I have copper minerals in rock that has been pulverized. These copper minerals are pure (native copper), chalcocite, chrysacolla, malachite, tenorite, cuprite and azurite. Does anyone know which acids will dissolve which minerals? I need this information as a lab has proposed to use $\ce{HF}$, $\ce{HNO3}$ and $\ce{HClO4}$ to perform an assay and I'm not sure it will work 100%.

  • 3
    $\begingroup$ most should dissolve in HNO3; though chrysocolla should require HNO3/HF mixture. Be cautious dissolving malachite and lazurite, both should dissolve readily producing a lot of CO2 gas. chalcocite would likely produce significant quantities of SO2 and NO2. And HF is not sweet water either. $\endgroup$
    – permeakra
    Dec 7 '16 at 23:03
  • $\begingroup$ Any idea as to what range Cu will be as wt %? // I also assume you're sampling a large amount of ore (dump truck size load) ground in a ball mill rather than trying to sample the "raw" ore rock by rock. $\endgroup$
    – MaxW
    Jan 22 '17 at 5:20

If I remember correctly, we (an analytical laboratory) would generally get all copper minerals into solution using a nitric/perchloric digestion, depending on the sample matrix. Unless the sample matrix as a whole were highly silicious in nature an additional HF digestion was not required. As commented above though, $\ce{HNO3/HF}$ may work for you also.

  • $\begingroup$ Hi in your opinion what assay would you use for tenorite. I have doubts whether you can use the same acid for native copper and tenorite. How long does the acid take to dissolve the native copper? $\endgroup$
    – Robert
    Jan 23 '17 at 6:14
  • $\begingroup$ Copper metal will be gone in a jiffy. Tenorite should have no problem at all going into solution refluxing in nitric/perchloric for several hours. Is that what you meant by assay, the digestion method or an analytical testing method for the copper after the prep? $\endgroup$
    – airhuff
    Jan 23 '17 at 6:19

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