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Comment by stareatgoats | Hacker News Reader

> The team also continues to look at the possibility of extracting other, lower-concentration materials from the brine stream, he says, including various metals and other chemicals

Lithium from desalination brines seems to be one potential (and promising) such [0], environmentally better in more than one way than the current methods of lithium mining [1].

[0] https://www.researchgate.net/publication/313372304_Towards_l...

[1] https://www.wired.co.uk/article/lithium-batteries-environmen...

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For a long time, bromine was an important product made from brine. But that market has fallen away, since the lions share used to be made into lead scavengers for leaded petrol. The bromine works at Amlwch on Anglesey closed in 2004: https://www.octelamlwch.co.uk/

The other obvious product would be magnesium, but they didn't isolate magnesium chloride at the bromine plant. The Wylfa nuclear power station was nearby, and Rio Tinto had an aluminium smelter nearby to provide a base load. Since magnesium is oftentimes produced through electrolysis a magnesium plant would have made sense, but somehow they didn't build one, likely for economic reasons.

You can also extract uranium from seawater, and use it to fuel nuclear reactors, and use the nuclear reactors to power your desalination.

Do you get enough volume for this to work? My intuition would be the levels of Uranium would be low enough that it would not be energy positive. Do you have more information about this process?

I remember some projects going on at MIT on this topic.

https://dspace.mit.edu/handle/1721.1/111821

Energy consumption of reverse osmosis is about 4kWh/t. The byproduct is a ton of brine. Sea water contains about 3ppb Uranium, so our brine contains 6mg of U per ton of fresh water produced.

A 1GW nuclear power station consumes about 1t of U per year and produces about 8000GWh of electricity in that time. So we need about 1mg/8kWh. We got 12 times that much.

So, it sort of works out. Of course, this assumes a breeder reactor and I pretended that brine is purified uranium. If breeders are commercialized, it might be worth looking into this. Right now, it isn't.

Awesome, thanks!

Nice analysis. But the premise of the discussion here is that people do the desalination for its own sake, not in order to harvest Uranium.

This [1] article from 2012. It presents a Uranium extraction method from seawater that would put the extraction cost at $300/kg. Nowadays the market price is about $70/kg. However, if method were to be applied to brine instead of regular seawater, maybe the cost would go down. Hard to see it going down by a factor of 5 though.

[1] http://large.stanford.edu/courses/2012/ph241/ferguson2/

I think you overestimate the energy in uranium. 8000GWh per tonne and year would be 28.8 TJ/kg, while the numbers I have seen is more like 0.7 TJ/kg (http://www.plux.co.uk/energy-density-of-uranium/).

What part of "this assumes a breeder reactor" did you not understand?

Oh I missed that!

So 4kWh/t is used to desalinate 2 tons of seawater that turn into 1 ton of freshwater and 1 ton of brine?

Googling a bit: it takes about 13 MJ to desalinate 1 m^3 of water by reverse osmosis. Seawater contains 3mg uranium per m^3, which gives 2 MJ, So it's not energy positive.

2/3rds power rebate on your desalination ain’t bad!

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