I have some powders that contain silver, $\ce{Ag2O, ZnO}$ and maybe some $\ce{AgO}$ Can I wash powders with $\ce{NaOH}$ to remove $\ce{ZnO}$ (as Sodium zincate) without any silver or silver oxides loss?


1 Answer 1


Your second suggest that you also want to save the silver oxides apart from zinc oxide. Sodium hydroxide won't help because it also reacts with silver oxides. So, you need a weak acid to selectively react with zinc oxide but neither silver oxide or silver. Hydrobromic acid will work because it reacts with zinc oxide to form zinc bromide which is highly soluble in water. leaving silver oxide and silver untouched. Silver bromide is also expected to form but hydrobromic acid is not strong enough to do that. Instead, if an alkali bromide salt was used, silver bromide would definitely form. From wikipedia article of zinc bromide:

$\ce{ZnBr2 · 2H2O}$ is prepared by treating zinc oxide or zinc metal with hydrobromic acid.

$$\ce{ZnO + 2 HBr + H2O → ZnBr2 · 2H2O}$$

The dihydrate can be dehydrated by passing it over hot $\ce{CO2}$

  • $\begingroup$ Thanks but I don't want to loss silver oxides too! You say washing with NaOH can dissolve silver oxides ? $\endgroup$ Jun 5, 2017 at 17:07
  • $\begingroup$ @user2779537 Your original question was to dissolve zinc and silver oxides leaving silver untouched for which NaOH method is a plausible way. Now, you are saying that you also want to save the silver oxide too for which my answer become obsolete. You should have mentioned before. Now I have to delete my answer and start again from scratch. $\endgroup$ Jun 5, 2017 at 17:13
  • $\begingroup$ Yes I am sorry, Also I said want to dissolve just zinc. I want to remove zinc without loss of silver and silver compounds $\endgroup$ Jun 5, 2017 at 18:29
  • $\begingroup$ zinc phosphate is insoluble in water so does it precipitate in solution ? If yes, it mixes with silver again! $\endgroup$ Jun 5, 2017 at 18:53
  • $\begingroup$ @user2779537 see edited answer. $\endgroup$ Jun 6, 2017 at 2:32

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