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Kinetics of adsorption and desorption of some organochlorine compounds on black carbon in a sediment
Author(s) -
Vrind Bea A.,
ten Hulscher Theodora E. M.,
van Noort Paul C. M.
Publication year - 2006
Publication title -
environmental toxicology and chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.1
H-Index - 171
eISSN - 1552-8618
pISSN - 0730-7268
DOI - 10.1897/05-405r.1
Subject(s) - desorption , adsorption , chemistry , sediment , reaction rate constant , gibbs free energy , carbon black , diffusion , environmental chemistry , kinetics , langmuir adsorption model , langmuir , thermodynamics , organic chemistry , geology , paleontology , physics , natural rubber , quantum mechanics
Rate constants for adsorption and desorption of four organochlorine compounds on black carbon in a sediment were determined from measurements of the rate of removal, by gas purge, of the organochlorine compounds as single solutes from a water‐sediment mixture immediately after addition of the solute to the system. The rates of removal fitted to a kinetic scheme based on Langmuir adsorption onto two types of sites in black carbon. The first‐order rate constants for desorption from these sites were comparable to those for slow and very slow desorption from sediment. The time needed to reach apparent equilibrium in the experimental setup, with 10 g sediment/L water, ranged from 13 to 166 h, depending on the sorbate and the adsorption process. These short times to equilibrium suggest no need to assume rate‐limiting diffusion from and to adsorption sites in this sediment. Average Gibbs free energies for adsorption of the four organochlorine compounds from the pure solid state were —10 ± 3 and —20 ± 3 kJ/mol for low‐energy and high‐energy sites, respectively, pointing to two different adsorption mechanisms.