Please help a total gold refining newbie!

[Anonymous]

I've decided to start a simple home refining business/ hobby, and I want to check out this process with you guys before I get started so I don't completely blow it. The gold I will be using is all 10-18k solid gold scrap. So, if I understand everything Ive read correctly, the best way to go about it would be...
1. Use a Hydrogen Peroxide/ HCl mixture to first dissolve base metals? Or is that only for plated gold?
2. Then use a 4:1 ratio of HCl to 70% nitric acid to dissolve the gold, then add urea to neutralize the nitric acid, filter it, and add sodium metabisulfate to precipitate the gold.
3. Do I then repeat step 2 for a higher purity, or is it already pure enough to test at 24k?
4. With resulting powder, melt with a high temp o2/ propane torch and pour into mold or whatnot. Now, how important is it to coat the mold/ crucible with borax or flux I guess it is called? Will this effect purity?
5. Sell it.

Does this sound about right? I've been looking all over this site, read the forum handbook ( I think it was from this forum, I found it through google), and this is what I have gleaned. Also, if I use an Erlenmeyer flask with a vacuum hose attached, can I just bubble the fumes from the AR reaction through water as a means of filtering them so as not to expose myself/ nearby metals to corrosion? I can't afford a fume hood yet, but I thought they would be water soluble. Any other information I have left out would be greatly appreciated. I plan on purchasing the chemicals this next week, and doing a trial run on a small amount of dental bridge I have before going into it full-throttle. Thanks, and I look forward to contributing to this forum once I have a full grasp on what I'm doing.

 

[lazersteve]

Welcome to the forum,

For mixed karat scrap you should inquart the gold first. I have a video demonstration of this on my website in the Gold videos section. Inquarting is the process of diluting the scrap to 25% gold by weight. Typically silver is used to alloy the gold to this level.

Once you have inquarted the gold and corn flaked it as shown in the video, proceed to the dissolving stage using 35% (70% nitric diluted with an equal volume of distilled water) to dissolve the silver and other base metals. I have a video in the silver section for 'Separating Silver from Gold' that will assist you in this step. Don't add salt as shown in the video, instead follow the instructions in the 'Cementing Silver' video once you have dissolved all the silver.

After the silver is separated from the gold you can proceed with the 4:1 HCl to nitric after the gold powder has been washed with boiling water followed by boiling HCl. Test the washes with stannous chloride to be certain you have not dissolved any gold in the wash process.

If any of the above is not clear study the General Reactions list in the Guided Tour Link below. If you still have questions post them and you will get the answers you need.

Steve

 

[teabone]

Be advised that a lot of dental bridges are an alloy of chromium/nickel and will even register on electronic gold testers as high karat white gold.

 

[4metals]

As a general rule I never advise anyone to use Erlenmeyer flasks as a vessel to dissolve gold scrap in. The reason being the shape. If you fill it too high, which is anything more than an inch or two, a runaway reaction can explosively expel itself out the top because as the diameter diminishes the pressure increases. Straight sided containers are good as are spherical reactors, then you have the good old fashioned plastic bucket.

I have attached a sketch for you to build a makeshift scrubber as you do not have a hood. The NOx fumes are not highly soluble in water and caustic solution will neutralize them better.

The reaction takes place in a plastic bucket with a tight fitting lid. On the side near the top put in a 1/2" pvc bulkhead fitting for the fumes to travel through. Attach a pvc thread by tubing adapter for the vacuum hose to go on to.

Now you will need 2 four liter Erlenmeyer flasks with tubing adapters, 2 one hole rubber stoppers to fit the top hole, 2 pieces of glass tubing to put in the hole in the rubber stopper so you can attach vacuum hose to one side of the stopper and have the bubbles of NOx come out the bottom of the tube. You'll also need enough marbles to fill both flasks 3/4 full.

Put the marbles in the flask and add water and some caustic to aid in the scrubbing, put the stopper in and work the glass tube to the bottom being careful not to spill the caustic liquid on you. Now connect the plastic pail to the first flask and to the second flask using vacuum tubing. Finally put a sink aspirator to pull a vacuum on a sink and connect it with vacuum hose to the last flask.

When you turn on the water the aspirator will pull a vacuum and you will see a bubble train form in the 2 flasks as air makes its way from the plastic bucket through both mini scrubbers. The purpose of the marbles is to make the exposure time of the bubbles to the solution longer and effectively scrub more completely.

This will scrub better than a vacuum source alone but still do it outdoors, possibly by attaching the aspirator to the end of a garden hose so it can all be outdoors.

I recommend, as Steve did, that you inquart as you have lots to learn. One way of slowing down the reaction is to pour your inquarted alloy into a bar, the decreased surface area will slow the reaction down generating a lower amount of NOx per unit of time making this method more effective. Another method is to shot the inquarted alloy and feed it in slowly.

Using 50% nitric, 50% distilled water the reaction should go to completion without heat. The finely divided gold that remains will also dissolve completely in aqua regia without heat. As a result you do not need a digesting vessel that can withstand the heat of a hotplate so plastic will suffice. Remember, tight fitting lid.

And while this may sound like a way around a fume hood, it is a best a band aid. Think fume hood!!!!

 

[Anonymous]

Ah, good idea with the 2x flasks and marbles as inline filters. Im curious, though... do I need to add silver like your video Steve says to do (does it need to be a 75%/25% combination) in order to inquart the gold, or can I just melt the jewelry/ etc. as it is and then pour it into the water? Will the nitric acid in this step dissolve the base metals (copper, nickel or whatnot)?

 

[lazersteve]

Inquarting requires that the ratio of base metal (or silver in this case) to gold be 3:1. This forms a 6 kt alloy that nitric can easily attack.

4Metals posted an Excel spreadsheet that computes the required silver, but I just use equal amounts of 10kt + 14 kt then add to it the total weight of the scrap in sterling silver scrap. For example: 10 grams of 10kt + 10 grams of 14 kt + 20 grams of 925 sterling silver.

Steve

 

[4metals]

If you inquart in silver, you dissolve in nitric. It will dissolve base metals and silver.

If you don't inquart, you dissolve in aqua regia. It will dissolve gold and base metals and leave you with silver chloride.

You're new at this, I suggest you inquart, you can always scrounge up a few sterling silver forks or spoons for the silver. When you get the hang of the inquarting routine you can try a few varied techniques, but learn to walk before you start running.

 

[Harold_V]

It's really simple. Get Hoke's book, read it, and follow her instructions.

I highly recommend you don't get too creative with refining until you become familiar with procedures that work. Guaranteed---if you ignore the advice you've been handed, you're going to come back to this forum and ask for a bail-out because you've created problems that you can't address.

"Walk before you run". It can't be stated any better.

Harold