Report on making bismuth vanadate yellow pigment
I found a few preparations for bismuth vanadate yellow pigment; only one did not require higher temperature calcining as the final step and that was
the one I followed (more or less). These were the starting materials. The technical grade sodium metavanadate is stated as 90% with no information on
what the rest is. For the stoichiometry I simply assumed 100% as I was keen to have bismuth nitrate in excess rather than sodium vanadate.
- A more-or-less 1N solution of nitric acid was prepared by adding 8g 70% HNO3 to a beaker with 100g water. pH ~ 1
- A 1N sodium hydroxide solution was prepared by adding 4g NaOH to a beaker with 100ml water. pH ~ 14
- 39.9g bismuth nitrate pentahydrate added to the nitric acid solution, stirred.
- 10g sodium metavanadate added to the NaOH solution, stirred.
- The sodium metavanadate quickly dissolved into a clear solution.
- The bismuth nitrate did not all dissolve, not after 30 minute stirring. An extra 50g 1N nitric acid was added, more dissolved but not all. Another
50ml was added giving some 200ml total, and this time the solution became completely clear.
- The procedure mentions to mix the solution but did not specify how. I decided to add the sodium vanadate to the bismuth nitrate as I thought it was
better to start from an acidic solution, taking into account the subsequent steps were about slowly increasing pH.
- Slowly add the sodium vanadate (metavanadate should have besome sodium vanadate after dissolving in the alkali medium) to the bismuth nitrate while
stirring.
- An yellow-orange suspension immediately formed which shifted to yellow as more was added. Below shows the color after all was added and a few
minutes stirring.
- Started to add a 30% NaOH solution dropwise while checking pH after every few drops, Until pH 3-4.
- Stir for one hour.
- Add NaOH solution to reach PH 6-7
- Heat to boil
- Boil for 3 hours
- After the boiling, the product seemed much heavier, it settled out quickly.
- Vacuum filter and wash in funnel. Easy to filter. Below shows the wet remainder. The filtrate was also very pale yellow, seems fine enough for a
tiny amount to go through the filter.
- Procedure calls for drying at 90 C, I put it on the steam bath for some 5 hours by which time the weight stayed constant.
- Soft dry powder, but I was a bit disappointed that there was now a bit of brown in the color after the drying! I soon realised that the "brown
sheen" disappeared if the product was compressed, as can be seen below. The product was then ground in a mortar for 15 minutes.
- Weighed the product and transferred to a glass vial. I then used a glass rod to tap down the product in the vial, it was interesting to see the
color change to more yellow was the product was compressed. Below photo show the difference between the upper 60% that was compressed more and the
lower 40%.
- 23g was recovered. This is some 4-5g more that the theoretical, I'm not sure if the product is still wet (and needs higher temp than steam bath to
dry completely) of whether there is a another reason. It seems dry and not at all sticky. The smears on the vial is from the glass rod tapping down.
Any other vanadates with interesting colors?
Footnote - the wet product attaches too well to the skin! I got some on my palm and had to wash with a brush to get it off.
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