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pH Effect in oxide flotation (20 replies)
What's the flotation system - mineralogy and sizing, reagents, equipment, etc?
We use the standard pax and NaHs, 70% Cu oxides, target grind is p80 -140 mesh. We have we cost for Rogers and Denver's for cleaners.
Sorry the auto correct messed my response. We have Wemcos for roughers.
Are you using Controlled Potential Sulphidisation or a g/t dosage of NaHS? At the elevated pH you may not need as much NaHS to reach the magical -600mV which may somewhat lower your float circuit pH.
We control our NaHs dosage by ORP, maintaining it around -100mv. At the elevated pH we are not using much.
You have reason. ORP is the best way to reach your target with oxide ore and depend of that you need to find exactly the ORP value that you need not all time is -600mv.
ORP is the best way to reach your target with oxide ore and depend of that you need to find exactly the ORP value that you need not all time is -600mv.
The -100mV will be Eh and there isn’t a linear relationship or conversion to Es. I have seen reasonable grade and recovery of copper oxide at circuit pH approaching 12, although the feed slurry pH has only been around 9.5.
Before you go playing with pH modification, do you have the ability to perform lab tests at lower Eh setpoints or failing that in the plant? In my experience we ran a setpoint around -450mV Eh (-600mV Es) in the roughing stage.
I mean that in that higher pH will decrease your slurry potential, so you may not have enough NaHS for CPS.
If you have a handheld Es probe that will also help if you can compare with when the circuit ran well.
Thanks for the suggestion we will try it in the lab. When pH approaches 11 it kills our flotation and we get poor recoveries. We did lab tests where we dropped the pH to 7 using acid and this doubled our Cu recoveries. I haven't seen this before and can't explain it.
You can use a dispersant (sodium polyacrylate) in the proportion of 300-500g / t during conditioning to improve the dispersion of the particles.
Seek out references to Red Dome. We had similar issues. NaHS speciation in solution is affected by pH and becomes less effective at higher pH while control system calls for higher dose which increases pH further!
To break this cycle we found a pre-float without NaHS effective as recovered free floating native copper and minor sulphide components and reduced subsequent NaHS demand.
At Yukon Zinc we use Sulphuric Acid in our Copper Circuit to lower the Ph. and increase silver recoveries.
We add the Sulphuric acid into the pre floats with a metering pump. We use our pre floats as an extra conditioner instead of a float circuit.
I am not sure of the strength of hand but I can let you know once I am back on site in a couple of days and as for corrosion that is not a problem.
Our starting ph varies depending on the ore but our target ph is around 9.4
It would be exceptional to experience a natural pH that high (10.5+)
The only few times I have observed this high a natural pH was for underground mines with over breakage of the backfill and this was as if lime was added in the grinding mills.
I would like for potential sources of cement in the feed. If this is the case, then eliminating/reducing the amount of cement present in the feed should help.
If it is not a case of cement in the feed, then it is another matter. However, -100 mV would be a typical Eh obtained with only an alkaline agent raising the pH to 10.5. To adjust the addition of the sulphidizing agent to the higher pH, I suggest reducing the Eh target by 60 mV for every pH unit above the more usual operating point. For example, if at the usual natural pH of 8.5, a sulphidization at -100 mV, then the sulphidization should be carried at -220 mV at pH 10.5 to approximately have the same reactivity.
The strength of the Sulphuric acid we use is 93% and is added to our pre floats as I mentioned earlier we are an underground copper lead zinc mine with paste back fill but very rarely do we get over breakage of the back fill.
Thanks for your comments, we add the acid in the conditioner tank to lower the pH to 9. We are doing a plant trial now. The dosage is about 3lbs/ton of ore. We are adding the NaHs in the head of our first roughers and the dosage we run is about 0.15lbs/ton. With these low dosages do you think it's still dangerous?
Recoveries seemed to have jumped up but we will run for a week to get more conclusive results. You are right the high pH is suppressing the Cu sulphides and we have achieved lower tails with the acid addition the last 2 days.
Yes we do have H2S sensors and there is no smell that we can detect. Our acid storage is not in the mill and we only move them when we are changing the totes out.
At high pH frothing effect gets reduced and flotation becomes sluggish causing high tailing loss. Increase frother dosage or reduce pH to 9.
Has anybody experienced extremely high natural pH (10.5+) in ore and hence affecting flotation? The high pH is inhibiting flotation and recoveries are dropping.Any ideas on how to overcome this, like dropping pH etc?