AUH-R,
I read the last few posts you made and tried to get an understanding of what you were doing, I did not completely understand it because I was unsure of the process you were following when you mentioned Sam's guide.
But it sounded to me like you may have been removing the copper and base metals from pins using HCl and peroxide, and then moved onto aqua regia with your remaining material.
Firstly, let me say thank you for the detailed response. I used HCL only.
First let me say a few concerns I have, you mentioned pouring off your acid with some fine gold down the sink, this should never be done, not only could this destroy the plumbing in your house, but it could get you put in jail for endangering the lives of others when they trace the copper and hazardous waste back up the pipe to your house, what you flush others will have to drink, and you will drink what others flush, either way these toxic metal acidic solutions are way too dangerous to all of our health to be poured down a sink, learn to use a stock pot, and learn to treat your waste, this should be done before you even think about dissolving metals in acids.
I just reread what I wrote and can understand where the ambiguity comes from. Please let me clarify. I filtered all my acid off into my waste drum and washed the residue left 4-5 times. This was then filtered into my waste store. When I was looking at the rust coloured pins left in the bottom of my coffee pot indoors I decided to rinse again a few times with H20 and this is what was poured down the sink. I take safety very serious, when I joined the forum I followed Steve's guide and read all the recommended threads. Here is a picture of my waste so far about 4.5 litres of purple/black used HCL mixed with about 2-3 litres of washes.
You talk of expelling the acid and testing with litmus paper to decide when you have done so, if you are talking about getting rid of free nitric acid in this discussion, you would still have a very acidic solution, you are not trying to change pH with this procedure, you do not need to or would you want to remove the acid completely, the metal salts would be acidic and it is desirable to have free acid in solution, you are just trying to remove the oxidizer (nitric) not HCl, although in the evaporation process to remove the nitric we will normally lose some of the HCl in the process, the litmus paper would do you no good here, and if you evaporated down so far as to change PH you would have a dried powder of cooked gold or base metal oxides (with much of your gold lost as fumes.
I think you're referring to the section where I said what I would differently next time. Having read the forum I would use a cell next time as the acid consumption was ridiculous for such a small amount of potential Au. However, I was trying to follow Hoke's guide specifically Chapters 7 & 5. Now Hoke advised in Chapter 7 to boil in HCL to rid the material of solder, she gives no mention of amounts to use and simply says scrap it off. This is when I found Sam's guide with much more detail on this part of the process. So what I was trying to say is next time I did this procedure rather than spend days boiling in HCL, I would do one long boil say 6 hours filter solution to waste, then keep rinsing with H20 and filtering until I was confident that there was no remaining HCL left. My thinking was then I could follow chapter 5 and use HN03 to get rid of the base metals, now most of the tin and lead was gone. Using the litmus paper I thought was the only sure way I would know if the HCL was absent.
Another thing that I seen, you said you wiped off your stir rod after adding the SMB you said you seen brown powder and a violet color of gold left on the paper, the brown reduced gold could be normal, but the violet color makes me think you have tin in solution, and so you could very possibly have a solution of colloidal gold that will not settle.
As soon as I added the SMB I had the brown powder on my stirring rod. I then tested my solution with Stannous to check if there was Au in the solution. I cleaned my rod on this same filter paper to see what would happen.
You talked of a brown precipitant that you think is silver or lead chloride, these chlorides are white not brown, copper I chloride is also normally white, gold will look black to brown or even light tan as a precipitant depending on how much other base metal is involved.
I have brown powder in the beaker with the SMB and also a small layer of copper I chloride. The brown/tan coloured residue left in the filter paper, what could that be?
You talked about boiling it down and leaving it to settle as a crust, you should not boil any solution with gold involved, and you should not evaporate it down to a crust.
I was trying to clean my flakes up at that point, the Au was not in solution, and I now conclude from your helpful post that the brown residue in the picture surrounding my flakes is some sort of copper/metal oxidize.
you also say you think you are having trouble because solution is too dilute, you say this after you have added your SMB, dilution at this stage is no problem, your problem are an accumulation of problems all the way through your process.
Thank you, I only thought that because when I evaporated the AR and added the HCL drops I was left with a tiny amount of syrup, say 10 ml and with all the additions of H20 I ended up with over 700 ml.
What I see is you do not yet have an understanding, of the processes, what you should be doing when and why, and what you should be expecting to see and understand what it is you are seeing.
Just having this chat with you has helped me a tremendous amount. I read Hoke almost daily and also C.W Ammen, I read this forum and various posts everyday. However, it does not matter how much I read, it was the same at university, It will not stick unless I do it myself. Also for me having a teacher/tutor is also very important for reassurance that I'm on the right track , if we could just do it from reading books there would be no need for lecturers, teachers etc...
My suggestion to fix this problem is something you may not wish to hear, but you are the one who asked for help, I say at this point get a large piece of clean copper buss bar and sit it in the solution you have now, check on it and stir it for three days, while doing this go to the safety section and study dealing with waste, brush off the copper into solution let the powders settle, decant the liquid and treat it for waste, rinse the powders and add rinse to your waste to be treated.
save these powders until you have read Hokes again (I know you said you read it 10 times, but you still need to understand it), practice the getting acquainted experiments, these will be a big help in understanding the reactions, and with these you get hands on practice to where you can see the reactions, and get hands on experience of what to expect, study more on the forum, now that you have seen some things, when you do you will have a better Idea of what we are talking about.
Thank you again, I did this, this morning:
Before you try to dissolve gold again I think you need a better understanding of the processes you use, spend the time needed to study and understand them.
Could not agree more! I learnt a lot through this experience, so even though I have no button to show this time it was a worthwhile journey and I feel valuable.
In summary; I never removed all the base metals especially copper as I had the tell tell signs of green all the way through the process I followed. I would never use HCL to remove the bulk of base metals. I would only use it for solder, then I would switch to HN03. When using SMB calculate the amount you suspect you need, if you don't see a dark cloud straight away, wait at least 2-3 hours, do stannous test before adding more SMB if you are sure you need too.
You have worked on a hard material here for a beginner with little understanding, and you chose some processes to begin with that would not be easy (at least until you gain a little more hands on experience), I suggest after you do study some more (do not skip the study, as the more you study the less problems you will have and the better your understanding to deal with them when they do rise), after you study try a more simpler process like memory fingers, to get a better understanding of how to process, without the problems of some of the more complicated methods, or materials.
I do hope this helps, I would also like to be able to give advice to help you out of this present mess, but at this point I do not think any other answer would help you to understand what you need to, to be able to recover and refine.