mystery alloy

[Geo]

I incinerated, milled, classified and gravity separated some IC chips. Normally, I leach the concentrated material to remove the base metal and leave me with relatively clean gold bonding wires to dissolve. I tried something new. I smelted the concentrates in a 4" melting dish with my cutting torch. This was hard to do and I don't recommend anyone try it. There's a lot of toxic fumes and white smoke. I knew there would be and took precautions. I poured the melted metal into a one ounce kit kat mold. There was roughly 130 grams in all of metal bars.
First oddity. Even though the majority of base metal was copper, the metal bars came out white metal. There was no copper tint as you can see in the pictures. The piece of copper metal is for comparison. I was going to try and part the copper out using copper sulfate.
Second oddity. The metal was extremely hard. I could not cut it with a knife blade. I tried to sand a spot and the fine grit would not scratch the surface.
Third oddity. It was very light. in the picture is one of the final bars that only filled half the mold. Even though it was only half a bar, it was over full so it was over the top of the mold. Copper and gold are close on weights so I was thinking it should be 15g at least. The eleven grams surprised me. You could hold all the bars and tell that it felt light for the amount of metal you were holding.
Since parting was out, I decided to leach the bars in nitric acid. The acid was slow to react even after heating. After an hour, the action had almost stopped so I assumed there was some sort of passivation happening. The bars seemed almost untouched. After letting everything cool, I noticed some black sediment. AH-HA! Some gold. So I set up a filter. The liquid seemed strange. Then I noticed why. It was very thick. It was slow to filter and there was a strange substance in the filter. It was like a clear jelly tinted blue with the copper nitrate. After removing the solution I was able to look at the bars. They were white but not metallic. There was a white crust that was easily broken with a knife tip. The metal under the white crust now looked like copper. The filtered solution is very pregnant with silver. A drop of HCl in a drop of solution creates an instant, almost solid white mass. The clear jelly resembles concentrated sodium silicate. There was never any hydroxide in the process. The concentrates did have a lot of silica die material. Any thoughts on what I created and how to avoid it later?

 

[anachronism]

The colour of your Nitric leach and the slow filtration is similar to the effects I have had when ashing and recovering gold from ash that contains Chromium.

The passivation of the acid when you put them in Nitric is also very similar behaviour to that which I have experienced. It can slow AR down almost to a stop. It's a truly horrid metal to get involved with during refining, and I hear that comment from other refiners.

That would be my deduction from my own experience Geo, however I'm sure that other theories will be presented.

Jon

 

[anachronism]

To add to the above post.

As you mentioned, you tried something different here and I do think your usual method was the correct one but no harm done. One thing to note, that is when you leach the base metals out of this material using a simmering HCl boil whilst it is the best method - you will find that the base metals will oxidise some gold and carry it up into solution. This effect is more pronounced if you have iron present. So make sure you filter your HCl solution and drop the gold from it with your usual precipitant.

Base metals can and will cause gold to go into an HCl solution.

With regards to the passivation. The base metal contaminants come into play- not just individually but collectively- because they also interact with one another and can give you a situation whereby there is a chain of metals being dissolved one at a time. So if you have one base metal that takes ages to go into solution before another base metal can be dissolved it can actually look as though the reaction has stopped when in fact it hasn't. It's merely dissolving the particular metal but taking ages to do so. I had a similar situation myself Geo and thanks to Dean for explaining the chemistry behind this to me in words I could understand.

Jon

 

[Geo]

Thanks Jon. I notice that I failed to state that I normally leach the base metal in nitric acid. I have found that there is, at least, a recoverable amount of silver in the base metal. I don't dissolve all if the metal from the chips as it would be too much metal to reasonably deal with. After incineration and milling, I do a magnetic separation and I classify the material through quarter inch expanded metal screen. Anything that doesn't screen goes back in the fire. What does screen goes through an aluminium window screen. Anything that doesn't screen goes back through the mill and anything that will screen goes through a 100 mesh screen. Again, anything that doesn't screen goes back through the mill. What passes through the 100 mesh is what I actually process. Bonding wires are small enough that 100 mesh is huge in comparison. This cuts down on the use of acids and time of dissolution. I plan on running all of the copper that has been accumulating through a parting cell to recover any values that I missed. I have done small samples of the copper along to see if I have been putting aside any gold. I found silver but haven't found any gold.

 

[kurtak]

Geo

Sounds like you have had silica (for lack of better term) alloy with your metal

how/what did you flux it with ?

Kurt

 

[autumnwillow]

Have you tried diluting the jelly like substance with water and see if it dissolves?

I have had the same experience before, everything was jelly like, I added some some water and it turned out to be just over evaporation from a long digest time.

I think there is some gold still trapped inside the bar so I would smelt the bar the again(use an oxidizing flux/flame). Re-melt then add some silver, then pour them as corn flakes, then digest in nitric then AR.

 

[upcyclist]

I guess that was my question: Why pour it as bars rather than as shot/cornflake? I know you've been here long enough to have a reason, and not be the usual "then I melted all my pins into a bar" like newer folks often do

 

[Geo]

Geo

Sounds like you have had silica (for lack of better term) alloy with your metal

how/what did you flux it with ?

Kurt

I do believe it was. I don't understand how silica can form an alloy. From wiki : "Silicon dioxide will neutralise basic metal oxides (e.g. sodium oxide, potassium oxide, lead(II) oxide, zinc oxide, or mixtures of oxides, forming silicates and glasses as the Si-O-Si bonds in silica are broken successively)".

The silica from the chips could have formed some kind of metal silicate. I still am not able to figure out the how. I gave up leaching with nitric acid and went to straight AR. It worked okay but the white crust that formed (which I assume is silica) caused bumping so bad I thought it would bust the beaker. It would expel gas so hard it would almost blow the watch glass off the beaker. Near the end and desperate to finish it without breaking anything, I added a little sulfuric acid and low and behold, the bumping nearly stopped.

 

[Geo]

Have you tried diluting the jelly like substance with water and see if it dissolves?

I have had the same experience before, everything was jelly like, I added some some water and it turned out to be just over evaporation from a long digest time.

I think there is some gold still trapped inside the bar so I would smelt the bar the again(use an oxidizing flux/flame). Re-melt then add some silver, then pour them as corn flakes, then digest in nitric then AR.

I made bars planning to part the copper in a small cell. I decided to work with what I had because I had never seen anything like it.

I guess that was my question: Why pour it as bars rather than as shot/cornflake? I know you've been here long enough to have a reason, and not be the usual "then I melted all my pins into a bar" like newer folks often do

Same as above.

Thanks guys for the replies.

 

[g_axelsson]

Silica and silicon isn't the same thing. Silica is basically quartz while silicon is the pure element.

Silicon is used in alloys, have a high melting point and is quite light.
To me it sounds like you managed to make a silicon-metal alloy.

Göran

 

[Geo]

I checked out silver/silicon alloys. They are sold commercially. Thanks Goran.

 

[anachronism]

Then again. Get an XRF gun put on it.

You must know someone with one and it would be interesting to see the results. I'm still not sold on the silicate/on alloy theory, but I at least am prepared to be wrong.

At most I'd go for an Aluminium Silicon Alloy but I think it's a reach.

What temperature were you melting at?

Edit:

Actually I'll put my money where my mouth is (as we say in the UK) if you can't find someone to XRF over there, then cut me a reasonable sized thin sample off and I'll collect it via Fedex/UPS and XRF it on a copper background and print the results on here Geo.

Jon

 

[Geo]

There was no aluminum in the mix. I melted with a Victor torch with an oxy/propane cutting tip. https://en.wikipedia.org/wiki/Oxy-fuel_welding_and_cutting
So about 4,000° F.

I'm going up to Elemetals in a couple of days. I'll see if I can get Jim to shoot it and print me the report.

 

[anachronism]

Please Geo. That would be great.

Edit: if you were melting that high would there not be a chance of Nickel in there too?

 

[Geo]

Well, there is the possibility of most anything, but, this is the incinerated and milled IC chip material mentioned earlier. There were no magnetics. I seriously doubt nickel would have been present. Mainly from chips, you will find after the magnetics are removed, copper, silver, palladium, aluminum and gold. There could be small amounts of lead and/or tin but still unlikely.