Ferrocyanide leach

[frank-20011]

hello everyone,

after all these Eco-goldex discussions i would try a ferro leach.

into two watch glasses i place a sollution of potassiumferrocyanide.

in the 1st glass without any substitutes, in the 2nd with one drop of H2O2 3% and a little Na2CO3.

in both glasses i place a few plated contacts from newer pc-connectors/connectors out of the play station 2 and some older plated parts from a cpu-socket out the early 90s

at first i put both glasses 1h under an uv-lamp...after that i let em stand over night in the dark.

at todays morning the plating from the parts out of the connectors are gone in both watch glasses but the plating at the cpu-socket-parts still remains and it remains too after i let stand both glasses outdoors for 1h...

why the plating on some parts still remains?

it remains after waiting a lot of hours during the plating of the parts which are clean now is gone within 10...20min?

have anybody experiences with ferro or ferri leachings?

best regards, frank!

 

[nickvc]

Frank with cyanide leaches you normally use some form of agitation in the solution, it could be flowing or simple stirring or dipping to keep exposing fresh leach to your values so it can dissolve them.

 

[frank-20011]

hello,

i can not think the plated objects are placed in a 5mm high layer of leaching sollution, in a 100mm tall watch glass and the watch glass itself was placed under the uv lamp, than at the window board (outside with aeration by the wind) and so i think there is enough motion in the sollution...

moreover this i take the glasses in my hands, within the leaching time of ~24hr, swirl the opjects in the sollution to judge the plating.


better i should start it again, without H2O2 but with motion by aeration.
for this what a concentration of K4[Fe(CN)6] should i use?
with NaHCO3 the pH is in the right range.

regards, Frank!

 

[Topher_osAUrus]

I hope Deano sees this and gives his valuable input. As I too would like to use the potassiumferrocyanide I have to leach some plated stuff.

I'm not for certain, but, I believe the ph needs to be around 11-12 for leaching.

I wonder how many of the ingredients on the eco-goldex are requirements for it to be a success.

 

[frank-20011]

hello,

"I believe the ph needs to be around 11-12 for leaching"

exactly, not more and not less, 11,5!

next thing is: after i few hr's i've noticed a withe sludge, a percipitat in my watch glasses. every time, not only at my latest test i've described above!
what's that?

regards, frank!

 

[Deano]

Potassium ferrocyanide leaching is the same as straight cyanide leaching, just with some iron complexes present.

You treat it exactly as you would treat a normal cyanide leach, pH of 11 or above for safety reasons, not for operational reasons.

If you raise the pH above 11 you will slow down the rate of leaching, this is the only effect.

Any white sludge formed is most likely to be associated with contaminants in you water supply reacting with the carbonate you are adding.

Try using NaOH for pH control and see if this gets rid of your sludge.

Depending on what and how you want to leach, levels of potassium ferrocyanide start at 0.1 grams per litre up to 5 grams per litre.

The more cyanide present the more oxidant you need to have present.

The higher cyanide levels are generally run with added oxidants such as peroxide etc.

These oxidants cause problems with zincing for gold from the solution, either these oxidants must be removed before zincing or the gold must be recovered by methods such as adsorption onto carbon.

Many commercial operators devise clever ways to keep the dissolved oxygen level of the leach solution high by plunging the leach solution from a pumped bleed stream, adding air immediately prior to a static mixer in a pumped bleed stream etc, this lessens the need for artificial oxidants.

Deano

 

[frank-20011]

Hallo,

and what do you think about the deplating of some of my contacts and the non-de-plating of others?

is an portable facial-solarium fine to do the job?
i can use it indoors, outside we have -5°C at themoment.

what do you think about leaching times at 20°C, pH11, no extra oxidiser respectively mixing by aeration and 1gm of pot. ferrocyanide?

regards, frank!

 

[patnor1011]

Leach need to be in motion. Occasional swirling is not enough. Best will be to make material to be in constant motion.

 

[Deano]

Depends entirely on the wavelength of the UV radiation from your solarium. Daylight is preferred for initial use because it covers all wavelengths in the UV spectrum.

Conditions are fine assuming that you are talking about 1 litre of solution and good mixing, like all leaches you have to keep fresh leach circulating at the face you want to leach.

If you are not getting leaching occurring there are two possibilities.

First is that there is a layer of something which is masking the metal and preventing leach access.

Second is that the metal has a composition which is resistant to the type of leach being used.

It is also possible that the layer of metal is thick enough that total removal will take much longer than other similar looking pieces.

Leaching times are totally dependent on leach composition and metal type and thickness, you have to run it and see.


Deano

 

[patnor1011]

I used handheld mapp torch to clean pins and material I wanted to leach. I did not used it extensively, just enough to burn any oils which might be on top of material.

 

[nickvc]

I would have thought a good wash in lye, use protection,would clean any grease off and it wouldnt affect the leach adversely as it needs to be alkali.

 

[frank-20011]

Hello,

the pins which are resist to my leach are out of a socket from a pentium 486 or 386...if you pull the processor out of the socket, you can lever the whole plastic part of the socket from the main board using a screwdriver.

the"pins" stay on the board, the are looking like little blades...like blades of screwdrivers.

normaly there shouldn't be any grease ore something like that on a mainboard...maybe it's some kind of hard gold but even this is no reason for the deplating in 24 hours.
remind: the platings from newer ide connectors and connextors out of the PS3 are gone within 1/2 hr.

at the weekend i hope to find time for a little test and yes: i will only use a little beaker with something arround 1l of sollution and not much pins, different types of different kind of devices but not much.

sadly it's so cold at the moment that the leach should freeze outside without heating.

best regards!

 

[frank-20011]

hello eberyone,

it's cold and snowy furthermore and so i decide to try it inside, not with sunlight but instead with light from an lightbulb with an uv-amount.

these lamps are made for reptile husbandry.

but with the changed circumstances: pH 10 with NaOH (instead Na2CO3), 1gr of K4[Fe(CN)6]/per litre of water, temperature 40°C, leaching time 4hrs, mixing of the sollution by bubbling air from an aquarium-aerator-pump it's the same as before: no real visible leaching and strange, cellulose-looking-precipitate in a clear sollution.
these strange paper-looking-fibres are clagged to parts bigger than 1mm in diameter.
in the one liter of these test sollution there are something arround 1 teaspoonfull of these strange white stuff after 4hrs of "leaching" time.

one mistake is the use of tap water but IF this is responsible for the precipitate it isn't clearly responsible for the "leaching" result. so i think.

have anybody tried ferro-leaching in the last time too?

best regards, frank!

 

[anachronism]

Hi Frank

Just for clarity could you alter your thread title to Ferrocyanide from Ferricyanide please? There's a marked difference between the two.

 

[frank-20011]

hello,

i do not know if it is possible to the moderater to change a threads title but to me it isn't!

for clarity you are right but for the chemistry, in this case!, it makes no big difference between ferro and ferri you can use both only ferri need a higher level of uv-radiation as ferro.

at least: sorry for my mistake, i don't know how often i will repeate these mistake again and again-ridiculous!

best regards!

 

[patnor1011]

They are tiny and too close together. There is no sufficient leach circulation in between them. That is my opinion.
Also Ph looks to be low and 1g in a liter looks to be too low concentration.

 

[g_axelsson]

Edited Ferricyanide -> Ferrocyanide in the subject of the first post.

Göran

 

[frank-20011]

Hello,

and thanks for the rectification!

Deno gave "levels of potassium ferrocyanide start at 0.1 grams per litre up to 5 grams per litre."
so i thought 1gm should be fine!

O.k., next time i will use a higher concentration AND not tap water, i hope this will prevent the flocculate.

1 put 1l of the sollutin in a wide 3000ml beaker...at the bottom of these beaker there are only, wait, i will count them: ~40 little pieces out of connectors, a little piece from cuttet fingers so there is realy, realy enough space between the parts for the clearly visible drift to purge everyone of them.

After yesterday and the hours under the lightbulb today i've placed the beacker outdoors, i know: that is much to cold.

some of the thinner plated parts (connector parts from the PS3) looking now more silverish than golden but older parts or such with a thicker plating like fingers from old rams looking still unattackted!

best regards!

 

[frank-20011]

hello,

i've tried it again, with a higher concentration of ferro but at ~10°C, a whole daylight leaching time outdoors and better control of pH no visible deplating, even on very! thin plated parts....

best regards!

 

[anachronism]

Dear Frank

Please post us a picture of the chemical label on your "ferrocyanide" container. Something isn't right here.

Jon