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DWol

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Cape Town

Ah very cool... This set me off on the right track. I think I found an inductive type explanation which I will try to go through.

So supposing we find ourselves in a given state, there is a chance, p, that we will transition to the other state and hence end up with length of 1. On the other hand there is 1-p chance that we will stay, and have a length 1 + L' where L' is the length of whatever happens after that. So the length, L, of our sequence is then:

``  L = 1(p) + (1-p)(1+L')``

But L' is just the next iteration of the same kind of process that produces L, and so their expected values should be the same, so L = L' leaving:

``  L = 1/p``

Which gels with what I found above... But on the other a little learning is a dangerous thing so I am not 100% confident that it is up to scratch.

Incidentally, my class was the last set who did not have intro statistics as a core course... Instead we did electromagnetism, used approximately never in the rest of the curriculum. Meanwhile statistics knowledge is something we had to cobble together over time as required. Each time the activation energy of finding a textbook and doing it properly from the start was just a little bit too high for what was at stake. It makes me wonder about the different roles of structured or formalised learning compared to figuring it out yourself. Knowing where to start looking is one of the big types of knowledge that a curriculum affords you I think.

Considering the circumstances, now is probably as good a time as any to bury the hatchet and dive into khanacademy or whatever. Personally that is probably what I will do as this has felt like a big hole in my competency for a while now. But on a general level, I wonder about when the right way is to dive in, mess around, fail, learn by doing etc. vs. deciding that you should rather let someone else guide the process, even if it means starting at a very basic level. I'm sure we go back and forth between these, and it's probably not meaningful to try and say that there is a "optimum" way...

In principle, yes. But it's probably not economically viable. Rare earth oxide prices are in the range of 10-100 USD per kilo. Platinum and gold go for ~1000 USD per ounce. Of course the tailings grades will be different but as far as I know these are the only metals which have gone through significant tailings reprocessing efforts. In SA that's also mainly because they had loads of material that had been mined 100 years ago when recovery was lower. I think copper might also reprocessed in a few places but I would guess only via heap leaching (stick in some plumbing and irrigate your dump with acid).

Interesting. I have a few thoughts.

Rare earth elements are currently sourced essentially from two distinct mineralogies: hard rock mining from igneous intrusions with the rare earths contained in e.g. bastnaesite and monazite (such as Bayan Obo in Inner Mongolia and Mountain Pass in California), and from ion absorption clays (for reasons above my pay grade these only occur in the subtropical belts hence their prevalence in southern China).

These two ores have some important distinguishing characteristics. Firstly, the hard rock ores tend to be enriched in the so-called "light" REEs (e.g. lanthanum, cerium) whereas the clays are somewhat enriched in the "heavy" REEs (e.g. lutetium, yttrium). They also have very different processing methods. Hard rock ores are processed in a more conventional way, via grinding/milling the ore, floating the valuables and then sequentially removing elements using solvent extraction. With maybe leaching in there somewhere... This is more or less similar to processing for the precious metals but as I understand it the large number and chemical similarity of the REEs makes this more resource intensive. On the other hand, in the clay ores the REEs are already in the free ionic form and are flushed out via ion exchange in heaps or vats.

Both of these processing methods are pretty nasty but one falls under the remit of large state-controlled enterprise and the other can be done by a dude with a spade and a vat full of salt water. So it's no surprise that there is a large unregulated industry around the processing of these clays, which is in turn responsible for some seriously hellish mining landscapes and environmental degradation. The Chinese government is apparently cracking down on that sort of thing which I can only imagine involves a lot of authoritarian police state tactics.

Coming back to the article, I wasn't entirely sure at what part of the above processes this advancement would fit in. The paper they are referecing seems to have used spent ceria polishing powder and lutetium crystal waste as the feedstock for their experiments (i.e. already very pure in terms of REE content). So it appears that this applies to the extraction phase - they first had to go through an alkaline roast and HCl dissolution before using the new solvent. This doesn't really enable making a big difference to the overall production process. In the conventional mining case, it will still need to produce masses of somewhat radioactive tailings, require massive amounts of energy to grind the ore and so on. Similar situation for the clay mining. It's an unfortunate reality that the amount of value added in a processing step tends to be inversely proportional to the environmental impact associated, and this technology seems to be acting on the end of the pipe.

DWol  ·  879 days ago  ·  link  ·    ·  parent  ·  post: Bitch Session #1: Technology Lows

This might be something that can help you? I.e. installing the apk directly and sidestepping Google Play which is what I assume is in your way...

DWol  ·  908 days ago  ·  link  ·    ·  parent  ·  post: Pubski: July 25, 2018

Hey, just a quick one as I'm on my phone: this is probably mad overkill but I can't help thinking that this is a good use case for many of the techniques mining exploration people use for mapping geological features (exploration geophysics).

It's not my personal focus but I think you'd have a good chance of finding the pipe using ground-penetrating radar or electrical resistance tomography (where I live the domestic sewer pipes are plastic but maybe you might have luck with a metal detector too). Some guys that I work with spent some time trying to use these to do realtime crevasse detection and I believe it's the same technique used for archaeological surveys. Whether it's a commercially available service with a reasonable price tag I'm not so sure.

Anyway as I said it's probably overkill but it immediately popped into my head so I thought I'd share. Cheers.

DWol  ·  997 days ago  ·  link  ·    ·  parent  ·  post: One small passage from "No Future Without Forgiveness" that really stands out to me.

I think it speaks volumes that even a group of people with a single goal in mind and the best of intentions in their hearts have to struggle in such a way. I think it speaks volumes as to why sometimes society seems really messed up.

Don't really think I have much insightful to say, but this thought up here is important. The question I am left asking is whether we are doomed to this? Will things get better in my lifetime? I heard someone say once that as a first pass estimate, it takes about as long for conflict to be resolved as the conflict had been going on in the first place. In SA that means we are only about 10% of the way there, according to the consensus for when the shit hit the fan.

I think the Arch is right in saying there's no future without forgiveness, but these days one has to wonder whether forgiveness has any value if it was given for free. 24 years is sadly enough time for us to collectively begin to forget the past, with the result being that no-one really knows what they gave away or gained anymore. It's a bad place to be because it means that now we can't even agree that we "have the same goal in mind". The irreversibility of that lost opportunity is honestly the saddest part for me.