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Kinetics and Mechanisms of Molybdate Adsorption/Desorption at the Goethite/Water Interface Using Pressure‐Jump Relaxation
Author(s) -
Zhang Peng Chu,
Sparks Donald L.
Publication year - 1989
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/sssaj1989.03615995005300040007x
Subject(s) - adsorption , chemistry , desorption , temperature jump , goethite , molybdate , ionic bonding , relaxation (psychology) , kinetics , equilibrium constant , ion , kinetic energy , analytical chemistry (journal) , thermodynamics , inorganic chemistry , chromatography , organic chemistry , physics , social psychology , psychology , quantum mechanics
Pressure‐jump (p‐jump) relaxation with conductivity detection was used to ascertain the kinetics and mechanisms of MoO 4 adsorption/desorption on goethite. A postulated reaction mechanism consisting of two consecutive elementary steps was examined and verified through kinetic and equilibrium studies. The first step is the formation of an ion‐pair complex through the electrostatic attraction between the protonated surface and the MoO 4 anion. The second step involves a ligand exchange process, whereby 1 mol of H 2 O is replaced by 1 mol of adsorbed MoO 4 from the surface. It is much slower than the first step. The forward and backward intrinsic rate constants for steps 1 and 2 are: k int 1 = 4019.2 mol −1 L s −1 , k int ‐1 = 391.5 s −1 , k int 2 = 1.888 mol −1 L s −1 , and k int ‐2 = 42.34 s −1 . A slightly modified triple layer model (TLM) was employed to calculate the distribution of ionic species on the goethite surface, in the α and β layers, and in the bulk solution at equilibrium and electrical parameters for the charged surface. Both equilibrium and kinetic data fit the postulated mechanism for the reaction steps and the modified adsorption model well.