wet vs. dry preciptation

[BJL1984]

I have been using the HCL/CL process for disolving foils from fingers and have tried using my SMB both as a dry powder and disolving it in distilled water first before adding to solution, its seems to give the same result each time fluid clears of all gold acording to stannous test, I was woundering if some of the more experienced guys could give me some insite on if it gives a better product wet or dry? If one tends to drag down more ofother metals that may be in solution? or if it even makes a difference, the only diffrence I can see is that the preciptation times are different but not sure if there is something i am missing. I have kept the batches i tried different ways seperate, but just want to get some clarafication on the matter before I move on to the AR process

 

[eeTHr]

One time, when experimenting with a small batch, I concentrated it down and didn't add any HCl afterward. When I added dry SMB, nothing happened at all.

I waited a little while, and still nothing at all happened.

Upon adding a little water, the solution instantly turned a chocolate brown, and settled out after awhile.

 

[kronix]

One time, when experimenting with a small batch, I concentrated it down and didn't add any HCl afterward. When I added dry SMB, nothing happened at all.

I waited a little while, and still nothing at all happened.

Upon adding a little water, the solution instantly turned a chocolate brown, and settled out after awhile.

From what I understand I think this is caused by the SMB needing water to convert to sodium bisulfite and then it can make SO2 gas to precipitate gold. If there's very little H2O in the solution it cant perform the proper conversions needed to precipitate.

 

[eeTHr]

kronix---

I agree. SMB with water generates the SO2 for precipitation.

 

[Geo]

not nit-picking but any acid that is a liquid contains a certain amount of water.for me it depends on the process.if im working with hcl/Cl, i use a SMB solution, if im working with AR i use SMB dry. the reaction is slow sometimes but i am very patient.the dry SMB let me know if and how much free nitric is in the solution by the reaction.

im not recommending anything, im just stating how i do it. everyone processes their own way and at their own speed.

 

[qst42know]

If you dilute to rid the solution of silver water isn't the issue. More often for me it's the space in the vessel. Dry SMB doesn't force me to split the batch.

 

[Palladium]

Dry here also.

 

[cnbarr]

Dry here also, the only precipitant I mix as a solution is oxalic acid.

 

[eeTHr]

not nit-picking but any acid that is a liquid contains a certain amount of water.

Well, you are right. I only did that concentrated drop attempt once, to see if it would produce larger particles which would settle faster. But the reaction to the small amount of water added was so pronounced that it convinced me that additional water is necessary (in addition to the dilution to get silver out) for precipitation to take place, for some reason. Maybe the remaining water, after concentration, is somehow "tied up," and not available to form SO2 from the SMB?