Baby steps, first refining

[IdahoMole]

I took 1.27g of gold recovered with nitric and placed it into a 100ml beaker, covered it with 10ml of 32% HCl. I placed this into the coffee pot with a sand bed and put it onto my hot plate and turned the heat to low-warm. I then added 1ml of 67% HNO3. About 2 hours later all of the gold had dissolved. The last tiny slivers took awhile to finish so I believe that most, if not all, of the nitric has been consumed. Next I added 5 or 6 drops of sulfuric acid. This made a hissing sound similar to water dropping on a hot pan which leads me to my first question. Is that sound normal or is it a sign of something in solution like excess nitric? After the sulfuric I added an ice cube and filtered. I have 60ml of solution after rinsing.
Today I plan on trying my first gold drop with SMB. Should I evaporate and rehydrate with HCl to eliminate free nitric or should I be ok considering how little was needed to begin with? If I go straight to SMB and there is free nitric are there visible signs of this that I should be on the lookout for or will I just get no gold drop? Do you see any noob mistakes I am about to make? Thank you for any advise.

 

[g_axelsson]

That sounds great!

The hissing sound when dropping sulfuric acid into water is normal, at least when it is hot. The concentrated sulfuric acid releases a lot of heat when mixed with water. So there is nothing strange going on.

Since you started with only 1 ml of nitric I don't think there is a lot left. The small amount left could easily be fought with a bit extra SMB. Precipitate as normal and if there still is a yellow tone to the AR add a pinch more of SMB.

Visual cues that there is still nitric left is if you initially get the gold to drop and it redissolve or brown NOx gas released.

One time early in my career I had a lot of nitric left and got two zones in the beaker, a top zone where the SMB had dropped the gold, a border where the gold hit the AR and dissolved again and a bottom layer with AR and gold chloride. That was the moment I decided to always denox my solutions. Later I also bought gloves....
That time I fought the nitric off by adding more SMB but it took quite a lot to get rid of the nitric.

Göran

 

[IdahoMole]

I got the gold dropped earlier today and most everything went well. I mixed 1.25g of SMB in a little distilled water, poured it in and gave it a stir. Within a few seconds it turned brown, like coffee. After 45 minutes, and a phone call, everything had settled nicely. I decanted into a filter and rinsed with a little HCl and water.
I used a buchner funnel and had a little trouble with it. Some gold got under the paper and slipped through so I ran it through another filter. Next time I will use a cone shaped funnel. Am I correct in thinking that a buchner funnel basically requires the use of a vacuum to be effective?
I also learned the value of spotless glass ware. The beaker I made the drop in had a water stain on the inside and the gold collected on it.
Aside from the filtering difficulties the process went smoothly. I know that my rinsing procedure is not up to par and I will work on that with the next batch. Right now I just want to melt a shiny little gold BB!

Thank you Goran for taking the time to chime in and clarifying the sound sulfuric makes when dropping into the AR.

I couldn't have made it this far without the contributing members of this site and Hoke's book. Thanks to all that came before me.

 

[FrugalRefiner]

Yes, you need to use a Büchner funnel with a vacuum. Without some vacuum to hold it down, the filter paper won't make a tight fit to the funnel and solids can slip by under the paper.

Dave