Purifying diammonium phosphate fertilizer & questions on oxidants, hypochlorite, and ammonium stability
Hi everyone,
I’m working with commercial diammonium phosphate (DAP) fertilizer as a starting material. Recrystallization from water is the obvious purification
method, but I’m trying to understand what other approaches are chemically reasonable—and which ones are a bad idea. My concern is mainly with
inorganic impurities, especially metal ions commonly present in fertilizer-grade material.
I’ve seen oxidants suggested in other purification contexts, so my question here is about compatibility and side reactions rather than oxidizing
organics. Is it chemically safe or reasonable to boil DAP in the presence of an oxidant such as hydrogen peroxide or potassium permanganate? Would the
ammonium ion decompose or be oxidized under these conditions, or does it remain largely inert in acidic or neutral phosphate media?
Related to this, I also wanted to ask about hypochlorite or chlorine chemistry in the presence of ammonium phosphate. Since ammonium–chlorine
chemistry is known to be hazardous, hypothetically, if chlorine gas were bubbled through an ammonium phosphate solution, would nitrogen trichloride
still be expected to form? Would the system tend toward phosphoric acid formation with nitrogen loss, or some other outcome?
As a side note, heating aqueous DAP solutions above ~70 °C does not appear to release ammonia, likely because ammonia loss is suppressed in solution;
does the DAP → MAP conversion mainly occur only in the solid state or at much higher temperatures?
Thanks!
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