Flotation Machines 2013

Flotation Machines

Mechanical flotation machines have experienced

of cell capacity (unit cell size).

Decade Largest Size

cu. ft. cu. m.

1940s 20 0.6

1950s 50 1.4

1960s 100 2.8

1970s 300 8.5

1980s 500 13.6

1990s 2,000 54.5

2000s 4,000 100

2010s 12,000 300

2020s (est.) 24,000 600

Mechanical cells operate horizontally with 4 or 6 tanks combined together as a single bank. Each cell

has its own impellor and the adjacent

Rougher banks are raised slightly above the scavenger banks to permit independent cell level control

and feed the scavenger bank through a control valve. Launders are hung on both sides o

collect concentrate and allow it to be pumped to the next stage (cleaners, recleaners, regrind circuit, or

back to the feed).

Over the years there have been many different flotation cell manufacturers

Wemco-Fagergren, Dorr-Oliver, Outokumpu, Sala,

unique impellor design.

Different Mechanical Flotation Cell Impellors.

ion machines have experienced considerable change over the past 60 years in terms


has its own impellor and the adjacent tanks are open allowing by-passing (short-circuiting) and recycling.


and feed the scavenger bank through a control valve. Launders are hung on both sides o


Over the years there have been many different flotation cell manufacturers – (Denver, Agitair,

Oliver, Outokumpu, Sala, Wedag, Booth, etc.) each of which has their own

Different Mechanical Flotation Cell Impellors.

st 60 years in terms


circuiting) and recycling.


and feed the scavenger bank through a control valve. Launders are hung on both sides of the tanks to


(Denver, Agitair,

each of which has their own

Different Mechanical

Outotec's TankCell® innovation has

that decade, most mechanical machines were rectangular or square in cross

such machines were open-flow meaning there was significant by

adjacent cells. The Tank Cell concept examined

the unit cell volume significantly. Each individual cell was separated allowing accurate down

sampling of internal tailings and concentrate samples.

control valve. The tanks in series must be lowered by a meter of so as one proceeds down the bank.

Outotec's TankCell

Cylindrical tanks appear to offer considerable advantages over

2

Mechanical Flotation Cell Shapes or Configurations.

has revolutionized flotation machines since the early 1990s. Prior to

that decade, most mechanical machines were rectangular or square in cross-sectional area and b

flow meaning there was significant by-passing and short-circuiting between

e Tank Cell concept examined fluid-dynamics flow conditions in each cell and increased

the unit cell volume significantly. Each individual cell was separated allowing accurate down

rnal tailings and concentrate samples. Each individual cell feeds the next cell through a


Air Dispersion

Outotec's TankCell

offer considerable advantages over rectangular ones. These include

the early 1990s. Prior to

sectional area and banks of

circuiting between

dynamics flow conditions in each cell and increased

the unit cell volume significantly. Each individual cell was separated allowing accurate down-the-bank

feeds the next cell through a


Air Dispersion

. These include:

3

- Lower cost to manufacture (cells can be custom-designed)

- Easier to control

- Lower energy to maintain the pulp in suspension and distribute air

- Significant improvements in hydrodynamics (reduced dead space)

- Reduced floor space per unit volume

The evolution of the TankCell® follows the development of a number of innovations that include the

Column cell (1964), the DAVCRA cell (1965), the Flash Flotation cell (1988), the Jameson cell (1990).

These cells reduce floor space per unit volume and permit installation of flotation within the grinding

circuit to recover final grade concentrate particles at coarser sizes than would normally be met in a

conventional flotation circuit.

Outotec's Flash Flotation Cell

Flash Flotation Installation and Control System.

4

Flotation Cell Selection

The selection of the size, number and type of flotation cells for a particular application depends on

two important factors:

- required flotation residence time; and

- dry solids recovery rate for a given:

- froth surface area (t/hr/m2), and

- concentrate lip length (t/hr/m).

Residence time is influenced by ore type - mineralogy, associations, liberation, kinetics, and reagent

additions (collector and frother). In terms of the amount of concentrate to be recovered, selection also

depends on ore type and characteristics such as particle size, specific gravity, water recovery, and

mineral grade. The stage of flotation is important. The rougher stage recovers 10% to 20% of the solids

in the feed while scavengers recover 5% to 15% while the cleaner mass recovery can approach 80%.

Lab-scale tests and scale-up factors determine the residence time required in the plant.

However, the froth carry-over flow rate (dry concentrate per froth surface area per hour, t/m2/hr) and

lip loading rate (dry concentrate per froth lip length per hour, 1.5 t/m/hr minimum and maximum) are

difficult to scale-up from the lab because the froth is continuously scraped-off during a lab test and the

type of process is batch rather than continuous flow through. So these values are determined via

calculation to give ranges that should not be exceeded by cell size selection and layout. With cleaner

cells where a high percentage of the solids are recovered into the froth phase, carry-over flow rate and

lip loading rate are much more important than residence time.

Application Rougher Scavenger Cleaner

Carry-over rate (t/hr/m2) 0.8 - 1.5 0.3 - 0.8 1.0-2.0

In most cases, a quick estimate of these carry-over constraints can be obtained by limiting the

residence time in any single cell to approximately 1.0 minutes. If the calculated value lies between 0.75

to 1.25 minutes, the circuit should perform well. However, should the design fall outside these ranges,

then one should perform a detailed calculation of carry-over rate per surface area and lip length.

If the residence time requirement is met with a certain cell size selection but froth carry-over rate

and/or froth lip loading rate are exceeded, one must increase the number of flotation cells (i.e., select a

smaller size cell) to increase the surface area or concentrate lip length. Unfortunately this solution can

add to capital costs as well as floor space and operating and maintenance (O&M) costs.

Outotec have recently customising the launder configuration to increase froth surface area and lip

length without increasing the number of cells, by designing several configurations for the TankCell®.

Different launder designs give a customized solution for each application and site. Launders can be

customized, even on retrofits, to improve recovery and save on operating costs. The correct froth

crowding characteristics will reduce air requirements as well according to Outotec.

Launder Configurations

- Central donut launder

- Internal launders

- External launders (smaller cells < 50 m3)

- Radial launders

5

Froth Depth / Pulp Level

Froth depth is also an important factor to achieve good quality/quantity trade-off. Generally the

roughers are controlled to a froth depth between 15 to 30 cm, while the scavengers will range between

5 to 10 cm. Cleaner cells will generally be operated with the highest froth depth possible - perhaps as

much as 200 cm, and on some column (or vertically configured) cells, froth depths as much as 1.2 m

have been observed. At these depths, wash water onto the froth phase is generally required to sustain

the froth. If the flow rate of concentrate becomes very low (changes in mineralogy or ore tonnage), then

the froth may require reagent changes (amounts and type) to be sustainable.

Example of Sizing a Flotation Circuit:

Design for 100,000 tpd of ore @ S.G. 3.0 and 40% solids

Calculate the volumetric flow rate of pulp into the cell:

Solids volumetric flow rate = (100,000/3.0)/(24*60) = 23.15 m3/min

Water volumetric flow rate = (100,000/1.0)*(0.6/0.4)/(24*60) = 104.17 m3/min

So the total volumetric flow rate = Q = 127.32 m3/min

From lab testwork, the scaled-up required flotation time = 12 minutes

So, the total required plant volume = V = 127.32 * 12 = 1,527.84 m3

Adjust for impellor, air hold-up, and froth phase = V * 1.2 = 1,833.4 m3

--------------------------------------------------

Try a unit cell size of 25 m3

Total number of cells required = 1,833.4 / 25 = 73.3 cells

Number of parallel banks required to

achieve 1 min residence time per cell = 127.32 * 1 min * 1.2 / 25 = 6.11 banks

For 6 banks: residence time / cell = 6 * 25 / (127.32 * 1.2) = 0.98 minutes (excellent)

Design: 6 banks of 12 cells = 72 * 25 = total volume of 1,800 m3

to give a total residence time of 11.8 minutes

---------------------------------------------------






Design: 3 banks of 12 cells = 36 * 50 = total volume of 1,800 m3


---------------------------------------------------

6

-------------------------------------------------------






Design: 2 banks of 12 cells = total volume of 1,800 m3


-------------------------------------------------------





For 1 bank: residence time / cell = 1 * 100 / (127.32 * 1.2) = 0.655 minutes (too fast)

Try 2 banks = 2 * 100 / (127.32 * 1.2) = 1.31 minutes (too slow)



-------------------------------------------------------





For 1 bank: residence time / cell = 1 * 150 / (127.32 * 1.2) = 0.98 minutes (excellent)



------------------------------------------------------


Total number of cells required = 1833.4 / 200 = 9.2 cells



For 1 bank: residence time / cell = 1 * 200 / (127.32 * 1.2) = 1.31 minutes (too slow)

Design: 1 bank of 10 cells = total volume of 2,000 m3


-----------------------------------------------------

7

-----------------------------------------------------





For 1 bank: residence time / cell = 1 * 250 / (127.32 * 1.2) = 1.64 minutes (very slow)



---------------------------------------------------

Finally, try the largest capacity unit cell size - Outotec's 300 m3 cell

Total number of cells required = 1833.4 / 300 = 6.1 cells



So a single bank will give a residence time / cell = 1 * 300 / 127.32 * 1.2 = 1.96 minutes (really slow)



-----------------------------------------------------

So there are several possible answers (there may be others):

The most flexible design is for a cell size of 25 m3 - 6 banks of 12 cells per bank

It gives the highest operating flexibility, but will use more energy and have increased maintenance costs.

If one bank must be shut down for maintenance, 83% of the plant capacity is still available.

The least expensive design is a cell size of 300 m3, however, the mill will have no flexibility and the cells

will be operating very slowly which will lead to level control problems.

Summary

Cell Residence Number Number Total Total

Size Time/Cell of of Cells Volume Residence

(m3) (min.) Banks per bank (m

3) Time (min.)

25 0.98 6 12 1,800 11.8

50 0.98 3 12 1,800 11.8

75 0.98 2 12 1,800 11.8

100 1.31 XX 2 9 1,800 11.8

150 0.98 1 12 1,800 11.8

200 1.31 XX 1 9 2,000 13.1

250 1.64 XX 1 8 2,000 13.1

300 1.96 XX 1 6 1,800 11.8

Probably the best trade-off between capital costs and operating flexibility would be the 75 m3 design.

8

Estimated Capital Costs

Capital cost of flotation equipment like most mining equipment scales up according to its capacity using

an exponent of 0.6. So the cost of a 300 m3 cell will be about 4.4 times that of a 25 m3 cell, yet will give

12 times the volume.

��

��= ��

��.�

= 4.44

But in our example, there are only six 300 m3 cells required compared to seventy-two 25 m

3 cells.

So the relative total capital costs of the two solutions will be

��300��25� = 4.44 ∗

6

72∗ 100 = 37%

For the different examples calculations, the following relative capital costs are obtained:

Cell Total Relative Total Relative

Size Number Unit Cell Cost Capital

(m3) of cells Cap. Cost Costs (%)

25 72 1.00 72.0 100

50 36 1.52 54.7 76

>>>>>> 75 24 1.93 46.3 64 <<<<<<

100 18 2.30 41.4 58

150 12 2.93 35.2 49

200 9 3.48 31.3 43

250 8 3.98 31.8 44

300 6 4.44 26.6 37

If the lip length and froth surface area constraints can be met with innovative launder design, then

perhaps 2 banks of six 150 m3 cells might be acceptable which would reduce the capital costs by over

50%.

Documents

Flotation Machines 2013