1. Review
“Kinetics of Arsenate Adsorption –
Desorption in Solis”
Sangyul Kang

2. Introduction
•
There have been two major types of arsenic
in nature; As (Ⅴ) under aerobic conditions,
As (Ⅲ) under anaerobic conditions.
•
Fe and Al oxides hydroxides have a high
affinity to arsenic.
•
The objectives
1) To quantify the kinetics of adsorption and desorption of arsenate in three soils
having different physiochemical properties
2) To assess multi-reaction (equilibrium-kinetic) modeling for its capability of
describing the retention as well as the desorption or release behavior of As(V) in
different soils.

3. Materials and Methods
•
Materials
1)Surface soils from the Ap horizon (0-10 cm) of Olivier loam
2)Sharkey clay
3)Windsor sand
•
Method
- Batch experiments were initiated by mixing 3 g of air-dry soil with 30 mL of As(V)
solution in a 40-mL Teflon tube.
- Test were performed in triplicate.
- shake mixture at 150 rpm on a reciprocal shaker  centrifuged for 10 min at 4000
rpm after each specified reaction time.
- A 1-mL aliquot was sampled from the supernatant at reaction times of 2, 6, 12, 24,
72, 168, 336,and 504 h.

4. Results and Discussion

5. Nonlinear sorption Isotherms
•
•
•
•
Nonlinear behavior
Nonlinear or concentration – dependent adsorption behavior is
characterized by the low values of the Freundlich parameter N.
N is a measure of the extent of heterogeneity of the sorption sites having
different affinities for solute retention by matrix surfaces.
• The N values for all three soils did not vary significantly after 24 h of reaction.
• Low N values may be indicatives of extensive heterogeneity of sorption sites in
these soils.

6. Adsorption kinetics
• Rapid --> Gradual or slow reactions --> continued As(V) retention with
steady decrease of As(V) concentrations with reaction time
• Results concur with the nonlinear forms of the isotherms.
• These findings are in agreement with the biphasic arsenic adsorption
behavior observed on several soil minerals

7. Desorption Hysteresis and Binding Phases.
• Distinct discrepancies between adsorption and successive desorption
isotherms clearly indicate considerable hysteresis for As(V) release.
• This observed desorption hysteresis might be due to kinetic retention
behavior(동역학적 체류현상), such as slow diffusion (21) and irreversible
retention

8. Multireation Modeling
• A major implication of this study is that contamination of soils with high
concentrations of arsenic could result in slow release for extended period of
time, that is, weeks or months
• A secondary implication is that describing retention (adsorption) and
subsequent release or leaching (desorption) by use of a multiple reaction
model of the equilibrium-kinetic-irreversible nonlinear MRM type provided
good overall predictions of the fate of arsenic in the soils examined in this
study.

9. Thank you