what happens?

[arthur kierski]

i have gold in a ar solution(tested positive with stannous)----to this solution i usually dilute ten times with water and add smb to precipitate the gold----sometimes the solution precipitates gold(becomes brown in collor ) and sometimes it does not precipitate the gold and i have to use a small trick that always works-----i add a few drops of naoh and the solution imediatelly darkens and precipitates the gold----i do not change the ph--i mantain the solution acid----
what happens when one adds a few drops of naoh?this method works for me always---unless there is no gold in the ar solution
thanks and regards to all,
Arthur

 

[NobleMetalWorks]

Do a PH test before and after you add Sodium Hydroxide. Sodium Hydroxide, or NaOH is alkaline. It should raise the PH level because it's an alkali.

When you add NaOH (Sodium Hydroxide(Lye)) to a solution with HCl (Hydrochloric Acid) in it, it raises the PH level, making it more caustic rather than acidic. You are basically making NaCl (salt) and H2O (water) or salt water.

When you use MSB, you neutralize any remaining HNO3 (Nitric Acid), then when you add NaOH you neutralize the HCl which should, from what I understand, precipitate everything out of solution.

HCl + NaOH = NaCl + H2O

Unlike NaOH, the hydroxides of most transition metals are insoluble, and therefore sodium hydroxide can be used to precipitate transition metal hydroxides also.

This is really my first attempt to explain something in chemistry terms, please someone correct me if I am wrong.

Scott

Edited for spelling

 

[4metals]

What is likely happening is you are "seeding" the precipitation with the caustic. The amount of caustic required to neutralize the acid is much more than a few drops but the few drops likely forms a hydroxide precipitate for a split second and it quickly redissolves. Often that is all the seeding the SMB needs to drop the gold.

 

[NobleMetalWorks]

What is likely happening is you are "seeding" the precipitation with the caustic. The amount of caustic required to neutralize the acid is much more than a few drops but the few drops likely forms a hydroxide precipitate for a split second and it quickly redissolves. Often that is all the seeding the SMB needs to drop the gold.

Thank you for explaining it, I was still trying to figure out exactly what is going on when I referred back to the post to see if someone answered.

Scott

 

[arthur kierski]

as i mentioned, the ph with the addition of naoh does not change radically----the solution remains acidic---4metals,you are right,the naoh added is not suficient to change the ar solution from acid to alkaline but liberates (seeds)the gold that the smd did not liberate--------any how ,it works always---
i read many threads from members that have dificulties in precipitating gold with smb and i would sugest that they use this method----my ar,is normally free of base metals because i always do a nitric pre treatment before using ar in the materials----i know that ,at this stage of the process,the ar contains mainly gold to precipitate---
thanks all of you for the replies
Arthur