I have seen many video's about how to purify potassium nitrate, but I have done it my self and found that they all left out an important step, so that's what I want to show you.
you first need to measure out your water and kno3. the way you do that is according to the chart, the solubility is 2.5 grams per ml at 100°c, so you divide the amount of kno3 you have by 2.5 and you then get the amount of water you need to add in ml.
in this case I have 100g of kno3 so I will need 40ml of water.
add the water and kno3 to a container you can boil it in.
when it reaches a boil and you can see that all the kno3 has diluted, quickly pass it through a thin cloth over a container to filter the pieces if dirt that might be in it. the reason you should pass it through the cloth quickly is that if you do it slowly it will cool and harden, stopping what you are doing and you have to start over.
you then put it into the freezer or fridge until its cold.
then when its cold, remove the stiff "goop" from the container, put it on a cloth then wrap it into a ball and TIGHTLY close it with an elastic or better yet a zip tie.
now for the missing step. put the bag in your watching machine, set it to spin and at its max rpm. the reason why this is important is to get an enormous portion of the water out of the kno3 which carries the impurities you wish to remove. What other tutorials tell you to do is just squeeze out or pour out the residual water then heat or let it dry. this leaves a lot of the water still with the kno3 and also impurities and your effort wasted.
remove the ball from the washing machine when its finished,open it then spread it out on a tray. Then put it in your oven at 50°c for 5-15 minutes if it has a fan in it. If not, a bit longer.in my case I have a microwave-oven so its mush faster.
then when dry, run it through a fine sieve then you are left with a very fluffy white powder of much higher purity than what you started with. I also find that when it is like this it is mush faster to ball mill because the particles are smaller and easier to break up. If you have any enquiries please feel free to contact me my email is: Nielsen.firstname.lastname@example.org