eri

lan

sed form 8 March 2004; accepted 9 March 2004

preparation plant tailings though there are contrary systems reported in the literature.

Int. J. Miner. Process. 74 (2Keywords: fine coal tailings; characterization; dewatering; dual flocculation

1. Introduction

The clarification of municipal and industrial waste-

waters by solidliquid separation techniques and the

removal of suspended particles are problems of grow-

ing environmental consciousness. Solidliquid sepa-

ration is important and complementary process in the

treatment of the concentrate and tailings in mineral

and coal preparation plants. Dewatering processes

generally involve some problems because of theD 2004 Elsevier B.V. All rights reserved.Abstract

Characterization of fine coal tailings using a variety of techniques reveal that it is composed of 30% clay minerals (kaolinite

and illite), 23% muscovite, 26% quartz and 20% coal with little amount of carbonate minerals. Various flocculant combinations

and their order of additions are utilized to understand the ability of dual flocculant systems on dewatering of these fine coal

tailings. Settling rate and turbidity are used as criteria for screening and measuring the performance of anionic, cationic and

nonionic flocculants. Dual flocculation of tailings has been tested with the aim of identifying if the synergy reported for mono-

disperse systems is also valid for multicomponent systems. While the nonioniccationic combination leads to the highest

settling rates, the lowest turbidity values were obtained when using the anionicnonionic combinations. The mechanism of

interaction of dual polymers with particle surfaces and their synergy are discussed with the help of settling and turbidity data.

The turbidity values obtained in mono-flocculation tests using nonionic and cationic flocculants and those made with dual

flocculation combinations reveal that this kind of flocculant combinations play an unfavorable role in the flocculation of coalMineral and Coal Processing Section, Mining Faculty, I

Received 29 January 2004; received in reviE. Sabaha,b,*, H. Yuzerb, M.S. Celikc

aMining Engineering Department, Engineering Faculty, Afyon Kocatepe University, 03200 Afyon, TurkeybTubitak-Marmara Research Centre, Materials and Chemical Technologies, 41470 Gebze, Kocaeli, Turkey

c stanbul Technical University, Ayazaga, 80626 Istanbul, TurkeyCharacterization and dewat

dual-floccu0301-7516/$ - see front matter D 2004 Elsevier B.V. All rights reserved.

doi:10.1016/j.minpro.2004.03.001

* Corresponding author. Mining Engineering Department,

Engineering Faculty, Afyon Kocatepe University, 03200 Afyon,

Turkey.

E-mail addresses: esabah@aku.edu.tr (E. Sabah),

Hayrettin.Yuzer@mam.gov.tr (H. Yuzer), mcelik@itu.edu.tr

(M.S. Celik).ng of fine coal tailings by

t systems

www.elsevier.com/locate/ijminpro

004) 303315presence of colloidal particles of different sizes,

shapes and specific gravities and their unique behav-

ior in an aqueous environment. The objective of

dewatering processes is often to obtain clear water

with low percentage of solids. The composition of

aqueous solution and particularly the type of electro-

lytes usually govern the interaction of species in

coal production methods are recently becoming wide-

spread, wastewater produced out of coal processing

E. Sabah et al. / Int. J. Miner. Process. 74 (2004) 303315304dewatering processes. Mechanical dewatering techni-

ques such as sedimentation and filtration and their

combinations are extensively used in mineral and coal

preparation plants.

The flocculation technique using polymers that

accelerates the settling of particles is the most com-

mon sedimentation method for dewatering of coal

preparation plant wastewater involving high percent-

age of fine particles. An effective solidliquid sepa-

ration of tailings is important both for producing good

quality circulating water and also obtaining an under-

flow with high percentage of solids; this in turn

enhances the performance of mineral processing

equipment in the plant and tailings dam as well.

There are numerous studies in the literature related

to the flocculation of coal wastewater including var-

ious types of minerals. A lignitic coal from Yozgat

region of Turkey was studied to identify the condi-

tions for optimum flocculant type and dosage (Sar-

ioglu et al., 2002). In a similar study, laboratory-scale

flocculation tests were conducted with an actual

wastewater containing clay from Omerler coal prepa-

ration plant to optimize the flocculant dosage and

type. This information was then used in the design of

the thickener (Malayoglu et al., 1998). Foshee et al.

(1982) used organic polyelectrolytes to achieve im-

proved wastewater clarification in a coal preparation.

In another similar study, the flocculation of coal with

xanthate or polyethylene was investigated (Maher,

1983). Bustamante and Rutter (1987) studied the

flocculation of minus 0.5 mm fine coal suspension.

Chandra et al. (1997) evaluated the effect of wash-

water on the performance of a cationic polymer as a

function of pH. Menon et al. (1987) investigated the

effect of coal and pyrites on settling behavior of clays

in a wastewater composed of coal and clay. Hussain et

al. (1993) characterized the clay minerals in Zongul-

dak coal preparation plant waste. Attia and Yu (1991)

investigated the flocculation and filtration of coal

slurries using hydrophobic flocculants. Tadros et al.

(1995) investigated the influence of addition of a

polyelectrolyte, nonionic polymer and their mixtures,

on the rheology of coal/water suspensions. Kaiser

(1993) investigated the application of combined floc-

culation in a pilot-scale coal preparation plant. Tao et

al. (2000) made a comparative flocculationfiltration

investigation using vacuum, hyperbaric, and centrifu-gal filters on an ultrafine ( 150 Am) clean coalincludes high percentage of ultrafine particles and

inorganic impurities. The treatment of plant wastewa-

ter according to the environmental standards requires

an effective and economic dewatering process.

Tuncbilek coal cleaning plant which was put inservice in 1996 receives 1000 m3 wastewater with

5.85% solids by weight (Metin et al., 1988). Consid-

ering 7000 tpy of operation a total of 410,000 tons of

solid waste is discharged. The success of dewatering

system depends on the improvements made on the

thickener parameters as well as the flocculant regime.

The optimization of these parameters in laboratory

studies will certainly make the plant trials successful.

In the present investigation, the presence of organic

and inorganic impurities in the Tuncbilek coal prepa-ration wastewater has been characterized and the

major performance criteria, i.e. settling rate and tur-

bidity have been used to find out optimum conditions

at which single or dual flocculants effectively work.

The synergetic effect of dual flocculation technique

reported for single mineral systems (Yu and Soma-

sundaran, 1996; Kuusik and Viisimaa, 1999; Fan et

al., 2000; Pearse et al., 2001; Ovenden and Xiao,

2002) has been tested in multicomponent systems

viz., Tuncbilek coal preparation plant tailings.

2. Experimental

2.1. Materials

The coal slurry sample used in the experiments was

taken from the discharge of fine tailings in Tuncbilekcoal preparation plant of GLI of Turkish Coal Enter-

prises, as indicated in Fig. 1. The representative

samples were transferred to the laboratory in barrelsslurry. Tripathy et al. (2001) investigated the perfor-

mance of sodium alginate-g-polyacrylamide (SAG)

flocculants synthesized by ceric ion induced redox

polymerization technique on both fine coking and

noncoking coal suspensions; in all cases, the SAG

showed better performance than the conventional

flocculants.

In coal preparation plants, large amount of water is

used for coal cleaning. Since full and half-mechanized(150 l) and discharged to a stirring tank (250 l).

(ASTM, 325 mesh). The oversize and undersize

fractions were dried at 105 jC until constantweight. The original tailings minus 0.18 mm in

size, and oversize and undersize fractions were

subjected to a number of qualitative and quantitative

analysis techniques.

The hardness of water and the concentration of

Mg2 + and Ca2 + in water were determined by volu-

E. Sabah et al. / Int. J. Miner. Process. 74 (2004) 303315 305Experiments were immediately started in order to

preserve physical and chemical properties of the

slurry.

Four high-molecular weight polyacrylamide-based

polymers were used in the flocculation tests. The

Fig. 1. A schematic illustration of coal preparation plant.detailed characteristics of each polymer are shown

in Table 1. Prior to flocculation tests, a homogeneous

stock solution (0.1%) of polymer was prepared using

distilled water. The stock solution was further diluted

to 100 mg/l for flocculation tests. Slurry pH was

adjusted by either HCl or lime solutions prior to

adding flocculants.

2.2. Methods

In order to recover coal from the suspension and

identify the nature of inorganic materials accompa-

nying coal, the slurry was sieved at 0.045 mm sieve

Table 1

Characteristics of polymers used

Commercial name Type Molecular weight C

Praestol 2540 Anionic 1520 million 40

Magnofloc 351 Nonionic 16 million

Praestol 611 BC Cationic 710 million 25

Praestol 857 BS Cationic 1215 million 70metric methods. The chemical composition of the

tailings was analyzed by X-ray fluorescence. The

particle size distribution was determined by Malvern

Mastersizer Particle Size Analyzer. The mineral

composition was determined by X-ray diffraction

(XRD) using a Shimadzu, XRD-6000. Carbon and

sulfur analyses on tailings were performed by a

Multilab-CS Determinator. The ash content was

analyzed according to DIN 51719 (Deutsche Indus-

trie Norm, 1967). Electrokinetic measurements were

conducted by means of Zeta-Meter 3.0, which is

equipped with a microprocessor unit capable of

directly measuring the average zeta-potential and its

standard deviation.

The flocculation experiments were carried out

using a Velp JLT4 jar test with a speed control. For

each test, 500 ml of original coal slurry (5.85% solids

by wt.) was taken in an 800-cm3 glass jar and mixed

for 2 min at 150 rpm to insure complete dispersion. In

mono-flocculation tests, a known amount of polymer

solution was added into the coal slurry while stirring

continued and then stopped after 30 s. In dual floc-

culation tests, a desired amount of polymer solution

was first added into the coal slurry. After the mixing

time of 10 s, the second flocculant was added and

stirred for 30 s at 150 rpm. The slurry height and

water interface as functions of time were recorded to

calculate the settling rate of the flocculated suspen-

sion. Following a 15-min of settling period, an aliquot

of the supernatant was used for measuring turbidity

using Velp 115 brand turbidity meter.

harge density (%) Supplier Effective pH range

(medium) Stockhausen 613

Ciba 58

(low) Stockhausen 114(high) Stockhausen 110

3. Results and discussion

3.1. Characterization of coal tailings

3.1.1. Mineralogical analysis

Microscopic observations made with original tail-

ings and those made on over and under size fractions

of 0.045 mm show that the oversize consists of almost

coal and undersize generally consists of aggregated

clay minerals and quartz. Other sulfide minerals

mainly of pyrite were also observed in the samples.

X-ray analysis was conducted on original and

0.045 mm tailings in order to identify the extentof non-clay minerals. Both samples exhibit similar

peaks of kaolinite, illite, muscovite and quartz as

shown in Fig. 2a and b. The results are similar to

the mineralogical compositions of the clays associated

with those in the Beye area of Tuncbilek reported byGungor and Turkmenoglu (1993).

3.1.2. Chemical analysis

The chemical compositions of the associated min-

erals were determined by XRF method as shown in

Fig. 3.

Chemical compositions of the original and 0.045mm tailings are not significantly different, except the

loss-on-ignition (LOI) values in 0.045 mm tailingsdue to the absence of organic matter, as shown in Fig.

3. Mineralogical analysis together with 15.04

16.14% Al2O3 confirms the existence of kaolinite

and illite in the tailings. The K2O content of 2.28

2.62% indicates the presence of muscovite. After

E. Sabah et al. / Int. J. Miner. Process. 74 (2004) 303315306Fig. 2. XRD peaks of original tailings (a) and 0.045 mm tailings (b).

f orig

E. Sabah et al. / Int. J. Miner. Process. 74 (2004) 303315 307accounting for the clay minerals, the remaining

40.7546.86% SiO2 refers to quartz. The low per-

centage of CaO and MgO indicates the presence of

few carbonate minerals in the tailings. The chemical

analysis coupled with the XRD results reveal that the

original tailings theoretically contain approximately

30% clay minerals (kaolinite, illite), 23% muscovite,

26% quartz and the remaining being coal and minute

amounts of carbonate minerals.

3.1.3. Carbonsulfur and ash analysis

Fig. 3. Chemical compositions oAsh content and carbonsulfur analysis of the

original, 0.045 and + 0.045 mm tailings are shownin Table 2. The quantity of carbon (18.83%) deter-

mined by chemical analysis agrees well with the coal

content of 20% calculated based on microscopic

analysis. This reveals that the organic material content

in the tailings is 1820%.

3.1.4. DTATGA analysis

DTATGA analysis of the original and 0.045mm tailings were made at a heating velocity of 10 jC/min. A sample of 23.1 mg for original tailings and

27.0 mg for 0.045 mm tailings were used. TheDTATG peaks are shown in Fig. 4.

The difference found in the DTA curves of original

and 0.045 mm tailings is ascribed to organicmaterial in the original tailings. The dominant peak

between 400 and 500 jC on the DTA curve anddrastic weight losses over 300600 jC temperaturerange in the TGA curve result from burning of the

coal. Because clay and carbon peaks overlap, the clay

peaks are not easy to distinguish. Since the 0.045mm fraction of the tailings contains less quantity of

coal, the DTA peaks of this fraction are more visible

and its weight losses are lower. The weight loss of

0.045 mm fraction is 20% of which 15% occurs inthe range of 320560 jC. The total weight loss oforiginal tailings is 33% of which 30% occurs between

320 and 580 jC. The weight losses determined fromthe TGA data well agree with the LOI values.

inal and 0.045 mm tailings.3.1.5. Particle size distribution

According to the Wentworth (1922) classification,

while the percentage of particles in the clay size

accounts for 28% ( < 4 Am), that in the silt size is62% (463 Am). The fine particles ( 63 Am) in thesedimentation environment are generally present as

fine quartz, clay minerals, phyllosilicate minerals like

chlorite and cerussite and fine coal. Percentage of the

particle in the sand size is 10% (> 63 Am). Theseparticles contain larger quartz particles, other silicate

minerals and coal particles.

The average particle size determined from the

GaudinSchuhman type of plot is 11.93 Am andthe percentage of slime size ( < 20 Am) constitutes71% of the overall material (Fig. 5). Specific gravity

determined from the Mastersizer instrument is 2.71

g/cm3 and the corresponding specific surface area is

0.5723 m2/g. The specific gravity of the pulp with

E. Sabah et al. / Int. J. Miner. Process. 74 (2004) 303315308Table 2

Ash, carbon and sulfur contents of tailings5.85% solids by weight is 1.038 g/cm3. Qualitative

and quantitative analysis results were used to identify

the properties of the plant tailings as illustrated in

Table 3.

3.2. Characterization of the suspensions

The ionic composition of water is important in the

flocculation of fine and colloidal particles. When the

hardness of water is less than 9 jF, because of therelation between hardness of water and the effective-

ness of a flocculant, the interaction between polymer

molecules and colloidal particles weakens. Therefore,

not only an inferior settling rate but also low turbidity

is obtained. The hardness of plant water from which

tailings are dewatered is 182 jF; this is way above theproposed limit value and falls within the class of very

hard waters because of high bivalent ion concentra-

tions (326 mg/l Mg+ and 184 mg/l Ca+). Colloidal

suspensions usually exhibit low resistance and high

Table 3

Properties of Tuncbilek coal preparation plant tailings

Parameters Tailing

Density, g/cm3 2.71

Surface area, m2/g 0.5723

LOI, % 30

Ratio of inorganic/organic material on

dry basis

81:19

Particle size interval, Am 0.4. . .180Ratio of slime size ( < 20 Am)particles, %

71

Average particle size, Am 11.93Ratio of clay size particle, % 28

Ratio of silt sized particle, % 62

Ratio of sand sized particle, % 10

Classification based on the international

soil classification triangle

Silty clay loam

E. Sabah et al. / Int. J. Miner. Process. 74 (2004) 303315 309conductivity. In our case, the conductivity value of

water consisting of tailings measured at natural pH is

high (2250 mS/cm) and varies with pH as shown in

Fig. 4. DTA and TGA data of original tailings (a) and 0.045 mmtailings (b).

Fig. 5. Particle size analysis and average particle size of the tailings.Fig. 6. Other properties of the plant tailings are shown

in Table 4.

The percent solids by weight of the plant tailings

show a heterogeneous structure because of its various

solid components. In order to isolate the effect of each

component, the original tailings was sieved at 0.045

mm screen and zeta-potential curves of undersize and

Mineral content Clay minerals,

muscovite and quartz

Ash content of original tailing, % 69.74

Ash content of 0.045 mm tailing, % 80.77Ash content of + 0.045 mm tailing, % 33.29oversize fractions are presented in Fig. 7 as a function

of pH. The original, 0.045, and 0.045 mm tailingsall show negative electrical charge in the entire pH

values. The absolute value of the negative electrical

charge increases rapidly with increasing pH. At about

Fig. 6. Variation of pH with conductivity value of the plant tailings

water.

original mixture is composed of coal, clay and quartz

particles and thus appears to be similar to the indi-

vidual fractions. Zeta-potential of quartz like coal is

governed by pH because the potential determining

ions for both minerals are H+ ve OH. This indicatesthat quartz and coal particles control the high zeta-

potentials observed in the neutral pH region of Fig. 7.

3.3. Dual flocculation tests

Oppositely charged or neutral dual flocculant com-

binations were tested to enhance the performance of

mono-flocculant alternative in coal preparation plant

tailings. The aim was to obtain more effective and

economic solidliquid separation by combining high

settling rate feature of anionic flocculant and low

E. Sabah et al. / Int. J. Miner. Process. 74 (2004) 303315310neutral pH, the absolute value of the original and

+ 0.045 mm tailings started to decrease again and

above this point zeta-potential variation remained

marginal. The isoelectric point of the + 0.045 mm

tailings, which is closer to the original coal (Table 2),

occurs at pH 2, but the iep of the original and 0.045mm tailings, which are composed of large amounts of

clay minerals and quartz, could not be measured. The

reason for a rapid decrease in the zeta-potential of coal

between pH 2 and 7 is ascribed to the effect of the

potential determining ions, H+ ve OH. Zeta-potentialcurve of the + 0.045 mm fraction is similar to that of a

lignitic coal with high ash (Abotsi, 1996; Laskowski,

2001).

Although original and 0.045 mm tailings havesimilar XRD and chemical analysis patterns, the lower

value of the LOI of 0.045 mm tailings compared tothat of the original tailings (Fig. 3), reveals the

removal of organic materials and also the large

amount of clay minerals (kaolinite and illite) in the

0.045 mm fraction. Microscopic studies on coal ashof + 0.045 mm fraction show that there are small

amounts of quartz which mostly remain in the 0.045mm fraction. This situation is also reflected in the

zeta-potential curves of 0.045 mm tailings which

Table 4

Properties of plant tailings water

Parameters Wastewater

Natural pH 8.3

% Solids by weight 5.85

Pulp density, g/cm3 1.038

French hardness, jF 182Ca++ concentration, mg/l 184

Mg++ concentration, mg/l 326

Conductivity, mS/cm 2250contain mainly of clay minerals and quartz. Since the

zeta-potential values particularly at high pHs are

moderate and in agreement with those given for

different kaolinite minerals in the literature (Ma and

Pierre, 1999; Tuncan, 1995), the tailings are inferred

to mostly consist of kaolinite rather than illite.

Zeta-potential curves of original, 0.045 and+ 0.045 mm tailings intersect at about pH 88.5 over

which the zeta-potential values vary between 25and 27.5 mV, as shown in Fig. 7. Again, the pHvalue in the intersection region of these three curves is

close to the natural pH (8.3) of the suspension. Theturbidity feature of nonionic and cationic flocculants

(Sabah and Cengiz, in press). Dual flocculant combi-

nations were selected on the basis of charge density,

typically used dosages and the order of their addition.

The flocculant quantity was determined on the basis

of optimum results obtained in mono flocculation

experiments with dual flocculation experiments kept

at 1:1 concentration ratio.

3.3.1. Anionicnonionic and nonionicanionic dual

flocculation tests

The desired settling rate performance was not

obtained with anionicnonionic flocculant combina-

tion, but a great improvement in turbidity was reached

with dual flocculants as indicated in Fig. 8a and b,

Fig. 7. Zeta-potential curves of undersize and oversize fractionsagainst pH.

E. Sabah et al. / Int. J. Miner. Process. 74 (2004) 303315 311respectively. The order in the legend also denotes the

order of flocculant addition.

When the nonionic flocculant was added first

followed by the anionic, settling rate increased rapidly

especially at high concentrations but reversing the

order of addition could not induce a significant

change in the settling rate even at high polymer

concentrations (Fig. 8a). The best result in turbidity

was obtained with anionicnonionic combination

compared to the anionic alone. Despite changing the

order of addition, marginal changes in turbidity

Fig. 8. Dual flocculation of coal tailings using anionicnonionic

and nonionic anionic combinations on settling rate (a) and

turbidity (b).were observed upon increasing the polymer dosage

(Fig. 8b).

Because of high ash contents and the accompa-

nying clay minerals in the plant tailings, when the

nonionic flocculant was added to the suspension

first, high settling rates were achieved only at high

flocculant additions. In this case, the contribution of

anionic flocculant on the settling rate appears to be

inferior. Nonionic polymers under these conditions

generally adsorb onto particle surfaces by means of

hydrogen bonds and van der Waals forces resulting

in relatively big primary flocs. Increasing anionic

flocculant dosage increases the floc size leading to

enhanced settling rates. Particularly, the flocs formed

at low nonionic flocculant dosages are very fine and

thus exhibit high turbidity but sharply decreases

upon adding an anionic flocculant and again deteri-

orate at very high dosages. Excellent settling rates at

the expense of high turbidity values obtained upon

adding an anionic flocculant alone was completely

reversed when using dual anionicnonionic floccu-

lant combinations, in other words, very low settling

rates and rather clear suspensions were obtained.

This illustrates the essential role of polymer confor-

mation on settling rate in dual flocculation systems.

3.3.2. Anioniccationic and cationicanionic dual

flocculation

Fig. 9 shows the effect of molecular weight of

cationic flocculant on the performance of dual

flocculation in the anioniccationic and cationic

nonionic flocculant combinations. The best synergy

was obtained upon first adding low-molecular weight

weak cationic flocculant followed by the anionic

flocculant. When the order of addition is kept the

same but high-molecular weight strong cationic is

used instead of weak cationic flocculant, settling rate

decreased and a marginal change in the turbidity

values were observed in high flocculant dosages.

When the order was reversed, in other words, anionic

flocculant was added first and the strong cationic

flocculant second, the stability of particles increased

but clear suspensions were only obtained at high

flocculant dosages.

Coal and the accompanying minerals which show

negative surface charges at natural pH undergo charge

neutralization as a result of electrostatic interactionsbetween particles and polycations. The magnitude of

flocs and consequently decreases the turbidity with

increasing polymer dosages.

Both weak and strong cationic flocculants adsorb

onto negatively charged particle surfaces by means of

electrostatic attraction and induce more or less charge

neutralization leading to low settling rates and turbid-

ity values. Addition of an anionic polymer to such a

suspension after charge neutralization does not favor-

ably contribute to the flocculation performance.

Improvement in suspension stability in dual

anioniccationic flocculation system imparts a re-

duction in settling rate and a rapid increase in

turbidity at low flocculant dosages. This is attributed

to the electrostatic repulsion between negatively

E. Sabah et al. / Int. J. Miner. Process. 74 (2004) 303315312interaction between the particles and functional

groups of cationic polymers increases with increasing

polymer dosage and charge density. Thus, particle

surfaces neutralize faster leading to small primary

flocs and in turn to a decrease in settling rate and

turbidity. When the charge density of the polymer is

weak, the mechanism of bridge formation is more

effective than charge neutralization; this results in the

formation of larger primary flocs with higher settling

rates. High-molecular weight medium anionic floccu-

lant added after low-molecular weight weak cationic

flocculant enhances the bridge formation resulting in

larger and more compact secondary flocs. As the

molecular weight of weak cationic flocculant is low,

it facilitates the settling ability of fine particles as big

charged particles and polymer molecules and also

those added the cationic and anionic functional

Fig. 9. Effects of anioniccationic and cationicnonionic dual

flocculant combinations on settling rates (a) and turbidity values (b).groups of complex structure. In this structure which

is called Symplex, polycations added to the sus-

pension after anionic flocculant, interact with poly-

anion resulting in the formation of primary aggregates

(Fig. 10). There is no any apparent interaction be-

tween negatively charged particles and Coulombic

forces formed at this point (Schuster et al., 1996).

At high flocculant dosages, a definite decrease in

turbidity values was observed due to an increase in

the number of aggregates (Fig. 9b).

3.3.3. Nonioniccationic and cationicnonionic dual

flocculation

As shown in Fig. 11, nonioniccationic and cat-

ionicnonionic flocculant combinations have no fa-Fig. 10. Mechanism of Symplex formation.

E. Sabah et al. / Int. J. Miner. Process. 74 (2004) 303315 313vorable effect on flocculation performance even at

high flocculant dosages. A marginal change observed

in settling rate and turbidity values at high flocculant

concentration indicates that the effect of both floccu-

lant combinations on the mechanism of floc formation

is very weak.

Marginal changes observed between the turbidity

values obtained from mono flocculation experiments

using nonionic and cationic flocculants and turbidity

values obtained from combination of both flocculants

show that this kind of combination plays a minimum

role on the flocculation performance of coal prepara-

flocculant combinations, the best synergy is achieved

with low-molecular weight weak cationic and anionic

Fig. 11. Effect of nonioniccationic and cationicnonionic dual

flocculation on settling rate (a) and turbidity values (b).combinations. For the same order, if high-molecular

weight strong cationic flocculant is used instead of

weak cationic flocculant, a reduction in settling rate is

observed but a marginal change in turbidity values is

obtained at high flocculant dosages. Cationic floccu-

lants, irrespective of their charge densities, in highly

negatively charged suspensions, are able to neutralizetion plant tailings. However, there are literature results

contrary to this finding. Lee and Liu (2000) obtained

good results on settling rate and turbidity values in

dewatering of synthetic fibre plant tailings using

cationicnonionic (1:1 ratio) combination by dual

flocculation technique but did not provide any infor-

mation about the slime composition.

4. Conclusions

Characterization of waste coal tailings using a

variety of techniques reveal that the original tailings

is composed of 30% clay minerals (kaolinite and

illite), 23% muscovite, 26% quartz and 20% coal with

minute amount of carbonate minerals.

The original tailings and over and under fractions

of 0.045 mm have exhibited negative zeta potentials

in the entire practical pH range. While + 0.045 mm

fraction (coal dominant) has an iep of about 2, the

0.045 mm fraction (clay dominant) yield no iep.Both fractions show similar zeta potential values of

25 mV in the natural pH of 88.5 indicating similarflocculation performance.

Dual flocculation of tailings has been tested with

the aim of identifying if the synergy reported for

mono-disperse systems is also applicable for multi-

component systems. When nonionic is added first

followed by anionic flocculant, settling rate rapidly

increases particularly at high flocculant dosages, when

reversing the order of flocculant addition no satisfac-

tory result was achieved even at high dosages. The

lowest turbidity values were obtained when using

anionicnonionic combinations, changing the order

of addition led to low turbidity values; both addition

modes resulted in a lower trend with increasing the

dosage.

Among anioniccationic and cationicanionicthe surfaces through electrostatic attraction and if

E. Sabah et al. / Int. J. Miner. Process. 74 (2004) 303315314Abotsi, G., 1996. Interfacial properties of coal: a guide to catalyst

loading and dispersion for coal conversion. CAER-University of

Kentucky, Center of Applied Energy Research, Energia, vol. 7,

No. 5, pp. 13.

Attia, Y.A., Yu, S., 1991. Flocculation and filtration dewatering of

coal slurries aided by a hydrophobic polymeric flocculant. Sep.

Sci. Technol. 26 (6), 803818.

Bustamante, H., Rutter, P.R., 1987. Flocculation of heterodisperse

suspensions of fine coal ( 0.5). Chem. Eng. Sci. 42 (4),809821.

Chandra, W.A., Smith-Palmer, T., Byron, R.W., 1997. The effect of

cationic polymers on flocculation of a coal thickener feed in

washery water as a function of pH. J. Appl. Polym. Sci. 64

(4), 783789.

Deutsche Industrie Norm, 1967. Bestimmung des Aschegehaltes

fester Brennstoffe Beuth-Vertrieb, Berlin DIN 51719.

Fan, A., Turro, N.J., Somasundaran, P., 2000. A study of dual

polymer flocculation. Colloids Surf. 162, 141148.

Foshee, W.C., Swan, M.J., Klimpel, R.R., 1982. Improvement in

coal preparationwater clarification through polymer floccula-

tion. Min. Eng. 34 (3), 293297.

Gungor, P., Turkmenoglu, A., 1993. The mineralogy of clays

associated with coals in Beye area of Tuncbilek-DomanicThe financial support of Scientific Researches

Commission (00.AMYO.01) of Afyon Kocatepe

University is gratefully acknowledged.

Referencesanionic flocculant is subsequently introduced, no

favorable performance is induced. When the order is

changed, the suspension stability is increased and

clear suspensions were attained only at high flocculant

dosages.

Despite increasing dosages in nonioniccationic

and cationicnonionic flocculant combinations, no

positive contribution to flocculation performance is

noted because settling rates and turbidity values show

marginal changes at high dosages, the effect of both

combinations on the mechanism of floc formation is

very weak. The turbidity values obtained in mono-

flocculation tests using nonionic and cationic floccu-

lants and those made with dual flocculation combina-

tions reveal that this kind of flocculant combinations

will not play a favorable role in the flocculation of

coal preparation tailings though there are contrary

systems reported in the literature.

Acknowledgements(Kutahya) Neogene Basin. 6th National Clay Symposium,

Istanbul. Turkish National Committee of Clay Science, Istan-

bul, Turkey, pp. 95109.

Hussain, S.A., Demirci, S., Ozbayaoglu, G., 1993. Identification of

clay mineral in coal and wastes from main coal washery, Zon-

guldak, Turkey. Appl. Clay Sci. 7 (6), 471482.

Kaiser, M., 1993. Application of combined flocculation for solid/

liquid separation in coal preparation. Aufbereit.-Tech. 34 (1),

1826.

Kuusik, R., Viisimaa, L., 1999. A new dual coagulant for water

purification. Water Res. 33 (9), 20752082.

Laskowski, J.S., 2001. Coal flotation and fine coal utilization. In:

Fuerstenau, W. (Ed.), Developments in Mineral Processing, vol.

14. pp. 3545. Chap. 3.

Lee, C.H., Liu, J.C., 2000. Enhanced sludge dewatering by dual

polyelectrolytes conditioning. Water Res. 34 (18), 44304436.

Ma, K., Pierre, A.C., 1999. Clay sediments-structure formation in

aqueous kaolinite suspensions. Clays Clay Miner. 47 (4),

522526.

Maher, G.G., 1983. Flocculation of coals and minerals by starch

xanthate or starch xanthate-polyethylenimine adducts. J. Envi-

ron. Sci. 26 (3), 2934.

Malayoglu, U., Akar, A., Seyrankaya, A., 1998. Developing sedi-

mentation criteria for slimes of Omerler coal washing plant by

flocculation. Innovations in Mineral and Coal Processing, 7th

International Mineral Processing Symposium, Istanbul, Turkey.

A.A. Balkema, Rotterdam, Brookfield, pp. 195200.

Menon, V.B., Woods, M.C., Mullins, M.E., Michaels, L.D., 1987.

Effect of clays on the settling behavior of coal and pyrite. Miner.

Metall. Process. 4 (4), 193195.

Metin, C., Oner, B., Ermisoglu, N., Coguplugil, N., 1988. The pastand current effects of the washery runoff waters on the environ-

mental pollution in GLIs Tuncbilek district II. InternationalMineral Processing Symposium, Izmir, Turkey. Ofis Printing,

Izmir, Turkey, pp. 829840.

Ovenden, C., Xiao, H., 2002. Flocculation behavior and mecha-

nisms of cationic inorganic microparticle/polymer systems. Col-

loids Surf. 197, 225234.

Pearse, M.J., Weir, S., Adkins, S.J., Moody, G.M., 2001. Advances

in mineral flocculation. Miner. Eng. 14 (11), 15051551.

Sabah, E., Cengiz, I., 2004. An evaluation procedure for flocculation

of coal preparation plant tailings. Water Res. 38 (6), 15421549.

Sarioglu, M., Cebeci, Y., Beyazit, N., 2002. Investigation of the

effects of some operating parameters using anionic and cationic

flocculants for removing solid material in the lignite. Asian J.

Chem. 14 (1), 388394.

Schuster, C., Kotz, J., Jaeger, W., Kulicke, W.-M., 1996. Wechsel-

wirkungen zwischen Klarschlammpartikeln und Polyelektro-

lyten. Chem. Eng. Technol. 68, 980984.

Tadros, T.F., Taylor, P., Bognolo, G., 1995. Influence of addition

of a polyelectrolyte nonionic polymers, and their mixtures on

the rheology of coalwater suspensions. Langmuir 11 (12),

46784684.

Tao, D., Groppo, J.G., Parekh, B.K., 2000. Enhanced ultrafine coal

dewatering using flocculation filtration processes. Miner. Eng.

13 (2), 163171.

Tripathy, T., Karmakar, N.C., Singh, R.P., 2001. Development of

novel polymeric flocculant based on grafted sodium alginate for

the treatment of coal mine wastewater. J. Appl. Polym. Sci. 82

(2), 375382.

Tuncan, A., 1995. Determination of physico-chemical properties of

some clay minerals in laboratory. 7th National Clay Sympo-

sium, Ankara-Turkey. In Turkish.

Wentworth, C.K., 1922. A scale of grade and class terms of clastic

sediments. J. Geol. 30, 377392.

Yu, X., Somasundaran, P., 1996. Role of polymer conformation in

interparticle-bridging dominated flocculation. J. Colloid Inter-

face Sci. 177, 283287.

E. Sabah et al. / Int. J. Miner. Process. 74 (2004) 303315 315

Characterization and dewatering of fine coal tailings by dual-flocculant systemsIntroductionExperimentalMaterialsMethods

Results and discussionCharacterization of coal tailingsMineralogical analysisChemical analysisCarbon-sulfur and ash analysisDTA-TGA analysisParticle size distribution

Characterization of the suspensionsDual flocculation testsAnionic-nonionic and nonionic-anionic dual flocculation testsAnionic-cationic and cationic-anionic dual flocculationNonionic-cationic and cationic-nonionic dual flocculation

ConclusionsAcknowledgementsReferences