Flocculant for AR and after dropping

[autumnwillow]

Though I have never tried using a floc on a pregnant AR. I have successfully used PAC(Polyaluminum Chloride) after precipitation for about 1 out of 3 times. That one had no effect whatsoever on the gold output and the floc worked well, gold settled within 10 minutes, even during washing it settled fast. The other 2 attempts did not make gold settle at all but had no effect on the output product.

I wonder if I could use the same floc on a pregnant AR?

Ferric chloride is also used as a floc and I think its presence makes gold powder/silver chlorides settle better.
My theory is that with SMB sometimes the gold will settle fast and sometimes it doesn't. I think this is due to the presence of ferric chloride.
With copperas the result is usually consistent, maybe some of the iron converts into ferric chloride? Not sure though I'm no chemist.

 

[anachronism]

You might want to work out which SMB drops don't drop easily and which ones do.

The answer to your conundrum lies there.

 

[autumnwillow]

You might want to work out which SMB drops don't drop easily and which ones do.

The answer to your conundrum lies there.

Did you mean "SMB drops dont settle easily"?
If yes, the answer is non diluted AR and pure gold does settle the fastest but that is not comparable when I used a flocculant successfully. It was literally just around ten minutes. Even during the washing they settled in less than a minute or two. Before I decided to use the floc it was sitting there for about an hour already. I couldn't wait any longer so I decided to use a floc even though I had already gone thru two experiences without success.

 

[g_axelsson]

I rarely wait more than a few minutes for the gold to settle. If I have a slow drop and have to wait for 15 minutes or more for a drop it is usually very weak gold chloride solution. The fine black gold is really hard to wash so I just decant most of the liquid and redissolve most of the gold with HCl + Cl or HCl + H₂O₂, then drop the gold again within minutes without any filtration between. All done in the same beaker.

The second drop has always been fast and the gold settles in just a minute or so at the max. Compared to keep washing the black fine gold and waiting for it to settle, redissolving and a second drop is faster and gives a better gold powder than messing with that black nasty stuff.

I always suspect that people having problem with SMB drop is doing it at a too high pH. SMB reacts with HCl to create SO₂.
I had a solution that was very low on HCl and adding SMB didn't drop any gold. Nowadays I use at least 10-20% HCl remaining or added to the gold chloride and I have never again had a solution that didn't drop the gold. And only dirty and weak solutions give that fine black gold powder.

And if you think I'm loosing gold that hasn't had time to settle, don't worry. I always let that last tiny bit gold go to the stock pot as well as HCl and water from washing the gold.

Göran

 

[nickvc]

Try a different precipitant and see if it works better, I like ascobic acid crystal but try ferrous sulphate, it needs to be clean to work well but even dirty ferrous works just more cleaning of the powders after precipitation.

 

[anachronism]

I've never used one yet. Yeah I see that it works for some but frankly I've never had the need so far. That wan't quite what I was getting at Willow, in response to your reply. I was more talking about what types of SMB drop present the most problem.

 

[autumnwillow]

I've never used one yet. Yeah I see that it works for some but frankly I've never had the need so far. That wan't quite what I was getting at Willow, in response to your reply. I was more talking about what types of SMB drop present the most problem.

Ahhhhh. I don't get it. What do you mean? What are the types of SMB drop that presents a problem? A sample perhaps?

 

[4metals]

I believe he either means what types of scrap is giving you trouble with the precipitated gold settling? Or what type of reducing agent are you using, sodium metabisulfite, ferrous sulfate, or sulfur dioxide, or one of the other options to reduce the gold?

So an answer to both questions should get this back on track.

 

[Geo]

Over saturation of the solution with SO2 (too much SMB) causes the gold to settle slowly because of too main factors. The solution is too diluted and the solution had too much suspended particles in it. Either of these makes for a slow drop. The SMB decomposes into SO2 as tiny bubbles. These bubbles is where the gold precipitates between liquid and gas on the liquid side of the bubble.

Normally, the gold accumulates on the outside of the bubble until it gets too heavy and breaks loose from the bubble and sinks to the bottom. If there is too much gas, the bubbles are smaller and more diffused. The gold precipitates on the outside of the bubble normally but the gold never gets heavy enough to break loose and the weight of the gold keeps the bubble from rising to the top where it burst on contact with the air sometimes depositing the gold on top of the liquid causing floating gold particles on top of the solution.

It's a matter of saturation. When this happens, heat the solution. It will force the bubbles to rise to the top clearing the solution. One of two things will happen, the solution is depleted of extra SO2 and the solution clears or there is free nitric and the dropped gold redissolves. Always use a catch pan as the powdered gold can redissolve quite violently causing a boil over.

 

[autumnwillow]

I believe he either means what types of scrap is giving you trouble with the precipitated gold settling? Or what type of reducing agent are you using, sodium metabisulfite, ferrous sulfate, or sulfur dioxide, or one of the other options to reduce the gold?

So an answer to both questions should get this back on track.

Iridium containing lots. These are the one's that don't settle properly and will make the AR solution cloudy even after filtering through a whatman #5 filter paper. I usually do not proceed to AR unless I have a golden brown powder after nitric digestion, but even if I do this I still get a dirty solution in AR which I think is due to the presence of Iridium.

SMB.

Geo,
I only add SMB in small amounts, some are in powder form some are in rocks form, I prefer to use the rock form since they settle at the bottom, if powders are present I mix them. I usually wait for the bubbling to stop before I add another teaspoon.

Could it be the sulfamic acid? I only use about half of the nitric required, like 80ml of nitric for a 200g refined weight expected. And usually the HCl content is about 800ml. When I use sulfamic it seems that there is a lot of free nitric still present as I use about 100ml (with 200g/L content). It is not prepared fresh though, they are stored as a liquid in an airtight container. I prepare them by boiling water then adding the sulfamic. Wait for it to cool then store it.

 

[Geo]

Have you tried heating the solution before adding the sulfamic crystals? It helps the reaction but be careful, adding sulfamic acid to a hot solution with free nitric acid can cause a boil over. Stirring is a must. Stir vigorously as you are adding the sulfamic acid. Add and stir until there is no more reaction.

 

[autumnwillow]

Have you tried heating the solution before adding the sulfamic crystals? It helps the reaction but be careful, adding sulfamic acid to a hot solution with free nitric acid can cause a boil over. Stirring is a must. Stir vigorously as you are adding the sulfamic acid. Add and stir until there is no more reaction.

Exactly this way.

 

[Geo]

If you are still having free nitric problems after this, let it cool and rest for the day or night and repeat. Also, a neat trick is to evaporate low and do the process described above and then add water back to the starting volume. For some reason, the sulfamic seems to work better in a condensed solution. If you do evaporate to try this, be sure to add the sulfamic acid in a saturated solution with water as the crystals may not have enough water in the gold solution to dissolve. If the crystals doesn't dissolve, it will not react as well.

 

[autumnwillow]

Geo,

Free nitric isn't my problem. It is gold powder not settling down as fast as it would when used with a floc.

 

[anachronism]

How many grammes per litre do you tend to have in your solutions?

Also are you talking about dirty recovery drops or the refined drops being problematic?

 

[Geo]

Add a small amount of sulfuric acid and bring the solution to a boil. It will settle quickly as it cools. Works like a charm.

 

[Geo]

As an aside, alum is used as a flocculant in water treatment. A flocculant helps clarify a solution so it can also be a coagulant. Something to help particles stick together so they will become heavy enough to settle faster.

 

[autumnwillow]

How many grammes per litre do you tend to have in your solutions?

Also are you talking about dirty recovery drops or the refined drops being problematic?

200g/1500L that includes the water for washing the remaining AR in the filter.

Both but not all the time for high purity drops. Only iridium containing lots for high purity drops.

 

[anachronism]

200g in one thousand five hundred litres???

 

[autumnwillow]

200g in one thousand five hundred litres???

Haha typo sorry! 200g/1500ml