Western Michigan University ScholarWorks at WMU
Master's Theses Graduate College
12-1972
An Investigation of the Froth Flotation Process as a Means of Concentrating Pulp and Paper Mill Sludge
Merwin Lee Miller
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Recommended Citation Miller, Merwin Lee, "An Investigation of the Froth Flotation Process as a Means of Concentrating Pulp and Paper Mill Sludge" (1972). Master's Theses. 2818. https://scholarworks.wmich.edu/masters_theses/2818
This Masters Thesis-Open Access is brought to you for free and open access by the Graduate College at ScholarWorks at WMU. It has been accepted for inclusion in Master's Theses by an authorized administrator of ScholarWorks at WMU. For more information, please contact [email protected]. AN INVESTIGATION OF THE FROTH FLOTATION PROCESS AS A MEANS OF CONCENTRATING PULP AND PAPER MILL SLUDGE
by
Merwin Lee Miller
A thesis Submitted to the Faculty of The Graduate College in partial fulfillment of the Degree of Master of Science
Western Michigan University Kalamazoo, Michigan December 1972
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGEMENTS
To those who guided, criticized, and encouraged this research
effort - particularly Dr. Raymond Janes, Dr. Stephen Kukolich and
James Kline - I extend sincerest gratitude and appreciation. The
extra time and attention given by Andre Caron is noted here, as is
the financial assistance given by the National Council of the Paper
Industry for Air and Stream Improvement. Also, the patience shown
by those involved indirectly and directly has been most valuable.
Merwin Lee M iller
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. iMASTERS THESIS M-4022 MILLER, Merwin Lee AN INVESTIGATION OF THE FROTH FLOTATION PROCESS AS A MEANS OF CONCENTRATING PULP AND PAPER MILL SLUDGE.
Western Michigan University, M.S., 1972 Ecology
University Microfilms, A XEROX Company, Ann Arbor, Michigan
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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS PAGE INTRODUCTION ...... 1
REVIEW OF LITERATURE ...... 4
Theory of Froth Flotation ...... 4
History and development of flotation ...... b
Theory ...... 5
Physical factors ...... 6
Chemical factors ...... 8
Flotation a id s ...... 9
Frothers ...... 9
Col lecto rs ...... 10
Modifiers ...... 10
Flotation of Papermill C larifierSediment ...... 11
Dissolved air flotation ...... 11
Carbon dioxide flotation ...... 12
Electroflctation ...... 12
Flotation of Industrial Wastes and Domestic Sewage ...... 12
Flotation Practiced by the Pulp andPaper Industry ...... 14
Flotation of Clay Mineral ...... 16
PRESENTATION OF PROBLEM ...... 20
EXPERIMENTAL SECTION ...... 22
Preparation of Synthetic Sludge andHomogeneous Systems .... 22
Sludge Analysis and Solids Determination ...... 23
Total s o lid s ...... 23
Suspended solids ...... 23
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. PAGE
Ash content ...... 2k
100-mesh material ...... 2k
Float sol i d s ...... 2k
Measurement of entrained a i r ...... 25
Flotation Procedure ...... 25
pH S t u d y ...... 26
Dosage Study ...... 26
Detention Study ...... 26
Evaluation of Collectors ...... 27
Flotation of Homogeneous Systems ...... 27
Freeness Effect on Float Solids ...... 28
PRESENTATION AND DISCUSSION OF EXPERIMENTAL RESULTS ...... 29
Froth S tab ility in D istilled Wa t e r...... 29
Effect of pH and Fiber Consistency on Frother Performance . . . 32
Flotation of Fiber Conditioned with Collectors ...... 3k
Effect of Freeness of Float Drainage ...... 37
Flotation of C lay ...... ^0
Effect of pH on Flotation of Synthetic Sludge ...... kk
Effect of Frother Dosage on Flotation of Synthetic Sludge . . . ^9
Effect of Detention Time in the Flotation Chamber on FI oat Sol i d s ...... 51
Flotation of Synthetic Sludge Using Collectors and Frother F -6 5 ...... 53
CONCLUSIONS...... 56
RECOMMENDATIONS ...... 58
LITERATURE CITED ...... 59
APPENDIX I Identification of Frothers and Collectors ...... 61
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LIST OF FIGURES AND TABLES PAGE
Fig. 1. Atomic model of k a o lin it e ...... 18
Fig. 2. Calculated and determined float solids versus Canadian Standard freeness ...... 39
Fig. 3. Effect of pH on the volume of froth produced by various f r o t h e r s ...... 46
Fig. 4. Concentration of float solids shows a direct relationship to volume of air entrained in the f r o t h ...... 46
TABLE I Froth Volume and Stability in Distilled Water .... 31
TABLE II Effect of pH and Fiber Consistency on Froth Flotation ...... 33
TABLE III Froth Flotation of 1.0% Fibers with Collectors . . . 35
TABLE IV Effect of Freeness on Float S o l i d s ...... 38
TABLE V Froth Flotation of 1.0% Clay with Collectors and Frothers F-61 and F-250 43
TABLE VI Effect of pH on Froth Flotation of Synthetic S lu d g e ...... 45
TABLE VII Effect of Frother Dosage on Flotation of Synthetic Sludge ...... 50
TABLE V III Effect of Detention Time in the Flotation Chamber on Synthetic Sludge Float Solids ...... 52
TABLE IX Froth Flotation of Synthetic Sludge Using Collectors and Frother F-65 55
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. INTRODUCTION
Water, a valuable natural resource, Is an essential element
for sustaining life. In addition to quenching our thirst, it is a
generator of power, a transporting medium for society and industry,
and an object of beauty and recreation. The main source of water
is from lakes and streams some of which receive domestic and
industrial effluent. Present political pressures and an aroused
public are pressing for surface water of improved quality. Because
of the strong pressure being applied, emphasis has been focused
towards establishing improved and more effective methods for
treating waste water.
The pulp and paper industry, one of the nation's larger
industries, has for many years been concerned with matters per
taining to conservation. Process water that enters a papermill
must ultimately be returned to the streams in conformity with
regional or local water quality regulations. Present effluent
treatment by primary clarification produces sludge which must be
further dewatered. The concentration and disposal of these resi
dues has long remained a major problem and expense to the industry.
Methods that have been employed for the reduction of sludge
volume include alternating drying basins, vacuum filtra tio n , and
centrifugation. However, drying basins are slow, occupy a large
land area, and in some instances cannot be adapted to the parti
cular si te.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2-
Since some sludges do not respond to centrifugation or vacuum
filtration, new methods for concentration are constantly being
proposed and investigated. One possibility is flotation which has
been used successfully in the pulp and paper industry for separa
tion of fibers from ink and recovery of reusable fibers from white
water. Thus, the application of froth flotation for concentrating
fibrous pulp and paper mill sludges merits investigation.
Flotation is a method of separation or concentration of sus
pended material from dilute solutions based on the a ffin ity of
properly prepared particle surfaces for a ir bubble attachment,
it is a very important and rather complex application of surface
chemistry which was firs t applied by the mining industry and
gradually adapted by various other fields. The firs t and most
thoroughly studied application, however, was in the field of
mineral engineering; and it is, therefore, appropriate to fully
examine this application.
The froth flotation process as practiced by the mining indus
try uses frothers to produce a foam in which the desired mineral
is trapped. The mineral industry employs a selective method in
which only the mineral particle becomes attached to air bubbles
and brought to the surface.
However, in the effort to concentrate papermill sludge using
the flotation technique, it is necessary to float all the consti
tuents to the surface. Sediments removed from the mechanically
cleaned c la rifie rs vary in composition and are complex in nature.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Gehm^ described the complex nature of these residues as containing
water in three phases as well as three general classes of suspended
solids all present in varying proportions. The water phases are:
1) free water which is readily removable, 2) in terstitial water which
can be removed by mechanical means, and 3) water of imbibition which
cannot be separated at all by mechanical methods since it is part of
the crystal lattice formed by the colloidal sols. The solid classes
are the fibrous solids which are readily separated from the liquid
phase if present alone, as is the second class which consists largely
of fillers. The third class, colloidal sols, is hydrophilic and to
a large degree controls dewatering of the entire mass, including the
firs t two classes of solids. These sols consist of such substances
as highly hydrated wood dust, fiber debris, ray cells, aluminum
hydrate, starches, dextrins, resins, and proteins all of which form
a protective coating on the lost fiber and f i l l e r .
A prerequisite to the successful application of froth flota
tion is to promote attraction between the gas and solid phase by
changing the surfaces from hydrophilic to hydrophobic. In the mining
industry this is accomplished by chemical treatment using organic,
heteropolar compounds that become oriented with the nonpolar hydro
carbon end extended outward to form a hydrophobic film on the
particle's surface. However, in dealing with sludge the problem
becomes complicated since the nature of the particles is so complex
and its composition is continuously changing.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. REVIEW OF LITERATURE
Although much has been done with dissolved air flotation,
a search of the literatu re revealed no published information on
the application of froth flotation to concentrate pulp and paper
mill sludges. Therefore, this review includes a section on the
theory and application of froth flotation as practiced by the
mineral industry. Investigations of other types of flotation by
the National Council for Stream Improvement on pulp and papermill
sludges as well as work done by others in the field of industrial
and domestic sewage are also discussed in this review.
Theory of Froth Flotation
H i story and development of flotation
The earliest patent which may be considered as relating to
the flotation process was issued to William Haynes, who in i860
recognized the difference in w ettability of various minerals by ( 2) oil and water . Since that time, flotation has passed through
three principal stages of development: 1) bulk oil flotation,
2) skin flotation, and 3) froth flotation. The fir s t two methods
have become obsolete and replaced by the third upon discovery
that a ir bubbles become attached only to hydrocarbon mineral
surfaces.
With the recognition that gas bubbles were an ideal buoyant
medium for carrying pretreated particles to the surface, froth
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. flotation became the most modern, e ffic ie n t, and widely practiced
method of separating and concentrating minerals from ore. Unless
the slurry contains a natural floater, the process involves tre a t
ment of the ore to create conditions favorable for attachment of
specific particles to a ir bubbles which carry the selected material
to the surface of the slurry and form a stable froth which is re
moved. Special additives have been developed to produce surfaces
of reduced w ettability and this has vastly extended the number of
materials possible to recover by flotation.
Theory
Flotation depends on the relative wettability and/or elec
trical charges of surfaces, but the mechanism of collection has
been an object of considerable speculation. Various hypotheses
have been proposed along with some experimental evidence to support
each theory.
In itia lly it was recognized that oil promoted adhesion of
particles to bubbles and this was rationalized by assuming the oil
adhered to both particles and bubbles thus bonding them together.
The presence of oil in the concentrates and none in the gangue
(3) added evidence to this view .
Taggart suggested that bubbles were formed directly at
the particle surfaces as a result of supersaturation in low
pressure regions created by the vortices of the impeller blades (3) upon agitation. Gaudin , however, indicated that rising bubbles
merely collide with particles and adhere to those which have an
aff i n i ty for air.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Additional theories proposed include the chemical or solubil
ity theory and various adsorption theories involving attachment of
the collector as an ion, a molecule, a monolayer, and a multilayer.
The solubility theory postulates the formation of an organometal1ic
compound on the mineral surface which is less soluble than the
mineral its e lf. Minerals that form these hydrocarbon-1ike surfaces
can thus be floated; whereas, materials that form more soluble
compounds are not floatable.
Recent investigations employing radioactive tracers and
electron diffraction techniques have contributed additional infor- (2 ) mation; however, no single theory has been fully accepted . Pre
sently more importance has been attached to contact angle, surface
tension, interfaces, and structure of the flotation reagents used
in the process. The procedure is of physiochemical nature involving
both physical and chemical factors with the major technical problems
concerned with chemical control of the material surface.
Physical factors
Physical considerations involve particle size, specific
gravity, surface wettability, and density of the slurry.
Fine particles in the near-colloidal size are difficult to
recover by flotation. Part of the problem is mechanical d ifficu lty
in bringing fine particles into contact with a ir bubbles. Other
problems are due to the difference between the surface of the older,
smaller particle and the freshly produced larger particle. Coarse
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. particles also are not effectively recovered. The upper lim it in
size for squat cylinderical particles can be related to specific (3) gravity and contact angle in the following equation'-":
scin i n a v , , - (s ■ _~ Q g d 2 minimum AT aw
T = interfacial tension of air-water (dynes/cm) aw g = acceleration of gravity
6 = specific gravity
d = particle diameter
0 = contact angle
if 0 is assumed to be 90 °, then d . = r^~aw 1 ^ ^ . maximum (6-l)g
For example, if the density was 3g/cm3, the equation resolves' to
r4 x 72 dynes/cm il/2 (3-1) 980 cm/sec
which equates to a particle diameter of 0.38 cm.
Surface w ettability is significant as it governs contact
angle between air and particle. If the contact angle of a mineral
is n il, water wets the solid in preference to air and air-solid
contact is impossible. A contact angle of 0° represents nonfloat-
a b ility , while an angle of 180° represents wetting of mineral by
air to the exclusion of water. No solid is known to give an air-
water contact angle larger than about 1 1 0 ° ^ . Contact angle can
be controlled somewhat with additions of flotation reagents.
Considerable interest has been given to the most effective
bubble size with arguments for both large and fine bubbles. Finer
a ir bubbles provide more surface area per unit volume of a ir and
hence more solid particles can be accommodated at the air surface.
However, energy is required to disperse gas and finer dispersions
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. require greater costs per unit volume. Buoyance due to gas varies
as the cube of the diameter; whereas, the buoyancy-consuming load
of minerals varies as the square of the diameter. It is conceiv
able that a bubble-solids aggregate produced could have a negligibl (3) specific gravity differential with the surrounding medium .
Chem?cal factors
Chemical factors considered in flotation include crystal
structure of minerals, structure and composition of water, chem
istry of flotation reagents, surface chemical reaction with mineral
and the natural association of minerals.
Host solids exhibit strong polar surfaces readily wet by
water, and therefore, lack an affinity for air. Surfaces free of
unsaturated bonds lack a ffin ity for hydrogen or hydroxyl ions in
water and preferentially attach to air. Consequently, successful
flotation of several minerals has been due to the development of
chemicals that form water-repellent surfaces either by reaction or
adsorption. These reagents are usually heteropolar, organic com
pounds selective to specific surfaces. Success in flotation has
also been augmented with reagents that form stable foam upon
mechanical agitation. These flotation aids, classified as either
collectors, frothers, or modifiers, work together to promote
bubble-particle attachment and thus selective separation of solid
particulate matter from a liquid phase.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 9
Flotation aids
Frothers
The main purpose of frothing agents is the production of a
froth capable of supporting the solid-1aden air bubbles until
removal from the flotation unit. Frothing agents provide a covering
film on the bubble which imparts a temporary toughness until further
stabilization is established by adhering mineral particles and other
adjoining bubbles. Usually a froth should break down rapidly
following removal from the flotation unit to allow volume reduction.
To create a froth the agent introduced must lower the surface
tension of water. Host organic compounds demonstrate this ab ility ,
but those effectively used are limited since frothers should be low
in cost, readily available, and effective in low concentrations.
Widely used frothers are pine o il, cresylic acid, and certain syn
thetic alcohols. These frothers are all organic, heteropolar com
pounds with the nonpolar radical repelling water while the polar
end attracts water. Molecules of these compounds occur at the bubble
walls with the polar end adhering to the water phase and the nonpolar
end turned toward the gas phase. Distribution of frother molecules
at the bubble surface imparts the required elasticity to enable the
rising bubbles to burst through the top layer of water and emerge at (2 ) the air-water interface intact and unbroken
Frothing a b ility of organic compounds increases with length
ening of the hydrocarbon chain up to seven or eight carbon atoms;
thereafter, frothing a b ility decreases. Frothing quality is
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essentially unaffected by the chemical bonding in the nonpolar
(3) region of molecule
Col lectors
Collectors are the heart of the flotation process since they
are the reagents which raise the contact angle on the solid
particle. Collectors, like frothers, are usually organic, hetero-
polar compounds with a polar and nonpolar radical.
To have good affinity for solid particles, collectors must
have polar, ionic, or chemically reactive groups as a portion of
their molecular structure. Collectors are conventionally classified
as either anionic, cationic, or nonionic. Anionic collectors include
xanthates, fatty acids, dithiophosphates, sulphonated or sulphated
fatty acids, sulphonated oils, glycerides, and alcohols. Cationic
collectors are amines and amine salts. Neutral hydrocarbon oils are
non-ionic reagents.
Modi fiers
Modifiers include all reagents whose principal function is
neither collecting nor frothing. They act as depressants, activators,
pH regulators, and dispersants. Depressants are any reagent which
inhibit or prevent adsorption of a collector by a solid particle and,
therefore, prevent its flotation. Activators enhance adsorption of
the collector and thus promote flotation.
Effectiveness of most flotation agents depend, to a large
extent, on the degree of alkalin ity or acidity of the pulp solution.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Therefore, it is desirable to operate at the optimum pH value for
a given reagent and slurry combination. Common alkalinity regulators
are lime and soda ash, whereas acidic pH control is usually obtained
wi th sulfuric acid.
At times certain minerals are contained in the pulp slurry
which tend to flocculate particles to such an extent as to interfere
with efficient flotation of the desired mineral. In this case it
becomes desirable to employ the aid of defloccu1ators and dispersants.
Flotation of Papermill C la rifie r Sediment
D i ssolved a i r flo tat ion
C arpenter^ studied extensively dissolved air or pressure
flotation. A variety of surfactant, collectors, and wetting agents
were used as flotation aids with pressures up to 120 psi and recycle
rates of 100, 200, and 300%. Tests performed with primary deinking
sludge were not successful due to the high concentration of fine
inorganic material. Boardmill sludge at 2% solids containing 35%
100-mesh fiber was thickened to k% dry solids using chemical dosages
of 3.5 to 5.0 lbs. per ton of dry material recovered. Sludge at
this in itia l solids could also be concentrated to comparable levels
by gravity thickening. Additional dewatering of floats by vacuum
filtra tio n was impeded by blinding of the f i l t e r media caused by the
presence of fine air bubbles within the sludge blanket. Centrifuga
tion was hampered by the low specific gravity of the air laden
material. Carpenter concluded that the process was not practical
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. due to high in itial and operating cost, the necessity of a delicate
balance of operating variables, and problems in further dewatering
of the sludge.
Carbon dioxide flotat ion
In a similar investigation^ carbon dioxide was substituted
for dissolved air. Theoretically the process could be operated at
lower pressures and recycle rates due to carbon dioxide's greater
solubility in water. However, no advantage over dissolved air
flotation or gravity thickening was revealed by flotation with
carbon dioxide.
Electroflotat ion
Floats of (>% solids were produced from boardmill sludge by
electroflotation where solids were floated by the gas evolved at the
negative electrode^. However, only a small fraction of initial
solids were floated; and because of a long time element involved,
this process did not appear practical.
Flotation of industrial Wastes and Domestic Sewage
Air flotation has been used to advantage for the thickening
of some light flocculant sludges. Compared to a picket fence type
gravity thickener, flotation units are more compact and have a shorte
detention time. Such advantages have stimulated interest in this pro
cess as waste volumes demanding treatment have rapidly increased.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 13
At present, there are some sewage treatment plants which have
experience in flotation applications. A small plant in California
treating 1.0 mgd of domestic sewage has reported flotation removal of
55% in suspended solids and 70% reduction in five-day B O D ^.
( 8) Hay has reported findings on an eight-month pilot plant
operation at Racine, Wisconsin. The unit operated under 30 to kO psi,
a recycle rate of 20 to 50%, a designed capacity of 25 gpm, and a
detention time of about 20 minutes. Results indicated a possible 56
to 65% suspended solids removal with float solids up to 3.65%.
Chase^ reported on another pilot plant operated at 25 gpm with de
tention times from 15 to 35 minutes. Flotation reduced suspended
solids from 1700 ppm to 120 ppm and produced floats of 2 to 3% solids.
Vacuum-type flotation units in California remove hulls and (9 ) ^ skins from food processing wastes . The units have a 2 gpm/ft
overflow rate and a detention time of 10 to 20 minutes. Flotation is
also employed to treat oil refinery wastes in California. One instal
lation which follows primary sedimentation ta n k s ^ treats up to 5.8
mgd with two 35~feet diameter units. Sedimentation reduced oil con
tent from 7500 mg/1 to about 115 mg/1. The flotation units operating 2 at a 2 gpm/ft overflow rate reduced oil content to 35 ppm.
Other miscellaneous oil and grease containing wastes; such as,
those from machine shops, airplanes and railroad car working f a c ili
ties, have been treated satisfactorily by flotation. Success has
also been achieved in treating waste from the manufacture of soap and
edible oils.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Experience has also shown that there are wastes to which
flotation cannot be successfully applied. Each particular sludge
has its own peculiar characteristics which limit operational para
meters and performance of the process and variables are involved
which must be studied in detail prior to application.
Flotation Practiced by the Pulp and Paper Industry
Treatment of white water from papermachines to remove fiber
and f i l l e r accomplishes a valuable savings in recovered material,
in addition to reducing stream pollution. One successful method
employed by the pulp and paper industry to reclaim white water solids
is the flotation save-all. These particular save-alls have been ( 12) found to operate at efficiencies usually over 96%
The principle of the operation is similar to that of ore
flotation. Air is dissolved in the white water and then after a
short detention time, the bubbles which attach themselves to fibers
and floes float to the surface and are removed by skimming. Flota- ( 13) tion save-alls operate at reduced and at atmospheric pressures
It is important to generate bubbles of appropriate size to achieve
effective flotation. The addition of reagents which reduce the
w ettability of the fiber surfaces improve flotation; whereas, addi- (l 2») tion of alum to a pH below 5.2 reduces fiber flo a ta b ility
Chemical coagulation or flocculation has been found necessary
to aid with the removal of very fine suspended particles. Alum,
caustic soda, activated silica, rosin size and sodium aluminate can
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. be used as coagulants or the promotion of flocculation can be
achieved by using fatty acids which react with aluminum ions to
form insoluble soaps In some cases colloidal glues are added
to stabilize the foam and provide greater a ir buoyancy. However,
activated silica sol or a polyacrylamide flocculant have been used
in placei off glue i O 6)
An electrophoretic investigation of the Sveen-Pederson process
has shown that the zeta potential is stabilized at a point near zero
by the combined effect of alum and Sveen glue. This effect provides ( 13) the necessary condition for flocculation . Others have claimed
that the purpose of the alum is to give the a ir bubbles a positive
charge and promote attachment to negatively charged p a rtic le s ^ ^ .
It is also believed that rosin size coats the fibers and clay parti
cles to give them a nonpolar, air-avid surface which enhances flota- ( 13) tion . In general, the flotation reagents required to achieve
adequate solids recovery depend on the solids and chemicals present
i n the wh i te water.
The pulp and paper industry has also utilized flotation as a
means to separate printing ink from wastepaper stock. The wastepaper
is first slushed until free of fiber clusters and then diluted to a
consistency of approximately 0.8%. The chemicals required for flo ta
tion are then added. When groundwood is present, these chemicals
consist of sodium peroxide, sodium silicate and soft soap with a
fatty acid content of about kl%. The sodium peroxide and sodium
silicate serve to detach the ink from the fibers. For deinking
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. groundwood-free wastepaper which is not likely to yellow in alkali,
caustic soda may be substituted for the sodium peroxide and sodium „ ( 18) s i1icate
The soft soaps form insoluble calcium soaps which create
sticky flakes for accumulating ink particles and air bubbles. The
subsequent rising a ir bubbles carry the agglomerate of ink particles
and sticky flakes to the surface leaving the fibers behind. Fiber
losses are kept at a minimum by sending the froth from the primary
cell to a secondary cell for refloating. The accepts from the
secondary stage are returned to the primary cell. Usually only a
few fibers are left in the rejects which leave the secondary cell at
(l8) approximately 3 ~ 5% consistency .
Flotation of Clay Mineral
Flotation of clay is used as a means to recover the mineral
and for separating it from other minerals for purification. Suspen
sions of clays resemble charged colloids, and these charged particles
can easily be floated using cationic col lectors ^ ^ . Kellogg^ has
shown that kaolin can be readily separated from quartz with amines at
pH 3 and reported flo a ta b ility in decreasing order as kaolinite, mica
feldspar and quartz. Effective separation of clay from other mineral
requires careful control of pH and ions which may be present in the
system.
Ultraflotation, a modification of froth flotation, is used to
separate titanium dioxide from k a o lin ^ ^ . As applied to kaolin a
carrier mineral (ground limestone), is reagentized with a collector
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. which is selective for titaniferous minerals. Use of this auxiliary
agent extends the application of flotation to ultrafine micron and
submicron size anatase particles which w ill impart a creamy yellow
shade to kaolin even when present in small amounts. This process
removes about 70% of the anatase and yields kaolin, the underflow
product, with an improved brightness.
Successful separation and flotation of minerals depends on
the adsorption of collector at their surface to create a hydrophobic
film to enhance bubble-solid attachment. Consequently, an under
standing of the surface chemistry of the mineral is important for
selecting the proper collector. Kaolin particles usually exist in
thin plates with slightly negative surfaces and positively charged
edges. In aqueous suspensions, the surface charge will be affected
by pH and the presence of other ions. A study of the idealized (21) atomic model of a two layered clay particle shown in Figure 1
w ill help in explaining its surface chemistry. The basic structure
consists of layers of a tetrahedral silicon oxide unit linked to an
octahedral aluminum oxide array by the sharing of oxygen atoms.
Multiple layers of this unit cell structure are held together by
hydrogen bonding between the hydroxyls of the aluminum oxide sheet
and the oxygens of the silica layers. Thus, when the clay particle
is fractured parallel to the silica and alumina sheets, it is most
likely to occur between these hydrogen bonded layers. The created
surfaces have hydroxyl groups and oxygen atoms exposed and thus lead
to slightly negative surfaces.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 18
TETRAHEDRAL SHEET
\J/ OCTAHEDRAL SHEET
\/ /\ O “ Oxygen □ - Hydroxyl ± - Aluminum
(a)
(b)
Fig. 1. Atomic model of kaolinite (a) planar schematic of coor
dinated atoms (b) 3-dimensional structure.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 19
Cutting the sheets perpendicular to the layers and breaking
the Si-0 or Al-0 bonds forms edge surfaces capable of possessing
positive charges. When placed in water, the silicon and aluminum
atoms become balanced by forming bonds with hydroxyl and other nega
tively charged ions. However, ionization can occur at a low pH and
leave the edge surface positively charged. Thus, the mineral surface
is sensitive to pH changes as well as the presence of other ions and
this helps to explain why the delicate control of pH and ions is
necessary to achieve effective separation of minerals by flotation.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 20
PRESENTATION OF PROBLEM
The preceding sections show that kaolin and cellulosic fiber
can be recovered by flotation processes. Since these two materials
are major components of pulp and paper mill sludge, it is plausible
that sludge in totality can be thickened by the process of froth
flotation. However, Gehm's^ review of the complex residues pre
sent in sludge indicates two apparent problems with the flotation
method for dewatering sludges. F irstly, fiber and f ille r become
coated with starches, proteins, resins, etc. and thus offer an en
tire ly different surface structure for air bubble attachment. There
fore, because of the complex nature of sludge components, preferen
tial separation of particles may occur resulting in a reduced
efficiency of solids recovery.
A second problem lies within the inherent characteristic of
fibrous sludges to hold water. Interstitual water of imbibition is
extremely d iffic u lt to remove since it is so tightly bound. This
amount of tightly bound water by various papermill sludges has been
related to the electrical double layer of the particles by Zettle-
moyer et_ a_l_. (22-24). Because of hydrophilic nature of cellulosic
fibers and the colloidal sols present, it is difficult to dewater
sludges by simply allowing them to drain. Thus, the type of fiber
present and the extent of its hydration would be influential in the
extent of sludge dewatering by the flotation process. Similarly,
residues from coating mills would also be expected to exhibit d e tri
mental effects on both the recovery and dewatering of sludge material
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 21
by froth flotation.
Thus, the purpose of this study was to evaluate in the lab
oratory the application of a frothing process to recover and de
water a synthesized sludge which simulated the residue obtained from
pulp and paper mill effluent c la rifiers. Numerous frothers were
investigated for their ability to collect particles and produce
floats of high consistency. In addition to the synthesized sludge,
single component slurries of clay and fiber were used to evaluate
different types of collectors and also the influence of clay and
fiber to control the degree of dewatering.
Variables; such as, pH, chemical dosage, fiber freeness and
in itia l sludge consistency were examined to determine their effect
on the frothing process. Drainage of floats in the flotation chamber
was followed as detention time was increased.
The process and reagents used were evaluated on the basis of
the efficiency of separating the solids from the liquid phase, the
clarity of the subnatant liquid phase and the extent of solids con
centration achieved in floats.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 22
EXPERIMENTAL SECTION
The experimental procedure described in this section was
developed in the laboratory for this project. Since the composi
tion and nature of papermill sludge continuously change, a synthe
tic sludge was prepared for use in evaluating the flotation process
and chemical reagents. Studies were conducted to examine the
effects of pH and chemical dosage for several frothers. A study
was performed to determine an effective detention time in the
flotation chamber for achieving maximum float solids and to
observe whether drainage occurred in the froth. A variety of col
lectors were evaluated for promoting flotation using one of the
better frothers under selected conditions.
Floats were produced from homogeneous systems of clay and
cellulose fiber to provide a better understanding of the surface
forces involved. Cellulose fiber floats were also produced from
varied in itial consistencies and at different freeness levels.
Preparation of Synthesized Sludge and Homogeneous Systems
The synthetic sludge was composed of k2% fiber, kl% clay,
10% starch, 5.9% papermakers alum [A12 (SO^)^ * 1SH^O] , and 0.1%
latex based on total dry weight.
The source of fiber was printed news which was beaten to 200
CSf in a Valley beater at 2% consistency. Stayco M starch was cooked
in a double boiler at 20% solids for 15 minutes at 180°F. English
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 23
Star clay was dispersed in a Waring blendor at 50% solids for 5 min
utes. The above three components were combined with the addition of
Dow latex 630 and alum. Total solids of the synthesized slurry were
adjusted to k% and the mixture vigorously stirred for 2k hours to
simulate the effects of retention in a field c la rifie r. At the com
pletion of mixing, the sludge was analyzed for total and suspended
solids, pH, 100-mesh material, and ash content.
The homogeneous clay slurry was prepared by dispersing English
Star clay in a Waring blendor for 5 minutes at 20% solids and then
diluting to 1.0%.
Fiber for the homogeneous studies was bleached softwood sul
fite pulp which was beaten to the desired freeness in a Valley
beater at 2% consistency with 5500 g of pressure and then diluted
to a lower consistency for flotation.
Sludge Analysis and Solids Determination
Total solids
Total solids were determined by drying a 100 g sample in a
tared evaporating dish at 103°C ± 2°C.
% Total Solids = X 10°
Suspended solids
A 100 g sample was filtered through Whatman #2, 11 cm tared
f ilt e r paper using a Buchner funnel. The f ilt e r pad was then dried
in an oven at 103°C ± 2°C.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 4
% Suspended Sol ids = x 100 100 (g) The subnatant liquid suspended solids were determined by
filtering 10 ml through 5.5 cm, §2 Whatman f i l t e r paper and dried
at I03°C - 2°C.
% Suspended Solids = ^ x 100 10(g)
Ash content
After drying the sample for total solids, the evaporating
dish was heated in a muffle furnace at 600°C - 25°C for 4 hours.
% Ash = ash wt- (9> x ioo d ry wt. (g)
100-mesh material
A 500 g sample was washed with tap water on a 100-mesh screen
for 5 minutes. The retained material was filtered and dried at
I03°C - 2°C.
% 100-mesh = dpy "+ - x 100 500 (g)
Float soli ds
The float solids were calculated by subtracting the subnate
suspended solids from the initial solids and dividing this quantity
by the total mass of the flo a t, all terms expressed in grams.
, in itia l sol ids-suspended solids ^ lnri % Float Solids = ^ t -■;------rrt------r— r — , x 100 500 + initial solids - subnate vol.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Measurement of entra i ned a Ir
The volume of a ir entrained in the system was recorded as the
volume increase over the in itia l volume.
Flotation Procedure
The frothing chamber was a Waring blendor model No. PB-5A
which was used to incorporate the foam into the system. The speed
of the blendor was set on low and reduced further with a Superior
Electric powerstat type 116B which had a constant setting at 50 for
all tria ls . Chemical additions were made with a 0.1 ml pipette
with 0.01 ml graduations. When no collectors were being used, the
frother was added just prior to the agitation period. In trials
where both collector and frother were used, the frother was added
after the collector had been mixed with the sample for one minute.
After one minute agitation of a 500 ml sample with frother present,
the solution was transferred to a 1000 ml graduated cylinder, which
served as the flotation chamber where air-to-solids contact was
accomplished. Control samples which contained no flotation reagents
were run with all systems. After the float had formed during the
detention time prescribed below, the subnatant liquid and entrained
air volumes were recorded. Suspended solids were determined on the
subnate of the tria ls with the synthetic sludge and float solids
evaluated as described in the previous section. Trials with the
synthetic sludge were conducted in trip lic a te and floats with the
homogeneous systems were duplicated.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. pH Study
The effectiveness of flotation reagents depends to a large
extent on the pH of the system. Therefore, one of the objectives
of this study was to determine an optimum pH range for each
frother. Slurry pH was adjusted with sodium hydroxide or sulfuric
acid and measured with a Beckman Zeromatic pH meter model No. 96.
Flotation of the synthetic sludge was done at pH levels of 4.0,
5.0, 6.0, 7.0, 8.0, 9.0, and 10.0 using 1.0% frother on a dry weight
basis on a sludge of 2.0% in itia l consistency. Detention time in
the flotation chamber was 20 minutes.
Dosage Study
In order to determine an optimum frother dosage for use in
further investigations, floats were produced from synthetic sludge
at different chemical addition levels. Dosages of 2.00, 1.00, 0.50,
0.25, and 0.05%, dry weight basis, were used at a pH of 7.0 and at
in itial sludge consistency of 2.0%. Detention time in the flotation
chamber was 20 minutes.
Detention Study
Detention time in the flotation chamber was varied to observe
the concentration of float solids versus time and measure float
drainage at the liquid surface. Six similar floats were produced
from synthetic sludge at a 2.0% in itia l consistency with pH at 8.0.
Dosage for frothers F-65, F-250, F-P0, F -1565 was 1%, and 2% for fro-
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. thers F-2^9 and F-AO on a dry weight basis. Refer to Appendix 11 for
identification and further information on these chemicals. Float and
subnate suspended solids, entrained air and subnate volume were deter
mined at intervals of 20 minutes, 1, 2, k, 8, and 2*4 hours. Control
samples which did not contain frother were also analyzed after 2h
hours.
Evaluation of Collectors
A variety of collectors were evaluated for promoting flotation
by using them in combination with frother F-65. A complete list of
the collectors used appears in Appendix II. The collector was added
firs t and given 1 minute to react with the sludge particles before
addition of frother. Frother dosage was 1.0% and the collector was
added in amounts of 0.5, 1.0 and 2.0% on a dry weight basis. Deten
tion time in the flotation chamber was 30 minutes.
Flotation of Homogeneous Systems
Flotation was performed with homogeneous systems of clay and
cellulose fiber to study the surface forces involved in collection.
The freeness of the fiber was 350 CSf. Anionic frother F-250 and
cationic frother F-61 were used to determine their effectiveness in
floating the negative particles. Since the foaming tendency of the
frother and the froth stability are affected by pH, flotation of the
homogeneous systems was conducted at pH's of b.O and 9.0. Homogene
ous clay slurries were maintained at 1.0% while fiber consistencies
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 28
varied from 0.1 to 1.0%.
Cationic collectors DN-80, AM-D, and anionic A-GPG, P-25, AF-
238, AP-710, AP-801, Z-6 and cationic polymer RT -763 were used with
frothers F-61 and F-250 for promoting flotation of the homogeneous
slurries. Refer to Appendix I for identification and further
information on these chemicals. Dosage was 1.0% dry weight basis
for frother and collector and detention time in the flotation chamber
was 20 minutes.
As a control and a further indication of foaming tendency and
froth stability of the two above frothers, frothing was done in
d istilled water with no particles present at pH's of 4.0, 6.0, 8.0,
and 10.0. Dosage was 0.02% by volume and the foam volume was
recorded in itia lly and at intervals of 100, 300, and 1200 seconds.
Freeness Effect on Float Solids
Floats were produced from 1.0% fiber suspensions at Canadian
Standard freeness values of 700, 500, 300, and 100. Cationic fro
ther F-61 was used alone and with cationic collector AM-D at a pH of
4.0 and 9.0. Anionic frother F-250 was also used by its e lf and
with anionic collector P-25. Dosage was 1.0% dry weight basis and
detention time was 20 minutes in the flotation chamber.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. PRESENTATION AND DISCUSSION OF EXPERIMENTAL RESULTS
Froth Stability in D istilled Water
The effectiveness of the flotation process was evaluated
according to its a b ility to separate solids from the liquid phase
and by the dryness of the floats produced. Achievement of good
separation and high float solids was consequently dependent upon
the volume and stab ility of the froth produced since larger foam
volumes increased the probability of bubble-solid contact and froth
stab ility provided structure and support to allow drainage of floats.
Thus, the foaming tendency and froth stab ility of the frother was
c ritic a lly important to the efficiency of the process. Since the
performance of most frothers is affected by pH, the foaming capacity
and froth stability was measured for two frothers at pH levels of
h.0, 6.0, 8.0 and 10.0 in d istilled water. The frothers evaluated
were F-250, a polypropylene glycol methyl ether which can be repre
sented by the formula CH^-(0C2Hg)x - OH and F-61, a cationic amine
complex. Frothing tendency was measured as the volume of froth pro
duced and s ta b ility was indicated by the rate of froth collapse.
The average results of this study are presented in Table I.
A definite pH effect occurred for both frothers. Greater
stab ility of froth was demonstrated for F-250 at increasing pH
levels as evidenced by the slower rate of froth collapse. Since the
collapse rate was faster at lower pH levels, the small difference in
in itial froth volumes was probably an effect of a short time lapse
before the fir s t reading was taken and the actual frothing tendency
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 30
was comparable at each level. However, the froth produced with F-61
was relatively stable at each pH level, but the initial froth volume
varied. The largest volume of froth with F-61 was at pH 6.0 and also
appeared slightly more stable at this level. Although F-250 dis
played a much higher frothing tendency than F-61, the stab ility from
F-61 was superior at all pH levels. In the experiments that follow
it also was found that the best performance of F-250 was at an ele
vated pH while F-61 performed best at low pH. This, of course, was
in agreement with the findings of this test.
Frothing tendency is of course a function of the frother's
chemical structure and its interaction with water, but the volume
of foam produced is also related to bubble size and foam dryness.
Froth s tab ility on the other hand is affected by bubble size, elec- (25) trical effects and small particles within the froth. Small bubbles
are more stable than larger ones; whereas, charge repulsion stab
ilizes bubbles and retards coalescence, as do small particles which
keep bubbles separated. The greater stab ility displayed by F-61,
a mixture of octadecyl amine and octadecyl guanidine, was most likely
the result of repulsion by the cationic frother. An alkyl amine;
such as F-61, has a pK value of approximately 10.6 and thus becomes
more ionized with decreasing pH and consequently exhibits greater
stab ility due to charge repulsion. On the other hand, the stability
of froth from F-250 was essentially unaffected by electrical effects (26) since the pK for an alcohol is 16 or greater. in the experiments a that follow it was noted that the froth of F-250 was stabilized by
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE I
FROTH VOLUME AND STABILITY IN DISTILLED WATER
Time
F rother ___rh In itial 100 sec 300 sec. 1200 sec. Entrained a ir volume (ml.) F-250 4. 0 300 70 30 15
6.0 320 85 30 15
8.0 345 200 65 15
10.0 340 270 150 15
F-61 4.0 175 160 150 130
6.0 200 200 200 190
8.0 130 125 125 95 CO in 10.0 110 100 90
Frother dosage - 0.02% by volume
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 32
the presence of the fine particles which prevent coalescence of
bubbles.
Effect of pH and Fiber Consistency on Frother Performance
A selection of frothers was evaluated for floating 0.1 and
1.0% fiber suspensions at pH's i*.0 and 9.0. The float solids pro
duced are presented in Table II.
Fiber consistency had lit t le or no effect at all on the
ability of the frothers to float the fiber to the surface. In all
cases except with F-65 at pH *4.0, fiber was collected. In almost
all trials the dryness of the floats could be correlated with the vol
ume of entrained a ir; with larger volumes allowing more drainage and
thus higher concentration of floats. In the one exception with F-61
at pH i».0 and 0.1% fib e r, such a large dense volume of froth was pro
duced that drainage was inhibited by the froth its e lf. Since the
fiber was efficiently floated at all conditions when sufficient froth
was produced, it was concluded that the fibrous particles were easily
entrapped by the a ir bubbles and that no conditioning with collectors
was necessary to promote bubble-solid attachment. However, the
solids content of the floats were extremely low since cellulose is
very hygroscopic and thus very reluctant to give up water. Con
sequently, but in agreement with Gehm^ , highly hydrophilic mater
ials such as cellulose fiber control the drying of fibrous floats as
well as the drainage of sludges.
The pH of the system had a noticeable effect on the volume of
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 33 TABLE I I
EFFECT OF pH AND FIBER CONSISTENCY ON FROTH FLOTATION
jjH ~ 4.0 pH - 9.0 Entra i ned Float Entra ined Float a i r Subnate soli ds a i r Subnate solids (ml.) (%) Frother (ml.) (ml.) (%) (ml.)
1.03 Fiber 1.01 0 0 Control 2 10 220 1.75 40 275 2.18 F-71 23 28 230 1 .82 F-350 18 140 1.37 118 365 3.57 F-250 20 190 1.59 220 1.75 F-61 85 360 3.45 35 265 2.08 F-1565 20 185 1.56 45 60 300 2.kb F-77 15 160 1.45 205 1.67 F-73 15 150 1.41 25 355 3.33 F-65 15 185 1.56 110 2.27 F-PO 20 170 1.49 45 285 F-AO 80 325 2.78 75 315 2.63
0.1% Fiber
settled - Control 0 settled 0 485 3.22 F-71 20 175 0.16 45 3.70 F-350 25 472 1.75 50 487 1 .10 F-250 20 220 0.41 15 455 3.22 F-61 172 465 1.41 43 485 482 2.70 F-1565 18 400 0.50 38 1.10 F-77 15 380 0.41 12 455 40 482 2.70 F-73 20 b70 1.64 20 470 1.64 F-65 5 sett led 3.22 F-PO 15 390 0.45 50 485 3.70 F-AO 15 b70 1.64 42 487
Detention time - 20 minutes in flotation chamber
Frother dosage - 1.0% dry weight basis
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3k
entrained air obtained. The greater volume was obtained at pH 9.0
for all frothers but two. F-61 as in the preceding section performed
best at pH k.O while F-AO was affected very lit t le by pH. The pre
sence of solid particles stabilized the froths with the volumes
presented in Table II s till existing after 20 minutes. Some of the
froths such as those from F-250 and F-65 displayed better sta b ility
against collapse with the higher concentration of fiber present.
The results of this phase of the study indicated that an
optimum volume of entrained a ir should be incorporated into the froth
for maximum concentration of solids. Below this critical volume,
insufficient separation of solids from the liquid phase is achieved
and l i t t l e drainage within the froth occurs. However, if the en
trained a ir volume is too large, added moisture is retained by the
extra air bubbles and thus reduces the overall dryness of the froth.
Flotation of Fibers Conditioned with Collectors
In this phase of the study, a variety of collectors were
evaluated for their a b ility to improve drainage from floats con
taining cellulose fibers. Frothing was provided by frothers F-250
and F-61 at pH's of k.O and 9.0. The control designates the float
produced with frother alone. The results are presented in Table III.
Comparison of the float solids in Table III to Table II shows
that no improvement in drainage was obtained by using the collectors.
Float solids drier than the control were only obtained when the add
ed collector provided increased frothing power. Thus with larger
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 35 TABLE I I I
FROTH FLOTATION OF 1.0% FIBERS WITH COLLECTORS
Frother F-61 Frother F- 250 Entra i ned Float Entra i ned Float a i r Subnate soli ds ai r Subnate soli ds Col lector (ml.) (ml .) (%) (ml .) (ml .) (%)
pH 4.0
Control 70 315 2.63 55 290 2.33 A-GPG 35 225 1 .78 160 380 4.00 P-25 20 135 1.35 105 360 3.45 AP-801 30 200 1.64 **5 245 1.92 AP-710 30 240 1 .89 20 110 1.26 DN-80 ko 275 2.17 15 50 1.10 Z-6 50 310 2.56 105 350 3.22 AF-238 60 330 2.86 45 280 2.22 RT-763 95 370 3.70 40 270 2.13 AM-D 120 390 4.35 55 275 2.17
pH 9.0
Control 25 190 1.59 100 310 2.56 A-GPG 35 230 1.82 150 370 3.70 P-25 25 190 1.59 90 310 2.56 AP-801 25 125 1.32 155 365 3.57 AP-710 30 145 1.39 55 270 2.12 DN-80 k7 260 2.04 35 240 1.89 Z-6 25 125 1.32 85 305 2.50 AF-238 50 280 2.22 120 340 3.03 RT-763 45 260 2.04 70 270 2.13 AM-D 210 395 4.54 50 250 1.96
Detention time - 20 minutes in flotation chamber
Frother and Collector dosage - 1.0% dry weight basis
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 36
volumes of entrained a ir, better drainage was possible. However, in
many cases the addition of collector resulted in an unfavorable
reaction and frothing action was reduced to a level below that of
the frother by its e lf. This behavior was obviously undesirable and
indicated that the frother and collector must be compatible. The
reduction in the volume of entrained air could be attributed to a
loss in frothing tendency or reduced froth stab ility as a result of
the formation of salts between oppositely charged collector and
frother. Collectors P-25, AP-801, AP-710, Z-6 and AF-238 are anionic
and obviously had a detrimental effect on the frothing produced by
cationic frother F-61 at pH 4.0 where this frother would be highly
ionized. Similar losses in frothing power occurred with the some
what anionic alcohol F-250 and the cationic collectors DN-80, RT -763
and AM-D at pH 9.0. Although the ionic nature of A-GPG was not
available, it appeared to be anionic since it was compatible with
F-250 and added frothing capability whereas it reduced the entrained
a ir volumes with F-61.
Flotation of cellulose fiber was not dependent on the type
of charge of the collector or frother. This result further sub
stantiated the conclusion that fiber collection by bubbles occurred
by physical entrapment rather than electrical attraction.
With all reagents studied, the fiber was effectively floated
to the surface; with the larger volumes of entrained a ir providing
better drainage of floats. However, the combination of frother and
collector was an important consideration since the compatibility of
these two reagents affected the volume of entrained a ir.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Effect of Freeness on Float Drainage
The fact that cellulosic fiber controlled the dryness of floats
indicated that fiber freeness would also be an important factor to
be considered in the concentration of sludge by the flotation pro
cess. Therefore, floats were produced from 1.0% fiber suspensions
at various freeness to measure this effect. The results are re
corded in Table IV.
Float solids have been presented as calculated and measured
values. Calculated values were determined by using the known weight
of in itia l fiber and the weight of water contained in the float which
was simply the difference between the in itia l and subnate volumes.
Measured float solids were determined by drying a lOg sample taken
from the top of the float. The higher solids obtained for the
measured results demonstrated the drainage effect that was taking
place within the float. This difference between calculated and
measured float solids has been graphically, illustrated in Figure 2
for floats obtained with F-6l at pH k.O and F-250 at pH 9.0 versus
Canadian Standard freeness. Not only was the top portion of the
float drier, but floats were also drier for the least refined pulp
fiber. This anticipated result was due to hydration of the fibers
from the beating action which fib rilla te d and frayed the fibers.
Consequently the increased surface area exposed increased numbers of
hydroxyls which in turn provided for a larger quantity of adsorbed
water. Thus as the degree of beating increased, the hygroscopic
nature of the fiber also increased and floats from well-beaten fiber
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE IV 38
EFFECT o f f r e e n e s s on f l o a t s o l i d s
pH - A.O pH - 9.0
Canad ian Entrained Float Entrained Float Standard a ir solids (?) air solids (?) Reagent F reeness (ml •) Calc. Det'd. (ml.) Calc. Det'd.
F-61 700 85 3.38 k.kS 25 1. 6A 2.31 F-61 500 90 3.03 A. 2k 30 1.56 2.35 F-61 300 85 2.86 A. 10 A0 1.96 2.80 F-61 100 80 2.63 3.A5 A0 1.92 2. 6A F-61 + AM-D 700 125 A. 00 5.57 315 8.33 6.96 F-61 + AM-D 500 115 3.33 A.79 270 A.76 6.05 F-61 + AM-D 300 125 3.33 5.0A 280 5.26 6.01 ; F-61 + AM-D 100 13° 2.9A A. 25 270 3.85 A.62 ! F-250 700 25 1.6k 2.38 85 2.38 A.30 F-250 500 30 1.5k 2.38 70 2.27 3.62 F-250 300 30 1,6k 2.09 75 2.17 3.31 F-250 100 28 1.6k 2.00 65 2.13 3.0A F-250 + P-25 700 30 1 .37 1.9A 80 2.50 A.00 F-250 + P-25 500 35 1 .kS 1.96 85 2.32 3.71 F-250 + P-25 300 A0 1.59 1.92 95 2.32 3.53 i F-250 + ! p-25 100 35 1.39 1.78 80 2.13 3.17
Detention time - 20 minutes in flotation chamber
Frother and collector dosage - 1.0? dry weight basis
In itia l solids - 1.0% fiber
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 39
5.0
4.0
'Q7 Float Soli ds .0
.0
a - D-250, measured
• - D-250, calculated
100 300 500 700
C.S.f.
Fig. 2. Calculated and determined float solids versus Canadian Standard
freeness.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 40
retained more water. This effect was the most pronounced in the
floats containing large volumes of entrained a ir where more drainage
could occur. Froths containing small volumes of a ir had li t t l e
opportunity to drain and the solids were approximately the same at
each freeness level.
Once again there was a correlation between the solids content
of the froth and the volume of entrained air. However, even with
large volumes of entrained a ir and relatively unbeaten fiber, the
consistency of the float was s till very low. This result demonstrated
again that cellulose fiber had an important effect on the drainage
of floats and that the dewatering of fibrous sludges would be highly
dependent upon the percentage and type of fiber content.
Flotation of Clay
Table V contains the results of flotation experiments using
frothers F-61 and F-250 with a variety of collectors to float 1.0?
clay suspensions at pH's of 4.0 and 9-0.
The results of this study show that the smaller clay particles
were not as easily collected by air bubbles as was the bulky fibrous
cellulose. In several instances only part of the clay was floated
or in two cases none at a ll. However, when floats were achieved,
they were more concentrated than the cellulose floats since clay is
less hygroscopic compared to cellulose. No floats were achieved in
control #1 in which the procedure was performed without any frother
or collector. In the second control, frother was used and collection
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. was achieved with F-61; whereas with F-250, failure of an effective
bubble-particle attachment resulted in an unstable froth which coll
apsed with a similar behavior as the frothing trials in distilled
water. The successful flotation by the cationic amine frother F-61
indicated that a favorable reaction occured between the clay and
frother and promoted bubble-solid attachment. This result is of
course in agreement with the literature in that successful flotation
of clay occurs with cationic amines. The solids content of the con
trol flo at, however, was not very high but this was due to the small
volume of entrained a ir which provided an ineffective separation
from the water phase for good drainage.
Complete collection of clay was accomplished with F-61 leav
ing a clear liquid phase beneath the froth. With additional en
trained air volumes within the froth using the collectors a still
more concentrated float resulted. However, there was not a direct
correlation between the volume of entrained a ir and the dryness
achieved by floats. Deviation was the result of large volumes of
froth retaining additional moisture at the extra surface created by
the bubbles. This was especially true in the tria ls with AM-D.
Yet, even with similar quantities of entrained air, there was a
wide variation in the dryness of the obtained floats as in the trials
with DN-80 and AP-710 at pH ^.0. Consequently it appears that the
cationic DN-80 was effective in reacting with the anionic surface of
clay to form a more hydrophobic surface which would not retain as
much adsorbed water as the unmodified clay with hydroxyls to hydro
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. gen bond to water. On the other hand, AP-710 is a fatty acid and
thus anionic and did not form a protective coating on the kaolin
particles to assist drainage.
Although successful flotation of clay was achieved using
anionic collectors, the contribution in promoting collection by
these charged reagents can not be readily evaluated. In the trials
performed with F-61 the frother was capable of collecting the clay
and the drier floats obtained with anionic collectors may only be an
effect of increased frothing power. In the cases with F-250 where
anionic collectors AP-801, a sulphonate, and AP-710, a fatty acid,
achieved flotation, large volumes of air were entrained within the
froth. Thus flotation may have been the result of physical entrap
ment rather than a promotional effect achieved by collector-kaolin
reaction. However, the dryness of the float with AP-801 compared to
that of DN-80 at pH 9.0 with equal volume of entrained air does in
dicate a promotional drying effect by this anionic collector. The
quality of the foam produced in retaining moisture and allowing
drainage would also appear to be an important consideration in using
flotation to concentrate fibrous sludges.
The partial floats were recorded when only part of the clay
was floated and the rest settled. The occurrence of this result may
have been due to insufficient dosage or adsorption of collector on
the clay surface for promoting bubble-particle attachment. The
quality of the air bubbles may also have been influential in the in
complete separation; such as, large bubbles will rise to the surface
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 43
TABLE V
FROTH FLOTATION OF 1.OS CLAY WITH COLLECTORS AND FROTHERS F-61 AND F-250
pH - 4.0 pH - 9.0 Frother - F- 61 Frother - F- 250
Entra i ned Entra i ned a i r Subnate Float a i r Subnate Float volume vo 1ume so f i ds vo 1ume vo 1ume sol ids Col lector (ml.) (ml.) (S) (ml .) (ml.) (%)
Control-1 0 settled no 0 settled no f loat float
Control-2 30 385 4.17 0 settled no float
DN-80 65 485 25.00 140 440 7.69
AP-801 35 settled parti al 140 492 38.46 float
AP-710 60 450 9.09 230 470 14.28
AF-238 95 430 6.67 90 settled part ia1 float
AM-D 350 460 11.11 410 450 9.09
P-25 65 480 20.00 105 sett 1ed part ia1 float
A-GPG 65 sett led parti al 200 sett led part ia1 float float
RT-763 90 445 8.33 30 sett 1ed partial float
Z-6 115 460 11.11 10 sett 1ed no float Detention time 20 minutes in flotation chamber
Frother and collector dosage - 1 .OS dry weight basis
Control-1 without flotation reagents; Control-2 with IS frother
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. kk
so fast that they separate from particles on the way to the surface.
Physical entrapment, however, was most likely responsible for some
collection when large volumes of air were entrained in the froth.
Results that contained only partial or no float point out
the sensitive nature of clay flotation. However, in the successful
tria ls , kaolin was completely separated from the liquid phase leaving
clear water beneath the froth. Finally, since kaolin is much less
hygroscopic than cellulose, the resulting floats with clay were
concentrated to a much higher level than those with cellulose fiber.
Effect of pH on Flotation of Synthetic Sludge
This phase of the flotation investigation was performed with
the synthesized sludge containing fiber, clay, starch, latex and
alum as described in the experimental section. The effect of pH
chemical dosage, float-draining time and conditioning agents were
evaluated for the flotation process with the synthetic sludge. The
results from the pH study using a variety of frothers are presented
in Table VI.
The volume of air entrained in the froth increased for all frothers
as the pH was elevated, but was the most pronounced for F-65, F-250
and F-AO as evidenced by the curves in Figure 3- The entrained air
volume for frother F-PO, F-1565 and F-249 increased only moderately
with rising pH. Frothers F-AO and F-15&5 were the best foamers at pH
4.0 and 5.0 and also gave the higher float solids at this pH; and,
therefore, would be good frothers in a fluctuating pH system. The
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 45
TABLE V I
EFFECT OF pH ON FROTH FLOTATION OF SYNTHETIC SLUDGE
pH Frother 4.0 5.0 6.0 7.0 8.0 9.0 10.0 Float soli ds {%) Control 2.02 2.10 2.08 2.44 2.48 2.60 2.68 F-65 3.33 3.15 3.85 4.73 4.69 5.06 4.92 F-250 3.65 3.86 4.28 5.00 4.96 5.29 5.29 F-PO 3.64 3.99 4.18 4.02 4.13 4.22 4.21 F-AO 4.02 A.23 4.06 4.32 4.65 4.78 4.64 F -1565 3.94 4.11 4.07 4.47 4.37 4.49 4.53 F-249 2.99 2.99 3.29 3.44 3.75 3.87 3.97 Subnate volume (ml.)
Control 0 9 0 100 100 110 120 F-65 163 183 223 256 273 273 266 F-250 153 170 216 226 243 250 240 F-PO 189 200 206 206 2.10 216 220 F-AO 190 203 223 236 253 246 246 F -l565 200 206 203 223 220 236 223 F-249 106 110 136 160 190 200 200 Solids removal eff i ci ency {%) F-65 97.5 95.5 97.9 98.4 97.6 97.2 96.3 F-250 93.1 94.2 96.2 98.4 96.8 97.7 96.8 F-PO 96.3 97.9 98.5 98.2 98.1 97.7 97.8 F-AO 98.3 98.5 98.9 98.9 98.8 99.1 98.8 F-1565 98.1 98.5 97.5 99.2 99.2 98.4 98.6 F-249 98.1 97.1 98.4 98.7 98.6 98.3 98.4 Entrained air volume (ml.)
Control 0 0 0 15 15 15 25 F-65 8 18 43 88 97 103 90 F-250 22 32 55 92 102 117 115 F-PO 20 40 47 43 55 58 53 F-AO 55 60 87 102 120 113 110 F -l565 50 52 55 67 68 70 72 F-249 8 12 23 27 38 40 50
Suspended solids were not determined on control due to small subnate volume.
Frother dosage - 1.0% dry weight basis
Detention time - 20 minutes in flotation chamber
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. erdcd ih emsin fte oyih onr Frhrrpouto poiie ihu permission. without prohibited reproduction Further owner. copyright the of permission with Reproduced Fig. Fig. Float Solids, % 21 Entrained Volume, ml . . fet f H n h vlm o foh rdcd y aiu frothers. various by produced froth volume of the pH on of Effect 3. g. 2.00 3.00 5.00 100 b. ocnrto o fot ois hw a iet eainhp o volume to relationship direct shows a solids float of Concentration f r nrie i te froth. the in entrained ir a of 10 •A< 20 5.0 30 * nrie Ar oue ml Volume, Air Entrained *t 0 6.0 7.0 60 8.0
80 9.0 100 10.0 b& b7
increase in the froth volume with rising pH can be attributed to
either a greater frothing tendency or improved froth stability.
However, since the entrained air volume was measured at various time
intervals and remained constant during the detention time at each pH
level, it was concluded that the froth was stable and the change was
due to increased frothing power. This conclusion was also supported
by the fact that the control displayed increased frothing tendency
at higher pH conditions.
Along with the increase in entrained a ir, there was a corres
ponding increase in the solids content of the flo at. This correlation
is illustrated in Figure b where the entrained a ir volume is plotted j against the solids concentration of the floats. This effect was
attributed to better drainage of the bulkier floats due to increased
support and better separation from the liquid phase. The float
solids reported in Table VI were determined from a 50 g sample re
moved from the top of the float and thus represented the drier por
tion of the float as was demonstrated in the study of freeness effects.
This method of sampling for float solids was not without warranty
since the lower section of the float containing reusable chemicals
can be recycled to the flotation chamber as practiced by the mining
industry. However, even the solids content of the drier portion of
the floats were not substantially high and the actual prominance of
these results, of course, depend on the application of the process.
If used to concentrate sludge as removed from primary settling tanks,
which was the in itia l consideration in this study, this process would
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. not be practical. Most c la rifie rs for pulp and papermlll waste
water treatment produce sludge at a solids content of at least
or higher before being further dewatered by some secondary process;
such as, centrifuging, vacuum filterin g or large drying basins.
With the flotation process, a secondary stage would s t ill be nec
essary; and, therefore, if used in conjunction with settling tanks,
flotation would increase the cost, time and space for water p u rifi
cation. However, it may be possible to substitute the flotation pro
cess for the settling operation which is not only space consuming and
slow, but its efficiency is highly dependent on the nature of the
solids and environmental conditions. The flotation process could be
applied at various locations in the mill where better control of
conditions could be maintained and since the rate of bubble rise is
faster than the settling of many solids contained in waste water,
the process could possibly increase the rate of water purification
and/or cut down on the space required. The actual applicability of
flotation, of course, would depend on the solids removal efficiency
and the operational cost, the latter of which was not a consideration
in this study.
The solids removal efficiency was calculated by difference
between the suspended solids of the subnate liquid and the known
in itia l sclids. These calculated values reported in Table VI show
a high efficiency of solids removal with an average value of almost
98%. There was no apparent difference in the solids recovery at the
various pH levels, and, therefore, it was concluded that the solids
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ks
were simply entrapped by the dense bubble mass moving upward and that
solid-bubble attachment was independent of pH at these conditions.
A large fraction of the clay was probably collected by the bulky mass
of a ir bubbles and fibers as they moved toward the surface. It can
only be concluded, however, that pH control was not critical for the
removal of solids if the system contained a high percentage of fiber
and the in itia l solids concentration was near the 2% level. At a
lower solids concentration; such as, exists in the clarifier influ
ent, or in less fibrous sludges, pH would be more critical to solid-
bubble attachment as has already been demonstrated in the homogeneous
clay systems.
Effect of Frother Dosage on Flotation of Synthetic Sludge
The effects of frother dosage on frothing power, collection
efficiency and solids concentration were examined with the synthetic
sludge at 2% in itia l solids and pH 7. The results obtained with
dosages of 0.05, 0.25, 0.50 , 1.00 and 2 .00% on a dry weight basis of
solids are reported in Table V II.
For frothers F-AO and F-2^9, there was a definite reduction in the
float solids, entrained a ir and subnate volume as the dosage was decreased
from 2.00 to 0.25 %; whereas, the change was very lit t le for the other fro
thers. A pronounced decrease in entrained air with corresponding
reductions in float solids and subnate volume occurred for all frothers
(except F-2^9) as dosage was further decreased to 0.05% which is
equivalent to one pound per ton of solids. However, the efficiency
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE V I I
EFFECT OF FROTHER DOSAGE ON FLOTATION OF SYNTHETIC SLUDGE
Frother dosage - dry weight basis
Frother 2 .00% 1.00% 0.50% 0.25% 0.05% Float soli ds (%) F-65 4.72 5.03 5.04 4.87 4.48 F-77 4.3 8 4.70 4.65 4.28 3.74 F-PO 3.97 4.73 4.46 4.46 3.72 F -l565 4.41 4.47 4.63 4.24 3.64 F-AO 4.26 4.28 4.04 3.68 3.44 F-250 4.63 4.91 4.41 4.61 3.87 F-249 4.49 4.04 4.00 3.28 3.36 Subnate volume (ml.) F-65 277 250 247 243 200 F-77 230 237 230 220 183 F-PO 237 223 223 223 173 F -l565 253 223 230 223 167 F-AO 247 200 160 173 130 F-250 273 237 247 250 190 F-249 250 200 160 153 137 Solids removal efficiency (%) F-65 31.5 98.2 98.5 98.4 98.5 F-77 98.3 98.8 98.4 98.9 98.6 F-PO 98.2 98.5 98.5 98.2 98.5 F -l565 97.1 98.2 98.5 98.7 98.8 F-AO 98.0 98.7 98.8 98.8 98.9 F-250 31.1 98.8 98.6 97.8 98.7 F-249 3 1 .4 98.6 98.8 98.7 98.6 Entrained a ir volume (ml.)
F-65 82 68 85 70 35 F-77 53 60 67 55 28 F-PO 53 57 65 52 25 F -l565 67 50 75 55 18 F-AO 62 37 25 32 13 F-250 88 78 83 72 30 F-249 85 47 37 23 13
Control - 2.62% float solids
pH - 7.0
Detention time - 20 minutes in flotation chamber
Initial solids - 2 .0%
£
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 51
of solids removal remained undiminished at the lower level of frother
addition as solids recovery averaged better than 38%. Again the
correlation between float solids and entrained air volume was evident
at 0.05 % frother addition where drainage was minimized due to in
effective bulk and support by the small a ir mass. However, separation
of solids from the liquid phase was good at the low dosage level and
could be effective at still lower additions of chemical by recycling
the lower section of the float and thus conserving frother. Since
the final solids concentration was not very high compared to the
in itia l solids content of the sludge, the process was much more im
pressive in its ab ility to remove solids from the liquid phase
rather than concentrating them further.
Effect of Detention Time in the Flotation Chamber on Float Sol ids
Drainage of floats (changes in suspended solids of the sub-
natant liquid and stability of the froths) was determined by analy
zing floats and subnatesat intervals of 20 minutes, 1, 2 , 4, 8 and
24 hours. Floats were produced from the six frothers using the
synthetic sludge at 2% initial solids and at pH 8 . The results are
presented in Table V III.
As shown in Table V III, the float solids and subnatant volume
increased with time for all frothers as drainage occurred in the
froth. Drainage as measured by the change in subnate liquid below
the float was not significant after a detention period of 2 hours.
The drainage which did occur was definitely related to the volume of
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE VIII
EFFECT OF DETENTION T IM E IN THE FLO TATIO N CHAMBER ON SYNTHETIC SLUDGE FLOAT SOLIDS
Frother (dry Time - i n the flotation chamber weight basis) 20 min. 1 hr. 2 hr. 4 hr. 8 hr. 24 hr.
Float solids (2)
1% F-65 5.24 6.01 6.23 6.13 6.22 6.43 12 F-250 4.89 5.16 5.45 5.82 6.09 7.32 2% F-249 4.94 5.73 6.07 6.29 6.71 7.33 12 F-PO 4.41 5.00 4.97 5.19 5.36 5.67 12 F -1565 4.77 5.38 5.49 5.73 5.85 6.08 22 F-AO 4.21 4.70 4.91 5.13 5.06 5.39 Subnate volume (ml .) 12 F-65 300 327 337 343 345 337 12 F-250 263 307 321 330 336 340 22 F-249 250 317 337 347 347 348 12 F-PO 247 283 300 310 317 317 12 F -l565 243 283 300 307 313 320 22 F-AO 243 280 300 300 303 305 Sol ids removal efficiency ( 2)
12 F-65 97.9 98.0 96.9 96.6 96.2 97.5 12 F-250 98.0 98.2 9-7.9 98.1 98.1 97.4 22 F-249 98.3 99.0 98.2 98.3 97.5 97.8 12 F-PO 97.2 97.6 97.7 96.5 97.3 97.7 12 F -1565 98.2 97.2 95.6 97.4 97.2 97.8 22 F-AO 98.3 97.8 98.3 97.8 97.8 98.1 Entrained a ir volume (ml.)
12 F-65 97 97 97 97 97 92 12 F-250 90 90 90 90 90 85 22 F-249 112 112 112 112 112 108 12 F-PO 62 62 62 62 62 60 12 F -l565 75 75 75 75 75 75 22 F-AO 63 63 63 63 63 52
pH 8.0
Control float solids - 3.642 after 24 hours
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 53
entrained a ir as can be seen by the correlation between volume of
entrained a ir , float solids and subnatant liquid.
The stab ility of the froth was quite pronounced as demonstrated
by the almost constant volume of entrained a ir. Entrainment of the
air in the froth provided the float with bulk and body not typical of
sludges of only ^ or 5% solids as a heaping handful or spoonful could
be held without overflowing. The significance of this feature, of
course, would be in the handling of the froth after its production.
Due to its stable structure and body, the froth could possibly be
transferred by conveyor belt, more easily trucked or perhaps sent
through a screw press for further dewatering. The structure of the
froth might also provide for faster drying of sludges in large dry
ing basins. However, if the froth was to be treated by vacuum
filte rs or centrifuges, the foam would need to be broken down to
facilitate treatment.
Collection of the solids into the froth was again highly
efficien t as efficiency of removal averaged better than 97%. Since
the suspended solids content of the subnate did not increase in the
2^-hour detention period, it was concluded that the fine solid
particles as well as the larger ones were well supported and con
tained within the froth.
Flotation of Synthetic Sludge Using Collectors and Frother F-65
A variety of collectors; which included fatty acids, amines,
xanthates, sulfonates, dithiophosphoric acid salts and surface active
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5b
agents were evaluated for promoting flotation of the synthetic
sludge with frother F-65. Frother F-65 was used in this study at
1.0% with collector dosages of 0.5, 1.0 and 2.0% on a dry weight
basis. The control was the float produced from similar sludge using
only the frother. The float solids from this study are presented in
Table IX. Indentification of the collectors can be found in Appendix
I .
Similarly, as in the homogeneous fiber system, the collectors
did not aid in the concentration of floats. In most cases the con
trol (frother only) produced a drier float. When float solids drier
than the control were obtained, there was a corresponding increase in
the volume of entrained a ir. Consequently, it was concluded that the
increase in float solids was due to increased drainage rather than to
any change in surface characteristics of the solid particles. Trials
in which the frothing tendency was reduced to a level below that of
the control again indicated the incompatibility of frother and collectors.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE IX
FROTH FLOTATION OF SYNTHETIC SLUDGE USING COLLECTORS AND FROTHER F-65
Float solids (%) Col lector Control Col lector Control Col lector Control dosage 1% dosage 1% dosage 1% Col 1ector 0.5% F-65 1.0% F-65 2.0% F-65
A-61 3.71 5.53 A.07 5.5A 5.21 5.87 A -18 5.03 5.53 5 .A1 5.5A 5.78 5.87 A-22 5.22 5.53 A.91 5.5A 5.89 5.87 A-GPG 5.67 5.53 5.86 5.5A 6.A5 5.87 A-OS A.99 5.53 5 .AA 5.5A 6.37 5.87
A-MA 5. A0 5.53 5.3A 5.5A 6.A3 5.87 A-AY 5. A6 5.53 5.A3 5.5A 5.98 5.87 AF-208 5.07 5.A5 5.78 5.27 5.97 6.22 AF-25 A. 83 5.A5 5.52 A.82 5.13 6.22 AF-2A2 5.21 5.A5 A.52 A.82 5.5A 6.22
AF-211 5.70 5.A5 5.12 5.27 5.83 6.22 AP-710 5.09 5.A5 A.A6 5.27 5.63 6.22 AP-801 5 .0A 5.19 5.0A 5.27 5.93 5.95 AP-825 5.09 5.A5 5.00 5.27 5.86 6.22 AP-A25 5.58 5.A5 A.95 5.27 5.97 6.22
R-1509 A.52 5.7A 5.06 5.58 A. 50 5.68 DE-80 A.89 5.7A A.27 5.58 A.A2 5.68 DN-80 A. 12 5.7A A. 26 5.58 A.39 5.68 AM-3037 A.3A 5.7A A.37 5.58 A.2A 5.68 RT-763 6.02 5.7A 6.15 5.58 6.10 5.68
P-25 5.89 5.7A 5.A7 5.58 A.75 5.68 AM-15A6 A.91 5.7A A.Al 5.58 A.83 5.68 F-A00 5.51 6.01 5 .A0 5.58 5.A3 5.95 Z-6 5.A7 5.61 5 . 1A 5.99 5.91 6.12 Z-l 1 A.97 5.61 A. 76 5.99 5.73 6.12 AM-D 5.23 5.61 5.02 5.99 5.32 6.12
pH 8.0
Collector and frother dosage - dry weight basis.
Detention time - 30 minutes in the flotation chamber
In itial sol ids - 2.0%
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 56
CONCLUSIONS
This investigation of froth flotation of synthesized pulp
and paper mill sludge has examined several important parameters and
their effects on this complex process. Based on the data obtained
and analyzed in this study, the following conclusions have been
formed. .
Collection of the solid particles by air bubbles was highly
efficient as approximately 38% of the sludge solids were floated to
the surface. However, the process was ineffective for dewatering
fibrous sludges. Drainage of the floats was affected by the cellu
lose content and directly related to the entrained a ir volume of the
froth. The hygroscopic cellulose fibers limited drainage by their re
tention of water while increased a ir content augmented water removal.
Bulky and fibrous cellulose was easily entrapped by the air bubbles
and floated to the surface; whereas, successful collection from a
clay suspension required a delicate balance of pH and collector ions.
Although the mineral collectors promoted collection of the clay
particles by themselves, they did not increase the dryness of floats
or solids removal efficiency from the synthesized sludge.
The pH had an important influence on the foaming power of the
frother and the stability of the froth. Some frothers were less
sensitive to pH than others and hence could be used over a wider pH
range. The sta b ility of the froth was greatly enhanced by the pre
sence of fine particles and the air entrained within the float pro
vided bulk which increased the body and structure of the froth.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 57
Although drainage of the floats was a very slow process, flo
tation its e lf was very rapid and the solid particles were quickly re
moved from the water phase by the rising air bubbles. Thus, the
greatest potential of the flotation process seemed to be its effici
ency of solids removal and alacrity of reaction rather than its
limited a b ility to concentrate fibrous sludges.
Furthermore, since the concentration of the floats obtained
were only comparable to those of sludges produced from gravity clari-
fie rs, it would not be practical to use the flotation process in
conjunction with settling tanks. Since the float would s t ill require
further dewatering, the process would only increase the time, cost
and space for wastewater treatment. However, due to its efficiency
and rate of solids removal, the flotation process offers potential
as a replacement for the time consuming and inefficient settling
procedure and, thus, should not be abandoned until further explored.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 58
RECOMMENDATIONS
Due to the rapid rate and efficiency of solids removal from
the water phase, certain aspects of froth flotation should be fur
ther investigated. The flotation process offers potential as a
replacement for primary gravity thickening and this area should be
studied. The process could possibly be adapted to certain locations
in the mill similar to the present method used for recovering fibers
from white water. Selective flotation is another possibility where
each component is recovered from the others at a separate stage.
Recommendations for future work would also include investigat
ing different types of collectors and frothers rather than those
specifically designed for the mineral industry. The effects of var-
ing the composition and including other sludge components than those
used in this study should be measured. Modification of cellulose
fiber by chemical reactions to change its hygroscopic nature should
be tried to reduce the water retention of the fiber.
Finally, design of flotation equipment needs to be developed
specifically for this type of work since the mining flotation devices
are not designed to concentrate pulp and papermill sludges.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LITERATURE CITED
1. National Council for Stream Improvement, "Manual of Practice for Sludge Handling in the Pulp and Paper Industry," Technical Bulletin No. 190, June, 1961.
2. Dow Chemical Company, "Flotation Fundamentals and Mining Chemicals, Midland, Michigan, 1965.
3. Gaudin, A. M. , "Flotation," 2nd edn., New York, McGraw-Hill Book Company, Inc., 1957*
A. Taggart, A. F. , "Elements of Ore Dressing," New York, John Wiley and Sons, Inc., 1958, p. 595.
5. Carpenter, Wi11iam L ., Flotation Thickening of Pulp Mill SIudges, Unpublished Work, National Council for Stream Improvement.
6. Caron, Andre L., Exploration of Novel Techniques for Sludge Dewatering, Presented at the 39th Annual Conference Water Pollu tion Control Federation, Kansas City, Missouri, 1966.
7. Chase, Sherman E., Sewage and Industrial Wastes, 30 (6): 783 (1958).
8 . Hay, T. T . , Sewage and Industrial Wastes, 38 (1): 100 (1956).
9. Mays, T. J ., Sewage and Industrial Wastes, 25 (10): 1228 (1953).
10. Fuerstenau, D. W., Editor, "Froth Flotation 50th Anniversary Volume," New York, The American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc., 1962, p. 101-102.
11. Sutherland, K. L., and Wark, I. W., "Principal of Flotation," Melbourne, Australasian Institute of Mining and Metallurgy, Inc., 1955, p. 335.
12. Stephenson, J. Newell, Editor, "Pulp and Paper Manufacture," Vol. 3, 1st edition, New York, McGraw-Hill Book Company, Inc., 1953, p. 35.
13. Casey, James P., "Pulp and Paper," Vol. 2, 2nd edition, New York, Interscience Publishers, Inc., I960, p. 862-865.
lA. Friend, William, Tappi, 29 (6): 172A (1956).
15. Poor, E. N., and Whitenight, H. A., Paper Trade Journal, 11A (9): 101 (19^2).
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 60
LITERATURE CITED
16. Reynolds, J. F., and Ryan, R. F., Tappi , ^t0_ (11): 918 (1957).
17. Harrison, W. D., Paper Trade Journal, 109 (7): 67 (1939).
18. Ortner, Herbert, Tappi, b8 (2): 37A (1965).
19. Sebba, F ., "Ion Flotation," New York, Elsevier Publishing Company, 1962, p. 97.
20. Green, E. W., and Hunter, J. L., U.S. Patent 2,990,958, 1961.
21. van Olphen, H., "Clay Colloid Chemistry," New York, Interscience Publishers, 1963, pp. 59-82.
22. Zettlemoyer, A. C., Micale, F. J ., Dole, L. R ., NCASI Tech. Bull. No. 212.
23. Zettlemoyer, A. C., Micale, F. J., Dole, L. R., NCASI Tech. Bull. No. 225, December, 1968.
2b. Zettlemoyer, A. C., Micale, F. J., Dole, L. R., NCASI Tech. Bull. No. 2bS , September>1971•
25. Adamson, A. W., "Physical Chemistry of Surfaces," New York, Interscience Publishers, 1966, pp. 387-^20.
26. Sykes, Peter, "A Guidebook to Mechanism in Organic Chemistry," John Wiley and Sons, Inc., New York, 1965, p. ^0.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. APPENDIX I
Identification of Frothers and Collectors
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 62
Key to Collectors
Ionic Symbol T r a d ’e Name Composition Charge
A-61 Aerosol ethanolated alkyl guanidineamine cationic C-61 complex
A-18 Aerosol disodium N-octadecyl sulfosuccina- anionic 18 ma te
A-22 Aerosol tetrasodium N-(l,2-dicarboxyethyl)■ anionic 22 N-octadecyl-sulfosuccinama te
A-GPG Aerosol not available not GPG available
A-OS Aerosol sodium isopropyl naphthalene anionic OS sulfonate
A-MA Aerosol MA sodium dihexyl sulfosuccinate anionic
A-AY Aerosol AY sodium diamyl sulfosuccinate anionic
AF-208 Aerofloat alkyl dithiophosphoric acid salts anionic 208
AF-238 Aerofloat alkyl dithiophosphoric acid salts anionic 238
AF-25 Aerofloat alkyl dithiophosphoric acid salts anionic 25 AF-242 Aerofloat alkyl dithiophosphoric acid salts anionic 242
AF-211 Aerofloa t alkyl dithiophosphoric acid salts anionic 211
AP-710 Aero pro fatty acid anionic moter 710
AP-801 Aero pro sulphonate anionic moter 801
AP-825 Aero pro sulphonate anionic moter 825
AP-425 Aero pro not available anionic moter 425
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Ionic Symbol Trade Name Compos? tion Charge
R-1509 Reagents not available not 1509 available
DE-80 Delamate fatty amine cat ion ic 80
DN-80 Delamin 80 stearyl and oleyl amine cationic
AH-3037 Aeromine amine acetate salt cat ion ic 3037
RT-763 Reten 763 Epi-chlorohydrin polyamide cationic
P-25 Pamak 25 tall oil fatty acid anionic
AM-15^6 Ami ne amine cationic SI 5^6
F-400 Floto 1*00 not available not available Z-6 Xanthate potassium amyl xanthate anionic Z-6
Z-l 1 Xanthate sodium isopropyl xanthate anionic Z-l I
AM-D Amine D dehydroabietylami ne cationic
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Key to Frothers
Symbol Trade Name Compos i t ion
F-AO Aer-O-Foam fire fighting foam
F-PO Pine Oil Yarmor F terpene alcohols
F-61 Aerosol C-61 ethanolated alkyl guanidineamine complex
F-65 Aerofroth 65 synthetic frother
F-71 Aerofroth 71 high alcohol
F-73 Aerofroth 73 alcohol
F-77 Aerofroth 77 straight chain, higher alcohols
F-2^9 Resin 2^9 kraft resin size
F-250 Dowfroth 250 polypropylene glycolmethyl ether
F-350 Pine oil Yarmor 350 terpene alcohols
F -l565 Frother S1565 not available
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.