I think desiccating the powdered reagent would help remove lumps (at least in preventing lump neoformation) but would desiccation alone collapse all lumps in a powder (say KCl as it lumps easily), or would the lump formation itself prevent desiccation of the molecules at their core?

What about vacuum?

The challenge is in doing it without adulterating the reagent and I'm not sure how to do that.

Ideally I'd vacuum heat the powder inside of a glass grinder but the budget for this is probably far beyond my means.

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    $\begingroup$ This question is btoad and is not clear what the requirements are. Do you assume lumps are due to moisture and dessication is needed? Reaction involves solutions, so lumps are not a big concern. Solid state chemistry requires grinding itself. Etc. Clarify the contest, such as scale, chemicals, purposes. ... $\endgroup$ – Alchimista Jun 15 at 11:19
  • $\begingroup$ I don't really know what causes lumps, so I'm welcoming any knowledge on the matter (I just assume moisture because I've seen powders lump in moist environments). I probably used the wrong word when writing "reagent": I mean any pure chemical species in solid (powdered) form. How do you grind a powder without contaminating it with whatever matter the grinder is made out of (if not also biological contaminants from it)? Is there any other way than grinding, that would just make the lumps collapse back into fluid powder? $\endgroup$ – Veritas Jun 18 at 13:38
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    $\begingroup$ All this depends on what purity is required. The levels of your precautionary concerns is indeed high. Normally chemicals are supposed to come in contact with quite some containers and tools whatever operation they are submitted to. Assuming that one knows materials and goals, lumps can be ignored, manually crushed by mean of a pestle, milled in machinery, and so on. Yes, most often lumps are caused by moisture, via surface dissolution and merging - and I would guess other interface mechanisms. $\endgroup$ – Alchimista Jun 19 at 12:14
  • $\begingroup$ @Alchimista: I guess for small quantities a glass pestle would be ok (and they are quite cheap). Do you know if there is machinery that would mimic that (e.g. grinding between rough glass cylinders or something)? What are my contamination risk with that? Si? Bo? I'm wondering if softer or harder materials contaminate the most (the former by a sort of soft erosion and the later by brittleness)? $\endgroup$ – Veritas Jun 19 at 13:04
  • $\begingroup$ One cannot really answer without knowing what is the aim. Making basil pesto and pharmaceuticals are totally different things. I guess in your case ceramic or glass pestle might work. It really depends on the level of purity of your chemicals as well as the final purity. At this level of concerns, the vast majority of chemistry labs would be totally unable to do their work. $\endgroup$ – Alchimista Jun 19 at 13:19

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