Cleaning Potassium Chlorate yield from electrolysis

[FrankRizzo]

Hey fellas. What's ways have you guys found for washing the remaining chloride contamination from a batch of electrolytically-produced potassium chlorate without losing most of the chlorate to the wash water? Edited August 16, 2009 by TheSidewinder

[TrueBluePyro]

what did you use for the anode and cathode? I havent made it my self but I have read a fair amount on the stuff. Using graphite is meant to be a bitch to clean your batch.

[Mumbles]

Did you even read the first post TBP?

 

The recrystalizations are said to be the best. Lead nitrate or silver nitrate will confirm lack of chloride. 2 should be pretty good. Chlorate is pretty insoluble very cold.

[Swede]

Frank, I think a two-fold approach works pretty well. If your batch started life as KCl, and you have harvested the xtals, likely they are fairly coarse, heavy buggers. No filter paper needed, I simply punched a few hundred holes in the bottom of a PE container, dumped the xtals in there, and step one is a modest wash with agitation (spoon) using ice water. Step two is a heavier wash with ice water + 25% alcohol. I don't know that wash #2 is needed, but I think it helps.

 

From there, I let the mass dry, and one recrystallization, plus yet another very light wash with ice water should give you yields above 90% from the original mass with very little chloride.

 

All the wash/waste water is brought to a boil to drive off alcohol and some of the water, and the waste is put back in the cell for the next run.

 

I've got a ton of raw chlorate from the cell, not recrystallized. I'll do a chloride check today just to see what we've got. This would be chlorate after the two washings, but no recrystallization. Be back in a few hours.

[Swede]

Frank, I did a couple of simple tests, more qualitative than quantitative. I prepared two solutions. Solution I was one gram of raw cell potassium chlorate, washed as described above when harvested, then dried, added to 100 grams distilled water.

 

http://www.5bears.com/perc/clcont01.jpg

 

Solution II used the identical chlorate stock as solution 1, except it had been recrystallized using TAP water, washed with ice cold distilled, then cold distilled + isopropanol, 25%. The washings were gentle and minimal to avoid loss of product.

 

I first tried a "Hach" chloride titration strip on solution I. It showed nil chloride, which I expected, because the strips I have are high-range. I was too lazy to set up for a true silver nitrate titration, but I did do a simple, visual check. In the next picture are three test tubes. On the left is solution I, next is solution II (the recrystallized stuff) and on the right is tap water here in DFW, Texas.

 

http://www.5bears.com/perc/clcont03.jpg

 

Into each was added 4 drops of 5% silver nitrate. The raw chlorate clouded, but not horribly, and I expected it. Solution II was beautifully clear, no sign of chloride. The tap water on the right is a good reference, and compared to Sample I, the raw chlorate was slightly cloudier, but not by much.

 

Our local drinking water has 0.036 g/l chloride. If I were to guess, I'd say Sample I was 0.060 g/l chloride. Since Sample I was prepared as a 10 g/l solution, that would mean it was 0.6% chloride by weight, which is close to a previous test I did. Reasonably clean stuff without the need to recrystallize, and if recrystallization is done, I think chloride could be considered nil. HTH

[FrankRizzo]

Thanks Swede, that's incredibly helpful!

[50AE]

Swede, do you know if lead nitrate will work the same way as silver nitrate ? I have a batch of it at home.

[FrankRizzo]

Yes. Lead chloride is also insoluble.

[Swede]

Swede, do you know if lead nitrate will work the same way as silver nitrate ? I have a batch of it at home.

 

Frank is correct but I'm not sure of the visuals that it will give you. Probably something similar, perhaps with the lead chloride dropping rapidly to the bottom, moreso than the ultra-fine silver chloride that seems more an emulsion like milk than a normal ppt. You'll see the lead chloride form, but there's something about the fineness of the evolved white silver chloride precipitate that is unmistakable and easily identified.

 

Because the silver chloride settles so slowly, I bet it'd be relatively easy to set up an optical rig if you wanted to get really fancy; a photoresistor or similar that changes resistance based upon the amount of light, along with a LED as a light source. More light = less silver chloride = less chloride. You could calibrate it with standards.

 

I'll try a side by side (Pb vs Ag nitrates) and see what it looks like.

[Swede]

50AE, I tried lead nitrate as a chloride detector - same concentration, 5% solution lead nitrate in distilled water, 5 drops added to a test tube with tap water, and it performed IDENTICALLY to the silver nitrate. I was amazed. I couldn't tell the difference at all. So it's good to go as a qualitative check.

[Mumbles]

As you discussed in the other thread, potassium carbonate and sulfate might be contaminates in the initial feed stock. These would both give false positives for chloride. Eh, I suppose recrystalization is required in any case. I'd definitely be a bit concerned about the sulfate. Some Ca/Sr/BaCl2 soln could be used to discern I guess.

[Swede]

I will try barium nitrate on some saturated chlorate, both raw and recrystallized, to see if there is any sort of visual indication of sulfate contamination. Potassium carbonate is extremely soluble, over 1 kilo per liter at room temp, and I would not expect potassium carbonate solids to form at any point in the process... it SHOULD get eliminated during the basic wash of the raw product.

 

Edit: I tried Barium nitrate on several samples, with one sample containing a speck of magnesium sulfate as a control. There was an obvious and visible barium sulfate precipitate from the control, but nothing visually from the other samples. This doesn't mean that sufate isn't there, the test just isn't sensitive enough.

 

I emailed Diamond crystal to see if they would divulge the impurities in their KCl. It is advertised as 99.1% pure. Morton brand KCl is listed as 99.7% pure, so if there is a choice, Morton would be the way to go.

 

Googling "Potassium Chloride water softening salt" yields dozens of hits. There are many brands out there. People use it here in the U.S. at least to minimize sodium in the water, and as being more environmentally friendly. I would assume any major hardware store would have these giant bags of KCl. Most seem to cost about $25 for 40 pounds, but I found a few that were $16 or so. Shipping would be insane, it's something you have to find locally, I think.

 

Even if you start with sodium salt, you'll still need KCl at some point for the conversion.

Edited July 20, 2009 by Swede

[farfalla1]

I will try barium nitrate on some saturated chlorate, both raw and recrystallized, to see if there is any sort of visual indication of sulfate contamination. Potassium carbonate is extremely soluble, over 1 kilo per liter at room temp, and I would not expect potassium carbonate solids to form at any point in the process... it SHOULD get eliminated during the basic wash of the raw product.

 

Edit: I tried Barium nitrate on several samples, with one sample containing a speck of magnesium sulfate as a control. There was an obvious and visible barium sulfate precipitate from the control, but nothing visually from the other samples. This doesn't mean that sufate isn't there, the test just isn't sensitive enough.

 

I emailed Diamond crystal to see if they would divulge the impurities in their KCl. It is advertised as 99.1% pure. Morton brand KCl is listed as 99.7% pure, so if there is a choice, Morton would be the way to go.

 

Googling "Potassium Chloride water softening salt" yields dozens of hits. There are many brands out there. People use it here in the U.S. at least to minimize sodium in the water, and as being more environmentally friendly. I would assume any major hardware store would have these giant bags of KCl. Most seem to cost about $25 for 40 pounds, but I found a few that were $16 or so. Shipping would be insane, it's something you have to find locally, I think.

 

Even if you start with sodium salt, you'll still need KCl at some point for the conversion.

 

 

Hey Swede, When are you going to try the Lead dioxide anode for perc production? I had been keeping up with your progress on the "thoughts on anodes " thead, and your blog, but it seems to have gone cold? All that research and work? I was really keen to see what the result was. I'm sure others would like to know if it works as well?

 

Tim

[Swede]

Hey Swede, When are you going to try the Lead dioxide anode for perc production? I had been keeping up with your progress on the "thoughts on anodes " thead, and your blog, but it seems to have gone cold? All that research and work? I was really keen to see what the result was. I'm sure others would like to know if it works as well?

 

Tim

 

Hi Tim, I got sidetracked on the data acquisition project, which soaked up several months. The data project is ready to go. It will measure voltage, current, and temperature throughout a run on an electronic chart, with the idea being to use the data to determine end-of-run conditions, among others. I'm still working the pH angle. I'd love to monitor pH continuously, but I don't think it is possible. I also got sidetracked a bit on the perchlorate cleanup, which bore fruit. There's no point in making perchlorate unless it can be made pure enough for normal pyrotechnic use.

 

The Lead Dioxide Anode that came out nice is patiently waiting in a plastic bag, hung up on the wall of my shop. With summer here, my work area is 130 f. (not an exaggeration). It is uninhabitable. When work recommences, the first thing will be a chlorate run with data recording, and the next will be a test of the LD anode, followed by more LD plating to see if it can consistently be done.

[50AE]

Nice, by performing a tap water test with lead nitrate it seems it contains very little chloride, my solution is transparent.

 

So yesterday I purified my KClO3 yield from 48h electrolysis. First I made a recrystallization of the raw chlorate and I let it crystallize to 0C. Then I did two washings with cold tap water. I tested a sample and it was chloride free and it's pH is 7.3.

[Swede]

Nice, by performing a tap water test with lead nitrate it seems it contains very little chloride, my solution is transparent.

 

So yesterday I purified my KClO3 yield from 48h electrolysis. First I made a recrystallization of the raw chlorate and I let it crystallize to 0C. Then I did two washings with cold tap water. I tested a sample and it was chloride free and it's pH is 7.3.

 

Excellent! May I suggest you check your lead nitrate chloride test by preparing a stock solution of table salt and water, to be sure it is performing properly. Dissolve 1/2 a gram of table salt in 100 ml of DISTILLED water for a 0.5% salt solution. In a test tube, add a few drops of your lead nitrate solution. The test should easily detect what is a 0.3% chloride (by weight) solution. That will give you confidence in your test. And I know I don't have to mention the lead nitrate is deadly poison. Use Epsom Salts to convert the used lead nitrate into lead sulfate, which is much less hazardous.

 

I'm glad to hear your experiments are going well.

[50AE]

My lead nitrate solution performs very well. I tested it as you said, I dissolved 0.5 grams of NaCl in 100mL distilled water, I added the poisonus solution and I obtained a white liquid of small crystals.

But it seemed that my tap water isn't much chloride free. I tested it and it produces a very small, but noticeable white mist. The same eyeballed concentration of lead chloride appears when I dissolve 2 grams of KClO3 in 100mL water.

 

Here is a photo of it. The pH is 7.5

 

http://img39.imageshack.us/img39/1048/img0282gpz.th.jpg

 

Also, I have copper sulfate, I think it should do the work to neutralize.

Edited August 16, 2009 by 50AE

[Arthur]

The simpla answer to Frank's original post is that you will need to wash and recrystalise the product but that all the wash waters will go back into the cell as part of the replenishment of the electrolyte -Water is needed chloride is needed and pH control is needed.

A Brit with a big cell once, used to run it at 80 amps for a week then turn it down to 25A this caused a lot of chlorate to form then as the surrent went down the solution cooled and he could syphon off the crystals in the lower layer.

[50AE]

Of course, I don't throw away the washing solutions, I return them it a big 1.5L bottle called "junk electrolyte". It will be used to refill the evaporated water of the cell.

[quicksilver]

I know this is a very old thread yet I wanted to drop in and say I finally make a workable lead dioxide electrode (+ Ti). My yield was similar to the MMO (+ Ti)I originally used. My test came back clear and I guess-estimate a .3-9% chloride level. My brand of KCl was "Nature's Own" via a torn open bag at Home Depot that I got for $7 (I've told this story to some folks here previously) Nature's Own is expensive as water softeners go but I look for damaged bags and offer the manager some $ for it, etc and get a good deal.

The PbO2 electrode was a simple thing as I looked at a motorcycle battery and they use something similar. I got a tube, coated it in wax and mixed the PB dioxide to saturation with epoxy and stuck a high chrome stainless steel butter knife vertically in it, let it cure and tested it via 30-50A 5Vdc power supply with a Ti cathode. I mix my solution HOT to I get a super saturated solution and use a 5 gallon plastic bucket with the top perforated and "exhaust" tube in the middle. My distance for that current level worked out to 3.5" and I kept my ph at 6.5 w/ HCl. For one Kg product I used 1.35-1.4 Kg KCl. This brand gave me the least problems. It also gave me the best yield going to KClO4 with virtually no wear on the cathode (the anode is Ti and is starting to roughen after quite some time however.

I found that MMO cathodes will give more chloride, the more wear on them you put. I CAN get some Iridium which I MAY try if I can get a friend to go in on it w/ me as they ain't cheap.... I have a VERY large supply of carbon gouging rods (I weld a bit & have a lot of equipment). But carbon discolors my yield so much so that I have to recrystallize 3x to get it totally clean. I only used "naked carbon" and graphite ONCE. :-( as that level of current will eat them in one batch. 150A @ 5Vdc eat 2150A stainless in one batch also. But I get my product in 2 days. Distance on 150A for 4gal worked out to wider than I had room for so everything got hot but I kept it SOMEWHAT cooler with an aquarium air pump & when water was needed I used ice. With higher current I can get perchlorate much faster as well.

 

 

Hey R. - call me sometime: I can't find your phone # since you moved.

Edited May 2, 2014 by quicksilver

[taiwanluthiers]

There's no need to use motorcycle batteries... problem is the LD there adheres badly, and epoxy can't stand up to cell condition on a continuous basis... Polypropylene and PE seems to stand up very well but there's no way that I know of to liquify them except heat...

 

Besides someone on ebay sells a titanium substrate LD anode...

[Mumbles]

I know this is a very old thread yet I wanted to drop in and say I finally make a workable lead dioxide electrode (+ Ti). My yield was similar to the MMO (+ Ti)I originally used. My test came back clear and I guess-estimate a .3-9% chloride level. My brand of KCl was "Nature's Own" via a torn open bag at Home Depot that I got for $7 (I've told this story to some folks here previously) Nature's Own is expensive as water softeners go but I look for damaged bags and offer the manager some $ for it, etc and get a good deal.

The PbO2 electrode was a simple thing as I looked at a motorcycle battery and they use something similar. I got a tube, coated it in wax and mixed the PB dioxide to saturation with epoxy and stuck a high chrome stainless steel butter knife vertically in it, let it cure and tested it via 30-50A 5Vdc power supply with a Ti cathode. I mix my solution HOT to I get a super saturated solution and use a 5 gallon plastic bucket with the top perforated and "exhaust" tube in the middle. My distance for that current level worked out to 3.5" and I kept my ph at 6.5 w/ HCl. For one Kg product I used 1.35-1.4 Kg KCl. This brand gave me the least problems. It also gave me the best yield going to KClO4 with virtually no wear on the cathode (the anode is Ti and is starting to roughen after quite some time however.

I found that MMO cathodes will give more chloride, the more wear on them you put. I CAN get some Iridium which I MAY try if I can get a friend to go in on it w/ me as they ain't cheap.... I have a VERY large supply of carbon gouging rods (I weld a bit & have a lot of equipment). But carbon discolors my yield so much so that I have to recrystallize 3x to get it totally clean. I only used "naked carbon" and graphite ONCE. :-( as that level of current will eat them in one batch. 150A @ 5Vdc eat 2150A stainless in one batch also. But I get my product in 2 days. Distance on 150A for 4gal worked out to wider than I had room for so everything got hot but I kept it SOMEWHAT cooler with an aquarium air pump & when water was needed I used ice. With higher current I can get perchlorate much faster as well.

 

 

Hey R. - call me sometime: I can't find your phone # since you moved.

 

 

I know that the carbon erosion from graphite electrodes can be quite fine, but have you ever tried to use a filter aid to remove it? Celite/diatomaceous earth is very commonly used as a filter aid to remove small particulates in all scales of filtrations. It might help to expedite the purification and thus increase recovered yield.