Magnesium hydroxychloride: A possible pH buffer in marine evaporite brines?

Bodine, Marc W.

doi:10.1130/0091-7613(1976)4<76:mhappb>2.0.co;2

Cited by 16 publications

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“…Equilibrium thermal decomposition of magnesium hydroxychlorides was also studied by Kelly and Kassner along with many others. [14][15][16][17][18][19] In particular, it was found that under equilibrium conditions, pure, solid MgOHCl decomposes to HCl and MgO at a temperature above 533 °C (806 K). [12,20] [1]…”

Section: Literature Reviewmentioning

confidence: 99%

MgOHCl thermal decomposition kinetics

Kashani-Nejad

Harris

2005

Metall Mater Trans B

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Experiments to determine the kinetics of the thermal decomposition of MgOHCl were performed. It was found that the decomposition of MgOHCl commenced at 649 K, and it directly converted into MgO and HCl without undergoing any intermediate step. Decomposition vs time data showed that the thermal decomposition of MgOHCl was a first-order process with respect to the amount of MgOHCl remaining, and the mass transfer of the product HCl gas away from the interface was likely the ratelimiting step. It was also found that the time required to completely decompose MgOHCl into MgO, more than 20 minutes, at the operating temperatures of electrolytic magnesium production processes, 600 °C Ϯ 50 °C, was significantly longer than the time required, less than 1 minute, to digest the solid magnesium chloride containing feed material into the molten salt electrolyte in these processes. Such delay in the decomposition would mean that any MgOHCl produced during heating and digestion of the feed would not be decomposed by the heat of the electrolyte and thus the persistent MgOHCl would dissolve into the molten salt electrolyte with potentially severe negative consequences on electrolysis cell operation.

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Section: Literature Reviewmentioning

confidence: 99%

MgOHCl thermal decomposition kinetics

Kashani-Nejad

Harris

2005

Metall Mater Trans B

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“…The potential, geochemical importance of magnesium chloride hydroxide hydrates was realized in the 1970s, as Bodine (1976) suggested that phase 3 may buffer pH in marine evaporites. Furthermore, their geochemical importance becomes more prominent, as phase 5 and phase 3 have bearing on the geochemical conditions of geological repositories for nuclear waste disposal in salt formations.…”

Section: Introductionmentioning

confidence: 98%

Experimental determination of the solubility constant for magnesium chloride hydroxide hydrate (Mg3Cl(OH)5·4H2O, phase 5) at room temperature, and its importance to nuclear waste isolation in geological repositories in salt formations

Xiong

Deng

Nemer

et al. 2010

Geochimica et Cosmochimica Acta

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“…The K sp for magnesium hydroxide is 1.25 Â 10 À11 at 25 1C. 110 This implies that as the aqueous film becomes increasingly basic during the OH reaction with chloride ions, hydroxide ions will become sequestered as solid Mg(OH) 2 and then as Mg 2 (OH) 3 Cl Á 4H 2 O. Another potential contributor to sequestering base is the uptake of CO 2 and formation of magnesium carbonate.…”

Section: Resultsmentioning

confidence: 99%

A new approach to studying aqueous reactions using diffuse reflectance infrared Fourier transform spectrometry: application to the uptake and oxidation of SO2 on OH-processed model sea salt aerosol

Shaka

Robertson

Finlayson-Pitts

2007

Phys. Chem. Chem. Phys.

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A new approach to studying aqueous reactions using diffuse reflectance infrared Fourier transform spectrometry: application to the uptake and oxidation of SO2 on OH-processed model sea salt aerosol. Diffuse reflectance infrared Fourier transform spectrometry (DRIFTS) is a powerful technique for analyzing solid powders and for following their reactions in real time. We demonstrate that it can also be applied to studying the uptake and reactions of gases in liquid films. Within the DRIFTS cell, a 10% (w/w) mixture of MgCl 2 Á 6H 2 O in NaCl was equilibrated with air at 50% RH, which is above the deliquescence point of the magnesium salt but below that of NaCl. This mixture of NaCl coated with an aqueous magnesium chloride solution was then reacted with gas phase OH to generate hydroxide ions via a previously identified interface reaction. This treatment, hereafter referred to as OH-processing, was sufficient to convert some of the magnesium chloride to Mg(OH) 2 and Mg 2 (OH) 3 Cl Á 4H 2 O, making the aqueous film basic and providing a reservoir of alkalinity. Subsequent addition of SO 2 to the basic processed mixture resulted in its uptake and conversion to sulfite which was measured by FTIR. The sulfite was simultaneously oxidized to sulfate by HOCl/OCl À that was formed in the initial OH-processing of the salt. Further uptake and oxidation of SO 2 in the aqueous film took place when the salt was subsequently exposed to O 3 . These studies demonstrate that DRIFTS can be used to study the chemistry in liquid films in real time, and are consistent with the hypothesis that the reaction of gaseous OH with chloride ions generates alkalinity that enhances the uptake and oxidation of SO 2 under these laboratory conditions.

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Magnesium hydroxychloride: A possible pH buffer in marine evaporite brines?

Cited by 16 publications

References 0 publications

MgOHCl thermal decomposition kinetics

MgOHCl thermal decomposition kinetics

Experimental determination of the solubility constant for magnesium chloride hydroxide hydrate (Mg3Cl(OH)5·4H2O, phase 5) at room temperature, and its importance to nuclear waste isolation in geological repositories in salt formations

A new approach to studying aqueous reactions using diffuse reflectance infrared Fourier transform spectrometry: application to the uptake and oxidation of SO2 on OH-processed model sea salt aerosol

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