Stannous chloride Colors?

In the forum handbook it lists stannous chloride test colors which are different than Hoke states.

The handbook says a platinum solution will show red, and Hoke says it will range from deep yellow to brown depending on strength.

The handbook has palladium as showing deep yellow to brown, and Hoke lists it as deep yellow at first then turning to blue-green.

Can someone address this basic question?

Any additional helpful hints on the use of stannous chloride would also be appreciated.

Don

eeTHr said:

In the forum handbook it lists stannous chloride test colors which are different than Hoke states.

The handbook says a platinum solution will show red, and Hoke says it will range from deep yellow to brown depending on strength.

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In my years in the lab, I don't recall ever seeing a platinum reaction that was red. The best description I can offer is that it will look like coffee, but if there is precious little in solution, it can be yellow, ranging down through a deep dark brown as the solution is more concentrated.

The handbook has palladium as showing deep yellow to brown, and Hoke lists it as deep yellow at first then turning to blue-green.

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Palladium is a bit of a chameleon. It can display all of those colors, and under very strange circumstances can be confused with a dilute gold solution. The big difference is it doesn't leave a purple stain on your spot plate (which I advise). If you have even a remote question about the presence of palladium, or if you have palladium in solution with gold and or platinum, it's wise to do a test with DMG, which is conclusive. Even traces of palladium will yield a bright canary yellow precipitate.

There's more to consider. If you have more than one metal in solution, it often pays to add a crystal of ferrous sulfate to the test drop you have placed in your spot plate (that's why I recommend a spot plate) to precipitate the gold. You can then test the solution for the presence of other elements of concern, using stannous chloride. Gold so precipitated will come down as a fine sheet of gold, or in minute particles that are anywhere from golden color to dark brown. The resulting tests are then much easier to read.

My advice to you is to obtain a grain or two of each of these metals and prepare standard solutions. If memory serves, Hoke provides guidelines. By doing so, you can witness the color reactions in person, so you can understand what you're seeing when you are testing an unknown solution. Testing is very important to achieving success.

Harold

Go with the photos of the q-tips that lazersteve has posted somewhere on the forum.
It's the same colors I always get for pt and pd .

pt- orange
pd- blue-green


Mark

Mark;

Thanks, I'll check that out. I've been to his site before, but I think I have a slight case of info overload lately!

Since you are getting the same results consistantly, I'm wondering what the source of your solutions are? Jewelry, eScrap, ore, or what? (I'm learning by doing some eScrap.)

It looks like other things in the solution can affect the stannous results sometimes.

Don

Harold;

Thank you very much.

I remember reading something somewhere awhile back (before starting to actually make some attempts at recovering/refining) about precipitating-out the gold first in a spot plate, like you just said, but I had totally forgotten about it. I think the differences in color descriptions threw me for a loop!

I was going to try to recover the metals for my standard solutions, but I can see that the probable impurities would confuse things. Especially if I make tests with different combinations and ratios of the PMs and also with some base metals, to be more able to guesstimate what's in a values solution.

I'll be getting a spot plate and DMG on my next chemical order.

Another question about stannous chloride testing solutions: There are several different formulas for making it, and whether directly with metalic tin or with dry stannous chloride, there are widely differing dilutions listed. Some with HCl only, all the way to large water dilutions. Does the higher pH of the high water dilutions make it easier to get color from less-diluted (more acid) value solutions?

Also, related to this, I read in your posts that you recommend more concentrated value solutions (I think you said because it precipitates larger particles). I read in Hoke that she recommends more diluted solutions (I think she said because the precipitation settles quicker).

What is the real scoop on both stannous chloride dilution, and also on value solution dilution, and how (or) do these two vary in relation to each other?

Don

Don,
Everything you mentioned and more such as cat cons, native gold, and electronic medical scrap.
You should be in a good area to collect some native gold.

You have to work with the stannous a little bit to figure it out.
I find that when it shows a positive test on my standard gold solution, it is good to go.

LazerSteve and others have alot of info posted about this on the forum.

Mark

Thanks, Mark.

I have been to the mountains, and did get a little gold there, but I haven't tried processing any of that yet as it is in storage at this time. But I will.

I have been experimenting with different dilutions a little, and I think I noticed some differences, but they weren't really accurate tests, just curious tries. It's always good to get experts' opinions, to keep from straying too far off track. And you never know when you might pick up a little jewel that's not mentioned elsewhere.

I notice that now that I have done a few solutions and precipitations that when I go back and re-read the forum that it becomes more understandable. You folks are a great help!

Don

Don,

I use this formula for making stannous and I always have the same results no matter what the source of the scrap is:

1) 2 grams of pure powdered tin
2) 30 mL 32% HCl
3) Heat until fizzing begins (this takes around 10 seconds depending on your heat source)
4) Stop heating and let react uncovered until the solution clears, the solution should be colorless.
5) Store in a sealed container out of direct sunlight
6) Undissolved tin should remain in the storage vessel at all times
7) Test against known PM solution once per week or when you suspect it is not working

Here's the photos of the positive swabs and the Rhodium stannous test:




and positive test of Rh (left vial) and Pt (right vial) in solution using heated stannous chloride:



Steve

Steve;

Awsome. Thanks a gazillion.

And I will be on your Website again soon, because I need a couple of things (and to watch some videos over again).

Don

Harold;

I'm still very interested in any information about these two questions, which got bumped up the screen by some other appreciated answeres, and themselves went unanswered---

eeTHr said:

Another question about stannous chloride testing solutions: There are several different formulas for making it, and whether directly with metalic tin or with dry stannous chloride, there are widely differing dilutions listed. Some with HCl only, all the way to large water dilutions. Does the higher pH of the high water dilutions make it easier to get color from less-diluted (more acid) value solutions?

Also, related to this, I read in your posts that you recommend more concentrated value solutions (I think you said because it precipitates larger particles). I read in Hoke that she recommends more diluted solutions (I think she said because the precipitation settles quicker).

What is the real scoop on both stannous chloride dilution, and also on value solution dilution, and how (or) do these two vary in relation to each other?

Don

Click to expand...

Like I said before---

eeTHr said:

It's always good to get experts' opinions, to keep from straying too far off track. And you never know when you might pick up a little jewel that's not mentioned elsewhere.

Don

Click to expand...

Curiosity isn't all that bad---sometimes you even learn something!

Don

eeTHr said:

Does the higher pH of the high water dilutions make it easier to get color from less-diluted (more acid) value solutions?

Click to expand...

My experience dictated that the level of HCl made no difference. The presence of nitric, on the other hand, generally spelled either a poor reaction, or one that was temporary. It was not unusual to see a reaction develop, only to disappear.

I read in your posts that you recommend more concentrated value solutions (I think you said because it precipitates larger particles). I read in Hoke that she recommends more diluted solutions (I think she said because the precipitation settles quicker).

What is the real scoop on both stannous chloride dilution, and also on value solution dilution, and how (or) do these two vary in relation to each other?

Click to expand...

It stands to reason that you will get more profound results when testing concentrated solutions. In my mind, I imagine the best case scenario being one whereby the testing solution (stannous chloride) is of such a concentration that it reacts properly, and will serve to help determine the level of concentration of values in solution. Said another way, if a trace displays equally as well as a heavy concentration, the testing solution tends to lose some of its value. You'll notice, when precipitating, as you near the end of precipitation, the reaction falls off. That's important in helping you judge the existing conditions.

As far as concentrated solutions of values go-----there are reasons to precipitate from both dilute and concentrated. The platinum group can refuse to come down at all, and often does, from dilute solutions. In that case, the heavier the concentration, the better. I experienced complete precipitation in rare cases, but generally got only a partial. The complete occurrences were always from heavy concentrations, and took place rapidly.

Gold is better precipitated from dilute solutions, so traces of silver will self precipitate and can be removed in filtration. Beyond that, I know of no particular benefits aside from not needing any cooling. That's assuming you precipitate with SO2.

I'm sure you have read that silver, for reasons not well understood, will behave as gold, staying in solution, following gold in spite of it being a chloride solution. You'd expect the silver to precipitate as chloride, but that is not the case. GSP has pointed out numerous times that by diluting the solution, the silver precipitates. I found that to be true in practice.

I had reason to work with concentrated solutions. Refining commercially, were I to dilute everything, I would have dealt with huge volumes, requiring the use of larger beakers, and more of them. By keeping my solutions concentrated, and using ice for precipitation, to provide the needed cooling, I could process several ounces of gold per liter. That may or may not be important to you.

Because my end product received a wash in ammonium hydroxide, traces of silver chloride that may have been included were eliminated. That would be of concern for gold that was used in making white gold, or for other applications, where silver was not allowed.

Also, related to this, I read in your posts that you recommend more concentrated value solutions (I think you said because it precipitates larger particles). I read in Hoke that she recommends more diluted solutions (I think she said because the precipitation settles quicker).

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It is not the case that fine particles settle quicker. It is more desirable that they are coarse, in which case they settle instantly. Fine precipitation often takes several hours to settle. The gold stratifies and can be observed slowly moving towards the bottom as a broad layer.

Hope this helps.

Harold

Harold;

You are very helpful, indeed! Thank you!

After much reading on this forum and other sites, and the Forum Handbook and Hoke downloads, and then going back and trying to make notes and organize the information, it still leaves some "in between" questions.

You brought it all together for me on the above questions, and more, in a "big picture" kind of way. Very much appreciated.

I had noticed, when I first started doing this a several weeks ago, the purple starting to show then disappearing. I wasn't sure if it was nitric, or just too much acid in general. Then I started boiling-down my solutions---so that's why it's been OK.

I get it that it's best to always make the testing solution the same, whichever formula is used.

I like to test different source materials to see what average values are in what type of stuff, and on small tests like that it's hard to get a concentrated values solutions, so I'm thinking of determining (if there exists) a formula which will be more likely to detect small trace amounts in un-diluted solutions. So this is one of the reasons I got to wondering about that, and thought it would be worth asking.

I had read where you said that when precipitating with SO2 that the gold will mysteriously drag down a tiny bit of palladium, but I didn't know about the metalic silver oddity. I did get some silvery particles which when re-disolved tested strongly for gold, and when re-precipited still looked silvery; so now I know what to try if that happens again. Once, I happened to add a lot of water into a greenish solution, and the next day the solution was blue, and there was the white powdery stuff on the bottom (that was before I read about silver, lead, and mercury chlorides, and boiling water re-disolving the lead chloride) and I was baffled. I thought I just had made a mess. I didn't expect silver, but I think there was some solder in my first solutions so it was probably mostly lead. So I should have diluted that type of solution more anyway, I just didn't know it. Glad that came up, thanks! (Also I think diluting for the silver chloride first is in Hoke, but I had lost it in the swirl of information I was trying to digest in order to just get my feet wet with this.) Recently I've been soaking anything with solder on it overnight in HCl, then boiling it the next day, to clean the solder off first, and that seems to be working pretty well.

And I don't remember anything at all about the SO2 generating lots of heat, and lately I've been thinking of using it, so thank you very much for including that.

And thanks for all your additional detailed discriptions---that does really help a lot. Every time something "different" happens in a reaction, I think "holy cow, what's that, what did I just do? So now I won't be so baffled!

Don


Changed "the gold will mysteriously drag down a tiny bit of platinum" to "the gold will mysteriously drag down a tiny bit of palladium"

Don,
Heat from precipitation is pretty much a non issue unless you have heavily concentrated solutions. What you'll discover if you do use SO2 and have too much gold in solution is that it hits a wall and won't precipitate. It happened to me countless times when I'd re-refine my gold. I started with roughly 18 ounces of gold in a liter, to which I'd add three liters of ice. By the time the gold was down, the iced solution was hot enough to be steaming----and often wouldn't precipitate the last traces of gold. I learned that adding just a little more ice did the trick. The solution was saturated with SO2, so the moment temperature dropped a little the gold came down. It was visibly obvious.

If you dissolve SMB in water before application, and you have gold concentration quite low (3 oz/liter or less), I don't think you'll even detect a change in temperature when you precipitate.

Regards any of your testing solutions, be they standard solutions or any of the indicator solutions, yes, by all means, always make them the same way. Also, test your stannous chloride against your standard gold solution regularly. As it ages and weakens, the reaction diminishes, eventually coming to a full stop.

Glad to hear some of the things I mentioned helped. That's the name of the game here, to assist others.

Harold

Early on, I bought the traditional mossy tin and made the stannous chloride solution as per the instructions I found - probably from Hoke. I mainly used it for PGMs since I had developed reliable visual indicators for the presence of gold in most types of solutions. As a result, it would sit around between uses and I often had to make a fresh batch when I needed it. I didn't like having to do this.

Later on, I stopped making the solution altogether. I just put a drop or two of the acid solution I was testing, from an eyedropper, on a piece of filter paper. The filter paper I chose was such that the drops generally stayed in one spot and didn't spread (wick) quickly. I then immediately added a couple of stannous chloride crystals from the tip of my pocket knife and finally added a drop of water, if needed. The colors were always vivid. I found that when there were two, or more, PMs, say, Au and Pt, the various colors spread slowly and appeared separated in fairly distinct rings. Sort of like paper chromatography. The type of filter paper I used was very important. I used S&S 596 paper, but I think they stopped making it. Some of the slower Whatman papers worked well. Coffee filters don't work well at all for this. I always thought it would be neat to use paper chromatography techniques (vertical paper strips with the bottom tip in the solution) for this but never got around to it.

I'm not suggesting that you use this. Just showing how I did it.

Harold;

Starting with eScrap, I don't think I'll have any teen oz/liter solutions any time soon, but all your points are helpful. Hoke mentioned that warmer solutions precipitate better, as in disolving the SMB in warm water instead of cool. But with your icing experience, it appears that there is actually a sweet spot temperature-wise that is optimum. Very good to know. Thanks again!


GSP;

Visual indicators for gold in solutions? I've never heard of anything like that. I'd be very interested in hearing how that works!

I thought about using the stannous chloride crystals directly, but in a spot plate (I use a white plastic measuring spoon as I don't have a regular spot plate yet), but I never got around to trying it. I've read where some people use a small copperas crystal like that, and I tried that and it worked (and as Harold said above, stannous also helps for further testing of the solution, with the gold removed). I'll try the crystals on both paper and spot spoon next time.

I too like the benefit of the multiple colors on paper. I only have coffee filters now, and I do notice that they are not as sensitive as the spot plate type of test. Hoke mentioned the alternate of blotting paper, but I don't think they even make that anymore. So I'm looking in the meanwhile for a better paper. Maybe pencil drawing paper? Or what they call construction or craft paper?

I also notice that the coffee filters seem to give a more defined and darker edge-line if the values solution has dried or nearly dried, and also there is a different pattern if you do the opposite and put the stannous chloride on the paper first. I happened to let a drop of values solution dry once, and tried the reverse wet and dry, but no multiple testing to verify the results yet. I thought about making up some "stannous papers" ahead of time to see if that would work, but I'm not sure how long they would last even in a sealed bottle. Maybe since they were dry they would last awhile. I was figuring on small rounds or squares, but strips would probably be easier to read or even put side-by-side to compare. So I'll try this next time I get a chance.

Thank you very much.

Don

Visual indicators for gold in solutions? I've never heard of anything like that. I'd be very interested in hearing how that works!

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First of all, I'm talking about determining whether any gold was left in an aqua regia solution after precipitating the gold with sodium sulfite. I most always dropped the gold in a white plastic bucket. I rarely got rid of the base metals before dissolving the gold. I final pured the gold in the melt, when necessary.

(1) When you whip up the solution with a sir rod, you get some foam. If the foam is whitish, with no yellow, there is essentially no gold present. Even with Cu or Ni, the foam will be whitish.
(2) Using good lighting, tilt the bucket slightly and quickly look for a yellow film on the bucket. Only gold will produce this film - iron won't.
(3) This is hard to explain. The last little bit of gold usually came down finer than the rest. When the copper and/or nickel solution is mixed with a little gold powder, in the absence of any yellow gold solution, it forms a very distinctive color that is hard to miss. Just a trace of gold changes the color.
4) Looking down into a beaker of solution, a very small amount of yellow gold solution will show up at the surface edge of the solution, even in a dark green solution. Using good lighting a a piece of white paper behind it helps it a lot to be able to see this. Here again, tilting the beaker will provide a temporary yellow film on the glass - use the white paper. Iron will do the same thing, but the yellow color is different - less yellow, if that makes any sense.

I used a combination of these each time. Number (3) was always very reliable.

GSP;

Wow. I've noticed some characteristics similar to what you just described, and wondered about them, but I don't have enough experience yet to relate them to any particular result.

I'm going to be paying more attention now, for sure! I guess it's time to start making notes each time.

I had to take a break from it, to make a fume hood. I finished it today, so I'll be trying it out soon, and also trying some of the tests I mentioned in my posts above.

Thanks a million!

Don

I should also mention the smell when using a sulfite to drop the gold - SMB, sodium sulfite, etc. After stirring well, when you have gold left in the solution, you will have little or no smell of sulfur dioxide (SO2). The sulfite chemical reacts with the acid and produces SO2 - actually, sulfurous acid, when in solution. When you have excess gold, less than enough sulfite will completely react with the gold and drop it and there will be no free SO2 and, therefore, no smell. When the gold is out, you will have free SO2 and a strong smell. I know I haven't explained this very well.

Warning: Do not stick your nose directly over the container to smell any chemical. Always keep your nose to the side and use your hand to slowly wave a little of the fumes to your nose. It's called "wafting". In the case of SO2, it doesn't take much to be able to smell it. I remember once opening an unmarked gallon jug full of an innocuous looking water-clear liquid and foolishly stuck my nose over the opening to smell it. It contained ammonium hydroxide and I was literally knocked to my knees. From that point, I ALWAYS used the hand wave method.

Of course, all of these methods are subjective. When you put several of them them together, however, with a little experience they can be quite reliable. I would suggest observing these phenomena and then proving them with stannous chloride tests.

Most reactions have changes that can be detected with the senses. Observation is very important in this business. Keeping notes is excellent.

The stannous chloride papers might be a very good idea. Let them air dry - no heat. Like you said, preservation might be a problem. Keep them in a dark sealed container. When they turn yellow, they are likely no good. Somewhere, I have a book that shows how to make all sorts of test papers. Here's an interesting one - pH paper from red cabbage:
http://chemistry.about.com/od/chemistryhowtoguide/ht/makephpaper.htm
http://chemistry.about.com/library/weekly/aa012803a.htm

GSP;

Once again I haven't done this enough times to notice any cause-effect relationship with the smell when using SMB.

One thing that I did find out is that I am one of those people who can't smell SO2 as the rotten egg oder. To me, the SMB gives off a sickly-sweet acid smell. I also have read that it can really mess you up if you continue to breath it, even kill you if you breath enough of it. I did notice a major amount of smell when I added way too much SMB!

I'll be checking for this turning point in the precipitation process next time (whithou sniffing it directly!)

I've had a few instances of wind shift, and getting a direct waft of fumes from HCl or AR. The last time it happened I vowed to stop processing after that batch and build a fume hood before doing anything further.

I finished the fume hood, but I'm still trying to decide how to terminate the vent pipe (4 1/2' PVC). Right now it goes downward off the porch almost to the ground, and I have a plastic bucket under it. I thought it might condense and drip most of it into the bucket, but it doesn't. There is not enough power from the fan to put it into water, so I'm thinking I'll need to make a condenser system and run it through water, or something with a lot of baffles which can drip to an outlet. Or maybe a filter setup? I'm trying to figure which would be easiest.

I have litmus papers on my list for my next chemical order, but I think I'll try the cabbage juice in the mean time. That's really good to know, actually. I have a $30.00 digital pH meter, but you need to keep them in water for at least two hours before using them, and calibrate them in known solutions at least daily, so a quick check would be handy. Also somebody on this forum suggested setting out some litmus papers around your work area if you are wondering how much acid might be floating around that you're not aware of. I also got an fume filter mask, with dual cartridges, at Lowe's the other day! It says it's good for HCl, but doesn't mention nitric or chlorine, but it's a step in the right direction. I'll see how it goes, and if anyone has any recommendations. Fumes are bad for you!

Thanks again for your help,

Don

Actually, the rotten egg smell is hydrogen sulfide, H2S. The SO2 smells a bit different. Sometimes, too much of many types of chemical fumes will deaden the senses and you don't know exactly what you are smelling. All you know is, it's painful enough to make you want to get the hell out of there.

If you get more than a little SO2 it your system, you'll also taste it for an hour, or so, no mater how much you rinse your mouth out. Nasty taste.

When I was in the Air Force, I taught a 40 hour course, once a month, on chemical, biological, and nuclear warfare to 30 or 40 bomb shelter managers, border patrol guys, etc. - even a General, or two. In the tech school I attended in Denver, to learn how to do this, they had "sniff kits", which was a set of about 20 big corked test tubes. Each contained about 10 ml, or so, of a different "war gas" - choking, blister, tear, etc. We removed the corks and waved a little of the fumes to our noses. The object was to be able to recognize the different gases in the field. One contained a cyanide compound and gave off the bitter almond smell and taste. I'm sure that all these were well diluted down. At the time, there was much experimentation in using LSD, somehow, as a psychoactive war agent. Unfortunately, it was not included in the "sniff kit."