AMIT 145: Lesson 5 Froth Flotation

Froth flotation is a physico-chemical separation process.

Separation is principally based on differences in surface hydrophobicity.

However, particle size and density have a significant impact.

Initial flotation patent and application was developed for graphite by the Bessel brothers (1877).

Similar to graphite, coal is naturally hydrophobic.

A microscopic image of flotation of particles
Microscopic flotation
[image 145-5-1]

Conventional Flotation

  • First developed in 1912.
  • Employed throughout the 20th century.
  • Low capital cost.
  • Due to mixing, several cells are used in series.
  • Hydraulic entrainment has always caused a battle between grade and recovery.
  • 10 tph/cell capacity
An example of froth flotation
Conventional flotation
[image 145-5-2]
Flotation diagram
Flotation diagram
[image 145-5-3]
Flotation cell diagram
Flotation Cell Diagram
[image 145-5-4]

Conventional Cell Development

Current emphasis is the development and optimization of large cells.

Power scale-up and froth recovery are issues.

Also, reduced number of units places an emphasis on ensuring high efficiency from each cell.

A common cell size in the coal industry is 28 m3.

Flotationi Cell Development Graph
Flotation Cell Development Graph
[image 145-5-5]

Flotation Columns

  • Initial column was invented in 1907.
  • Commercial development was minimal until the 1980’s due to sanding of particles in the bottom of the cell.
  • The ability to use wash water to remove entrainment revived the interest in flotation columns.
  • L/D ratio is also significant for ultrafine particles.
  • The coal industry is shifting to larger columns, up to 4.5m diameter and greater.
  • Types: CoalPro, Microcel, Jameson.
Flotation column diagram
Flotation Column
[image 145-5-6]

CoalPro (CPT) Flotation Column

  • Developed by Cominco Research and owned by Eriez Manufacturing
  • Coarse Bubble Size Distribution
  • Good Dispersion w/Sparger Water
  • High Aeration Rates
  • Low Energy Input
  • Typically Use for Deslime Circuit
Coal Pro (CPT) Flotation Column
Coal Pro (CPT) Flotation Column
[image 145-5-7]
Coal Pro 2
Coal Pro 2
[image 145-5-8]

CPT Bubble Generation System

A diagram of SlamJet Bubble Generation Technology
Slam Jet Bubble Generation Technology
[image 145-5-9]

CPT Flotation Column

CPT Flotation Column
CPT Flotation Column
[image 145-5-10]

Microcel Column Flotation Technology

  • Developed by Virginia Tech in the late 1980’s.
  • Licensed by Eriez Manufacturing.
  • Reduced Bubble Size
  • Tight Bubble Size Distribution
  • Increased Capacity
  • Additional Pump
  • Higher Energy Input
  • Typically Use for By- Zero Circuit
Microcel Column Flotation Technology
Microcel Column Flotation Technology
[image 145-5-11]

Microcel Bubble Generation

A diagram of Microcel Bubble Generation
Microcel Bubble Generation
[image 145-5-12]

Installation

Photos of an installation
Microcel Installation
[image 145-5-13]

Column Installation

Column Installation
Column Installation
[image 145-5-14]

Jameson Cell

  • Developed by Dr. Graeme Jameson and owned by MIM Ltd.
  • Self-aspirating system with froth washing.
A diagram of a Jameson Cell
Jameson Cell
[image 145-5-15a]
A photo of a Jameson cell
A Jameson Cell
[145-5-15b]

Flotation Recovery Fundamentals

A flotation process has two distinctly different phases:

  1. Collection Zone
  2. Froth Zone

Both the collation zone (RC) and froth zone (RF) recoveries determine the overall recovery.

Using linear analysis, the overall recovery (R) can be determined:

R = \frac{R_{C}R_{F}}{R_{C}R_{F} + 1 - R_{C}}

Flotation recovery diagram
Flotation Recovery
[image 145-5-16]

Collection Zone Recovery Parameters

A diagram of Collection Zone Recovery
Collection Zone Recovery
[image 145-5-17]

Collection Zone Recovery, RC

The recovery of a given component in the feed is a function of:

  • Flotation Rate, ki
  • Particle Residence Time, Tp
  • Hydrodynamic Conditions

Using Levenspiel’s axial mixing equation, collection zone recovery can be determined by

R_{C} = 1 - \frac{4\mathit{a} exp(0.5 Pe)}{(1 + a)^{2} exp(0.5 \mathit{a} \mathit{Pe}) - (1-\mathit{a})^{2} exp(-0.5\mathit{a} \mathit{Pe})}

a = \left ( 1+\frac{4k\tau _{P}}{Pe} \right )^{0.5}    Pe=\left ( \frac{L}{D} \right )^{0.53}\left ( \frac{V_{t}}{\left ( 1-\varepsilon \right )V_{g}} \right )^{0.35}  Mankosa et al. (1992)

Pe → 0, Perfectly mixed conditions → R_{c} = \frac{k\tau _{p}}{1+k\tau _{p}}

Pe → ∞, Plug – flow conditions → R_{c} = 1-exp(-k\tau _{p})

Flotation Rate, ki

The flotation rate is a measurement of how fast a particle is recovered in the collection zone.

The flotation rate of a given component can be quantified by:

k = \frac{3Vg}{2Db}P = \frac{1}{4} SbP

P = probability of flotation int he collection zone;

Vg = superficial gas velocity;

Db = bubble diameter;

Sb = superficial bubble surface area rate

A diagram of floatation
Flotation Rate
[image 145-5-18]

Probability of Flotation

The probability of flotation is a stochastic function of three sub-processes that occur in the collection zone:

  • Probability of Collision, PC
  • Probability of Attachment, PA
  • Probability of Detachment, PD

P = PCPA(1-PD)

For bubble sizes typical in flotation:

PC = (\frac{D}{P})^{2} \left [ \frac{3}{2} + \frac{4Re^{0.72}}{15} \right]

Controls the lower particle size limit associated with the flotation of a given particle type.

A diagram describing the probability of flotation
Probability of flotation
[image 145-5-19]

Collection Zone Recovery Parameters

A diagram highlighting collection zone recovery parameters
Collection Zone Recovery Parameters
[image 145-5-20]

Flotation Rate Differential Effect

A chart depicting an increasing air rate in flotation rate differential
Flotation Rate Differential Effect
[image 145-5-21a]
\frac{\partial m}{\partial t} = - kM

= mass floated per unit of time

k = flotation rate (min-1)

t = flotation time (min)

M = mass flotation cell

SpeciesNo CollectorCollector
1k = 1.0R = 68%K = 2.0R = 80%
2k = 0.25R = 33%k = 1.0R = 68%

Typical Flotation Residence Times

MaterialTypical solids concentration for roughing applications, percentTypical residence times for roughing applications, minutesTypical laboratory flotation times, minutes
Copper32-4213-166-8
Lead25-356-83-5
Molybdenum35-4514-206-7
Nickel28-3210-146-7
Tungsten25-328-125-6
Zinc25-328-125-6
Barite30-408-104-5
Coal4-83-52-3
Feldspar25-358-103-4
Flourspar25-358-104-5
Phosphate30-354-62-3
Potash25-354-62-3
Sand (Impurity Float)30-407-93-4
Silica (Iron Ore)40-508-103-5
Silica (Phosphate)30-354-62-3
EffluentsAs received7-124-5
OilAs received4-62-3
A diagram of Recovery Zone Parameters
Recovery Zone Parameters
[image 145-5-22]

Froth Recovery, RF

Recovery through the froth phase can be achieved as a result of one of the following:

  • Bubble-Particle Attachment
  • Particle Entrapment
  • Hydraulic Entrainment
A diagram of froth recovery
Froth Recovery
[image 145-5-23]

Flotation Carrying Capacity

Feed Size (Micron) Target Capacity (tph/m2)
Minus 600

Minus 150

Minus 45

150 x 45

1.8-2.6

1.0-1.4

0.6-0.9

1.8-2.2

Example:

3m diameter column

CC = 1.2 tph/m2

Froth = 1.2 x Area

= 1.2 x 7.065 m2

= 8,5 tph

A photo of a flotation vat
Flotation Carrying Capacity
[145-5-24a]

Froth Washing Fundamentals

Selectivity in a flotation process is typically achieved on the basis of differences in surface hydrophobicity.

However, selectivity is based on all recovery mechanisms as well as hydrodynamic conditions.

Selectivity can be enhanced by:

  • Maximizing flotation rate differences.
  • Eliminating or Minimizing Entrainment.
  • Selective Detachment.
  • High length-to-diameter ratios.
Froth washing images
Froth Washing Fundamentals
[image 145-5-25]

Hydraulic Entrainment

A diagram of hydraulic entrainment
Hydraulic Entrainment
[image 145-5-26]

Froth Washing; The Original Flotation Column Benefit

A disagram showing machanical versus column flotation
Froth Washing: Original Flotation Column Benefit
[image 145-5-27]

Pan-Type Froth Wash Water System

An image of pan-type froth wash water
Pan-type Froth Was Water
[image 145-5-28]

Wash Water Ring System

An image of a wash water ring
Wash Water Ring
[image 145-5-29]
An image of a wash water ring
Wash Water Ring
[image 145-5-30]

Entrainment Effect on Separation Performance

A chart showing entrainment Effect on separation performance
Entrainment Effect on Separation performance
[image 145-5-31]
A photo of a separator column
Entrainment Effect on Separation Performance
[image 145-5-32]

Typical Flotation Cell Dimensions

Trade NameLength
(m)
Width
(m)
Depth
(m)
Pulp Volume
(m3)
Denver 1001.521.521.222.8
Denver 2001.831.831.595.7
Denver 3002.102.101.898.5
Denver 4002.302.302.1211.3
Denver5002.702.701.9814.2
Wemco 441.121.120.510.57
Wemco 661.521.680.691.7
Wemco 841.602.131.354.2
Wemco 1202.293.051.358.5
Wemco 1442.743.661.6014.2
Wemco 1643.024.172.3628.3

Wemco Convention & Outotec Tank Cells

A table of Flotation Cell Engineering Data
Flotation Cell Engineering Data
[image 145-5-33]

Outotec Tank Cells

ModelCell Volume (m3)Diameter (m)Lip Length (m)Froth Area (2)Air Flow (m3)Motor (kW)
TankCell-552.04.73.02.811
TankCell-10102.56.34.74.318.5
TankCell-20203.17.97.16.737
TankCell-30303.69.49.79.045
TankCell-40403.810.010.610.055
TankCell-50504.712.716.515.0110
TankCell-70705.314.121.319.0110
TankCell-1001003.016.327.525.0132
TankCell-1301306.417.631.028.0160
TankCell-1601606.819.035.232.0185
TankCell-2002007.220.140.036.0250
TankCell-3003008.022.049.045.0300
An image and diagram of an Outotec
Outotec Tank Cells
[image 145-5-34]
A diagram of cell to cell tanks
Internal dart valve used to control the tailings flow rate from cell-to-cell. [image 145-5-35]
Data table of Outokumpu Svedala Flotation Cells
Outokumpu Svedala Flotation Cells
[image 145-5-36]
A table of Flotation Cell Engineering Data
Flotation Cell Engineering Data
[image 145-5-33]
A table of Dorr-Oliver Square and Round Cells
Dorr-Oliver Square and Round Cells
[image 145-5-37]

Flotation Circuits

Flotation circuits are typically comprised of rougher, scavenger and cleaner flotation banks.

Rougher and scavenger banks are focused on recovery and thus provide maximum residence time.

Rougher banks can be large with the number of cells being 5 or greater.

Scavenger cells are the last line of defense for avoiding losses. Therefore, they are generally larger in size and numbers.

Cleaner banks are focused on product grade and thus provide low residence time. As such, the number of cells are lower and the cells smaller.

Column flotation is sometimes used as cleaners.

A diagram of a flotation circuit
Recycle streams are important to maximize selectivity and thus efficiency.
[145-5-38]

Rougher-Scavenger-Cleaner Effect

Rougher-Scavenger-Cleaner Effect
Rougher-Scavenger-Cleaner Effect
[image 145-5-39]

Cadia Processing Facility

Cadia Processing Facility
Cadia Processing Facility
[image 145-5-40]

Cadia Metallurgical Balance Sheet

StreamCuAu
Head Grade (%, g/t)0.190.77
Concentrate Grade (%, g/t)26.381.0
Overall Recovery (%)77.971.2
Dorè Recovery (%)---11.3

Gold Flotation Circuit

Gold Flotation Circuit
Gold Flotation Circuit
[image 145-5-41]