Separating gold from lead cloride

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Paruima

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Aug 4, 2019
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I'm trying to search for past threads about separating valuables from the by products of HCl and solder. Can someone please direct me as I'm guessing someone has posted on this in the past.

I've searched using the following two phrases:
1. Separating gold from solder
2. Separating gold from lead cloride

It's possible I miss it but I didn't see anything that answered my question.

Here is why I'm asking. I removed solder from gold plated printed circuit boards and gold pins etcetera, using HCl. Over time I've saved the reagents and now would like to recover the small amount of gold that was suspended in the solder.

I have a fairly clear solution with white salt precipitation along with a small amount dark precipitation (gold?) I'd like to separate the two and process. Lead cloride is slightly soluble in hot water but it would take a huge amount of water and then there is a lot of clean up. So I'm wondering the best way to proceed.

It isn't much gold so I'm mostly interested in the education

Thanks in advance for any direction
 
Lead is pretty insoluble as a chloride, whereas gold chloride is more soluble as a salt in the same solution.


Decant the powders after they settle well to the bottom pouring off, the solution from the powders, add water to the powders, and bring the temperature up heating the water as high as you can without causing the water to boil, or roll.

Lead chloride is much more soluble in hot water than in cold water, silver chloride is not any more soluble in the hot water than cold, but the light fluffy silver chloride likes to float around if the water is disturbed or stirred or in turmoil or boil of gases escaping the solution, so we need to keep the water as hot as possible yet as still as possible giving time for the light fluffy silver chloride to settle., before decanting the solution to a cooling jar.

Letting that water cool will precipitate the lead chloride so the water can be reused (saving volume of waste to treat, returning this cooled water, reheating it we can dissolve more lead chloride and repeat.

Having a second batch of water and a second cooling vessel may add a little more waste to be treated, but can speed up the process, while the previous water is cooling.

The black powder could be gold or could be silver chloride (which has reacted to light,.

We can go different ways from here:
Dissolve the silver leaving the gold.

One method which can be dangerous if not done properly, the danger can come from not acidifying the silver amine solution, the process of which involves using ammonia, which can make a sensitive explosive compound of diamine silver, becoming dangerous if the solution is not dealt with properly,

A safer alternative is to dissolve the silver chloride using sodium thiosulfate (but that too seems to come along with its own set of problems.

Dissolving the gold leaving most of the silver chloride behind, can be a better option in many cases.
Letting solution settle overnight and using freezing cold or ice to help precipitate the little bit of silver chloride that does go into solution with the gold before decanting and filtering cold.
 
Add a small amount of sulfuric acid to the solution. Add a few mils at a time and stir. The lead will convert to lead sulfate and settle quickly. It packs tightly when fully settled and the solution can be decanted from the solids. Once all of the liquid has been filtered, add a little water to the solids and rinse it into the filter. In my experience, lead sulfate is porous and the solution will pass through with little clogging.
 
If you have enough solder to warrant recovery, add extra tin until the tin content reaches or surpasses 95% and then part the tin out of solution using electrolysis.
 
In my personal opinion, it depends on what your after and why.

Changing lead to a sulfate works well where you are trying to remove lead ions from a solution.

Although where you are dealing with lead chloride (which is already insoluble salt or not in solution as chloride ions) and where the lead can be separated from the original solution can be decanted or filtered from the chloride solution and the insoluble lead chloride can be dissolved in hot water (in order to separate the lead chloride from other metals or chloride salts).

In order, to convert all the lead chloride (such as a large volume of insoluble chloride salts) within the original chloride solution, attempting to convert the lead chloride to lead sulfate may not be such a good idea.
As it is difficult to get all of the insoluble lead chloride salt in a chloride solution to convert into becoming a lead sulfate salt, without heat and driving of the previous chlorides with the heat of evaporation...
Separating the lead chloride from the chloride solution, where it can work better to convert the lead chloride to lead sulfate, but it may again not be the best choice or direction to go.

Silver is often used in alloys of solder, as well as often being used in gold alloys.

Where insoluble silver chloride a white salt is mixed with lead chloride a white salt gold or other insoluble salts or metals is involved, converting the chloride salts to sulfate salts may not be the best choice, as it would make separating lead from silver more difficult or could cause other problems to deal with in the different areas of your recovery process of recovering the metals...
 
I suppose it depends on whether the gold is in solution or is still a solid. In the case of dissolved gold, there's no other good way of removing the lead from solution. If the gold is still solid metal I wouldn't want to precipitate lead sulfate on top of it. If it did happen, it would need to be cupelled to remove the lead or a really prolonged boil to remove the lead sulfate.
 
As an aside, lead chloride crystals will still convert to lead sulfate rather easily as lead favors sulfur ions over chlorine.
 
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