Cooling Idea

[Xytrell]

Your tap water has dirt in it?

[frothychimp]

Deionized water is cheap if you do it right. Don't buy it...make it. I pay $49.00 per year for an industrial deionizer I use for my YAG system. It's the size of a scuba tank and has an inlet and outlet. Regular tap water goes in and filtered, deionized water comes out. You should be able to get them from any water filtering company that services industrial customers.

[Xytrell]

How much power does it use?

[buffo]

It doesn't use any power. It's filled with mixed-bed resin beads. That is, small plastic spheres with ion exchange sites on them, just like the crap inside your water softener.

You regenerate the anionic resin with sodium hydroxide and it picks up the OH- ions on the surface of the beads. Then you regenerate the cationic resin with hydrochloric acid and it picks up the H+ ions.

Then you mix the two types of resin together, stick them in a tank, and run water through it. (Plug flow - top to bottom. There is a tube that runs to the bottom of the tank to allow the water to exit the top after passing through the resin bed.)

The cationic resin absorbs positive ions (like sodium and calcium) and gives off H+ ions. The anionic resin absorbs negative ions (like sulfate, nitrate, and carbonate) and gives off OH- ions. Those H+ and OH- ions combine to form more water (H2O), and since you've effectively filtered out all the other ionic impurities, what you are left with is pure water.

The resistivity of the water (when continuously recirculated through the resin bed) can approach 18.3 megohms. Note that ultra-pure water is highly aggressive and will quickly loose it's resistivity. Exposure to air for a few minutes is enough to reduce ASTM type 1 quality water (>10 meg ohm) to ASTM type 2 levels (>1 meg ohm) But you don't need anything close to that level of purity for laser work. ASTM type 2 is more than enough. (The distilled water you buy at Walmart isn't anywhere close to even ASTM type 2, to say nothing of type 1.)

As you pass water through the resin bed, the ion exchage sites will be used up. Eventually, they'll be filled with all the ionic impurities that they've removed from the water. At this point, the resin is said to be "exhausted". You need to separate them and regenerate them as above. Resin can be resused many, many times, but it's so cheap that some small lab systems actually use disposable cartriges.

If you'd like to produce your own de-ionized water at home, contact your local water filtation company and tell them you want a "mixed bed deionization tank". A 1.2 cubic foot tank stands about 4 feet tall, is about 9 inches wide, and weighs about 75 pounds when full of resin and water. Culligan is a well-known supplier, along with US Filter. Check your yellow pages.

Note that you'll probably want a prefilter as well, to remove sediment. Also, a carbon filter is a good idea, as it will remove chlorine and other organic (non-ionic) contaminants. Finally, a post-filter after the resin bed is also a good idea.

Adam

Disclaimer: I worked as a field service technician for Continental Water Systems, formerly a division of Millipore, for 2 1/2 years working on Reverse Osmosis, Auto-Di, and other high purity water systems.

[300EVIL]

Neat! I never knew you could regenerate an ion exchanger. I have one on my YAG I was going to throw it away. Now I need to separate the resin beads to treat one type with acid and the other with a base? How do I separate the beads?

[weartronics]

How do I separate the beads?

In a typical mixed-bed disposable filter? Tweezers and patience.

[300EVIL]

In a typical mixed-bed disposable filter? Tweezers and patience.

HA! I think I'll pass.... I see they have ion exchange media for aquariums. Can I just buy that and replace the media in the filter?

[allthatwhichis]

My water purification system uses salt to recharge the "beads"...

[buffo]

300Evil;

If you only have a small cartridge DI tank, it's probably not worth it to try to regenerate. Also, most cartridge systems are sealed, so you can't easily empty and re-fill them. However, you could replace the cartridge system with a larger tank system. That might save you money in the long run.

If you have a larger tank, you can just take it back to your local Culligan dealer and they'll regenerate it for you (for a fee, of course). Resin regeneration is economical in large batches, but for something smaller than 1 cubic foot it's just not practical.

To separate the resin, you remove it from the tank and backflush it in a large vessel. The beads have different densities, so over time they will stratify. Then you pump a slurry of the anionic beads out first (into a separate regeneration vessel). Throw a couple valves, and you can send the remaining cationic beads to another regeneration vessel.

When the regeneration is complete, you flush the resin with DI water to get all the regeneration solution out, and then you mix the two batches together (using air) and fill up your tank(s) again.

Aaron:

Your system is a softener. It is filled with cationic resin. You regenerate it with salt (sodium chloride) so that when it's in operation it will remove hard water minerals (calcium and magnesium ions) and exchage them for sodium ions. You either have a well, or your city water comes from a well, thus it has high hardness. (Which is bad for your fixtures and your water heater.) A water softener is worth it anytime you've got more than a couple grains of hardness. (Here in Charleston we get our water from a surface water supply, so hardness isn't an issue.)

Hypothetically speaking - if you were to regenerate your resin with acid (basically empty the salt tank and fill it with HCl), and then buy a second unit filled with anionic resin (which would be harder to find, plus you'd need sodium hydroxide in the salt tank), then you could plumb the two units in series and have a separate bed deionization unit. It would be capable of delivering ASTM type 2 quality water, which would be good enough for most hobbyist uses. To get to type 1 standards though, you need a mixed-bed unit, and that's not practical because you need to remove the resin and separate it before you regenerate it.

Adam