Sorption of 2,4,6-Trichlorophenol in Model Humic Acid−Clay Systems

Abstract

Humic acids and clays are important soil components that influence the sorption and desorption of organic contaminants; however, it is unclear how humic acids influence the sorption of organic contaminants onto clays and their subsequent desorption. Sorption and desorption of 2,4,6-trichlorophenol (2,4,6-TCP) by and from humic acid-modified K + -and Ca 2+ -montmorillonite and -illite were compared with unmodified clays using batch equilibration methods. Commercial humic acid and the humic acid extracted from forest soil were employed in this experiment. The adsorbed amount of 2,4,6-TCP by commercial humic acid was almost twice as large as that adsorbed by the extracted soil humic acid. More 2,4,6-TCP was sorbed onto K + -and Ca 2+ -illite than onto K + -and Ca 2+ -montmorillonite. K + clays were more effective in adsorbing 2,4,6-TCP than Ca 2+ clays. Sorption of 2,4,6-TCP on humic acid-modified Ca 2+ -and K + -montmorillonite and -illite increased as compared with unmodified clays. The sorption nonlinearity of 2,4,6-TCP on humic acid-modified Ca 2+ -and K + -illite increased remarkably as compared with the unmodified clays. The sorption nonlinearity of 2,4,6-TCP on humic acid-modified Ca 2+ -and K + -montmorillonite increased slightly in contrast to unmodified montmorillonites. By comparing sorption and desorption results, we observed hysteresis for all sorbents including humic acids, clays, and humic acid-modified clays. Sorption nonlinearity and hysteresis were dependent on the structure of humic acids. Higher aromaticity of humic acids resulted in greater sorption nonlinearity and desorption hysteresis. In addition, sorption capacity (K f ′) was positively correlated with the humic acid content of the sorbents. These results show that modification of humic acids on clays can not only increase the adsorption ability of clays but also affect the sorption nonlinearity of 2,4,6-TCP, and the desorption hysteresis was probably due to the structural characteristics of humic acids.

Mechanistic study of PFOS adsorption on kaolinite and montmorillonite

“…Humic acid (HA) is a major component of organic matter and plays a predominant role in many physical, chemical and geochemical processes in the environment [17,18]. HA is generally attached with clay minerals, and thus significantly affects their surface electrostatic properties.…”

Part IV—sorption of hydrophobic organic contaminants

“…A general observation is that the increasing nonlinearity and aromaticity are concurrent with diagenetic maturity. Thus, nonlinear sorption is attributed to the contribution by aromatic carbon fractions in SOM because of their diagenetic maturity and condensed nature (Xing 2001b;Ding et al 2002;Wang et al 2005). A positive relationship between aromaticity and sorption capacity was also observed (Gauthier et al 1986;Chin et al 1997;Chiou et al 1998;Perminova et al 1999).…”

Clay mineral dependent desorption of pyrene from soils by single and mixed anionic–nonionic surfactants

“…The 3:7 surfactant mixture showed the lowest F oc value for montmorillonite. Clay minerals were key sorbent materials for surfactants [42,57], and clay minerals lead to a higher sorptive ability than soil organic matter [58]. However, lower soil organic matter (shown in Fig.…”