Comment by nkoren | Hacker News Reader

Comment by nkoren | Hacker News Reader

I would be significantly less skeptical about this if it were significantly less ambitious.

I'm sure there are low-hanging opportunities where this makes a good amount of sense. Places where there are olivine-rich mine tailings -- somehow uncontaminated by heavy metals -- adjacent to a tropical shoreline. In those instances, then yeah, I'm sure it makes good sense to just shove them over to the beach and let decomposition do its thing.

However, pitching this as THE solution to carbon sequestration is much more problematic. At gigaton scale, you're going to run out of mine tailings quite quickly. After that, you're talking about mining fresh olivine, from locations that are increasingly distant to tropical shorelines.

This would incur tremendous energy costs, and I'm skeptical that its balance would work in favour of olivine. How much does energy is required to mine a 1,000kg of olivine? How much energy is required to move it (say) 100km to the shore? If that net energy were applied to other forms of carbon capture, would it sequester more than 1,250kg of Co2? If so, then in that instance at least, olivine sequestration would be a bad idea.

Even if the energy balance works out favourably, I'm still not sure it's a good idea. Mining doesn't just have energy impacts, it has tremendous land impacts. 7 cubic miles per year of olivine is a very large amount of material. If you don't like the local impacts of mining gold and copper and coal and shale and sand and gravel, then this would have an environmental impact similar to all of those put together. Which is too much impact. It is probably preferable to pursue a less-efficient sequestration strategy than to engage in something with this kind of side-effects.

So I'm afraid that the way this is being presented will trigger a lot of skepticism / opposition. This is a shame, because in certain edge-cases I suspect it's quite a good idea. Even if this only addresses a small percentage of the total problem, every little bit helps. I'd hate to see the baby get tossed out with the bathwater.

We are not pitching this as "THE" solution, but as "a" solution that can scale up to and beyond the global level of yearly CO2 emissions. Even after the "low-hanging opportunities" it makes a good amount of sense, as mining olivine is not difficult and there are large reserves on every continent.

You are incorrect that olivine mining at a large scale would incur tremendous energy costs, it will not. I would suggest you check out this model of a 5,000 tonne per day open pit mining for porphyritic rock. (This model also includes 5,000 tonnes per day of "waste" rock which will likely not be wasted in our use case) http://costs.infomine.com/costdatacenter/miningcostmodel.asp...

In this model, which is not in any way optimized for environmental efficiency, it requires a diesel fuel quantity of around 4,751 liters/day to mine the 5,000 tonnes. At 2.68 kg of CO2 per 1 liter of diesel, that generates 12,732.68 kg of CO2 per day. That 12,732.68 kg = 12.73268 tonnes of CO2. The 5,000 tonnes of olivine mined will eventually weather and sequester 6,250 tonnes of CO2 (1 tonne of olivine sequesters 1.25 tonnes of CO2), for a net capture of 6,237 tons at the mine.

We have life cycle assessment that calculates the CO2 penalty and loss on efficiency, including milling and transport to locations less than 300 km (186 mi) at around a 4% loss [1].

Just for your information and for others, from a financial perspective the mining in that model costs $7.32 per ton, and then the transport and milling/crushing only costs about $3 per ton, so olivine could be transported to a beach at around $10/ton, with the price per ton of CO2 sequestered at less than $10.

You are also incorrect regarding the mining impact. The mining of things like shale requires fracking and the injection of sand and chemicals, our mining is simply open pit. Essentially, you open a pit on the surface and simply dig it up. As mentioned above, it is not all that energy intensive either.

For global CO2 level removal in terms of mining, it would likely require 30-50 mines in the wet tropics, preferably at a level of greater than 100 million tons/year (due to economies of scale).[2] There are large reserves on every continent and plenty near coastlines[3]. If you wanted to open fewer mines, you could theoretically find a few large reserves. For example, there is an open pit mine in Bingham Canyon that has an excavated volume of over 25 km^3, which would be the equivalent of 2-3 years worth of the volume of material needed.

Don't worry about this idea getting "tossed out with the bathwater," if anything we will actually be removing CO2 from the bathwater and de-acidifying it at the same time ;)

[1] Environmental Life Cycle Assement of CO2 Sequestration Through Enhanced Weathering of Olivine https://projectvesta.org/science/#dflip-df_978/1/ [2] https://projectvesta.org/science/#dflip-df_77/9/ [3] https://projectvesta.org/science/#dflip-df_90/25/

This is a great response, thank you. It seems like one issue with climate change is that the scale of the problem is so large, any significant mitigation sounds intuitively unrealistic. It's clear that you've put a lot of work into looking at the whole picture though, and I'm excited to hear more results as you scale up pilot testing.

4% loss of what? I’m not following.

When 1 tonne of olivine weathers, the chemical reaction removes 1.25 tonnes of free CO2 from the environment in terms of stoichiometry. However, in the process of mining, milling, and transporting that olivine to that beach, we emit approximately .05 tonnes of CO2 ourselves. That .05 of a tonne is 4% of the 1.25 tonnes of CO2 that was removed in the weathering process. So, in a CO2 life cycle assesment of net emissions, that considered the "loss."

i.e. it’s like a slot machine where you pay $0.05 and then get E[Y] = $1.25 back (in carbonbucks). Sounds like a great deal vs. 4% loss (and a fast way to pay off carbon debt).

How does this compare to the lifecycle net efficiency of other methods of carbon capture/abatement, e.g. wind turbines, nuclear solar panels/farms, EVs, afforestation? Any references for such estimates?

Thanks for responding to my criticism and taking it seriously! The energy costs for this are indeed a lot less than I had imagined. I've seen plenty of appealing sequestration concepts where the numbers definitely don't work out, so I appreciate you doing the math on this!

I would push back, however, on the land impacts of mining. Open-pit mining is exactly what I was referring to, and it doesn't have a good reputation with me. I have encountered many open-pit mining projects which were extremely destructive with regards to habitat, watersheds, groundwater, etc. (Arguably much moreso than things like fracking, TBH.) A massive increase in open-pit mining therefore sets off significant alarm bells for me.

Now, it's possible that I'm suffering from selection bias here: I only hear about open-pit mines when they're bad, and when they're benign they sail right under my radar. Maybe, on average, they're fine.

But that's not the kind of thing I'd take on faith. What would convince me is a site-specific Environmental Impact Report which illustrates how a 100MT/year olivine mine could operate without causing severe regional damage.

https://en.wikipedia.org/wiki/Glensanda This super quarry is in a very scenic area of the west coast of Scotland and supplies 6M tons of granite aggregate yearly and apart from the quay you would not know it is there, so it can be done reasonably sensitively.

That's a really interesting and well-done mine -- thanks for introducing it to me!

This project proposes mining at a scale that is cumulatively about 8,000 times greater than Glensanda. But if they could all be done so sensitively, then indeed, perhaps it could work.

I've still got a lot of cognitive intertia about the impact of open-pit mining, and would definitely need more convincing about this. But I'd be open to being convinced.

Interesting so land area of world / 8000 gives 1 Glensanda per 18600km2. Area of UK is 242000km2 so we would need about 13 Glensanda sizes quarries in the UK. Of course it would be fairer if were weighted by amount of harm done to the climate per country, so we should have more per km2 than an undeveloped country, but even so doesn't seem like that large an impact.

I don't think land area is the metric to use here. Quaries need to be located close to the coast, in order to minimise shipping costs. There's a lot of land in the interior of continents which would not be suitable for this kind of operation.

So probably a better metric is total length of coastline. The UK has 12,429km of coastline, out of a world total of 356,000. So that would imply 279 Glensanda-sized quaries in the UK.

Good news for the UK (and bad news for everyone else): weighting by amount of harm done to the climate wouldn't work. In addition to being located near coastlines, the quarries need to be located in tropical and subtropical regions. So in fact there wouldn't be any quarries in the UK.

Looking at this source: http://chartsbin.com/view/ofv, it appears that there's about 275,000km of suitable coastline. The top 3 countries would be: Indonesia (1,592 Glessandas), Phillipines (1,056 Glessandas), and Australia (749 Glessandas). I'm not sure whether or not that's feasible. But at a smaller scale, as a partial solution to sequestration, it seems within reach.

Are there underwater/ocean floor sources you could mine/release into the ocean?

Indeed as Eric explaines, this isn't "THE" solution. We will need a portfolio of solutions. Of which mineralization of one of them. And all bigger projects need good guidance. Pol Knops

I would be less skeptical if they weren't selling jewelry.

It's a shame because the responses given here on HN seem well thought out, yet the site gave me the impression of making a quick buck on peridot necklaces. I mean, is that really going to fund anything meaningful?

Reply on news.ycombinator.com