consolidation of Loss Gold thread

[Yggdrasil]

Exactly, silver and copper were the biggest pollutants. We need 999 and 995 carats to sell products. Focusing on the subject of washing (copper and silver) is related to the unfavorable surface of the gold ingot after the final melting. To solve this problem, we were advised to wash the gold powder better. it's true?

I added a lot of water in one operation. According to Frugal refiner, I do not think we had silver in the gold powder.
But in the last operation, I made the solution with more concentration and we had silver in end.

If we filter the silver chloride well and use enough precipitate, not more, wash the gold powder well with hot water more time, the problem of Cu an Ag will probably be solved.is it true?

The copper would be out, but the silver is pretty close to not soluble in water.
So there is where and why some of our member use Ammonia.
Dilute Cold solution before filtering with a fine filter will remove this.
This should be done before precipitation of the gold.

Edit:
Did you figure out the plastic pipe function in your tank?
If not it is supposed to fill the dead space above your ball valve in your tank.
Such that all solution is stirred and agitated.

 

[Gold.refinery]

https://goldrefiningforum.com/threads/getting-pure-gold-shining.325/

Washing gold powder with a large volume is practical in this way !!!??

 

[nickvc]

These are images from another system. This is the smallest system I have ever worked with, I have photos of larger ones but these will suffice as an example. This is the tank where the gold is dropped and it is filtered. Basically they are all simply raised tanks which allow a filter to fit beneath. They usually have a slightly coned bottom to allow complete drainage, and some type of effective mixing. The photo on the top left shows the gold rinsed and sucked dry on removal from the tank, to it's right is the tank with the filter seen below. The next photo is just the system at another angle, and the last shows the mixer blade which is permanently fixed in the tank.


View attachment 50255View attachment 50256View attachment 50257View attachment 50258

4metals wouldn’t simply turning the tumbler on for a few turns. after precipitating the gold negate the need for a stirrer ?

 

[4metals]

4metals wouldn’t simply turning the tumbler on for a few turns. after precipitating the gold negate the need for a stirrer ?

The tumbler is only used for digestion, the cementation tanks are used to precipitate. It is difficult to empty solids from the tumbler.

 

[4metals]

You recommend, for example, for 15 kg of scrap that requires 15 liters of nitric, add 5 liters, after calming 5 liters, and finally the final 5 liters.
Doesn't that cause more unresolved gold?

First do the math, better yet use the attached spreadsheet and go to the weight of the scrap, this example is 15kg or 482.25 ounces. The chart is in increments of 5 so choose the closest number. At 480 ounces you need 51.2 liters of Hydrochloric Acid and 12.8 liters of Nitric Acid. Add the gold first then all of the Hydrochloric Acid, then 1/3 of the Nitric Acid wait until you can see the red fume slow down then the second 1/3 of Nitric Acid again wait for the reaction to subside, and add the final 1/3 of the Nitric Acid. This is aqua regia at a 4:1 ratio and should effectively dissolve your scrap material.

 

[4metals]

other way ; Can we just add hydrochloric acid and nitric acid for only 1/3 of the total scrap, then filter the solution, then add 1/3 of the total acid and so on.

That is a lot of extra work and you will be filtering and essentially doing the labor 3 times when the system is capable of doing the entire lot once.

 

[4metals]

During the first 20 to 40 minutes of the acid reaction, we always have some white fume (with a low chlorine odor) in the chimneys after the scrubber.After the peak of the reaction, it ends.

This is not a good thing, from the neighbors' point of view.Of course, no one has objected so far.

What chemistry are you using in your scrubber? What is the airflow through your system, what is the volume of your scrubber? These three factors determine the ability of the scrubber to effectively scrub your fumes.

Many years ago I knew a Russian chemist who worked in the NYC jewelry district. He was shocked to see a fume scrubber and when I asked him what he used for the fumes he said "refine at night. plenty wind!"

We are in the middle of discussing your chemistry to get the refining right, I think going off into a discussion of your fume scrubbing will be a distraction. Why don't we wait until we get past the refining and are discussing waste treatment and fumes.

 

[4metals]

Regarding the amount of precipitate, of course we see the reaction, but knowing the amount of material will help. Due to the toxicity of the precipitate and the health hazards, we do not like to see the reaction too often. Produces gas during settling.

I went back and looked at the photo you sent of your precipitation tank. The exhaust port looks to be about 2". That seems a bit inadequate to remove the fumes you will generate adding the chemicals and mixing. If you look at the system photos I attached earlier of a similar system their exhaust is about 4". That produces 4 times more exhaust. That is something you will have to address and deal with.

Please explain more about the color change of the solution at this stage.

When the karat solution is dissolved it is usually green. The gold is actually yellow and it effects the color of the green. If you see it enough, you will be able to see the color shift from a bright vibrant green to a dull dark green when the gold has dropped. This is true with concentrated acids and karat gold.

In the case of the stannous test, a few minutes after the end of the deposition reaction, we take a small amount of solution from the top of the tank to test, is this correct?

Your opinion is that if the gold deposit is done with experience and confidence, there is no need to leave the solution overnight, which is great for the production process. it's true?

It is best to get some solution from the lower depths of the tank not just the top but if it is mixed well yes it is correct.

And overnight should never be in the process for precipitated gold. Generally I like to see the digestion run at the end of the work day so the acid can slowly finish any dissolving overnight and be cool in the morning. The gold can be filtered, rinsed, and precipitated (and most likely melted) by lunchtime. The dissolving process is the longest process.

 

[4metals]

In the case of washing powders, if we wash them with hot water, for example 5 times, will the copper chloride and the remaining base metal salts be washed ??
Also, washing several times causes gold to escape or not?

In the case of drying, in the last operation, we left it on the filter for 30 minutes, it dried a little, but it was not desirable.
I did not notice the drying of a large volume of gold sponge in the funnel.

Washing requires a strong stream of water to move the sponge about to rinse off the clinging acid that travels with the gold. That is the source of the. most contamination. Some refiners prefer to remove the gold from a filter and place it in a deep plastic tank so they can agitate and blast the gold with water, I always got by with a wand with a flat spray nozzle that I held close to the gold and moved it with the spray, avoiding splashing gold out of the funnel. Not saying I never shot some gold out of the funnel but with practice I got better.

If the funnel has sufficient suction it should be able to dry the gold sufficiently. You have to keep the pump running to provide constant suction to dry the gold.

 

[4metals]

I know that it is not problem to melt wet powder in a cold crucible, but the volume of our crucible is 5 kg and it is cold for the first time, then it is poured.

The size of your furnace is cause for concern. Refining has become a confusing industry. Once upon a time crucible capacities were rated in pounds of aluminum they could hold. Red brass was used for a time as well. Most clay graphite bilge crucibles are still rated by pounds of aluminum. But today a lot of induction furnaces are rated based on their capacity of pure (refined) gold. If your crucible is rated 5kg of 24k gold it is too small.
When you melt your lots together to make a refining lot you will have the best success if you melt everything in the lot in one crucible and this way all of the shot will be the same karat and the same silver content. If you do smaller melts and mix the shot you have a few things to account for which can cause errors. First you have to add the gold contents of all the bars together to come up with an expected yield, much simpler with a single pin representing the entire lot.
If you have 2 different lots and the silver content varies by as little as 1% that shot will not dissolve as well as the shot with lower silver. To get the best digestions, melting it all together is the best scenario.
I know every self respecting refiner puffs out his chest and says “I melt with induction”. Well I’m old enough to have been around long before induction came to refining and for cost vs ounce capacity you cannot beat a gas furnace. Today you can get a gas furnace that holds a # 20 crucible for cheap and use it just to melt your bars into process lots. Your induction is fine to melt your final product or quickly melt smaller bars customers bring in, but having an old fashioned gas furnace tucked away in a corner will make your expected yield calculations easier and allow you to check on your individual bar assays as the final composite melt should produce the product of the individual bars. Plus all of the shot will be the same assay and prevent lots with higher Silver from causing lower yield's due to Silver Chloride encrustation.

 

[orvi]

There are two circles at the top of the reactor where we can see the reaction.

You recommend, for example, for 15 kg of scrap that requires 15 liters of nitric, add 5 liters, after calming 5 liters, and finally the final 5 liters.
Doesn't that cause more unresolved gold?

other way ; Can we just add hydrochloric acid and nitric acid for only 1/3 of the total scrap, then filter the solution, then add 1/3 of the total acid and so on.

During the first 20 to 40 minutes of the acid reaction, we always have some white fume (with a low chlorine odor) in the chimneys after the scrubber.After the peak of the reaction, it ends.

This is not a good thing, from the neighbors' point of view.Of course, no one has objected so far.

Regarding the amount of precipitate, of course we see the reaction, but knowing the amount of material will help. Due to the toxicity of the precipitate and the health hazards, we do not like to see the reaction too often. Produces gas during settling.

Please explain more about the color change of the solution at this stage.

In the case of the stannous test, a few minutes after the end of the deposition reaction, we take a small amount of solution from the top of the tank to test, is this correct?

Your opinion is that if the gold deposit is done with experience and confidence, there is no need to leave the solution overnight, which is great for the production process. it's true?

In the case of washing powders, if we wash them with hot water, for example 5 times, will the copper chloride and the remaining base metal salts be washed ??
Also, washing several times causes gold to escape or not?

In the case of drying, in the last operation, we left it on the filter for 30 minutes, it dried a little, but it was not desirable.
I did not notice the drying of a large volume of gold sponge in the funnel.

I know that it is not problem to melt wet powder in a cold crucible, but the volume of our crucible is 5 kg and it is cold for the first time, then it is poured.

It is wise to add the nitric acid stepwise. If the reaction gets too violent, it tend to boil in the vessel, and all the fizzing in the reactor create aerosols that carry the dissolved gold up the vent pipe. Eventually, they will stick to the walls of the tube and recondense back to the vessel. But if you have only 2" pipe, the flow velocity of gases/aerosols inside that tube will be 4 times more rapid than in 4" piping (area is pi x half diameter squared - so for 2" => 3,14" sq. ; for 4" => 12,5" sq. = vast difference) as 4 metals pointed out. That will cause some small ammount of gold to be carried with gasses eventually.
White fumes - i do not expect any salts to be produced in the process which are white, except silver chloride - that I doubt will go in gas out of scrubber. White fume could well be evaporated hydrochloric or nitric acid. If reaction is violent and boil, quite a bit of HCL and HNO3 could be boiled off.

It is very good to wash the precipitated gold with HCl, water and then ammonia. Different wash has different affinity to clean the gold from impurities. HCL will wash the CuCl very well (CuCl will form if you add too much precipitant = precipitant will firstly reduce gold, but if there is excess of it, it will reduce Cu(II) to Cu (I), which is much less soluble). HCL also removes some silver chloride, but it need to be washed repeatedly if you want to achieve some good cleaning efficiency for silver. Ammonia wash is much better in terms of reducing silver content, with ability to also wash the copper.
In larger apparatus, it could add quite a bit of work to wash numerous times. You also create waste which should be treated afterwards.
If you use excess of hydrazine (what you done apparently from the Cu precipitation), there will be no oxidizer left. So washing even numerous times with boiling HCL nor ammonia will not dissolve the gold. You can always test the washes with stannous to make sure. Stannous always tell you.

Also, washing the gold with HCl (hot) has benefit of coalescing the gold, so it could help to coalesce small particles that could pass the filter to the mother liquor.

There is also the possibility to clean the gold with proper oxidizing flux (eg nitrate/soda to remove copper when melting). But I do not know if this is suitable for operation this large. I think more experienced guys here will add to this.

 

[Gold.refinery]

This video shows the different components of the filter.

 

[Yggdrasil]

This video shows the different components of the filter.

To my eyes the filter was too small or wrongly installed.
Is the liquid sucked to another tank under vacuum?

 

[Gold.refinery]

To my eyes the filter was too small or wrongly installed.
Is the liquid sucked to another tank under vacuum?

Yes, it is transferred to another tank. What do you mean by small? The diameter of the inner ring is 60 cm.

 

[silver1]

To my eyes the filter was too small or wrongly installed.
Is the liquid sucked to another tank under vacuum?

Not part of this discussion, but based on the same concept that i built mine out of. Powered by a Shop Vac. I took the cheap route! Wonder what's the price on that thing?

 

[4metals]

This video shows the different components of the filter.

As Yggdrasil said the filter paper appears to be too narrow to fill the diameter in at least one place. If the paper does not fit under the ring that you place on top to hold the paper down solution and values will go under the paper and cause poor filtration.

Typically filter paper is available in the diameter to match the diameter of the fabric filter which makes placing it in the filter much easier. You can make a cardboard template by tracing the fabric filter and using scissors cut the paper before putting it in. Makes for a better seal as it will lay flat and it just makes life easier.

This type of filter is made to work off a double diaphragm pump. Double diaphragm pumps can run dry with no damage to the pump and will create a vacuum to pull the liquids through the filter. Then the pump will transfer the liquids to wherever the plumbing connects.

You had mentioned that your gold sponge did not dry sufficiently on the filter. This makes me question wether you have a double diaphragm pump which can pull a decent vacuum. What type of pump do you have? Maybe a photo?

 

[Gold.refinery]

What type of pump do you have? Maybe a photo?

 

[4metals]

That appears to be a double diaphragm pump. It feeds from the top, where the intake can be switched by a valve? And the bottom is the discharge.

Also, after looking closer at your video, I see the bottom of the filter is flat. That makes it all the more important you open it up after every use and rinse the liquids on the bottom clear.

 

[Yggdrasil]

Yes, it is transferred to another tank. What do you mean by small? The diameter of the inner ring is 60 cm.

I meant the filter paper do not cover the whole area.

 

[4metals]

I think Gold Refinery realizes by now that filtration is critical to the final purity of his gold. Showing us detailed photo's has been helpful because it is easy to spot small inconsistencies, as Yggdrasil just pointed out.