AMIT 145: Lesson 5 Froth Flotation – Mining Mill Operator Training

Contents

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 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

CPT Bubble Generation System

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

CPT Flotation Column

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 Bubble Generation

Installation

Column Installation

Jameson Cell

Developed by Dr. Graeme Jameson and owned by MIM Ltd.
Self-aspirating system with froth washing.

A photo of a Jameson cell — A Jameson Cell
[145-5-15b]

Flotation Recovery Fundamentals

A flotation process has two distinctly different phases:

Collection Zone
Froth Zone

Both the collation zone (R_C) and froth zone (R_F) 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, R_C

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

Flotation Rate, k_i
Particle Residence Time, T_p
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 â†’ 0, Perfectly mixed conditions â†’ $R_{c} = \frac{k\tau _{p}}{1+k\tau _{p}}$

Pe â†’ âˆž, Plug – flow conditions â†’ $R_{c} = 1-exp(-k\tau _{p})$

Flotation Rate, k_i

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, P_C
Probability of Attachment, P_A
Probability of Detachment, P_D

P = P_CP_A(1-P_D)

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

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

Species	No Collector		Collector
1	k = 1.0	R = 68%	K = 2.0	R = 80%
2	k = 0.25	R = 33%	k = 1.0	R = 68%

Typical Flotation Residence Times

Material	Typical solids concentration for roughing applications, percent	Typical residence times for roughing applications, minutes	Typical laboratory flotation times, minutes
Copper	32-42	13-16	6-8
Lead	25-35	6-8	3-5
Molybdenum	35-45	14-20	6-7
Nickel	28-32	10-14	6-7
Tungsten	25-32	8-12	5-6
Zinc	25-32	8-12	5-6
Barite	30-40	8-10	4-5
Coal	4-8	3-5	2-3
Feldspar	25-35	8-10	3-4
Flourspar	25-35	8-10	4-5
Phosphate	30-35	4-6	2-3
Potash	25-35	4-6	2-3
Sand (Impurity Float)	30-40	7-9	3-4
Silica (Iron Ore)	40-50	8-10	3-5
Silica (Phosphate)	30-35	4-6	2-3
Effluents	As received	7-12	4-5
Oil	As received	4-6	2-3

A diagram of Recovery Zone Parameters — Recovery Zone Parameters
[image 145-5-22]

Froth Recovery, R_F

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

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]

Entrainment Effect on Separation Performance

A photo of a separator column — Entrainment Effect on Separation Performance
[image 145-5-32]

Typical Flotation Cell Dimensions

Trade Name	Length (m)	Width (m)	Depth (m)	Pulp Volume (m³)
Denver 100	1.52	1.52	1.22	2.8
Denver 200	1.83	1.83	1.59	5.7
Denver 300	2.10	2.10	1.89	8.5
Denver 400	2.30	2.30	2.12	11.3
Denver500	2.70	2.70	1.98	14.2
Wemco 44	1.12	1.12	0.51	0.57
Wemco 66	1.52	1.68	0.69	1.7
Wemco 84	1.60	2.13	1.35	4.2
Wemco 120	2.29	3.05	1.35	8.5
Wemco 144	2.74	3.66	1.60	14.2
Wemco 164	3.02	4.17	2.36	28.3

Wemco Convention & Outotec Tank Cells

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

Outotec Tank Cells

Model	Cell Volume (m³)	Diameter (m)	Lip Length (m)	Froth Area (²)	Air Flow (m³)	Motor (kW)
TankCell-5	5	2.0	4.7	3.0	2.8	11
TankCell-10	10	2.5	6.3	4.7	4.3	18.5
TankCell-20	20	3.1	7.9	7.1	6.7	37
TankCell-30	30	3.6	9.4	9.7	9.0	45
TankCell-40	40	3.8	10.0	10.6	10.0	55
TankCell-50	50	4.7	12.7	16.5	15.0	110
TankCell-70	70	5.3	14.1	21.3	19.0	110
TankCell-100	100	3.0	16.3	27.5	25.0	132
TankCell-130	130	6.4	17.6	31.0	28.0	160
TankCell-160	160	6.8	19.0	35.2	32.0	185
TankCell-200	200	7.2	20.1	40.0	36.0	250
TankCell-300	300	8.0	22.0	49.0	45.0	300

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 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

Cadia Processing Facility

Cadia Metallurgical Balance Sheet

Stream	Cu	Au
Head Grade (%, g/t)	0.19	0.77
Concentrate Grade (%, g/t)	26.3	81.0
Overall Recovery (%)	77.9	71.2
Dorè Recovery (%)	---	11.3

Conventional Flotation

Conventional Cell Development

Flotation Columns

CoalPro (CPT) Flotation Column

CPT Bubble Generation System

CPT Flotation Column

Microcel Column Flotation Technology

Microcel Bubble Generation

Installation

Column Installation

Jameson Cell

Flotation Recovery Fundamentals

Collection Zone Recovery Parameters

Collection Zone Recovery, RC

Flotation Rate, ki

Probability of Flotation

Collection Zone Recovery Parameters

Flotation Rate Differential Effect

Typical Flotation Residence Times

Froth Recovery, RF

Flotation Carrying Capacity

Froth Washing Fundamentals

Hydraulic Entrainment

Froth Washing; The Original Flotation Column Benefit

Pan-Type Froth Wash Water System

Wash Water Ring System

Entrainment Effect on Separation Performance

Typical Flotation Cell Dimensions

Wemco Convention & Outotec Tank Cells

Outotec Tank Cells

Flotation Circuits

Rougher-Scavenger-Cleaner Effect

Cadia Processing Facility

Cadia Metallurgical Balance Sheet

Gold Flotation Circuit

Collection Zone Recovery, R_C

Flotation Rate, k_i

Froth Recovery, R_F