ph of NaOCl made through electrolysis of NaCl brine

Quote: Originally posted by Traveller

[...] did not alter the original ph of the brine, would this, technically, not be a hypochlorous acid generator, as the shift from OCl to HOCl begins if the ph of NaOCl bleach falls under 11.86?

Quote: Originally posted by weiming1998

The electrolysis of salt produces Cl2 at the anode and H2 (and also NaOH) at the cathode. The NaOH and Cl2 reacts in situ to form NaClO. Because some chlorine gas will inevitably escape from the solution instead of reacting, there will be a small amount of NaOH in the solution. This will raise the pH. NaClO dissociates to HOCl in neutral solution. That is true, but NaOH is also formed. Since HOCl does not contribute to the pH that much, it will only take somewhere near 0.01M of NaOH+HOCl before the pH goes above 12. Then the OCl- ion is generated. So, technically HOCl is generated at the beginning of electrolysis, but only a very small amount will be generated before it starts generating NaClO instead.

Quote: Originally posted by Traveller

Weiming Coincidentally, there is another reason I am interested in NaClO and HOCl. I am pursuing an effective way of recovering ultra fine gold from a bench of clay. There is a method that was used right up until the late 1890's that involved chlorine, both in hypochlorite and gas form. From what I can gather, Cl2 gas was pressurised into vessels of ore and water at 60 psi. I believe hypochlorous acid was made this way. It also seems that the higher the percentage of HOCl present, the faster gold went into solution as a chloride. Cl2 + H2O = HOCl + HCl Because it made HCl, I would think the ph would be lowered slightly here. Interestingly, the OCl/HOCl shift mandated by ph will have the ratio of HOCl to OCl at 100%/0% at a ph of 5. The other recovery method I read about involved the manufacture of what was called a "chlorine solution" from the electrolysis of salt water. Read the following article from the 1890's and tell me what you think. If what you say is true, the solution would have been far too basic to allow any HOCl to be present. It is possible they were adjusting the ph with HCl and the author was unaware of this. Also, do you think it possible they were making sodium chlorate (NaClO3)? I know that if the temperature of the electrolysis chamber gets over 50° C. it will stop producing NaClO and produce NaClO3. Would it be just as or more effective at putting gold into solution? Anyways, here is the article: -------------------------------------------------------------------- Electrolytic Precipitation of Gold 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.

Quote: Originally posted by Traveller

I have thought the same thing myself. Many mines in this period had their own chlorine works where the gas was made from sulphuric acid and chloride of lime. It is just possible that the inner and outer jar of the cell the author spoke of was the membrane required to keep Cl2 and NaOH from reacting. It may have been simpler to produce electricity onsite than to haul in H2SO4. It may also have been they were making NaClO and bringing the ph to neutral, by adding the appropriate amount of HCl, and thus still ending up with HOCl at a neutral ph. I've found these 100+ year old articles can be both articulate in detail and maddeningly vague at the same time. Unfortunately, they are about the only source of information, as cyanide leaching came on the scene about 1900 in a big way and chlorine leaching was abandoned almost overnight. What do you think of the gold oxidizing potential of chloric acid (HClO3) made from sodium chlorate as opposed to hypochlorous acid?

Quote: Originally posted by Traveller

I thought this too, at first, and this is also the basis of a leach promoted worldwide as the Igoli Process. Large amounts of HCl are added to a NaOCl solution and great amounts of Cl2 gas are given off. Its promoters sincerely believe it is the Cl2 gas coming in contact with gold that puts the gold into solution. However, with Cl2 having no oxidising potential in the gaseous state, I do not believe this to be the case. I believe it to be HOCl doing the work, just as it is the active ingredient when disinfecting. If a very minute amount of HCl was added to NaClO, would we not see the following reaction, given the amount of NaOH in our solution? NaOH + HCl = NaCl + H20 If this were the course it followed, it would seem possible to gently lower the ph of the NaClO solution to neutral, thus converting most of the OCl ions to HOCl. It should also be noted that Cl2 gas will not come out of solution until the ph drops below 5. [Edited on 27-1-2013 by Traveller]