Re: [geo] Enhanced weathering of olivine in seawater: The efficiency as revealed by thermodynamic scenario analysis - ScienceDirect

2018-02-03 Thread Renaud de RICHTER 
This article was available online since 16 September 2016
The approach is said as "* independent from local or regional factors as
temperature, related kinetics, mineralogy, etc. * ".

Seems neither to take into acount the real world, biology and numerous
existing siderophores existing in solution: "*When Fe-bearing olivine
undergoes weathering in an oxic environment, Fe(III) hydroxides will
inevitably be formed, and as a result of this acidifying process, CO2 could
be released to the atmosphere*. "




2018-02-02 21:41 GMT+01:00 Andrew Lockley :

> https://www.sciencedirect.com/science/article/pii/S0048969716319258
>
> Science of The Total Environment
> 
> Volume 575
> , 1
> January 2017, Pages 536-544
> 
> Enhanced weathering of olivine in seawater: The efficiency as revealed by
> thermodynamic scenario analysis
> Author links open overlay panelJasperGriffioen
> 
> Show more
> https://doi.org/10.1016/j.scitotenv.2016.09.008Get rights and content
> 
> Under a Creative Commons license
> 
> open access
> Highlights
>
> •
>
> Measures may be needed to lower the atmospheric CO2level and combat
> climate change as well as ocean acidification
> •
>
> Enhanced weathering of olivine in marine environment is such a measure
> •
>
> The efficiency of olivine weathering depends on the Mg/Fe fractions of
> olivine and precipitation of secondary minerals or not
> •
>
> For Fe-rich olivine, CO2 may be released to the atmosphere and ocean pH
> might decrease during oxic olivine weathering
> Abstract
>
> Enhanced weathering of olivine has been suggested as a measure to lower
> the atmospheric CO2 level and it might also mitigate ocean acidification.
> This study aimed to characterise how olivine can weather in seawater, to
> elucidate the role of secondary precipitation and to ascertain the
> efficiency in terms of molar CO2 removal per mole of olivine dissolution.
> Geochemical thermodynamic equilibrium modelling was used, which considered
> both the variable mineralogical composition of olivine and the kinds of
> secondary precipitates that may be formed. The advantage is that such an
> approach is independent from local or regional factors as temperature,
> related kinetics, mineralogy, etc. The results show that the efficiency
> falls when secondary precipitates are formed. When Fe-bearing olivine
> undergoes weathering in an oxic environment, Fe(III) hydroxides will
> inevitably be formed, and as a result of this acidifying process, CO2 could
> be released to the atmosphere. This might also enhance ocean acidification
> when Fe-rich olivine becomes used. Ocean alkalinisation only happens when
> more than 1 mol/kgH2O Mg-rich olivine weathers. Maintenance of
> supersaturation for calcite or aragonite as holds in seawater reduces the
> efficiency by about a factor of two compared to the efficiency without
> secondary precipitation. Precipitation of sepiolite as Mg silicate reduces
> the efficiency even more. Magnesite precipitation has a similar effect to
> Ca carbonate precipitation, but according to the literature magnesite
> precipitation is improbable at ambient conditions and relatively low
> supersaturation. When less than 0.05 mmol olivine/kg(seawater) weathers the
> efficiency is slightly different than at higher intensities, due to strong
> buffering by seawater alkalinity.
>
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[geo] Enhanced weathering of olivine in seawater: The efficiency as revealed by thermodynamic scenario analysis - ScienceDirect

2018-02-02 Thread Andrew Lockley 
https://www.sciencedirect.com/science/article/pii/S0048969716319258

Science of The Total Environment

Volume 575
, 1
January 2017, Pages 536-544

Enhanced weathering of olivine in seawater: The efficiency as revealed by
thermodynamic scenario analysis
Author links open overlay panelJasperGriffioen

Show more
https://doi.org/10.1016/j.scitotenv.2016.09.008Get rights and content

Under a Creative Commons license

open access
Highlights

•

Measures may be needed to lower the atmospheric CO2level and combat climate
change as well as ocean acidification
•

Enhanced weathering of olivine in marine environment is such a measure
•

The efficiency of olivine weathering depends on the Mg/Fe fractions of
olivine and precipitation of secondary minerals or not
•

For Fe-rich olivine, CO2 may be released to the atmosphere and ocean pH
might decrease during oxic olivine weathering
Abstract

Enhanced weathering of olivine has been suggested as a measure to lower the
atmospheric CO2 level and it might also mitigate ocean acidification. This
study aimed to characterise how olivine can weather in seawater, to
elucidate the role of secondary precipitation and to ascertain the
efficiency in terms of molar CO2 removal per mole of olivine dissolution.
Geochemical thermodynamic equilibrium modelling was used, which considered
both the variable mineralogical composition of olivine and the kinds of
secondary precipitates that may be formed. The advantage is that such an
approach is independent from local or regional factors as temperature,
related kinetics, mineralogy, etc. The results show that the efficiency
falls when secondary precipitates are formed. When Fe-bearing olivine
undergoes weathering in an oxic environment, Fe(III) hydroxides will
inevitably be formed, and as a result of this acidifying process, CO2 could
be released to the atmosphere. This might also enhance ocean acidification
when Fe-rich olivine becomes used. Ocean alkalinisation only happens when
more than 1 mol/kgH2O Mg-rich olivine weathers. Maintenance of
supersaturation for calcite or aragonite as holds in seawater reduces the
efficiency by about a factor of two compared to the efficiency without
secondary precipitation. Precipitation of sepiolite as Mg silicate reduces
the efficiency even more. Magnesite precipitation has a similar effect to
Ca carbonate precipitation, but according to the literature magnesite
precipitation is improbable at ambient conditions and relatively low
supersaturation. When less than 0.05 mmol olivine/kg(seawater) weathers the
efficiency is slightly different than at higher intensities, due to strong
buffering by seawater alkalinity.

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