Am currently working on some ceria zirconia mixed hydroxide and I am looking to salvage as much Cerium out of the material as possible. I have
attempted to dissolve the material in 60% wt nitric acid and 99% of it dissolves however, the result is a mix solution of both cerium and zirconium in
solution. I have done some titration experiments to see how cerium (III), (IV) and zirconium precipitate, (I added 3.1:1 ratio of H2O2 to some cerium
nitrate to create a Ce(IV) solution). Since they both are soluble around the same pH, a seperation via precipitation seems difficult.
and can see that some people have worked in this area before.
My final goal is to end up with a solution of Cerium nitrate.
Am greatful for any adviceblogfast25 - 17-11-2010 at 13:43
Zirconium is amphoteric. Fusing the virgin product mix with soda or better caustic soda will convert the zirconium into sodium zirconate (Na2ZrO3 in
its simplest form - there exist various zirconates depending on fusion conditions, acc. literature). Cerium however forms no anions of that kind.
After fusing, the zirconium can be removed from the frit by leaching with strong HCl which converts the zirconate to zirconyl chloride, leaving behind
the mixed ceria.
My thread on zircon fusion could be of interest for your project:
Also cerium is fairly easily converted between Ce(III) and Ce(IV), with the +4 state resembling Zr, Hf, and Th in its chemistry. This can be useful
for removing traces of Ce from the Zr and in purifying the cerium fraction.
Jarvisone - 24-11-2010 at 04:36
Thanks for the advice.
I took a sample of the slurry and added to it 50% NaOH as the paper suggested and fired in a kiln over night at 600.
A very hard solid was formed and was welded to the sides of the cruiple but removed it into a pestle and Mortar and ground the solid into a powder.
Added to this was alot of DI water to form a clear yellowish solution and two layers of solid. A large yellow solid fraction settled at the bottom of
the tube and a small white layer on top of this.
Im assuming the white layer is Zirconium based and the yellow Ce based but have yet to analyses it fullyblogfast25 - 24-11-2010 at 07:10
Hmm… in my experience sodium zirconate will have formed (that is also what the paper - and similar ones to it – claims). But upon addition of
water the zirconate hydrolyses to Zr(OH)4: sodium zirconate cannot exist in aqueous solution. Zr(OH)4 is indeed snow white and freshly prepared it
dissolves readily in hot 20 %w (or higher) HCl giving a solution of ZrOCl2.8H2O (that’s not its structural formula, BTW).
The alkaline calcined ceria should resist the attack of HCl almost completely, so leaching of the frit with hot, strong HCl and filtering should
separate the the soluble ZrOCl2 from the insoluble ceria. I guess the ceria will have to be digested by fusing with bisulphate or 100 % H2SO4 +
ammonium sulphate.
A test for ZrOCl2 is simply to slowly add alkali to the solution: white Zr(OH)4 starts dropping out from about pH =5 - 6 (depending on
concentrations). The precipitate can the easily be redissolved in acid.
The yellow may be iron pick up, if you used an iron crucible.
You can make life a little easier by soaking the freshly cooled frit in water or strong HCl overnight: hydrolysis/part dissolution of the frit will
weaken the hard matrix… Jarvisone - 26-11-2010 at 06:09
You suggest digesting the ceria fraction with H2SO4 and Ammounium sulphate. This should yield cerium ammonium sulphate?
Im not expecting it to all dissolve but no matter how strong the acid or how hot i boil it, there is always solid remaining behind, even after a good
4 hours. Is there a reason return on this method of extraction of Cerium?blogfast25 - 26-11-2010 at 06:32
You suggest digesting the ceria fraction with H2SO4 and Ammounium sulphate. This should yield cerium ammonium sulphate?
Yes. The purpose of the ammonium sulphate is to allow you to heat the conc. H2SO4 to much higher temperatures (boiling point elevation), thereby
promoting the digestion of the ceria. Whether that yields all the Ce as ceric (IV) I’m not sure. Similarly fusing with dry sodium or potassium
bisulphate get to much higher temps than H2SO4 alone.
The remaining residue may not be ceria at all but stuff like zirconia (+hafnia), silica or other totally acid insoluble oxides like niobia and
tantalia which may require a second fusion with pure NaOH or KOH or fuming with anhydrous HF or 40 % HF…
