[macinjosh]

Ok, hear me out. If stripping these minerals from the land had a negative impact wouldn’t stripping them from ocean water (which is the medium containing life, unlike ore) may also have negative consequences?? Seems to me like a pretty drastic alteration of ocean water chemistry in the long term. What if animal biology expects the magnesium to be available?

[danans]

That's true if the minerals extracted are consumed completely.

Metals however, are often the most recyclable materials we use, because unlike carbon-based materials like plastics, metals often have useful properties in their elemental state, or as alloys that can be melted down and reused without the loss of those properties or of much material.

Most aluminum, for example is recycled, because the cost of recycling it is lower than the cost of mining new material.

[throwaway4aday]

The concern isn't that we'll completely deplete the ocean, that would be a monumental task. The worry is about what happens at the "mining" sites. Those are going to be in continuous operation for a long time.

[danans]

Assuming that the magnesium is coming from the seawater and not the seabed, would we not expect currents to re-balance the concentration? In fact, we would design the facilities to ensure that it happened.

[throwaway4aday]

Correct, the question that should be asked here is what happens to all of the water after we've removed the minerals we need from it? Do we just pump it back into the ocean? The outlet would need to be far enough away from the inlet to avoid dilution. What impact does that have on marine life? We know that concentrating those minerals into brine when we extract water through desalinization is harmful so how harmful is doing the opposite and depleting the water of the minerals?

Also, those intakes for water are going to be massive. How are we going to make them fish safe? Dolphin safe? Plankton safe? This is a major problem in hydroelectric dams.

Third, what's providing power for this process and where is it located?

Fourth, what are the second order effects of replacing a lot of steel production? Will this make all of the remaining products where steel can't be replaced a lot more expensive? I doubt you can use magnesium as a replacement for the girders used in buildings. Magnesium is only as strong as mild steel so pretty much everything that requires any tensile strength will still need to use steel.

[yellowapple]

My idea is to combine this with desalination. California could permanently end its droughts and become a major magnesium supplier in one swell foop.

[throwaway4aday]

You'd also need to think up good uses for the sodium chloride or dump it somewhere. The sulfate, potassium and calcium would probably be useful if they could be easily separated but the sodium and chloride ions are by far the majority and are not going to be profitable in comparison to the current operations we use to obtain them.

[yellowapple]

> You'd also need to think up good uses for the sodium chloride or dump it somewhere.

Okay, so California ends its drought permanently and becomes a major supplier of magnesium and table salt.

Slightly-less-facetiously: sodium chloride has all sorts of industrial uses (on top of its culinary uses). The good uses are, in other words, already thought up in droves.

Further, most salt production already entails taking seawater and pulling out the water. Ain't too much of a stretch to, you know, actually keep the water instead of letting it evaporate into the atmosphere.

[jillesvangurp]

Eh no. Oceans are big. Really big. Unbelievably big even. We're talking about filtering tiny fractions of ocean water, and nowhere close to all of it. Literally a drop in the ocean in comparison.

So, no. This is not a serious concern.

[IntrepidWorm]

Speaking strictly of mineral removal this rings true. However, processing large volumes of seawater can still have a detrimental effect on the local ecosystem, because pumping large volumes of seawater is extremely stressful to all of the seawater-loving organisms that get pulled along for the ride.

[jerf]

See also the trouble around desalinization plants.

In absolute terms, we couldn't hope to remove enough salt from the oceans to be even so much as detectable in the absolute sense, but in local terms water with increased salinity can cause problems. Oceans are not hives of life everywhere you look, it's really just in spots, and those spots are generally right where we want to be and to put our desalization plants.

Plus the high-salt and normal ocean water are much more resistant to mixing than our intuition would suggest. They will eventually mix, but the high-salt water can go a surprisingly long way first.

[rlucas]

See also, thermohaline circulation. A major factor in the global climate is the flow of water pulled north along the Atlantic's surface due to the sinking of denser, saltier water.

Not going to be an issue with your average desalination plant, but certainly proves the point that water masses can behave differently in big, non-trivial ways due to their salinity.

[scarby2]

there have been desalination trials with spreading the brine over a much larger area releasing much smaller quantities at each outlet. AFAIK these have been quite successful

I'm unsure on the impact of costs. Maybe we just pump it into the salton sea....

[jillesvangurp]

Depends. Shallow coastal waters without a lot of currents would be an issue. That's often the issue with desalination. The solution is running pipes to deeper waters where whatever you can pump there is going to be a drop in the ocean. Pipes and pumps are of course more expensive.

[justinator]

<Eh no. Oceans are big. Really big. Unbelievably big even.

Every time there's a natural resource humans want to exploit, this is almost always been an argument, and it's almost always been wrong.

"look how many fishes are in the river! You can walk across the river by standing on the fishes!"

"Look how trees are in this forest! You can't see the end!"

Not to get all Derrick Jensen on this, but a red flag has been raised in my mind, as has my left eyebrow.