# Salt Water Electrolytic Cell



## Traveller11 (Sep 21, 2010)

Hello

I was just reading a Brazilian patent held by a company named CETEM in Brazil for an electrowinning process. CETEM seems to be dedicated to removing cyanide and mercury worldwide from small gold mining operations and is working on alternatives to mercury amalgamation. This is one of them.

Essentially, the ore/ concentrate is finely ground and roasted or otherwise oxidized to oxidize sulphides in the ore/concentrate and cut back on current requirements in the cell. It is claimed that the raw ore can be placed in the cell but will take more electricity to work through the sulphides.

Large quantities of salt are mixed with water and placed into a plastic vessel. An anode and cathode (both of which can be graphite or titanium) are placed into the saltwater and DC current is applied. Gold is deposited on the cathode and a recovery rate of + 95% is claimed in a 2-4 hour period. The only requirement beyond this is that the concentrate/ore be somehow kept stirred; possibly with a motorized paddle or a guy with a gas mask and a paddle.

From my experience in water treatment, I can see this is basically a sodium hypochlorite generator. According to the patent, hypochlorite is further oxidized to perchlorate; an oxidizer with 4x the affinity for dissolving gold as cyanide has.

Other than the production of chlorine gas while in operation, this process seems better suited to the amateur as the handling of acids is not required.

Bob


----------



## lazersteve (Sep 21, 2010)

Here's an old thread along the same lines:

Salt Cell

Steve


----------



## Traveller11 (Sep 21, 2010)

Steve

That was very interesting reading. I was especially impressed with the use of the fused silica cup to contain the anode. Would this cup stop silver chloride from passing through it? I ask this because I klnow that the placer gold I am attempting to recover is about 90% gold with the rest mostly silver.

Bob


----------



## Wyndham (Sep 23, 2010)

I have been rereading the post on the salt cell and have a question on the titanium wire.Is it dissolved as the other wires are in the anode bath? There is a company called reactive metals out of AZ that has titanium wire as well as niobium wire. They sell this for jewelry but would be great for our uses. One other thing about the flower pot, I make pottery and it seem that what the anode cup is no more than a cup partially fired to about 1800 deg f any higher than that it starts to becomes fully fused and non porous.
Does the pore size other than too big have any effect on the reaction?
Ok on to the last part, if fine to micro fine placer gold in concentrate material were placed in a clay bowl wit a titanium plate on the bottom attached to the anode PS, would that surface area of the plate induce the current into the concentrate to possibly dissolve the gold into the solution? 
I'm thinking about the beach gold that is so fine it's hard to recover with traditional means.
Wyndham


----------



## Traveller11 (Sep 23, 2010)

Wyndham
From what I can gather, the actual thing putting gold into solution is the compound perchlorate; a molecule made up of one chlorine atom shielded by four oxygen atoms. Reputedly, it has an affinity for dissolving gold 4x greater than cyanide. This unit is, essentially, a sodium hypochlorite (clorox) generator. The hypochlorite ion is further oxidized to perchlorate.
One design on this procedure I looked at had the placer material in a separate vessel with the electrolysis unit in another. The perchlorate laden electrolyte was pumped from the electrolysis chamber through the placer material and returned to the chamber where the gold it put into solution was deposited on the cathode. In other words, neither cathode or anode actually are in contact with the placer material or, for that matter, anywhere near them.
I wonder why the anode is placed in the clay/ fused silica pot; especially in the case of placer material. If the cathode was in the pot, the pot/fused silica cup would act as a filter and only allow gold laden electrolyte to reach the cathode. This, from all accounts, is the one great difficulty of this process; collecting the gold from the cathode. I should think it very handy to have a fused silca cup with only gold in it all ready to be fired.
Regards
Bob


----------



## Traveller11 (Sep 23, 2010)

Wyndham
I forgot to mention that the unit with the electrolysis chamber separate from the leaching vessel did not have the required stirring mechanism for the placer material mentioned in the original patent. 
It was felt that, between the design of the placer material chamber and the flow of electrolyte introduced at the bottom of said chamber, enough mixing would occur to allow the electrolyte contact with all of the placer material. 
Regards
Bob


----------



## Traveller11 (Sep 23, 2010)

Wyndham
Re: fine beach gold. What a coincidence, this is what I am working on, too. Let's keep in touch as we may be able to help each other.
Regards
Bob


----------



## T3sl4 (Sep 23, 2010)

Two glaring problems with this:

1. Perchlorate has no affinity for anything. It's completely inert in the body, aside from one notable exception: the body thinks it looks like iodide, so it fits into the machinery, but the machinery can't stick anything to it, unlike iodide. The result is hypothyroidism, because perchlorate displaces iodide in the machinery. The cure is the same as for radioactive iodine poisoning: take an iodide pill to force real iodide into the system good as new. Perchlorate is so unreactive, almost the only thing you can do (aside from concentrating it to >70% pure acid) is heat it to >400C where it finally decomposes.

2. Perchlorate is rather difficult to produce. To give you some idea, consider that a perchlorate cell smells weakly of ozone. There is some serious electrochemistry going on in that cell! It can only be produced with certain anodes: platinum and lead dioxide are the most important. Other metals, semimetals (like graphite) and compounds (like MMO) are unable to oxidize chlorate to perchlorate, either due to breakdown (graphite) or the potentials don't work out (i.e., oxygen gas is produced instead).

It seems to me, to heap ore into a salt cell, the intent is to dissolve gold, as the chloro complex, using hypochlorite or, better yet, if the pH is kept low, free chlorine. So you get an intermediate a lot like HCl/bleach makes. Then this is plated on the cathode, because...it's the cathode.

The downside to a salt cell is, chlorine evaporates rapidly at low pH, so you have to keep adding acid if you want to keep it on the chlorine side. With no additions, the pH gradually drifts up to the 9-10 range, which is quite basic, and I'm guessing gold isn't soluble there (aside from cyanide), even with the mess of hypochlorite present.

The overall result of salt electrolysis, assuming a suitably inert anode, is chlorate, then once all chloride is used up, perchlorate. Chlorate represents a loss, because it's not very reactive, so you'll need a very low pH (1-2) to keep it active as well (at low pH, chloric acid disproportionates to chlorine, which would be, HClO3 + 5 HCl = 3 H2O + 3 Cl2).

There is one thing. If you use a divided cell, you can keep the base around the cathode only (since the cathode is churning out hydrogen gas and hydroxide), which lets the anode bubble out pure chlorine gas. No need for extra acid. You need some way to carry gold ions to the cathode (otherwise, I suppose the barrier clogs with Au oxide?), which implies cyanide. Which is bad, and which eventually leaves the cathode cell (cyanide = anion = attracted to anode), meaning it becomes a consumable. No good.

Running such a cell sounds like a very irritating and corrosive prospect. You will absolutely need a fume hood and a few pounds of graphite.

Tim


----------



## Traveller11 (Sep 23, 2010)

Tim
Well, I was afraid it seemed to good to be true. However, the inventors of this process seem to think it a superior system. This may be only hype and wishful thinking, of course.
Rather than attempt to discuss things I don't fully comprehend, I will c/p the patent below for your perusal. It is registered with the Brazilian Patent Office under PI 0205482.
If the moderators of this forum prohibit c/p'ing from other sites, please delete this post and notify me that I may supply the link.

Here it is:

Electrolytic process for the opening of refractory gold concentrates and simultaneous return of the gold contained 
"Electrolytic process for the opening of refractory gold concentrates and simultaneous return of the gold contained." This application for a patent (pi), an electrolytic process for the treatment of gravitational concentrate containing sulfides and / or synthetic mineral species, called refractory, and elemental gold encapsulated in the matrices of sulfides, which occurs in the first instance , the opening and dissolution of the sulfides contained (pyrite, chalcopyrite, pyrrhotite and arsenopyrite), resulting in the formation of sulfate ions and then with the course of electrolysis, the dissolution of gold and its alloys with simultaneous electrowinning of these elements in surface of graphite or titanium cathodes. The reaction system (Figure 1) consists of an electrolysis reactor (5), where electrodes are inserted, namely: one or more of graphite anodes and / or titanium (2), two or more cathodes of graphite or titanium (1) being provided with a mechanical stirrer (4), responsible for the suspension of concentrate solution of sodium chloride and connected to a continuous power source andlor DC pulse, or even rectified or pulsating current asymmetry ( 3), responsible for maintaining the levels and forms of power more appropriate. The dissolution of the sulfide concentrate occurs as the result of the reaction of the oxidant species generated by chlorine (heat-and hcio) from the dissolution of chlorine gas (Cl ~ 2 ~), which is generated as a result of oxidation of chloride ions (ci ^ - ^) on the surface of anodes. With electrolysis time, gold and its alloys, are dissolved by chlorate ions generated by oxidation of hypochlorite ions, produced constantly, and simultaneously by different routes. Moreover, the hydrogen (H ~ 2 ~) and the reduction of dissolved metal ions (AUCLI ~ 4 ~ -, AgCl 2 ~ 3 ~ ^ - ^, cu ^ ^ +2), resulting from oxidative processes, to their elemental states, on the surface of cathodes of graphite or titanium (2), constitute the main steps of the proposed procedures. 

The wording may seem difficult to follow as this text is a translation from the original Portugese.
Regards
Bob


----------



## T3sl4 (Sep 26, 2010)

That sounds about like I described then.

I say it'll work, but maybe not as magically as you might've hoped. If the gold sticks to the cathode, seperation will be easy enough. If it's present as foam or flakes or something, it will probably wash off in the flow and you won't get anywhere. Maybe a mesh bag around the cathode would fix that, without the possible problems a full divided cell might have.

Ohh... for ores that aren't pure (i.e., containing other metals), you'll dissolve everything, with the possible exception of silver (since AgCl is quite insoluble; PbCl2 is soluble enough to allow lead to plate across, however). So you'll get a mixture of iron, copper, nickel, whatever else goes into solution. This might actually be an advantage, since the iron and copper crud might hold the values in place mechanically. Then you do the usual purification process on metal, instead of having to leach all that ore. In fact, just blasting it with nitric acid might suffice, which is quite handy because the gold falls off, leaving your electrode clean for more.

Tim


----------



## Traveller11 (Sep 26, 2010)

Tim

Thank you for your reply. 

One of the reasons I was looking at this setup was the hope that it would be fairly selective in only bringing gold to the cathode. I can see now that it may not do that but, as you stated, a wash with nitric acid may remove all the unwanted metals; as long as there is not too much unwanted metal.

This leads me to another point in leaching or electrowinning that I do not understand. As the material I am working with is a beach placer, the majority of the base metals I will be dealing with are magnetite and hematite; both of which are oxidized forms of iron. There is also a small amount of pyrites; a sulphide of iron. I cannot determine, from following threads on this site, whether or not oxidized forms of iron (or sulphides) will be dissolved in leaching or electrowinning processes. If they do not dissolve, I am on my way to success. Can you help me with this?

As to recovering the gold from the cathode, earlier in this thread Lazersteve posted a link to another thread on this site titled "Salt Cell". A New Zealand fellow was using a salt electrolyte in his cell to dissolve and recover plated jewellery. He had a bowl with a fused silica cup in the centre of it; both the bowl and cup containing salt water. The cathode was placed in the large bowl and the anode, an alligator clip, was attached to the jewellery and placed inside the fused silica cup. He seemed to have great success with this, even claiming that he smelled no chlorine (?) from this process.

What I was wondering is, if the fused silica cup will let gold in solution go through it, would it be possible to place the cathode in the fused silica cup instead of the anode? This way, when the process is completed, I would have placer material in the big bowl and gold in the fused silica cup. What do you think?
Regards

Bob


----------



## lazersteve (Sep 26, 2010)

Here's another thread with my anode from a test run of the salt cell a few years back:

Karat Gold Salt Cell

The cell worked, but eventually stalled out. I was using a fused silica crucible as my membrane. 

Steve


----------



## Traveller11 (Sep 26, 2010)

Steve, 

While I have your attention, can you tell me if oxidized forms of iron (ie. magnetite, hematite and iron pyrites oxidized by roasting) will be dissolved in either the acid/clorox process or this salt water cell?

Bob


----------



## lazersteve (Sep 26, 2010)

Bob,

I don't see any reason why they should not, but they would also interfere with the dissolution of the gold if they are present in any quantity. For this reason, as much as possible they should be removed before going after the gold. I have used acetic acid and also citric acid to help remove excess iron oxides when they are masking gold from dissolving. Fluxing the ore with a collector for the values may also help if you are set up for furnace operations.

Several years back a guy I know told me that a metallurgist at a large mining operation told him that large amounts of iron in ore would contributed to a phenomenon know as 'pregnant robbing'. He was using the BDG (aka: DBC/dibutyl carbitol) route of extraction at the time. 

Sorry I can't be of more help, but hopefully my comments will bring others forward with comments of their own.

Steve


----------



## Traveller11 (Sep 26, 2010)

Steve,
Sorry to keep asking you so many questions. One last one, though, and then I promise to give you a break.
To remove these iron oxides, the pyrites and any other base metals from my placer material, do you think your Hydrochloric Acid/Hydrogen Peroxide process would be successful?
Bob


----------



## lazersteve (Sep 26, 2010)

Bob,

Straight HCl should work. 

I would stay away from any wet combinations that dissolve gold along with the base metals just to keep everything in step. Acid peroxide (AP) will dissolve iron and micron gold, but will eventually become fouled and lose reactivity, leading to a big mucked up mess from the partially dissolved base metals and cemented values.

Like I said before, concentrate on selectively removing as much of the base metals first with the more 'mild' reagents, then go for the precious metals once the base metals are removed.

Steve


----------



## T3sl4 (Sep 27, 2010)

Incidentially, soaking rocks in acid generally leads to gunk, at least that was my experience. The gunk comes from the insoluble alumina, silica and clay type materials leftover, so you get a difficult-to-filter gel.

The easiest way to remove other stuff is a soak in acid. It may take a very long time to dissolve everything, as iron requires a low pH to dissolve, and it doesn't go quickly. Large grains may take a very long time indeed. The easiest way to leach, of course, is put everything in a column (or if you've got a lot to do, try an HDPE barrel with holes punched in the bottom) and let the acid soak through. Fresh acid, at the top, does the most, then it gradually gets more spent as it drains down. At the bottom, it's all used up (presumably). Add more, and the top is even cleaner, the middle is somewhat cleaner, and the bottom is starting to dissolve. Etc. Eventually, the top fraction is pretty darn clean, having been washed so many times, and the stuff on the bottom can go to the top of the next run, and so on.

Without a strong oxidizer, the gold won't dissolve during this step. So you put it in the cell next, and that should do it.

Steve: do you have any idea if the fused silica got clogged, possibly by gold as I suggested earlier? If so, it could be very difficult to clean out...

Tim


----------



## Traveller11 (Sep 27, 2010)

Tim
I've seen citric acid suggested many times on this site for dissolving iron into solution.
I checked citric acid out and it seems to come in many percentages; even a powdered form.
What percentage is recommended for pre-leach acid washing and can this be made from the powdered form?
Regards
Bob


----------



## T3sl4 (Sep 27, 2010)

Citric acid is neat stuff... it tastes lemony, and very sour! 

Idunno how much. Heap some in and see?

Tim


----------



## Barren Realms 007 (Sep 27, 2010)

I think I have about 600 lbs of the citric acid in dry form being given to me in then next few days, it is food grade. I might be willing to part with some.


----------



## T3sl4 (Sep 27, 2010)

Dayum... you could make a whole city pucker with that!

Tim


----------



## Traveller11 (May 22, 2012)

I am reviving this thread because, after careful study, I think I have finally figured out what the designer of this process had in mind.

I think, and correct me if I'm wrong, this process involves an electrolytic sodium hypochlorite generator, a leaching vat and an electrowinning unit; all rolled into one.

I recognized the sodium hypochlorite generator part because I operate a small water system here and we have been looking at purchasing a NaClO generator to cut down on our disinfection costs. This setup will not produce chlorine gas. The chlorine gas generator is similar but has a two part cell with a membrane separating the anode and the cathode side, generating Cl2 on one side and sodium hydroxide (NaOH) on the other with hydrogen vented. In the electrolytic cell described in the gold recovery process, without a membrane, chlorine gas exists only briefly at the anode and is instantly converted into sodium hypochlorite.

So, in this unit, sodium hypochlorite is generated and, I'm guessing, puts gold into solution and then, through electrowinning, deposits it at the cathode. It was further improved in design by having the salt brine and the cathode and anode in a separate container from the ore. As sodium hypochlorite was generated by electrolysis, it was pumped to the vessel containing the ore and flowed through it, from top to bottom, and returned to the electrolysis vessel where, presumably, gold leached from the ore is deposited.

The burning question in my mind is, will this process put base metals into solution, and, if it does, will they be deposited at the cathode along with the gold?

http://www.artisanalmining.org/casm/sites/artisanalmining.org/files/publication/Veiga_Replacing_Hg_in_ASM%20Operations.pdf

Pges 48 & 49


----------



## Traveller11 (May 28, 2012)

Okay, I realize now I was wrong again. Further study has cleared things up.

I assumed this setup was making sodium hypochlorite but the literature kept referring to the production of sodium chlorate. I became concerned, as our water system is seriously entertaining purchasing a sodium hypochlorite generator to make on demand bleach, from salt, for disinfecting drinking water. Sodium chlorate is not a good thing to have in drinking water and the Maximum Acceptable Concentration in drinking water, set by Health Canada, is 1.0 ppm.

It turns out that the electrolytic process for making both, from salt brine, is identical. The only difference is the temperature of the electrolyte. Below 50° Celsius, it will make sodium hypochlorite. At 50-70° Celsius, the cell will make sodium chlorate.

According to what I have read, this higher temperature is achieved by applying higher elecrical amperage to the electrodes. I had always wondered why sodium hypochlorite generators only made a concentration of .8% sodium hypochlorite bleach (or less, as opposed to household bleach at 3-6%) and it seems to be because it would take higher current to do this and it is likely the higher current would increase the cell temperature to the point of making sodium chlorate. Or, it could just be that .8% is the most economical level to make bleach at and it is no problem to just increase the dosage going into the water, rather than wasting current trying to make a higher concentration.

Anyways, it looks like the agent at work in this cell is sodium chlorate (NaClO-3), a very powerful oxidizer.


----------



## Traveller11 (May 28, 2012)

Traveller11 said:


> Okay, I realize now I was wrong again. Further study has cleared things up.
> 
> I assumed this setup was making sodium hypochlorite but the literature kept referring to the production of sodium chlorate. I became concerned, as our water system is seriously entertaining purchasing a sodium hypochlorite generator to make on demand bleach, from salt, for disinfecting drinking water. Sodium chlorate is not a good thing to have in drinking water and the Maximum Acceptable Concentration in drinking water, set by Health Canada, is 1.0 ppm.
> 
> ...


----------



## butcher (May 29, 2012)

Traveller11,
T3sl4 Tim can help you understand these cells better, he has expierience in this field.

I like the discussion here.


----------



## Traveller11 (Dec 1, 2012)

Well, I've kind of ignored the salt water electrolytic cell as my life has been very busy this last while. However, before I die of old age (LOL) I am determined to build this thing and try it out.

Looking back at the information available on it, I noticed a couple of things. The first is that they recommend using a plastic tub as the container for the cell. I think this provides us with an important clue as to the compound being generated by the cell. As I stated earlier, the electrolysis of brine will make one of two things (or both) depending on the temperature of the brine. This temperature is directly controlled by the amount of amperage applied to the electrodes.

Below 50° Celsius (122° F.), this cell will produce sodium hypochlorite. Between 50-70° Celsius (122-158° F.), it will produce sodium chlorate. However, I don't imagine the change occurs abruptly. At 40-50° C., there is likely a mix of NaClO and NaClO-3 being produced. It also seems unlikely that anyone would be running this process in a plastic tub with temperatures approaching 70° C. (158° F.). Plus, as this is designed for artisanal miners without access to large amounts of electricity and processing large amounts of ore at once, I would tend to think this cell is meant to operate at a lower temperature and produce a greater volume of sodium hypochlorite.

While they say to use a graphite rod as the cathode in this process, they do not mention what to use as the anode. From another thread on here, I learned that a stainless steel anode will break down quickly in this application. Could a graphite rod be used as the anode or would a titanium rod be better? Where would a person acquire suitable graphite rods for this purpose?

Because the cathode and anode are immersed in the ore being treated, any gold collecting at the cathode will fall right back into the ore. I've read about "cathode bags". If the cathode was contained in one of these, would it collect the precipitated gold inside it, isolating it from the ore? Would it be simpler just to suspend a plastic cup in the brine, just above the ore, and place the cathode in it?


----------



## Geo (Dec 1, 2012)

Lazersteve sells graphite electrodes on his website. you could place the cathode in a porous container like a clay flower pot.


----------



## Traveller11 (Dec 1, 2012)

Thanks Geo. Do you think the graphite would not break down if I used it as an anode?


----------



## Geo (Dec 1, 2012)

if it does, it will be very little. from what i understand about it, the electrodes are unaffected by chlorine. i followed a very old thread involving saturated salt electrolyte cell and tried a few experiments. i tried to dissolve the base metal from pins while leaving the gold plating whole. it dissolved the whole mass including the piece of stainless steel i was using as an anode. i used the graphite electrode from a 6v lantern battery and placed the pins in a porous cup placing the graphite electrode on top of the pins to try and contain the gold solution as it dissolved. i used a piece of copper as the cathode hoping to selectively remove copper. again, the pins dissolved but the cup did not hold the gold as there was gold throughout the electrolyte and the cathode eroded badly. the only bright spot was the graphite electrode did not show any wear.


----------



## Traveller11 (Dec 1, 2012)

Sounds good. I'll check out Steve's site and order some graphite rods.


----------



## Traveller11 (Dec 1, 2012)

I checked out Steve's online store and he doesn't seem to sell graphite rods. I did find graphite rods on Ebay, though. Think 1/2" would be thick enough?


----------



## jimdoc (Dec 1, 2012)

Here is a website that may help;
http://www.graphitestore.com/index.asp


----------



## Marcel (Dec 2, 2012)

I did try the salt cell a few months ago and wheter my setup was correct or not, it appeared to me that this cell does nothing else but:
- create Cu(II)Cl
- dissolve unlying copper layer, so that gold will fall off.

I measured the amperage from the start and it was very low when starting, so I added more salt to the solution, which increased the current (because the electrical resistance of the water was reduced by the salt). Then I got some light blueish solution which turned out to be Cu(I)Cl and Cu(II)Cl. So all this salt cell experience led me to another experiment:
Take your AP solution and add anode and cathode to it and the whole AP process will run much faster.
Solution is electrically conductive, so there is no need to interconnect each part you put in the solution.
Of course the process is different from dissolving gold, it is the good all AP process just with a turbo. In the electrochemistry it is all about energy. If you add energy - in which form ever, heat or electric energy, this energy will speed things up.
I somehow doubt that the salt cell will dissolve gold in a timely manner and very efficient. There is chlorine in there from the salt, there is copper in there from the material. All you are doing here is just an altered (very slow at the start) *AP process*. That is the truth about the salt cell to me.
Skip the the salt and start with AP+electricity right from the start and you may find a good process in there.
Salt cell is a myth to me.


----------



## Traveller11 (Dec 2, 2012)

First off, this process was not designed for recovering plated gold from copper based metals. It was designed to recover gold from ores and placer materials. It is a variation of the +100 year old "Plattner's Process" for extracting gold with chlorine. The description below, from an 1898 paper, tells you why the copper in your material made your cell unsuccessful:

"The most scientific and perfect mode of gold extraction (when the conditions are favourable) is lixiviation by means of chlorine, potassium cyanide, or other aurous solvent, for by this means as much as 98 per cent of the gold contained in suitable ores can be converted into its mineral salt, and being dissolved in water, re-deposited in metallic form for smelting; but lode stuff containing much lime would not be suitable for chlorination, or the presence of a considerable proportion of such a metal as copper, particularly in metallic form, would be fatal to success, while cyanide of potassium will also attack metals other than gold, and hence discount the effect of this solvent."

Plattner's Process involves introducing chlorine gas, under pressure, into a chamber containing ground ore and water. Once dissolved in water, chlorine becomes hypochlorous acid and hydrochloric acid. It is the hypochlorous acid that puts the gold into solution.

In the electrolytic salt cell, sodium hypochlorite is produced, along with some sodium chlorate. Adding sodium hypochlorite to water also gives us hypochlorous acid, along with sodium hydroxide. 

It is felt by some that it would be simpler to just use Clorox (sodium hypochlorite bleach) and create chlorine gas by adding hydrochloric acid to it. It is not quite as simple as that. If you have 6% Clorox bleach, it means you have 6% sodium hypochlorite in 94% water. The obvious question is: Why doesn't the 6% sodium hypochlorite combine with the 94% water to form hypochlorous acid? The reason is simple; during the manufacture of Clorox, sodium hydroxide is added to raise the ph of the bleach up over 12. If the ph of Clorox falls below 11.86 (say by dilution with water) the sodium hypochlorite decomposes rapidly. However, sodium hypochlorite produced in an electrolyic cell does not have this extra amount of sodium hydroxide added to it. 

Because it requires an acidic solution to dissolve gold in this process, a fair amount of hydrochloric acid must be added to the Clorox to not only convert it to hypochlorous acid but to also bring the ph down into an acidic range. In Plattner's Process and the saltwater electrolytic cell, if we assume a ph of 7 in the water being used, the process itself creates enough acid (hypochlorous acid from sodium hypochlorite and chloric acid from sodium chlorate) to bring the solution into the correct acidic range to dissolve gold.


----------



## Traveller11 (Dec 2, 2012)

T3sl4 said:


> Incidentially, soaking rocks in acid generally leads to gunk, at least that was my experience. The gunk comes from the insoluble alumina, silica and clay type materials leftover, so you get a difficult-to-filter gel.
> 
> The easiest way to remove other stuff is a soak in acid. It may take a very long time to dissolve everything, as iron requires a low pH to dissolve, and it doesn't go quickly. Large grains may take a very long time indeed. The easiest way to leach, of course, is put everything in a column (or if you've got a lot to do, try an HDPE barrel with holes punched in the bottom) and let the acid soak through. Fresh acid, at the top, does the most, then it gradually gets more spent as it drains down. At the bottom, it's all used up (presumably). Add more, and the top is even cleaner, the middle is somewhat cleaner, and the bottom is starting to dissolve. Etc. Eventually, the top fraction is pretty darn clean, having been washed so many times, and the stuff on the bottom can go to the top of the next run, and so on.
> 
> ...



If iron requires such a low ph to dissolve, wouldn't it be simpler to keep the ph of the chlorine solution higher and just not dissolve the iron at all?


----------



## Traveller11 (Dec 3, 2012)

A further variation on Plattner's Process, source unknown:


"Electrolytic Precipitation of Gold"








0

Share on Tumblr

Email
Share






In order to perform the electrolytic precipitation of gold, from the filtration vessel the gold chloride solution was conducted into the outer or battery jar of an electrolytic cell. The electrode of the outer cell was connected with the negative pole of a dynamo and the electrode on the inner cell was connected with positive pole or terminal of the dynamo. The gold solution was sent into the jar near the bottom and slowly circulated upwards, and at the same time a current of electricity was passes through the cell. When the reaction was produced, the gold chloride was decomposed and felt like a shower of fine spangles to the bottom, while the liberated chlorine passed into the inner cell where it was absorbed by the water circulating and formed a chlorine solution.

The receiver was charged with chlorine solution generated by the electrolysis of salt. The unit comprised a battery, a conductor from the electrode in the large battery jar to the negative pole of the electrical generator, the conductor from the electrode in the porous cell to the positive pole of the generator, a reservoir containing a saturated solution of sodium chloride, which passed to the battery through a pipe and a reservoir containing water connected by a pipe with a porous cell.

In order to treat the ore more effectually with the chlorine solution it was advantageous to expel the air from the chlorinator. For this purpose the chlorinator was provided with a valve, so that the air contained in the chlorinator passed out as the chlorine solution passed in. the valve was closed immediately the air was expelled. The chlorinator after disconnected was slowly revolved by means of a pulley and strap from an engine, or in other suitable way until the gold was dissolved as a gold chloride. The time required for treatment in the chlorinator varied from one to two hours according to the characteristics of the gold ore treated. The ore and solution were discharged into a suitable filtration vessel placed beneath the chlorinator. The vessel was a shallow vat constructed of oak or other material, the lower part was made cone-shaped and of the same capacity of the chlorinator.

The vat was closed by a cover bolted down. In the center of the cover there was hopper-shaped inlet for receiving the ore and solution from the chlorinator. A perforated diaphragm covered with asbestos cloth, over which was advantageously placed a layer of other suitable filtration media such as ground asbestos, which was fixed from one to two inches below the top of the vat. The gold chloride was washed out of the ore by a stream of water from a tank. The water entered the vat through a pipe at the lowest part and percolated upwards through the ore until the gold content in the solution was extremely low. It was important to take samples of the solution to determine the presence of gold. A sliding door in the bottom of the vat was opened and the residue from the ore as discharged by means of a large outlet opened into a truck placed underneath.

The gold chloride and water descended through a pipe into a receiver and was conducted from the receiver into the outer or battery jar of the electrolytic cell. The gold solution flowed into and entered the jar at the bottom and slowly circulated upwards and at the same time a current of electricity was passé through the cell to reduce and precipitate gold from the solution into a perfectly pure state, upon the bottom of the jar, from where it was removed. The chlorine was liberated at the same time at the electrode in the inner or porous cell and in contact with the water circulating and formed a chlorine solution, which was sent to receiver vessel."


----------



## Traveller11 (Dec 4, 2012)

What is really interesting about the last bit of +100 year old material I posted (previous post to this one) is that it proves the gold is not put into solution by electrolysis. Rather, a "chlorine solution" (sodium hypochlorite/sodium chlorate) is created by electrolysis and piped to a leaching barrel where the gold is actually put into solution. What is unique here is that the gold in solution, or auric chloride, is filtered and piped back to the unit where saltwater is undergoing electrolysis. There, it is divided into gold and chlorine gas; the gold dropping to the bottom of the electrolysis chamber and the chlorine going into solution again to be piped back to the leaching chamber.

In other words, it is a chlorine leaching solution generator, leaching vat, electrowinning unit and leach recycling unit all in one. And, once the operator is finished, a liberal dose of sodium thiosulphate will neutralize everything in the chambers.

I've spent the last couple of days trying to find a design of a streamlined unit similar to what is described in the last post, with no luck. In this newer design, rather than the chlorine solution being made in one unit in a batch and piped to the leaching unit, only to be returned to the electrolysis unit once leaching is finished, this design called for a continuous loop. The ground ore was placed in a tub of saltwater. The electrolysis unit, also full of saltwater, was located beside this tub. A plastic pipe led from the electrolysis unit to the bottom of the tub, entering it there through a bulkhead fitting. A pump was located on this pipe to bring solution to the tub or "leaching vat". A motorized paddle is immersed in the leaching tub and turned slowly to keep the chlorine solution in contact with all of the ore. The water overflows through a port near the top of the leaching tub and returns by gravity to the electrolysis unit, passing through a filter on the way.

The electricity is turned on and sodium hypochlorite/chlorate is produced in the electrolysis unit. After a period of time the pump is turned on, sending hypochlorite/chlorate (in reality, hypochlorous and chloric acids at this point) to the leaching tub and bringing fresh saltwater (and eventually auric chloride) back to the electrolysis unit where the gold from the auric chloride is deposited on the cathode and the chlorine is transformed into hypochlorite/chlorate. The cycle is continued for up to four hours or until no more gold is seen depositing at the cathode.


----------



## butcher (Dec 4, 2012)

Will this help? http://chemwiki.ucdavis.edu/Analytical_Chemistry/Electrochemistry/Case_Studies/Industrial_Electrolysis_Processes


----------



## Geo (Dec 4, 2012)

Butcher, you may have answered a question i had on another thread. thank you.


----------



## Traveller11 (Dec 4, 2012)

butcher said:


> Will this help? http://chemwiki.ucdavis.edu/Analytical_Chemistry/Electrochemistry/Case_Studies/Industrial_Electrolysis_Processes



The Chlor-Alkali cell is identical to the salt water electrolytic cell except for one thing; there is a membrane separating the anode side of the cell from the cathode side. This membrane stops the chlorine produced at the anode from reacting with the sodium hydroxide produced at the cathode, thus producing chlorine gas on demand from salt.

Our water system tried to find a mini version of the Chlor-Alkali cell to make chlorine gas for disinfecting drinking water. This is much safer (and cheaper) than shipping and storing pressurized bottles of chlorine gas. Plus, salt is easier to store and does not decompose, as sodium hypochlorite solutions do. Unfortunately, the only Chlor-Alkali cells we could find were very expensive and produced chlorine gas in amounts far beyond our needs.


----------



## butcher (Dec 4, 2012)

If you could use chlorine to dissolve the gold on one side of the split cell, adding salt as needed, I would think if current and conditions were in certain limits the gold chloride would form, instead of generating chlorine gas (or limiting chlorine gas that would evolve), once you had gold in solution it could be precipitated out of solution, or possibly plated out of solution, the membrane or salt bridge could keep gold on one side of the cell.

For ore the problem of base metals and all of the other chemistry involved in the ore, would possibly cause havoc with the electrolyte, but for ore maybe you could use the chlorine cell to generate chlorine and use the gas to volatize gold from ore in a roasting furnace where the suspended red hot powdered ore >900 degrees C is falling through the flue gases with chlorine gases rising through this flue, the ore could also be pre-roasted with NaCl, to help pre-chlorinate the ore, of course capturing these volatile metal gases in a scrubber, here the sodium hydroxide generated in the cell may come into play, although building a furnace and maintaining it safely would be difficult, it would possibly be easier to just bubble chlorine gas into a crucible fixed with an ability to capture volatized metals (such as gold chlorides), and try to chlorinate the gold in the gold left in the crucible (crushing the melt when cooled to powder and dissolving the now water soluble gold and other metal chlorides.

Even simpler would be to concentrate the finely ground powdered ore, roast it and use the chlorine generator to bubble chlorine gas into a hot solution liquid leaching process.


----------



## Gratilla (Dec 8, 2012)

After having read the thread, together with all its side links and parallel threads, with interest, I'm wondering whether the long journey is nearing a destination?

The details so far:-

Electrodes: Platinum, Lead Dioxide, Titanium, Graphite?

Electrolyte: How many kg NaCl per 1,000 l water ... or does it matter?
a) Page 48: Seawater - approx *32kg*, 
b) Page 48: 1 mole/liter - *58kg*,
c) Page 48: *100kg*/ton of ore.
d) Chlor-Alkali cell - *260kg*
e) Saturated soln - *359kg*

Unit Design: Electrodes in same or separate containers? Pump? Convection currents? Membranes? Semi-porous ceramic/clay pots?

Voltage/Eh/pH/Temp: Pourbaix diagrams of Eh against pH would be useful.

In some ways this saltwater cell is an electrochemical equivalent of SSN (Saturated Salt Nitric leach), but with control over the voltage. And both are broad spectrum, that is they will leach the base metals before the Au and PGMs. (To specifically target Au in black sands, cyanide is probably the way to go.)

On the plus side though, both systems will also leach the PGMs ... and solvent extraction with butyl diglyme (or diethyl malonate) will extract close to pure gold (irrespective of base metals etc in the aqueous fraction).


----------



## Traveller11 (Dec 9, 2012)

Gratilla
There seems to be some question as to just how selective for gold this leaching method is. If you read the thread I started in "Prospecting, Mining, Ore Concentrates & Geochemical" which is titled "Recovery of gold from ores with chlorine in 1898", you will notice they are using a chlorine solution which should be almost identical to the chlorine solution produced electrolytically; namely, a solution of hypochlorous and hydrochloric acid in water at a ph of 5-6.

In this article from 1898, they described grinding ore to a fine pulp and roasting this ore in furnaces and then sending the ore to the leaching vats, with NO attempt to remove base metals such as iron. As iron is the 4th most abundant element on the planet and I am sure their ore had some iron in it, I can only assume this method did not put iron into solution.

Another article I read from the 1890's talked about why ores are roasted. It is not only to free gold up from sulphides. The article said that, by converting elements such as iron to its oxides, it made the iron far more resistant to the leach and prevented it from going into solution.

Once again, they said that copper in the ore, especially in its metallic state, was poison on the leaching process.

I would like to continue this discussion on the "Prospecting, Mining, Ore Concentrates & Geochemical" forum so as to avoid duplication of posting. Also, this has more to do with mining than anything else, so this might be a more appropriate place to discuss chlorine leaching.


----------

