, Hg⁰) within its micropores and mesopores through Van der Waals forces. This mechanism is particularly effective for mercuric oxide (Hg²⁺), as it frequently exists in flue gas in an ionic form and is readily captured via electrostatic interactions.
Chemical Adsorption (The Key Mechanism):
Standard activated carbon possesses limited adsorption capacity for elemental mercury (Hg⁰); consequently, it is frequently modified by loading elements such as sulfur (S) or iodine (I). Sulfur exhibits a strong affinity for mercury, reacting to form stable mercuric sulfide (HgS), which precipitates within the pores of the activated carbon, thereby achieving highly efficient removal.
Advantages of Modified Activated Carbon
Impact of Sulfur Loading on Adsorption Performance:
Studies indicate that adsorption performance is optimal when the sulfur loading content is 10%; conversely, excessive sulfur loading (e.g., 20%) leads to a decline in performance due to pore blockage.
Optimal Preparation Conditions:
By utilizing activated carbon with a carbon tetrachloride (CCl₄) adsorption value of 60, subjecting it to a 24-hour impregnation period, and employing an S/C feed ratio of 14%, one can obtain activated carbon with a sulfur loading of 10.89%. This process also achieves a solvent recovery rate of 90%, making it well-suited for industrial-scale production.
Other Modification Methods:
Loading halogens, metal oxides (such as CuO or Fe₂O₃), or introducing heteroatoms—such as nitrogen or chlorine—can also serve to enhance the chemical adsorption of mercury.
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