Perchlorate weirdness

[Download]

I purchased a lead dioxide anode and made some sodium perchlorate over the last 6 weeks.

 

To remove chlorates I added HCl until the PH was less than 1. I then made the mistake of adding the whole lot to a stainless steel container and started boiling to get rid of the HCl. I immediately stopped doing that once it started turning brown and dug through the pantry until I found some sodium bicarbonate to neutralise the whole lot with. I then ordered some actual lab equipment because this has happened before. I now have to filter the whole lot again.

 

I ordered indigo carmine powder from a food supplier and made up a 1g/L solution. Following Exrockets, I added 1ml of test solution and 3ml of HCl and heated it, I then added 5ml of what I wanted to test. I used a 1:10k KCl03 solution first to test to see if it worked. The colour disappeared after a few minutes so I went ahead and repeated the test with my NaClO4 solution.

 

It has stayed blue, except that some of the dye has clumped into some sort of mass. The only difference I made was using a hot bath instead of boiling (no glassware I'm comfortable putting on a burner, it will be a few days before that gets here).

 

Any idea what is going on? I assume some sort of soluble iron or chromium (or an alloying agent) product is causing this and not to worry, but I'd like to be sure first.

 

Picture: https://i.imgur.com/W4ThqeX.jpg

[Arthur]

Congratulations you've just discovered that stainless steel (any stainless steel) is eaten away by hot acid chloroxy species (OCl to ClO₄ ).

 

You should study the professional process which is well described in several patents available online. The critical bits are 1/ using the differences in solubility of chlorides and chlorates to ppt out and recover good chlorate simply, and 2/ to use KCl solution to ppt out Kperc preferentially in small crystals leaving any remaining lower chlor0xy comps for reuse and recycling in the chlorate cell. The calculations matter! You need to calculate the amount of perc made (as NaClO₄) and calculate tha amount of KCl needed to ppt this out without adding too much - you don't want to feed KCl back in the recycle stream. Remember that all chloroxy species are problems outside the cell so be sure to reuse all that you can. If you dump much down the drain, you've dumped some money there and reduced your yield, and in a small town could even stop the local sewage works, All chlorate cell wastes kill plants, even a wet boot print could leave a trail of brown grass.

[Download]

Congratulations you've just discovered that stainless steel (any stainless steel) is eaten away by hot acid chloroxy species (OCl to ClO₄ ).

 

You should study the professional process which is well described in several patents available online. The critical bits are 1/ using the differences in solubility of chlorides and chlorates to ppt out and recover good chlorate simply, and 2/ to use KCl solution to ppt out Kperc preferentially in small crystals leaving any remaining lower chlor0xy comps for reuse and recycling in the chlorate cell. The calculations matter! You need to calculate the amount of perc made (as NaClO₄) and calculate tha amount of KCl needed to ppt this out without adding too much - you don't want to feed KCl back in the recycle stream. Remember that all chloroxy species are problems outside the cell so be sure to reuse all that you can. If you dump much down the drain, you've dumped some money there and reduced your yield, and in a small town could even stop the local sewage works, All chlorate cell wastes kill plants, even a wet boot print could leave a trail of brown grass.

I knew this and have done the calcs. I ran the cell until there was very little chlorate left. It didn't take much HCl (less than 20ml) to remove the chlorate. I am going to throw what doesn't precipitate out back into the cell for the next run though that is more for the perchlorate left over, not the lower chloroxys.

 

I'm more interested to know what is going on with the chlorate test.

Edited October 27, 2020 by Download

[WSM]

I knew this and have done the calcs. I ran the cell until there was very little chlorate left. It didn't take much HCl (less than 20ml) to remove the chlorate. I am going to throw what doesn't precipitate out back into the cell for the next run though that is more for the perchlorate left over, not the lower chloroxys.

I'm more interested to know what is going on with the chlorate test.

 

 

In my experience, the indigo carmine test had problems with sulfates/sulfites (I was using SO₂ from carefully added metabisulfite solution to destroy residual chlorate in sodium perchlorate solution). I switched to using N-phenyl anthranilic acid solution to test for the presence of chlorate (a test mentioned in Swede's blog or personal communication), and it worked well without interference.

 

WSM

[WSM]

In my experience, the indigo carmine test had problems with sulfates/sulfites (I was using SO₂ from carefully added metabisulfite solution to destroy residual chlorate in sodium perchlorate solution). I switched to using N-phenyl anthranilic acid solution to test for the presence of chlorate (a test mentioned in Swede's blog or personal communication), and it worked well without interference.

WSM

 

 

Sulfates interfere with the indigo carmine test by giving the same result as chlorates do. The N-phenyl anthranilic acid test is immune to sulfates or sulfites present, and accurately detect the chlorates present without interference.

 

Sadly, it's hard to come by and once mixed doesn't last long (none of my chlorate detecting reagents do, unfortunately). A spot test using minute amounts of dry reagents might be the most economical answer to the lack of stability of my chlorate testing chemicals.

 

WSM

Edited November 30, 2020 by WSM

[sefrez]

I have had some weird results using the indigo carmine test, probably due to simply using blue food dye number 1. In the end, it works. You just have to be a bit more attentive to the color change, but it is definitely there.

 

I'm not posting needing help, as I have already devised a "standard" that works for me. Mainly I am posting because I have not seen anyone else describe my experience and acknowledge that it actually still works.

 

So, upon looking up details on indigo carmine, I find out it is a water soluble dye derived from indigo. It has the interesting property that it is blue for ph <~11.4 and transitions to yellow for ph going above that (and is reversible.) So add an acid it should probably stay blue? Perhaps so. In researching I have failed to find anything on the contrary. But the mixture making up the food coloring behaves differently. For high ph, it is consistent - goes yellow and is reversible. However, when I reduce the ph to below perhaps 2-3 (can't remember exactly), it goes yellow as well. Initially I thought the dye was being destroyed as would happen in the presence of chlorate and therefore knew it would be a useless test as it would always return a positive, true or not. It turned out however that this change in color at low ph was also reversible just like that in the alkaline region. I still figured the test wouldn't work but tried it anyway - just looking for any difference between a control test (no chlorate) and one containing chlorate. No difference is evident at room temperature (or at least the transition is very slow,) but upon being the two to a boil, the control remains yellow and the chlorate containing one goes clear on the order of a second or two (~1ml total test volume in test tube.) Without much difficulty I was able to detect chlorate at 17ppm by mass. This is the chlorate mass proportion of the whole test solution containing the chlorate. Therefore it is not standardized to say, correlate a lower threshold of chlorate ppm in a "perchlorate" sample, although that could be done. Given I could have easily added more chlorate to the same test solution volume and still accurately detected its presence, ppm chlorate in relation to perchlorate sample could probably be brought down a few factors.

 

I still don't know what is forming with the addition of an acid (I have tried both HCl and H2SO4) giving the yellow color. Its a little harder to differentiate the test result (yellow = negative, clear = positive) vs (blue = negative, clear = positive), but it works.

 

I wonder if those mentioning other compounds (like sulfates) interfering with the test are actually experiencing what I am and a mistaking "clear <-> positive" for "yellow <-> still negative / equivalent to blue for our purposes.) I initially didn't realize the distinction.

 

If the solution goes "clear" with the addition of HCL and having not added suspected chlorate, try adding a base to being the ph back to ~7. If it goes back blue, I think if you acidify again and look more closely, you will see the solution is differentiable from a pure H2O solution (or a true test positive which appears the same to me) under the same form / lighting conditions - in my case appearing yellow.

[WSM]

I have had some weird results using the indigo carmine test, probably due to simply using blue food dye number 1. In the end, it works. You just have to be a bit more attentive to the color change, but it is definitely there.

 

I'm not posting needing help, as I have already devised a "standard" that works for me. Mainly I am posting because I have not seen anyone else describe my experience and acknowledge that it actually still works.

 

So, upon looking up details on indigo carmine, I find out it is a water soluble dye derived from indigo. It has the interesting property that it is blue for ph <~11.4 and transitions to yellow for ph going above that (and is reversible.) So add an acid it should probably stay blue? Perhaps so. In researching I have failed to find anything on the contrary. But the mixture making up the food coloring behaves differently. For high ph, it is consistent - goes yellow and is reversible. However, when I reduce the ph to below perhaps 2-3 (can't remember exactly), it goes yellow as well. Initially I thought the dye was being destroyed as would happen in the presence of chlorate and therefore knew it would be a useless test as it would always return a positive, true or not. It turned out however that this change in color at low ph was also reversible just like that in the alkaline region. I still figured the test wouldn't work but tried it anyway - just looking for any difference between a control test (no chlorate) and one containing chlorate. No difference is evident at room temperature (or at least the transition is very slow,) but upon being the two to a boil, the control remains yellow and the chlorate containing one goes clear on the order of a second or two (~1ml total test volume in test tube.) Without much difficulty I was able to detect chlorate at 17ppm by mass. This is the chlorate mass proportion of the whole test solution containing the chlorate. Therefore it is not standardized to say, correlate a lower threshold of chlorate ppm in a "perchlorate" sample, although that could be done. Given I could have easily added more chlorate to the same test solution volume and still accurately detected its presence, ppm chlorate in relation to perchlorate sample could probably be brought down a few factors.

 

I still don't know what is forming with the addition of an acid (I have tried both HCl and H2SO4) giving the yellow color. Its a little harder to differentiate the test result (yellow = negative, clear = positive) vs (blue = negative, clear = positive), but it works.

 

I wonder if those mentioning other compounds (like sulfates) interfering with the test are actually experiencing what I am and a mistaking "clear <-> positive" for "yellow <-> still negative / equivalent to blue for our purposes.) I initially didn't realize the distinction.

 

If the solution goes "clear" with the addition of HCL and having not added suspected chlorate, try adding a base to being the ph back to ~7. If it goes back blue, I think if you acidify again and look more closely, you will see the solution is differentiable from a pure H2O solution (or a true test positive which appears the same to me) under the same form / lighting conditions - in my case appearing yellow.

 

 

That is good work.

 

The next time I'm testing "SO₂ treated" perchlorate solutions for the presence of chlorate ions, I may have to determine the pH of the sample and see if a buffered sample tests accurately with the Indigo Carmine reagent. If that is the case, I can minimize my use of "harder to come by" reagents and use the less expensive option.

 

Thanks for the detailed description of your observations and thoughts.

 

WSM