Recrystallization and Tests
Entry posted by Swede
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With four excellent KClO3 batches under my belt, I figured it was time to move on to additional processing. Those apparently "in the know" on various forums claim that a good MMO anode will make KClO3 that really doesn't need further refinement. The first and simplest test was to take some of the raw crystals from the cell, and test them for residual chloride, as KCl salt. These rough crystals have had only the lightest of washings when harvested, as I did not want to dissolve too much of the chlorate salt even with the ice-cold water that I used.
To test for KCl content, I attempted to dissolve exactly 10 grams of the raw crystals in distilled H2O. At room temperature, this was a bit too much salt, so I simply heated it somewhat to ensure any KCl in the crystals would find their way into solution.
Out come the incredibly useful Hach chloride titration strips. Without these, I would be forced to set up a tedious and expensive silver nitrate titration rig with each test. These strips are awesome; highly recommended.
The strip revealed a chloride concentration of 0.32 grams per liter chloride ion. This translates to 0.67 grams per liter KCl salt. With a bit of math, and considering the sample weighed 10 grams, the following is revealed:
The 10 gram sample consisted of 9.933 grams of KClO3, and 0.067 grams of KCl, or expressed as a percentage, the 10 gram sample was 99.3% pure, assuming KCl is the only adulterant. Not bad!! Apparently even a relatively crude washing will eliminate KCl salt as a problem. But this result is so good that I am a bit suspect... I will repeat the test at a later date with another batch.
The next step was the recrystallization of a portion of the crude KClO3 so as to further purify a sample, and ultimately to have, on hand, some pyro-ready KClO3. I don't have any uses for it, yet. I respect and understand the challenges it presents as an oxidizer. I do want to have some relatively pure KClO3 though, for research and testing.
Per Wouter, 280 grams of raw crystals were dissolved in 800 ml of boiling water.
It took a while on my war-torn Thermolyne hot plate, and I had to add another 20 ml or so of water, but it did eventually dissolve. I checked the pH of the boiling solution and found it to be slightly acidic. The addition of 4 drops of concentrated NaOH brought the pH up to maybe 8.0, give or take.
Interestingly, and alarmingly, there was more insoluble crud than I had anticipated. There were flecks of some sort of material floating on top...
These, I am confident, are very small portions of polyethylene from the cell walls, rim, and lid, or from some of the platic fittings I used. But worse, at the bottom, were black granules, very small, but numerous. I am hoping that these are not MMO particles from the anode, but rather are leftover pieces of acrylic from the black lid of the tower cell. I will be able to verify this one way or another by recrystallizing some KClO3 from one of the earlier batches, which had no black plastic in the system. If they are MMO particles, then I may need to consider dropping the amperage a bit in the future.
Faced with these insolubles, I was forced to hot filter the boiling solution, rarely a fun chore, as the crappy coffee filter paper really weakens with heat. It went OK, though, and all the insolubles were trapped in the filter paper, leaving a clear solution in the beaker. Pre-wetting the filter paper with water will minimize the amount of saturated KClO3 solution that becomes trapped in the paper itself.
As it cooled, the crystals began to form almost immediately, and while I could have rushed things, I let them form naturally overnight in my beer fridge to maximize prettiness. The aesthetics of crystals never ceases to entertain me. By the way, no comments from the spectators on my beer choice. This is driven by cheap friends who buy nothing but lite beers. I myself love English bitters, ales, and other quality yummies! 
Besides, this leaves more $$ for pyro stuff.
This morning, the workbench was set up to capture these lovely crystals. I thought about washing them with cold water, but given the ultra-low chloride content, I decided to simply rinse them with ethanol, counting on any undesireables simply being trapped in the water, which of course goes right back into a cell after being recharged with KCl.
My precious.....
After drying, the crystals look perfect. Yield was 240 grams, or 85% of the starting mass. Again, something to remember, the "lost" KClO3 will live again as future crystals, since it goes back into the cell and helps saturate the electrolyte. I am going to check the melting point and recheck the chloride ion content... beyond that, there is little I can do, or really need to do. Recrystallization is a time-proven method to purify, and KClO3 is a perfect candidate for it, demonstrating an excellent solubility change with temperature.
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