Thanks. Indeed, Schuiling and de Boer* did a flask study but only measured olivine effects on tap water pH. Seawater was not used, DIC and alkalinity were not measured, nor were controls done. As far as I know the other relevant papers on marine silicate CDR simply model dissolution rates using various assumptions. While I may be missing something, it would seem that discussion of marine silicate CDR potential would benefit from some carefully controlled and measured lab and field experiments using well characterized seawater and silicate mineral(s).
Greg * http://www.earth-syst-dynam-discuss.net/2/551/2011/esdd-2-551-2011-print.pdf "Three Erlenmeyer flasks were filled with 250 ml tap water and 30 g olivine from Norway with a grain size of 0.71–1.4 mm and three others with 250 ml tap water and 30 g olivine 20grit (2–5 mm) from Turkey. A third experiment was carried out with a 50/50 mixture of both. The Erlenmeyer flasks were put on a table top rotary shaker, so that the grains kept rotating along the bottom. The Erlenmeyers were open to the air, permitting CO2 exchange. In all cases the tap water had an initial pH of 8.22, and the olivine grains had been washed to remove any attached dust. 554 3 Results Grains of both sizes became visibly rounded (Fig. 1). The abraded fine material caused the water in the bottles with fine-grained olivine to be cloudy. In the bottles with coarse- grained olivine the water was a milky white, opaque suspension (Fig. 2). Already after 56 h the pH had risen to 8.82 in one bottle with coarse-grained olivine. After 1, 4 and 10 days the pH in one of each of the two series of bottles was measured. In a bot- tle with fine-grained olivine the pH had risen to 8.91 after 24h, and in a bottle with coarse grains to 9.02 (Table 1). This implies that the coarse grains had produced more slivers than the finer grains, likely due to their greater mass and consequently heavier 10mutual impacts. In this experiment the olivine reacted with a limited, fixed amount of water. Thus, logically the accumulation of reaction products slowed down and even- tually stopped the reaction (Table 1), contrary to shallow marine settings where water refreshment is continuous and the tiny slivers, together with the dissolved magnesium and silica, are carried away. 15Figure 3 shows the grain size distribution of the material that was scraped oð the grains in the test with 50/50 coarse and fine grains. The amount of scraped oð material was 9 g (30 %), considerably more than the amounts in the single grain size experi- ments which were slightly over 1 g in the separate fine and coarse fractions. The pH in the 50/50 mixture rose to 9.42 in 12 days. About 50wt% of the abraded particles 20is 5 μm or less (Figs. 3 and 4). Such fine grains of olivine weather fast, as is evident from the rapid rise of pH during the experiments. The rate of solution may have been further increased by the deformation that grains undergo when they are strained. The phenomenon of enhanced dissolution of fine particles by repeated particle impact and rubbing is well known in the field of mineral processing, where it is called mechanical 25activation (Tromans and Meech, 2001)." >________________________________ > From: Parminder Singh <psing...@gmail.com> >To: geoengineering@googlegroups.com >Cc: andrew.lock...@gmail.com; gh...@sbcglobal.net >Sent: Tuesday, September 30, 2014 10:59 PM >Subject: Re: [geo] Natural olivine beaches > > > >Hi, > >Schuilling carried out experiments where modest surf action was imitated by having olivine grains rotate slowly along the bottom of an Erlenmeyer, the water turned an opaque white after a few days of rotation, the pH of the solution had gone up, and many of the slivers had already turned into neoformed grains of brucite, a mineral known to carbonate fast. > >As for beaches you can find them in Hawaii, Turkey, Galapagos Is. just a few >to mention. > >Regards, > >Parminder > >On Wednesday, October 1, 2014 11:19:31 AM UTC+8, Greg Rau wrote: >Agree that the silicate mineral sand idea needs testing. I'd first start in >the lab with a flask of freshly ground olivine in chemically well >characterized, sterile seawater. I would then put this on a shaker table in >the dark and let the sand and water gently slosh back and forth for a few days >and then measure the SW alkalinity and DIC again. this would give you and >idea of the efficacy and kinetics under ideal conditions. Measuring this in a >beach setting would be trickier, but possible. My guess is that there are >synergies with sediment respiration/microbes that hasten silicate weathering. >Add in some fresh sediment to the above flask and see what happens. >> >> >>Greg >> >> >> >>>________________________________ >>> From: Andrew Lockley <andrew....@gmail.com> >>>To: geoengineering <geoengi...@googlegroups. com> >>>Sent: Tuesday, September 30, 2014 11:28 AM >>>Subject: [geo] Natural olivine beaches >>> >>> >>> >>>Hi >>>The proposal for olivine weathering on beaches seems to pass a common sense >>>test. >>>However, there's been a lack of detailed discussion about the occurrence and >>>function of natural olivine beaches, as far as I'm aware. >>>There are a lot of beaches in the world. Olivine is pretty common. How much >>>of a sink is natural beach chemical and mechanical weathering of olivine? >>>It should be easy to find at least one location where there's massive >>>quantities of olivine sand, and take detailed measurements on the carbon >>>sink. >>>I know there's at least one such beach in the literature, but I can't recall >>>discussions of others, nor detailed quantitative research on erosion and >>>sequestration rates at this site >>>Can someone enlighten me as to why this has seemingly been overlooked for >>>detailed study? >>>A -- >>>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 geoengineerin...@ googlegroups.com. >>>To post to this group, send email to geoengi...@googlegroups. com. >>> >>>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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