Zinc... I give up..

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John,

Welcome to the forum.

What purity is the zinc? I've run into some issues before with zinc that contains a very fine sand like substance as an impurity. The sand substance ends up mixed in with your metals and won't dissolve with the acids normally used in processing the precipitated metals.

Steve
 
John,

The website doesn't have a working link to the ebay store, did you just phone in your order? What's the guys ebay seller ID?

Steve
 
Steve, you are the greatest!! Thanks for that comment about the sand, it just made something quite, quite clear to me!!!!!
 
Lou,

As you know from our recent PM's I've been struggling to get a handle on the processing of Rh. I've recently found that sand was introduced as an impurity via the zinc flour that was not pure (I even passed it thru a 200 mesh screen before use). I have since switched to a higher purity zinc for my precipitations. Now I'm faced with the task of eliminating the 'sand' from my previous batches. I know HF will do the job, but I think I'll try converting the silicates (?) into a soluble form instead. Since they are so fine, I'm not 100% sure they are silicates, but the residue is something along these lines. I wish I knew how the zinc flour was being produced as that may tell the real story.

This little facet of information has had me baffeled for sometime, but now I know the real truth as to why my yields were higher than expected, and the residues were impervious to the acids I normally use. The 'sand' impurity was the solution (for me anyway).

I'm glad I could give something back to you Lou for all the help you have provided me ( both privately and publically). :wink:

Thank you,

Steve
 
Wow guys, sorry to hear this, I think I could have been of some help.
I bought some cheap zinc off ebay a long time ago and found this out by just trying to disolve some in hcl that it had a bunch of undisolvables.
Guess I should have brought this up.
I always figured that I had just bought some real junk.
I would think the thing to always do then, is to just disolve some in hcl to see if it is really just zinc.
Randy
 
Randy,

For me I felt pretty foolish when I identified the problem, I should have known better.

It's just another good example of GIGO. If you put garbage (from any source) into your reactions, the garbage is bound to come out. It also makes crystal clear the importance of knowing exactly what is in all of your reagents before you use them.

The bad zinc I had was also purchased from ebay. I discovered it was the zinc after noticing that a fine brownish powder in my precipitations would never fully dissolve. After a lot of head scratching I back tracked and tested my zinc and found the culprit.

Steve
 
Pawnbroker Bob said:
Go to a local boat or marine/fishing supply. You can buy cast solid zinc anodes for boat motors and hulls. Not really cheap but available.

Pawnbroker Bob
Click to expand...

This is a great place to get zinc. All boat hauls have zinc anodes and can be bought at marine supplies shops.
 
Steve, you can use hot lye or potash solutions to dissolve silica. Alternatively, consider using ammonium bifluoride (''dry'' HF).

Story time:
Let's just say that I was dissolving some PGM sponge material that a member here had sent me. Everything was going fine but I kept seeing a recurrent precipitate that reminded me very much (it was a milky suspension) of something called Cab-O-Sil, which is basically fumed silica powder, a very, very fine powder. I removed it through microfiltration processes and this gummed up my filters and really ticked me off. What should've been a day's work became a week long endeavor.

I did a powder XRD on a sample of the material and confirmed my suspicions. I also dissolved a sample in HF and played around with it to see if I couldn't hydrolyze it back out in the filtrate but that's another story and another problem...


Anyway, long story short is that the zinc that many people here are using is contaminated with silica, SiO2. Steve's comment here in this thread helped me make the real causal link and establish that this is something that other people are experiencing rather than only the client who sent me his precipitates. It was the straw that broke the camel's back so to speak. I'm used to using pure zinc powder out of a supply house like Fisher--and that comes with complete analysis and any additives are noted. It's also murderously expensive to get it shipped (1200 mesh zinc is considered pyrophoric) so I hadn't considered possible reagent contamination, rather I thought it was residual artifacts from his other processes (which some still is!).

Now that I see others experiencing this phenomenon, I know what its cause is-- that fine silica powder decreases flammability and flowability and makes the material much easier to ship. It also makes it cheaper by adding bulk. I'm so thoroughly vexed at having my time wasted by these damn scoundrels selling inferior products to my customers and friends that I'm considering buying 100# of good material and parting it out!! Zinc is the premier material for dropping values. It washes out nicely, unlike iron and copper, it's also relatively cheap, and very fast, and also about idiot-proof.

Again, thank you Steve for confirming my suspicions and you are right about garbage in, garbage out. I realize that not everyone has access to quality, standardized chemicals, but there is something beautiful about not needing to worry about what reagents you're using.

Lou
 
Lou,
Count me in if you part out some bulk zinc.
Mine came from Ebay as well, and I would
rather avoid any problems when dealing with
pgm's. I am sure others will also realize that
buying from you would be a smart move also.
Jim
 
I got zinc powder from a fireworks supply site. As far as I can tell, it is pure zinc. Kinda pricey but it got me going quickly.

http://www.skylighter.com/
 
If you look around on the pyrotechnic supply sites they also sell alumina ceramic grinding satellites made for grinding fireworks materials to fine powders in tumblers. If your source had ground less expensive zinc shot to powder themselves in a tumbler your powder will contain aluminum oxide dust as well. The fellow selling pyrotechnic supplies on ebay right now as well as three additional pyrotechnic supply web sites on the open web (one guy, four venues) indicated to me a commercial source for the zinc dust he sells.
 
That should have been three venues. Northstar/American/Jumpin jack flash pyro supplies. The source he indicated was http://www.purityzinc.com/
In the ultra pure line 325 mesh.
 
Nobody wants to sell reagent grade zinc to individuals in large enough quantities to be economical.

Lou, the next time you order some, I would be willing to purchase some from you as well as pay you back for the zinc you've sent me.
In the meantime, If anyone knows how to get the sand out of it before using it, that wouldn't take forever or cost a fortune, please let me know as I have 5 lbs. that I would prefer not to toss out.

Mark
 
Mark, next time you need zinc, I'll make sure you get the reagent grade material. Setting up an account with Fisher or another chemical supply house can be daunting (or these days, impossible) as it requires a business license/codes that specifies chemical industry or research lab. Don't worry about the zinc this time around.

Remember that you pay for the purity from the chemical supply house and it isn't cheap. Good news is, there are no questions about contamination when you order ACS reagent grade, it is what it says it is on the bottle. I think it will solve your sand issues.

As for getting the cab-O-sil fumed silica out of it, hell if I know. I think it's no good, unless you want to digest all of your metal precipitates in HF to get the damn sand out of them!!
 
Mark,

I've ordered some solid zinc that I'll be turning on a lathe to make some pure zinc turnings. I should have the bars by the end of the week. I'll make some turnings this weekend and try them out. If they work fine I'll have plenty for sale (50+ pounds).

I'll keep you posted Mark.

If anyone else is interested I'll be selling the turnings on my website once I confirm their usefulness.

Steve
 
I might be interested in the turnings assuming you can provide certs on the purity of the metal.

Also, I don't know about machining zinc, but if you use any lubricant for the cut, be sure to remove it with some sort of solvent!


Lou
 
Lou,

I don't have the purity specs, but I can send you a sample when I get the zinc and you could analyze it if you like. I don't have access to any way to confirm it other than using some for a precipitation and seeing what residues I find.

I've tried two different forms of powdered zinc and I'm running into the same problem each time... a fine insoluble brown residue (sand?).

Steve
 
Steve, I've had this sand issue happen to me while processing crude precipitates from several of my clients. It got to be so bothersome due to the destruction of my filtering setups and it was such a time waste, it was cheaper for me ultimately to spend the $35/lb on reagent grade ACS certified zinc which I knowworks. I shipped it out to some people here to save me time and help them get on track. Inferior reagents: garbage in, garbage out.

For me, it is a very fine silica flour that has come up multiple times and powder XRD indicates it as being silica. I talked to some friends about it and was told that it is Cab-O-Sil, a fumed silica product that is used to improve flowability of the zinc powder and decrease its flammability. Conveniently it adds mass to the zinc, but it is not intended as a bulking agent.
Regardless, it is a nuisance to be sure and has cost me some expensive frit glass filters and unnecessary delays in processing times!!!

I'm not so much concerned about metals contamination in your zinc as I am about insolubles like silica. I would be glad to assay a little bit of it and see what residues are left after digestion. I'd rather pay you top dollar for a product that works than send it to some supply house.

Regards,
Lou
 

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