As the peridotite rocks may be some distance from the desalination plant, the rationale for injecting to the rocks and not taking the MgCl2 back to sea would be to avoid the piping and pumping costs of the return journey. The Samail Ophiolite, for example, appears to be some 50 km from the coast. If however the rocks are on the surface and in close vicinity this option may be interesting. (Author) On Sunday, 1 February 2015 20:47:32 UTC, Greg Rau wrote:
> Unclear why the HCl would be injected underground. How about neutralizing > this above ground with silicates to (re)generate MgCl2 for ocean disposal > (House et al. 2007), or for thermal decomposition to MgO, addition to ocean > and hence doubling the alkalinity addition to the ocean relative to > desalination alone? However, the energy and monetary costs of doing all of > this doesn't seem to be any bargain. > Greg > > ------------------------------ > *From:* Andrew Lockley <[email protected] <javascript:>> > *To:* Renaud-KdeR <[email protected] <javascript:>> > *Cc:* [email protected] <javascript:>; geoengineering < > [email protected] <javascript:>> > *Sent:* Sunday, February 1, 2015 11:39 AM > *Subject:* Re: [geo] Re: The olivine reaction > > Attached > > > On 1 Feb 2015 18:25, "Renaud de_Richter" <[email protected] <javascript:>> > wrote: > > *Thanks to Magnesium, desalination plants could become net absorbers – > rather than net emitters – of carbon dioxide* > http://www.rsc.org/chemistryworld/2015/01/desalination-plant-carbon-dioxide-source-sink > > > Switching desalination plants from carbon dioxide source to sink > 22 January 2015 Katie Lian Hui Lim > <http://www.rsc.org/chemistryworld/more/?author=896> > > A UK researcher has proposed a new process to decompose waste > desalination brine <http://xlink.rsc.org/?doi=10.1039/c4ew00058g> using > solar energy that could allow desalination plants to act as a sink rather > than a source of atmospheric carbon dioxide, and *help to neutralise > ocean acidity*.1 > (P A Davies, *Environ. Sci.: Water Res. Technol.*, 2015, DOI: > 10.1039/c4ew00058g <http://xlink.rsc.org/?doi=10.1039/c4ew00058g> (This > paper is free to access.)) > > Approximately 30 billion m3 of freshwater is produced by desalination > each year, and this is predicted to double within the next decade > <http://www.globalwaterintel.com/market-intelligence-reports/> to meet > global demand. To combat the increased energy consumption and carbon > dioxide emissions associated with this growth in capacity, research efforts > have turned to employing renewable energy. > In the system devised by Philip Davies > <http://www.aston.ac.uk/eas/staff/a-z/dr-philip-davies/> at Aston > University, magnesium chloride in waste brine is hydrolysed by energy > generated by heliostat fields to magnesium oxide, which is discharged to > the ocean. Due to its alkaline nature, this subsequently neutralises ocean > acidity and gradually removes carbon dioxide through the conversion of > magnesium oxide to bicarbonate, similar to ocean liming, with the advantage > that the neutralising material is sourced from the seawater itself rather > than mined. Hydrochloric acid produced as a byproduct could potentially be > sequestered into silicate rocks. > Although this approach would increase the energy requirement of the plant > by 50%, Davies calculates that this is offset by the carbon dioxide > absorption capacity; each plant would remove 18,200 tonnes of carbon > dioxide per year rather than emitting 5300 tonnes. This would result in > 0.4% of anthropogenic carbon dioxide emissions being absorbed given a > doubling in the current desalination capacity. > Davies acknowledges that lowering the energy required to dewater brine > prior to decomposition would be a major benefit. ‘Not much energy is needed > to decompose magnesium chloride in brine to magnesium oxide, which makes > the use of solar energy potentially very attractive,’ he says. ‘If we could > find better ways to dewater the brine this would become very energy > efficient as a means of avoiding carbon dioxide.’ He also warns that the > effects of magnesium oxide discharge on local marine environments should be > thoroughly assessed, a sentiment echoed by Silvano Mignardi > <http://www.dst.uniroma1.it/Mignardi>, an Earth scientist at the Sapienza > University of Rome in Italy: ‘Environmental issues involved in the ocean > discharge of magnesium oxide and in the management of hydrochloric acid > have to be carefully evaluated.’ > Phil Renforth > <http://www.cardiff.ac.uk/earth/academic-staff/dr-phil-renforth/>, a > geo-environmental engineer from Cardiff University, highlights that a major > advantage of Davies’ process is that it can be appended to existing > technology. ‘This approach may allow the industry to transform itself from > a carbon dioxide villain into a force for good in the climate change > debate. > > > Le mercredi 28 janvier 2015 14:16:16 UTC+1, Schuiling, R.D. (Olaf) a > écrit : > > I think that not everybody realizes that some 300 million tons of CO2 > are captured every year by the weathering of basic silicates, notably the > most common one, olivine. To demonstrate this, the diagram below shows the > analytical data of some 20 spring water samples in olivine rocks in Turkey. > It shows what happens when rain falls on soils on top of olivine rocks. The > rainwater contains essentially only some CO2 and has a pH in the order of > 6. Then it penetrates the soil, which has much higher CO2 concentrations in > the soil atmosphere than in the atmosphere above. Dead plant material is > decaying, the soil fauna is breathing, both releasing CO2, so the CO2 > concentration of the soil atmosphere is often hundred times or more higher > than in the atmosphere. The water equilibrates with this high CO2 > concentration. Then it seeps into the rock, and reacts with it, releasing > magnesium to the solution, and the pH rises to values around 7.5 to 8.5. > This weathering reaction can be written as > > Mg2SiO4 + 4 CO2 + 4 H2O à 2 Mg2+ + 4 HCO3- + H4SiO4 (so the CO2 is > captured as bicarbonate in solution). > > At some point this water is emitted again as a spring. This spring water > is very healthy, and we often had to wait in line for the many people who > collect this spring water in containers and jerrycans to bring home. Most > of the water flows away in small brooks, and finally reaches the sea, where > the calcium and magnesium are used by plankton, corals and shellfish to > form limestones and dolomites, the ultimate sustainable storage of the CO2. > Just as an afterthought: so if we irrigate semi-arid land on top of > olivine massifs, we have a cheap way to fix CO2 by increasing the number > and the volume of springs in such rocks, Olaf Schuiling > I attach the paper in which these data were published > > \ > > > > > > > > > > > > > > > > > > > > > > > > ® > > > > Fig.1: Concentration in meq [Ca2+ + Mg2+] in spring waters. Total > carbon as mg CO2. > ® composition of rain water. > > > -- > You received this message because you are subscribed to the Google Groups > "geoengineering" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected] <javascript:>. > To post to this group, send email to [email protected] > <javascript:>. > Visit this group at http://groups.google.com/group/geoengineering. > For more options, visit https://groups.google.com/d/optout. > > -- > You received this message because you are subscribed to the Google Groups > "geoengineering" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected] <javascript:>. > To post to this group, send email to [email protected] > <javascript:>. > Visit this group at http://groups.google.com/group/geoengineering. > For more options, visit https://groups.google.com/d/optout. > > > -- You received this message because you are subscribed to the Google Groups "geoengineering" group. 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