Small precip particals.

Ok This might be my first technical question(s).

I have been using the nitric / HCL (AR) method

I am processing fingers foils, and cpus etc.. I know this method is not the best choice for this type of scrap but I am just trying to learn one thing at a time and I started with the AR process so until I get a firm understanding I don't want to move on to another (most likely better) process for my scrap. The amounts are only training amounts and all of my reactions have taken place in the 500ml reactor, keeping the sample and the chemicals to a minimium while I adjust to the process.

My typical run looks like this:

I add my sample to the reactor. Add water, heat up to about 100 F and I give it a nitric bath. When reaction is over I filter the fluids out and add them to the silver stock pot. I then cover the sample with water and heat it up. I add the hcl. I then use 70% nitric and alternate between the two (HCL and the Nitric) until the reaction is complete. I then boil down to a syrup.
I use HCL to get it back to a fluid and boil down again. I then cool and dilute the sample 3x with water. I add the proper amount of sulphuric. I let it settle overnight and the bottom of the container is covered in a grey white precip the next day. I decant and I use a millipore u40 vacuum filter setup to filter the fluid. The filters go on for further processing. Now on to the drop. Here is where I have yet to get a real grasp of the concept. I have SMB and Ferrious sulfate. I have had better drops with the smb but that could be due to many factors. Anyway I mix the SMB and add to the solution. I have added it to the solution that is at room temps and I have tried heating the solution. I am not sure yet which is best. Anyway every drop seems to have one thing in common. The precip is ultra fine powder like.... I understand the amount of Au going in is small. Does this sound correct? I test with Stannous and it shows clear of PM. I then filter and re-run the filtered gold powder and then smelt.

Here are my questions.
1. The precip is ultra fine, not granulated or fiber like. Is this to be expected?
2. Should I stick with SMB or Ferrious?
3. When mixing the precipiant I have read hot, warm and cooled. What is the correct temp to mix up the precipiant?
4. What is the suggested temp of the actual solution when doing the drop? I have seen the added Ice method, Heated, and room temperature methods.
5. Lastly I have the Stannous white flakes. I have read, and finally confused myself on mixing it. Do I mix the flakes with HCL or is that just for making Stannous from scratch with Tin? Or do i just mix it with water? I currently use water until the flakes disolve. I do have a sample vial of known gold bearing solution in it so I can test my stannous. I have not mastered the colors yet so I am unclear on the typs of PM my solutions contain as my mixing of my stannous might be weak, strong or even the wrong mixing agent, but I can tell when the test shows no Pm's left in sol.

I just ran out of nitric and I guess I might learn the poor man's AR or the AP method. I just don't want to move on as I have not got a hold on AR just yet, well actually my issues are with the precip phase so maybe I am wrong about not understanding the AR process. Also I have had little to no trouble with excess nitric as I pay close attention to the addition of nitric in the actual reaction steps and in combination with the boiling off method, seems to keep my nitric in check. I understand the right way is possibly not to use nitric at all... sh!t I am overwhelmed...ok. enough for now.


Finally will someone tell me if there is a built in spell check in the forum or do I need to copy and paste in word to run a spell check and then paste back to the forum to have my terrible spelling corrected?

Thank you.

John S.

John,

The most likely reason why your gold is coming down ultrafine is the high dilution of the solution when precipitating.

Here are a few suggestions to help your gold agglomerate and settle quickly:

• The step of diluting with water is included to lower the solubility of unwanted chlorides so they can be filtered out. Instead of diluting with three volumes of water, cool the pregnant AR with ice cubes, let them melt, then filter cold. Water expands when it freezes so ice has more volume than the same weight of water, hence ice dilutes the solution less than the same volume of water, and the lower temperature achieves the same desired result of forcing unwanted chlorides (silver, copper, and lead) out of the cold solution.
  
  
• Don't dissolve your SMB in water, add it dry with the solution at room temperature. As long as your solution is not super saturated with gold and other metals, there should be enough water in it already from the acids to initiate the reaction of the SMB to SO2 (ref: Common Reaction Equations). If you notice your SMB is settling to the bottom as a white solid and stirring does not cause the white powder to dissolve, then add a small amount of water to get the SO2 production going. Add small amounts of SMB with stirring until you see a color shift in the solution. Once the solution color shifts towards brown check for white solids at the bottom (undissolved SMB), stir, and add a little water if necessary. You should begin to smell SO2 (coughing and sneezing set in if you inhale too much so be very careful here) when the additions are complete. If your dry SMB additions form a thick foam on top accompanied by red-brown fumes then you have excess nitric in the solution and it will require more SMB to kill off the excess free nitric. This excess nitric condition will also cause your gold to briefly form a brown powder which redissolves. If this happens then the solution will require either more evaporation, more SMB, or the use of another reagent (either urea or sulfamic acid) to remove the nitric.
  
  
• After the solution begins to precipitate and no red-brown fumes or foaming are present when a small amount of SMB is added, the color of the liquid should be pale green to nearly crystal clear. You can check the solution color with a white plastic spoon. Dip the spoon in the surface of the solution and lift it out along the wall of the beaker. Examine the color of the thin layer of the solution against the white of the spoon as it flows off of the plastic spoon and down the wall of the beaker. There should be no tint of yellow to the liquid.
  
  
• Place the uncovered solution in a catch basin on a hot plate set to med-low heat and allow it to warm and settle (10-15 minutes typically). Do this under a fume hood or outdoors in a well ventilated area as these are the choking fumes of SO2 I mentioned above. When the gold has settled to a thin ( or thick if you have a lot of gold!!) layer across the bottom test the solution with a swab or spot plate for dissolved values. The Guided Tour link below has a Reaction List link with descriptions and photos of all of the stannous chloride color test results.
  
  
• Remove from heat and decant off the clear solution leaving your gold powder behind.
  
  
• Follow the normal clean up process for the brown powder as detailed in the Guided Tour --> Reaction List.

Gold tends to agglomerate best and settle fastest when clean, concentrated, and warm. So the more pure gold you can fit in the smallest volume of clean solution the better it sticks together. An acidic solution also helps the fine particles to join together in extreme cases of purple colloidal gold being formed.

Steve

No their is not a forum spell check.
Usually I will write my whole post in word, spell check, then open the post to forum window and copy/paste the whole thing at once.

Actually I like this better since it is easy to go back to reread any parts I am unsure of to give the best answer without multiple postings or edits.

Tom C.

The Google toolbar has a spell check function. You would have to give up a stripe of space on the top of your browser window though.

It doesn't know many chemical names though.

Wow, thank you all. Steve, I read your first line and you hit it right on the money. My dilutions were heavier than they should have been. I am going to print out your reply and take it home and read it tonight. Thank you so much. I am really taking this seriuosly and I have had my nose to the grinding wheel putting in my time and getting my butt kicked, but it is all coming together really well. I have watched all of your videos as well as all of the videos and posts I can find from the top 5-7 members here. I really don't know what to say about you all (you know who you are). I want to build a floating shrine and dedicate it to you guys but instead I will just say thank you for helping us. Hopefully one day I can contribute in a way that might help you guys, but that is unlikely. For now all I can do is try to document on the forum my trials and errors as I progress.

I have done some amazing things in my life. This somehow by far feels like the biggest acomplishment and most chalenging (asside from parrenting, which the jury is still out on weather or not I am a good one, I try my best but the little buggers don't come with a manual.)

Anyway, we got a little snow and the kids want to go fourwheeling. So I have got to bounce!!.

Thanks again and I can't wait to read more.

John S.
(PS I will begin spellchecking from now on!!)

Firefox has a built in spell checker that works quite well. It uses American spelling, which is somewhat frustrating to us Canadians who like our extra "u"s.

Al

Thank you Steve for taking the time to leave a detailed reply. It means a lot.
Tomorrow I will go back in and practice what you have taught me. I have to get a fridge moved into my lab for the ice maker, but with some modifications I can use the fridge as a chiller source for my condenser!!

I have a question concerning personal preference. I am not ready to move into the electrical stripping processes yet. Could you or other senior members tell me what you think is the best process (no details needed, just the name) for e-scrap gold recovery?

Currently I am using the AR method. I ran out of HN03. I have some Sodium Nitrate in a bag that is older but the actual date of purchase is unknown. I have read your poor mans AR posts. So excluding the electro-cell, which would you suggest I focus on now that I am faced with either re ordering HN03.

Should I:
1. Stay with AR and my current method using 70% HN03? (expensive, but I am most familiar with)
2. Stay with AR and substitute the HN03 with Sodium Nitrate?
3. Move on and learn AP or
4. Move on and learn Acid / bleach ?

Thank you for your time, members.
John S.
P.S. Working under the new properly functioning fume hood has made a tremendous impact on my safety and functionality. That translates directly to the quality and even the ..gulp....the FUN of recovering and refining of PM's. It just keeps getting better. Having just started out, if any newbee asked me what is the single best purchase he or she could make...the answer has to be a proper working fume hood. Not only does it serve it's primary duty and pull harmful fumes out, but working under the slanted thick plexi protects your face and torso from acids. I wish I had it when I made my stupid mistake of adding peroxide to my hot, AR solution with sulfuric acid in the mix.

AP acid peroxide (copper II chloride etch) is an extremely useful tool, as copper is a main component in electronics (other base metals will also etch or break down to powders in this solution but that is a different story, as they are not normally wanted in this solution), I recommend anyone wanting to learn recovery of values from electronic scrap learn this process.

HCL/Bleach dissolve gold and some PGM, it like aqua regia (these metals will need to be clean as possible from base metals), it is actually easier to work with than aqua regia, and has its own advantages, and disadvantages compared to aqua regia.
Also I highly recommend.

Memory fingers and the two above processes you will learn a lot, it is easy if done right.

Laser Steve's web site is the place to learn these basics, (see his link above), also reading through the forum (earlier posts I like seem have more details (2007 up when things on the forum were developing).

Hey John. Another reason for small precipitate is a dirty solution. Your method lends itself to this issue. Nothing wrong with what you are doing, however a side effect of the method ( base metals still in solution) is a fine precipitation. I find it makes it much harder to wash the gold. Use heat to settle. The particulate's will glom better with heat keeping them in motion.

If you can find ( modify your method) a way to eliminate the base metal being carried over....your issue should decrease dramatically.

Thank you Butcher. That is exactily what I needed to know, I will adjust accordingly.

Glondor: Thank you. I do treat all samples with a nitric bath first (and the samples are ground up well, almost dust like to give tha acids a better surface to eat). Then I filter it off. Then I proceed with the AR process. I dilute 3x and add sulf acid. I let settle overnight and then filter. I am going to use Steves reply about the ice method next time. How would I be leaving base metals in sol?
Is it in my dilution of the 3x? I though the nitric bath would eliminate the base metals and the dilution and sulf acid additions would settle out the silver and lead?? Please advise. You might be 100% correct as I am way to new. The last run although ultra fine, did come out very pure 10x better than my first button. I even took the sample to a jeweler and he looked the gold over and said I had acomplished a very pure sample based on the shot I took to him. (no Assay)..

I am open to any ideas. I am going to run another sample and follow Steve's advise. I will wait until I hear back from you to see if I can improve the process of removing the base metals.

Thanks again.

John S.

I guess the question is what size batches do you run and what amount of nitric do you use for the first leach. With the batches I do I usually find it takes 2 or 3 leaches with nitric to remove all the base metals. A good rule of thumb is 4 ml 50/50 nitric/water per gram of material. ( sometimes more sometimes less. Just wondering if your reaction stops because the nitric is spent or the base metal is gone. If the base metal is gone, your good. But if it stops because your nitric is spent and you assume you have the base metal done, move to your next step, you carry base metal with you .

Hmmm. Great question. I do not have an answer. You might be correct and I might have just figured that if the reaction stops I am done. ... I will run my next sample and collect this data. I think my process was that I covered the sample in water. I heated it. I added the nitric in a small amount until I see the reaction start. I then let it run out and then add just enough to get it driving forward again. I did this until the reaction stopped. BUT, due to the fact that each subsequent additon of the nitric takes longer to start going, I might have jumped the gun and assumed it was finished, which would have left base metals!! ahhhh.. I see the light.

Thank you so much. My plan now (now that I am out of Nitric and Butcher advised to try the AP method) is to switch to AP. I will use the nitric bath to eliminate the base metals according to your observations. I will then drop the Au using Steves detailed post.

I will take better notes going into the reaction as I was getting complacent in my note taking. Then I will update this thread with my results. It will be about a week, as I have to order some chemicals, and then actually process the sample and then report back.

Thank you for your observation and input.

John S.

This thread highlights the forums awesomeness!!!!
A newb, getting real good clean advise from those up the food chain..