Zinc Turnings Vs Solid Bar and the heat of the Reaction

[awbrew]

Hi guys, I been Useing zinc for a while now to precipitate PM's. I have the soild bars of zinc. I started out drilling them so I would have the turnings. Lately I have gotten lazy and have been just using the whole bar.(I know that the platinum sticks to the bars and I not worried with that though, I will eventually get those pm's back when the bar is disolved.).

HCL/CL leach( Platium,pladium,and sisters)

What my real question is there a difference of how fine the particles are when they Precipitate. And is that proportional to heat of the reaction.

It seems that the bars get a slower reaction and therefore not as much heat in the vessel. And therefore a more fine Precipitate uniformly in suspenion in the liquid.

Where as the turnings on the hand go more quickly into solution and temp of the reaction seems hotter in the vessel. And maybe the particles clump together better and fall out of suspension more quickly. Effecting a better precipitation.

Is this difference of temp in the reaction directly proportional to the size of the percipate and a better precipitation?

Thanks

 

[butcher]

It could be due to the acid being more reactive when heated thus effecting the replacement of metals from solution with the more reactive metal, also the solution may circulate better moving the solution around and into contact with the metal bar more, also if acid is more reactive it would form more gases, like hydrogen from the reaction, these bubbles loosening cemented metals from the bar easier.

Just a guess.

 

[awbrew]

Hi Butcher, It been awhile since I last talked to you. that would make sense the extra gases makeing a better seperation. you know what I'm talking about that sometimes when you look down in the beaker the liquid droped more complete and the top liquid is more clear. I know steve had us using the turnings. Probably for this reason. I also noticed that when I us the Bar that the PGMs lightly coat it, and I think this is reduceing the surface area and slowing down the reaction some what.

Thanks for the reply brother...