Sulfurized activated carbons and their mercury adsorption/ desorption behavior in aqueous phase

Sulfurized activated carbons (SACs) are of the most recent forms of modified sorbents with high affinity toward mercury. The adsorption/desorption behavior of SACs has not been studied in detail in liquid phases. The study was carried out with the aim of recognition of similarities and differences in the properties and performances of SACs and activated carbons (ACs) exposing to aqueous-phase mercury. In this study, three different sulfurizing agents including dimethyl disulfide (DMDS), elemental sulfur (S), and sulfur dioxide (SO₂) were tested for AC sulfurization (each under the optimal conditions). Sulfurization with DMDS at room temperature led to the formation of elemental sulfur and sulfide/disulfide on the AC surface; however, sulfurization at higher temperatures with SO₂ and powdered S resulted in the formation of more stable organic forms such as thiophene and oxidized sulfur. The equilibrium mercury adsorption capacity of AC– DMDS was so larger than AC and other SACs. On the other hand, the largest surface area drop and consequently the slowest mercury adsorption rate belonged to this sample. However, AC–S and AC–SO₂ led to moderate increase in mercury equilibrium adsorption capacity; they showed several advantages resulted from their extended porosities and more stable sulfur functionalities. The more accelerated adsorption especially at initial stages of contact in batch modes and negligible entry of sulfur compounds into the treating wastewater were of their important advantages. Mercury desorption was also studied and compared using several acidic and potassium halide solvents. The possibility of applicability of SACs in consecutive mercury adsorption/desorption cycles was also investigated.

Keywords
Adsorption; Desorption; Mercury; Sulfurized activated carbon; Wastewater treatment