I have an alloy containing different metals such as Al, Cu, Ni, (Zn, Pb, Sn, Ag, Si in small amount < 5%). How can I separate Cu and Ni from this alloy?

I tried to dissolve alloy in sulfuric acid, but it didn't work.

Then I tried to dissolve it in mixture of nitric and sulfuric acids and I managed to dissolve 400 g out of 1000 g. I noticed a thin black layer on alloy piece, which I suppose can be nickel oxide, which can be obstruction in dissolving alloy.

How can I prevent formation of this oxide layer?

  • $\begingroup$ Apparently a Ni Al Bronze ( will also contain Fe and Mn, plus tramp elements). Likely one would need to go back to electroplating out the copper as is done in copper production. It is a relatively corrosion resistant alloy so will not dissolve easily. $\endgroup$ Jul 12 '21 at 17:04
  • $\begingroup$ See: chemistry.stackexchange.com/questions/34371/… $\endgroup$ Jul 13 '21 at 4:23

First, the alloy $(0.5$ to $\pu{2 g})$ should be treated by $\pu{10 mL}$ nitric acid $32\,\%.$ All metals will get dissolved, except tin and silicon, which will be transformed into insoluble dioxide $\ce{SnO2}$ or $\ce{SiO2}$. Dilute in $\pu{100 mL}$ hot water. $\ce{SiO2 + SnO2}$ will make a gelatinous precipitate, that can be eliminated by filtration. Add $\pu{0.2 g}~\ce{Na2SO4}$ and $\pu{0.2 g}~\ce{NaCl}$ in order to remove lead and silver: lead sulfate $\ce{PbSO4}$ and silver chloride $\ce{AgCl}$ will precipitate, and are eliminated by filtration.

The remaining solution contains aluminum, copper and nickel. If you want to separate copper, you may add $\pu{2 g}$ potassium iodide $\ce{KI},$ that will make a precipitate of copper(I) iodide $\ce{CuI}$ according to the reaction

$$\ce{2 Cu^2+ + 5 I^- -> 2 CuI(s) + I3^-}\tag{1}$$

So copper may be separated as a white precipitate ($\ce{CuI}$). This reaction is specific. In the final solution, nickel can be separated with dimethylglyoxime. Add $\pu{10 mL}$ of a dimethylglyoxime $(\ce{C4H8N2O2})$ solution $(1\,\%$ in ethanol). Add slowly some ammonia $\pu{2 M}$ up to the $\mathrm{pH}$ is just greater than $7$. An intense red precipitate of nickel dimethylglyoxime $\ce{Ni[C4H5N2O2]}2$ appears and can be filtrated:

$$\ce{2 C4H8N2O2 + Ni^2+ -> Ni(C4H7N2O2)2 + 2 H^+}\tag{2}$$

This reaction is specific, and the other metals do not interfere.

  • 4
    $\begingroup$ Nice - this was pure analytical chemistry which is not taught today. Which book do you consult Maurice? $\endgroup$
    – M. Farooq
    Jul 12 '21 at 20:15
  • 4
    $\begingroup$ @M. Farooq. You are right. Qualitative analysis is not taught any more today. But it was what we did every day in the lab when studying in the university to obtain our diploma in chemistry in the years 1970. We studied in the lab the properties of all elements, including arsenic, mercury, cyanides. There was no accidents. These experiments were taken from books like F. P. Treadwell, Analytical Chemistry, 1924. Difficult to find in present bookshelves. $\endgroup$
    – Maurice
    Jul 13 '21 at 8:05
  • $\begingroup$ "This reaction is specific, and the other metals do not interfere". While the reagent is specific to nickel, it can also detect other metal ions which might be an interference like cobalt or palladium. Moreover, there was a study which discussed removal of heavy metals like lead, iron and zinc from waste water using dmg. $\endgroup$ Jul 13 '21 at 12:55
  • 2
    $\begingroup$ @Nilay Ghosh. Cobalt does also react with dimethylglyoxime, but only at high levels of concentration. It produces a blue color, but the rection is not very sensitive. With nickel, the reaction is visible even at nanomole levels. . Furthermore, cobalt does not produce a precipitate, just a blue color. $\endgroup$
    – Maurice
    Jul 13 '21 at 13:49

Fresenius' analytical scheme is also one possibility, although it is not as direct. More information can be found in Harvey's Analytical Chemistry 2.1 Libretext. I bring this up to highlight that even though this is a classical technique, it is still mentioned in some analytical textbooks still in active use.

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  • 1
    $\begingroup$ What is the full name of the book which mentions Fresenius' analytical scheme? Thanks. $\endgroup$
    – M. Farooq
    Jul 14 '21 at 3:52
  • $\begingroup$ @M.Farooq Analytical Chemistry 2.1 (yep, that's what Harvey named it). In addition to the Libretext link in the answer, you can find it here. FWIW, I use this text for my non-majors quant chem class and it works reasonably well. $\endgroup$ Jul 14 '21 at 11:06
  • $\begingroup$ Thanks. Oh I thought you had the original translated book of Fresenius. $\endgroup$
    – M. Farooq
    Jul 15 '21 at 14:53

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