Abstract:

Two BC(black carbon) samples, BC700 and BC400, were prepared from China fir wood by pyrolytic charring at 700 and 400℃, respectively. The sorption behavior and mechanisms of tributyltin(TBT) on the two BC samples were evaluated as a function of seawater pH and salinity. The results indicated that BC700 had a higher specific surface area but lower content of organic matter than BC400. TBT sorption on BC700 was primarily a physical adsorption process while hydrophobic partitioning also significantly contributed to TBT sorption on BC400. Increasing salinity from 5 to 35 g/kg facilitated TBT sorption by 1.03-2.12 times as an overall result of the enhancing effective concentration of TBT because of 'salting-out’ and the reducing role of electrostatic interaction because of BC surface charge neutralization. Environmental pH had a significant influence to TBT forms in the solution. It was found that TBT existed in both cationic(TBT⁺) and uncharged species at pH=4.00 and 6.25 but mostly in uncharged species(TBT) at pH=8.00. TBT sorption reached maximum at pH=6.25, as compared to pH=4.00 and 8.00, due presumably to multiple mechanisms involving electrostatic interaction, physical adsorption and hydrophobic partitioning between TBT and BC. In addition, XPS spectra showed that the binding energy of Sn_3d5/2 peak shifted higher with decreasing pH, confirming the TBT-BC electrostatic interaction. Therefore, sorption of TBT on the BC700 was mainly physical adsorption and electrostatic interaction while hydrophobic partitioning also significantly contributed to TBT sorption on BC400.

Key words: Black carbon, Tributyltin, Sorption mechanism, Salinity, pH