Froth Flotation (Sulphide & Oxide)

Froth Flotation (Sulphide & Oxide) 2017-04-04T06:57:31+00:00
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Undesired Fines/Ultra-fines at Tank Flotation (13 replies)

Zander Barcalow
2 years ago
Zander Barcalow 2 years ago

We are running Outotec 50 m3 Tank Cells followed by Wemco Cells (8 m3), in Tanks we just float fines/ultra-fines even gangue, but in Wemco it is desired flotation, is there any idea what is going on? The point is our feed slurry is pumped directly from Conditioners to Tank Cells as Rougher stage and the Tailing of Rougher is transferred to Wemco (8 m3) as Scavenger stage.

At Rougher we just have maximum 10% recovery since just fines and ultra-fines are floated containing a lot of gangue particles. On the other hand, we have high grade and high recovery at Scavenger cells which is not usual in other circuits.

The Tank mechanical parameters are set up already by Outotec in Manufacture, do you mean we must reset up again?

Our foams from Tank Cells are very weak and low weight, apparently nothing inside. If we increase the frother, more gangues will be floated, if we increase air, more turbulence tends to overflow the slurry.

Dizzy Flores
2 years ago
Dizzy Flores 2 years ago

If I understand Abbas's comment he is saying he gets different performance out of the OK tank cells and his Wemco's. This could have something to do with the setup of the cells, amount of agitation and air volumes in the cells, the list is endless.

Carmen Ibanz
2 years ago
Carmen Ibanz 2 years ago

Can you advise what the size and retention time is for the OK cells and the WEMCO cells.

My first guess would be that your OK cells are acting as conditioners, and it is not about specific cell performance. I am assuming that your OK cells are in good condition, level control good etc.

What is your mineralogy and what is the typical response in the Laboratory. What conditioning time is required?

Where is your primary collector being added, at the conditioner or earlier?

I have often seen in operating plants the first cell in a row of 5-7 cells acting as a conditioner and true flotation really starting to occur in the second cell.

Zander Barcalow
2 years ago
Zander Barcalow 2 years ago

The Size distribution is 80% below 200 mesh by considerable amount of fines/ultra-fines even inside the feed ore at mine. Your assumptions about the Tank Cells regarding mechanical performance and instrumentation/control is true. The residence time for each tank (50 m3) is about 4.5 min and we have 3 rows in parallel each consisting 6 tanks in series (18 total). We can estimate about 25 min Rougher time in total depending to variation of feed tonnage. For Wemco Cells, we have 1 min residence time for each cell (8 m3) and we have 14 cells in series within each of 4 parallel rows.

The minerals are consisting mainly Oxide Copper minerals (Malachite/Pseudo-Malachite) by low amount of non-oxidized sulfide. Unlike Oxide minerals, all sulfides are floated in Tanks.

Before Tanks we have 3 Conditioners (150 m3) in series, we are adding Collector in First conditioner and the Sulfidiser (NaSH) and frother in second and last conditioner.

My primary idea is since we have weak layer of Hydrosulfide/Sulfide on copper oxide particles, because of high turbulence inside the tank, the collector could not catch the temporarily adsorbed layer before the layer disappeared, or likely due to height of Tanks, the foam cannot collect and float coarser particles whereas fines/ultra-fines could be floated easily, it means some issues with gravity forces.

Ace Levy
2 years ago
Ace Levy 2 years ago

I have seen a similar occurrence in a lab flotation test for phosphate ore where the fines/ultra-fines floated rapidly and then the coarser material had to be picked up in the scavengers. The diagnosis was that the fines/ultra-fines were preferentially consuming the collector. We could add extra reagent to the rougher and recover the coarser materials....maybe the analogy holds true for your sulphide float.

Secondly, are your coarse particles too big for the depth of the flotation cell, again relating this back to phosphates and the use of shallow flotation cells to minimise the distance the coarse particles have to travel to the lip of the flotation cell.

Carl Jenkins
2 years ago
Carl Jenkins 2 years ago

If I understand your posts correctly, you are doing what is commonly referred to as BULK flotation. In bulk flotation, both sulphides and oxides are floated together. In Zambia we found that DIFFERENTIAL sulphide followed by oxide flotation was better than bulk flotation. Chrysocolla is very difficult to float even with NaHS. Other thing I notice is your sequence of adding NaHS followed by a collector, which I suppose is a Xanthate, is WRONG. The idea is you add NaHS to alter the oxides' surface to sulphide 'like' so that it becomes amenable to collection by xanthates. You should, therefore, be adding NaHS first, condition it for 5 minutes AT LEAST and then add collector. If you do that, may be your flotation in tank cells will improve. BTW what is your dosage for NaHS?

Jean Rasczak
2 years ago
Jean Rasczak 2 years ago

Both rougher and scavenger should have high recovery. Grade of scavengers should be controlled to be roughly equal to the rougher feed grade. You have both high grade and high recovery and this is quite strange to me. For any stage of flotation high grade comes with poor recovery. High recovery will yield low grade concentrate.

I suspect that you have a problem with the sequence of reagent addition. And also, the conditioning time might not be long enough so that the rougher stage behaves like a conditioner like. I recommend you rearrange the sequence of reagent addition (since sulfidizer must come prior to collector addition). Longer conditioning time may be needed to improve the flotation. Do not try to make good grade from the rougher stage. Higher grade has to be achieved using cleaners and recleaners.

1. I suspect that you will have a problem of reagent consumption. Fines and ultrafine particles will have very large surface area. Thus it requires more reagent addition than normal. I suggest you go back to adjust your milling or comminution steps. You may adjust by reducing the residence time in the mill (SAG or ball mill). By this you will get less amount of overgrinding. Please keep in mind that the recirculating materials back to the mill will be increased also.

3. If there is not much improvement, you may have to do coarse grind and coarse flotation and apply regrinding of the rougher concentrate before cleaning stage.

Zander Barcalow
2 years ago
Zander Barcalow 2 years ago

According to what we have experienced in old Wemco Cells, the NaSH addition (24% concentration) and conditioning must be quickly followed by Flotation, otherwise the temporary adsorbed layer of sulfide on Oxide will be disappeared due to high turbulence inside the Machine and reaction of NaSH with Oxygen and its quick neutralization.

The best solution was to have collector in all cells primarily (mainly added in Conditioner) and just add NaSH partially in each cell to perform flotation cell by cell and stage by stage. Indeed, the NaSH which is added to the conditioner is not existing after second or third cell!

If we bypass the Tank cells and transfer the slurry from conditioner to Wemco cells, there will not be any problem! All fine/coarse minerals will be floated by normal grade.

But the problem has arisen since we planned to increase our recovery/production by Tank Cells, those tanks just float fines/ultra-fines.

About the Sulfides, we have a Pre-flotation stage before Oxide Conditioning and small amount of sulfide is coming to Oxide just if we have low performance there.

Regarding high consumption of reagents, that's is really happening here now. Even we increased the dosage of all reagents, but in Tanks we have just fines/ultra-fines. However, if we pump exactly this slurry to Wemco Cells, we will get both coarse and fine minerals.

I also have to mention that the source of fines/ultra-fines here is from mine and oxidized zones which were under high alteration during millions of years. The suggestion was to add some Dispersant inside the mills (AG+Ball) to discharge the fines without over-grinding.

Sugar Watkins
2 years ago
Sugar Watkins 2 years ago

If correctly sulphidized, oxides, esp Malachite floats readily as my experience shows. You haven't indicated NaHS dosage and NaHS conditioning time. If the problem is with fines and ultra-fines from ROM itself, then you will have to go for a washing circuit in the crushing and screening stage so that your mill feed is devoid of primary fines. Removing primary fines will also reduce your reagent consumption as the fines unduly consume large proportion of reagents due to high surface areas. From what you are saying, the Tank cells are not performing as envisaged and that should worry you a lot. You may require longer conditioning time for NaHS. Do a few lab tests at different conditioning times to know optimum time.

Marshal Dienes
2 years ago
Marshal Dienes 2 years ago

The recovery of fine particles is negatively affected by the turbulence inside of reactor. The lower weight of them can introduces difficulties to be collected by the bubbles and it are lost by hydrodynamic of fluids. Other point is the cavitation of bubbles closely of impeller.

You can try use of oil to aggregation of fine particles to best recovery and after you can use of other stage to clean it with specific cells such as Jameson cells or columns.

Marshal Meru
2 years ago
Marshal Meru 2 years ago

Mineralogy from the rougher stage concentrate may need to be checked to enable visualisation of whether concentrate from rougher stage is coming from real flotation or its suspended gangue given the agitation and viscosity of the pulp including pulp density? Was surprised in one plant whereby the finer you grind the more gangue you float. PSD? The ore mineralogy can be such that there may be need do initially float the gangue first after the conditioning stage and discard it off? Few lab trials with different reagent suit in between rougher stage and scavenger? Not an expert but learning.

Bill Rico
2 years ago
Bill Rico 2 years ago

The OK cells have much higher shear forces and turbulence in the collection zone than WEMCO cells. Normally this is a positive attribute of OK cells when floating fine ore, however, given your comments about how fragile the NaHS attachment is, it may be scrubbing off the NaHS. Is it possible to reduce the tip speed of the agitator, or are you at the minimum already?

Jean Rasczak
2 years ago
Jean Rasczak 2 years ago

You still haven't indicated how much NaHS you use. Over addition of NaHS can lead to the symptoms you have mentioned. Do you have instruments to measure the redox potential for flotation feed? You urgently need to optimize NaHS addition.

Ace Levy
2 years ago
Ace Levy 2 years ago

I think you need to be aware about the froth carry rate limit so that could be easier to understand the stability of the froth. Also the type of the reagents employed such as collector type, frother, activator and the running pH of the slurry with proper conditioning time. However, the air flow rate which will carry the bubbles is also an important factor to be aware as well as the temperature. If possible you can do the lab teat regrinding the collector dosage and investigate other floatability factors in details.

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