1

ELIMINATION OF POLLUTANTS IN WASTEWATER BY SEPIOLITE

E. Sabah1, O. Özdemir

2, B.Armağan

3, M.S. Çelik

2

1Kocatepe University

Mining Engineering Dept.,

Afyon, 03000 Turkey 2Istanbul Technical University

Mining Engineering Dept., Mineral and Coal Processing Section

Ayazaga, 80626 Istanbul-Turkey 3Istanbul Technical University,

Environmental Engineering Dept.,

Ayazaga, 80626, Istanbul, Turkey

esabah@aku.edu.tr

ABSTRACT Sepiolite is a hydrated magnesium silicate with micro and

mesoporous structure. Its fiber morphology and the

presence of alternating blocks and tunnels that grow in the

fiber direction make it an ideal material for a variety of

organic and inorganic contaminants. In this study, the

amenability of sepiolite to various chemicals such as ionic

surfactants, heavy metal ions, pesticides, and aromatic

compounds is illustrated with examples using the

literature and our data as well. It is shown that sepiolite is

indeed a potential natural clay mineral that can be

conveniently used in wastewater treatment systems.

1. INTRODUCTION

Contamination of wastewaters stemming from

industrial sites such as chemical and metal industries is a

challenging problem. In particular, transport of toxic

chemicals through soil and contamination of ground and

surface waters is of imminent threat to human life and the

environment. High level of heavy metal ions and toxic

chemicals in our beaches and seas may reach the threshold

values. Particularly, Marmara Sea, Izmit Gulf, Istanbul

Strait (Bosphorous), Golden Horn and Iskenderun Gulf in

Turkey are regions of intense environmental pollution.

High levels of waste discharged from numerous factories

(textile, food, paint, soda, paper, fertilizer, and mining)

located along the Tasucu-Iskenderun coastline poses an

environmental concern and metal ion measurements show

the values of Hg, Cd and Sn sometimes to exceed the

limiting concentrations [1]. Again, Mersin, Iskenderun and

Antalya seaports exhibit intensive sea traffic and sea

transportation is known to account as an important mode

of petroleum and petroleum derivatives.

The removal of these contaminants has received

considerable attention in recent years. Conventional

methods of removing organic contaminants include

chemical precipitation, ion exchange, filtration and

electrochemical treatment. More sophisticated techniques

like solvent extraction, biosorption, and ultra filtration are

either expensive or cannot cope with high concentrations

of contaminants. All these methods have significant

disadvantages such as incomplete ion removal, high-

energy requirements and production of toxic sludge or

other waste products that require further disposal.

There is an upsurge of interest in recent years to utilize

clay minerals in environmental studies. Sepiolite is a

hydrated clay mineral with fibrous structure. The presence

of micro pores and channels along with the elongated

nature of the particles and the fine particle size accounts

for the high surface area and the capacity to adsorb various

organic and inorganic molecules chemicals. It is an ideal

type of natural raw material to assist environmental

protection. More importantly, sepiolite is mined in large

quantities in two Mediterranean countries, Spain and

Turkey.

In this study, the ability of sepiolite to remove heavy

metal ions (Zn, Pb, Co, and Cd), aromatic amines, dyes,

pyridine derivatives, fuel oil, kerosene, pesticide and

herbicide are examined in the light of literature data.

2. PROPERTIES OF SEPIOLITE

A thorough understanding of the capacity of clay

minerals to adsorb organic and inorganic species is

essential in order to predict the fate of these pollutants in

the environment. Minerals, such as phyllosilicates, are

often employed in environmental protection processes.

They have large surface areas and negative charges on the

external surface and thus can be used in adsorption

processes.

Sepiolite, which belongs to phyllosilicates group, is a

natural hydrated magnesium silicate with

Si12Mg9O30(OH)6(OH2)4H2O and exhibits a fibrous

structure composed of talc-like ribbons [2]. Structurally it

is formed by an alternation of blocks and cavities (tunnels)

that grow up in the fibre direction (c-axis). Each structural

block is composed of two tetrahedral silica sheets

sandwiching a central sheet of magnesium oxide-

hydroxide. Owing to the discontinuity of the silica sheets,

silanol groups (Si-OH) are present on the ``external

surface'' of the silicate particles (Fig. 1). These groups are

located at the edges of the channels and are directly

accessible to reagents allowing the preparation of organic-

inorganic materials derived from sepiolite containing

2

different surface organic functions [3]. Sepiolite has

enormous absorption capacity owing to its molocular sieve

feature (Figure 1).

Figure1. A schematic cross-section of fibre morphology in

sepiolite.

This high surface area of sepiolite as well as its porosity

can be modified by acid of thermal treatments [4, 5, 6, 7,

8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18].

3. WATER POLLUTION AND ITS

REMOVAL BY SEPIOLITE

Water is undoubtedly the most precious natural

resource on our planet. When toxic substances enter

vaious water bodies, they get dissolved or lie suspended in

water or get deposited on the bed. This results in water

pollution which adversely affects aquatic ecosystems.

Pollutants can also penetrate and contaminate the

groundwater.

Water pollution has many sources (Table 1). The most

severe pollution is the city sewage and industrial waste

discharged into the rivers. Today, many people dump their

garbage into streams, lakes, rivers, and seas, thus making

water bodies the burial place of cans, bottles, plastics, and

other household products. In the past, people mostly used

soaps made from animal and vegetable fat for all types of

washing. But most of today’s cleaning products are

synthetic detergents and come from the petrochemical

industry. Most detergents and washing powders contain

phosphates, which are used to soften the water among

other things. These and other chemicals contained in

washing powders affect the health of all forms of life in

the water. Intensive cultivation of crops causes chemicals

from fertilizers (e.g. nitrate) and pesticides to seep into the

groundwater. Waste water from manufacturing or

chemical processes in industries contributes to water

pollution. The effects of water pollution are not only

devastating to people but also to animals, fish, and birds.

Polluted water is unsuitable for drinking, recreation,

agriculture, and industry. It diminishes the aesthetic

quality of lakes and rivers. More seriously, contaminated

water destroys aquatic life and reduces its reproductive

ability.

3.1. Heavy Metal Removal

Heavy metals are notable source of pollution both in the

aquatic and soil environments. The removal of this

pollution has received much attention in recent years.

From an environmental protection point of view, heavy

metal ions should be removed at the source in order to

avoid pollution of natural waters and subsequent metal

accumulation in the food chain. The ability of clay

minerals to adsorb heavy metal cations is an important

property in the context of the increasing contamination of

the aquatic environment and soils by toxic waste.

Various researchers have obtained succesfull results to

remove heavy metals such as Zn2+

, Cd2+

, Cu2+

, Ni2+

ve

Co2+

from waste waters. The removal of heavy metal ions

using sepiolite is shown in Figure 2. The adsorption

capacity of different types of clay for Zn2+

follows the

order of sepiolite (Orera) > sepiolite (Vallecas) > bentonite

> palygorskite (Bercimuelle) > illite > kaolinite &

palygorskite (Torrejon) > perlite. The clays with the

greatest specific surface area (Orera sepiolite and Vallecas

sepiolite) and clays with the greatest CEC (bentonite)

show the strongest adsorption capacity for Zn2+

. Therefore,

all subsequent studies were performed with the sepiolite

(Orera) which may be used as a low-cost adsorbent for the

effective retention of Zn2+

, Cd2+

and Cu2+

and, to a lesser

extent, of Ni2+

. The retention of the metal cations follows

the sequence of Cd2+

> Cu2+

> Zn2+

> Ni2+

.

Figure 2. Adsorption isotherms of sepiolite [19].

3

Table 1. Some common pollutants and their origins [20].

Pollutant Where it comes from? Sediment Land surface erosion

Pavement and vehicle wear (tyres,

brakes etc...)

Atmosphere

Spillage/illegal discharge

Organic matter (eg leaf litter, grass,

droppings)

runoff water from washing cars

Weathering of buildings /structures

Nutrients Organic matter

Fertilisers

Sewer overflows/septic tanks leaks

Animal/bird droppings

Detergents (car washing)

Atmosphere

Spillage/illegal discharges

Oxygen demanding

substances Decaying organic matter

Atmosphere

Sewer overflows/septic tank leaks

Animal/bird droppings

Spillage/illegal discharges

PH (acidity) Atmosphere

Spillage/illegal discharges

Decaying organic matter

Erosion of roofing material

Micro-organisms Animal/bird droppings

Sewer overflows/septic tank levels

Decaying organic matter

Toxic organics Pesticides

Herbicides

Spillage/illegal discharges

Sewer overflows/septic tank leaks

Heavy metals Atmosphere

Vehicle wear

Sewer overflows/septic tank leaks

Weathering of buildings/structures

Spillage/illegal discharges

Oils and surfactants Asphalt pavements

Spillage/illegal discharges

Leaks from vehicles

Car washing

Organic matter

Increased water

temperature Runoff from impervious surfaces

Removal of riparian vegetation

The adsorption data is fitted to the Langmuir equation

and found to well describe the adsorption process of Zn2+

,

Cd2+

, Cu2+

and Ni2+

onto sepiolite (Orera). The amount of

adsorbent (Orera sepiolite) of 10 g/l is an oppropriate dose

for the retention of Zn2+

, Cd2+

and Cu2+

of initial

concentrations of 50 mg l/1 at pH = 4. The adsorption of

the four metal ions onto sepiolite (Orera) increases with

increasing the pH. The adsorption of Cd2+

by sepiolite

(Orera) decreases slightly with an increase in ionic

strength. In addition, the influence of complexing ligands

used in the finishing industry processes and ultimate non-

hazardous disposal of the spent sorbent are other important

considerations [19].

Brigatti demonstrated that heavy-metal ion sorption by

sepiolite is fast at the beginning and then proceeds slowly,

mostly for cations with a cation–water coordination sphere

similar to that of Mg2+

[21]. Most importantly, except for

Co2+

, the rate and efficiency of sorption seem to be

independent of interfering ions. Heavy-metal sorption by

sepiolite decreases in the order of Pb2+

,

Cd2+

,Co2+

,Zn2+

,Cu2+

, and depends roughly on the size of

the cation. Brigatti reports that small ions are preferred as

elution proceeds, indicating that not only the structural

channels but also octahedral sites at the edges of the

channels are involved in the sorption process [21].

Heavy-metal desorption reactions are also governed by

the size of the heavy-metal cation; Cu2+

, Zn2+

, Co2+

, Cd2+

and Pb2+

ions undergo fast and their release is virtually

complete by the end of the experiment. Comparison of

Zn2+

release reactions using Na+ and Mg

2+ solutions

indicates that affinity is always in favour of the indigenous

Mg2+

ions; the site number available for Mg2+

ions is

therefore greater than that for Na+. Finally, the calculation

of the kinetic constants (k) for the sorption and desorption

reactions indicate that these constants are usually higher

for large cations, which further confirms that different

sites and bonding types are involved in exchange reactions

[21].

Figure 3 illustrates the uptake of cobalt by sepiolite

where adsorption density is plotted against the residual

cobalt concentration. The magnesium released from

sepiolite is also presented. The cobolt ion is found to

undergo ion exchange with the magnesium in the

octahedral layer of sepiolite at equivalent quantities, i.e 1-

1 exchange. It is interesting to note that cobalt ion exhibits

hydrolysis reactions at natural pH of pH 8.5.

Approximately, above 10-3

M of cobalt concentration the

precipitation of Co(OH)2 was observed indicating that the

isotherm given in Figure 3 is actually that of abstraction

rather than adsorption [22].

Figure 3. Adsorption isotherm of sepiolite/cobalt system

(S/L: 0.05, pH: Natural, Cond. Time: 2h) [22].

4

A preliminary note reported by Helios-Rybicka

indicates that sepiolite is receptive to metal ions in varying

degrees. The adsorption was found to increase in the order

of Ni<Cd<Zn [23].

Similar results were obtained in this study. The

adsorption changed in the order of Ni<Co<Pb. The

measured Mg concentrations in solution increased with

increasing the initial added metal ion concentration [24].

The exchange of magnesium from the octahedral sheet

indicates that the adsorption mechanism of metal ions is

governed mainly by ion exchange mechanism. However,

the hydrated radius and state of cation, i.e. whether the ion

is the form of Men+

or its hydrolysis products, MeOH+ or

MeOH 2+

can change the magnitude and also the mode of

adsorption.

3.2. Ammonia Removal

Wastewater produced from municipal, agricultural and

industrial sites creates ammonia nitrogen that subsequently

mixes into lakes, rivers and particularly drinking water

reservoirs. Ammonium nitrogen decreases the dissolved

oxygen required for the aquatic livings and also

accelerates the corrosion of metals and construction

materials. Therefore, raw water with high ammonia

concentration must be treated before it reaches the

consumer and also wastewater before arriving at the

receiving water. Biological nitrification and

denitrification, air stripping and ion exchange are the most

preferred methods both in terms of performance and cost

[25,26,27]. The results of ammonia removal from a

synthetic water using sepiolite are shown in Figure 4. In

this study, a series of fixed and fluidised bed ion exchange

column runs were conducted to identify the ability of

sepiolite to capture ammonia. The breakthrough curves

were constructed against bed volume for different bed

heights of 27, 33 and 50 cm, which correspond to the

material loads of 100, 125 and 180 g, respectively. It is

seen that the overall sorption capacity of ammonia by

sepiolite is apparently low due to low exchange capacity

of sepiolite [28].

Figure 4. Breakthrough curves of original sepiolite against

bed volume for different bed heights.

3.3. Removal of Pesticide Chemicals

The term "pesticide" is a composite term that includes

all chemicals that are used to kill or control pests. In

agriculture, this includes herbicides (weeds), insecticides

(insects), fungicides (fungi), nematocides (nematodes),

and rodenticides (vertebrate poisons). The extent of

pesticide contamination in water is of much concern

because of the potential health hazards associated with the

entry of these compounds into the food chain of humans

and animals. Decontamination and disposal of these

hazardous waste chemicals is a complex problem [29].

The adsorption of thiram, a kind of a pesticid, onto acid-

heat treated sepiolite is shown in Figure 5. In contrast, the

curves of Figure 5 show wellmarked plateau that might

indicate according to Giles the formation of complete

monolayer of thiram molecules covering the sepiolite

surface.

5

Figure 5. Adsorption isotherms of thiram on acid-heat

treated sepiolite [29].

The removal efficiency (P) calculated for acid-heat

treated sepiolite ranged from P=14% at 10°C up P=52% at

40°C. The H value estimated in this experiments indicate

that the adsorption process of thiram on acid-heat treated

spiolite is exothermic. The comparison of thiram

adsorption onto sepiolite and activated carbon indicate that

the latter yields much higher adsorption [29].

The adsorption isotherms obtained for the removal of

various phenoxyalkanoic acid herbicides from water using

modified sepiolite is given in Figure 6.

Figure 6. Adsorption isotherms and linear Henry's Law

isotherms of various phenoxyalkanoic acid herbicides on

modified sepiolite [31].

The shapes of these isotherms were of L type, according to

the classification of Giles. Adsoprtion of herbicides onto

DS decreased in the order of 2,4-DB>2,4,5-T>2,4-

DP>2,4-D>MCPA. Sepiolite is identified by a strong

d(011) X-ray reflection at 12 Å [30]. For S and DS, these

values were found as 12.2Å and 12.4 Å, respectively. This

means that the organic layer thickness was not sufficient

for the adsorption of these herbicides [31].

3.4. Uptake of Surfactants

3.4.1. Adsorption of Cationic Reagents on Sepiolite

The use of flotation reagents such as cationic amine

type reagents in the flotation of silicates, oxides and salt

type minerals results in the contamination of process

water. These aliphatic and aromatic compounds are also

used in the production of pigments, rubber, and pesticides

leading to substantial organic wastes. Adsorption process

is usually applied to those wastes that cannot be removed

by biological techniques.

Figure 7. Adsorption isotherms of sepiolite/DTAB and

sepiolite/HTAB systems at natural pH of 8.5. Solution

temperature 25°C; S/L=0.05; Cond. Time: 2h [32].

The adsorption isotherms of original

sepiolite/quaternary amines system given in Figure 7 are

characterized by three distinct regions with different

slopes. While the adsorption of amines shows a gradual

increase in the first region, the increase in the second

region is rather sharp. Despite significant differences in

the rising part of the adsorption isotherms for two

surfactants of different chain length onto sepiolite

adsorbent with 68 m2/g of specific surface area, the

adsorption densities overlap at the onset of plateau

(Region III). The solution concentration in Region III

reaches saturation which indicates that both quaternary

amines concomitantly attain a region of micellar

6

interactions and in turn point out the differences in the

adsorption mechanisms of DTAB and HTAB molecules in

each region.

The adsorption isotherms of DTAB and

HTAB/original sepiolite systems at 25°C show that HTAB

with 16 CH2 groups exhibits higher adsorption densities

compared to that with DTAB of 12 CH2 groups. This

finding is particularly pronounced in the region of

hemimicelle formation where the curves become steeper.

Moreover, despite considerable differences in the rising

part of the adsorption isotherms for two surfactants of

different chain length onto a sepiolite adsorbent, the

adsorption densities almost coincide at the onset of plateau

(Region III) where the solution concentration reaches

saturation. This emphasizes the crucial finding that it is

adsorption and not absorption that is the driving force for

the uptake of surfactant molecules.

3.4.2. Adsorption of Aromatic Amines on Sepiolite Aromatic amines are synthetic organic compounds

which are used in the manufacture of dyestuffs, pigments,

rubber products and acriculture chemicals. These varied

applications suggest many possible modes of entry into the

environment, ranging from direct discharge to conversion

of azodyes to the parent aromatic amine through bacterical

action [33].

Figure 8. Adsorption isotherms of aromatic

amines/sepiolite system at 20oC [33].

Figure 8 shows the adsorption isotherms of the

aromatic amines on heat activated sepiolite at 200°C for

10 h. These adsorption isotherms were classified as L type,

according to the classification of Giles. According to the

study, the activated sepiolite is more effective in removing

p-acetylaniline than in removing p-bromoaniline and p-

toluidine. And, the highest values of the adsorption

capacity and specific surface area also correspond to the p-

acetylaniline, and the lowest ones to the p-toluidine [33].

3.4.3. Adsorption of Cationic Dye on Sepiolite Textile plants discharge highly colored industrial

wastewater which are toxic to some microorganisms and

may cause direct destruction or inhibition of their catalytic

capabilities [34]. For that reason, adsorption has been

extensively used in industrial processes for either

separation or purification. The removal of colored and

colorless organic pollutants from industrial wastewater

using potential adsorbents is considered as an important

application of adsorption processes. An interesting study

was made on adsorbing of such reactive azo dyes (Everzol

BlackB, Everzol Red 3BS, Everzol Yellow 3RS H/C) used

in adsorption experiments, which are onto both natural and

modified sepiolites. Since the reactive dyes have negative

sulfonate groups, they are repelled by the negatively

charged sepiolite surface. This induces a relatively low

adsorption capacity, as shown in Figure 9. The adsorption

isotherms of reactive dyes onto both natural and modified

sepiolites are seen in Figure 9 [35]. The adsorption density

of modified sepiolite shows a good performance and

increases up to 200 mg/g with increasing equilibrium

concentration until 100 mg/l above which the adsorption

density remains nearly constant. The results generally

indicate that sepiolite could be a potential candidate for the

removal of azo dyes.

Figure 9. Adsorption reactive dyes onto natural and

modified sepiolite

3.4.4. Adsorption of Anionic Reagets on Sepiolite Anionic surfactants that constitute the main ingredient

of detergents and some flotation reagents are also

extensively used in mineral processing applications [36].

In concentration operations including flotation, the

presence of such surfactants if discharged into wastewater

can be detrimental to living species. Therefore, the

7

elimination of surfactants from wastewater is important to

protect public health. A study was made to investigate the

amenability of uptake of typical anionic surfactants

sodium dodecylsulfate and sodium

dodecylbenzenesulfonates by sepiolite and identify

mechanisms responsible for the adsorption. Adsorption of

SDS and SDBS onto sepiolite is presented in Figure 10

[22,37].

The adsorption isotherm exhibits three regions of

interest. The first region, which is characterized by the

regular molecular interactions on the sepiolite surface,

extends up to approximately 10-3

M residual surfactant

concentration. The second region marks the onset of

precipitation of magnesium alkylsulfate or

alkybenzenesulfonate and or hemimicelle formation.

Finally, the third region represents the plateau region. In

the second region, the formation of both hemimicelles and

magnesium sulfonate precipitate are equally plausible on

thermodynamic grounds, because the appearance of

precipitation in the bulk is an indication that surface

precipitate is forming on the sepiolite surface. Surface

precipitate and hemimicelles show similarities and are

thermodynamically indistinguishable [36].

Figure 10. The abstraction isotherms for both SDS and

SDBS onto sepiolite

3.5. Adsorption of Pyridine Derivatives on

Sepiolite

Contamination of drinking water supplies by various

compounds from industrial plants represents a potential

hazard on the health and well being of the general public.

On the other hand, aminopyridines are currently finding

increasing medical applications [33].

Figure 11 shows the adsorption isotherms of

sepiolite/2-aminopyridine and 2,2'-bipyridyl systems at

25°C [38]. In this study, the adsorption behavior of

pyridine derivatives, i.e. 2-aminopyridine and 2,2'-

bipyridyl onto sepiolite, a natural clay mineral, has been

investigated by bottle adsorption and IR-spectroscopic

techniques. The results indicate that 2-aminopyridine and

2,2'-bipyridyl molecules adsorb onto sepiolite through

hydrogen bonding of the amino groups to the water

molecules in the octahedral sheet and to the surface

hydroxyls (Si-OH) in the tetrahedral sheet. These findings

reveal that pyridine molecules not only adsorb onto the

external surface of sepiolite but are also incorporated in its

channels and tunnels with adsorption taking place at

corners and /or edges depending on the position of water

molecules.

Figure 11. Adsorption isotherms of sepiolite/2-

aminopyridine and sepiolite/2,2'-bipyridyl systems at 25

°C.

3.6. Adsorption of Petroleum Products on

Sepiolite

Table 2 shows the effect of amount and type of

absorbed liquid on 10 g dolomitic white sepiolite. At

constant amount of adsorbent, the order of sorptivity of

different petroleum products on sepiolite in its natural

form is as follows engine oil > Fuel-Oil> Kerosene.

Table 2. Effect of amount and type of absorbed liquid on

10 g sepiolite by weight [39].

Amount of

Liquid (g) Weight Absorption (g)

Kerosene Fuel-Oil Used Eng.

Oil

10 6.58 7.28 7.50

20 6.64 7.70 10.92

30 8.18 7.92 11.25

40 6.80 8.19 12.01

50 - - -

Average 7.05 7.77 10.42

8

4. CONCLUSION

Sepiolite is receptive to a range of organic and

inorganic chemicals. In this study, it is clearly shown that

sepiolite is not an absorbent but adsorbent, i.e. it

undergoes typical chemical interactions with the

adsorbates. While the main mechanism of uptake of

organic and inorganic chemicals is ion exchange other

mechanisms viz., hydrogen bonding, electrostatic

attraction, and hydrophobic bonding are also operative in

the system either concomitant with or proceeding to ion

exchange reactions. It is shown in a number of studies that

sepiolite can be used in drinking or wastewater treatment

systems.

5. REFERENCES [1] Topbaş, M.T., A.R. Brohi, and M.R. Karaman, “The

Pollution of Environment”, The Publications of Ministry of

Environment, Ankara, 1998.

[2] G.W. Brindley, and G. Pedro, Report of the AIPEA

Nomenclature Committee, AIPEA Newsletter, 1972, 4, pp. 3-4.

[3] E. Ruitz-Hitzky, “Molecular access to intracrystalline tunnels

of sepiolite”, J. Mater. Chem,. 2001, 11, pp. 86-91.

[4] J.L. Ahlrichs, C. Serna, and J.M. Serratosa, “Structural

Hydroxyls in Sepiolite”, Clays and Clay Minerals, 1975, 23, pp.

119-124.

[5] A. Jimenez-Lopez, J.D. Lopez-Gonzalez, A. Ramirez-Saenz,

F. Rodriguez-Reinoso, C. Valenzuela-Calahorro, and L. Zurita-

Herrera, “Evolution of Surface Area in a Sepiolite as a Function

of Acid and Heat Treatments”, Clay Minerals, 1978, 13, pp. 375-

384.

[6] F. Rodriguez-Reinoso, A. Ramirez-Saenz, J. De D. Lopez-

Gonzalez, C. Valenzuela-Calahorrro, and L. Zurira-Herrera,

“Activation of a Sepiolite with Dilute Solutions of HNO3 and

Subsequent Heat Treatments”: III. Development of Porosity, Clay

Minerals, 1981, 16, pp. 315-323.

[7] S. Yariv, and L. Heller-Kallai, “Thermal Treatment of

Sepiolite-and Palygorskite-Stearic Acid Associations”, Chemical

Geology, 1984, 45, pp. 313-327.

[8] D.C. Golden, J.B. Dixon, H. Shaden, and L.A. Kippenberger,

“Palygorskite and Sepiolite Alteration to Smectite under Alkaline

Conditions”, Clays and Clay Minerals, 1985, 33, pp.44-50.

[9] Y. Sarıkaya, N. Biçer, C. Biçer, H. Ceylan, and I. Bozdoğan,

“The effect of heat activation on the properties of adsorption

capacity of a dolomitic sepiolite”, 2nd National Clay Symposium,

Ankara, 1985, pp. 221-227.

[10] Y. Grillet, M. Cases, M. Francois, J. Rouquerol, and J.E.

Poirier, “Modification of the Porous Structure and Surface Area

of Sepiolite under Vacuum Thermal Treatment”, Clays and Clay

Minerals, 1988, 36, pp. 323-342.

[11] J.P. Pariente, V. Fornes, A. Corma, and A. Mifsud, “The

surface Acidity and Hydrothermal Stability of Sepiolite

Derivates”, Applied Clay Science, 1988, 3, pp. 299-306.

[12] H. Çetişli, “The surface acid-base properties of Eskisehir

Sepiolite”, the Journal of TUBITAK Doğa TU Engineering and

Environmental, 1989, 13, 2, pp. 213-227.

[13] U. Shuali, M. Bram, M. Steinberg, and S. Yariv, “Infrared

Study of the Thermal Treatment of Sepiolite and Palygorskite

Saturated with Organic Amines”, Thermochimica Acta,

Amsterdam, 1989, 148, pp. 445-456.

[14] H. Çetişli, and T. Gedikbey, “Dissolution Kinetics of

Sepiolite from Eskisehir (Turkey) in Hydrochloric and Nitric

Acids”, Clay Minerals, 1990, 25, pp. 207-215.

[15] M.A. Vicente Rodriguez, J.D. Lopez Gonzalez, and M.A.

Banares Munoz, “Acid Activation of a Spanish Sepiolite.

Physicochemical Characterization, Free Silica Content and

Surface Area of the Solids Obtained”, Clay Minerals, 1994, 29,

pp. 361-367.

[16] M.A. Vicente Rodriguez, J.D. Lopez Gonzalez, M.A.

Banares Munoz, and J. Casado- Linarejos, “Acid Activation of a

Spanish Sepiolite: II.Consideration of Kinetics and Physico-

Chemical Modifications Generated”, Clay Minerals, 1995, 30,

pp. 315-323.

[17] S. Balcı, “Effect of heat decomposition and acid activation

on the porosity of sepiolite”, 1st Industrial Raw Materials

Symposium, Sept. 1995, pp. 221-231.

[18] Y. Sarıkaya, and Y. Coşar, “Effect of Heat and acid

activation on the properties of adsorption capacity of Eskisehir

Sepiolite”, 8th National Clay Symposium, Kütahya, 1997, pp.

147-154.

[19] A.G. Sanchez, E. Alvarez Ayuso and O. Jımenez De Blas,

“Sorption of heavy metals from industrial waste water by low-

cost mineral silicates”, Clay Minerals, 1999, 34, pp. 469-477.

[20] NSW EPA, “Water Pollutants & Their Origin”, NSW

Environment Protection Authority, Sydney, Australia, 1996.

[21] M.F. Brigatti, C. Lugli, L. Poppi, “Kinetics of heavy-metal

removal and recovery in sepiolite”, Applied Clay Science, 2000,

16, pp. 45–57.

[22] E. Sabah, M. Kara, M. Cınar, and M.S. Çelik, “Abatement

Of Mineral Processing Wastes By Sepiolite”, Development of

Non-Renewable Resourches Challenges and Solutions, Edited

by, H. El-Shall, A. Ismail and B. Moudgil, 1997.

[23] E. Hellios-Rybicka, “Sorption of Ni, Zn and Cd on

sepiolite”, Clay Minerals, 1985, 20, pp.525-527.

[24] Kara, M., “Adsorption of metal ions onto Sepiolite”,

Doctoral Dissertation, Istanbul Technical University, Istanbul,

1999.

[25] B.W. Mercer, L.L. Ames, C.J. Thouhill, W.J. Van Slyke,

and R.B. Dean, “Ammonia removal from secondary effluents by

selective ion exchange”, J. Water Pollution Control Federation,

1970, 42, 2/2, pp. 95-107.

[26] T.G. Reeves, “Nitrogen removal: A literature survey”, J.

Water Pollution Control Federation, 1972, 44(10), pp. 1895-

1908.

9

[27] H.L. Culp, G.M. Wesner, and G.L. Culp, Handbook of

Advanced Waste-water Treatment, 2nd ed., Van Nostrand

Reinhold Co., New York, 1978.

[28] M.S. Çelik., B. Özdemir, M. Turan, G. Atesok, “Removal

Of Ammonia By Sepiolite Using Fixed And Fluidised Bed

Column Reactors”, Water Science and Technology: Water

Supply, 2001, 1, pp. 81-88.

[29] E. Gonzales-Pradas, M. Villafranca-Sanches, M. Socias-

Viciana, F. Del Rey-Bueno, and A. Garcia-Rodriguez,

“Adsorption of Thiram from Aqueous Solution on Activated

Carbon and Sepiolite”, J. Chem. Tech. Biotechnol., 1987, 39, pp.

19-27.

[30] G.W. Brindley, and G. Brown, “Crystal structures of clay

minerals and their X-ray identification”, Mineralogical Society,

London, 1984, pp. 105-109.

[31] G. Akçay, and K. Yurdakoç, “Removal of various

Phenoxyalkanoic Acid Herbicides from Water by Organo-clays”,

Acta Hydrochim. Hydrobiol., 2000, 28, pp. 300-304.

[32] Sabah, E., and Çelik, M.S., Adsorption Mechanism of

Quaternary Amines by Sepiolite, Separation Science and

Technology, Accepted, 2002.

[33] E. Gonzalez-Pradas, A. Valverde-Garcia, and M.

Villafranca-Sanchez, “Removal of aromatic amines aqueous

solution by activated sepiolite”, J. Chem. Tech. Biotechnol.,

1990, 47, pp. 15-22.

[34] H.M. Asfour, M.M. Nassar, O.A. Fadali, and M.S. El-

Guendi, “Color removal from textile effluents using hardwood

saw dust as an adsorbent”, J. Chem. Technol. Biotechnol., 1985,

35A, pp. 28-35.

[35] A. Armağan, O. Özdemir, K. Alp, M. Turan, “Abatement of

Textile Wastewater using natural clay minerals”, IX. Balkan

Mineral Processing Congress, İstanbul, 11-13 Sept. 2001,

pp.591-594.

[36] K.P. Ananthapadmanabhan and P. Somasundaran, Colloids

and Surfaces, 1986, 13, pp. 430.

[37] O. Özdemir, F. Arslan, M.S. Çelik, “Adsorption of long-

chain Benzensulfonates onto Sepiolite”, 3rd Industrial Raw

Materials Symposium, 1999, pp.114-123.

[38] E. Sabah, and M.S. Çelik, “Interaction Of Pyridine

Derivatives With Sepiolite”, Submitted to Journal of Colloid and

Interfaces Science, 2002.

[39] H. Kurama, D. Öz, and M. Kaya, “Technogical evaulation

of Turkish sepiolites”, Changing Scopes in Mineral Processing,

Kemal, Arslan, Akar and Canbazoğlu (eds), 1996, pp. 407-414.