ScrapMetalJunkie said:
I have a lot of palladium spring end clippings, like a whole ziplock bag full. Does anybody have a good method for refining these clipping?
Per the underlined --- dilute nitric
Although nitric will dissolve Pd - in order to do so the nitric needs to be concentrated - that is (like dissolving silver) 67 - 70 % nitric diluted 50/50 with distilled water - AND it needs to be HOT - & even at that it is very slow at dissolving the Pd --- that is a result of where it sits on the reactive series of metals
In other words - although nitric can/will dissolve Pd - it is MUCH less reactive to the nitric then nitric reaction to metal above Pd in the reactive series - such as copper or silver which are MUCH more reactive to nitric
Therefore you can take advantage of "how reactive" nitric is to the different metals
Examples; - copper is "very" reactive to nitric - 50/50 nitric/D-water will dissolve copper without any need to heat the nitric (other then the heat created from the reaction) & it will do so in a "relatively" short time (a few hours) the example here being say 5 or 10 pounds of gold plated pins in a plastic 5 gallon bucket will dissolve the pins in 4 -5 hours
on the other hand - if you put 5 - 10 pounds of silver in a 5 gallon bucket with the same 50/50 nitric it would take several days to dissolve the silver- & then it may not dissolve all the silver (as the acid gets weaker & weaker the more metal it dissolves) which is why we put silver in a beaker & put it on a hot plate to dissolve silver --- the acid (nitric) needs the added heat of the hot plate to keep the reaction going on the silver because the silver is so much less reactive to the nitric then the reactivity of the nitric to copper
Like wise - Pd is even less reactive to nitric then it is to silver - so not only does it take heat to dissolve Pd with nitric - it also take
more time to dissolve the Pd
So you can take advantage of this fact - you have a "small" Pd wire brazed to a "thin" copper bus bar
therefore - if you dilute the nitric more then 50/50 & do "not" apply any heat - the acid will be to weak to react with the Pd - but will still react with the copper --- thereby dissolving the copper but leave the Pd (wires) undissolved & sitting in the bottom of your reaction vessel (beaker or bucket)
Keep in mind that it takes (about) 4 time more nitric to dissolve copper then to dissolve silver
It takes (about) 1 gallon of 67 -70 % nitric to dissolve (about) 2 pounds of copper - where as the same gallon of nitric will dissolve (about) 8 pounds of silver
As an example (in your case) say you have 2 pounds of the clipped bus bar points - you will need (about) 1 gallon of nitric to dissolve the copper - put the points in a 5 gallon bucket - put 2 gallons distilled water in the bucket (you don't want tap water as the chlorine in tap water can make a weak AR which may - or not - result in dissolving "some" Pd) --- then add 1/3 to 1/2 of the nitric (I think you will be safe at half your acid - because a half gallon acid to 2 gallons water is already quit diluted) let that react until the reaction slows down (about 2 -3 hours) then add half of your remaining acid - wait for the reaction to slow down again (another 2 - 3 hours) then add the remaining acid --- if you start in the morning - by the end of the day (depending somewhat on the outside temp) the copper should be dissolved with the Pd wires in the bottom of the bucket --- if the outside temp is below 60 - 70 F it may take a day & half to 2 days to dissolve the copper
Or if you don't have nitric you could "boil" the clippings in HCL to dissolve the nickel braze to release the Pd wires from the copper bus bars --- but then you have to "try" to separate the VERY small wires from the much larger copper bus bar clippings --- a real pain in the you know what --- because the HCl wont dissolve ether the copper or the Pd
Or - you could dissolve the copper with the CuCl2 method - but like dissolving gold plated pins with CuCl2 that will take DAYS to dissolve the copper
I have never used the CuCl2 method (because I have always had nitric) but as I understand it - with that much copper it could take a couple weeks --- maybe someone that knows more about the CuCl2 method could chime in on that
Kurt
