Some questions about recovery problems

A friend of mine quit his gold recovery hobby and we traded some items. He tried to explain as best he could, what was what and now I got some plastic buckets with old AP, old AR, and a some other jars with liquids.

Some of the issues I identified already, I was hoping you guys could give me some answers on how to move further and solve the issues:

1: He used Poor Man's AR (KNO3) to dissolve the gold from ceramic CPU's. A lot of around 40. All gold seems to be dissolved but, he forgot to filter off the AgCl, so now I'm stuck with a nice layer of precipitated gold, with a layer of silver chloride. How can I best separate the two ? Should I just convert the AgCl with NaOh, or H2SO4 and use nitric to remove the silver ? And will I not lose gold this way ?

2 My friend used too much H2O2 in AP, in some cases he made a 50/50 mix and in some cases he used 6% H2O2, and now I have this 50 litre lot of dirty brown AP, with some gold dissolved in it.
Is it possible to recover gold from an AP soluton with too much and too strong hydrogen peroxide, or is the gold just lost ? Since cementing with copper is no option, what options are there, if there are any.

3. He also tried to remove the solder mask of some gold plated boards, like the pcb's in the picture. After he boiled the boards in hot NaOh with some 6% H2O2 he discovered a lot of the gold plating is gone, and he is sure it is in the NaOh solution. The solution has a thick black precipiate on the bottom, could this be soms cemented gold because of the copper, iron and tin? He cooked the boards with a parts still on them, thinking to remove the parts on the pcb and remove the solder mask aswell. Where the gold plating used to be, there is now this with plastic strip where the gold once was, other boards are plain black, this could also be precipitated gold with base metals? And how to clean up that mess ?

4. A jar with 1 litre of bown AP had a scoop of SMB added and gave a thick with precipitant at the bottom, I'm thinking it could be lead from the solder, as he used unpopulated boards. My friend thinks it was silver chloride, but I think it can not be SNCl, but it has to be a contaminent contaminant from the base metals, or a copper salt ?



I will take it 1 project at a time, but every bit if information would help in labeling the jars and buckets with steps to do in the future.

Thanks, and I know it's a lot, my friend realy got in over his head and he figured out gold recovery like this was not for him..

1. Redissolve any gold with AR. This will effect the AgCl very little. After you are sure all gold is dissolved, filter the solution and remove any AgCl. Neutralize any excess nitric acid and precipitate the gold.
2. Filter the solution and remove any solids. Add some heavy copper metal to the solution. Wait a few days and remove any undissolved copper and filter the solution again. any solids may be PM's.
3. Never boil PCB's in NaOH. Just a hot bath and only for a minute or so. If you overheat the boards, it can "set" the solder mask and it can't be removed with NaOH. No need to add oxidizer. The gold is most likely still there. Now it is discolored and blackened. Take one of the boards in question and using a piece of clean cloth, rub a metal surface and see if the black will rub off. The gold plating will shine right up.
4. Why? If AP is brown, it is saturated with copper and can not hold gold in solution. I would guess it was some salt of copper.

There is one other option for the AP, as you have boards with gold still on from the lye bath just put the boards into the AP with a bubbler, with luck the base metals on the boards will cement out any gold already in the AP and free the foils from the boards ready for refining.

Take all of the boards out of the solutions and put them into separate containers for now. Keep the AR, AP and NaOH separate for now. Keep the boards that were in different solutions separate for now (AP covered boards with AP covered boards etc).

Filter everything. Keep any powders wet "in case there's any AgCl".
Keep the boards wet "if possible", so any powders on them don't stick too much.

Denox the AR and test with stannous.
Check the AP with stannous, if negative, process it for waste.

Acidify the NaOH using HCl, test with stannous, if negative, process for waste same as you would with the AP. You may need to lower the PH down to around 2, before adding iron.

Before, during or after processing the solutions, evaporate what you can. Properly dispose of what you can.

If anything is positive with stannous, put in copper to drop out any PMs.

Process the boards after most of the solutions are dealt with.

If I was in your situation I would go through it one project at a time. These are my though on it and I'm sure you will get more replies with alternative methods. Be sure to read them all and compare drawbacks and merits for them all and you can recover all the gold.

Some materials can have a too low gold content for it to be practical and economical to recover the gold, but as long as you don't throw the material away the gold can be recovered.

1. Precipitated gold and AgCl. Dissolve the gold again and filter. Precipitate the gold from the filtered solution.

1. Alternative if the silver chloride have dried up. Treat the AgCl + Au mixture with NaOH, this converts the silver chloride to silver oxide, stir and crush any clumps of white silver chloride. Filter and wash. Now you can either incinerate and leach the silver with nitric, or melt into a silver gold alloy.

2.Why isn't putting a copper bar into the copper chloride an option? The peroxide has probably been used up by this time. If it is a emerald green color it consists of CuCl₂ and can be used to process more pcb:s. Test if there is any gold or palladium in solution. There might be in the sediments, as Geo wrote.

3. Lye doesn't dissolve gold. Period! If gold plated surfaces turns black or silver it is basically two reactions. First, with a lot of components still on the boards there can be all kind of batteries formed by all the different metals, copper, tin, iron, zinc, nickel... This starts to electrolytically deposit tin back from solution and can cover the gold with a thin white metal layer. Secondly, if the gold is very thin the surface under the gold could react and turn into some black oxide. The gold can still be there buried in the black residue or maybe flaked off. If lye has dissolved tin there is probably small amounts of gold in the fine particles collecting at the bottom of the vessel.
These boards have only thin flash plating and I'm pretty sure that there is no gold under the solder mask. Any solder on the board dissolves the tiny amount of gold into the solder and this is released as a fine slam when the solder is dissolved.

Just as Nick wrote I would use these boards in the copper chloride from 2, it would recover any gold in solution while the gold flash add to any gold in the sludge at the bottom. Just don't use any more peroxide, a bubbler is enough.

4. Copper(II) chloride and SMB in excess precipitates copper(I) chloride, CuCl, as white crystals. Filter off the barren solution (check for any dissolved values just in case with stannous) and then dissolve the white crystals with HCl.
If it doesn't dissolve in HCl then it is probably tin that reacted with the SMB. In that case, dissolve the gold in AR, filter, precipitate and you will have your gold.

I wrote half of this response before falling asleep so if it sounds like I'm not acknowledge any ones comments it's just because I don't want to rewrite it all again.

Göran

Thank you guys for all the replies ! I first have to take in all the information before I can make any comments further. When my friend brought the stuff over and explained what he did or did not do, I was thinking OMG ! In total I have 1 50 ltr drum with all the AP, 4 buckets with all the PCB's in clean water with dishsoap, and large jars with AR, a bucket with the crushed ceramic cpu's and a shoebox filled with used paper filters.

So, I have a lot to read, a lot to do, a lot to think about...