Strange White Material While Parting--Help--

[qgold]

This problem just started happening and I would like to know what you guys think.
3 samples per pin pull are used, a regenerate grade nitric @ 68% is used with distilled H2O, 4 9s fine Ag is used and lead Assay cups. Mabor #7A Cupels are used and Coors #7 porcelain parting cup are used for parting and annealing. Cahn microbalances are used as well. ( Sample never leaves coors cup ) 3 to 27 samples are run at a time prior to this problem and now I'm just doing 3 at a time to try and resolve this. Here is my process. All our assays are in the range of 55% to 65% Au.

Cupels are placed in a 750c oven for about 15 min to rid moisture.

.5 grams Au sample + 1.5 grams fine Ag grain placed in assay cups.

Placed in 950c oven for 18/20 min--Remove and cover till cooled--nice clean dore!

Remove dore and brush clean--not rolled or hammered

Parting cups are placed on 168f hot plate with 1 part nitric 2 parts distilled h2O

Samples are placed in cups until reaction is finished.

Decant with distilled H2O

Cups filled with 2 parts nitric 1 part distilled H2O

When reaction is finished, decanted X2 with distilled H2O.

Dried on hot plate to remove H2O

Annealed in 750c oven and weighed.

I have done this day in and day out with great results but now I have this issue and have no idea where it came from or how to rid it. Looks to me like white salts??? as soon as the nitric hits the dore you can see it turning cloudy white. In order to solve this I made sure a ALL my supplies are new and from our same suppliers.


Thanks a lot,
Eric

 

[qst42know]

I don't know if this is what you are experiencing but a while back there were reports of gold being cut with iridium.

What is the source of your material?

 

[qgold]

Everything from clean karat sheet to jewelry karat scrap. Thing is, I have old pin samples that tested good with no problems but now, samples from the same old pins produce the problem now?

Thanks,

 

[lazersteve]

Have you performed any tests on the white material?

Does it darken when exposed to light?

Is is soluble in any mineral acid, hot water, ammonium hydroxide, or other base?

Does it melt when heated? If so at what temperature?

Knowing what the material is may give you a clue as to it's origin.

Steve

 

[butcher]

"a regenerate grade nitric @ 68% is used with distilled H2O, 4 9s fine Ag is used and lead Assay cups. "

I would test the nitric for chlorides, maybe silver chloride?

 

[qgold]

Thanks guy's will do both today and get back!

 

[goldsilverpro]

as soon as the nitric hits the dore you can see it turning cloudy white

I agree with Richard Butcher. The only time I have ever experienced this (exactly as you described it above) in an assay was when the nitric (or the water used to dilute the nitric) was contaminated with chlorides - it doesn't take much. If it is silver chloride, it will dissolve in a little ammonia. I would try this before drying the sample just as a test. You may have to warm it. Collect the ammonia solution and acidify it with a little HCl. The AgCl should re-precipitate as a white cloud.

 

[qgold]

Thanks GSP will do!

 

[qgold]

as soon as the nitric hits the dore you can see it turning cloudy white

I agree with Richard Butcher. The only time I have ever experienced this (exactly as you described it above) in an assay was when the nitric (or the water used to dilute the nitric) was contaminated with chlorides - it doesn't take much. If it is silver chloride, it will dissolve in a little ammonia.

Bingo !

It was my water, Thanks a lot everybody! Life is good once again. Don't know what happened to it as it always in a clean sealed glass container.
Oh well-Live and learn. I know this was my first post but believe me I have read just about everything twice on this forum,some stuff 3 and 4 times. Some very knowledgeable people here.
Thanks again,
Eric

 

[goldsilverpro]

Maybe, when you cleaned the glass water container, you rinsed it in tap water, which is likely to contain chlorine/chlorides. You should rinse it several times in distilled water before filling it.

If you're buying the distilled water in 1 gallon jugs, I wouldn't buy the cheapest brand you can find. I actually bought some once that contained chlorides. In my estimation, the most reliable distilled water I have found in a store came from Walgreen. I think they sell 2 different qualities and the purer, more expensive one, is about twice the price (about $1.75/gal, the last time I bought it). Cheap, considering what you're using it for.

 

[Barren Realms 007]

Find a dehumidifier for an A/C system and use the water it produces.