GSP said:
Steve, do you have more data on this - or, your original source for your statement? Seems iffy, to me, but there could have been some isolated usage, I guess. Have you yet thought of an economical, efficient, fast way to use either of them on a grand scale? You could very well be on that threshold.
Chris,
I was using AP and HCl-Cl long before I realized it was used in bigger refineries as I have mentioned.
Here's the reference for my statement:
Small Scale Refining of Jewelers Wastes by Roland Loewen pg.175-176 C1995 said:
Hydrogen Peroxide and hydrochloric acid will dissolve gold. This is used in several refineries. One refiner reported that the recovery of PGMs was much improved when hydrogen peroxide rather than nitric acid was the oxidizer. The known affinity of platinum and palladium for nitrogen compounds make this a believable conclusion. Unless extended boiling of solutions to remove nitrogen compounds is done it is quite possible that some forms of nitrogen could combine and hold PGMs.
We have no experience with hydrogen peroxide oxidation. The use of the 50% grade is reported. We speculate that the metal is in hydrochloric acid solution and is treated by adding the H2O2. Because hydrogen peroxide is an unstable material considerable care in its use is needed. The stream of peroxide should not be introduced under the solution because of the chance of draw back to the supply tank. There the metals present will likely catalyze peroxide decomposition which can be explosive.
Hydrogen peroxide is a very reactive chemical. It also decomposes and a product of decomposition is a gas (oxygen). In low concentration and with a stabilizer this decomposition is slow. At high concentrations and/or in the presence of a catalyst (many metals are such catalyst) this decomposition goes at explosive rates. Damage can be severe.
A through education in the characteristics of hydrogen peroxide must proceed any work with this material. The manufacturers of hydrogen peroxide can usually give considerable information and advice.
The dissolution reaction is probably :
2Au + 3H2O2 + 6HCl = 2AuCl3 + 6H2O
I have also found this same formula in several texts.
What is odd to me about his mention of the use of peroxide is his lack of references cited on the source of the material. He has references throughout the book (just about every paragraph) on many subjects, but not this one. Just above this section he mentions HCl and Chlorine gas without reference also.
I experimentally stumbled across the use of AP for stripping base metals around three years ago. I've owned this book for less than a year. I used AP to dissolve my first batch of monolithic capacitors around two years ago. The 3% stuff is super slow, but it works very well on Palaldium. I reallly dislike evaporating nitric acid based PGM solutions. With AP this problem is solved.
As for up scaling the reaction, yes. I have penciled out a contraption to use AP in a continuous configuration which works with circulating pumps, filters, and electrolytic reactions. Theoretically you can electrolytically rejuvenate the AP as it's saturated and recover the copper moss, returning the rejuvenated solution to the reaction vessel. In essence you can dissolve pounds of copper based pins in a very short time and retrieve the gold foils when the copper is gone. The copper ends up in a separate bucket in mossy form.
I built a prototype and turned it on, but the spent AP I used was too saturated when I first started the device
. Huge amounts of chlorine gas were evolved in just a few seconds of operation. Ideally you would start with a fresh solution and turn on the electrolytic cell to maintain the proper CuCl2 concentration to affect rapid dissolution while plating out the dissolved copper.
Steve
