Jarosite dissolution rates and nanoscale mineralogy

Madden, M. E. Elwood; Madden, Andrew S.; Rimstidt, J. Donald; Zahrai, S. K.; Kendall, Matthew R.; Miller, Matthew A.

doi:10.1016/j.gca.2012.05.001

Cited by 111 publications

(53 citation statements)

References 80 publications

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“…In Al-and Fe-phosphate precipitation experiments, Hsu (1976) demonstrated rapid formation of Fe-oxides, which they attribute to the much larger first hydrolysis constant for Fe 3+ of 2.5 × 10 -3 (Lamb and Jacques 1938), compared to the first hydrolysis constant of Al 3+ (1.05 × 10 -5 ) (Frink and Peech 1963). We therefore postulate that the non-stoichiometric dissolution of amorphous Fe-phosphate and the slow dissolution rates relative to amorphous Al-phosphate observed in these experiments may be due to the precipitation of secondary Fe-oxyhydroxide phases, similar to the findings of Huffman (1960), Siever andWoodford (1979), andElwood-Madden et al (2012), and due to the much larger first hydrolysis constant for Fe 3+ than for Al 3+ .…”

Section: Discussionsupporting

confidence: 77%

“…Elwood-Madden et al (2012) observed incongruent jarosite dissolution thought to be dependent on iron oxyhydroxide reaction products formed in solutions at pH > 3.5. Siever and Woodford (1979) described the development of a precipitated poorly crystalline Fe hydroxide layer, armoring mineral surfaces of mafic minerals such as fayalite, hypersthene, basalt, and obsidian.…”

Section: Discussionmentioning

confidence: 90%

“…(Parkhurst and Appelo 1999;Roncal-Herrero and Oelkers 2011;Elwood-Madden et al 2012) (Table 4), and was found to be undersaturated with respect to all of these minerals. As described above, the synchrotron micro-XRD and TEM analyses indicate the possible presence of goethite and bernalite in the unreacted amorphous Fe phosphates, and nano-crystalline strengite and an iron oxyhydroxide in the reacted material, with reaction progress toward strengite also indicated by the XANES results.…”

Section: Discussionmentioning

confidence: 99%

“…Saturation indices were calculated for each steady state condition using PhreeqC (Parkhurst and Appelo 1999), for strengite, variscite, goethite, hematite, maghemite, vivianite, ferrihydrite, 10 nm goethite, 10 nm maghemite, 10 nm hematite, and gibbsite using values from (Parkhurst and Appelo 1999;Roncal-Herrero and Oelkers 2011;Elwood-Madden et al 2012) (Table 1). Due to the uncertainties in the solubilities of amorphous Al-and Fe-phosphates (Roncal-Herrero and Oelkers 2011) saturation indices were not calculated for the amorphous Al-and Fe-phosphates.…”

Section: Calculationsmentioning

confidence: 99%

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Dissolution rates of amorphous Al- and Fe-phosphates and their relevance to phosphate mobility on Mars

Hausrath

Tschauner

et al. 2014

American Mineralogist

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Phosphate is an essential nutrient for life on Earth, and therefore if life exists or ever existed on Mars it may have required phosphate. Amorphous Al-and Fe-phosphates rapidly precipitate from acidic solutions and amorphous Al-phosphates likely control phosphate concentrations in some natural waters on Earth. The amorphous fraction of martian soils has also been shown to be enriched in P, and amorphous phosphates are therefore also likely important in the phosphate cycle on Mars. Despite this importance, however, few dissolution rates exist for amorphous Al-and Fe-phosphates. In this study, dissolution rates of amorphous Al-and Fe-phosphates were measured in flow-through reactors from steady state concentrations of Al, Fe, and P. A pH-dependent rate law, log R = log k -npH was determined from the dissolution rates, where R is the dissolution rate, k is the intrinsic rate constant, and n is the reaction order with respect to H + . For amorphous Al-phosphate, log k = -6.539 ± 1.529 and n = 2.391 ± 0.493. For amorphous Fe-phosphate, log k = -13.031 ± 0.558 and n = 1.376 ± 0.221. The amorphous Al-phosphate dissolves stoichiometrically under all experimental conditions measured, and the amorphous Fe-phosphate dissolves non-stoichiometrically, approaching stoichiometric dissolution as pH decreases, due potentially to Fe oxyhydroxides precipitating and armoring grain surfaces. Perhaps due to these effects, amorphous Al-phosphate dissolution rates are approximately three orders of magnitude faster than the amorphous Fe-phosphate dissolution rates measured under these experimental conditions. Amorphous Al-phosphate dissolution rates measured in this study are also faster than published dissolution rates for the crystalline Al-phosphate variscite. The rapid dissolution rates measured in this study therefore suggest that, if these phases are present on Mars, phosphate would be rapidly released into acidic environments.

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Section: Discussionsupporting

confidence: 77%

Section: Discussionmentioning

confidence: 90%

Section: Discussionmentioning

confidence: 99%

Section: Calculationsmentioning

confidence: 99%

See 2 more Smart Citations

Dissolution rates of amorphous Al- and Fe-phosphates and their relevance to phosphate mobility on Mars

Hausrath

Tschauner

et al. 2014

American Mineralogist

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“…It has been shown that ionic substitutions could alter the unit cell parameters from ideal jarosite and consequently influence the dissolution rates and solubility of jarosite [e.g., Elwood Madden et al ., ; Kendall et al ., ; Savage et al ., ]. The incorporation of weight percent levels of Br − into our Br‐jarosite and Br,Cl‐jarosite samples may significantly distort the structure and make the bonds more susceptible to being attacked during aqueous alteration and thus reduce the stability relative to halogen‐free jarosite.…”

Section: Resultsmentioning

confidence: 99%

Behavior of bromide, chloride, and phosphate during low-temperature aqueous Fe(II) oxidation processes on Mars

Zhao

McLennan

Schoonen

2014

J. Geophys. Res. Planets

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Assessing hydrodynamic effects on jarosite dissolution rates, reaction products, and preservation on Mars

et al. 2015

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Jarosite flow-through dissolution experiments were conducted in ultrapure water (UPW), pH 2 sulfuric acid, and saturated NaCl and CaCl 2 brines at 295-298 K to investigate how hydrologic variables may affect jarosite preservation and reaction products on Mars. K + -based dissolution rates in flowing UPW did not vary significantly with flow rate, indicating that mineral surface reactions control dissolution rates over the range of flow rates investigated. In all of the solutions tested, hydrologic variables do not significantly affect extent of jarosite alteration; therefore, jarosite is equally likely to be preserved in flowing or stagnant waters on Mars. However, increasing flow rate did affect the mineralogy and accumulation of secondary reaction products. Iron release rates in dilute solutions increased as the flow rate increased, likely due to nanoscale iron (hydr)oxide transport in flowing water. Anhydrite formed in CaCl 2 brine flow-through experiments despite low temperatures, while metastable gypsum and bassanite were observed in batch experiments. Therefore, observations of the hydration state of calcium sulfate minerals on Mars may provide clues to unravel past salinity and hydrologic conditions as well as temperatures and vapor pressures.

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Jarosite dissolution rates and nanoscale mineralogy

Cited by 111 publications

References 80 publications

Dissolution rates of amorphous Al- and Fe-phosphates and their relevance to phosphate mobility on Mars

Dissolution rates of amorphous Al- and Fe-phosphates and their relevance to phosphate mobility on Mars

Behavior of bromide, chloride, and phosphate during low-temperature aqueous Fe(II) oxidation processes on Mars

Assessing hydrodynamic effects on jarosite dissolution rates, reaction products, and preservation on Mars

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