Chemical Forums
Specialty Chemistry Forums => Citizen Chemist => Topic started by: SteveE on January 16, 2018, 09:50:43 AM
-
Hello Everyone
I was a gold prospector years ago. Occasionally I would find gold in quartz specimens. I'd like to dissolve some of the quartz off these specimens to expose more gold. Before 9-11, HF acid was pretty much easily obtainable. Since 9-11, it's a little more difficult. I've tried Armour Etch with some piss poor results and never expected it would work in the first place. Is anyone aware of an HF acid substitute that can dissolve quartz?
-
Also, would nylon fishing string dissolve or degrade in HF acid or a substitute?
-
Nylon will be vulnerable to any strongly acidic or basic solutions.
You can dissolve quartz (or any silicon/silica based material) in hot concentrated NaOH. I don't know how long it will take.
-
Nylon will be vulnerable to any strongly acidic or basic solutions.
I'd like to find some type of flexible string, wire or something I can wrap around the specimens to hang them in the solution without touching the bottom of the beaker. Is there something cheap that's impervious to acids or bases?
-
When I've digested clay minerals (which contain a lot of silicates), I've found success using nitric / fluoroboric acid systems at very high temperature in a microwave digester. But this was small amounts (<200 mg), so YMMV.
Can you find Teflon string? Teflon is impervious to just about everything.
-
When I've digested clay minerals (which contain a lot of silicates), I've found success using nitric / fluoroboric acid systems at very high temperature in a microwave digester. But this was small amounts (<200 mg), so YMMV.
Can you find Teflon string? Teflon is impervious to just about everything.
I'm looking for something a little less complex then nitric / fluoroiboric acid at high temps.
The Teflon string sounds like it might work but couldn't find it listed as such. Is PTFE the same thing?
-
Yes, PTFE is basically the same thing.
There's really not a whole lot that will completely dissolve silica. HF is mostly the only game in town. NaOH or KOH will etch it, but the dissolution is really slow.
-
Yes, PTFE is basically the same thing.
There's really not a whole lot that will completely dissolve silica. HF is mostly the only game in town. NaOH or KOH will etch it, but the dissolution is really slow.
Do you really think sodium hydroxide would dissolve quartz even if it does work slowly? I'm in no hurry and as a matter of fact, slower might be better since I wouldn't have to watch it as much as I did using HF acid.
-
No, I don't it's a very viable option.
-
I ran the math for KOH etching. This source (https://cleanroom.byu.edu/KOH) shows etching rates of 1-2 microns microns/hour in hot, 20% KOH. This would result in noticeable dissolution over months.
My math is taking their 20% KOH at 90°C:
(1500 nm/hour)(24 hour/day)(30 day/month)(1nm/1E7cm)=0.072 cm/month. Not a lot, but its something.
What about buying sodium or potassium fluoride and acidifying the solution with HCl?
-
The reaction would be limited by the solubility of silica, which is very low in water.
-
Thanks guys. I'm getting a lot of helpful information here. Some things I never thought of as well.
I'm not planning on removing pounds of quartz. I have four specimens. I figure between all of them, I need to remove 10 to 12 grams of quartz. One alone will need 4 or 5 grams removed with the rest split between the other 3.
-
The reaction would be limited by the solubility of silica, which is very low in water.
Can someone give me an general idea how much KOH it would take to dissolve 10 to 12 grams of quartz?
-
What about buying sodium or potassium fluoride and acidifying the solution with HCl?
I'm assuming this is a procedure to make HFL.. Is this a dangerous process or can it be done safely? I have a chemistry background from when I was younger. As a hobby and worked in a chemical factory.
-
Polypropylene and polyethylene are cheap and they resist many acids and bases, but not heat. +80°C would already be a lot.
Stainless steel should resist NaOH and KOH but not HF. Some cooking sieves are made of it and they resist heat.
The answer to slow etching is crushing to a fine powder. Ball mill?
-
Polypropylene and polyethylene are cheap and they resist many acids and bases, but not heat. +80°C would already be a lot.
Stainless steel should resist NaOH and KOH but not HF. Some cooking sieves are made of it and they resist heat.
The answer to slow etching is crushing to a fine powder. Ball mill?
I want to remove quartz from a couple gold in quartz specimens in situ to expose more gold. Not put the specimens into a ball mill and grind to a fine powder.
Tried to take a couple pictures but I couldn't post them because the files are too big. I'm not quite sure what to do.
-
This is a picture of the two specimens. I simply want to remove some of the quartz surrounding the gold.
-
A fine powder will be dissolved more quickly because there is less thickness to go through. The standard path to fine powder is a ball mill.
-
I understand that but I would have to destroy the specimens if I were to put them in a ball mill. What I'm trying to do is dissolve the quartz from the gold leaving the gold intact thereby creating a 3D web of gold.
-
I'm sorry Steve, but do to what you are asking is going to require a source of fluoride ions.
-
I am assuming that acidifying sodium or potassium fluoride with HCL acid will produce HFL acid. What would be needed to produce one liter? And what strength HFL would this produce?
Thanks
-
You can use powdered CaF2, which I believe works pretty well to form HF in situ in the presence of concentrated sulfuric acid.
Do be careful, however. This chemistry is fairly hazardous and proper waste disposal can be challenging.
-
Silica is soluble in molten KF-KCl around 1000K. This could go faster that the acid's action.
I wonder: is HF better than KF to dissolve silica in water?
Handling HF: I hope this would be done near to the next shower with unlimited water supply and near to the next hospital. That is, not in the wildness. HF is not just any acid.
-
Silica is soluble in molten KF-KCl around 1000K. This could go faster that the acid's action.
I wonder: is HF better than KF to dissolve silica in water?
Handling HF: I hope this would be done near to the next shower with unlimited water supply and near to the next hospital. That is, not in the wildness. HF is not just any acid.
Don't worry. I have plenty of experience working in a chemical plant as well as a lab technician.
-
Hello Everyone
I have one last question. As you know, I plan to suspend the gold and quartz specimens in HF acid using Teflon tape.
Can anyone recommend a certain type of clear plastic or glass beakers I can use that are resistant to HF acid? The idea is to suspend the specimens in HF acid using Teflon tape so I can see what's going on without having to constantly picking them up and observe them.
Thanks
-
Most polyolefin plastics have good chemical resistance - polypropylene or HDPE plastic would probably be OK. Teflon would be best, particularly if you plan to do any heating, but expensive. Don't use glass or metal, although you could use those if they have a thick chemical resistant (plastic) lining.
I suggest testing any container with a little bit of your acid first to be sure.