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Adsorption of Mercury(II) by Kaolinite
Author(s) -
Sarkar D.,
Essington M. E.,
Misra K. C.
Publication year - 2000
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj2000.6461968x
Subject(s) - adsorption , chemistry , silanol , kaolinite , ionic strength , mercury (programming language) , inorganic chemistry , chloride , nickel , aqueous solution , nuclear chemistry , catalysis , mineralogy , organic chemistry , computer science , programming language
Adsorption of Hg(II) by kaolinite was investigated as a function of solution pH, ionic strength, and the competitive or complexation effects of ligands (Cl, SO 4 , PO 4 ) and metals (Ni and Pb). Mercury(II) adsorption from a 0.6 μ M Hg(II) solution was primarily influenced by pH. The Hg(II) adsorption edge was described by a pH 50 (pH where 50% adsorption occurs) of 3.4 and a pH max (pH where maximum adsorption occurs) of 4.4. At pH values above the pH max , Hg(II) retention decreased with increasing pH. Chloride and Ni shifted pH 50 from 3.4 to 7 and 4.1, respectively. Nickel and Pb reduced the amount of Hg(II) adsorbed throughout the pH range examined. Ionic strength and the presence of SO 4 and PO 4 had relatively little impact on the Hg(II) adsorption envelope. The adsorption of Hg(II) was predicted through the application of the triple layer model (TLM) by assuming that the kaolinite surface was composed of equal proportions of silanol and aluminol groups. The TLM model suggests that the silanol group was responsible for retaining the bulk of the adsorbed Hg(II), through the formation of the ≡SiO − ‐HgOH + outer‐sphere, and the ≡SiOHg OH − 2 and ≡SiOHgCl 0 or ≡SiOHgOHCl − (Cl system) inner‐sphere species. The ≡AlO − ‐HgOH + outer‐sphere complex accounted for a small percentage (<15–35%) of the adsorbed Hg(II). The TLM results suggested that Hg(II) adsorption by both ≡SiOH and ≡AlOH sites on kaolinite should be considered to predict adequately Hg(II) retention.