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Influence of Biochar on Deposition and Release of Clay Colloids in Saturated Porous Media
Author(s) -
Haque Muhammad Emdadul,
Shen Chongyang,
Li Tiantian,
Chu Haoxue,
Wang Hong,
Li Zhen,
Huang Yuanfang
Publication year - 2017
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2017.06.0223
Subject(s) - biochar , deposition (geology) , colloid , ionic strength , chemistry , chemical engineering , porosity , geology , sediment , pyrolysis , paleontology , organic chemistry , aqueous solution , engineering
Although the potential application of biochar in soil remediation has been recognized, the effect of biochar on the transport of clay colloids, and accordingly the fate of colloid‐associated contaminants, is unclear to date. This study conducted saturated column experiments to systematically examine transport of clay colloids in biochar‐amended sand porous media in different electrolytes at different ionic strengths. The obtained breakthrough curves were simulated by the convection–diffusion equation, which included a first‐order deposition and release terms. The deposition mechanisms were interpreted by calculating Derjaguin–Landau–Verwey–Overbeek interaction energies. A linear relationship between the simulated deposition rate or the attachment efficiency and the fraction of biochar was observed ( R 2 ≥ 0.91), indicating more favorable deposition in biochar than in sand. The interaction energy calculations show that the greater deposition in biochar occurs because the half‐tube–like cavities on the biochar surfaces favor deposition in secondary minima and the nanoscale physical and chemical heterogeneities on the biochar surfaces increase deposition in primary minima. The deposited clay colloids in NaCl can be released by reduction of ionic strength, whereas the presence of a bivalent cation (Ca 2+ ) results in irreversible deposition due to the formation of cation bridging between the colloids and biochar surfaces. The deposition and release of clay colloids on or from biochar surfaces not only change their mobilizations in the soil but also influence the efficiency of the biochar for removal of pollutants. Therefore, the influence of biochar on clay colloid transport must be considered before application of the biochar in soil remediation. Core Ideas We examined the transport of clay colloids in biochar‐amended sand porous media. Clay colloids were more favorably deposited in biochar than in sand. The half‐tube‐like cavities on biochar surfaces favor deposition in secondary minima. Core Ideas Clay colloids were reversibly and irreversibly deposited in biochar in 1:1 and 2:1 electrolytes, respectively.