Evaluating fertilizer grade AN and the added impurities

Evaluating the nitrogen level in X-0-0

Each fertilizer has an analysis table that tells you the percent of nitrogen (N) - phosphorus (P2O5) - and potassium (K2O) by weight. Urea is 46-0-0, and ammonium nitrate is 34-0-0. Both of these products contain nothing but nitrogen, but the nitrogen is at different percentages. Urea contains 920 actual pounds of nitrogen per ton, and ammonium nitrate contains 680 actual pounds of nitrogen by ton (2,000 x 46% = 920 and 2,000 x 34% = 680).

Fertilizer grade AN bought in garden stores etc today are full of impurities like anti waking agents, ammonium sulphate, NaCl, Ca(NO3)2, sodium bicarbonate and other impurities.

The N-P-K numbers are a fertilizer convention for percentages of elements that plants need in fairly large amounts. These numbers aren't what you're looking for as a chemist seeking raw materials. What you want is an ingredients list. As for purifying this fertilizer, you'll have to look up what's in it, and how the impurities differ from ammonium nitrate, before you talk about what purification method you've chosen. Unfortunately, there are several ways to purify/distill AN based on the compounds it is mixed with. Crystallization is one method of refinement but it doesn’t work properly if there are certain compounds in the mix.

If the fertilizer is a mixture of ammonium nitrate, superphosphate (that's fertilizer jargon for Ca(H₂PO₄)₂₎) and trace metals (usually as chelates,) recrystallization can give you a pure solid. You will have to be sure any and all impurities are complete insoluble in water/ethanol/methanol /whatever to say that recrystallization is a good purification method. If that's not the case, you'll have to do fractional crystallization, an important beginner purification method in college classes.

Potential problems:

- Learn the solubility table on AN (NH4NO3) in hot methanol

- Methanol is relatively expensive...

Questions I haven’t been able to answer through my research:

- Is there a way to replace the methanol with another product? Will ethanol work?

The "N" in fertilizer can come from a variety of sources -- potassium nitrate (provides some "K"), calcium nitrate (plants need Ca for strong cell walls), or even urea. They can be converted to ammonium nitrate (the first two easier than the last one,) but that's a roundabout way of addressing your need for ammonium nitrate.

The closest alternative today, I believe, is 27-0-0 or something similar. If you are unsure which additives are added and the effect it has, research the specific products offered by your national suppliers and ensure that you get ammonium nitrate with minimal additives. There are various ways to purify fertilizer which is based on the specific additives. Unfortunately, I am not competent enough to give you a specific guide on each additive and the various methods which can be used to remove the specific additive.

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