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Techniques for CollectorsLiquid for cleaning water soluble specimens.

2nd Jul 2015 01:50 UTCJoseph Taggart

What is a cheap, safe liquid for cleaning micro samples of water soluble efflorescent minerals in an ultrasonic cleaner?

2nd Jul 2015 02:28 UTCDoug Daniels

My guess would be alcohol, but then, micro, efflorescent, and ultrasonic? Doesn't sound like a good combination any which way.

2nd Jul 2015 02:48 UTCNelse Miller

The conventional advice to try a new technique first with an expendable specimen should always be followed. Also, "rubbing alcohol" is 70% isopropanol and 30% water. Try the denatured alcohol available in home improvement stores. I have used it to dry some porous specimens that just don't want to dry out.

2nd Jul 2015 04:46 UTCDoug Daniels

Yes, Nelse, I was thinking the higher % alcohols (90+%). Just wonder whether they would dehydrate any hydrated efflorescents.

2nd Jul 2015 09:02 UTCRock Currier Expert

You can't get 100% ethanol by distilling it do the the formation of an azeotrope. I think that if you used pure ethanol it might pull some of the loosely held water out of some of the minerals you might want to clean. I don't know how some of the pure "higher" alcohols might work.

2nd Jul 2015 11:54 UTCEvan Johnson

Just speculating, but to break the azeotrope, based on my experience working in labs, you might try adding magnesium sulphate to an otherwise concentrated solution. It should hydrate and precipitate out. Obviously not a large-scale thing, but might work.

2nd Jul 2015 14:44 UTCReiner Mielke Expert

Pure ( +99%) methyl hydrate is what I use to clean such minerals but not in an ultrasonic. My concern about using an ultrasonic would be, are they explosion proof ? If not then I would only try it outside with a good wind blowing. Although I have never tried it carbon tetrachloride should work as well and it is not flammable although it is far more toxic and expensive than alcohol.

2nd Jul 2015 15:15 UTCJeff Weissman Expert

Any petroleum-based solvent, or even lighter fluid, may work - but NOT in any type of powered device due to explosion hazard. Alcohols are a bad idea, as they can adsorb atmospheric water and then attack the specimen.

Best maybe to gently expose specimen to compressed air or use an artist brush to clean - no liquids involved.

2nd Jul 2015 16:54 UTCD. Peck

I would not use alcohols either, as they contain water. As Rock pointed out, pure alcohol can not be produced by distillation. Further, alcohol and water are miscible. Pure anhydrous alcohol is very expensive. I wonder if acetone would work . . . but I would not use it in an ultrasound cleaner.

2nd Jul 2015 17:23 UTCReiner Mielke Expert

I have never experienced any adverse effects on water soluble minerals using methyl hydrate. My understanding is that the alcohol absorbs water, in other words "ties" up the water preventing the water from dissolution. However I imagine there is a saturation point where this is no longer true, maybe 10% water?

2nd Jul 2015 22:18 UTCAlfredo Petrov Manager

Pure alcohol can partially dehydrate some very hydrous water soluble minerals. And alcohol is not a good cleaning agent anyway. Few liquids clean as well as water, unfortunately.

3rd Jul 2015 00:02 UTCLuca Baralis Expert

A warning against "denatured alcohol available in home improvement stores".

The red, common, kind can dye your specimen!

3rd Jul 2015 00:13 UTCJoseph Taggart

Thanks everybody for your suggestions. In the past I have used anhydrous ether in an ultrasonic cleaner (double boiler style -- ether in a small beaker in water filled ultrasonic cleaner) to clean flow proportional counter, detector wires, for an X-ray machine. The ether is expensive, unstable (peroxide buildup in the can over the years, can cause an explosion), The fumes require its own explosion proof refrigerator (trust me even in a sealed steel can, the fumes escape and make your food taste horrible). I have made anhydrous alcohol in the past, but wanted to avoid the effort. I will try the suggestion of testing different organic liquids on a scrap of the mineral, but I was hoping someone else had already done this work, and had a good liquid to suggest. If anyone reads this topic in the future, its never too late to make a suggestion.

3rd Jul 2015 15:51 UTCD. Peck

Joseph, glad you understand the hazards of using ether. But I would not use it in an ultrasonic cleaner under any circumstances. Any spark with vapor present could be a disaster.

13th Aug 2015 01:28 UTCJoseph Taggart

I did some experiments and have concluded that a mixture of alcohol and water does not "tie up" the water, and rubbing alcohol (70% isopropyl alcohol, 30% water) still dissolved a lot of table salt. After waiting for someone's simple suggestion here with no luck, I decided to spend the effort and dehydrate the rubbing alcohol. In organic chemistry we dehydrated reagent grade alcohol by mixing "Drierite" with the "hydrated alcohol", and then filtering it through a piece of filter paper. Not having any Drierite handy CaSO4 + (0.5)H2O I thought I could make some from some gypsum (heat for 1 hour at 400* to 450* Fahrenheit). If you try this, the temperature is critical - not higher, not lower. Rather than spending time doing this, however, I decided to use some already prepared Plaster of Paris. To prepare the anhydrous isopropyl alcohol, I poured an excess of Plaster of Paris into a jar with a screw on lid containing 70:30 isopropyl rubbing alcohol. After periodically shaking and allowing the mixture to settle, after a day I decanted the liquid into a smaller jar having a lid with a seal, by pouring through a coffee filter. So far I have tested the anhydrous isopropyl alcohol in a "double boiler set up ultrasonic cleaner" on samples of Lasalite, and Hummerite. I limited the time the samples spent in the ultrasonic cleaner to about about a half minute each which was the time it took for the worst of the dirt to have fallen off. I then removed the samples from the alcohol and placed them on a paper towel to dry. I have inspected the samples under a microscope and I am very satisfied.

My ultrasonic has a lid, and I kept it handy - just in case I needed to cut off the oxygen supply from a fire. You might want to keep some sort of lid handy, but make sure you inspect the lid for sealing either the jar or the tank of the ultrasonic cleaner. Check it before you need it.

13th Aug 2015 08:35 UTCRock Currier Expert

That is a very good and useful method you described. You might considering writing it up in an article. You might try it on a few other water soluble minerals like halite and hanksite since that is most people write in wondering about how to improve and or clean. If the results are the same I'm sure you method will become a standard cleaning procedure for evaporates.

13th Aug 2015 16:19 UTCReiner Mielke Expert

You seemed to have overlooked the last part of my statement: "ties" up the water preventing the water from dissolution. However I imagine there is a saturation point where this is no longer true, maybe 10% water?

13th Aug 2015 16:26 UTCSteve Hardinger 🌟 Expert

If you want to use rubbing alcohol, start with 91% rubbing alcohol (91% 2-propanol, 9% water), readily available here in the US.

Or consult a practicing organic chemist. I know a few.

13th Aug 2015 16:34 UTCJeff Weissman Expert

Its all about relative chemical activity, equilibrium behaviors and time required to approach equilibrium, and propensity for hydration, and not absolute values. Hopefully someone on the forum with experience in these issues will weigh in with better clarification. Mixtures of water and alcohol (or similar) will have a certain behavior when exposed to other substances that react to water, in chemical terms expressed as activity. How much water will interact with a dry substance depends not only on the concentration of water in the solvent, but how the water is "attracted" to the solid - the driving force or activity for hydration. There will always be some interaction between hydrating agents and dry substances - in chemical terms a measure of activity towards interactions with water.

Joseph's approach to make a solvent that is as dry as practical, though the use of a highly active drying agent - in this case CaO, lime, ensures that the remaining activity of water in the solvent (if any remains at all) is extremely low - thus he can use his very low water activity solvent to clean dry substances, lasalite and hummerite in this case, safely, as we assume the activity for hydration of the minerals is less than that of lime. If the solvent was not thoroughly dried before being exposing to the minerals, even a low concentration of water, much less than 10 %, will have some activity towards solvating the minerals. What concentration of water can be tolerated in the solvent before damaging minerals needs to be determined experimentally.

As an example, suppose you dried the solvent with lasalite (if you had this much) and then used the dried solvent to clean lime. I would expect the lime to be attacked by remaining water, as lime will extract more water from the solvent than an already partially hydrated mineral such as lasalite. The relative extents of the interactions between remaining water and lime would depend on, quantities of materials used (excessive solvent and/or excessive drying agent), time, temperature, pressure and partial pressures, grain size of the solids used, etc...

Consider quartz - generally considered to be insoluble. At high pressures and temperatures, the solubility of quartz and silicates in hydrothermal solutions is well known as the chemical activity of water is very high under these conditions. I have dissolved quartz using steam, at low pressures, but at 950 °C, where the activity of water is sufficiently high to attack a substance that normally is nearly insoluble at room temperature. Other minerals, gypsum comes to mind, that will be slowly attacked by water at room temperature, but sufficiently slow that one could clean gypsum specimens in water

Joseph - we need pictures to see how effective your method is!

13th Aug 2015 16:47 UTCReiner Mielke Expert

Joseph did not use lime as a drying agent rather Plaster of Paris which is dehydrated gypsum ( anhydrite?).

13th Aug 2015 17:58 UTCAlfredo Petrov Manager

Just because one uses pure alcohol, without any water in it, does not necessarily mean that it will be useful for cleaning all water-soluble minerals - Pure alcohol can destroy some of the more highly hydrated water-soluble species by partially dehydrating them.

13th Aug 2015 20:15 UTCJoseph Taggart

Your comments are all very good and the worry of dehydration was the reason I only cleaned the specimens for 30 seconds, and then only on lesser quality specimens at first.

Rock, for cleaning larger specimens of evaporite minerals let me tell you what Dick Jones (Arizona field collector and Mineral Dealer) did when he broke through the crust of a dry lake bed into a brine pool with large thenardite crystals in the clay at the bottom of the pool. To clean the muck off the specimens he used the super saturated brine to clean them without attacking them. In fact I believe he even brought home a bucket of the brine to continue his preparation work at home. For someone who wanted to clean halite specimens, I would suggest buying a bag of salt used for regenerating water softners and mixing it with water until saturated. To make sure the brine stays saturated, add an excess of salt so some remains undissolved on the bottom.

The gypsum dried at 400* to 450* is the hemihydrate of CaSO4 know as plaster of Paris or the mineral bassanite and can absorb moisture relatively rapidly in a reversible reaction. If dried at too high a temperature the CaSO4 becomes the mineral Anhydrite which absorbs moisture so slowly it takes geologic time, and is impractical as a desiccant. I used the hemihydrate to dry the alcohol, because I had previous experience (under the brand name Drierite) with it in my organic chemistry class.

Joe Taggart

14th Aug 2015 06:44 UTCRock Currier Expert

Joe,

I, Dick Jones and Gary Novak collected together on Soda Lake and I may have helped him carry that bucket of brine off the lake. Pictures are posted on Mindat.

14th Aug 2015 17:54 UTCJoseph Taggart

Rock,

Its a small world, who'd have thought that the very thing I was telling you about, you were actually involved in. Great pictures! I thought other people might like to see the brine pools without having to spend time searching through all your posted pictures. To save them time here is a hot link they can click on:

http://www.mindat.org/gallery.php?cform_is_valid=1&frm_id=pager&min=&loc=&u=2982&potd=&pco=&d=&showtype=1&photoclass=&filtmin=0&filtcountry=0&loctxt=&keywords=soda&mycol=&orderxby=1&submit_pager=Filter+Search&cf_pager_page=2

Joe

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