In the preliminary experiments reported in the paper, the pyrolysed sea salts mixed with seawater were solubilised quite quickly using CO2, which I interpreted as conversion to bicarbonate. For me it seems the issue would be whether the MgO (or MgCO3 intermediate) can absorb the carbon dioxided before sinking to the ocean floor - which would depend on the particle size I guess (author).
On Monday, 2 February 2015 14:33:13 UTC, Oliver Tickell wrote: > > It look interesting, however I am unconvinced. It turns out that the > seawater acidity is lowered only by concentrating out HCl, in potentially > huge amounts. Some of this may displace existing manufacture of HCl by > chemical industry, but beyond that it's a hazardous waste. Then there is > the problem of MgO discharge: as soon as the ocean is made alkaline, that > provokes precipitation of carbonate, rather than formation of HCO3- as > solute. And then there is the increased energy use, which even if from > solar panels, might be more effectively used to displace fossil generation. > > Oliver. > > On 01/02/2015 19:39, Andrew Lockley wrote: > > 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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