Coarse Particle Flotation: impact ontailings management systemsJuan Francisco Schwarze, Rodrigo Kong and Pablo Vargas

Agenda• Introduction• Brief overview• Impact of CPF process• Flocculation• Thickening• Sand dam building• Water reclaim• Conclusion

Introduction• Froth flotation has been the standard process for getting the value of copper

sulphides.

• Flotation has two main requirements: water and grinding to liberate commercial species.

• Flotation is effective in a narrow range of particle sizes (38 a 250 µm).

• Smaller particles are lost because the probability of bubble-ore collision and retention drops.

• Bigger particles are lost because ore can be occluded, or a small part it can be exposed.

• The solid particle weight could be greater than the bubble pushing force.

Introduction• There is no technological proven solution to get a small range size after the

grinding process.

• After the normal flotation, the obvious temptation is to recover the value of the tailings.

• It must be noticed that coarse ore particle recovery implies the grinding of them to liberate ore and to get a commercial-grade product.

• It could impact on some downstream process as thickening, sand dam building, and tails depositing.

• This potential impact is presented in this paper.

Brief overview• As we know, It is not possible to get the complete recovery in the flotation process

and the recovery of coarse particles open an opportunity.

• The recovery of copper from Salvador’s tailings was important because of the impact in the locals between 50´s and 80´s.

• The same concept was applied by Chuquicamata and El Teniente, where cascade flotation scalping occurs in a sequence of concrete launders.

• El Teniente’s facility is operated by Valle Central. The collected particles are grinded before to be fed to flotation circuit that include rougher and cleaner stages.

• Other example is Mantos Blancos which classify the rougher flotation tails and derives the coarse fraction to the regrind stage (Huls 2006).

Brief overview

Río Salado facilities,Chañaral, Chile (W.Griem 1990)

Brief overview

Valle Central,Chile

Brief overview• One of the most recent technological innovations is the pneumatically assisted

fluidized bed flotation, represented by Hydrofloat™ cells.

• It has been successful in coarse particle recovery because of the contact bubble-coarse particle occurs in the middle of an air bubble fluidized bed, the diminished turbulence allows the coarse particles to rise, and multiple bubbles can support the particle.

• This technology requires a deslimed slurry to be effective, so a previous granulometric segregation is mandatory.

Brief overviewFeed slurry

Concentrate

Tails

Flotation air

Teeter water

Teeter bed

Rise rate

Eriez Hydrofloattm flotation cell

Source: Eriez

Impact of CPF process

Rougher Flotation

Regrinding + Cleaner Flotation

Size

C

lass

if.

CPF

Ore from Grinding

Final Product

Tailings Facility

Grinding

Product

Tails

Fine Fraction

Typical diagram of the CPF process:

Source: Arcadis

Impact of CPF processAs it was mentioned previously, the CPF could impact on the following tailings operations:

• Thickening and the flocculant performance

• Sand dam building

• Water reclaim impact

Flocculation• It is known that flocculation is more efficient under the presence of coarse

particles, where flocculant molecules can fasten and then catch fine particles easier.

• In addition, the presence of finer particles increases flocculant consumption.

Thickening• The particle size affects the thickening process.

• Coarse particles have a higher sedimentation speed than fine particles. This can be described with the Stokes Law.

• The drag coefficient is higher over finer particles than coarser particles.

Particle size (R)

Terminal velocity(ut)

Particle size (R)

Drag coefficient (CD)

• The coarse particles vanishing due to a CPF process implies a lesser terminal velocity and a higher drag coefficient in thickeners, reducing the solid percentage in the underflow.

Thickening

Full tails sedimentation

Slime sedimentation

Source: Arcadis

Sand dam building• A sand dam operation includes a classification stage, where coarse particles are

segregated and used to build the dam or wall.

• One of the most relevant conditions is the effective control of fine particles (under 75 µm).

• Another requirement is the number of coarse particles available to build the dam. It depends on the definition of the grinding product.

• For some specific projects the availability of sand is not enough for the dam realization. There are a few projects where the recovery was sacrificed in order to ensure the dam. In others, the dam should be designed based on a mix of sand and borrowed material.

Sand dam building• A client asked Arcadis to study for their impact on the tailings design if they

implement a CPF process to improve their copper recovery.

• The table shows that the classification operation time is increased by a CPF implementation.

Scenario Períod Tails (t/d)

Coarse

particles in

tails (t/d)

Coarse

particles to

dam (t/d)

Run time

(%)

Without

CPF

1 124.509 33.443 22.032 65,9

2 124.509 33.443 23.256 69,5

3 124.509 33.443 24.643 73,7

With CPF

1 124.399 29.292 22.032 75,2

2 124.399 29.292 23.256 79,4

3 124.399 29.292 24.643 84,1 Source: Arcadis

Water reclaim• Arcadis has given support to many clients, allowing it to build a strong database.

Based on it, it has developed a model of the water balance of any tailing facility.

• According to this model, water losses are due to evaporation (~30%), infiltration into the soil and resaturation (~10%), and retention (~60%) (Loyola 2020).

• The concept of retention is related to how much water is trapped by the consolidated solid particles, and it is proportional to the void ratio.

Water reclaim• In a CPF process about 10 to 15% of the coarse particles are missed.

• This results in a finer granulometric distribution that implies an increment in the retention according to Arcadis experience (Troncoso 2018).

• Applying these concepts to the referred client, an increment in water losses of about 0,5% can be estimated.

• Implementing a CPF process would impact water reclaiming negatively because it affects the most important component of water losses.

Water reclaim

1%

6%

11%

16%

21%

26%

31%

36%

41%

5% 15% 25% 35% 45% 55% 65% 75% 85%

Gra

vim

etri

c R

esid

ual

Mo

istu

re w

(%

)

-74 µm fraction (%)

Increment in the waterretention because offine particles content

Source: Arcadis

Conclusion• Mining process engineers have always wanted to get more from the ore, and the

opportunity to increment the production via the recovery of coarse particle values allures them. But it must not forget side B of this option.

• There are some risks, among others, related to the thickener operation, the build of the deposit dam, and the availability of recycled water for the process.

• The authors’ recommendation is to evaluate and balance the pros and contras of the CPF implementation, including the impact on downstream facilities.