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Pyrrhotite Depressant in Polymetallic Flotation (9 replies)

Carl Jenkins
9 months ago
Carl Jenkins 9 months ago

Does anyone have any experience with using pyrrhotite depressants in polymetallic ore flotation? What products did you use and how effective was it?

Bob Mathias
9 months ago
Bob Mathias 9 months ago

The number one depressant is reagent starvation. In polymetallic ore pyrrhotite does not compete very well for collectors, and the use of starvation dosages is far more effective than trying to depress pyrrhotite once it has been activated.

The number two depressant is lime. In general, flotation of pyrrhotite is depressed in the range of about pH 9.3 and above. Note that this is not just a pH effect - sodium hydroxide and sodium carbonate are not particularly effective.

The third depressant is redox (eH). When the redox is low, pyrrhotite is depressed. This does not usually involve redox modifiers - more commonly, one finds that after a regrind the selectivity versus pyrrhotite goes up (more strongly than the effects caused by liberation alone).

The fourth depressant is ethylene diamene (EDA) and its longer chain equivalents (diethylene triamine or DETA, triethylenetetramine, or TETA). This is typically applied either upon oxidated pulps or in combination with sulphur dioxide, according to the methods described by in the proceedings of the 19th IMPC.

The fifth depressant is extensive oxidation. This seems non-intuitive in light of the low-redox comment that I made, but the mechanisms are different. At low redox you de-sorb collector. Under intense oxidation, you form iron hydroxide layers that respond poorly to collector. Thus on either side of the oxidation spectrum you see depression, and in the middle you see flotation. The oxidative approach was the basis of the INCO SO2-air process for pyrrhotite removal.

Of the above, their prevalence and usefulness is the same as the order in which they are presented.

9 months ago
Gruppen 9 months ago

Depending on your deposit and your grinding media, another possibility is to use sodium metabisulphite as a dispersant for iron oxides/hydroxides on the surfaces of the sulphide minerals. You are then able to recover the valuable sulphides at a lower collector dose than otherwise (i.e. it increases the effectiveness of the collector starvation strategy as outlined above).

In the 'old days' cyanide was sometimes used, but its use in flotation depressant applications is much less common these days due to environmental and safety considerations.

Zander Barcalow
9 months ago
Zander Barcalow 9 months ago

Further to earlier comments, the use of Cytec 7260/61 can be effective. Need to be careful with dosage though. If the pyrrhotite is not depressing through the basic methods as described (low and selective collector and increased pH), you really need to get a good understanding of the mineralogy.

9 months ago
Oberfuhrer 9 months ago

Some excellent suggestions made by you and others which parallel the techniques used for pyrite depression - with collector starvation through staged additions an universally attractive strategy when separating minerals with similar or 'troublesome' responses. Cyanide as previous notes is very effective however not popular. MBS is of course reductive i.e. low redox, and like high pHs with lime, works very well in depressing pyrite. Aeration works well as a pre-treatment in cyanidation circuits.

However, as it recommends, conducting some mineralogical studies would be useful - you may find out that the pyrrhotite is Fe-deficient (monoclinic) and thus magnetic, meaning that magnetic separation is a processing option (cf. Sudbury practices).

Bill Fraser
9 months ago
Bill Fraser 9 months ago

Just adding a few points not already covered above:

Know your pyrrhotite and how much nickel there is in solid solution as well as pentlandite as <5 um flames. The more nickel in solid solution and the more pentlandite flames, the more difficult it will be to depress the pyrrhotite. Also, hexagonal pyrrhotite behaves differently than monoclinic pyrrhotite. In the worst case, monoclinic pyrrhotite could be removed via magnetic separation.

Communicate well to management the losses in nickel recovery to be anticipated from depressing/rejecting the pyrrhotite. In the best cases, this could be as low as 5% of the nickel in the feed. In the worst cases, this could be as high as 15-25% of the nickel in the feed.

It is often easier to prevent the flotation of iron sulphides via the use of short and/or branched chain collectors added at starvation levels of collectors, and suitable conditions (notably alkaline pH), than depressing after it has floated once. To be blunt - do not expect selectivity against pyrrhotite with n-amyl xanthate.

Control of the oxidation-reduction state of the pulp prior to introduction of the collector is often critical. Note that in a very simplistic observation about the ethylene-di-amine family of pyrrhotite depressant is that its use "restores" the flotation selectivity to that which could be achieved if oxidation of the pulp had been kept to a minimum.

In laboratory testing, one needs to have a close look at the grinding environment - media and shell - as well as the procedure used to transfer the ground slurry into the flotation cell. Poor selection of the grinding environment and procedures designed without regards to minimization of oxidation of the pulp can make it nearly impossible to manage pyrrhotite flotation.

Jean Rasczak
9 months ago
Jean Rasczak 9 months ago

It is always useful to know the ore mineralogy and the response of your ore to different reagents, we once had an experience dealing with high presence of pyrrhotite on a Cu/Zn ore, we tried all the treatments mentioned before, and they were not working well, we realized that the quality of the water used during the process had a negative impact of the flotation performance of the valuable minerals and Fe species, if there is a high content of Calcium (over 120 ppm) and SO4 this could be an issue. Because the formation of CaSO4 affects the efficiency and selectivity of the collectors during the flotation stage. We controlled the selectivity on the copper circuit based on this approach, and the selectivity of the zinc circuit was achieved with a depressant called Pionera F-200.

Bill Fraser
9 months ago
Bill Fraser 9 months ago

You bring in an excellent point which is too often overlooked - the quality of the process water. With a high proportion of water recycling from the tailings pond, and/or from a tailings thickener, the presence of high levels of calcium and sulphate ions impacts the selectivity of the flotation process.

The vast majority of laboratory flotation test programs are performed with fresh water. Improvements in selectivity arising from a reagent recipe may be aided, or impeded, by the ions present in the actual plant process water. Sometimes suspended solids or organic matter in the water reclaimed from the tailings pond may also impact flotation.

No reagent screening test program should be considered complete without confirmation testing using actual plant process water, or a synthetically made one.

Furthermore, the development of a new deposit should include pilot testing with reclaimed tailings water - especially if the reagent recipe to achieve selectivity departs from the most common ones. This is to minimize risks associated with the scale-up to commercial operation with a high proportion of recycled water as process water.

9 months ago
Standartenfurer 9 months ago

Process water is the most obvious thing that differs from the bench scale to pilot plant to actual plant. It takes enormous amount of efforts to persuade people to look at the water quality by showing them surface analysis of their activated/depressed minerals. Unfortunately, not many plant metallurgists go this route to investigate the root cause.

Using the site water for laboratory testing or make artificial water was very helpful for leaching plants as well. The final question is if a plant is quite big can you afford to bring the water quality to the level at which it will not affect the recovery?

It needs to be mentioned that recycling water quality depend on mineralogy or the ore and its' origin and can change due to the ore composition. Those changes can be foreseeable and actions can be planned.

Sugar Watkins
9 months ago
Sugar Watkins 9 months ago

Cyanide depresses as carriers of copper. It is not recommended in the case of copper ores. The lime with the selective collectors is most advisable.

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