Observations from a newbie

[bswartzwelder]

I have read with great interest what the forum has had to offer. It is quite obvious there are many experts here and I wish to publicly thank them at this time for all the help they have given me and others over time. For some of the chemical processes, I have noted the following. Please correct me if I am wrong. Constructive criticism is a very useful learning tool provided you learn from your mistakes and the mistakes of others.

Read the Safety precautions associated with the various chemicals you will be using. Use the necessary gloves, mask, apron, and any other safety gear to protect yourself against accidents. Have a backup plan if an accident does happen. Most of these reactions involve giving off gasses which can be anything from a major nuisance to deadly. Work under a fume hood or outdoors away from the fumes. Keep pets and Children away. Have the Material Safety Data Sheets (MSDS) of any chemicals being used close at hand. Use good chemical procedures like recapping acids and other solutions immediately after using them. This may prevent a spill or mitigate the problems associated with a chemical spill. It also helps keep you from putting the wrong lid on the wrong chemical when using more than one liquid.

AR - Aqua Regia (old process) For thousands of years, Aqua Regia has been a process for purifying gold. You add 3 measures of Hydrochloric acid with 1 measure of Nitric acid. Add in your gold bearing precious metals (PMs), and let everything dissolve. Get rid of the excess Nitric acid by boiling (not a great idea since you will lose some PMs), evaporation, or killing it with something like urea. Filter out anything which doesn't dissolve. Precipitate the gold with Sodium Metabisulfite. Test the remaining solution with Stannous Chloride to make sure all the gold has dropped (precipitated). If Stannous test is positive, add more SMB to finish dropping the gold. Other PMs other than gold may be present.

Pros: Old, reliable method used for centuries. Can get gold approaching 99.95% pure.

Cons: It is very wasteful of Nitric acid which can be expensive. You are working with acids.

AR - Aqua Regia (new process) Start out with enough Hydrochloric acid to dissolve all the PM's you will be working with. Add the PM bearing materials. Slowly, in small steps, add Nitric acid utill everything dissolves. Drop gold with SMB. Test remaining solution with Stannous Chloride.

Pros: Can get gold approaching 99.95% pure. Does not waste Nitric acid. Therefore more cost effective.

Cons: May not be as fast as old AR method. Still working with acids.

AP - Acid/Peroxide. Great method for dissolving base metals leaving gold behind. Excellent for printed circuit boards (PCBs). Don't confuse the use of PCBs in this post for anything else like Poly Chlorinated Bi-Phenyls. Start out with enough Hydrochloric acid to dissolve the base metals. Add the printed circuit boards. Next add Hydrogen Peroxide. It may help to agitate the solution mechanically or with air bubbles. After a while, the base metals dissolve, leaving gold surface mounted components and sometimes solder mask behind. You may need to add more Hydrogen Peroxide and/or acid as the reaction slows down. Check solution for gold/other PMs with Stannous Chloride. Filter, rinse with Hydrochloric Acid and then water. Repeat as required to get the gold clean.

Pros: Does a good job of lifting gold plating from circuit boards. Materials needed are readily and cheaply accessible.

Cons: Can be a very slow process. Some gold may be dissolved in the process. Gold left in the process will still have to be refined. Does not use Nitric Acid.

A/Cl - Acid/Chlorox - Start out with enough Hydrochloric Acid to dissolve all the metals you will be processing. Add your metals. Next add Chlorox. The metals will dissolve in the solution. You may need to add more Chlorox and/or acid if the solution slows down and/or stops working. Drop the gold with SMB. Test the solution with Stannous to make sure all the gold has dropped. Filter gold and wash in Hydrochloric Acid and then rinse with plain water. Repeat as required to get the gold clean and bright.

Pros: Works very well at dissolving gold. I am not certain of the purity of the final gold product, but suspect it will be quite high since this method looks a lot like the AR method without the use of Nitric. All materials needed are relatively inexpensive and readily available.

Cons: Does not require Nitric acid. May be slower than AR method.

Sodium Hydroxide - (NaOH) Used to remove solder mask from printed circuit boards. Add enough Sodium Hydroxide in cold water to make a 20% solution. Slowly heat until all NaOh has dissolved. Add your circuit boards to the solution. Continue raising the heat slowly until it is almost at the boiling point. (Best not to boil it because you don't want this stuff splattering all around.) Keep at this temperature for five minutes. Remove the PCBs and place under slowly running water. Some of the solder mask should wash off by itself. You may use a small brush to see if more of the solder will clean off. If it doesn't, dry the boards with a paper towel and replace in the hot NaOH solution. Check frequently.

READ HOKE! I know this is probably a bit of an oversimplication since I have not gone into any detail of whether it should be used for karat gold, gold filled or any other gold bearing material. It was not meant to be an in depth description of the processes. It was meant only as my own personal observation from reading the way other members of the Forum have been doing things. Above all, READ HOKE! This cannot be overstressed.

 

[niteliteone]

Thank you.
Good job.
You've been here less than 3 months and have learned so much.
Again thank you.

Tom C.

Ps. I like to place the material in the container first then add the acids. I feel this has less chance to splash acids.

 

[butcher]

Well done.

 

[element47]

Generally well done:

Possible correction: You wrote:

AR - Aqua Regia (new process) Start out with enough Hydrochloric acid to dissolve all the PM's you will be working with. Add the PM bearing materials. Slowly, in small steps, add Nitric acid utill everything dissolves. Drop gold with SMB. Test remaining solution with Stannous Chloride.

Should be:

AR - Aqua Regia (new process) Start out with enough Hydrochloric acid to dissolve all the BASE METALS you will be working with. Add the PM bearing materials. Slowly, in small steps, add Nitric acid utill everything dissolves. Drop gold with SMB. Test remaining solution with Stannous Chloride.

 

[butcher]

I would say eliminate the base metals before dissolving values in any form of aqua regia.
Very seldom do you wish to dissolve base metals with the values, basically never if you can help it.

I liked bswartzwelder, version he was only talking about dissolving precious metals, I presumed he already eliminated the trash and the base metals.

(if I did add something to it would be add a small gold button and some heat to make sure the nitric was eliminated before trying to precipitate, but much depends on conditions the reaction was performed under, so this may not even be needed, or test with prill of urea).

I did not see a whole proceedure's written , but just some outlines of some of the different methods one can use.

I see no reason to pick it apart, it can be a good tool for new members who are looking for what to search for, actually I would like to see bswartzwelder, add more notes to this as he learns more.

 

[Harold_V]

Should be:

AR - Aqua Regia (new process) Start out with enough Hydrochloric acid to dissolve all the BASE METALS you will be working with. Add the PM bearing materials. Slowly, in small steps, add Nitric acid utill everything dissolves. Drop gold with SMB. Test remaining solution with Stannous Chloride.

Absolutely not!
I have never endorsed the concept of dissolving everything along with the values. The base metals should have been eliminated prior to even thinking of AR.

There are exceptions. They are not common.

Harold

 

[spooks69]

I'm setting up my 2 car detached garage as a workshop. How Cold is too cold for a sulfuric cell, or AP to properly work?

 

[butcher]

Personally I would not work in a two-car garage (if I had one it would be used for other purposes), especially if I kept tools or other things that would corrode, on small scale with fume hood or other arrangement you maybe able to limit the corrosion, but I still would think twice.

I have six acres so my work space is far from my house, all my work is done outdoors, Hot summer, cold winter, rain or snow, I use appliances to heat solutions when needed, and even to chill when needed, also I may take advantage of the temperatures outside like summers heat or winters snow to chill, or even warm days to dissolve metals salts and cold nights to crystallize them.

The cell will generate its own heat, besides some splashing (corrosive liquids) I would guess most of the gases formed would be hydrogen and oxygen depending on conditions.

Acid peroxide can generate oxygen and possibly HCl gas (very corrosive), under some conditions. Depending where you live and if your garage is or will be heated you may want to heat the acid peroxide, which can increase these gases.

Personally if I had a small back yard I would put up a small shed back there away from the house or the neighbors house, or some other arrangement, for refining, and keep the garage for other purpose which are acid and fume free, as there may be many other processes you may be using later, so moving the operation now you would not be tempted to just do them in the garage later.

Acid peroxide will work cold as will most any chemical reaction, but the colder it is the slower is the chemical reaction, heat speeds reaction time but also volatile gases in solution do not stay in solution long (oxygen in this case), so unless you add more oxygen with added heat acid peroxide slows down. I will not be able to give you a certain temperature but will just say you do not want extremes hot or cold, in summer my acid peroxide work good, in winter I heat it for it to work good.