bob800
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Analysis of rocks\minerals without HF
I always thought it would be fun to do a qualitative analysis of various rock\minerals, with only classic "wet" chemical methods. However, it seems
that acids like HCl or HNO<sub>3</sub> would leave silicate-based rocks unscathed... Are there any substances (other than HF or fluorides)
that could be used to dissolve them?
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vmelkon
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Good question. I asked once why companies don't extract minerals from silicates. They tend to go for oxides, carbonates, hydroxides, chlorides.
Perhaps heating with carbon at high temperature would so something? Arc furnaces are used to reduce SiO2 to Si.
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bob800
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Quote: Originally posted by vmelkon  | | Perhaps heating with carbon at high temperature would so something? Arc furnaces are used to reduce SiO2 to Si. |
Interesting idea... while I don't have access to an arc furnace, here's another use of high temperature fusion from Manual of Chemical Analysis of
Rocks (available here).
| Quote: |
In a portionof 1 gram, silica, alumina,total iron as ferric oxide, manganese, lime, strontia, magnesia and titanium dioxide are determined.
The powder is fused with five times its- weight of mixed sodium and potassium carbonates, the melt dissolved in hydrochloric acid and
evaporated todryness,thus renderingthe silica insoluble. The silica is filtered off and in the filtrate alumina, ferric oxide,titanium
dioxide and phosphoric anhydride are precipitated, first by sodium acetate if manganous oxide is to be determined,or by ammonia water if this is to be
neglected. After filtration the precipitate is dissolved in nitric acid and reprecipitated by ammonia,and this repeated if there is much magnesia
present. The precipitate is ignitecl and weighed,and then brought into solution by fusion with acid potassium sulphate. This is dissolved in water,the
ferric iron reduced by hydrogen sulphide,the excess of this boiled off,and the total iron determined by titration with potassium permananganate.
Titanium dioxide is determined in the same liquid by the colorimetric method, which consists in comparing the intensity of color of a known volume of
the titrated fluid after oxidation by hydrogen peroxide,with that of a standard solution of titanium colored in the same way.
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Would the fusion with carbonate require arc-furnace temperatures as well?
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bahamuth
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Really hot phosphoric acid eats through quartz/glass as butter, perhaps the silicates will suffer the same fate...
Any sufficiently advanced technology is indistinguishable from magic.
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watson.fawkes
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| Quote: Originally posted by vmelkon | Good question. I asked once why companies don't extract minerals from silicates. They tend to go for oxides, carbonates, hydroxides, chlorides.
Perhaps heating with carbon at high temperature would so something? Arc furnaces are used to reduce SiO2 to Si. |
The resulting silicon is quite soluble in many molten metals. Ferrosilicon, for example, comes in any number of concentrations. I'm
not sure if iron and silicon are fully miscible (there are, albeit, silicides formed), but if not it's pretty close.
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bfesser
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| Quote: Originally posted by bob800 | | I always thought it would be fun to do a qualitative analysis of various rock\minerals, with only classic "wet" chemical methods.
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Likewise, I have thought about doing this for some time. In addition to the common analytes (Na, K, Ca,
Mg, etc.), I'd like to quantitatively determine the Fe/Mn content of a certain group of carbonate/oxide-bearing rocks.
Perhaps
concentrated or molten NaOH or KOH in a plastic beaker or Ni crucible?
If you think this would be fun, I could send you some samples taken from specimens in my rock/mineral collection that I've been trying to positively
identify. Perhaps when I get around to doing the analyses myself, we could compare data.
Some samples I plan to work with:
<ul type="circle"><li><a href="http://en.wikipedia.org/wiki/Bentonite" target="_blank">bentonite</a> <img
src="../scipics/_wiki.png" /> from Platteville Fm. (weathered ash from Appalachian volcano?)</li>
<li>Mt. St. Helens ash from <a href="http://en.wikipedia.org/wiki/1980_eruption_of_Mount_St._Helens" target="_blank">May 18, 1980
eruption</a> <img src="../scipics/_wiki.png" /></li>
<li>Fe-bearing ore (carbonate?)</li>
<li><a href="http://en.wikipedia.org/wiki/Niobrara_Formation" target="_blank">Niobrara chalk</a> <img src="../scipics/_wiki.png"
/></li>
<li>various limestone (CaCO<sub>3</sub> dolostone
(MgCO<sub>3</sub> — to determine Ca/Mg
ratio</li></ul>
[Edited on 7/9/13 by bfesser]
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chemrox
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You don't want to use HF? I don't blame you. Total digestions are usually done with HCl/HNO3 but the minerals are generally sulfides. Query the
usgs library. There are many analytical wet-chem procedures that have been developed and written up over the years. Maybe peroxy acids can get your
silicates into solution. I'm speculating and I dislike getting answers that are speculation. On the other hand your answers are there if you spend
the library time. Good luck.
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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bob800
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| Quote: Originally posted by bfesser | If you think this would be fun, I could send you some samples taken from specimens in my rock/mineral collection that I've been trying to positively
identify. Perhaps when I get around to doing the analyses myself, we could compare data.
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U2U sent.
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UnintentionalChaos
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| Quote: Originally posted by bfesser |
<li>Mt. St. Helens ash from <a href="http://en.wikipedia.org/wiki/1980_eruption_of_Mount_St._Helens" target="_blank">May 18, 1980
eruption</a> <img src="../scipics/_wiki.png" /></li> |
Lithium metaborate fusion and flame AA.  At least, that's what we did in
instrumentation lab.
See also "Mount St. Helens Ash from the 18 May 1980 Eruption: Chemical, Physical, Mineralogical, and Biological Properties. Science. 1980, 4461,
1116-1125"
I used to have (maybe still do but I can't find it) a copy of this paper.
<!-- bfesser_edit_tag -->[<a href="u2u.php?action=send&username=bfesser">bfesser</a>: fixed
broken image(s)]
[Edited on 7/9/13 by bfesser]
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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bob800
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Thanks to all who replied! I did some googling and it appears that much can be done with a block of charcoal, a blowpipe, and some borax and carbonate. See: http://archive.org/details/manualdetermina01penfgoog
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feacetech
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I use mixed HCl/HNO3 or HClO4 on fine ground phosphate rocks and serpintine rocks to digest for quantative analysis.
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Poppy
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Even lemon juice can dissolve some rocks, though some quartz looking parts are apparently left behind. Thus you could theorically extract the "useful"
part of of it, not sure if the silicon bearing compounds are chemically bound to the other minerals
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daragh8008
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Molten NaOH is great for silicon as mentioned above. It's the only thing I've seen eat a 1cmX1cm silicon wafer in 15 seconds. Don't let the 1ft jet
flame put you off! Although silicon oxides are a lot less energetic.
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bfesser
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While browsing the <a href="http://www.usgs.gov/" target="_blank">USGS</a> website, I found two geochemistry PDFs. They may not be
particularly helpful for the chemistry, but are worth mentioning.
<strong><a href="http://pubs.usgs.gov/of/2011/1193/OF11-1193.pdf" target="_blank">Inorganic Chemical Analysis of Environmental
Materials—A Lecture Series</a></strong>
<strong><a href="http://pubs.usgs.gov/of/2011/1187/pdf/ofr2011-1187.pdf" target="blank">Quality Assurance and Quality Control of
Geochemical Data: A Primer for the Research Scientist</a></strong>
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