Help with Purifying Nitrate Salts
I have available to me fertilizer grade KNO3 (White Powder) and cold pack grade NH4NO3 (White Prills) and have attempted purification of those
products through recrystallization and I have encountered some issues:
1. There was some very fine dirt/sediments in both products that make the solutions slightly murky and it cannot be filtered with either qualitative
filter paper or 3 coffee filters.
2. When heating both products in a toaster oven to dry them they seem to burn and turn brown, the ammonium nitrate even charred in small spots. I
took the brownish ammonium nitrate and dissolved it in some water and the solution was very brown and from what I know NH4NO3 decomposes into only
gasses meaning theres something organic in in the fertilizer and the solution resembles the supersaturated KNO3 fertilizer that I have recrystallized.
3. After I recrystallize my KNO3 the crystallized salt retain this brownish appearance unlike the bright white powder form it comes in.
4. Red nitration bath when using NH4NO3, not the typical brownish cream.
In my recrystallizations I always maximize the amount of salt in a minimum of water and decant into another beaker to remove any rocks left behind,
this immediately crystallizes the salt at the bottom of the new beaker, I would assume this would be the source of my problems since it crystallizes
so fast that it traps the impurities within the crystal structures. To fix this problem would it be wise to dissolve 30% of maximum of the salt at
100C, as this would leave some room if the temperature were to drop suddenly when pouring.
Also my NH4NO3 from my cold packs leaves a murky white solution which cannot be filtered with my filter papers, is it possible that the suspended
solid is actually something organic that is causing it to brown while drying? How can I remove this? It also turns a dark red when mixed with sulfuric
acid to make a nitrating bath and my yields are always poor but I attributed the yields to the nearly 10% water by mass of the salt which I tested
when I dried it out, which is subsequently where I found these other issues...
Any insights would be great and I will be trying different techniques in my recrystallization efforts. I seem to be finding more problems than I solve
in my chemistry hobby. It always seems so simple on paper. 
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