Excess Nitric in AR problem?

[JH123]

I leached my crushed CPU's in nitric. Then to heated AR adding only a small amount at a time until no visible gold was seen. I was being careful not to have excess nitric to deal with. After straining the solution I have a jet black color solution, SMB was added and no color change as I am use to. Possibly 3-4 grams of black powder precipitated when I am expecting 4 times that amount. More SMB was added with no change and little if any extra precipitation.

Will there be any precipitation at all with excess nitric? I figured if it continued to eat at disolving gold and metals, it would use itself up and there would be metals insolution only if there is excess nitric, is this correct?

Could the color of my solution being contaminants,could that be preventing a good precipitation?

 

[NobleMetalWorks]

Test with Stannous

If Au is present, heat slowly and try SMB again, are any fumes produces? If so continue to add small amounts of SMB until there are no fumes, did anything precipitate out of solution? If so, test with stannous to make sure there is no more Au in solution. If there is try to precipitate by using more SMB, if not then you are finished, if nothing happened try adding a small amount of Sodium Hydroxide, this sometimes will start the precipitation.

Scott

 

[ericrm]

your expecting 16 grams of gold from cpu
this seem to be a hell of a big batch, could you describ what kind and how much cpu youve treated

 

[JH123]

Evidently Eric smells a rat so this being my first go at CPU's if i'm off bad on expected yield I'll not be suprised as there is lots of misinformation on yields that I have come across. I had around 20 486's and 386's combined about 8 of the pinless 286's in the link below of Phils, and a dozen to 15 mixed half were fiber based. Also a couple gold legged, capped IC's. Whats your opinion?

 

[ericrm]

i dont know the exact yields of your cpu
but for a lot like yours when i sell it i would have about 150/200$ witch tell me if on your first shot you did have 3 or 4g au gold ,you did very well.
BUT the 4g you have, is it recovered or refined twice, because i suspect that your a little high with the 4 g

 

[Palladium]

Will there be any precipitation at all with excess nitric?

When you have excess nitric it will eat up your smb until a point of equilibrium is reached. If you have gold participating and then redissolving then your have excess nitric in solution. If you have any gold that stays on the bottom of the beaker and don't dissolve then your excess nitric is used up.

 

[robertpdickson]

To the group I have a question about neutralizing excess Nitric Acid in an AR solution. I know Hoke's method and many decribed on here. Is the use of Magnesium a quick approach to neutralizing Nitric and does it cause any adverse side effects in Gold percipitation?

 

[jimdoc]

To the group I have a question about neutralizing excess Nitric Acid in an AR solution. I know Hoke's method and many decribed on here. Is the use of Magnesium a quick approach to neutralizing Nitric and does it cause any adverse side effects in Gold percipitation?

You want to get rid of base metals in refining, why would you want to add another? Hoke's method is best, why even add urea when you don't have to.

Jim

 

[butcher]

Well I can think of a good metal to use to help get rid of free nitric acid in a solution of HAuCl3 (aqua regia),

A pure gold button, no added impurity, and the gold is recovered, for more details of the process see Harold's post's on this subject.

 

[robertpdickson]

Well JimDoc and Butcher....when you got a point you got a point. Makes sense to me. Thanks for the insight and opinions. Always help to get another's point of view.

Thx