pH

[gmiller]

After my recent go round with HCL-Au not dorpping the Au, it occurred to me that adjusting the pH of our solutions may be a viable way of dropping metals. Does anyone know what specific pH each individual PM will drop out of solution? I know that there might be a range of readings in witch each will drop. Anyone got a chart they might be willing to post or a link to such a chart?

I know I can drop everything below copper on the electro-chemical /electro-motive scale by super saturating my solution with copper, but I'm hopeing to selectivly drop the other PMs by adjusting the pH, thus eliminating the use of several chemicals.

Thanks,
Gary

 

[goldsilverpro]

This has been discussed before. The problems I've always had, at least with base metals, was that there are overlaps of the precipitation of the metals at the various pH levels and nothing drops cleanly.

 

[lazersteve]

All of the charts I've seen are from the waste water industry and do not contain data on precious metals.

Here's one I posted some time ago:

pH Precipitation of Base Metals

Steve

 

[gmiller]

Thanks to Platdigger and lazersteve, and all the rest of you on the forum. I knew it had been discussed before, but using the search engine produces so many hits for "pH" or "preciptation" that it is nearly impossiable to search thu all of the hits. There is SOOOO much information here I don't know how anyone can keep track. I guess that sometimes we have to rely on responces from those who may have posted the needed information in order to find it.

My thought is to precipitat in spit of the overlaps and then clean up what has precipated. I'll have to take a real close look at the precipation tables to see if that would work. I'll Keep you posted.

Thanks all
Gary

 

[goldsilverpro]

A problem I've found with those charts is that they are based on pure controlled systems and not the complex mixtures of real life solutions. Things don't always work exactly as predicted by the charts.

 

[butcher]

I tried ph selective precipitation, could not get any decent result as GSP stated sometimes real chemistry and books can have many variables, temperature passsing end point before reaction is completed chemically, my impatience, and contamination of solutions and many variables,I predict. unlike books or formulas chemistry does not always follow predicted science, we can write an equation but the chemicals may not follow our equation as we predicted and they may have many changes involved before reacting to make products we predict. PH is a good way to precipitate the metals for waste treatment if you are not after selectivity.
using the metal as a reagent to precipitate and electromotive series I believe is more predictable for selectivity precipitation, or sometimes chemicals that may affect one metal and not the others in solution, but even then I believe that both metals reactant and metal being precipitated may not have definite lines, and some of both can be in solution at once to some degree, even with chemicals sometimes we need a slight excess to get all of our product out of solutions

 

[goldsilverpro]

Good post, Richard.