Beaker popping during the final stages of the nitric boils.

[Amol Gupta]

I experience this during parting the inquarted silver.
The initial nitric boils go well, but during the final boils I experience acid popping(exploding at times) out of my beaker.
I have the beaker covered with a watch glass, but I have cases where acid pops out of the beaker(along with some gold at times).

The boils go as follows, I place the beaker on the hot plate and after some time the dilute acid starts boiling, after some time as the acid is boiling the beakers starts popping.

What's different between the initial and the final boils is i progressively reduce the amount of nitric acid solution(nitric acid + distilled water) I add each time but I make sure the gold is covered to the top.

I have also had instances of popping during the final boil in distilled water.

I'm pretty sure I am not the first one experiencing it.
Is this because of excessive heating....?
Is the reduced amount of acid solution the problem...?(I doubt because I've also had popping during distilled water boils.)

Seems pretty dangerous to me, would somebody please care to explain why such popping happens and how to avoid it in the first place.

Thanks Regards.
Amol.

 

[4metals]

Your hot plate is too hot. You should get the liquid hot enough to boil modestly and the acid reaction will proceed nicely. fill a beaker with water and find the setting on your hot plate to get the water boiling moderately not violently and use that setting.

Another thing is you need to cover the metal you are boiling with enough acid to cover it and, in fact, submerge it by at least 1/2".

In my opinion you have too much heat and not enough liquid.

 

[Amol Gupta]

Your hot plate is too hot. You should get the liquid hot enough to boil modestly and the acid reaction will proceed nicely. fill a beaker with water and find the setting on your hot plate to get the water boiling moderately not violently and use that setting.

Another thing is you need to cover the metal you are boiling with enough acid to cover it and, in fact, submerge it by at least 1/2".

In my opinion you have too much heat and not enough liquid.

This was my guess as well, I'll make sure to switch off the hot plate once my solution starts boiling an see if I experience any popping.

I'll also make sure to get a temprature probe.

Thanks @4metals you are a life save(literally).

 

[Amol Gupta]

I'll also make sure to add more acid next time.

 

[FrugalRefiner]

You may also benefit by adding a few "boiling beads". When you're boiling a liquid, the bubbles need someplace to start. Your metals provide this at the beginning, but as they dissolve there are fewer places for these bubbles to form. The liquid gets really hot, until a bubble starts and then really takes off into a BIG bubble which can pop and burst out of your beaker. Boiling beads are small glass beads which provide the place for bubbles to form in a more controlled manner.

Dave

 

[Alondro]

You may also benefit by adding a few "boiling beads". When you're boiling a liquid, the bubbles need someplace to start. Your metals provide this at the beginning, but as they dissolve there are fewer places for these bubbles to form. The liquid gets really hot, until a bubble starts and then really takes off into a BIG bubble which can pop and burst out of your beaker. Boiling beads are small glass beads which provide the place for bubbles to form in a more controlled manner.

Dave

I made some of those with simple glass marbles shaken in a can with some round pebbles. Scuffed up the glass surface and made lots of points for boiling.

 

[4metals]

I had a client who processed a lot of gold by inquartation. His typical feed was a combination of sterling silver and karat gold. The typical Gold ran about 20% in his parting. He used a gas stove and couldn't control the heat enough to prevent bumping. Boiling chips worked for him. The only down side is the gold buried the chips and he had a hard time fishing them out. He was a Silver refiner so he shipped his 99% fine gold out to refine and used the cemented parting Silver for anodes.

He never fluxed the gold when he melted it and it usually came out nice but from time to time any beads he missed were melted and left an ugly glass blob on his semi refined gold. I told him if he refined those parted gold sponges he would make purer gold without glass blobs. He never thought it was worth it.

 

[cejohnsonsr1]

Along with everything else that has already been said, don’t premix the acid. Cover the material with distilled water and then add the nitric acid slowly in small amounts, using just enough to do the job. (Incremental dosing) Sreetips has several series of videos that demonstrate the process of inquarting and parting. I highly recommend watching it.

 

[Amol Gupta]

I'm not sure if this is related but I was using a watch dish that was much larger for the beaker, it covered the spout and was limiting the amount of vapours that could escape resulting in expulsions that were a lot more violent, opening the spout a bit allowed for the vapours to escape, I still had some popping but a lot less violent.

 

[Amol Gupta]

I made some of those with simple glass marbles shaken in a can with some round pebbles. Scuffed up the glass surface and made lots of points for boiling.

Using glass marbles seems like a decent idea, how many glass marbles did you use..?
I have a 1/2lt beaker I which I process about 50gms of fine gold.

 

[Amol Gupta]

I had a client who processed a lot of gold by inquartation. His typical feed was a combination of sterling silver and karat gold. The typical Gold ran about 20% in his parting. He used a gas stove and couldn't control the heat enough to prevent bumping. Boiling chips worked for him. The only down side is the gold buried the chips and he had a hard time fishing them out. He was a Silver refiner so he shipped his 99% fine gold out to refine and used the cemented parting Silver for anodes.

He never fluxed the gold when he melted it and it usually came out nice but from time to time any beads he missed were melted and left an ugly glass blob on his semi refined gold. I told him if he refined those parted gold sponges he would make purer gold without glass blobs. He never thought it was worth it.

Well filtering pregnant aqua regia with glass beads seems to be an issue to me, the glass beads will tear the filter paper.

 

[Yggdrasil]

Well filtering pregnant aqua regia with glass beads seems to be an issue to me, the glass beads will tear the filter paper.

Read it again.
He filtered the liquid, not the glass chips.
But since the glass chips was covered in undisdolved Gold, sometimes some glass followed the Gold when trying to separate them.
This led to glass in the Gold when melting it afterwards.

Marbles are much easier to separate.

 

[Martijn]

If you have a hotplate no need for boiling stones. Use a stainless steel pan or corningware dish and fill it with a layer of dry sand to evenly spred the heat and protect your beaker from high heat.

Just make sure to wipe all sand of before you set it down to prevent scratching the bottom.

 

[orvi]

If you have a hotplate no need for boiling stones. Use a stainless steel pan or corningware dish and fill it with a layer of dry sand to evenly spred the heat and protect your beaker from high heat.

Just make sure to wipe all sand of before you set it down to prevent scratching the bottom.

It depends. I had runs when hotplate created bumping in the beaker/boiling flask.

If there aren´t enough nucleation sites in the liquid that is heated, it will superheat and then bump. This is well known in chemistry. Typical case is shooting the contents of test tube heated over Bunsen burner - classic scene during first or second analytical chemistry lab course, when students learn this interesting phenomenon. Of course if you overheat the wall of the beaker, it is more likely to bump. But it happened to me that hotplate set to 200 °C bumped the liquid in the beaker quite actively.

Read it again.
He filtered the liquid, not the glass chips.
But since the glass chips was covered in undisdolved Gold, sometimes some glass followed the Gold when trying to separate them.
This led to glass in the Gold when melting it afterwards.

Marbles are much easier to separate.

In fact, crushed glass don´t make very good boiling stones - it has very smooth surface. The idea behind boiling stones is that surface of them is porous, with very small cavities and convex places - where, due to high curvature, liquid start to boil at lower temperature. It is seemingly absurd when you first think about it, but surface tension works not only for droplets, but also for pores. It is described by Kelvin equation - simply said, higher the curvature, lower the vapor pressure = lower the boiling point.

From common materials, best boiling stones are made by crushing some older dining plates or ceramic cups. Not from porcelain/china, but classic ceramics. Porous enough for the effect to be nicely visible. Also, cut capillary tube is a good boiling starter, but much more difficult to get rid of. But it can be very fascinating to watch how liquid is boiling on the surface, not bubbling from the bottom

 

[Yggdrasil]

It depends. I had runs when hotplate created bumping in the beaker/boiling flask.

If there aren´t enough nucleation sites in the liquid that is heated, it will superheat and then bump. This is well known in chemistry. Typical case is shooting the contents of test tube heated over Bunsen burner - classic scene during first or second analytical chemistry lab course, when students learn this interesting phenomenon. Of course if you overheat the wall of the beaker, it is more likely to bump. But it happened to me that hotplate set to 200 °C bumped the liquid in the beaker quite actively.



In fact, crushed glass don´t make very good boiling stones - it has very smooth surface. The idea behind boiling stones is that surface of them is porous, with very small cavities and convex places - where, due to high curvature, liquid start to boil at lower temperature. It is seemingly absurd when you first think about it, but surface tension works not only for droplets, but also for pores. It is described by Kelvin equation - simply said, higher the curvature, lower the vapor pressure = lower the boiling point.

From common materials, best boiling stones are made by crushing some older dining plates or ceramic cups. Not from porcelain/china, but classic ceramics. Porous enough for the effect to be nicely visible. Also, cut capillary tube is a good boiling starter, but much more difficult to get rid of. But it can be very fascinating to watch how liquid is boiling on the surface, not bubbling from the bottom

I have no idea on how boiling chips look like, but it was a reply to emphasize that it was glass among the Gold and not glass in the liquid poured through the filter.

 

[Amol Gupta]

I have no idea on how boiling chips look like, but it was a reply to emphasize that it was glass among the Gold and not glass in the liquid poured through the filter.

The comment was with respect to dissolving the parted gold in aqua regia, once you choose to dissolve the parted gold and then filter the solution the glass beads will cause an issue.

 

[Yggdrasil]

The comment was with respect to dissolving the parted gold in aqua regia, once you choose to dissolve the parted gold and then filter the solution the glass beads will cause an issue.

If you read the post we now are discussing, the glass was never in contact with any filter.
It was the remains after parting and the glass chips was small and covered in Gold.
This lead to that some glass chips followed the Gold to the melting.

At least that was how I interpreted it.

This was not a comment to your process but an attempt to clarify that there was never a danger for the filter.

Read this post carefully, no AR here:
https://goldrefiningforum.com/threa...-stages-of-the-nitric-boils.34721/post-374125

 

[Amol Gupta]

If you read the post we now are discussing, the glass was never in contact with any filter.
It was the remains after parting and the glass chips was small and covered in Gold.
This lead to that some glass chips followed the Gold to the melting.

At least that was how I interpreted it.

This was not a comment to your process but an attempt to clarify that there was never a danger for the filter.

Read this post carefully, no AR here:
https://goldrefiningforum.com/threa...-stages-of-the-nitric-boils.34721/post-374125

. I told him if he refined those parted gold sponges he would make purer gold without glass blobs.

Refining parted gold, my best guess is refining here is through aqua regia.

 

[4metals]

Yes and no. If the required purity is 995 a parting process will be sufficient. If you want to attain .9995 or better a second refine in aqua regia would be required.

 

[orvi]

I have no idea on how boiling chips look like, but it was a reply to emphasize that it was glass among the Gold and not glass in the liquid poured through the filter.

Boiling chips are anything that has sufficiently porous surface which allow to onset boiling in controlled way. Small pieces of crushed ceramics, dedicated ceramic beads, even pumice-like materials which will eventually float on the surface... I seen numerous materials used for this purpose.

I just felt that I will add some insight into this field, as I rarely seen anybody use boiling chips in refining. Of course, it is needed only in very special occasions, and that is probably sole reason it isn´t discussed here