Chloride content in Nitric Acid

[rakesh123]

Hi Everyone ..

I have been refining gold using the aqua regia process ... I have refined about 20 Kgs so far ( in small batches). Now totally i got a huge loss ... after checking everything my friend suggested that we test the chemicals which we have used. Since he is a chemical engineer I asked him to proceed ahead with the chemical testings and what he found was that the nitric acid (72% concentration) which we had been using has chloride in it, being <1 PPM and according to him the content should not be more than 1 PPM and due to this recovery of the gold from the solution becomes difficult and every time we melt the gold powder some amount of it evaporates or flies away.

My question is:

1) What should be the normal chloride presence in the nitric acid?
2) Is there any way of recovering the gold if it has been mixed with the chloride?
3) Is it true that if the chloride content in nitric acid is more then it is harmful to precious metals such as gold or platinum??

We have kept all of the solutions as it is ... we have not drained out anything yet.

looking forward to your replies

Thank you

 

[g_axelsson]

Add some silver or silver nitrate, the chloride should precipitate as silver chloride and give you nitric acid with very low chloride content.

Be aware that HCl can move from one vessel to the next as fumes. I had a beaker with silver nitrate in it sitting close to one with HCl in it and it went hazy in the top of the solution by HCl fumes being absorbed and creating silver chloride. Nowadays I always tries to keep different acids as far as possible from each other.

Göran

 

[Barren Realms 007]

Hi Everyone ..

I have been refining gold using the aqua regia process ... I have refined about 20 Kgs so far ( in small batches). Now totally i got a huge loss ... after checking everything my friend suggested that we test the chemicals which we have used. Since he is a chemical engineer I asked him to proceed ahead with the chemical testings and what he found was that the nitric acid (72% concentration) which we had been using has chloride in it, being <1 PPM and according to him the content should not be more than 1 PPM and due to this recovery of the gold from the solution becomes difficult and every time we melt the gold powder some amount of it evaporates or flies away.

My question is:

1) What should be the normal chloride presence in the nitric acid?
2) Is there any way of recovering the gold if it has been mixed with the chloride?
3) Is it true that if the chloride content in nitric acid is more then it is harmful to precious metals such as gold or platinum??

We have kept all of the solutions as it is ... we have not drained out anything yet.

looking forward to your replies

Thank you

You need to give some more information on your process before an answer can be given. If you are recovering your gold from AR there will be chlorides from the HCL you are using.

information you need to supply.

1. What type of material you are processing?
2. What other metals you are processing that are included with your starting stock of gold?
3. Are you removing all the other metals besides your gold before you put your gold into solution?
4. How do you know you are loosing gold?
5. Did you have an assay run on your starting material before you started processing your material?
6. Can you give a break down off your complete process?

 

[FrugalRefiner]

Hi Everyone ..

I have been refining gold using the aqua regia process ... I have refined about 20 Kgs so far ( in small batches). Now totally i got a huge loss ... after checking everything my friend suggested that we test the chemicals which we have used. Since he is a chemical engineer I asked him to proceed ahead with the chemical testings and what he found was that the nitric acid (72% concentration) which we had been using has chloride in it, being <1 PPM and according to him the content should not be more than 1 PPM and due to this recovery of the gold from the solution becomes difficult and every time we melt the gold powder some amount of it evaporates or flies away.

My question is:

1) What should be the normal chloride presence in the nitric acid?
2) Is there any way of recovering the gold if it has been mixed with the chloride?
3) Is it true that if the chloride content in nitric acid is more then it is harmful to precious metals such as gold or platinum??

We have kept all of the solutions as it is ... we have not drained out anything yet.

looking forward to your replies

Thank you

Rakesh,

There are many things in your post that are confusing to me. I'm not meaning to pick your post apart, but if you can clarify some of the information, members may be better able to help you.

Since you're using aqua regia, you should know that it is a combination of hydrochloric acid (HCl) and nitric acid (HNO₃). Hydrochloric acid is a chloride of hydrogen, so I don't understand how a trace of chloride in your nitric acid is causing any problem. Now, if you're using just nitric acid to leach base metals and silver prior to using the aqua regia to dissolve the gold that remains, then it could dissolve a bit of gold.

You said "he found was that the nitric acid (72% concentration) which we had been using has chloride in it, being <1 PPM and according to him the content should not be more than 1 PPM". Maybe you just made a mistake in typing. "<1 PPM" means "less than 1 PPM". Your friend says it should not be more than 1 PPM. It's not more than 1 PPM, it's less than 1 PPM.

Next, you say "due to this recovery of the gold from the solution becomes difficult and every time we melt the gold powder some amount of it evaporates or flies away." Again, maybe this is a translation issue. A trace (or even more) of chloride in your nitric acid would not cause any problem in precipitating the gold from solution. Remember, you're using hydrochloric acid to dissolve the gold, so it is already a chloride solution. As far as gold powder evaporating or flying away. Both can happen. Gold powder can "fly" away if it is very fine and you get too strong a torch flame too close to it too fast. You can literally blow the powder out of the melting dish. But that doesn't have anything to do with chlorides in your nitric acid. It's a matter of technique in using the torch. As far as gold evaporating, chlorides of metals can vaporize and be lust in the fumes from your melting dish. Your gold powder should be well washed before drying and melting to eliminate any remaing chlorides or you could experience losses. But again, the aqua regia you use always has extra chlorides because you always use a bit of excess HCl, so proper washing is important because you precipitate your gold in a chloride rich solution.

"My question is:

1) What should be the normal chloride presence in the nitric acid?
2) Is there any way of recovering the gold if it has been mixed with the chloride?
3) Is it true that if the chloride content in nitric acid is more then it is harmful to precious metals such as gold or platinum??"

1) Unless you're buying very expensive grades of nitric, there is always going to be a trace of chloride. <1 PPM should be fine.

2) It is mixed with a chloride in the aqua regia, as described above.

3) I'm not really sure what you're asking. I can't imagine how it could harm the metals. Can you rephrase your question?

Dave

Looks like a couple of others have answered while I was typing. I'll post this anyway.