Mysterious by-product after cell use

[Luster]

Greetings All,
I have been a member now for about a year and this being my first post I would first like to extend my deepest appreciation and gratitude to all those that have helped so many newbies like myself especially the senior members.
I have been reading Hoke and this forum to understand the basic principles of refining but have encountered a puzzling result using the cell process.
My first use of the cell was 1kg of gold watch cases, seemed rather successful with no apparent problems I thought, when I was discourage to see how little the yield was of only .9 gr button. I viewed the results as experience gained and rationalized the watch case were of low gold value.
The problem occurred on my second attempt using the cell. The following are the steps that lead to the mysterious by-product.

-Evaporated excess water from sulphuric acid by boiling. This solution was saved from the first cell process. After reduction the acid colour was very dark black with same coloured clumped particles around edge

-Poured concentrated sulphuric acid into a 8" x 10" Pyrex pan, setup cathode and anode

-Processed 2100g of plated bracelets at 454g batches over a week's time

-At first I was waiting for the amps to drop to zero before taking out items
realizing revise plating was taking too long

-Items looked copper when taken out of cell


- Reduced process time when amp gauge showed a 2 amp drop

-Items then had a silver appearance
View attachment 2

-After de-plating was complete the sulphuric acid was poured out, what was left was about 1/2 inch thick of black like pudding that clung to the bottom of pan.

-scraped out and rinsed pan of black material into coffee pot

-Added 50 ml of HCL and slowing add 25ml of Clorox bleach

-Resulting solution was very dark green and deep yellow around edge of solution, a definite more green/yellow solution

-Also matter was still at bottom of pot thinking more time for dissolving and left it overnight

-Next day no change so proceeded to filter and filtered out a reddish brown paste


-Solution still green yellow but a lighter green

-Proceeded to drop gold by slowly adding to solution two spoons of SMB

- Colour change to light green then to a murky green

-Left to settle for three days now with very litter powder in bottom of pot


My question then is what and how did this reddish brown paste come to be and is it possible that there is no more gold or is it within the reddish brown paste?

If anyone can help with an answer to this mystery I will forever be appreciative

 

[Geo]

did you test the solution after you precipitated to see if there was more gold present? the first time you used the acid it was contaminated with copper, alot of copper. when you used it on the next batch it probably could not hold any more copper and made a deposit of red copper mud. the cell well strip the base metal when it heats up so you have nickel, copper, palladium and maybe a little PT in the mud. test your solution with stannous chloride and see what pops up.

 

[Luster]

Thank you Geo for your reply. As per your advice I tested the solution and came up with a fasle positive maybe to an exesive amount of SMB

How can copper be delete from the sulphuric acid?
What would be the best way to extract PM from red mud?
And would you not think there would have been more gold in 2.1Kg of jewellery?

Thank you for any replies in advance...Luster

 

[Geo]

the way i reduce copper content in my sulfuric may not be the correct way but it works for me. first i dilute the sulfuric 1 part sulfuric to 3 parts water then filter. then i evaporate the water back out and this causes the copper to deposit in crystals. its not 100% but the acid comes back a golden yellow color just like i started with. i start with a generic brand drain opener and it works good for me. i would boil the mud in hcl acid for 15 minutes and then rinse with tap water. then boil in ammonium hydroxide (white ammonia in the detergent isle) for 15 minutes then rinse in tap water and see what you have left. gold should not be effected by these washings. take any remaining material and dissolve in hcl+cl and test with stannous chloride.

 

[texan]

I try not to do a violent boil. I let my solutions simmer with a good steam coming off. A violent boil will cause values to be lost.

Texan

 

[Harold_V]

I try not to do a violent boil. I let my solutions simmer with a good steam coming off. A violent boil will cause values to be lost.

Texan

A great deal depends on what you're boiling. If you are boiling wastes, such as from a jeweler's polishing machine, a hard boil is almost mandatory. It keeps the particles in suspension, limiting their ability to accumulate on the bottom, where they become overheated and fuse to the beaker. In such an instance, all that is required to crack the beaker is to stir the material, exposing the overheated glass to the solution within.

When you must do a hard boil, keep the vessel covered with a watch glass. The vast majority of fluids condense and drip back to the vessel. That drastically limits any potential losses.

Harold