<p>This was also asked in Chemistry Stack Exchange, where it was noted that barium sulfate is insoluble in water and generally insoluble in acids.  A quick check reveals that indeed the other minerals can be dissolved in nitric acid and so should yield to aqua regia.  Thus barite is the troublemaker.</p>
<p>Barite can be dissolved in hot alkaline chelating solutions, as described <a href="https://jpst.ripi.ir/article_707.html" rel="nofollow noreferrer">here[1]</a>.  This, of course, is not compatible with the acidic solvent you intend to use to dissolve and measure the gold.  It is not clear from the reference whether a pretreatment with such a chelating agent to remove the barite before placing in aqua regia would work when the barite is intermixed with the alkali-insoluble sulfides listed in the question.</p>
<p>Reference</p>
<p>1.
Bader Salem Ba Geri, Mohamed A. Mahmoud, Reyad A. Shawabkeh,  Abdulazeez Abdulraheem, &quot;Evaluation of Barium Sulfate (Barite) Solubility Using Different Chelating Agents at a High Temperature&quot;, <em>Journal of Petroleum Science and Technology</em> <strong>7</strong>(2017), 1, 42-56.</p>

CC BY-SA 4.0
2020-12-02T21:17:38.323Z
What about the sulfides? Especially the arsenopyrite and pyrite?
asdchem
CC BY-SA 4.0
2020-12-02T21:19:08.337Z
Soluble with reaction in nitric acid
Oscar Lanzi
CC BY-SA 4.0
2020-12-03T22:03:23.320Z
Sorry, I am  writing on behalf of my wife. She makes harsh decisions.
asdchem
CC BY-SA 4.0
2020-11-22T15:43:21.900Z
2021-08-28T11:20:52.297Z
2021-08-28T11:20:52.297Z
Oscar Lanzi
<p>I was looking into these specific minerals: arsenopyrite, pyrite, chalcopyrite, barite, calcite, dolomite. I investigate issues with tellurides not showing expected gold concentrations.</p>
<p>There is gold predicted at the site where these samples are. We tried to prove the presence of gold through aqua regia tests, but the resulting gold concentrations are low. My suspicion is that the majority of the gold resides as an inclusion in these minerals, and the aqua regia test won't be able to show that because of its inability to dissolve the host.</p>

<geochemistry><mineralogy><minerals>
Are there any sulphides, sulphates, carbonates that cannot be dissolved by aqua regia?
asdchem
# Are there any sulphides, sulphates, carbonates that cannot be dissolved by aqua regia?

(Asked by: username_0 on 2020-11-16)

I was looking into these specific minerals: arsenopyrite, pyrite, chalcopyrite, barite, calcite, dolomite. I investigate issues with tellurides not showing expected gold concentrations.

There is gold predicted at the site where these samples are. We tried to prove the presence of gold through aqua regia tests, but the resulting gold concentrations are low. My suspicion is that the majority of the gold resides as an inclusion in these minerals, and the aqua regia test won't be able to show that because of its inability to dissolve the host.

**Tags:** geochemistry, mineralogy, minerals


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## 1 answers

### Answer by username_1 on 2020-11-22. Score: 3 | Accepted answer

This was also asked in Chemistry Stack Exchange, where it was noted that barium sulfate is insoluble in water and generally insoluble in acids. A quick check reveals that indeed the other minerals can be dissolved in nitric acid and so should yield to aqua regia. Thus barite is the troublemaker.

Barite can be dissolved in hot alkaline chelating solutions, as described [here[1]](https://jpst.ripi.ir/article_707.html). This, of course, is not compatible with the acidic solvent you intend to use to dissolve and measure the gold. It is not clear from the reference whether a pretreatment with such a chelating agent to remove the barite before placing in aqua regia would work when the barite is intermixed with the alkali-insoluble sulfides listed in the question.

Reference

1.
Bader Salem Ba Geri, Mohamed A. Mahmoud, Reyad A. Shawabkeh, Abdulazeez Abdulraheem, "Evaluation of Barium Sulfate (Barite) Solubility Using Different Chelating Agents at a High Temperature", *Journal of Petroleum Science and Technology* **7**(2017), 1, 42-56.

> **Comments:**
> **username_0**: What about the sulfides? Especially the arsenopyrite and pyrite?  
> **username_1**: Soluble with reaction in nitric acid  
> **username_0**: Sorry, I am  writing on behalf of my wife. She makes harsh decisions.  

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