First Attempt at PGM drop

[midaselm]

Hi All,

I attempted to drop my first PGMs today from a hcl/cl cat con leach, as per LazerSteves videos and have a few questions. I never attempted anything like this but am so far happy with my results .

First off I leached with a 12% hcl and added cl ( the very first time we added cl it was coloured and scented ! really should have checked first)
Added small amount of CL every few days . There was 2 cats in there.

I filtered as per videos, and then used a Whatman number 5 filter under vacuum on leach. Was left with a nice red / orange solution that when tested with Sannous, turned red. (pic 1)

When bringing the PH up, though it seemed to take a lot of soda ash to get a colour change, I was also PH testing along the way with paper. The mix was very frothy (pic 2 ) . Before I approached ph 2-ish instead of getting a white precipitate in beaker , I got more of a salt / crystal forming in beaker and floating. (Pic 3) There was a colour change but was still very foaming on top (pic 4).

Eventually the foam disappeared and the crystals settled, so I added zinc 150 mesh form. The reaction lasted for well longer than a few minutes , it did drop Black powder, but did not make the white salts disappear. I did two additions of zinc . I tested the liquid with stanneous and got no reaction for PGMs, so did not add any more zinc. (I did however take a test-tube of the liquid added zinc , no real reaction, but then added heat and seemed to get more pgm dropping- well the zinc turned black anyway)

I decanted off the main liquid into filter and this is the resultant powder in a 1 litre beaker. Pic 5., there is visible black powder, grey/ blue (zinc maybe) and salt like substance (pic 6 ). The decanted liquid came through the whatman number 5 had still a tint of black to it and no real powder in the filter, the coffee filter seems to get most of it .

So any ideas on where i went wrong anyone? Could the initial bleach have had a soap in it that is ruining things?
Did I not PH up enough / too much maybe?
The ambient temp here today was prob 12 Celsius so would the heat effect reactions? (When test tube heated i got better results with zinc) should i wait till it get warmer here or use heat pad when adding ph and zinc ?
Am I using the wrong whatman filter , is the black in the fitered liquid PGMs ?
Or as ive never even seen black powder ,should my dropped black powder have these salt like parts?

Thanks a million,

 

[midaselm]

oh and forgot to add that after washing it off a few times , i have covered with distilled water , but its still bubbling

 

[midaselm]

i didnt upload pic 6 ....

 

[kilo17]

I am by no means a pro at this but that is a lot of black. I think you have a ton of Zinc in it and if you wash it with dilute HCl you will be left with a much smaller amount (probably barely enough to cover the bottom of the beaker) of PGM black.
Keith

 

[kilo17]

I would say that your yield may be in the 2-4 gram range... Keith

 

[lazersteve]

The soda ash step is meant to reduce the acidity of the solution to conserve on zinc consumption, since you only used 12% HCl you could have skipped this step.

Using zinc turnings or shavings would have produced a more easily black powder that is settles and filters more easily.

Looks like you are on track aside from a little excess zinc which is not uncommon.

Steve

 

[midaselm]

Thank Steve / Kilo for the input, very much appreciated ,

will add some HCL and try digest the excess zinc and see what i get.

I think the soda ash part was needed as the ph was 0,and took a lot of ash to bring ph up .

Is is safer at the start to add excess zinc and then HCL zinc away ? Would this be a safer way to make sure all pgms drop from solution ?

I have another batch ready to go now , that was done with 38% hcl and colourless and unscented bleach so hopefully there will be no soaping / frothing of the mixture , and i can get it done with less zinc .

Again , thanks a million for the help ,

 

[midaselm]

update....

so added hcl to burn off the excess zinc , but now the black powder is so fine it remains suspended in liquid almost, i figure this is from the fine mesh zinc i used. I vacuum filtered using whatman 5 paper but it took 36 hrs to filter a 1.5 litre amount. The black powder was stuck to the papers and would not really come off the filter when spraying it off .

So at this stage I think it may be best to just start over again, and hopefully I can get precipation of pgms in a less fine form, I have a second batch leaching there and am wondering if I can just add the tin, pgm + leach mix I have from this attempt to the next batch or would this cause me any problems with the second batch? Hopefully I can get some zinc turnings by then, and get better results maybe.

Also any advice about what spec whatman papers should i be using .

thanks
k