Best method of the fast precipitation maximum percent of PGM from Aqua Regia solution

[orvi]

Thanks, I'm tending towards cementing by copper Maybe you know how to calculate the amount of sulfamic acid to neutralize the remaining HNO3 in pregnant AR solution? Or is its excess not critical and its amount can be calculated from the initial amount of nitric acid in Aqua Regia?

The ammount of de-noxing agent isn´t possible to calculate, if you do not know how much nitric you have still in the juice. Theoretically, you can titrate small sample and then go with whole vat... But I will do it steadily to the point where reaction stop. It takes some time for sulfamic to dissolve in AR solution, so add slowly. And stir it well.

 

[Ultrax]

If you do not get a reaction, that means remains of nitric aren´t present. That is fine, unless you know you leached everything from the solution. Because if you do not have nitric in there, you aren´t leaching PGMs. Nitric decompose over time in hot AR, and byproducts are chlorine, NOCl and NO2 - that means your oxidizer just fizz away without effect slowly. Be aware of this fact. You need to add sulfamic acid to at least warm solution, not cold. During de-noxing with sulfamic, nitrogen and nitrous oxide are evolved, so be careful.

Does the rate of decomposition of nitric acid in aqua regia depend on temperature? What is the optimal temperature for leaching of PGM? Thanks for the help!

 

[orvi]

Does the rate of decomposition of nitric acid in aqua regia depend on temperature? What is the optimal temperature for leaching of PGM? Thanks for the help!

Yes, of course. Higher the temperature, quicker the decomposition. When AR is cold, gaseous active decomposition products like chlorine and NOCl are more soluble in it. When heated, decomposition is quicker and also the gasses escape the hot solution quicker.

This is a very broad question. I am not an expert in leaching PGMs, so I can only tell you - higher the temperature, quicker the dissolution. But it comes with cost of replenishing "dead" nitric acid. You have sulfidic ore... that is very different from metallic PGMs.
Maybe some PGM guys out there could give you an answer.