The carbon welding rods are copperplated, and the copper must be removed before using them to make chlorates. This is done by electrolyzing the rods in salt water. I used a steel plate (a piece of coffee can) as the cathode (-), and I connected the copper plated carbon rod as the anode (+). I dissolved salt in the water, and used either 6V or 12V, depending upon how well they were conducting. I swtiched voltages to try to keep the current below the suggested rating of my charger, which is 10 amps.
I would submerge the carbon rod, and adjust it's position, and/or depth to get an acceptable current flow. Then I would set the timer for 20 minutes, and go do something else. When the time was up, I had a nice clean carbon rod. However, due to the depth of my salt water, I could only electrolyze 1/2 of the rod at a time. So, I would flip over the rod, and repeat the electrolysis of the other end. This was a bit slow, but it works well. The rods I got cost 43 cents each, and were 3/8" by 12".
Discard the salt water, it should NOT be used in making chlorates!
I cut the tops off of two milk jugs, to allow it to hold at least 2 liters of liquid, and be able to get the electrodes into the liquid. While I used two jugs, someone could probably be able to use anywhere between 1 - 4 jugs, provided the voltage is adjusted to get the proper current flow (discussed later).
I fashioned steel electrodes by cutting up a coffee can. I tried two shapes for steel electrodes, and found that the shape and orientation of the electrodes are important. I tried both a flat electrode, and a rain gutter shaped electrode, but much smaller. The gutter shaped electrode worked MUCH better than the flat electrode. The flat electrode produced MUCH less chlorate than the gutter shaped (U-shaped) electrode. Because of this comparison, I will concentrate on the use of U electrodes instead of flat in this description. The U electrode was about 6 to 8 inches long, and had a trough which was about 1 inch diameter for the length of the electrode. This trough is where the carbon electrode is to be positioned during the electrolysis, with the trough facing down (i.e. like an upside-down gutter). This U electrode was positioned diagonally into the jug, and the carbon rod is placed below it in the trough. I cut out some soft plastic insulators to try to keep the two electrodes from touching. The purpose of shaping the electrodes like this, was to force any chlorine produced at the anode to be drawn into the area of the cathode by the flow convection created by the bubbling of hydrogen gas from the cathode. The chlorine then reacts with the sodium hydroxide produced by electrolysis at the cathode, to produce sodium hypochlorite. It is important to make certain that as much chlorine reacts with the cathode products as well as possible, otherwise you lose chlorine (you will anyway), and the process will be less efficient, and you will get less chlorate as a result. The hypochlorite produced later reacts to form chlorates.
Each jug was set up with the two electrodes in them. Each jug will be refered to as a "cell".
In each cell, put 2 liters of warm water, and dissolve some salt. You will need to decide how much salt you want to dissolve, because the more salt you use, the more chlorate you will get. Also, there is a lower limit, below which you will not get any chlorate to crystalize out in the final steps, because you won't have enough chlorate to exceed the solubility, and will stay in solution. Also, the more salt you use, the longer it will take to electrolyze the liquid. I would suggest somewhere between 1/2 cup to 2 cups of salt per cell. Refer to the table below to determine how much salt you wish to use. REMEMBER HOW MUCH SALT YOU USE, you will need to know this to figure out how long you are going to electrolyze the salt, as well as to determine how much potassium chloride to add at the end to crystalize the chlorate out.
amount Minimum Better
salt amp-hours amp-hours
1/2 cup 240 300
1 cup 480 600
1 1/2 cups 720 900
2 cups 960 1200
NOTE: I used 3/4 cup salt in mine, and got about 9 grams of potassium chlorate per 100 ml of liquid when I was done. This is not proportional though, because you will always lose about 7 grams per 100 ml because of the solubility of chlorate. You can use these results to guess how much you might get from yours. I also electrolyzed mine with 480 amp-hours, instead of between 360 - 450 amp-hours as shown above.
OPTIONAL: You can add 1 to 10 grams of potassium dichromate per cell to increase yields. The cells will still work without it, but not quite as well. I added 1 gram per cell.
Connect the charger's plus wire to the carbon rod of the first cell. connect a wire (at least 12 guage) between the steel electrode and the carbon rod fo the next cell. Interconnect other cells if they exist, by wiring the previous cell's steel electrode to the next cell's carbon rod. Finally, on the last cell, connect the charger's minus wire to the steel electrode.
Turn on the charger, and monitor the current being drawn. I've found for mine, that between 8 to 10 amps seems about right. Adjust the positions of the carbon rods with respect to the steel electrodes. Also you can adjust (maybe) the depth of the carbon rods. Adjust the positions and/or depths to get about 8 to 12 amps of current. Once you have established the current, you will need to monitor it periodically, to try to keep it as constant as is possible. Perhaps, if you have a very high current capacity power supply, you could use higher currents, but you will also need to cool the liquid to prevent the temperature from getting much above 40oC !!
Once you know how much current you are running, you can compute how many hours you will need to let it run. Take the number of amp-hours (from the above table), and divide that number by the number of amps being drawn. For mine, using 3/4 cup salt, I should have run it 360 - 450 amp-hours, and I was drawing 8 amps on average. So, it came out to about 45 - 56 hours of operation, but I let it go for 60 hours. You can let it run longer (within reason), and you might get a little more yield, but if you let it run too long (maybe 50 - 100% longer), you could be to getting perchlorates formed as a by product. I did not get any detectable perchlorates in mine.
Watch the temperature also. If it gets above 40oC (104oF), you should consider running a fan near it to cool it. It should be operating between 30 and 40oC. It will work above 40oC, but the carbon rods will errode away more rapidly at higher temperatures. While running the electrolysis, you will probably expect to change each carbon electrode (or at least re-position it), every 24 - 36 hours, depending upon how hot the liquid is runnning.
Monitor the liquid level. Add water as needed to keep the liquid level roughly constant.
After completion of the electrolysis, You will need to crystalize out the final potassium chlorate.
Shut off the charger, and remove the electrodes without disturbing the sediment at the bottom of the cells. Carefully pour off the liquid into another non-metalic container (I used milk jugs). You might consider letting the liquid stand over night, to allow more carbon to settle out, but that is not necessary at this point.
I added an equal quantity of potassium chloride to each cell, as salt I had originally used. I used volumetric measurements, which means for each cup of salt used, you need to add 1 cup of potassium chloride to each cell. I warmed the liquid up to get the potassium chloride dissolved. If it is difficult to dissolve, you may need to move the liquid to a glass container, and heat the liquid on a stove. Also, if you are having difficulty dissolving the potassium chloride, you might consider adding some water in small amounts, until it is dissolved. If you add water, make certain the liquid is hot, otherwise you may dilute the liquid too much to be able to crystalize out the chlorate!. If the conversion to chlorate was not very eficient, you could have a problem dissolving the potassium chloride, and the final product could have significant amounts of either salt or potassium chloride as well.
NOTE: If you work by weight instead of volume, multiply the weight of salt you started with by 1.3. That will be how much potassium chloride to use in the above step.
While the liquid is still hot, after dissolving the potassium chloride, you will need to filter the liquid to remove the suspended particles of carbon, to produce a pure white crystaline product. Coffee filters don't work well enough, and you may need to get real chemistry lab filter paper to remove the black. If the black clogs up the filter, you might consider filtering before adding potassium chloride. I filter afterwards because my potassium chloride is not pure, and has insoluble impurities which also get filtered out. You may need to adjust the proceedure to what you are working with.
NOTE: You can also try using coffee filters with some diatomaceous earth in it to filter through. Diatomaceous earth is available from swimming pool supply houses for filtering pool water. It is a good material to filter out small particles (like carbon).
Take the clear filtered liquid, and put it in a freezer. Let it cool down very low until you can either get frost on the outside of the container, or until you start to see ice crystals. You should see a layer of crystals on the bottom of the container, as well as a few floating on the top due to the surface tension of water.
Remove the liquid, and pour off some clear liquid to use later. Prepare some ice water - as cold as you can. Pour off as much clear liquid as you can without losing any chlorate. Then, pour the crystals through either filter paper, paper towel, or (preferably) a cloth shop rag. Use the liquid you first poured out, to rinse any excess crystals which didn't come out with the rest of the crystals.
If you used a shop rag, you can pick up the rag, and squeeze out the excess liquid, leaving a ball of crystals. Take a small quantity of ICE COLD WATER, and moisten the crystals enough to make a thick slurry. Then squeeze out the excess water again. This helps to rinse away any salt left in solution. You can repeat the rinsing and squeezing a couple times to help purify the chlorate.
You can save the clear liquid to electrolyze again - it is mainly salt water with some potassium chlorate and chloride in it also.
Set the crystals out to dry.
You're done.
Commercial production uses the following amounts of electricity to make chlorates and perchlorates:
chloride to chlorate: 118 amp-hours per mole salt at a cell voltage of about 3.3 volts.
chlorate to perchlorate: 69 amp-hours per mole at a cell voltage of about 6.1 volts.
While carbon / steel electrodes work well to make chlorates, they don't work well to make perchlorates. Commercial perchlorate producers commonly use either lead dioxide or platinum as the anode material.
Solubilities:
Chem MW COLD @ 0oC HOT @ 100oC
Sol gm/100ml sol gm/100ml
NaCl 58.45 35.7 39.12
KCl 74.55 34.7 56.7
KClO3 122.55 7.1 @ 20oC 57
KClO4 138.55 0.75 21.8