Improved uptake of mercury by sulphur-containing carbon nanotubes

Sulphur containing multi-walled carbon nanotubes (S-MWCNTs) and sulphur-containing activated carbon (S-AC) were employed as adsorbents for the solution uptake of both inorganic and organic forms of mercury. The results revealed that both materials could adsorb mercury at the parts per billion (ppb) level. The adsorption performance of S-AC was substantially reduced in the presence of excess SO₂ while that of the S-MWCNTs was not affected, indicating the superiority of the S-MWCNTs over S-AC. The amount of mercury adsorbed by S-MWCNTs was enhanced by higher sulphur content, increasing contact time and increasing pH. Adsorption by the S-MWCNTs and S-AC were affected by changes in pH but not by the presence of competing ions (Pb²⁺, Cd²⁺ and Cu²⁺ and Cl^-). This also applied to the uptake of mercury from a real industrial effluent. The Freundlich Isotherm provided the best description of the equilibrium adsorption giving a maximum uptake capacity for Hg (II) as 72.8μgg^-1 for S-MWCNTs and 44.7μgg^-1 for S-AC. Preliminary results also reveal that S-MWCNTs can be used for the treatment of industrial wastes that are rich in mercury and contain multiple competing anions and cations. Both S-MWCNTs and S-AC may be regenerated with thiourea.