minerals | free full-text | the effect of conditioning on the flotation of pyrrhotite in the presence of chlorite | html
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pyrrhotite depressant in polymetallic flotation - froth flotation (sulphide & oxide) - metallurgist & mineral processing engineer
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.
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).
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.
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).
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.
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.
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.
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.
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.
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a review of pyrrhotite flotation chemistry in the processing of pgm ores - sciencedirect
The chemistry of pyrrhotite flotation using xanthate collectors is reviewed with respect to the processing of PGM ores and the recent results from captive bubble contact angle measurements at the University of Utah are presented. In some cases a low flotation recovery of PGM may be due to the surface state of pyrrhotite particles under conventional flotation conditions (open to air and pH 9.0).
Thermodynamically pyrrhotite is not stable and reacts relatively quickly with its environment. Natural/collectorless flotation of pyrrhotite is observed only under a low oxidation potential in acidic solution. Its surface is easily oxidized to ferric hydroxide/oxide under conventional flotation conditions, creating a hydrophilic state at the pyrrhotite surface and low flotation recovery even though xanthate collectors can be adsorbed. Under these conditions, activation by copper is not easily achieved. These observations reported in the literature have been confirmed by captive bubble contact angle measurements. Based on the analysis of previous research, conditions for improved pyrrhotite flotation and increased PGM recovery are suggested.
flotation recoverybysize comparison of pyrrhotite superstructures with and without depressants - sciencedirect
Monoclinic (Fe7S8) and hexagonal (Fe9S10) pyrrhotite flotation recovery by particle size.DETA/SMBS depressant effects on monoclinic and hexagonal pyrrhotite.Feed characterization (mineralogy, mineral Ni deportment and liberation/associations).
This paper is a continuation of a labscale flotation scoping study completed on a NiCu sulfide ore that incorporated the use of diethylenetriamine/sodium metabisulfite (DETA/SMBS) pyrrhotite depressants. The scoping test work showed depressive effects on both hexagonal (Hex Po; Fe9S10) and monoclinic (Mono Po; Fe7S8) pyrrhotite superstructures with DETA/SMBS. This work investigates pyrrhotite superstructure flotation, with a focus on recoverybysize with/without depressants (DETA/SMBS). From the baseline rougher test (pH 9.2), it was observed that Hex Po floated primarily in intermediate size classes (10100m) while Mono Po floated largely in finest sizes (<10m). The likely contributing factors for this flotation difference were substantial surface passivation sustained by Mono Po over Hex Po which also permitted a larger degree of surface activation for Hex Po by Cu2+ and Ni2+ ions. Baseline scavenger tests (pH 8) showed similar superstructure flotation across all size classes, suggesting that mildly alkaline conditions did not cause significant surface passivation on Mono Po and thus did not hinder xanthate collector uptake by either superstructure, yielding similar floatabilities. This combination of DETA (150g/t) and SMBS (300g/t) was found to be very effective at depressing both superstructures for an ore containing 28% pyrrhotite (42% of which was Hex Po), especially in the intermediate and coarse size classes (>30m). After DETA/SMBS conditioning, both Mono Po and Hex Po recoverybysize was identical, flotation was largely observed in the fine fraction (<10m) regarded as weakly floatable Po. The major factors that caused measurable differences in the superstructure flotation responses: alkaline conditions (pH>9); presence of activating ions (e.g. Cu2+ and Ni2+) and superstructure reactivity towards oxygen.