Note: HOCl and HClO, plus NaClO and NaOCl are the same formulas, just written differently.
Okay, I got all of the parts from Ebay; the graphite bar from Israel, the titanium pipe from Latvia and the battery charger from China. I have given up on the Chinese battery charger and purchased a good 6/12 volt, variable amperage battery charger from Walmart. I have also decided not to use the titanium pipe as an anode, on the advice of another member, as it turns out that, if the titanium is not platinized, it requires an immense amount of current to use it in electrolysis. What I did was saw the graphite bar in two lengthwise, making two electrodes.
I also found out that modern battery chargers require a battery to be hooked to them before they will begin charging. To facilitate this, I drilled 1/4" holes in the top of each electrode, crimped eye connectors on to the end of two pieces of 12 gauge wire, and connected these to the electrodes with 1/4" stainless steel nuts, bolts and washers. On the other end of the wires, I connected the two alligator clamps salvaged from the Chinese battery charger.
With the battery charger connected to a 12 volt battery and the anode and cathode immersed in an ice cream bucket half filled with heavily salted water and liquefied clay that hopefully contains fine gold, and the alligator clamps from the electrodes connected to the battery terminals, I started the charger on 12 volts at 2 amperes.
Predictably, a large amount of bubbles began surfacing around the negative cathode. A little later, a much smaller number of bubbles were noticeable at the positive anode, and this was to be expected, as well. The bubbles at the cathode (-) are hydrogen, and as they were in the majority, they are proof that the cell is working at an appreciable efficiency and doing the following:
NaCl + H2O + e = NaClO + H2 (NaClO being sodium hypochlorite or bleach)
As the pH of the solution was still likely below 8, about half of the NaClO would instantly convert to the powerful oxidizer hypochlorous acid (HClO) which is, along with NaCl, what we need to put gold into solution as AuCl3.
The much smaller numbers of bubbles rising at the anode (+) were chlorine gas (Cl2) and their existence is proof of the inherent imperfection of this process, small as it is. When the electrolysis of the brine solution first dissociates everything, different components are attracted to the anode and different components to the cathode. Sodium, oxygen and hydrogen are attracted to the cathode and form the strong base sodium hydroxide (NaOH). Chlorine gas is attracted to the anode. In a perfect world, these exist only for a fraction of a second before re-combining to make NaClO (bleach) and H2. When this does not happen, we begin to get a buildup of sodium hydroxide (NaOH) in our solution and, as it is a base, it begins to make the pH rise.
The rising pH should be countered by the chlorine gas (Cl2) at the anode but is not for two reasons. As Cl2 gas evolves, most will dissolve in the surrounding water, giving us the following reaction:
Cl2 + H2O = HCl + HOCl (hydrochloric acid and hypochlorous acid)
The hydrochloric acid (HCl) is a very strong acid and counters the base NaOH in the following formula:
HCl + NaOH = NaCl + H2O (interestingly, right back where we started)
However, the hypochlorous acid (HClO), although a powerful oxidizer, is a very weak acid, and does little to affect the pH of the solution. Making matters worse, the Cl2 lost to the atmosphere does not make any acid and, with the predominance of the NaOH, the pH of the solution will ultimately rise to between 9-10. I think the addition of the stirring paddle shown in the diagram would help here. If the solution is not moving, it would not take long before the water around the anode was saturated with evolving Cl2 and unable to accept more. If the water were moving, there would always be fresh unsaturated water around the anode ready to dissolve Cl2 and diminish the amount of Cl2 escaping to the atmosphere.
Another reason for the constant stirring of the ore, so I am told, has to do with silver chloride (AgCl). Most gold contains some silver and it reacts in this process as well, making AgCl. While stirring the ore will keep it well exposed to our solution, it turns out that AgCl, being an insoluble chloride, tends to deposit a coating on everything in the ore. When this coating covers a particle of gold, it prevents it from contacting the solution. As it is not adhered very strongly, constant movement of the ore and the abrasive action of other particles easily knocks the AgCl from the gold particles.
As this process requires the NaClO to be in its lower pH alter ego state of HClO in order to oxidize gold (see HClO/NaClO chart a few posts back), and the optimum pH seems to be from 7-8 in order to keep about a 50/50 mixture of NaClO/HClO, it is necessary for us to artificially lower the pH as it begins to rise. To do this, we need a good pH tester (one decimal) to monitor the pH of the solution. If it does rise above 8, minute additions of HCl or even acetic acid (vinegar) are enough to bring it back to the desired level, closer to neutral. One important thing, we do not want this solution to become acidic, and a pH of 6 is about as far as we dare stray. Any lower, and two things occur. At a pH of 5, our solution will begin to give up great amounts of chlorine gas (Cl2). It will also be acidic enough to break the oxygen/base metal bonds of any oxides in our ore. In particular, the acidic solution will begin to break up the oxides hematite and magnetite, in our black sands, and the liberated iron will immediately go into solution INSTEAD of gold. This last part cannot be stated strongly enough.
The big question still remains, will the gold, once liberated at the cathode, merely fall to the bottom below the cathode, or will it plate out and adhere to the graphite cathode? I have had it suggested that both will happen but, of course, only one is possible. To this end, I have written to a graduate student at UBC who, along with his professor, was involved in an artisanal miners program dedicated to eradicating mercury from Third World artisanal mining operations. This electrolytic process was part of that program, and I believe one or both of them actually saw a prototype in action, and might be able to tell us where the gold ends up. Believe it or not, this electrolytic process was originally designed to recover mercury from placer mining tailings. While it worked exceptionally well at recovering mercury, the tailings, unbeknownst to the operators, also contained a great amount of ultra fine gold that the mercury had been unable to amalgamate with, and this electrolysis process also recovered 95% of that gold. Another question I have is, if the AuCl3 is broken up at the cathode, liberating Cl2 to make more HClO, and the gold does NOT adhere to the cathode, what stops the liberated gold from simply re-reacting with more HClO to make yet more AuCl3?
One thing for sure, I am not only making chlorine gas; I am also making bleach. Shortly after turning the current on, I moved the anode and ended up sticking my fingers into the solution. Because of the almost neutral pH, there was no stinging or burning but I could definitely smell Clorox on my fingers.
I think the next step is to construct a proper bracket to hold the electrodes, followed by some sort of stirring mechanism to keep the ore and solution in motion. As I said before, any stirring mechanism in contact with the solution either must be made from plastic or, if made from steel or aluminum, coated with plastic to keep these base metals out of contact with the chlorine solution. Even stainless steel is not immune to chlorine. The only affordable metal one could use would be titanium, and I suppose a paddle made from titanium pipe and blades could be fashioned; either fastened together with titanium screws or bolts or welded with titanium welding rod (is there such a thing?). Another thing to do is to begin monitoring the solution pH to begin to get an idea of how often it is necessary to intervene and lower the pH.
It may be necessary to build an isolation chamber for the cathode employing anion exchange membranes, if it turns out the gold does not plate onto the cathode. These membranes would allow the passage of AuCl3, Cl2 and NaOH but prevent gold and ore from re-mixing. Once again, AgCl coating the membranes could become a problem.
Slow process but, hopefully there is progress being made here.
Bye for now.
