I was messing around with some fertiliser grade K2SO4, noticing that by dissolving in hot water not a clear solution was obtained at all...
The solubility limit @ 100 C for K2SO4 is listed in Wiki as 24.1 g / 100 g water, so a solution of 120.5 g of the virgin product was made with 500 ml
of boiling water, simmering the solution with reflux for about 10 minutes.
It was then hotfiltered using a preheated funnel + filter and setting the clear filtrate aside, covered with clingfilm. The filtrate yielded a nice
crop of clear crystals of K2SO4 on cooling...
The residue was washed amply with clean hot water, then dried at 150 C for an hour. The residue appears to make up about 7.6 w% of the virgin K2SO4
product. It's a light powdery substance, light grey in colour.
It doesn't react with 20 % HCl at RT. When a little of it is dropped in 95 % H2SO4 at RT some of it discolours to a much darker colour but I suspect
that this may be due to fibres from the filter paper (contaminating the residue) getting dehydrated... With conc. H2SO4 no other reaction is
noticeable at RT. I'll see if heating changes anything with HCl and H2SO4 tomorrow...
These observations seem to exclude halides and carbonates. I was thinking maybe CaSO4 but the residue appears a little too dark for that... Any
ideas?
[Edited on 19-9-2010 by blogfast25]hissingnoise - 19-9-2010 at 12:29
The last FG K2SO4 I messed around with contained a very fine sand and what looked like powdered seed hulls - probably added to make the fertiliser
flow more easily. . .
unionised - 20-9-2010 at 03:17
It would be cynical to ask what adding sand to K2SO4 would do for their profit and loss account.
To be fair, the stuff probably starts of full of junk and they just don't waste time and effort removing it.
[Edited on 20-9-10 by unionised]blogfast25 - 20-9-2010 at 08:49
Yes, fine sand or some low grade kaolin it might be. Might try to fuse it with NaOH on a rainy Sunday...12AX7 - 20-9-2010 at 11:23
CaSO4, especially if you are using hard tapwater (but not to the tune of 8%!).
TimEclectic - 20-9-2010 at 11:29
Likely just part of the strata they mined for the fertilizer? Or clay added to help prill it.blogfast25 - 20-9-2010 at 12:12
CaSO4, especially if you are using hard tapwater (but not to the tune of 8%!).
Tim
I used soft, cheap mineral water for this. With sulfates that gives inevitable a small amount of cloudiness. I can assure you 8% is as clear as peas
'n bacon soup...Satan - 20-9-2010 at 12:36
Or it can be coated (if its granulated) with something, to slow down absorbing moisture from atmosphere.blogfast25 - 21-9-2010 at 08:08
Or it can be coated (if its granulated) with something, to slow down absorbing moisture from atmosphere.
Hmm... it's possible but it looks very much like an unsophisticated, quarried and milled product. It doesn't look crystalline at all until I
recrystallise it...blogfast25 - 21-9-2010 at 08:12
