Is there any common substance (mineral) that will filter out or absorb
salt when salt water passes through it?

Let's help fresh-water poor countries solve their drinking water
problem. I envisage digging canals through a mineral of some sort that
will allow the water to pass through and retain the salt. The
salt-free water is collected and the salt-saturated mineral is dealt
with. I envisage elaborate tunnels with saltwater  entering one end
and fresh water coming out the other.

Is this, or some derivation of this scheme, remotely possible?

---

Clarification of Question by augusta-ga on 29 Nov 2004 01:34 PST

I meant to write "...common substance (mineral?)...".

I got this idea after visiting the Yucatan peninsula and learning that
it is on a porous limestone shelf. I don't know how limestone reacts
with salt water, but it started me on that train of thought.

The answer here would depend on the composition of salt (I hope you
are not talking about common salt ie NaCl).

And I do not personally think that a simple mineral would be
available, otherwise people would by now have definitely come up with
a cheap solution to convert sea water to fresh water.

If it were possible then surely someone would have discovered the
methodology as opposed to distillation?

But who knows?

By salt water I mean ocean water, sea water. I think it is NaCl that
makes it salty, yes?

Sorry, no such mineral exists... Closest thing I can think of are
ion-exchange resins, but the costs would be sky high compared to a
simple solar distillation.

http://www.solaqua.com/solwatdis1.html

Well, the saltiness of sea water is not derived only by common salt.
It's a complex mixture of various elements and to remove all of them
would definitely be a Herculian task.

Here's a small writeup which I found on the net:

SEA WATER IS NOT SIMPLE...
Scientists have studied the ocean's water for more than a century, but
they still do not have a complete understanding of its chemical
composition. This is partly due to the lack of precise methods and
procedures for measuring the constituents in sea water. Some of the
problems confronting scientists stem from the enormous size of the
oceans, which cover about 70 percent of the Earth's surface, and the
complex chemical system inherent in a marine environment in which
constituents of sea water have intermingled over vast periods of time.
At least 72 chemical elements have been identified in sea water, most
in extremely small amounts. Probably all the Earth's naturally
occurring elements exist in the sea. Elements may combine in various
ways and form insoluble products (or precipitates) that sink to the
ocean floor. But even these precipitates are subject to chemical
alteration because of the overlying sea water which continues to exert
its environmental influence.

This site gives the composition of sea water:

http://ozreef.org/content/view/25/2/

All the very best in your quest. If such a compound/mineral could
indeed be discovered, we can surely say goodbye to the world's water
woes.

Hi Augusta,

I'm sure I had discussed the existence of desalination plants with a
friend. I did not pursue the topic further. Talk of costs got in the
way of further thought.

Is distilling and evaporating one and the same? If sea water was
heated, would we expect to find some of Winsplit's 72 elements still
remaining in the condensation?

Phil

ps No apologies for my lack of correct scientific terminology here people.

Here is the entry on desalination from Wikipedia.

http://en.wikipedia.org/wiki/Desalination

Desalination
From Wikipedia, the free encyclopedia.

Desalination refers to any of several processes that removes the
excess salt and minerals from water in order to obtain fresh water
suitable for animal consumption or for irrigation, sometimes producing
table salt as a byproduct.

One way to remove brine from the water is putting water under pressure
and pumping ethane through it. Almost immediatly crystals appear at
the top made of pure water and ethane. These crystals can be melted
and then the water allowed to go into a container. Because of the
structure of the molecules of this substance it only picks up water
and ethane, leaving the salt behind.

Desalination of sea water has long been used on ships, submarines and
islands, where cost is not the dominating concern.

Desalination for brackish water is already commonplace in the U.S.,
where it is used to meet treaty obligations for river water entering
Mexico.

Desalination of ocean water is common in the Middle East, where a
number of countries use oil-fired stills to provide city drinking
water.

The price of desalination is rapidly declining. A modern, large,
efficient plant is within 20% of the cost of developing a new, local
source of fresh water. Desalination stills now control pressure,
temperature and brine concentrations to optimize the water extraction
efficiency. Other methods of desalination include reverse osmosis and
pressure barrier osmosis. Nuclear-powered desalination could be very
economical on a large scale.

Augusta,

Considering that you asked the question, I must thank you for answering mine.

Phil