the order of precipitation

[Pilgrim2850]

Hi Everyone,

Is there a post on the order of all the metals for precipitation? If not are the metals precipitated in there atomic # order? Thanks and blessings, larry

 

[lazersteve]

Larry,

Metals are precipitated in order of activity generally speaking. Conditions such as pH, concentration, solubility, and temperature may also affect this.

The activity series of metals can be located on my website in the documents section or on wiki and numerous other places on the web.

The metals higher up the Activity Series will displace the metals lower on the chart.

Steve

 

[Pilgrim2850]

thanks a bunch Steve................larry

 

[Harold_V]

The only comment I'd add is that it's far easier to wash precipitated gold than it is to wash precipitated platinum or palladium salts, each of which readily dissolve in water. As a result, my choice was always to precipitate gold first, but then it was always the predominant metal in solution as well. The predominant metal may dictate, depending on the metal in question, and the relative volume of other metals that are intended to be recovered.

Gold that is precipitated from a solution that is contaminated with palladium tends to come down with a fair amount of palladium. It doesn't wash out easily-----so a second refining is often a requirement for good separation.

Harold

 

[Pilgrim2850]

Thanks Harold.........it's always great to have your imput from your wealth of knowledge.


larry

 

[markqf1]

Harold,

When you say that the pt and pd salts are readily dissolved with water, ... would you use the same nh4cl and naclo3 method to reprecipitate them from the water?
Seems like the ph would have to be lowered?

Mark

 

[Harold_V]

would you use the same nh4cl and naclo3 method to reprecipitate them from the water?
Seems like the ph would have to be lowered?

Because of the failure of dilute solutions of platinum and palladium to precipitate their values, I'm of the opinion that you wouldn't achieve success. It's possible the solution could be evaporated, but with the residual ammonium chloride, I question what might come of the process. It would be desirable to filter the solution before precipitation (after evaporation), which likely would not be possible due to the added reagent. I imagine you'd experience crystal growth, preventing filtration.

According to Hoke, and in keeping with my personal experiences, by washing with a ammonium chloride solution instead of just water, dissolution is greatly reduced, if not eliminated. In my situation, where I didn't have to account for any of the platinum metals, what little that got dissolved was simply poured into the stock pot, where it was recovered for future processing.

Sorry I'm not more help. The platinum metals were not my specialty, although I processed a fair amount of platinum and palladium.

Harold

 

[markqf1]

Thanks Harold.
That seems to be the best technique, as I have read here, and abroad.
Some things seem to never change.

Mark

 

[skippy]

Ok, so if you want to refine a dilute solution of pgm values, am I right to think that first step is to cement out the PGMs as metal with zinc? I know... buy Hoke's book

 

[Harold_V]

Ok, so if you want to refine a dilute solution of pgm values, am I right to think that first step is to cement out the PGMs as metal with zinc?

I'd avoid zinc unless the solution was quite clean. In this case I'd likely use copper, to eliminate cementing down more copper. If your purpose was to simply recover the values with no consideration for purity, then, yes, I'd use zinc, or even scrap steel, which is much cheaper and readily available in my world. May be different for you in yours.

I know... buy Hoke's book

You got it right. Read Hoke! But understand that there is nothing for me to gain if you do, aside from not having to answer the same questions over and over. I do not stand to profit by the book in any way, nor am I affiliated with the book in any way. It was simply the book that made the difference between me wanting to refine, and knowing how. If it worked for me, it can work for others, assuming they're able to follow instructions and don't think they're more clever than the writer.

I'm quick to remind you, and anyone that cares to read my words, that I am not a chemist. Everything I know about refining is the result of studying Hoke. She told it straight, and right, and did so in a way that even people like me can understand her message.

Buy Hoke's book. It's the best thing you can do if you're interested in refining.

Harold