Auxiliary Material for
Behavior of Bromide, Chloride and Phosphate during Low
Temperature Aqueous Fe(II) Oxidation Processes on Mars
Yu-Yan Sara Zhao, Scott M. McLennan, Martin A. A. Schoonen
(Department of Geosciences, State University of New York at Stony Brook, Stony Brook, NY)
Journal of Geophysical Research, Planets, 2014
Introduction
This Text01.pdf file contains two parts of supplemental information.
Part A is the Scanning Electron Microscopy (SEM) images of six synthetic Fe-bearing minerals
described in Section 2.4 and Table 2.
Part B is a supplemental material to Section 3.3 and provides the details of determining
adsorption isotherms of single adsorbate Cl- and Br- for the three HAL-free Fe-minerals. The
experimental methods and results are summarized.
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Part A. Scanning Electron Microscopy (SEM) images of synthetic Fe-bearing minerals.
Figure S1. SEM images of synthetic Fe-bearing minerals described in Section 2.4 and Table 2.
Elements detected by Energy-Dispersive X-ray Spectrometer (EDS; insets in SEM images) were
consistent with the X-ray fluorescence spectrometry (XRF) analyses. The Au detected in goethite
and hematite samples was introduced by the gold-coating pretreatment prior to the SEM analysis.
In jarosite samples, the Au peak overlaps a S peak. (A) HAL-free jarosite. (B) Cl-jarosite. (C)
Br-jarosite. (D) Br,Cl-jarosite. (E) HAL-free goethite. (F) HAL-free hematite.
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Part B. Adsorption isotherms of Cl- and Br- for HAL-free -hematite, -goethite, and -jarosite
In the preliminary adsorption experiments, adsorption isotherms of single adsorbate Cl- and
Br- of the three Fe-minerals were determined before making multi-adsorbate solutions of Cl-, Br-,
SO42- and H2PO4- (results that are discussed in Section 3.3). Here, the experimental methods and
results of determining adsorption isotherms are summarized.
Experimental methods:
NaCl and NaBr adsorbate solutions (unbuffered) were prepared at concentrations of 0.5, 1,
1.5, 2, 3, 5, 7 and 10 mM. In each experiment, 25 mL of adsorbate solution were transferred to a
50 mL centrifuge tube and then 1 mL of mineral slurry (0.1 g/mL; unbuffered) was added to the
tube. These tubes were then capped and put in a water bath maintained at 25 ºC for 3 days for the
reactions to reach equilibrium (based on previous kinetic studies dealing with similar systems
[e.g., Chitrakar et al., 2006; Gao, 2001]). During the reaction period, the tubes were agitated by
hand every 24 h. At the end of each experiment, all the tubes were centrifuged and the
supernatant solutions were collected and passed through 0.2 µm filters. The pH of each solution
was measured immediately after sampling.
Results:
The adsorption isotherms of Cl- and Br- (from NaCl or NaBr solution) on HAL-free hematite, -goethite, and -jarosite are shown in Figure S2. Similar trends of uptake of Cl- or Br(in the range of 0~10 mM) were observed on all three HAL-free minerals. Uptake of Br- on the
mineral surface increased with increasing equilibrium concentrations of Br-. On the other hand,
sorbed Cl- scattered in a narrow range with increasing equilibrium concentrations, and was much
lower than sorbed Br-.
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The isotherm data were modeled using Freundlich and Langmuir equations. Cl- data were
poorly fit by either Freundlich or Langmuir models (R2 ranged from 0.55 to 0.83). On the other
hand, adsorption isotherms of Br- were better fitted with the Freundlich equation x/m = KCn,
where (x/m) is the amount of bromide adsorbed on the solid phase (mg Br/g), C is the
equilibrium bromide concentration in the solution phase (mg Br/kg), and K (mg/g) and n
(dimensionless) are Freundlich constants. The constant n refers to the interaction between
exchange sites in the adsorbent and Br- ions. A high value for n (> 1) indicates favorable
adsorption [e.g., Chitrakar et al., 2006]. Uptake of Br- on goethite is considerably higher than
that on hematite or jarosite. Freundlich isotherm constants and R2 values of isotherms of bromide
on all three HAL-free minerals are given in Table S1.
Table S1. Freundlich isotherm constants of Br- calculated for HAL-free -hematite, -goethite
and -jarosite
HAL-free
minerals
Hematite
Goethite
Jarosite
Solution
NaBr
NaBr
NaBr
Freundlich constants
K
n
13.7
1.3
985
2.2
3.94
1.0
logK
1.14
2.99
0.595
R2
0.989
0.984
0.984
* HAL-free = halogen-free.
References:
Chitrakar, R., S. Tezuka, A. Sonoda, K. Sakane, K. Ooi, and T. Hirotsu (2006), Phosphate
adsorption on synthetic goethite and akaganeite, J. Colloid Interface Sci., 298, 602-608.
Gao, Y. (2001), Surface electrical properties of goethite and adsorption of phosphate and
arsenate on iron oxyhydroxides in high ionic strength solutions, Ph.D thesis, Dept. of
Earth and Planet. Sci., McGill University, Montreal, Canada.
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Figure S2.
Figure S2. Adsorption isotherms of Cl- and Br- with (A) HAL-free hematite, (B) HAL-free goethite, and (C) HAL-free jarosite. The
initial absorbate solutions were unbuffered. Sorbed Cl- scattered over a narrow range whereas sorbed Br- increased with increasing
equilibrium concentrations.
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