A Clever New Approach To Desalination

jbeaupre writes "The Economist reports on progress by a company called Saltworks on using saline gradients to do the heavy lifting of desalination. In essence, Saltworks uses solar energy or waste heat to concentrate sea water. They then use the ionic gradient between the concentrated brine and two sea-water streams to pull ions from from a 3rd sea-water stream. It appears to work with entropy by trading the reduced entropy of the desalinated water against the increased entropy of 'mixing' the brine and the other sea-water streams. The article only discusses Na and Cl, but even just removing these ions is a step in the right direction."

Comments

ion bridges cost? Consumable?

[140Mandak262Jamuna]

The key piece of the work is an ion bridge. This has to permit the travel of one kind of ion but not the other, i.e. Na+ or Cl-. Looks like this material could be expensive. It might plug up need to be periodically replaced. How expensive these are? How non toxic these are? What is needed to manufacture them? These are the questions we need to ask.

Re:ion bridges cost? Consumable?

[Vesvvi]

More important than the cost is the question of effectiveness.

In their diagram, they have this schematic in the critical location:

[Salt water]<----(+)----[Brine]----(-)----->[Salt water]

Chemically, that "equation" just doesn't balance without an input of energy.  It doesn't matter what kind of "ion bridges" they put into place between the brine and salt water reservoirs, or what the concentration of salt exists in the brine or salt water, it will require some energy to offset the entropy increase.

It's possible that they have some active system in place in the bridges, but it's going to take some kind of energy input which is missing from their explanation.

Re:ion bridges cost? Consumable?

[AcidPenguin9873]

Not everyone reading Slashdot has a degree in chemistry or chemical engineering. I appreciated OP's questions since I had the same ones. I appreciate your answers but not the attitude that I had to endure when reading your post.

Plug up with what? You naturally would have a mechanical filter to keep the crap out. It's not a major problem.

You answered the dumb question but failed to answer the smarter one. Does the ion bridge ever somehow lose its effectiveness after a good amount of use? If it does, it will need to be replaced. How often does this happen? How much water can one of them desalinate before needing replacement? If it never needs replacement because of *use* (not mechanical crap getting in the way), then that's great, but I don't know the answer. Again, I do not have a degree in any of this stuff, so please enlighten me.

Re:ion bridges cost? Consumable?

[nutshell42]

Not everyone reading Slashdot has a degree in chemistry or chemical engineering. I appreciated OP's questions since I had the same ones. I appreciate your answers but not the attitude that I had to endure when reading your post.

The attitude of the GP was the problem. "These are the questions we need to ask", as if they were non-obvious and revolutionary. Whenever there is a post about an invention on /. the easiest way to get "+5 (Group-Wank)" is to write that it will never work because the inventors overlooked an issue a drunk chimpanzee could come up with. Then a thread ensues where everyone congratulates themselves on saving the world yet again.

You are right, the GP's questions were interesting and should have been answered in the article (which is for laypersons) and because they weren't it's good that someone answered them here on /.

The problem is that the GP posed the question in a way that implied he knew what he was talking about and was making a statement about the invention, instead of admitting that he had no idea and was asking for clarification. jm2c

Re:Maybe

[AdamHaun]

No, it's not inaccurate, unless you're claiming that protons don't have a charge. The ions here are nothing like wires. In a wire, the atoms (nuclei and nonconductive electrons) are fixed in position while the conduction band electrons are free to move from atom to atom. But in this desalinization process, the nuclei themselves actually move -- that's what makes it desalinization. The sodium and chlorine ions are true charge carriers. Ion conduction is not uncommon. Here's some more info on that:

http://amasci.com/amateur/elecdir.html

Re:Reverse osmosis?

[stevelinton]

No. It does look a bit similar but it isn't. In reverse osmosis the water has to pass through the membrane, driven by high pressure pumps, leaving its impurities behind.

In this version the impurities pass through the membrane (two separate membranes in fact) driven by an electrical current. Cleverly, the electrical current itself is generated by the salt passing through other membranes out of the highly concentrated brine that you made in your solar ponds.

Re:Real Question - Please Answer

[Anonymous Coward]

Does the word "nigger" actually personally offend you? Or do you avoid it and frown on its use because you feel like you're supposed to? Real question, and maybe as an AC you can give a truly honest answer.

The word doesn't offend me. I avoid it because I realize that others may be offended by it, and I do not understand the complex history of its word. Besides, there are plenty of other ways to refer to other human beings besides the color of their skin. Consider their first and last name, for instance.

It's also,important to remember that it does not have to denote a race or skin color. I tend to evaluate people based on their actions, and I have learned that the epithet could be applied to many of the people that post flamebait as AC. You are what you do, this is your hood, and your question is just some more mostly worthless graffiti. I say mostly worthless because it DOES show YOUR true color, no matter your race.