[Grangersteve]

I am performing an extraction of nitrate from river samples (as detailed by i.e. Chang et al (1999) Can. J. Fish. Aquat. Sci. 56. 1856) which uses Silver oxide to form Silver nitrate via a series of extraction steps. This process has generated a large quantity of silver waste products which have all bee stored in a jar, these are primarily Silver bromide and Silver chloride. As Silver oxide is expensive to purchase I was sondering if there was any way to 'regenerate' this waste back to Silver oxide.

[Fleaker]

Add a slight stoichiometric excess of sodium hydroxide to your wet silver halide. This will give you Ag₂O.

[Grangersteve]

Many thanks for your reply. Is this something you are familiar with, do you have any specific details or can you point me in the direction of some literature that might inform me? This sounds like a remarkedly simple process and could save me quite a lot of cash!

[Grangersteve]

Also, while I am thinking about it. Silver nitrate is photosensative, and the silver halides also appear to react in light. What is happening to these in compounds in light?

[MOTOBALL]

An old textbook (1958) says

"Silver oxide, Ag2O, separates as a blackish-brown precipitate when a caustic alkali is added to aqueous silver nitrate, but is generally contaminated with silver carbonate."

Caustic alkali usually means NaOH, which VERY readily absorbs CO2 from air to give Na2CO3; hence the silver carbonate.

Since you have variable (unknown) amounts of mixed AgCl/Br, cannot give you specific directions. However, in general terms, add NaOH solution---test small aliquots of  the clarified supernatant (from filtration or centrifugation) until no further pptn. is observed.

Separate the Ag2O (filtration/centrifugation) and re-suspend in water to remove xs. NaoH (or wash on filter pad). Repeat several times. Store moist.

Darkening of silver compounds in  light (basis of photography)--Photodissociation to produce finely divided Ag.

[Grangersteve]

Thanks for this, it seems to confirm what the previous post described. However, unless I am misunderstanding what you are saying, I dont have an aquious solution of any silver compound. Both my silver chloride and silver bromide are solid forms and therefore I dont not undertand how by adding NaOH I will get a precipitate of Ag2O.
Do you mean add NaOH to my solids silver halide and it will be reacted to Ag2O anyway? Any idea what the waste products of this reaction are in the supernatent (in terms of disposal)?

[MOTOBALL]

You are correct; insoluble AgCl is the basis of the qualitative analysis for silver. 

It may be as simple as originally posted by Fleaker, or

(1)  I wonder if treatment of solid AgX (X= Cl/Br) with NaOH soln. will give a coating of insoluble Ag2O around a core of AgX ??

(2) AgX can be solubilised by xs. NH4OH as an "ammine" complex.  Possibly add conc. NaOH to this to ppt. Ag2O; may or may not need heating to displace NH3 ligands by OH-

(3)           BUT
"[moist silver oxide] dissolves in xs. of ammonia to give a solution which on exposure to air deposits a black explosive compound called Fulminating Silver, Ag3N." !!!!!!!

You might generate one or the other, or a mixture of both. Tread lightly here, even if you are in a fully-equipped lab. with hoods, face shields etc.


You need some input from an experienced inorganic chemist.