Geo
Well-known member
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?
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?