Reno Chris
Well-known member
- Joined
- May 5, 2011
- Messages
- 274
Here is a little example / tutorial of one way to deal with grey metastanate powder:
So the original reason I searched out this forum was that I inherited several pounds of gold plated pins (There is a novel way of acquiring PM scrap). The pins belonged to a friend of a friend, then when he passed away my friend got them after helping the guys wife sell off a bunch of his mining equipment, and when my friend passed away a few years later, after helping his wife sell off a bunch of his mining related equipment, I ended up with the pins and a jar of gold foils intimately mixed with a gray powder. I did see notations on the forum about the metastanate that may form, but I figured that a number of forum members deal with this from time to time, so I should be able to handle it also. So I digested the pins in nitric acid which I had on hand. It worked fine for the digestion of the copper, but just like the bottle of foils in gray powder, my nitric digestion generated a gray metastanate powder that was impossible to separate from the gold. Turns out the body of the pins was a phosphor-bronze, and probably had 3 to 6 % tin by weight.
That is shown in the first picture which is both my foils and the the jar of foils with gray powder combined.
So after reading the forum and seeing various way of dealing with the problem, I decided to try digestion in strong hydroxide solution. I figured if I needed to let it stand all summer to fully digest, I really didn't care. I've now had this stuff for several years anyway. I let the whole thing settle overnight and poured as much water as possible off. I then added about a teaspoon (maybe 20 grams) of Potassium Hydroxide into about 150 ml of foils and metastanate solution mixture. The light gray powder darkened fairly quickly to a darker gray. I let it sit for a few hours, but I did no incineration, heating or other unusual procedures. Afterward while stirring the mix, I noticed that it was very uniform, and so I added water to see what it would do. As I expected, the metastanate had formed a colloidal suspension allowing the gold the settle and separate. (see photo No. 2) (for forum members who don't know about colloids, Google it and look at the wikipedia entry). I then just poured off the colloid after allowing time for the gold to settle and repeated the process of adding water, settling the gold and pouring off until the liquid above the gold was clean and clear. (See photo 3). It was slick and very easy, so I wanted to share it with you all.
So the original reason I searched out this forum was that I inherited several pounds of gold plated pins (There is a novel way of acquiring PM scrap). The pins belonged to a friend of a friend, then when he passed away my friend got them after helping the guys wife sell off a bunch of his mining equipment, and when my friend passed away a few years later, after helping his wife sell off a bunch of his mining related equipment, I ended up with the pins and a jar of gold foils intimately mixed with a gray powder. I did see notations on the forum about the metastanate that may form, but I figured that a number of forum members deal with this from time to time, so I should be able to handle it also. So I digested the pins in nitric acid which I had on hand. It worked fine for the digestion of the copper, but just like the bottle of foils in gray powder, my nitric digestion generated a gray metastanate powder that was impossible to separate from the gold. Turns out the body of the pins was a phosphor-bronze, and probably had 3 to 6 % tin by weight.
That is shown in the first picture which is both my foils and the the jar of foils with gray powder combined.
So after reading the forum and seeing various way of dealing with the problem, I decided to try digestion in strong hydroxide solution. I figured if I needed to let it stand all summer to fully digest, I really didn't care. I've now had this stuff for several years anyway. I let the whole thing settle overnight and poured as much water as possible off. I then added about a teaspoon (maybe 20 grams) of Potassium Hydroxide into about 150 ml of foils and metastanate solution mixture. The light gray powder darkened fairly quickly to a darker gray. I let it sit for a few hours, but I did no incineration, heating or other unusual procedures. Afterward while stirring the mix, I noticed that it was very uniform, and so I added water to see what it would do. As I expected, the metastanate had formed a colloidal suspension allowing the gold the settle and separate. (see photo No. 2) (for forum members who don't know about colloids, Google it and look at the wikipedia entry). I then just poured off the colloid after allowing time for the gold to settle and repeated the process of adding water, settling the gold and pouring off until the liquid above the gold was clean and clear. (See photo 3). It was slick and very easy, so I wanted to share it with you all.
