Table Top Shaker Experiment Grian-on-Grain Collisions


A very basic experiment with a tabletop shaker can demonstrate the weathering rate of olivine and show how the tumbling motion creates small particles, that themselves weather faster. There are other factors of an open-air, tropical beach with tumbling that, can further accelerate the process, such as a constant refreshing of warm water and the presence of marine animals.

Erlenmeyer flasks were put on a table top rotary shaker so that the grains kept rotating along the bottom. The flasks were open to the air, permitting CO2 exchange. Three different grain sizes were used, the images below show coarse grain sizes. The tap water had an initial pH of 8.22, and the olivine grains had been washed to remove any attached dust.

Olivine Before Desktop Weathering Experiment

Coarse (2-5mm) olivine grains in clear water, with a pH of 8.22 at the start of the experiment.

Olivine After 10 Days of Weathering

The shaking process caused the olivine to break into fine pieces and caused the water to become cloudy. After 6 hours the pH had risen to 8.82 and after 24 hours, the pH had risen to 9.02.

The flasks with the coarse olivine were cloudier and had a higher pH, which shows that coarser grains produce more slivers than the finer grains, because of their greater mass and heavier impacts. This type of experiment shows that any calculations that do not take into account the importance of grain-to-grain collisions on weathering rate are not applicable to our plan for accelerated weathering on beaches.

Further, the full weathering rate was limited here by the lack of refreshing the water. A build-up of reaction products causes a significant slowdown in weathering. Most criticisms of the concept of enhanced weathering make their calculations based on stationary olivine. They do not take either grain-on-grain collisions or the refreshing of water into account.

Therefore, papers that attempt to comment on the feasibility of accelerated silicate weathering, all incorrectly calculate the olivine weathering rate. This includes papers such as those of Lal (2008), Hangx and Spiers (2009), Köhler et al (2010), Pronost et al. (2011) and others. Their rates are not applicable to our project because they do not make calculations that take into account the effects of motion on the silicate coatings, grain-on-grain collisions, warm temperatures, marine animal usage of olivine, and/or the refreshing of water.

Last updated on May 18, 2020
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