Precipitation from SX (MIBK)

Hey all, let me start by thanking everyone for doing what they do here. I've learned a lot since coming here and I really appreciate all you folks sharing information and looking out for one another. This is truly a beautiful community.

So, down to brass tax. I need a hand, even if its just a link to some literature on the subject (I'm fairly chemistry literate) on precipitating Au from MIBK or 4 methyl 2 pentanone. I came into a bottle of this from my job where they were going to get rid of it since it had been hanging around taking up space for a few years. I've gotten pretty comfortable by now with the more traditional refining methods and so I figured i would try a small experiment with solvent extraction. I had a ~.6g button laying around that had gotten contaminated likely with tin from a dirty melting dish. After some hemming and hawing and research on how to part the two I did manage to find success. Once i felt satisfied with this separation the remaining, very porous and crumbly remains of the button were dissolved in poor mans AR along with a small inclusion of some crumbs of 10k scrap from a separate venture. Once the reaction and dissolution was complete the solution was filtered and denoxxed via evaporation and reconstitution. The resulting solution was green with copper and had a total volume of maybe 70mL. This was placed into sturdy solvent resistant centrifuge tubes and 20mL of MIBK was placed in each (two tubes used as the solution volume exceeded that of the tube) and they were shaken out. I have to say I was really impressed with the separation. The organic phase turned a beautiful yellow color and the aqueous phase remained copper green. A pipette was used to separate the phases and the pregnant organic phases were combined in a third centrifuge tube. A few extra mL of fresh solvent was shaken through the barren aqueous phase to be certain it was completely vacated, it was, and these "rinses" were added to the pregnant solvent.

Now before doing this I searched here and elsewhere and really found only information on BDG. In which oxalic was used as a reducing agent. I also found a post in which Lou and another member (deano? Or noidea? Are these the same person?) discuss SX preferences and MIBK and oxalic as a precipitating agent are brought up there but not in much detail.

I tried using oxalic today and have had no success thus far. To my 45mL of pregnant MIBK I added 10mL of water containing an excess (in relation to a 1:1 ratio with my expected gold) of oxalic acid and shook.there's been nothing happening. I tried gentle heating as well after transferring to a suitable vessel. A darkening of the aqueous phase occurred but so far there's been no visible reaction. Any one have any experience with this stuff? I appreciate the help. This is only a hobby for me and as I've mentioned I did a small test run. So if this doesn't work out its not too big a deal. I would still like the satisfaction of having this work for me however! If only there was mention of this stuff in hoke! its about the only thing she doesn't cover!

Totally working haha just was not patient enough. This is gonna take a LOOOOOOOOONG time to precipitate fully the way its going so far though.. Still would appreciate any advice though on how to do this the right way. Thanks guys!

Needs refluxed with it.

Plenty of metal extraction methods seem to take a long time, which is why people say 'patience' a lot.
Overnight, a week, a month even.

Hexone is a bit carcinogenic, so reflux in a fume hood with iced water in the condenser.

Is it carcinogenic? I work with it a lot and quite like the smell of it!

Lou

Isn't MIKB the one that causes really bad headaches in some people or did I get that wrong?

Jon

Yeah I think some people do get headaches from it. So far so good for me though. And yes, it smells fantastic hahaha. I try and keep my vapor exposure to a minimum though. I don't know how many more brain cells I can afford to lose!! Anyhow, reflux is something I am not equipped for.. hmm.. Well, I have been looking for a reason to buy a condenser.. As far as precipitating from this is there an ideal concentration here for oxalic? Since I knew I wasn't really worried about partition coefficients or solubilities in this step I didn't really think too much about it. Just over 1:1 oxalic to Au into about the same amount of h2o as I had of MIBK. I know i need enough water in there to make a lot of contact when shaken. Thanks guys

Also I wish I had realized hexone was a cover all name for all 6 carboned ketones I bet I would have had at least a somewhat easier time with doing research for this little project.

Your oxalic can be saturated solution. Those are usually 100 g/L or so when very hot. Tough to get it into solution.

Excess oxalic can be recycled. Just separate it off in the separatory funnel.

You can't distill it all to dryness and recover the hexone straight away because the oxalic acid will volatilize/sublimate into the condenser.

Hey I did manage to get all or most out of it today! I don't have a heat/stir plate at home so I brought it into work today and kept it in the fume hood next to my work station throughout the day. I poured everything into a narrow necked erlenmeyer (no reflux at work either) and stirred for most of the day at room temp and saw some slight progress. About an hour and a half before I started heating it on low with a thermometer to keep everything far under boiling (117C for MIBK I think?? 100 for h2o obviously.. My temp maxed out at 75ish I think) at this point I was able to give it some more attention and kept a close eye on it. By the end of my shift I had an almost colorless organic phase, just purple from colloidal gold being whipped in from stirring. I know i lost some hexone to evaporation because I had nothing to condense it in, but the sponge I got out is gorgeous. I just filtered everything off through a whatman filter which even caught the weird suspended "sludgey looking" particles at the interface between phases. I'm letting the last of everything settle out before I separate. I'm definitely not equipped enough to do this often at home, although id like to be eventually, but I'm certainly happy with the results. And yeah Lou the last thing I would want is oxalic acid recrystalizing blocking and shattering a brand new condenser I haven't even bought yet, although that would be my luck!