Regularities in mercury cation sorption by a lignin-based sulfur-containing sorbent

   The unfavorable environmental situation in the town of Usolye-Sibirskoye (Irkutsk Oblast, Russia) determines the relevance of investigating and applying a new lignin-based sulfur-containing sorbent for purification of groundwater from mercury compounds.   The sorbent was synthesized on the basis of waste products of epichlorohydrin (1,2,3-trichloropropane), sulfur, and lignin. The IR spectrum of the sorbent under study showed the presence of an S–S bond in the region of 445–465 cm-1. Intensive absorption of Hg2+ ions in the regions of 2800–2950 cm-1 (valence vibrations of C–H bonds in CH and CH2 groups) and 1460 cm-1 (deformation vibrations in CH2 group) was observed. Absorption of Hg2+ ions by lignin fragments was accompanied by a change in the vibration band of S–S bonds, which splits into two bands of higher frequencies than the νS–S band in the original sorbent. The optimum sulfur content, which ensures the maximum sorption activity of the sorbent, was found to be 53.25%. The mercury sorption isotherms at 20 and 60 °C are described by parabolic dependencies with determination coefficients of 98.9 and 98.6 %, respectively. The kinetic curve at 20 °C and 40 °C is approximated by a hyperbola and a cubic polynomial with determination coefficients of 97.9 and 96.2 %, respectively. The reaction order (first order at 20 °C and second order at 40 °C) and the reaction rate constant (0.0876 min-1 at 20 °C and 0.00014 min-1 at 40 °C) were determined. At 20 °C, the sorption rate of Hg2+ was established to be significantly higher and the sorption time to be faster than those at 40 °C. Therefore, mercury sorption by the proposed sorbent should be carried out at 20 °C in order to reduce energy consumption.