Maybe let it stand in a sonicating bath for a while?

its hydrolysis occurs, you should just diminish pH addinig HNO3

For chemical dissolution, you can add few drops of hydrofluoric acid (chemical digestion in a teflon beaker) then dry it and return back to the initial volume using water. In general case, the zirconium matrices are more stable to hydrolysis and can be diluted in HNO3 if complexed with (F-)

You can also dissolve in acidic water (HNO3), filtrate and evaporate. The obtained salt should be fully soluble then. If your Zr salt contains impurites insoluble in water, at least you get rid of them.

Thank you for your input, guys! As a short feed back - neither sonication nor heating up to 50-60°C helped, at least on the scale of couple of hours. Further addition of nitric acid has improved the solubility a lot, now I have 2 M solution of nitric acid and 0.4 M of zirconium, and solution is only slightly turbid, almost transparent. I am a bit surprized it needed that much of acid.

For those reading the thread, the issue is still not completely solved. I will have to try out the suggestion of Arnaud but everyone is kindly welcome to contribute your pieces of experience. Is there any simple way to dissolve the oxynitrate?

The following equilibria can be considered for the dissolution of zirconium(IV) oxynitrate (also called zirconyl nitrate) in aqueous nitric acid:

(i) ZrO(NO3)2 ↔ 2NO3- + (ZrO)2+

(ii) H2O + (ZrO)2+ + NO3- ↔ ZrO(OH)+ + HNO3

In spite of the expected common ion effect of NO3- on solubility, the (acid) pH contributes favourably to stabilize the solution by avoiding the precipitation of zirconium oxide hydroxide, what could occur in slight alkaline solution:

(iii) ZrO(OH)+ + OH- ↔ ZrO(OH)2

A small update for those, who will read it facing the same problem with dissolution of zirconium oxynitrate: technical support of Alfa-Aesar contacted me. They say they actually don't expect clear solutions in water due to chloride residuals originating from the synthesis route. This contamination can be removed by filtering (with 0.2 um filter).

some more information I've found:

(https://answers.yahoo.com/question/index?qid=20080813040530AAX0kvb)

The solubility of Zirconyl ions in an aqueous is usually considered very low. (see reference below).

Typically a saturated solution is made by stirring the Zirconyl nitrate in boiling or almost boiling water, cooling the solution and then vacuum filtering it through a warm porcelain filter.

Source:

J. Kragten, Atlas of Metal-Ligand Equilibria in Aqueous Solu-

tion, Ellis Horwood, Chichester, UK, 1978.

An article confiming that substantial excess of acids is needed:

http://pubs.acs.org/doi/abs/10.1021/je60071a015

Zirconyl salts will be existed in dissolved form only in strongly acidic solutions due to theirs ability to hydrolyse.  Dissolution in high excess with warming, filtering in hot and cooling will results  the best solution.

Thanks László. Why filtering in hot not in cold state?

Because during cooling some target salt can be crystallized out, and if it is, that will be contaminated with the non-dissolved parts.  If you have lower Zr-compd. concentration in the solution than the solubility limit, you can filter the solution at room temp. as well, of course. .

The amount of water of crystallization is not precisely given, I usually use 4 in my calculations, which leaves certain room for errors. If precision was critical, the amount of water would need to be experimentally controlled for each batch of powder.

Hi, Roman, I also met the same problem. The alfa technical staff also told me there are a little residual Cl- in ZrO(NO3)2*xH2O. Do you know the content of residual Cl-, which is much important for my chemical synthesization? Thanks.

I also contacted Alfa's staff and they told me there is a little Cl- residual. Can anybody tell me the content of residual Cl-?

Hi,

I usually dissolve 0.1g ZrO(NO3)2.6H2O (from Sigma aldrich) in 5 ml of distilled water in closed container on stirrer (in room temperature for 10 min).

most of the time it dissolve totally, and sometimes almost (!!!!).

i dont know what is the different of these days, but increasing the time of stirring doesnt work to have a better dissolving, i increase the temperature up to 40C and still it doesnt dissolve completely.

i should tell you that if i add another nitrate to zirconyl nitrate and then want to dissolve them in water together, they wont dissolve at all,even in 10ml of water.

i attached a paper about solubility of zirconyl nitrate.I hope that it will help you.

Use ultrasonic, you should be able to get a clear solution within 30min

@Faeza Soroush, I saw you mentioned that your Zirconium(IV) oxynitrate hydrate possesses x = 6. I just want to reconfirm with you how you are able to determine the x because at my lab, I use the same product from the same supplier and my collegue told me that the x = 5. However, I checked in literature and I saw some authors used this product but from different suppliers and they found x to be 2.3 . 

So, I just want to know what is the right value of x for this product because i don't want to miscalculate the weight of the precusor which  will  be used in my experiments. 

Thank you in advance for your reply. 

@ Visot Mao, that should not be too difficult to find out. Take some not too small amount of your chemical, weigh it with a crucible, and calcinate at a temperature of, say, 1000°C. You'll find the amount of zirconia produced from the initial oxynitrate - the rest is simple maths.

@ Junming Sun, this was one of the first things we tried and did not at all help

Hi Roman,

I actually use aqueous solutions of this salt quite frequently in my work, so hopefully I can be of some help.

In the past, I have purchased the Zr oxynitrate salt from Sigma-Aldrich, which comes as a mixture of large clumps and fine powder (I have not purchased the Zr oxynitrate salt from Alfa Aesar, but I am assuming that this is the same/similar). The fine powder dissolves more readily than the large clumps, so I will crush the large clumps using a mortar/pestle or selectively weigh out only the fine powder. Then I will heat a vigorously stirring solution of water to near boiling (probably 80-90 degrees C). I then add small portions of the salt to the water, waiting until the salt is fully dissolved before adding the next portion. After I add the last of the salt, I will let this solution stir for 30-60 minutes. (note: if you heat this solution too long, it will congeal and you will never get your stir bar back!). I will then let the solution cool to R. T. (still stirring) and then dilute appropriately to whatever concentration I am aiming for (using a volumetric flask). The solution will still be slightly cloudy, but filtering with 0.45 um syringe filters will yield a clear, colorless solution.

Good luck. Let me know if this works for you!

P.S. I have a manuscript in preparation that details this procedure. Hopefully it will be out soon!

Thanks for sharing! I've recently salvaged milkywhite and partly congeled solutions of fairly old ZrO-nitrate by adding 1 mole citric acid per mole Zr and adjusting pH to ~5.5 by adding ammonia.

@Visot Mao,

I have sigma aldrich one, it's written on the box of product (x~~6)

you can check it in sigma aldrich website also (Degree of hydration, ~6 ) which i send you the address of this page below.

I hope it will be useful for you

http://www.sigmaaldrich.com/catalog/product/aldrich/243493?lang=en®ion=IR

Zirconium oxynitrate has a rather low solubility. I would suggest to convert it to zirconium tetranitrate pentahydrate, by mixing the oxynitrate with concentrated HNO3 and stirring for several hours until the solution becomes clear. Then, evaporate the liquid at temperatures under 100°C to get the well soluble tetranitrate pentahydrate.

Thank you Dominik for sharing this information. I'm just curious about the concentration, please could you share with us your experience?