flotation-teory

8/7/2019 flotation-teory

1/29

Froth Flotation1

Froth Flotation


2/29


3/29

Froth Flotation3

materials, such as coal, may be successfully separated up to 1600 m (10 mesh) in some

systems.

Froth flotation has been used in the minerals processing industry since the mid-1800s

with many of its broad-based applications to mineral recovery extensively developed

between 1900 and 1925. Today, at least 100 different minerals, including almost all of

the worlds copper, lead, zinc, nickel, silver, molybdenum, manganese, chromium,

cobalt, tungsten, and titanium, are processed using froth flotation. In 1997, the estimated

worldwide mineral production, using froth flotation, was two billion tons. Another major

usage of froth flotation is by the coal industry for desulferization and the recovery of fine

coal, once discarded as waste. Since the 1950's, flotation has also been applied in many

non-mineral industries including sewage treatment; water purification; paper de-inking;

and chemical, plastics, and food processing. The development of froth flotation

continues today with the need to recover minerals from increasingly poorer grades of ore,

as well as its non-traditional application to other types of materials.

There are several different types of froth flotation systems in use today including the

mechanical type, of which there are many subtypes, and the flotation column. The type

of froth-flotation apparatus to be used in this experimentation is the batch, sub-aerated

mechanical type shown in Figure 1. While this is a laboratory scale unit capable of

handling up to 5 L (5 x 10-6 m3), the same equipment type and principals are used at the

industrial level up to 7,000 ft3 (200 m3). A photograph of a 1000 ft3 unit is shown on the

title page (source: Mining Engineering, 31, 1979, p. 785).


4/29


5/29

Froth Flotation5

Objectives

The purpose of this experiment is to investigate the various aspects of the froth-flotation

separation of materials using a batch, laboratory-scale mechanical flotation apparatus

commonly used in industry for separation research and development. Experimental

parameters will be varied to determine their effect on the froth-flotation separation

including the types and concentrations of collectors, frothers, and modifiers (depressants,

activators, and pH regulators). The conditioning times; solids loading and weight

fractions; agitator speed; aeration rate; particle densities, sizes, and shapes; and the

temperature may be varied. Data analyses will include determination of the grade and

recoveries of the more desired material with respect to the effect of the experimental

parameters, as well as determination of the kinetics of the separation process. Qualitative

observations should also be documented to serve as bases for additional conclusions

concerning possible behavior of the system with respect to the quantitative results. Based

upon the experimental results, the different separation outcomes should be compared and

contrasted and optimal parameter ranges should be postulated for the separations. Scale-

up considerations of these laboratory results to larger flotation systems and their use with

multi-stage separations may also be investigated. As an experimenter, you are to decide

what to investigate and are responsible to develop the appropriate experimental

methodology to achieve viable separations, data, and analyses. It will be easy to identify

numerous hydrophilic feeds. An excellent selection for a hydrophobic solid is fine

activated carbon. Characterize your feed by composition and by particle size of each

component. Use sieves to characterize particle sizes.


6/29

Froth Flotation6

Background

Wettability

Froth flotation involves three phases solid, liquid, and gas and the corresponding

potential phase interfaces solid-liquid, solid-gas, liquid-gas, and solid-liquid-gas. The

hydrophobic (aerophilic) or hydrophilic nature of the solids at the solid-liquid-gas

interfacial region is determined by the wettability of the solid. A parameter that

characterizes wettability is the contact angle at the three-phase interface (Figure 2). The

contact angle, , is related to the respective interfacial surface tensions, SG, SL, and LG,

by Youngs equilibrium equation,

cosLGSLSG += . (Eq. 1)

In Figure 2, point P is the solid-liquid-gas interfacial region. If the liquid-water drop

spreads over the solid, the solid is hydrophilic characterized by a contact angle of 0o <

< 90o between the water drop and the solid surface at P. At these angles, air bubbles do

not readily adhere to hydrophilic solids in water. Conversely, when the solids are not

Figure 2. Relative Equilibrium States for a Water Droplet at a

Solid Surface Indicating Various Wettability Regimes.

SG

LG

SL Solid

Water Drop

Air

SL SL

SG

SG

LG LG

Hydophylic Regime0o < < 90o

Intermediate Regime = 90o

Hydophobic Regime90o < < 180o

P P P


7/29

Froth Flotation7

readily wetted by water, the solids adhere to the air bubbles and the characteristic contact

angle is 90o < < 180o, and these solids are said to be hydrophobic (or aerophylic). An

intermediate regime, = 90o, may exist where the solid does not exhibit either strong

hydrophilic or hydrophobic character.

The hydrophilic or hydrophobic character of the solid expressed by the contact angle is

an idealized representation in its application to froth flotation. In practice, it is not

necessary to actually obtain a hydrophobic solid as defined by a > 90o. Contact angles

in flotation systems typically do not exceed 100

o

. What is more important is that the

system is operated in such a manner that one of the solid components has a greater

preferably a substantially greater hydrophobicity than the other solids from which it is

to be separated. It has been found that a of at least 20o is necessary for bubble

attachment and successful flotation, and s > 20o are desirable for effective separation.

Many materials, such as minerals, are nonpolar and are more naturally hydrophilic than

hydrophobic in water. However, there are also many exceptions such as coal with a

natural = 45-60o and talc with a natural = 88o (see the bottom of Table 1 in next

section).

Thus, in order to obtain a successful separation using froth flotation, it is usually

necessary to selectively enhance the hydrophobicity of one of the solid components that

is otherwise hydrophilic or not strongly hydrophobic. This selective modification of the

wettability of solids in froth flotation is obtained using additional reagents termed

collectors.


8/29

Froth Flotation8

Collectors

To invoke selective hydrophobicity, substances know as collectors are used. Collectors

are typically heteropolar organic substances they contain both nonpolar and polar

chemical groups. The nonpolar end is almost always a long-chain or cyclic hydrocarbon

group that is hydrophobic. The collector must be able to attach to the solid, and it does so

through its polar end, which is typically an ionic group termed the solidophil group.

When the solidophil group of a suitable collector contacts a mineral at a surface site that

can chemically interact with the solidophil group, the collector bonds to the surface of the

mineral via chemisorption or ionic bonding. The nonpolar end of the collector then

orients outward from the solid surface forming a nonpolar chemical envelope

surrounding the solid particle, inducing hydrophobic behavior on an otherwise

hydrophilic solid surface. The solid particle can then more readily attach to an air bubble

(Figure 3) via the hydrophobic end of the collector.

Consequently, a key to successful froth flotation is to selectively induce, using a suitable

collector, hydrophobicity on the desired material to be recovered while retaining

Figure 3. Collector Alignment at the Solids Surface.


9/29

Froth Flotation9

hydrophilicity of the nondesirable material. It should also be noted that the strength of

the induced hydrophobicity of the mineral via the collector is directly relatable to the

length of the hydrocarbon group while the strength and selectivity of the collectors ionic

bonding is controlled by the type of solidophil group.

There are many different types of collectors, and they are classified as to the type of ion

(anionic or cationic) that is formed upon their dissociation in aqueous solutions. For

example, sodium oleate, C17H33COONa, is a widely used collector for minerals

separation. It is comprised of a long-chain, nonpolar hydrocarbon group, R = [C17H33],

which is hydrophobic and a polar carboxyl group, [COONa], which is the solidophil

group. Upon dissociation in water, the solidophil group is anionic or

This anionic carboxyl group will bond with minerals that contain alkali-earth metal

cations such as Ca, Ba, and Mg, as well as carbonate, oxide, and sulfate minerals.

Other widely employed anionic collectors include the xanthates, containing bivalent

sulfur, that are highly selective collectors in the separation of sulfide minerals. The

xanthate anion is

R O C

S

S

R

O

C

O


10/29

Froth Flotation10

Other types of collectors are used in froth flotation including dithiophosphates and alkyl

sulfuric salts that are also anionic collectors. The later include sodium dodecyl sulfate and

sodium lauryl sulfate, used in detergents. The later have the sulfo-solidophil group

Cationic collectors are less widely used. The most common types contain amine groups,

such as aniline and pyridine, but cation attachment to most minerals is typically weak.

They are also typically water insoluble and require the presence of acids to induce

solubility. However, cation collectors are used for silicates and other oxides, including

some rare earth oxides.

As previously discussed, the effect of collectors on the hydrophobicity of solids can be

related to the contact angle, . Examples of contact angles modified by various collectors

for various minerals are indicated in Table 1, as well as those for naturally hydrophobic

materials for comparison.

R O

S

O

O

O


11/29

Froth Flotation11

Table 1. Contact Angles for Various Solids and Collectors(adapted from Encyclopedia of Chemical Technology 4th Edition, Vol. 11 (1997) p. 88.

Solid Collector and Conditions (degs)

colemanite 5 x 10-3 M sodium oleate 43

copper metal 1.5 x 10

-4

M sodium oleate 93fluorite 1 x 10-5 M sodium oleate, pH = 8.1 91

galena 1 x 10-3 M potassium ethyl xanthate 60

ilmenite 1.3 x 103 M sodium oleate solution, T = 75oC, pH = 8 80

silica 1.1 x 10-5 M dodecylammonium chloride, pH = 10 81

graphite water 86-96

coal water 20-60

stibnite water 84

sulfur water 85

molybdenite water 75

talc water 88

iodyrite water 20

Frothers

In addition to collectors, another important component in successful flotation is the

presence offrothers. Once its surface is rendered hydrophobic, a solid particle must be

able to attach to an air bubble. While it may be possible to initially obtain solid particle

attachment to air bubbles in an agitated liquid under aeration alone, these air bubbles are

unstable and quickly break down due to collisions with other bubbles, solid particles, and

the vessel walls. In addition, the bubble size may not be sufficient to effectively carry a

solid particle to the surface of the liquid. Consequently, additional materials, termed

frothers, are added to promote the formation of stable air bubbles under aeration.

Frothers, like collectors, are typically comprised of both a polar and nonpolar end. The

nonpolar hydrophobic ends orient themselves into the air phase. Bubble wall strength is

enhanced by simultaneous strong polar-group and water-dipole reaction (hydration) at the

air-liquid interface resulting in greater bubble stability due to a localized increase in

surface tension.


12/29

Froth Flotation12

Frothers are generally classified by their polar groups with the most common being the

hydroxyl (OH), carboxyl (COOH), carbonyl (=C=O), amino (NH3), and sulfo (

OSO2OH andSO2OH) groups. Table 2 lists some common frothers according to their

chemical grouping. Effective frothers typically contain at least five or six carbon atoms

in their straight-chain, nonpolar group to obtain sufficient and stable interaction with the

air phase. For branched-chain hydrocarbons, the number of carbon atoms in the nonpolar

group may range up to sixteen. However, a frother must be at least slightly soluble in the

liquid medium and increasing the straight-chain-hydrocarbon length (perhaps up to a

maximum of eight, e.g., octyl alcohol) will eventually lead to too low of a solubility for

effective frothing. Thus, a suitable frother must provide a balance between sufficient

nonpolar interaction with air and solubility in water. With respect to the polar groups,

one or two are usually sufficient to interact at the liquid-air interface to provide sufficient

frothing properties, and additional polar groups provide little benefit.

Most of the frothers in Table 2 are hydroxyl-group-type frothers, and, thus, have little

collector properties. However, because of the inherent heteropolarity of collectors, a

collector can also serve as a frother in some systems. This is true of the carboxyl-type

frother, sodium oleate, and the sulfo-solidophil fatty acids. Certain collector/frother

combinations may also exhibit a synergistic separation effect. However, one designs a

flotation system based upon a collector specific to the modification of the surface

properties of the solids required for separation. The type of frothing agent is a secondary

consideration that is chosen after the collector to provide suitable frothing conditions and

noninterference with the collector or separation system.


13/29

Froth Flotation13

Table 2. Examples of Frothers.

Frother Formula

Aliphatic Alcohols

MIBC (4-methyl-2-pentanol)

di-acetone alcohol2-ethyl 3-hexanol

CH3(CH2)nCH2OH, n = 35

CH3CH(CH3)CH2CH(OH)CH3

(CH3)2(OH)CH2COCH3CH3(CH2)3CH(C2H5)CH2OH

Cyclic Alcohols

pine oil (terpineol)

eucalyptus oil (cineole)

C10H17OH

C10H16O

Phenolscresol

xylenol (e.g., xylitol)

CH3C6H4OH

HOCH(CHOH)3CH2OH

Alkoxyparaffins

1,1,3-triethoxybutane CH3CH2CH(OC2H5)CH(OC2H5)2

Polyglycols

poly(propylene glycol) monalkyl etherspoly(ethylene glycol)s

R(OC3H6)nOH, n = 25, R = CH3, C4H9R(OC2H4)nOC2H4OH, n = 2-5

Othersulfo-cetyl alcohol CH3(CH2)14CH2OSO2OH

Modifiers

Additional modifiers such as activators, depressants, dispersants, and pH regulators are

also commonly used in froth flotation. Activators may be added to chemically

resurface the solid to increase the interaction with collectors that are otherwise

ineffective alone. Depressants form a polar chemical envelope around the solid particle

that enhances hydrophilicity or selectively prevents interaction with collectors that may

induce unwanted hydrophobicity. Dispersants act to break agglomerated particles apart

so that single particles interact with the collectors and air bubbles. Regulators are

commonly used to control the pH since the hydrophobicity of systems is often optimal

within a certain pH range. Frothers also often need a certain pH range in order to form

stable bubbles. The presence of reducing agents may also serve to prevent the presence

of soluble ions due to oxidation that may undesirably activate certain minerals.


14/29

Froth Flotation14

Separation Kinetics

It should be emphasized that the overall dynamics and kinetics of froth flotation

separation involves the surface phenomena of the collectors chemical envelope

surrounding the solid particles and its hydrophobic nature. While one must still consider

the particle size and mass of the material since these affect the ability of the bubbles to

successfully transport the solid particle, the type of material that lies beneath the

hydrophobic envelope, once it is established, has little affect on the separation.

Consequently, if enough conditioning time has been provided for collector action to

selectively render the desired solid particles hydrophobic, the remaining overall

separation is essentially dependent only upon the efficiency of the bubble and solid-

particle interactions (assuming the particle size and density are within a suitable range).

The overall flotation efficiency,EF, of the separation system may be defined by

EF = EC EA ES (Eq. 2)

whereEC is the collision efficiency,EA is the attachment efficiency, andES is the stability

efficiency of the bubble-solid interaction. It is convenient to express the overall

separation or flotation rate, rs, by

ns Ck

t

Cr =

=

d

d(Eq. 3)

where Cis the concentration of the desired component (the hydrophobic component) in

the frothing tank; t is time; n is the order of the process, n = 0, 1, 2,; and kis the

flotation rate constant. This approach to flotation rate modeling is analogous to that used

in chemical-reaction kinetics. It must be re-stressed that this rate expression is for the

overall separation process and not the reaction of the collector at the solids surface.


15/29

Froth Flotation15

In kinetic modeling, one often assumes a reaction order and subsequently determines the

accuracy of that assumption based upon the experimental data. However, in practice for

all but the simplest processes, there are often undeterminable or unknown system

relationships. Kinetic modeling assuming a first-order process permits one to at least

compare systems. This is often termed a pseudo-first-order assumption, and Eq. 3 with n

= 1 has been found to adequately model most flotation systems comprised of a single

solid-particle size and hydrophobic strength.

Solution of this equation assuming pseudo-first-order kinetics, n = 1, yields the integrated

rate expression

ktt eCC

= o (Eq. 4)or

tkC

Ct =

o

ln (Eq. 5)

where Ct is the concentration of the desired component (the hydrophobic component) in

the frothing tank at time tand Co is the concentration of the desired component at t= 0,

the beginning of the separation. Note that the ratio Ct/Co is the fraction of the desired

component remaining in the tank at time t.

Based upon bubble-particle capture modeling, the flotation rate constant may be

expressed by

Vd

hEGk

b

F

2

3= (Eq. 6)


16/29

Froth Flotation16

where G is the gas flow rate; db is the average bubble diameter; and V and h are the

volume and depth, respectively, of the particle suspension. If k is known, then the

flotation efficiency,EF, can be estimated from Eq. 6 for a given system with known db.

The flotation rate constant, k, can be determined from a plot of ln [Ct/Co] vs. t(see Eq. 5)

from experimental data. If this plot is linear, then the assumption of overall first-order

separation kinetics is valid. However, in actual systems this plot often exhibits

nonlinearity that is usually attributable to a distribution of particle sizes and varying

hydrophobic strengths of the solids. The result is a distribution of flotation rate constant

values. The recovery rate is then represented by a sum of a series of exponential terms,

and the plot of ln [Ct/Co] vs. twill exhibit curvature.


17/29

Froth Flotation17

Experimental Equipment

The principal experimental apparatus used for this lab is the D-12 Lab Flotation Machine

manufactured by the Denver Equipment Company. A general schematic of the apparatus

appears in Figure 4. Further details about this unit are provided in the manufacturers

equipment manual available in the lab. The apparatus provides recirculation and

agitation to maintain thorough mixing and solid/liquid suspension. Other types of

agitators/mixer heads are supplied with the equipment; however, all experimentation

should be done with the installed agitator unless directed otherwise by the instructor.

Figure 4. Details of the Denver D-12 Lab Flotation Machine(photo by John Murphy).

RPM IndicatorSpeed-Adjustment

Knob

Height-Adjustment

Handle

Speed Adjustment

Lock Ring

Height-Adjustment

Stop Knob

Power Switch

Motor

Frothing TankEffluent Lip

Agitator Assembly

Agitator ShaftHousing

Aeration Valve

Frothing Tank

Support Column

Base

Belt Housing


18/29

Froth Flotation18

The vertical position of the agitator is adjusted by pulling out the stop knob on the left-

hand side of the unit and turning the lever on the right-hand side (Caution the agitator

assembly is heavy). The rotation speed (rpms) of the agitator is varied by turning the

knob at the top of the motor at the back of the unit (Caution only change the motor

speed with the motor running). An rpm tachometer is located at the top of the unit. To

change the agitator rpms, back off the lock ring (the knurled ring) and turn the top knob

clockwise to decrease the speed and counterclockwise to increase the speed. Retighten

the lock ring. Air, via a petcock valve located near the top of the agitator shaft, is

introduced through the shaft into the aqueous solution to promote frothing. This aeration

is controlled and metered using a rotameter and needle valve.

Flotation tanks are available in various sizes ranging from 1.5 to 5 L. The flotation tanks

are designed with an effluent lip to allow the froth to exit for collection in the froth-

collection trays. Both stainless-steel and acrylic tanks are available. The acrylic tank

may be used to qualitatively view the particle, bubble, and fluid behavior under agitation.

The 1.5 L stainless steel tanks (2 are available) should be used for all other

experimentation unless directed otherwise by the instructor.

A temperature-controlled, heated water bath is available for operation at elevated

temperature using the 1.5 L tanks. Only distilled water (available in the lab) should be

used in the heating bath. The temperature set point is chosen via a dial located at the top

of the immersion heater. A temperature meter and thermocouple are used to monitor the

heating bath and flotation tank.


19/29


20/29

Froth Flotation20

General Methodology

The following procedures outline the general methodology for running most froth

flotation experiments with the equipment in the lab (see next section for specific

separations).

1.) For ambient temperature operation, choose the desired frothing-tank size and

place it under the agitator. A cutout under the frothing tank will center it. Lowerthe agitator to the desired height (typically to . from the frothing-tank

floor). Caution firmly grasp the adjusting handle before disengaging the stop

knob and ensure that the stop knob is fully engaged when finished.

2.) If using the heating bath for elevated temperature operation, only the 1.5 L

stainless-steel tanks can be used. Insert the frothing tank into the empty heating

bath, centering it on the standoff on the floor of the heating bath. The frothing-tank effluent lip should nestle over the cutout along the top of the heating bath.Place the 1 in. high tray support under the heating bath and position the heating

bath against the back of the flotation units main-support column. Lower the

agitator to the desired height (typically to . from the frothing-tank floor).

Adjust to center the agitator in the frothing tank. The frothing tank will firstneed to be filled with water to enable it to settle in the heating bath. Thus, do the

following in conjunction with Step 3 fill the heating bath with distilled water to

within 1 to 2 from the top of the heating bath. Place the froth diverter (a bent

aluminum panel) over the lip of the frothing tank with the bent, side supportsfacing down.

3.) Measure out a suitable amount of distilled water and fill the frothing tank with

the agitator in place. For a 1.5 L tank, this amount is ~1.3 L of distilled wateryielding a liquid height approximately below the effluent lip of the frothing

tank.

4.) Place a froth-collection tray (3 or 4 plastic ones are available) under the effluentlip of the frothing tank. Position several other froth-collection trays nearby so

that they can be readily replaced during a run.

5.) Turn on the agitator and set the desired agitator speed using the set knob andrpm-indicator dial. Caution change the agitator speed only with the motor

running and always retighten the lock ring when finished with the adjustment.

6.) Open the aeration petcock valve at the top of the agitator shaft and the ball valveon the rotameter-inlet line, and set the airflow to the desired setpoint using the

needle valve on the rotameter inlet line. Calibrate and record the airflow.


21/29

Froth Flotation21

7.) Adjust the liquid height in the frothing tank if excessive spillage occurs at a

given speed and airflow. Record the new volume.

8.) Turn off the aeration at the ball valve on the rotameter-inlet line. Leave the

aeration petcock valve open.

9.) Pre-sieve the desirable-component and gangue solids to obtain particle sizes that

enable subsequent separation by sieving and quantitative weight analyses after

flotation. Record all sizes.

10.) Weigh out the desirable-component and gangue solids to obtain the desired

weight fraction. If a pre-mixed solids sample is used, determine the weight

fraction. Record all weights.

11.) Weigh out the desired amounts of collector, frother, depressant, promoter, etc. If

liquid, measure out using a graduated cylinder or volumetric flask. Record all

values.

12.) Record the temperature of the frothing tank using the thermocouple. If using the

heating bath, set the heating bath to the desired temperature using the immersion

heater set-point dial (calibrated in oF). Maximum operating temperature should

not exceed 75oC. Monitor the heated-bath and frothing-tank temperatures untilthe desired temperature is obtained.

13.) Calibrate the pH meter using suitable calibration solutions (see the instructor).

Record the pH in the frothing tank.

14.) Pour the solids mixture to be separated into the frothing tank and allow mixing.

15.) With the aeration still off, separately add any promoters, inhibitors, pHmodifiers, collectors, and frothers and record the time, temperature, and pH after

each addition. A conditioning time (~typically 1 to 2 min. although it may be an

im) should follow each addition, and the sequence of the additions and their

conditioning times recorded. Note any qualitative observations of the frothingtank solution such as dispersion or coalescence of solids, bubble formation, etc.

16.) To begin froth-flotation separation, turn on the ball valve at the rotameter-inlet

line and record the time. Froth should build and begin to elute over the effluentlip of the frothing tank and into the froth-collection tray. A plastic spatula may

be used to sweep the froth off the top of the frothing tank and into the froth-

collection tray, especially if it tends to froth over the sides of the frothing tank.

Depending upon the amount of froth, the froth-collection tray may need to beswitched over time. Record the times for froth-collection-tray switches to obtain

time-based, separation information. Note any qualitative observations during the

separation with time including froth amounts, discernable presence of solids in

the froth, bubble-size distribution, bubble stability, etc.


22/29

Froth Flotation22

17.) When frothing ceases, shut off the aeration at the ball valve on the rotameter-

inlet line and record the time. Record any final qualitative observations.

18.) Separately wash out each froth-collection tray with distilled water into filter

paper (coffee filters work well) placed in a suitably fine sieve to prevent any

solids loss.

19.) Raise the agitator and rinse any remaining froth and solids back into the frothing

tank using distilled water. Remove the frothing tank.

20.) Separately wash out the frothing tank with distilled water into filter paper (coffee

filters work well) placed in a suitably fine sieve to prevent any solids loss.

21.) Remove the filter paper from the sieve, seal with tape, and label accordingly.

22.) Dry the samples in the filter paper in a drying oven at 75100 oC. Record the

drying time and temperature.

23.) When dry, re-sieve each sample based upon the initial sieve-size distribution to

obtain separation of the solids. Alternatively, if one of the solids is magnetic,

use a magnetic plunger or magnetic separator to separate.

24.) Weigh each separated sample and calculate recovery and grade (purity) obtained

in the separation. Note any total sample loss.

25.) Empty the water bath at the end of the experimental period, and return allsamples, reagents, and equipment to their proper place.


23/29

Froth Flotation23

Suggested Separations

Your group or your instructor can identify a synthetic mixture to study.

Fluid Phase

Water (do not use other liquids)

Frothing Agents

Dowfroth

MIBCOthers that you identify (have the technician or instructor order them if necessary)

Hydrophilic Particles

Each group has the responsibility of selecting a hydrophilic particle. Use the sieves tocharacterize the size of the particles (dry).

Hydrophobic ParticlesAn excellenthydrophobic particleis extremely fine activated carbon. Use the mortar andpestal to crush the activated carbon, and use the sieves to characterize the size of the

particles (dry).


24/29

Froth Flotation24

Suggested Separation Experiments for Copper and Ilmenite

Sodium oleate, C17H33COONa, which is soluble in water serves as both a collector and

frother in a number of metal and mineral separations. It can be used in the separation of

copper metal from gangue, such as sand, and ilmenite from zircon in water. Table 3 lists

the various sample and reagent materials available in the lab (Caution note the

warnings at the bottom of this table). Sodium oleic acid is used as the reagent to prepare

the sodium oleate solution. Please note that this reagent is relatively expensive.

Maximum molar concentrations up to 3 x 10-4 M (which is ~0.1g of oleic acid for the 1.5

L tank) should be used for each run, but less if possible (1.5 x 10 -4 M usually works

well). Copper metal is available in two presized samples (150 mesh and 40,+60 mesh).

Presized sand is available (50,+70 mesh), as well as common beach sand which may be

sieved. Ilmenite and zircon are available both as a mixture (~22% by weight ilmenite)

and as separate samples, all unsized. Other reagents listed in Table 3 are potential

frothers, pH regulators, and depressants that may be used.

A total solids loading of 50 g of material is suggested for the 1.5 L cell using sodium

oleate concentrations up to 3 x 10-4 M. Typical weight fractions of 1040 % for the

desirable component are also suggested to minimize sample usage.


25/29

Froth Flotation25

Table 3. Materials for Froth Flotation of Cu/Sand and Ilmenite/Zircon

Material Aldrich # or Other CAS #

Sodium Oleic Acid** 23,397-8 143-19-1

Copper (-150 mesh)*** 26,607-8 7440-50-8

Copper (-40, +60 mesh)*** 26,608-6 7440-59-9

Sand (-50, +70 mesh)*** 27,473-9 -Beach Sand (common, unsized) - -

Ilmenite (FeTiO3) DuPont -

Zircon (ZrO2SiO2) DuPont -

Ilmenite(~22%) Zircon mixture InProsys (DuPont) -

Starblast staurolite (FeOAl2O3SiO2H2O) DuPont -

Sodium hydroxide** VWR # VW6720-1 1310-73-2

Calcium Oxide - -

Hydrochloric acid*, ** - -

Sodium metasilicate*** 30,781-5 6834-92-0

Sodium dodecyl sulfate** 86,201-0 151-21-3

Poly (propylene glycol) monobutyl ether 43,810-3 9003-13-8

Propylene glycol amyl ester (DowFroth-250TM) Dow -

*Please see the instructor before handling this reagent.**Gloves should be worn when handling any of these reagents or their solutions.

***Avoid breathing any of the fine powders especially copper.

The following are suggested froth-flotation experiments using sodium oleate solution

(maximum of 3 x 10-4 M) for copper and ilmenite separation from sand and zircon,

respectively.

Investigate the effect of pH and pH regulator concentration and determine the

optimum pH range for separation alkaline pH regulators such as caustic soda

(NaOH), lime (CaO), or soda ash (Na2CO3) may be used. Note that it will be

necessary to first dissolve these reagents in water on a hot plate at ~75 oC before

addition to the frothing tank. Operation in the acidic range may also be investigated

using hydrochloric (HCL) or sulfuric (H2SO4) acids. These pH modifiers may also

serve as dispersants, depressants, and activators in some systems.


26/29

Froth Flotation26

Investigate the effect of depressants that may inhibit any hydrophobicity of the

gangue material sodium metasilicate, Na2SiO3, is a potential depressant of

siliceous materials such as sand and zircon. It is also a pH regulator.

Investigate the effect of particle size on the separation both the desired component

and the gangue material size may be varied.

Investigate the effect of agitator speed (rpms) on the separation.

Investigate the effect of aeration on the separation perhaps allowing separation

using lower sodium oleate concentrations.

Investigate the effect of conditioning time for various modifiers on the separation.

Investigate the effect of temperature on the separation temperature ranges from

room temperature to 75oC may be performed.

Investigate the viability of using alternative or additional frothers allowing

separation using lower sodium oleate concentrations high-molecular-weight

alcohols, such as poly (propylene glycol) monoalkyl ethers [R(OC3H6)nOH, where n

= 2-5 and R = CH3, C4H9] such as poly (propylene glycol) monobutyl ether and

propylene glycol amyl ester (Dowfroth-250TM) act as frothers.

Investigate the rate of separation by determining concentration versus time over

short time intervals the kinetic effects of particle size; aeration; solids loading;

collector, frother, and modifier types and concentrations; and temperature may be

thoroughly investigated (see Additional Analyses section).


27/29

Froth Flotation27

Data Analysis

The following are outlines of the types of analyses that may be performed. The

application of these analyses will be determined from the types of experiments chosen.

Calculate the % grade, G, or purity of the concentrate stream (the hydrophobic

stream) from 100conc

des

=

m

mG where mdes is the weight of the desired component

(usually the more valuable mineral) in the concentrate stream and mtot is the total

weight of the concentrate stream. The % increase in % grade between the original

weight fraction of the desired component and the weight fraction in the concentrate

may also be reported.

Calculate the % recovery, R, of the desired component in the concentrate stream

(the hydrophobic stream) from 100feed

des

=

m

mR where mdes is the weight of the

desired component in the concentrate stream and mfeed was the weight of the desired

component in the feed stream before separation. Percent loss of the desired

component via the tailings stream (the hydrophilic stream) may also be reported.

Create plots of grade and recovery vs. agitator speed, pH, temperature, and

concentrations of frother, collector, pH regulator, depressant, activator, etc. that

were determined in the experiments. Similarly, create grade vs. recovery plots for

comparisons.


28/29

Froth Flotation28

Compare the results of other mineral processes e.g., tabling, mineral jigging,

cycloning, and centrifuging often used in lieu of, or in conjunction, with that of

froth flotation, specifically with respect to particle size, efficiencies, grade and

recovery, cost, and other factors.

Apply scale-up design procedures to froth flotation based upon the experimental

results.

Additional Analyses

The following are additional analyses that require more extensive data collection.

Determine the rate constant, k, of the separation process for a given set of conditions

by experimentally determining concentration versus time and applying the rate

expression, n

d

dkC

t

Crs =

= , assuming a pseudo-first-order process (n = 1) where

Cis the concentration of the desired component (the hydrophobic component) in the

frothing tank and tis time. Create a normalized plot of ln

o

t

C

Cvs. twhere Ct is the

concentration of the desired component at time, t, and Co is the initial concentration

at time, t = 0, the beginning of the separation. Determine the first-order rate

constant, k. If the process is not first order, investigate other possible rate

expressions.

Determine the rate constant, k, behavior with temperature, T, of the separation

process given a set of conditions and apply the Arrhenius relationship,

TEAk

R/ae= , whereA is the frequency factor,Ea is the activation energy, and R is


29/29

the gas constant. Create a plot of ln kvs. 1T

1. DetermineA andEa and relate these

to the dynamics of the separation.

General References

Kirk-Othmer Encyclopedia of Chemical Technology 4th Ed., Vol. 11 (1997) pp. 81-106.

Kirk-Othmer Encyclopedia of Chemical Technology 4th Ed., Vol. 23 (1997) pp. 478-536.

Perrys Chemical Engineers Handbook, 5th Ed., (1984) pp. 21-46.

McKetta, John J., Encyclopedia of Chemical Processing and Design, Vol. 23 (1985) pp.454-506.

Last Update: August 2001

flotation-teory

Documents