The main usage of electrochemistry is in Cu/Mo separation. In Peru many companies control the ORP for this application. I remember outotec has CHEMA, which was tested in some applications.

I would say that using Ep (pulp potential) - a.k.a. ORP, REDOX - to control the addition of NaHS for Cu/Mo Separation is a very limited application of the measurement. It is similar to using pH to control the addition of lime, soda ash, or sulphuric acid.

The hurdle which has not yet been passed is the use of Ep on the bench and in the plant to identify the conditions for optimum separation and, from this knowledge, the inclusion of this parameter in developing process control strategies. For example, increasing flotation air rate will accelerate the rate of flotation of the desired minerals AND lead to a higher Ep which could reduce selectivity against the gangue minerals.

Electrochemistry is a very important issue in flotation; I have done a number of projects where choosing the right pulp electrochemistry in flotation may improve your mineral flotation response. As said, controlling the ORP down-the-bank in a Cu/Mo flotation circuits will reduce the NaHS consumption significantly. In general, choosing the right pH/ORP values will results in a collector less flotation for some minerals.

Controlled Potential Sulphidisation (or CPS) is also used when floating oxidised sulphide minerals (copper species especially) as well as to reactivate, or clean the surface of sulphides during multistage polymetallic flotation circuits. This is typically integrated with the addition of an ORP modifier such as NaSH.

This practice is used at a number of locations in African, Chile and Australia that I have worked with as well as throughout the mining world.

You are correct when he says that potential is a very important issue in flotation. The flotation of many species is strongly influenced by pulp potential, with the flotation of chalcopyrite (as an example) best at oxidising (or positive) potentials around 300mV (SHE). At these potentials, the adsorption of xanthate onto chalcopyrite is increased and thus flotation kinetics enhanced. Furthermore, at these potentials the selectivity between chalcopyrite and pyrite is improved, thus pyrite recovery can be reduced.

At very low pulp potentials, the flotation of chalcopyrite is depressed, and thus this strategy is used during molybdenum flotation. Specifically, the pulp potential during molybdenum flotation is typically very low at -400 to -500mV (SHE), a range where molybdenum will still float but chalcopyrite will not. Again, this is a matter of improving selectivity between the desired species (molybdenum) and the undesired species (in this case the chalcopyrite).

You made some good points, In the case of CPS, ideally one wants to measure Es rather than ORP. However the Es proved has proved difficult to apply in practice so an ORP probe is used.

Note that ORP measures the 'net' redox potential and, in the case of an ion-specific potential measurement such as Es, if the aeration or collector addition rate is changed, then the ORP will change and the Es value will need to be checked (with a laboratory probe).

Many things contribute to ORP: oxidants, reductants, temperature and of course pH. Note that the flotation system is basically an oxidising environment (air saturated system) unless one adds significant amounts of reducing species (sulphidisers, collectors, etc.).

We [BOC Gases] looked into the role of ORP quite seriously and there are only really a few separations where it is critical: increasing the rate of chalcopyrite flotation as mentioned, ensuring that galena floats (more about [DO] than ORP), depressing collector activated copper sulphides (e.g. sulphidizers and chalcopyrite), chalcopyrite-galena separations and enhancing the depression of iron sulphides (more about [DO] and oxidation than ORP). I may have one or two but otherwise, ORP is not critical as we would have liked to believe.ORP turns about to be a handy way of measuring or controlling these intended reactions

Everybody seems to be interested in ORP and believes that it does play a role in mineral separations and a plant operation.

We used to do surveys of flotation circuits for customers or would be customers using the good reliable TPS meter, measuring ORP, [DO], pH, temperature, conductivity and Es [ if requested]. People in operation absolutely loved them and made requests - it became a routine 'check up' - like the 'health of the plant' whenever we visited a site.

Finally, as you would agree, ORP is particularly important during milling when significant amounts of sulphide minerals present. This ORP is largely controlled by ball type and the amount of iron sulphide present. And this seriously affects the flotation behaviour of mineral separation systems.

Electrochemistry? Whilst a lot of work has been done in this field, in my opinion a lot of work remains to be done to develop an understanding that can be usefully applied by plant operators. He was at the forefront in CPS for a while and did some good work and I agree entirely with his comments about ORP vs. Es. I have in some plants observed huge Es variation over a very narrow ORP variation range, so what is the right ORP? And as mentioned Es in nigh impossible to measure accurately in flotation plants. So many variables affect electrochemistry including residence time in float cells.

DO, pH remain our most trusted guides I believe.

Has there any application of electrochemistry on coal flotation?

Coal, being naturally hydrophobic, can be floated however the residence time rarely exceeds 30 seconds in practice. Occasionally pyrite is present and this is depressed by standard means. So I would suggest that there is very little call for electrochemical control in coal flotation.

Prompt by what programs you process the data? What electrodes using? I work with complex ores.

An applied industrial plant research was performing for polymetallic secondary copper sulphides (Bn, Cv and Tenantite), zinc marmatite, lead sulphide, pyrite, argillic Muscovite. Two Mettler Toledo controller by PLC using platinum and reference electrodes to adjust Eh -150mv as a sharp resultant area where the sodium hydrosulphide controls the copper solution ions to avoid the Zinc activation for the rougher-scavenger copper concentrate and regrind before cleaning. At grinding stage the use of H2O2 reduces the galvanic Pb-Fe that dissolves copper ions to produce in selective bulk feed to copper flotation. The Copper quality black concentrate goes to maximum 47%Cu, and minimum yellow concentrate 18%. Set points for Eh, pH controllers were used from previous lab test results. New industrial Brazilian plant from Copper Bornite Vale were using similar approach at pilot plant.

Electrochemistry industrial control still is in progress and requires better sensibility of electrodes, if so the floatation under this variables control could be the top process.

Would the H2O2, an oxidant, actually promote a more intense galvanic interaction?

Applied grinding of polymetallic iron sulphides mineral in stainless balls wear media has a strong reduction environmental aqueous potential media at around -270 mv and pH 4. Rechemberg rest potential measure of Py 658 mv and Gn 395 which this difference is enhanced due to metallic iron over the other sulphides as electron donors. Some searchers uses instead stainless steel media to alleviate the reduction environment, here the H2O2 improves the oxido-reduction survey to -90 mv. Before to add the collectors and produces Xanthogen - chemisorption on Copper, Lead sulphides.

What name of Soft which you used for process date analyse? Do you have any articles for that question. Thanks!

There is a chapter (Ch. 9) in "Electrochemistry for Chemists" by D.T. Sawyer, A. Sobkowiak, and J.L. Roberts, Jr. (2nd Ed.), 1995, John Wiley & Sons that discusses O2 redox couples and has a lot of information on the subject.

It is also a general electrochemistry book with a bunch of more practical information than say Bard & Faulkner, etc.

I will find this book. I work with this set of electrodes: Pt, Mo, Ag, pH and EM. Doing now copper nickel ores. The problem is that a very large output of magnesium oxide, tell me how to deal with it.

There is a large amount of literature in peer reviewed journals and conferences attended by industry people in this area. While the influence of Eh on sulphide flotation is undisputed it has not seen a large take up by industry as Eh is hard to measure and interpret on large Volumetric flow and oxygenated slurries that are not in steady state, that it is hard to maintain the electrodes to give reproducible results, and it is also hard to actually change the Eh in practice, while of course the optimum Eh may change with ore type. Of course there is the well documented case of Cu-Mo separation where a strongly reducing potential can be applied with nitrogen gas, but the more subtle and variable separation of one sulphide mineral such as pentlandite from another such as pyrrhotite has been more difficult to put into practice. There has been work on controlling the Eh by Outotec (OK-PCF) and it has been shown that closely controlling the Eh after grinding under reducing conditions can assist pentlandite recovery while depressing pyrrhotite as an example. In most cases flotation with a combination of gases is required to control the Eh. I am happy to consult in this area.

I am a specialist in electrochemistry, working many years in flotation and hydrometallurgical processes; I would like to know what is specifically required to do the work. We can probably make it.

I'm interested in studying the electrochemistry and international practice.

Very interesting discussion! A few of the issues with using ORP in flotation are:

What is the reference electrode? Ag/AgCl is a common one in industry while Hg/HgCl is a common one in research. There is a -41 mV differential between the two. There is a huge difference between the solution potential, Eh, which is dominated by the oxygen reduction reaction, and the pulp potential, Ep, which is indicative of the readiness of the sulphide minerals for flotation. Eh is easily measured using platinum sensing electrode. Ep can be measured using a gold sensing electrode or a mineral electrode.

The main reason why platinum "can't" sense what's happening on the mineral surfaces is because of its electro-catalytic activity for the oxygen reduction reaction. If one desires to know how the sulphide minerals "feel", either uses a mineral electrode or a gold electrode. If one desires to know how strong the driving force for oxidation of the pulp is, use a platinum electrode.