What do you know about the liberation characteristics of the copper minerals v. pyrite?
Is the pyrite liberated at the grind size you are using?
Do you have any water chemistry data to share?

I have not really looked at the liberation characteristics, i just used the plant grind size which i think the pyrite might still be locked with the copper mineral. maybe I should take the sample of each fraction size for mineralogy analysis?
No i don't have any water chemistry data, i have not looked at that.

pH plays a major role in process. Before changing parameters confirm from lab tests different pH Vs Recovery and grade and then fix the parameters. In plant practice actual pH will be very nearer to it. Even high pH depress copper. Keep minimum pH and try NaCN. Even at low pH NaCN depress pyrite. You try 1st in lab and then try in plant.

Flotation of copper at different alkaline pH from 7 up to 10 and using different Xanthates as collector vs recovery of copper may give some clue. Minimum Pyrite obtained in copper concentrate is the starting point for further flotation testwork. Depressing Pyrite is always a tricky matter. The non- float is naturally your Pyrite Concentrate after cleaning .

Lacking liberation you will lose copper recovery when increasing pyrite recovery. Of course that may happen to some extent in any case.

Additional details would help - What are operating conditions (reagents, pH, etc.). How high was the pH, what was aeration process, etc. Is this a porphyry ore or massive sulfide, etc?

I would check your liberation as suggested previously. If you're dealing with massive's (I assume chalcopyrite or other Fe bearing minerals) you'll need to ensure you're getting as much liberation as economically feasible. The same could be said for disseminated ores too. Oxidising the iron sulphide will probably reduce your recovery as it would be hard to not oxidise any of the CuS minerals.
Trying to recover copper sulphides (possibly with a dash of Fe mixed in) and reject FeS2 is not a battle I would enjoy.
If your Cu minerals are reasonably free of Fe (e.g chalcocite, covellite, cuprite which I doubt as your recovery seems to be linked to the pyrite recovery) have you considered magnetic separation?
And one for you experts as I'm not familiar with or worked with them, would spirals be able to separate the liberated Iron and the Copper minerals in the ore by the weight of the minerals? Maybe spiralling cyclone u/flows? There's a little more than 1 g/cm^3 difference in their densities.

In the work I conduct I have seen that altering the pulp chemistry can play huge roll in better selectivity against Pyrite. Typically changing media type from Forged steel to High chrome media can alter pulp chemistry to more oxidizing (or less reducing) conditions. You find your copper species have improved kinetics and the amount of iron sulfides to the concentrate is lower. Pyrite has a stronger affinity to float in reducing condition.

Using reagents, I have seen the great success with MX5149 (not a depressant) to improved selectivity against Pyrite...I think from Cytec. Conducting a few test the improvement in selectivity against Pyrite was impressive. Some mines in Zambia now only uses this reagent.

Aeration with Metabisulfite is another way to depress pyrite effectively. Use of NaCN is not the preferred way these days mainly due to environmental regulations and health concerns. Most concentrators would prefer a non-cyanide route to avoid permitting and various contamination issues etc. MBS is used in North and South America to depress pyrite in Cu flotation.

The question posed was bound to see a number of diverse responses covering territory from change in collector, pH, Eh (ie pulp chemistry changes from change in media), etc. because the issue of rejecting (depressing) pyrite is complex and very ore specific. So you're best going to basics and conducting laboratory tests under different conditions with materials that work well as supposed pyrite depressants as documented in the literature. Bulatovic's "Handbook of Flotation Reagents" is an excellent start. For instance, Cytec's S-7261A depressant, napthalene sulfonates, lignosulfonates, dextrin, quebracho, etc or synergistic blend combinations of the above (and some suppliers do sell them) are a good staring point, because unlike SMBS or lime which have high dosage requirements or cyanide which has a dangerous EHS profile, these can be tested at lower dosage. Running such reagents on cleaner or regrind circuit streams also has the added advantage of using less. Needless to say the problem is tricky to get the reagent scheme and pulp chemistry optimized.

Depending on your ore type, liberation by size, operating conditions, i.e. pH, Eh, conditioning time, etc. I worked on a porphyry copper ore from Philippines before where I found that dithiophosphate worked better in depressing pyrite in the rougher stage. I experienced a copper-gold massive ore type where thionocarbamate seemed to work better. Also, SMBS is a common pyrite depressant.

It is hard to depress pyrite but not to depress copper minerals. I resolve my pyrite problem with changing collector type (xanthate with thionocarbamate ), more stages of cleaning and more lime. But problem with pyrite in copper ore is very, very tricky to be described in few words.

Are you sure that the problem is only pyrite? maybe you need a Minerology study, because can be another type of iron sulfides, pyrrotite for example. so when you know what is the mineralogy, you can do all the test: Grinding to liberation, improve pH to depress pyrite, improve reagents (Aero 5100 and Aero 3894 of Cytec are very selective in copper flotation) select a depresser, and all the parameters to improve your flotation.

I have been following very well and i did reply to the questions posed whether i know the mineralogy of the ore very well and if it was fully liberated at the grind size am operating at,,,most of all am carry out more research on the reagents that have been suggested. am so grateful and i have learned a lot from you people, my 1st step will be to check the grind size then go on to using the suggested reagents.