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]> >To: Renaud-KdeR <[email protected]> >Cc: [email protected]; geoengineering <[email protected]> >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]> 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 >>A UK researcher has proposed a new process to decompose waste desalination >>brine 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 (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 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 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, 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, 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 à2 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]. >>To post to this group, send email to [email protected]. >>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]. >To post to this group, send email to [email protected]. >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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