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Author: Subject: Solution strength for dissolving mineral impurities
ReconRabbit
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[*] posted on 14-6-2024 at 03:02
Solution strength for dissolving mineral impurities


Hi all,
A while back I had some rough quartz that I was intending to clean up but it had some soil stains that I couldn't remove with mechanical cleaning. A rockhounding book I have recommends that muriatic acid be used, but I'm concerned about chlorides forming and staining the white quartz, plus having a large container of hydrochloric acid is a significant hazard in my home due to the other people living here.
I was hoping I could use an oxidizing solution for this purpose. I have attempted soaking the sample in ~0.1M aq. oxalic acid; it may have been too weak to have a visible effect. Should I try a stronger solution or a different species? Thanks!
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[*] posted on 14-6-2024 at 07:49


Oxalic acid can be good at dissolving iron and some other transition metals since it makes water soluble complexes. You might need to use a more concentrated solution though, and apply some heat. If it doesn’t work, the “dirt” might be composed of more inert silicates, which would likely not be touched by HCl either.



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[*] posted on 14-6-2024 at 10:26


Quote: Originally posted by ReconRabbit  
Hi all,
A while back I had some rough quartz that I was intending to clean up but it had some soil stains that I couldn't remove with mechanical cleaning. A rockhounding book I have recommends that muriatic acid be used, but I'm concerned about chlorides forming and staining the white quartz, plus having a large container of hydrochloric acid is a significant hazard in my home due to the other people living here.


Regretfully if you dont know the staining material, then HCl (muriatic acid or maybe Nitric Acid are your best bet. Most chlorides are soluble in water, so are nitrates.
I think they wont stain your quartz (as soluble material can be washed away)
But I understand the hazzard of having strong acids in your house, and by large container, I think you have a big piece of quartz.)

If the container is in a ventilated area, maybe inside another container. CAREFULLY labeling and advising your family, the risk will be reduced.
HCl and nitric acid are volatille acids, meaning that they will produce some fumes with time, try not to have metal tools nearby or they will get rusty.

try not to use concentrated acids but diluted. (common muriatic acid is 20% aprox HCL - depends on brands- so diluting by 1 part of acid + 2 parts water can be use. Heating increases attack time, but should be done outside (because of fumes) and in a glass heating resistant container - not directly from heat, but in a water bath.
Do not use stainless steel or other material for heating acids.




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ReconRabbit
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[*] posted on 14-6-2024 at 12:16


Quote: Originally posted by Texium  
Oxalic acid can be good at dissolving iron and some other transition metals since it makes water soluble complexes. You might need to use a more concentrated solution though, and apply some heat. If it doesn’t work, the “dirt” might be composed of more inert silicates, which would likely not be touched by HCl either.


The sample crystal is fairly large (roughly 5x5x6 inches) and as RU_KLO stated it's inadvisable to use a stainless steel heating vessel, so what works? Wide bottomed beaker? I'd like to go as far as I can without heating, so I'll look for a stronger solution. The stains are the orange-brown color characteristic of iron deposits around here.
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[*] posted on 14-6-2024 at 12:28


If using HCl solution, the reaction can be accelerated with H2O2
This doesn't really help with the hazards involved, as it makes the solution more dangerous, but should allow the job to be completed much sooner.

If your primary stain is metal based, a few drops of HCl applied directly to the sample should produce an immediate result. Informing you if this method would work.

I have soaking samples in warm sodium bicarbonate solution and removed many organic surfaces stains.

Sulfide stains are the hardest to remove, because they are usually part of the sample.
About 1000mi south of nyc, white quarts is colored by water inclusions in the crystal. Boiling is not recommended as you can end up with sand.




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[*] posted on 14-6-2024 at 13:04


Just use muratic acid, you likely have more dangerous chemical under the kitchen sink. The new "green" product already comes prediluted to 20% so you don't even have to worry about fumes anymore.
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[*] posted on 14-6-2024 at 17:45


Quote: Originally posted by ReconRabbit  
I'm concerned about chlorides forming and staining the white quartz, plus having a large container of hydrochloric acid is a significant hazard in my home due to the other people living here.

The only problem I see is health hazard. Chlorides won't be a problem since they are soluble.

If you're still wary or using good old HCl, try citric acid and a toothbrush. Rubber gloves are good but not essential. Make a solution of citric acid, put it on a cup, and dip the toothbrush every now and then while scrubbing the stains. It is a really boring task but it is safe. And wear an apron or a dark colored shirt.

It may also happen that the stains are really part of the quartz. I have some small crystals somewhere that are naturally stained.

Edit: A wire brush is even better. Toothbrush...

[Edited on 15-6-2024 by bnull]




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[*] posted on 15-6-2024 at 08:00


Thanks for the suggestions. I'll get some muriatic from the hardware store and hopefully something HDPE I can use for mixing/combining materials. I'll also try the citric acid with a wire brush as I have plenty of that.

Edit: It is harder to find muriatic acid than I thought. All of the easily available pool chemicals for chlorinating water are sodium hypochlorite tablets.

[Edited on 15-6-2024 by ReconRabbit]
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[*] posted on 16-6-2024 at 04:55


In my part of the US muriatic acid is found in most hardware stores in the paint section and at most lumber yards. I pay about $8 for a gallon of very clean HCl. It comes in a white container with a yellow label. I believe the name brand is Sunnyside.



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[*] posted on 16-6-2024 at 14:00


Its frequently used to etch concrete to expose the aggregate. Check that section of your hardware store.



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[*] posted on 29-6-2024 at 17:37


So, after abrading the surface and leaving the rock in a saturated citric acid solution, I didn't see a change. I'll try to find stronger solutions, but even after checking the section for concrete etchant (I was specifically told that I would find muriatic acid there) the only thing I could find was urea monohydrochloride.
Someone on another forum recommended "Calcium-Lime-Rust CLR" (Lauric acid). I will report anything that happens using that. The presence of sulfides is all too likely though.
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