If you re-circulate water from tailings ponds you may be getting a build-up of frother in the water. This especially prevalent in areas where cold weather slows evaporation. Another area to investigate is if mining is proceeding through old mine workings where there may be old timbering. Humic acid is generated which will cause voluminous persistent froth.

Can you please give us some more information to go on? Specifically what minerals are you floating, what is their particle size, what gangue minerals are present (especially clays), what reagent suite are you using (obviously including frother type and dosage) and where is the problem occurring (pump boxes; float cells, product or tailings thickener)?

Excessive froth: There are few cases where gear box oil leakages enter flotation circuit through spillage cleaning and feeding to Flotation circuit. Please confirm such leakages and arrest them. One drop of oil contamination is very dangerous to flotation. It not only creates excess forth but also reduces gold recovery.

Here is my contribution at your problem:

You must test the water you are using because water's hardness is very important in froth flotation. In my experience, when the water hardness is dropping you will have an...

I agree, please check the production stopes, if any pine wood supports exists in the old galleries. As you know pine oil causes excessive froth in flotation, and it affects cell performance, slurry transfer and thickening.

When you say excessive froth I assume you mean volume of froth that persists with time after collection that causes problems in froth handling. "Excessive" froths can be caused by surface active agents in mill feed or by fine hydrophobic particles or other factors. It is possible to use crude but effective measures of froth stability to define froth behaviour such as froth half-life to define stability and contributing factors.

Let me explain with more detail about my question:

We are studying to float a sulfide ore. The Ore basically contains sulphide minerals dominated by pyrite, together with ancillary marcasite and traces of copper sulphides, accounted for 5 to 7 percent by weight of the ores. These sulphide minerals were emplaced in silicate rich host together with minor iron oxides.

In the Lab stage (Ore variability Bench scale tests) has evidenced problems with the natural occurrence of excessive frothing even without aeration or addition of frother. The condition for the flotation tests was: 25 g/t CuSO4 - 35 g/t PAX. 70 g/t Aero 208 and the optimum grind were p-80 106 microns. The overall gold recovery was 90%.

Pilot testing also has showed this behaviour (Excessive frothing), the actual cause for this could not be ascertained but after the pilot testing, was suspected that Alunite that was known to constitute approximately 3.0% of the head sample by mass could have caused this.

To try to resolve this problem, the sample was washed twice before feeding the pilot plant and including the use of depressants like Starch (- 100 g/t). Results showed considerable improvements in froth control, But with an effect on Gold recovery (+/- 5% Gold loss in the case of use of starch). Was proved that the samples were not contaminated with oils or similar (Drill hole samples were taken, under strict quality procedures), and the water used for the pilot plant, was fresh water.

Subsequent testing including the analysis of the effect of the alunite and find another solution to control the frothing. The use of cationic flocculants like CP 624 (0.096 kg/mt) with sodium silicate appear be a feasibly solution without gold loss. Testing also showed very little soluble Al was present in the freshly milled ore. Consequently, soluble Al does not appear to be responsible for the observed issues with excessive natural frothing of the ore.

As you can see, many testing including bench scale and pilot have been carried out on this project, at this moment the real causes of the excessive frothing are not well known.

I agree with you that Alunite may be your problem, not as a soluble mineral but as a clay-like statically charged mineral, hence the relief from cationic flocculants. It is the clay coating on the froth that makes the bubbles stable, and thus hard to break. I'd suggest you contact a major reagent supplier like Cytec to see which reagent suits your operation.

Aluminum hydroxide-sulphate containing high grade of Ag-Au-Bi, as precipitate in occlusion host into spongy pyrite used to appear in this kind of ore. It is not a piggy back electrostatic talc figure that is why excessive reagents addition unjustified turns the froth viscous.

I believe there is also technology developed by Xstrata Technology to solve froth handling problems at McArthur River Mine, NT. At McArthur River a very fine, sub-10 micron regrind stage is employed which, along with the presence of significant hydrocarbon, causes the froth to be very stable indeed especially in cleaning. It is possible to use more water to dilute the cleaner feed to reduce the amount of fine hydrophobic solids reporting to the froth phase per unit length of cell to reduce froth stability, but of course the residence time in the cells is compromised. There are mechanical devices to de-aerate the froth and break it. Some reagents are also able to break stable froth and have been used depending on what is causing the excessive froth. The main inputs are: fine hydrophobic minerals, process water, and reagents. Some long chain collectors’ act as frothing agents and it is possible to discern the relative contributions and synergies in experiments. For example, a collector may cause frothing in process water (measure the stable froth height with gas flow in a column which gives a measure of froth retention time and the froth decay after the gas flow is discontinued which gives a measure of the froth half-life) but may be more or less impactful with solid particles. In studies, the froth recovery is related to the froth residence time and the froth half-life. There was an AMIRA project called P541 on froths, frothing and frothers that researched this. A practical paper that may help is:

Tsatouhas, G., Vera, M., and Grano, S., (2005) Case studies on the Performance and characterisation of the froth phase in industrial flotation circuits, in Centenary of Flotation Symposium, (Aus. Inst. Min. Metall. Publ.), G. Jameson ed., pp 377-384.

Ultrasonic processors will break froth as it passes through the cavitations zone. We have Ultrasonic Troughs and Ultrasonic Tubular reactors that can be customised to fit inline. We can process as many tons per hour as you like, just let me have the figures. There is virtually no time delay and the foam/froth collapses. De-foaming and degassing of liquids is one of the many advantages of ultrasonic processing.

see https://www.911metallurgist.com/froth_flotation/excessive-frothing-at-cleaner-flotation-for-low-grade-gold-sulphide-ores