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Silver will only stay in solution in any quantity in a concentrated leach solution. Once it is diluted the silver chloride will drop.
Open leaches will dissolve fine PGM's in ore.
I've used both open leaches and pressurised leach systems for this using HCl/ Hypochlorite
 
Thanks a lot.
So in a high silver situation, Cyanide based or SSN will be favourable?

The ThioCyanate Deano was telling about seem really interesting, but there was no information on how much silver it can hold.
Maybe do some tests 🤓😏

Bye the way good to see result from your bacterias, treat them well.
Always interesting to hear from you.
 
I have no experience with SSN, cyanide or thiourea leaches. Dean is the one to talk to there.
My thoughts are that SSN will produce Silver Chloride too. Much of what I do contains high quantities of Silver as Tellurides, Sulfides or Silver Halides.
Using an agitated or rotating leach system stops the Silver Halides passivating the other metals in the ore during leaching.
The ore residue can be treated with NaOH and the Silver recovered by smelting or leaching afterwards.

Cheers Wal
 
FrugalRefiner said:
Jon, this thread has already been cleaned up and archived in the Library. From time to time, as new posts add to the content, and time allows, one of the moderators will undertake to copy the thread to an area where we can work on it, move the new, deserving posts to the Library copy of the thread, then clean up the detritus of the process.

This is an open forum. Every member is free to post wherever they choose. We do ask that they try to choose an appropriate section of the forum when creating a new thread. We also ask that if they study the forum and if they have questions about a thread, they post their questions in that thread rather than starting a new one which simply adds to the fragmentation of information.

When we add a thread to the Library, we provide a link to the original thread and Encourage members to add to the original thread.

This is not the first time you have felt the need to question the way I, or other moderators, post or moderate this forum. If you have a problem with the way I post or carry out my responsibilities as a moderator, I suggest you contact the board administrator, Noxx, and voice your complaints to him.

Dave
Click to expand...
I've been looking for the library in here a couple of times, but so far it has eluded me. I'm not able to comfortably navigate the new forum yet. It is more action/sosial media centric than the old forum that had information as its focal point.
If anyone knows how to find it directly I'd be grateful.
 
fishaholic5 said:
I have no experience with SSN, cyanide or thiourea leaches. Dean is the one to talk to there.
My thoughts are that SSN will produce Silver Chloride too. Much of what I do contains high quantities of Silver as Tellurides, Sulfides or Silver Halides.
Using an agitated or rotating leach system stops the Silver Halides passivating the other metals in the ore during leaching.
The ore residue can be treated with NaOH and the Silver recovered by smelting or leaching afterwards.

Cheers Wal
Click to expand...
Thanks Wal.
I was pondering your reply and revisited.
So you tank leach the ore with mechanical agitation?
And smelt after leaching. From that I assume your tanks are not that massive, 200-1000 liter, smelting 20-50 kgs at a time?

Have you tried agitation by compressor and air?
Am I getting something wrong here?

Edit.
Just saw smelting or leaching, so the NaOH to convert AgCl to Silver oxide so it can be leached or smelted directly?
 
Yggdrasil said:
Thanks Wal.
I was pondering your reply and revisited.
So you tank leach the ore with mechanical agitation?
And smelt after leaching. From that I assume your tanks are not that massive, 200-1000 liter, smelting 20-50 kgs at a time?

Have you tried agitation by compressor and air?
Am I getting something wrong here?

Edit.
Just saw smelting or leaching, so the NaOH to convert AgCl to Silver oxide so it can be leached or smelted directly?
Click to expand...

Yes, tank leaching with mechanical agitation, to stop the Silver Halide from passivating the other metals it must be continually abraded off them. Angled rotating systems work best and I often use marbles in the mix to help.
The scale can be from bottles ( I use 1.5 litre PET milk bottles for sample runs of 200g) buckets or cement mixers ( coat with epoxy or modify to take a 120 or 200 litre poly drum)
For a larger scale the same thing can be done with a cement truck.

Using air for agitation is not as effective.

Most of my leaching is relatively small scale, using 20L buckets and approx. 5L of ore per bucket.
This is mostly for ease of manual handling and because the focus of my work is now on the use of microorganisms rather than making money.
My vessels for cementation, precipitation or bacterial recovery from the leach solutions are 20-1000 Litre.

Yes, the Sodium Hydroxide is to convert the Silver Halide to Silver Oxide so that the ore residue can be leached or smelted directly.
I've used this system on ores that contained over 10% Silver by weight.

Cheers Wal
 
Just a question, how low initial gold concentration does these leaches take?

Cyanide species can leach from as an example only, say 500ppm to 0.01 ppm
ThioCyanate and saline from ?? to ??
Saline Hypochlorite from ?? to ??
Of course there are a plethora of factors involved, but there may be a general rule/hunch.
Anyone with a tip here?
 
Deano.
Thanks for a beautiful thread.

We have been trying the Hypochlorite leach, since we have no experience with it,
we don't know if there will be color change or anything like that when the leach pick up gold.
I don't even know a small thing like if it will evolve bubbles during leach.

We do suspect it has leached some, but the results are inconclusive.
Will stannous work, how about SMB, will that drop what is in the test leach?

Will Carbon or Resin be best for production leach?
We struggle and wonder if the salt may be the issue, we tried a electrolytic cell, but I guess the gold concentration may be too low.

Regards Per-Ove
 
Hypochlorite leaches have a leach rate between cyanide and aqua regia, it is unlikely that you will see bubbling from gold but if you have a lot of base metals in the ore you may get some bubbling from these as they dissolve.
All leaches will dissolve all of the available gold in an ore, they will not dissolve occluded gold in quartz etc as they cannot access it.
Hypochlorite leaches will dissolve sulfides and make gold occluded in these sulfides available for leaching, the leaching rate of these sulfides is slow as the particle size is usually larger than the gold particles in them.
If you have a lot of sulfides in the ore there is a good chance that you will run out of hypochlorite before you have leached all of the gold.
Use a handheld ORP meter to check when you need to add more hypochlorite on the first few runs then add hypochlorite on a time basis for later runs, checking before additions are made.
The hypochlorite additions will raise the solution pH, use a handheld pH meter to check pH and adjust with HCl as necessary.
The chloride ions will lower the actual pH readings on your meter, if you are reading pH7 on the meter you will have a true reading between 6 and 7 depending on the chloride ion level in solution.
Usually you try for a meter reading of 7 so that you are working in the safe range of 6 to 7.
There is always some free chlorine in the leach but by working in the pH range 6 to 7 you minimise the free chlorine level to where it is not a health hazard.
Always only put the meter probes into the leach solution when you want to get a reading, after reading you rinse the probes and leave them halfway in a container of water.
Metal recovery is always done with carbon, the leach will destroy resins.
Metals will be reduced to the native form on carbon so you do not want to run the carbon as CIP, you will attrition the gold etc from the ore.
Best method of recovery is to pack the carbon in canisters and flow the leach liquor through them without disturbing the carbon.
Always keep in mind that all wetted surfaces must be made of nonmetallic materials, the leach will dissolve metallic surfaces.
The only realistic way to check for gold levels in the leach liquor is by AAS, you will have such a high level of oxidant that reduction testing by stannous or similar is not conclusive.
Recovery of the gold from the carbon is either by cyanide stripping or ashing of the carbon.
Deano
 
Having tried this leach with Deanos supervision I can tell you it works but needs almost constant monitoring and attention much more so than cyanide and even AR , you cannot set up and walk away for more than about 15 minutes in my experience.
 
Deano said:
Hypochlorite leaches have a leach rate between cyanide and aqua regia, it is unlikely that you will see bubbling from gold but if you have a lot of base metals in the ore you may get some bubbling from these as they dissolve.
All leaches will dissolve all of the available gold in an ore, they will not dissolve occluded gold in quartz etc as they cannot access it.
Hypochlorite leaches will dissolve sulfides and make gold occluded in these sulfides available for leaching, the leaching rate of these sulfides is slow as the particle size is usually larger than the gold particles in them.
If you have a lot of sulfides in the ore there is a good chance that you will run out of hypochlorite before you have leached all of the gold.
Use a handheld ORP meter to check when you need to add more hypochlorite on the first few runs then add hypochlorite on a time basis for later runs, checking before additions are made.
The hypochlorite additions will raise the solution pH, use a handheld pH meter to check pH and adjust with HCl as necessary.
The chloride ions will lower the actual pH readings on your meter, if you are reading pH7 on the meter you will have a true reading between 6 and 7 depending on the chloride ion level in solution.
Usually you try for a meter reading of 7 so that you are working in the safe range of 6 to 7.
There is always some free chlorine in the leach but by working in the pH range 6 to 7 you minimise the free chlorine level to where it is not a health hazard.
Always only put the meter probes into the leach solution when you want to get a reading, after reading you rinse the probes and leave them halfway in a container of water.
Metal recovery is always done with carbon, the leach will destroy resins.
Metals will be reduced to the native form on carbon so you do not want to run the carbon as CIP, you will attrition the gold etc from the ore.
Best method of recovery is to pack the carbon in canisters and flow the leach liquor through them without disturbing the carbon.
Always keep in mind that all wetted surfaces must be made of nonmetallic materials, the leach will dissolve metallic surfaces.
The only realistic way to check for gold levels in the leach liquor is by AAS, you will have such a high level of oxidant that reduction testing by stannous or similar is not conclusive.
Recovery of the gold from the carbon is either by cyanide stripping or ashing of the carbon.
Deano
Click to expand...
Since we are new to this and the ore is somewhat refractory/Special we are doing a lot of trials.
This is what we have notice so far:
Stannous do not work as expected as per information. It gives a precipitate in stead of colloidal color change.
There are no color change.
Stannous tests show less return after long time 7 hours seem half of two hours.
All this is per information, so we will proceed to carbon column in circuit.
Is it best to let the leach finish and then pump it throuhgh, or constant pumping?

Regards Per-Ove
 

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Gold chloride will happily adsorb onto any iron oxides which are part of the ore as well as adsorbing onto some quartz types, it will do this to a greater degree than gold cyanide will.
In order to minimise the adsorption effect it is best to run a continuous bleed stream of liquor through a carbon column in order to keep the gold tenor in the pulp to a minimum, this low tenor will minimise adsorption effects.
The bleed stream is usually monitored before and after the carbon column by AAS to ensure that there is enough active carbon in the column to keep the pulp gold tenor low.
The weight of carbon in the column is around one tenth the weight of liquor passed through the column in an hour, you use AAS to establish if, for your particular ore, you have enough carbon present in the column to remove the gold values.
You also check the liquor to see when breakthrough of gold in the column occurs, this is when you change the carbon for fresh carbon.
Deano
 
Deano said:
Gold chloride will happily adsorb onto any iron oxides which are part of the ore as well as adsorbing onto some quartz types, it will do this to a greater degree than gold cyanide will.
In order to minimise the adsorption effect it is best to run a continuous bleed stream of liquor through a carbon column in order to keep the gold tenor in the pulp to a minimum, this low tenor will minimise adsorption effects.
The bleed stream is usually monitored before and after the carbon column by AAS to ensure that there is enough active carbon in the column to keep the pulp gold tenor low.
The weight of carbon in the column is around one tenth the weight of liquor passed through the column in an hour, you use AAS to establish if, for your particular ore, you have enough carbon present in the column to remove the gold values.
You also check the liquor to see when breakthrough of gold in the column occurs, this is when you change the carbon for fresh carbon.
Deano
Click to expand...
Thanks Deano
 
If you have one ton of carbon in your container then you would start with a flow rate of 10 tons of liquor per hour through the carbon, scale this back to whatever size operation you are running.
You adjust the flow rate up or down depending on what the assay numbers tell you about the adsorption level in the column.
If you have high grade areas of gold in your ore then you will have to have a second carbon column in series with the first column, this has two functions.
The first is to recover gold from surges in the gold tenor in solution when first leaching the ore sample.
The second is to use a bypass line to run your liquor through the second column when the first is off line for stripping the carbon.
Deano
 
Thanks again Deano.

How much metals are normal to load up on AC with this leach system?
Single digit grams or double digit grams per kilo?
All are variables depending on the actual situation, I know, just as an expectation for scaling.
Regards Per-Ove
 
Last edited:
You usually would expect low to high single digits grams of gold per kilo of carbon, not only ore type dependent but carbon activity dependent.
The gold chloride is reduced to metal on the carbon so if the gold comes as an initial flush most of it will just load on the surface of the carbon and clog access to the high storage pores.
Deano
 

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