Have you tried NaHS to reduce ORP (Eh) to very low levels as is done for depression of copper minerals the selective Cu-Mo flotation?

In general collectors are adsorbed on mineral surface. You can do leaching with acids. Leaching chemicals depends on which mineral needs to be leached. But I want to know why you want to strip Collector.

The notion of this work was to strip copper collector form a Cu-Au system which should eliminate/minimise chalcopyrite and use PAX to float pyrite. Will try NaHS!

The HS- and S2- directly displace collector from a sulphide surface rather than by changing the ORP. The amount required to strip collector from the surface of a copper sulphide mineral is significant and I suspect that the residual HS-/S2- concentration would inhibit the flotation of pyrite.

As an intermediate step to remove this residual concentration prior to flotation of the pyrite, the addition of a base metal salt (e.g. copper sulphate) to precipitate the sulphide ions is suggested. In addition, aeration in the presence of base metal ion will also oxidise the HS-/S2- species.

It is tough to remove adsorbed collectors at the best of times; copper sulphides being the worst case. As suggested, highly acidic conditions may work (works better for xanthates) as well as high temperatures.

It may also help to identify the minimum collector addition rate i.e. a starvation regime to ease the requirements of the subsequent removal technique.

Conversely, it may be a better approach to allow the remaining copper sulphides to float with the pyrite and then depress the pyrite with NaHS at least you recover the copper sulphides as a product.

If dithiophosphate is attached to chalcopyrite you have to ask why the chalcopyrite is still in the tailings stream; too fine to float in the available retention time, not enough collector coverage, not liberated enough etc. Knowing the answer to that question it may suggest an alternative approach.

The suggestion is worth following up with possibly using lime (you have plenty available) rather than NaHS do depress pyrite.

Really good point!

Why is there chalcopyrite still in the tailings?

Fines, composites, insufficient residence, the suggestion that it would float with the pyrite (=more flotation time) suggests the latter and no doubt fines.

There is quite a bit you do chasing this 'lost' chalcopyrite, including more residence, more flotation, intensity, etc. rather needing to suppress chalcopyrite flotation by stripping collector from its surfaces.

I hinted at it in a later response, two comments after your initial comment, viz.

"The notion of this work was to strip copper collector from a Cu-Au system which should eliminate/minimise chalcopyrite and use PAX to float pyrite. Will try NaHS."

After copper flotation, OK Tedi float the pyrite for environmental management.

We are doing some work on the Pyrite plant for environmental management. We are required (statutory) to discharge <1%S to the environment, however, no plant parameter (PAX dosage, pH, eH, Grind size, density, frother dosage, ore type, level, aeration rates etc) seem to have any correlation at all. Hence, we are embarking on finding a parameter that may have influence on pyrite tails grade.

Chalcopyrite are being lost to the copper tails are retention time as we have decreased the flotation feed densities (and grind size), in the fines especially the -38um fractions from our cleaner circuit, unliberated binaries.

We tried using NaHS but did not work for us, it just killed the froth. We will try at pH as suggested.

It sounds like you need more float cells. Typically pyrite is recovered in a scavenger circuit or a separate pyrite circuit with additional collector. You can add copper sulphate to improve the kinetics. Just let the pH drift from the copper circuit.

You should get some assays or mineralogy done to identify which species contain sulphur. If the sulphur is present as sulphate you will not recover it with conventional flotation. Send heads and tails for total sulphur, sulphide sulphur, and sulphate sulphur. Some sulphates don't digest well and therefore don't show up in the sulphate assay but do in the total sulphur assay. If you can demonstrate that you have recovered all the sulphide sulphur you are done.

Target the final tails should not have more than 1 % sulphur for compliance of environmental management.

May think or try the following route

•Float chalcopyrite and pyrite together as bulk concentrate and subjected it to second stage separation in a Metso HGMS magnetic separator exploiting the magnetic susceptibility property difference in pyrite and chalcopyrite.

•The bulk concentrate may also be separated with Mineral spirals as there exists a density nominal difference.

Test works to establish the strength in conceptual path. Since we are processing bulk concentrate so HGMS or mineral spiral sizing cost incurrence will be less compared to the processing of Tailings.