Hydrometallurgy: Leaching in Heap, Vat, CIL, CIP, Merrill–Crowe, SX Solvent Extraction

Hydrometallurgy: Leaching in Heap, Vat, CIL, CIP, Merrill–Crowe, SX Solvent Extraction 2017-03-23T09:50:58+00:00
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Chlorination Leaching of Refractory Ores (31 replies and 1 comment)

Sugar Watkins
1 year ago
Sugar Watkins 1 year ago

I am currently in a pilot phase here in Costa Rica to determine the viability of using mechanical means (centrifugal concentration) for primary recovery from whole ores and lixiviation as the secondary / final recovery, but a cyanide alternative. I have read about extraction of Au by Chlorination Leaching of whole ores as was done in the late 1800s (Plattner) as well as some modern proprietary versions (Mintek - CETEM).

Alan Carter
1 year ago
Alan Carter 1 year ago

What about this non-Chlorination process http://is.gd/0jDQ2W

It ´d been such lack of info about, in Chile it didn't work due the hidden interests but in minor scale like the one that I´d been experimenting I got good results nevertheless it requires some heat to get the lixiviation working adding expenses at a big scale. A patent search will reveal that there have been many processes utilising chloride based oxidation processes for refractory, metallic and oxidised gold ores.

David
11 months ago
Sugar Watkins
1 year ago
Sugar Watkins 1 year ago

I had that doc filed away, had breezed over it awhile back but just now read it again thanks to your reminder. Intec developed their own chloride version and patented a mixed Halide (hybrid) lixiviant that operates at +80 degrees C. Their public documentation is interesting and gives some useful clues without revealing the proprietary portion.

I am attempting to design a chlorine leach (sodium hypochlorite) as a starting point. Sort of simple baseline to allow me to make some initial observations about the reaction and over time develops the leach further (thinking about going into a paint store and tailoring a compatible white base paint to your needs). I am attempting to design the "base paint" - lixiviant. Our budget won't allow licensing from proprietary sources as we are a small operator. Initially I'll be testing the leach at ambient temperature and pressure in a sealed vessel similar to the Plattner process. I do not have a background in the chemistry but will seek technical advice as I go along. I have some parameters learned from the public domain and some consultation from a chemistry source. There are still a few missing pieces to the puzzle. As you can see I am new to this field (lixiviation) so please excuse my ignorance. My background is mostly recovery from placer ores, this new project is strictly hard rock.

Part of the objective is to identify ore types that lend to a simple process as I evaluate the viability of toll processing ores from local artisanal sources. Also the viability of recovering values from the mercury contaminated waste (tailings) from artisanal sources (I have proven out +90% recoveries of Hg using mechanical means). So as you can deduce the feed stock will vary greatly. A "one size fits all" lixiviant is logically not realistic but I do believe there is a niche here somewhere to be discovered. This will all take place in a framework of greener alternatives to traditional processes. I have spent the last year testing a variety of ores and how they behave using mechanical concentration means (centrifugal and gravity) and sizing the milling for optimum recovery of the sulfides (this is ongoing); and then testing an acidic leach. This next phase will be to develop a floatation method for primary recovery and test an alkaline leach (halide). The benefit to the halides is the ability to oxidize gold bearing sulfides and put the Au into solution by keeping the ORP and pH within certain parameters - and then the key being to overcome the factors that spoil the reaction.

Missing pieces, keeping in mind ambient temperature and pressure:
Why copper and silver can be an issue and can somehow spoil the reaction, slow it down or inhibit dissolution of Au - the question is how to overcome these issues.

Preference of method and vessel - either in situ production of chlorine species (oxidants) in a zero pressure vessel (with a scrubber) or a premix formula in a sealed vessel under low pressure (similar to Plattner)!

Sturmbann
1 year ago
Sturmbann 1 year ago

Intec is the process since in addition to the chlorination leaching use a bromide highly oxidation agent either for oxides and sulphides.
http://is.gd/jGjRUB

I use to go to the basics when am stuck up on some issue.

Bill Rico
1 year ago
Bill Rico 1 year ago

Intec International Projects is the owner of the Intec Gold Process (and other Intec Process technologies, including rare earth extraction and recovery), and DCS Technical in Australia is the key provider of technology services.

Over the last two years, we have made considerable advances and clever innovations in the Intec Gold Process, particularly for the processing of arsenopyrite, but more generally for a wide range of gold-bearing concentrates.

Unterstarm
1 year ago
Unterstarm 1 year ago

There is no one universal method for processing sulfide ores because they can contain a variety of different metals in all different ratios of one to another. Additionally, once you crush the ore down and concentrate it you have a high sulfide concentrate unless you are processing sulfide free ore. Something that may help someone out it has worked really well for me but still takes a lot of time. I’ve experimented with aqua regia and found it is really useful in processing it but is not needed in most cases. Well here it goes if you have a low sulphide content gold mineral break it does and separate it all till all you see is the yellow shiny stuff then by weight mix a about a 50/50 ratio of it with pure malleable silver. Put your silver and low sulphide content in the bottom of a clay crucible and cover it with about 3 times weight of borax then let it go in your kiln till it hits 2000 degrees and give it some time to react. Pour your mix into a cone mold let it cool then break off the borax on top of your prill. Now you should have a prill that is a brittle gray on upper portion and a little gold/silver button at bottom. Break off the little button from the bottom if you reached high enough temperature it should separate if not it will be stuck with the gray stuff. Take your gray section of the prill and crunch it up and put it into a clean silica graphite crucible with no flux heat that up to about 2000 degrees and let it sit at 2000 degrees for a bit. Give it a little swish as your pulling it out of kiln then pour into a pre-heated mold. Let it cool and clean the carbon scale off the outside now you should have treatable gold/silver mix. If you have high gold content sulphide ore you should see a nice gold looking bar if not it may have been mostly silver. If you’re processing a high sulphide content gold ore this will not work. With high sulphide gold ore break it down and separate it till all you see is the yellow shiny stuff then take that and put it into a hydrochloric acid solution and let it sit for a week or so swirling it in bottom of container occasionally. Pour off your acid and save in another container so you can use it later just add a little new hydrochloric to perk it up again, clean your gold sulphide on bottom with water and use same process above. If your acid turned a nice yellow you can extract the gold out of it with small amounts of zinc just add small amounts until your acid turns clear this part is fun as it seems like magic watching it. Do not overdue the zinc though just a little bit at a time until it slowly removes the yellow out of acid. Well if you did all this stuff right you should be very happy with the results and you do not ever need to roast sulphide as long as you break it down into small enough particles.

Paul Morrow
1 year ago
Paul Morrow 1 year ago

Nichromet both has a process that uses chloride and bromide to leach gold from refractory ores high in sulphides.
I also suggest you look at papers by Dr. Corby Anderson that use alkaline sulfide leaching to extract gold from refractory ores. The latter can be run at modest temperatures and lower pressures than smelting.

Bill Fraser
1 year ago
Bill Fraser 1 year ago

Does this book by Kuster describe the chloride leaching of gold ores that was used in California late 1800's before cyanide came along? For those interested in halide lixiviation of gold ores, I found the book by Prof. Thomas Kirke Rose of the Royal School of Mines: The metallurgy of Gold" very informative. Six editions were published between 1890 and 1910. It not only describes chlorination, but also informs on the action of bromine and iodine.

Alan Carter
1 year ago
Alan Carter 1 year ago

Yes and there is a very short description about the chlorination through chlorine generation from manganese!

Sturmbann
1 year ago
Sturmbann 1 year ago

I read the paper about Outotec chlorination, is very important to link the leaching with the SX and Outotec is linking this, Intec has not the integrate solution. Also there are other possibilities for the Chlorination on other minerals.

Paul Morrow
1 year ago
Paul Morrow 1 year ago

My understanding from reading Anderson's papers is that the gold does not leach with the arsenic. The gold can be separated from arsenic and other elements that are leached from the sulfides.

Alan Carter
1 year ago
Alan Carter 1 year ago

By reading the book mentioned earlier, in the first pages there is stated that a solution containing sodium nitrate, sodium bisulphite and sodium chloride can dissolve gold anyone have some experience about it? There is not much literature about!

Bill Rico
1 year ago
Bill Rico 1 year ago

Linking chloride leaching to solvent extraction can be problematic at times. The principles are simple enough in the laboratory, but the industrial practice can be complex, with the potential for crud formation and other problems. The trouble implementing the Skorpion Process for zinc is a good example of this, and it took them several years of plant operation to reduce the issues.

Using the Intec Process, we have developed some clever ways of avoiding the need for solvent extraction, and for integrating with existing technologies to keep the new technology component of a project limited and to keep the costs down. Unfortunately, these are proprietary so I can't discuss them here.

We have also treated arsenical gold feedstock over 6% arsenic, and there is no practical limit that I am aware of to what the Intec Process could handle.

Oberstorm
1 year ago
Oberstorm 1 year ago

Leaching of gold in chlorine media was industrially practiced before cyanide was used for this purpose. As such the chemistry is actually well documented:

Gold leaching
Oxidation reaction:
Au + 4Cl- = Au(Cl)4- + 3e

Reduction reaction:
1.5Cl2 + 3e = 3Cl-

Other metals
All metals will leach in this environment.

The Eh-pH diagram for the gold chloride system is also well known. You can find a copy here: http://is.gd/yuv6os
More information is available here: http://is.gd/SiIIUu

A note of warning: toxic chlorine gas can be emitted from the process even if chlorine is not used directly. This is dependent on solution pH and concentration. Additionally; material of construction must be carefully selected as chloride ions can be extremely corrosive even for stainless steel.

A lot of data is available in old and archived chemistry texts as this process was used more than 100 years ago. This process has come under investigation again in the last 15 years as it is seen as an alternative to cyanide leaching for certain gold concentrates.

Sugar Watkins
1 year ago
Sugar Watkins 1 year ago

Yes, I am finding that there is a fair amount of known chemistry concerning leaching of gold in a chlorine media slowly putting the pieces together. Here are a couple of recent studies (2012 - 2014) done at the University of Tehran on reactions with sulphide ores:

http://is.gd/TvmXHM
http://is.gd/F8ee5p

Oberstorm
1 year ago
Oberstorm 1 year ago

Thank you for the two recent articles. I am glad to hear that you are putting the puzzle together bit by bit. I reviewed my sources. There are two distinct schools of thought here:
The refractory concentrate and then leach the liberated gold by normal cyanidation processes.

And leach the gold out of the concentrate in one step. Some work was done on electrolytic production of NaOCl in the pulp. Scheiner and his colleagues were some of the pioneers you may find some good data here

http://is.gd/Zsvim0
http://is.gd/LK6dmm

It is also worth noting that hypochlorite leaching was also evaluated for Molybdenite. It may be worthwhile to see if they published any useful information.

Some good extractive metallurgy history can be found here:
http://is.gd/WrFnYb

Did you try the chemistry on some of your concentrate yet?

Ace Levy
1 year ago
Ace Levy 1 year ago

Does someone know in detail the effect of particle size on the chlorination processes? I am currently testing towards an ore P80 = 140 um with calcium hypochlorite and sodium chloride; however the leaching results are not encouraging.

Alan Carter
1 year ago
Alan Carter 1 year ago

Did you check pH? Critical issue according to this humble p.o.v. and working like a real volcano in the solution by adding sodium bisulphate to reach pH 7.5 Why not to add SO4H2 to your NaCl solution?

Ace Levy
1 year ago
Ace Levy 1 year ago

Yes, we are following the pH, and the results show a final pH between 5 and 7. I think my problem is that the free gold is not available to form a stable complex due to a low Eh achieved, this is around 500 mV, and maybe the reason is the high size of the particles.

Honestly we have not added H2SO4 due to the formation of the same during the stage of oxidation of the sulfide matrix; in fact, there is a marked drop in pH during the process, even down to pH 3. Please tell me what would be your idea of adding acid in the starting?

Sturmbann
1 year ago
Sturmbann 1 year ago

H2SO4 + NaCl = HCl, so HCL is form and this reacts with gold. (Better with Br-speed the chemical reaction

Alan Carter
1 year ago
Alan Carter 1 year ago

Once you've chloridric in solution! How is gaseous chlorine kept in solution rather than been released due the acid ph? The other thing, is it feasible to set polished iron metal in solution to recover copper and then re-dissolve it in chloridric to recover the less reactive precious metals?

Ace Levy
1 year ago
Ace Levy 1 year ago

In fact we add NaCl in order to form HOCl and Cl- which will go to react with the sulphur matrix in a first stage, therefore will react with Au producing AuCl4- on a second one. I'm not sure if this last part is happening. Anyway, do you propose make a wash with HCl?

Sugar Watkins
1 year ago
Sugar Watkins 1 year ago

From what I have researched the operational pH should be around neutral, between 6-7. At this pH level there is still a high production of hypochlorous acid, the primary oxidant. Adding acid is beneficial only if necessary to adjust the pH, maybe small amounts of HCL or even a light acid like acetic acid - on the other hand, the starting pH is lowered during the reaction caused by the natural production of HCL and hypochlorous acid. Adding strong acids to the liquor are of no benefit and are a misconception that the leaching environment needs to be very acidic. It does not as is typical of the Halide leaches. Also, at neutral pH chlorine gas will not be produced. It is critical that the ORP be around 1000mv. The key to maintain a highly oxidative environment is having a sufficient quantity of hypochlorite. Sodium hypochlorite liquor is preferred over calcium hypochlorite - additional hypochlorite could be produced during a batch leach by adding NaCl to the liquor, or maybe in situ production like a salt cell or electrolyser (?). That being said, I have not tested these theories but are based on recent works by others as well as the 100 year old Plattner process. I read an interesting conversation online recently that coincidently goes along with these same theories, a man from Canada who is in the water treatment business (chlorination) who was working out the chemistry for a chlorine leach for his black sands. I have no qualified opinion about his theories although he makes some interesting comments - posted on a forum for small scale miners.

Alan Carter
1 year ago
Alan Carter 1 year ago

That`s the way to keep chloro in doing the oxidation work in solution rather than release it to the environment by adding chloridric. I am full of this copper in solution as well a yellow almost orange precipitate. Got it attached to iron line set in the pregnant solution in spring shape and it turn into copper right away and from that the orange-yellowish precipitate. Pregnant solution turn red by adding ammonium hydroxide and from the copper got what it look like silver by treating it with chloridric along with some gold flakes.

Paul Morrow
1 year ago
Paul Morrow 1 year ago

I read the two papers by the Tehran scientists and I am intrigued. If I understand it correctly, sodium chloride and calcium hypochlorite were each added to the leaching solutions at about 200 dm3. Initial pH was best at 11 and declined. The optimum pH to maintain HOCL in solution is 3.5-7.5. You stated the pH should be around neutral 6-7. My reading of the paper indicated that the pH levelled off around pH-5 with the optimal conditions.

This appears to be a new procedure (although I have not read most of the literature). It does appear to have advantages such as no use of strong acids like HCL or H2SO4. Consequently, there is less danger to the chemists or small-scale miners. It appears to give a higher recovery (82%) of gold than some of the earlier papers dealing with refractory gold ores. It looks very good for a refractory ore. Also, it runs at ambient temperature (25oC) rather than higher temperatures usually used with refractory ores (i.e., pressure oxidation, roasting).

However, a close examination of the table that shows the changes in elemental compositions in the concentrate indicates that other elements are also leached into solution. This is also the case with the IGoli process developed by Mintek. They have a paper that shows how to precipitate most of the heavy metals from solution. Hence, it should be possible to remove them from the leaching solution to form a safe precipitate.

Not explained in the paper is how to selectively remove the gold from the leaching solution. The IGoli paper indicted that this can be done using met-bisulfite. Another paper indicates that carbon can be used to extract gold from the hypochorite solutions.

Have you tried any of these procedures?

Sugar Watkins
1 year ago
Sugar Watkins 1 year ago

You have iron, copper, gold and silver all in solution? You are doing a refining process? If you are refining, try asking the boys over at the Gold Refining Forum!

Alan Carter
1 year ago
Alan Carter 1 year ago

I found out that all its related to PGM`s also I found through internet a document from Cape Town University related to the study for PGM´s based in the different oxidants and found that there is a process almost similar to chlorination but instead to have sodium chloride it is mixed with aluminum chloride + chloridric acid + sodium chlorate, in the ore that am working on, it is based mostly in bromargyrite in the oxidation zone, one of the PGM that I`d been treating it`s palladium and rhodium, however I tried this path this afternoon and got white precipitation from SMB and kind of yellow precipitation with ammonia chloride, yellowish orange by adding ammonia hydroxide and am waiting to see what is going to be with chloridric and sodium nitrite tomorrow, I use to treat the bromargyrite with ammonia thiosulfate and then to precipitate the values from solution by setting a copper plate inside the solution, it gives a black flakes precipitate, the ones that finally I melt with sodium carbonate to obtain a very brittle black powder. I got the web page in my laptop so I`ll direct it to you as soon as I reach it

http://is.gd/MHycsH

Dizzy Flores
1 year ago
Dizzy Flores 1 year ago

I wish you well: almost 20 years ago I assisted at a cyanide gold plant in Guanacaste that was just a couple of miles downstream from a site where coligalleros were still operating a mercury operation.

Environmental regulations were harsh then so have probably only become stricter. My only advice is to ensure 100% that no chemicals leave the site: chlorides can be a bad as cyanide on local fish. 

Obergruppenfuhrer
1 year ago

This is a very interesting discussion and certainly an area where value can be created if the correct process can be defined for leaching refractory ores or concentrates. My comments are as follows:-

Chlorination leaching of floatation concentrate could be a route for treatment of refractory ores instead of roasting, BIOB or POX - some companies are also testing fine grinding and oxygen injection using shear reactors in alkaline cyanide systems. Direct leaching of ores becomes very expensive using chlorine systems.

I have tested leaching of gold in worked out mining areas using thiourea in an acid environment - results, leaching and absorption onto carbon was remarkable. The problem however was the environmental issues associated with thiourea. There is a lot of literature on this. Will follow your valuable comments and discussions!

Paul Morrow
1 year ago
Paul Morrow 1 year ago

There are two new papers (and a third in press) that used glycine and hydrogen peroxide to first leach copper and sulphur, then to leach the gold (third paper in press). The second paper used glycine and hydrogen peroxide to support heap leaching. The papers look promising.

This process can apply to carbonaceous Gold ores with high quantity of pyrite?

Gruppen
1 year ago
Gruppen 1 year ago

Bear in mind that the Intec Process, though extensively studies and trialled has never found commercial success.

Chlorination was applied widely during the second half of the nineteenth century in the Australian and North American goldfields but rapidly fell away after the advent of cyanidation. Later it was applied to high value products like Merrill Crowe slimes to recover a very pure gold.

David
11 months ago
David 11 months ago

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