I made a mistake - refining Au with AR

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butcher said:
g_axelsson said:
butcher said:
Here I wash the powders in a solution of sodium hydroxide, to help convert remaining chloride salts to salt water, and rinse this salt water out of the powders very well, I do this to try to remove chlorides from the powders before incineration.
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Hi Butcher, can you explain why you wash the gold powder with sodium hydroxide and exactly what chloride salt it is ment to remove?

You add NaOH to a mixture of metal chlorides and HCl creating metal hydroxides and NaCl. NaCl is soluble in water but so is HCl too. In incineration the NaCl isn't volatile but HCl would have gone away as gas. Many metal chlorides are soluble in water but many metal hydroxides are not.
Two of the most common contaminants is copper and silver. Copper chloride is weakly soluble in water but copper hydroxide is even worse. To get rid of copper chloride or copper hydroxide you would need to wash it in concentrated HCl. Silver chloride isn't soluble in water but adding NaOH only converts it to silver oxide which isn't soluble either. It would be better to wash it with ammonia to get rid of silver chloride.
I can only see a more contaminated end product as a result of a NaOH wash.

/Göran
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My intent here is not to remove metals from solution, with the sodium hydroxide wash (these metals are removed later in the process with acids), but to convert and remove as much chlorides as possible in a water soluble solution before the incineration of these powders, as far as the base metals we will remove them later in the process, and it does no harm to convert their chloride to oxides before the incineration process, and we are roasting these metal powders for several reasons, besides removing oils or carbon-ous trash, to remove the previous acids used or salts of those acids used on, or which formed these powders, in this case chloride salts, these could be in the form of silver chloride, lead chloride, copper chloride, or just other forms of residual acid or chloride salts in our metal powders, the other reason for incineration is to help oxidize base metals, this can be oxidizing the tin which is such a problem in solution or other base metals in the powders, oxidizing the base metals will help later when we are using acids to dissolve these base metals from our more valuable metal powders.

Gold chloride as well as silver chloride can be volatile when heated strongly, as in the roasting of the powders.

The hydroxide wash and rinses I believe can help to convert and oxidize silver helping to keep our losses down in the roasting process.
This treatment I also believe will help to convert chloride salts (like silver chloride copper chloride Etc), to oxides and at the same time help to make a water soluble sodium chloride salt easily washed away in hot water rinses. Helping us to remove most of the chloride as water soluble salts, which if left in these powders could vapor off some of our gold in the incineration process.

As you know we can have chlorides or residual acid in the powders after using an acid like HCl, as you said the salt NaCl is easily soluble and washed away with hot water, where lead or silver chloride may have formed in these powders can cause some loss of gold in the chloride fumes of the roasted materials
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Didn't think of the gold chloride and possible losses there. Thanks!

Silver chloride should turn into silver oxide from the NaOH wash but copper chloride is turned into copper hydroxide and then turned into copper oxide in the incineration.

/Göran
 
Dear All,

I thought that I was out of trouble, but far from it.
Let me explain again in short what I did.
I inquartated gold (mostly 18K, alloyed with silver and copper), put it in nitric acid, washed the rests with distilled water, prepared a solution of aqua regia - here I made a mistake, I used way too much nitric acid - put the rests from the inquartation into the AR, let the reaction go, put some drops of H2SO4 in the solution, when I wanted to precipitate I ran out of sodium met bisulphite - no wonder, because of the excess nitric acid, so I had to wait until today to proceed. Following Butcher’s advice, I put copper in one of the flasks and this reaction is still going on - the AR is very, very dark green at the moment and it is still bubbling. In the other flask, which I considered more or less depleted (it is the flask where I put most of the SMB in the first time) - this solution does not look green, but pale yellow - I also put some copper, but there was barely a reaction. The copper turned black and started to fall apart, very, very slowly - after one night, there was hardly any effect. I put more SMB in this solution. At first (the first seconds), the reaction seemed to be normal, then it got a coffee colour (dark brown, not transparent). It has been standing there for more than two hours by now, it still looks the same. I do not know what to do with it. Can someone please help? I do not understand what is happening.

Thank you for reading and with best regards,

Will
 
it sounds like the flask with the yellow solution had very little excess nitric. what you observed as the copper turning black and falling apart was your PM's cementing and falling off. take the piece of copper from the flask and gently shake it in the spent solution to dislodge any more loose powder. completely remove the copper from the flask and place it in a clean vessel (it still has gold stuck to it) and let all the powder settle in the flask. carefully decant the solution into another container so you dont disturb the powder in the bottom. decant as much as possible without pouring out any powder. add water (distilled if you want but completely unnecessary at this point) and heat to a boil. allow to cool and all powder settle and decant as before. repeat this rinse until the water stays clear. now you can dissolve the powder with your choice of acids. i would recommend hcl/Cl and avoid the use of nitric as you are working with powder this time. the same process applies here, add the hcl first and then add the bleach in very small increments and give it a little shake and a half minute before adding more. stop adding when the powder is dissolved. either wait till the next day or gently heat the solution to a gentle boil for about ten minutes and allow to cool. you may now precipitate your gold.
 
Thank you very much Geo. I will follow your advice.
This has been a nerve racking experience so far.

With best regards,

Will
 
The excess nitric acid can put copper into solution as the acid reacts with it, this copper will stay in solution, (unless something reduces it, like adding SMB) after the nitric is consumed, the copper will dissolve into solution and give electrons to any dissolved valuable metals ions in solution (metals below copper in the reactivity series of metals), gold ions in solution receive the electron from the copper the gold now reduced with all of its electrons becomes a metal powder falling to the bottom of the vessel, the copper losing its electron is oxidized into solution as copper ions.

Adding more SMB to this solution will begin to precipitate a copper powder, these will mix along with any values you may have had cement in the solution, these copper powders can be cleaned up later. You should not add SMB to this cementing process, let the copper metal do its job of giving electrons to the gold ions so the gold will cement as gold metal powders.

When you said the solution changed yellow it makes me believe you could have had iron in the solution.

If the solution is not acidic enough the cementation can take a fairly long time, too acidic of a solution just consumes more copper metal into solution just dissolving copper to use up excess acid.
 
Thank you. You people are worth your weight in gold ...
It's going well at the moment. I'm following Geo's and Butcher's advice.

Thank you again,

Will
 
Hello,


I am in trouble again.
I followed Butcher’s and Geo’s advice for both flasks.
I dropped the gold with copper in both flasks, I decanted the first flask, boiled the rest with water - this is going well - I will refine this later on.
The second flask is another story: the original mistake was to put way too much nitric acid in the AR. I had to put an unbelievable amount of copper in the solution (I didn’t weigh it), nonethelss this morning the nitric acid was eating away the copper (although slowly). There was residu at the bottom of the flask - which I assume is gold for the most part. I am running out of time, so I thought that I could put some SMB into the solution, which I did. The reaction was still violent; then the SMB set at the bottom of the flask as white powder - it did no longer dissolve. So, I had a residu of gold and other metals and SMB powder at the bottom of my flask, all mixed. I did not know what to do exactly, so I put water in it. Now I have again a dark, coffee-like, non-transparent solution (it’s ca. 800 ml.). How shall I proceed now?

I am sorry for all this trouble. If I could find myself a refiner over here, I wouldn’t try to do this myself, but now I have to.


With best regards,


Will
 
Will, when you add SMB to a copper saturated solution, the excess copper converts to copper sulfate. CuSO4 is a blue crystal but its anhydrous form is a white powder. CuSO4 reacts strongly with concentrated hcl. take all the powder from the reaction and rinse it well. remove all the copper metal you can see. add the powder to a heat resistant container and add to this enough hcl to cover all the material well. it should start dissolving as soon as the hcl is added. slowly heat the solution until all the white powder is dissolved. any black powder remaining will be your values.

as for your AR solution. heat it to a slow boil to expel any excess SO2. to this solution, add a quarter the volume of your solution in hcl to the AR solution and start the cementing process over until there is no more reaction with the copper.
 
Good morning,

I am still at it.
I tried to do what Geo and Butcher told me.
This is what I did and these are the results so far.
First the problem: this is about flasks with AR which an excess of nitric acid in them. I tried to precipitate the gold with SMB, but this did not work.
Last evening, I tried to boil the flasks, putting HCL in the solution. It reacts violently when it reaches a certain point, after that it dies out again. It also creates an incredible amount of fumes. After this, I put the flasks outside for the night. This morning, the solution is dark green, with white powder at the bottom - obviously the SMB is still there. There are also some crystals (it’s getting cold at night here already, 3- 4 degrees C.). I am not sure how to proceed. Shall I try to precipitate with SMB? Should I boil the solution further, adding more HCL, until the SMB is gone? I do not know and I do not want to make a mistake.

Thank you for reading and with best regards,

Will
 
filter the solution and test it with stannous chloride to ensure the presence of gold. at this point, id be wondering where my gold is at. testing is the only way to know for sure. do not throw away the filtrate. whatever the white crystals are, it needs to be tested for PM's as well.after you have tested the solution and have gotten a positive test result. post here the results and someone will try and help you figure it out.
 
Hello Geo,

This is what happened today.
We’re starting from the flasks with a dark solution and white powder at the bottom.
I am pretty sure that this powder is SMB.
I poured the filtrates into other flasks, leaving the powder where it is and precipated the gold with SMB.
I ended up with some gold - but not enough - with filtrate and with white powder. Both the filtrate and the powder tests positive for gold using stannous chloride. And so, now I am at a loss again … I can repeat what I did before (adding HCl to the filtrate, boiling it and try to drop the gold), but I do not understand why all the gold didn’t drop from the first time (which is actually the second time already). As for the powder, I have no clue how to deal with it; I simply do not know.
Thank you for your advice, I do appreciate.

With best regards,

Will
 
I would not try to use SMB to precipitate anything from solution, copper metal will replace metals from solution.

After cementing values from solution using copper.

I would suspect the powders from the cementation to be a combination of what values you had in solution, copper salts from too much SMB, salts of metals and all of the acids or chemicals used previously, like chlorides, nitrates, sulfates.

some of these salts will be water soluble and many will not be.
adding acid to these salts can redissolve values into solution, depending on what they may contain.

I would wash the powders boiling hot water, to attempt to dissolve any water soluble salts, then neutralize these powders, and wash again any water soluble salts, testing washes for values, and letting these decanted washes settle as they may contain a bit of valuable powder carried off while decanting, along with other metals like insoluble lead salt which may have settled out from cooled solution, these powders from the wash would be sent to my collection of filters to be processed later, the wash solution if tested barren with the stannous chloride test are sent to the waste bucket.

Incinerate these cemented powders before trying to remove base metals, this will remove previous salts (salts of acids used previously), and other contaminates, that could have changed the chemistry of the next acid you choose to dissolve the base metals from your more valuable powders.
 
Thank you very much Butcher, your help is much appreciated.

I will do what you say.
I had no idea that this was going to be so difficult.
I learned some lessons. First, I used way too much nitric acid in my AR and, second, I used way too much SMB when precipitating.
It's very stupid, but it won't happen again.

With best regards,

Will
 
actually Will, this is all very simple to someone that has already done it enough to know what to do in a crisis. the main thing to keep in mind is, unless you throw it away, theres no way to destroy gold.you can change its state. heck, you can even evaporate it away in the air (not as difficult as you might think). your gold is still there, the fun is in finding it and getting it back to a metallic state.
 
Hi Geo,

I know. It's a matter of 3 or 4 grams right now, which is hidden in 4 liters of filtrate and some powder right now.
I want to get it out. It's a lot of money. I will try to drop the gold with copper today. I spent an enormous amount of time on this.
Thank you for your help.

Will
 
Spending a little time in the evening with a hot cup of coffee and a good book reading can save you a lot of trouble and grief, we usually recommend Hoke's.
 
I read Hoke in the meantime. It's amazing how simple it sounds when you everything right, right from the start.
There are things I just didn't know, such as taking out the excess of nitric acid.
I will never end up in this mess again ...
 
Will,
I feel you really only made one small mistake, jumping in with both feet before you had a clear understanding and were ready.

Although it sounded like you did some study before beginning you missed some important small details, like not using copper instead of silver to in-quarter your gold, although it works your copper will use about four time's the amount of nitric acid as silver, not diluting your nitric acid to part your gold and copper, this would use much more nitric acid and would not work as well as the more dilute nitric would have, not removing free nitric acid from the aqua regia, before trying to precipitate the gold.

With recovery and refining sometimes the devil is in the small details.

This is why we suggest, studying, and working with Hoke's getting acquainted experiments, and doing these experiments and those to learn the testing procedures for detecting precious metals in solutions, following her procedures, and other modifications to those procedures you will learn here on the forum, working at first with small tests getting an understanding of what to expect before putting your all of your valuable materials into the pot and having that pot boil over, when trying to evaporate off your nitric acid and then standing there scratching your head with all of your gold spilled in the dirt is no fun.

You will learn a little bit getting out of this mess, but not that much, you will learn more, from studying and, doing the small experiments, starting off small and working your way up.
 

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