Here I will give a summary of how I prepared ammonium molydate, (NH4)2MoO4, from the mineral molybdenite (MoS2).
My procedure followed that of Walton in his "Inorganic Preparations," (forum library).
Af first I tried to ball-mill the ore and work with the resultant powder. This was unsuccessful probably due to low MoS2 content. I next worked with
high-grade scrapings from my ore samples, which was successful. Here's a summary from my notebook:
"Try #3: Scraped some MoS2 from a 2nd piece of molybdenite. Wt = 0.51g. Decided that the ignition needs the full heat of the Tirill burner (MAPP
gas). The highest temperature measured w/TC = 550°C. Should have had at least 600°C. Need Meker burner. All the gray MoS2 did eventually turn to
dull yellow after full heat was applied for 1/2hr. Wt of fired product = 0.43g. Finished product (cooled) looks almost white!
For the conversion to (NH4)2MoO4 added 3 mL water. Then added 1.1 mL 13.3N NH4OH. Mixed and then heated on steam bath. Filtered into an evaporating
dish and allowed to air dry. Pure white crystals of (NH4)2MoO4 formed. Wt = 0.29g. Yield on crystallization = 44%. Phosphate test was positive.
[Edited on 31-5-2013 by Magpie]
[Edited on 1-6-2013 by Magpie]chemcam - 31-5-2013 at 09:55
I have never seen this process before, it is interesting. So then it must be the Tetrahydrate of Ammonium Orthomolybdate or is it dry? How do you get
to Ammonium heptamolybdate, "(NH4)6Mo7O24" or even distinguish between them easily?
I have never seen this process before, it is interesting. So then it must be the Tetrahydrate of Ammonium Orthomolybdate or is it dry? How do you get
to Ammonium heptamolybdate, "(NH4)6Mo7O24" or even distinguish between them easily?
My product is dry white crystals that glisten. I don't know if it is a hydrate or not. What does Walton's procedure say? For some reason I cannot
open it now. My DjVu reader isn't responding for some reason.
I'm sorry I can't answer your other questions - maybe someone else can.chemcam - 31-5-2013 at 14:02
Oh that's no problem at all, magpie, I have not done ANY research at all on this topic I was just seeing if you had known offhand. The only thing I
know is that there are a few types of this compound and I saw that you added water that's what made me think hydrate but I know some don't work that
way. Anyway cool experiment I'll add it to my to-do list. Ozone - 31-5-2013 at 18:26
Excellent ground-up preparation of a most useful reagent!
As always!
O3blogfast25 - 1-6-2013 at 04:19
Nice preparation, Magpie. Didn't realise it's quite so easy to synth.
I sell this product commercially and it isn't a hydrate, I don't think it has any hydrates. That's quite common with ammonium salts anyway.Lambda-Eyde - 1-6-2013 at 04:39
Nice prep, Magpie. Has anyone tried this procedure starting from MoS2 grease?Magpie - 1-6-2013 at 07:45
[Edited on 1-6-2013 by Magpie]blogfast25 - 1-6-2013 at 08:41
I don't know about the grease but for Molykote P37 (Dow Corning) I found a density of 1.21 (their product datasheet).
Assuming the greasy phase is about 1 g/cm3 and for MoS2 the density (Wiki) is 5.06 g/cm3, that would point to an MoS2 content of just over 20 w%. Not
bad. The grease would have to be removed with solvent extraction.
Re. the powder from eBay ('> 98 % MoS2'), at $9.99+ shipping for 25 g, I think buying it as a reagent would be cheaper.
[Edited on 1-6-2013 by blogfast25]Bezaleel - 3-6-2013 at 08:40
I doubt this is (NH4)2MoO4.nH2O. From the preparations of the simple molybdate, I remember that you need to keep the NH3 concentration high by force.
When you dissolve MoO3 in 5% ammoniacal solution in water, you will get the paramolybdate, (NH4)6[Mo7O24].4H2O. The crystals forming from evaporation
at standard conditions in air are also white and glistening.
The regular molybdate can only be crystallised from a strongly ammoniacal solution. Since you used 13.3N NH4OH, this may be the case, but it depends
(I guess) on the speed of evaporation. If you redissolve the crystals, and measure the pH, you will know the composition of the crystals, since the
paramolybdate reacts quite neutral, whereas the orthomolybdate of ammonium reacts alkaline.
Moreover, it is the paramolybdate that normally forms the Keggin cage structures containing various atoms, such as, e.g. phosphorous.
A sensitive test is the addition of a few drops of chromium alum or another soluble Cr(III) salt to the solution of your crystals. If you have the
paramolybdate, you will get a chameleon reaction (check here), ultimately yielding a pink substance. If not, you will get a green or greyish precipitate of Cr(OH)3.watson.fawkes - 3-6-2013 at 17:05
I don't know about the grease but for Molykote P37 (Dow Corning) I found a density of 1.21 (their product datasheet).
[...]
Re. the powder from eBay ('> 98 % MoS2'), at $9.99+ shipping for 25 g, I think buying it as a reagent would be cheaper.
No doubt. McLube (yes, that's really the name) sells three different grades MoS2 powder in sizes from 1 lb. cans to 250 lb. drums. No pricing on the web site. Given that I didn't see their name on other
products, I'm guessing they act as a material wholesaler.
