Bergaya F. Handbook of Clay Science

Подождите немного. Документ загружается.

Handbook of Clay Science

Edited by F. Bergaya, B.K.G. Theng and G. Lagaly

Developments in Clay Science, Vol. 1

r 2006 Published by Elsevier Ltd.

693

Chapter 11.3

CLAY LINERS AND WASTE DISPOSAL

K. CZURDA

Angewandte Geologie, Universita

t Karlsruhe, D-76128 Karlsruhe, Germany

As populations grow and technologies advance, the type and quantity of waste

produced keeps on growing. As a result, waste disposal became a huge environmental

problem. This chapter is concerned with waste encapsulation in relation to environ-

mental clean-up and protection. The term ‘encapsulation’ refers to the sealing of

waste body by geological and engineered liner systems. In most cases, such systems

partly consist of clay liners with varied modiﬁcations. Thus, encapsulation systems

are as varied as the environments in which they are built, and the components of an

encapsulation system are as multiple and complex as the wastes themselves. For all

waste types, encapsulation is the only option if the waste has to be permanently

isolated from the accessible environment (Caldwell and Reith, 1993). The require-

ments for an encapsulation system are basically the same, whether the waste is mu-

nicipal refuse in a landﬁll, hospital debris in a low-level waste dump, or mixed wastes

of diverse industrial production/construction activities. This leads us to the need to

classify wastes because encapsulation systems consist of engineered liner components

according to the magnitude of the risks which are associated with the waste.

From the beginning, sophisticated engineered liners should meet two requirements:

(i) to guarantee practical imperviousness so as to prevent leachates from inﬁltrating

the environment and (ii) to possess retention or at least retardation properties pre-

venting contaminant migration by convection and diffusion (Drescher, 1997). In many

cases—but not absolutely—the surface barrier (layer) may be slightly permeable, al-

lowing further decomposition of sanitary wastes by precipitation moisture. Because of

the different functions of the surface and the base encapsulation barriers, different

state-of-the-art systems were developed (Fig. 11.3.1). In practice, clay liners are

designed so that most of the required properties are optimally expressed (Fig. 11.3.2).

11.3.1. WASTE CATEGORIES

Different waste compositions require different sealing units. For example, it is not

economical to use a multilayer system for inert construction wastes or to design an

DOI: 10.1016/S1572-4352(05)01022-6

identical system for sanitary landﬁlls and toxic industrial wastes (Br adshaw et al.,

1992). For this reason, all regional waste repository regulations ha ve to categorise

wastes not according to the input of waste components but mainly in terms of

leaching the waste and quantifying the contaminant content (Czurda, 1992). The

Groundsurface

Technical

barrier

Geologic

barrier

Ring

drainage

Supporting

dam

Waste

Surface liner

Drainage

system

Groundwater table

Base liner

Fig. 11.3.1. Multibarrier system for waste encapsulation. Geologic in situ barriers and en-

gineered technical barriers (compacted mineral layers and geomembranes) are the main parts

of the system.

131011

100

percent coarser by weight

8 4 212 9 7 6

100

percent finer by weight

0.001 0.002 0.006 0.02 0.06 0.2 0.6 2 6 20 10060

grain diameter [mm]

range of hydraulic permeability (k) [m·s

-1

]

clay

silt

middle

sand

middle

gravel

middle

stones

fine coarse fine finecoarse coarse

Fig. 11.3.2. Practical imperviousness is the main function of liner systems. Hydraulic perme-

abilities are expressed as k coefﬁcients in ms

1

. The range of kp10

7

1

is considered as one

of the most important barrier features of mineral sealing units in the national regulations.

Grain size distribution areas 10, 11, and 12 refer to this.

Chapter 11.3: Clay Liners and Waste Disposal694

European Union, most European countries, the USA, Canada, Japan, etc. follow

this system, ending up with similar waste categories. Taking radioactive waste into

account leads to the following classiﬁcation scheme:



inert construction and industrial waste,



domestic waste,



toxic industrial waste,



incineration ashes and slags, and



radioactive waste.

Nuclear waste repositories have to follow special national regulations and are not

further treated in this chapter.

As an example for waste assignments, some thres hold values accordi ng to

German regulations (Gassner, 1991;TASiedlungsabfall, 1993; Deponieverordnung,

2002) are shown in Table 11.3.1. They are close to European Union values

(EU-Richtlinie, 1999).

11.3.2. MINERAL BARRIERS

Clay rocks, clay mineral admixtures, and zeolite admixtures are the most impor-

tant and widely used natural materials for constructing mineral barriers within en-

gineered sealing layers. These materials are also used as constituents of in situ

geological barriers, i.e., waste deposit location. The use of alternative materials such

as amorphous silica, ﬂy ashes, ﬂy ash zeolites, clay remnant s from coal ﬂotation, etc.

is not discussed.

Table 11.3.1. Assignment criteria for waste categories according to the German regulations

TA-A and TA-Si. Selected examples. Category I is inert waste, category II is domestic waste,

and category III is toxic industrial waste. The leachable parts are listed as examples for very

common toxic waste constituents

I II III

Conductivity p6000 mS/cm p50000 mS/cm p100000 mS/cm

Uniaxial strength X50 kN/m

X50 kN/m

TOC



p20 mg/L p100 mg/L p200 mg/L

Phenols p0.2 mg/L p50 mg/L p100 mg/L

Mercury p0.005 mg/L p0.020 mg/L p0.100 mg/L

Cadmium p 0.050 mg/L p0.100 mg/L p0.500 mg/L

Lead p0.200 mg/L p1000 mg/L p2000 mg/L

Sulphate p500 mg/L p1400 mg/L p5000 mg/L

Soluble part p3% p6% p10%



Total Organic Carbon

11.3.2. Mineral Barriers 695

A. Clay Rocks and Clay Minerals

In using clays and zeolites and other ﬁne-grain material for sealing purposes, two

main issues are relevant: (i) leachate retention due to low-hydraulic conductivities

and (ii) toxic constituent retention or retardation due to adsorption, precipitation,

redox processes, and other mechanisms. Soil barriers, containing enough clay min-

erals with adequate properties to provide low permeability, are used extensively to

prevent rapid advective migration of various leachates from waste disposal sites

(Hiltmann and Stribrny, 1998). The clayey barriers vary from thin geosynthetic clay

liners (GCL) of 1–3 cm thickness, to compacted clay liners (CCL) up to 300 cm in

thickness, to natural undisturbed clayey barriers up to 30 m or more in thickness.

The hydraulic conductivity of undisturbed clayey deposits depends on the miner-

alogy, environment of deposition, and stress history of the deposits. The same holds

true for GCL and CCL.

Clays attract water, other polar liqui ds, and cations. A dried-out clay will expand

as it adsorbs water between its layers and particles when placed in an aqueous

solution. If toxic ions are present in the solution, they can adsorb on the charged clay

surface mineral by ion exchange. Thus, clays can accept or release ions depending on

the concentration of the ions in solution relative to that on the surface. These ions,

e.g., from the leachate, are not ﬁnally ﬁxed but can participate in further exchange

processes depending on the chemical environment.

The nature of the cation s initially present at the clay mineral surface (derived, for

example, from the marine environment) is of decisive inﬂuence on adsorption po-

tentials. According to the diameter of hydrated cations and their valency they are

differently adsorbed by the clay surface mineral and are therefore exchangeable in

different quantities. For example, Na

-bentonites are especially suitable for base

liner construction. Because of their high-swelling potential and adsorpt ion capacity,

they fulﬁl the requirements for a high degree of imperviousness, and a high con-

taminant retention potential. Table 11.3.2 shows the cation exchange capacity (C EC)

and speciﬁc surface areas of some clay minerals and other materials. The theoretical

speciﬁc surface areas of smectites and vermiculites of 750–800 m

/g are only effective

when the contaminants can fully penetrate the interlayer space. This may be the case

for ion exchange with pure inorganic ions (see Chapter 12.10) and suitable organic

cations (see Chapter 7.3) but doe s not often apply to the adsorption of neutral (non-

ionic) compounds.

B. Zeolites

Zeolites show a high potential as contaminant adsorbents due to their highexchange

capacity and selectivity for certain cations, such as NH

,Pb

,Cd

,Sr

, and

other metal ions, especially after ‘activation’ by sodium chloride. The selec tivity of

certain zeolites for speciﬁc chemicals is controlled by their pore size and charge

Chapter 11.3: Clay Liners and Waste Disposal696

properties. By analogy with clay minerals, the substitution of Al

for Si

in the

structure leads to a net negative charge and a high CEC for most natural zeoli tes.

Natural zeolites occur in sediments, lava vesicules, deuteric-altered plutonic rocks,

and hydrothermal systems associated with alkaline volcanic rocks. Since natural

zeolites generally derive from volcanic glass, they are of widespread occurrence.

Fig. 11.3.3 shows the isotherms for the adsorption of Cu

from deionised water

and a 0.01 M CaCl

solution by clinoptilolite (a very common natural zeolite) and

–clinoptilolite (Huttenloch et al., 2001). The isotherms are curvi-linear, and can

be described by the Freundlich equation: c

¼ K

where c

denotes the amount of

the solute adsorbed per unit mass of adsorbent, c

is the equ ilibrium solute con-

centration, K

and n are empirical parameters speciﬁc of the adsorbate-adsorbent

interaction.

11.3.3. WASTE DEPOSIT MULTIBARRIER SYSTEMS

Waste deposits can in principle be constructed as underground storages and at the

surface as slope storage, slope dump, or depression storage. Common domestic waste,

incineration residues, inert construction wastes, etc. may be stored at the surface.

Underground storage as a special deposition mode is not treated in this chapter.

A. Base Liners

Base liner systems must be able to prevent leakage of contaminants from the waste,

and their inﬁltration into the subsoil. These systems have to prove a high potential for

retaining toxic materials by adsorption, precipitation, and/or redox processes (Rowe

et al., 1995). Adsorption on mineral surfaces mainly occurs by ion exchange. In many

cases toxicants can be retarded during their migration through the sealing layers.

Table 11.3.2. Cation exchange capacity (CEC) and speciﬁc surface area of some clay minerals

and other materials

Adsorbent CEC (cmol(+)/kg)



Speciﬁc surface area (m

/g)

Allophane 50–100 500–700

Kaolinite 3–15 10–20

Illite 10–40 50–100

Montmorillonite 70–120 10–800

Vermiculite 130–210 1–800

Fe– +Al–(hydr)oxides (pH 8.0) 3–25 25–40

Humic material 150–250 about 800



¼ meq/100 g.

depending on the participation of internal surfaces; lowest value represents the external speciﬁc surface

area.

11.3.3. Waste Deposit Multibarrier Systems 697

Figs. 11.3.4a, b shows an example of a base liner constructed according to Ger-

man regulations for inert and domestic wastes. The essential components are com-

pacted clay layers, and in case of domestic wastes, a geomem brane in addition to the

mineral layers and of course the geological barrier (Fig. 11.3.5). The basal system

contains a leachate collecting layer, connected to a puriﬁcation plant. There are

different leakage detection systems on the market.

B. Surface Liners

The exclusive function of the surface liner is to prevent precipitation water from

inﬁltrating into the waste. In case of household wastes, the capping system has to

have a gas drainage system. Capping layers for all types of waste are therefore

constructed with a drainage layer (usually 16–32 mm gravel) in case of leaks in the

system.

As in the case of basal systems, CCL and geomem branes are the prevailing sealing

elements (Fig. 11.3.6a, b). But there is an important difference in the clay mineral

composition of the CCLs. Whereas the base CCL-clay should contain 2:1 layer clay

minerals (e.g ., montmorillonite, vermiculite), the surface CCL-clay should contain

1:1 phyllosilicates (e.g., kaolinite) as index minerals. The 2:1 minerals enable retar-

dation by adsorption and a high degree of impermeability to be obtained, while the

1:1 clays of the surface sealing unit, combined with a sand/silt matrix, are practically

impermeable but have a low-adsorption potential. Because of the small particle size,

a sand–silt–kaolinite admixture for the mineral surface sealing can have a very low

permeability (k

¼ 10

210

212

cm=s).

Fig. 11.3.3. Adsorption isotherms of Cu

on natural and Na

clinoptilolite in deionised

water and 0.01 M CaCl

solution (1 g samples in 40 mL copper salt solutions, contact time

96 h, at 20 1C). The CEC of clinoptilolite is 720 mmol(+)/g and of Na

–clinoptilolite is

900 mmol(+)/g.

Chapter 11.3: Clay Liners and Waste Disposal698

11.3.4. CONCLUSIONS

For hazardous industrial wastes and toxic sanitary landﬁlls, we have to locate a

site that functions primarily as a geologic barrier with k

o10

–6

m/s and at least 3 m in

thickness. In case of inert (non-toxic) wastes a geologic barrier is not necessary. It is

essential, however, to follow the multibarrier concept and to add on top of the

geologic barrier a system of engineered barriers and drainage layers. The engineer ed

barriers comprise as a core unit the combined CCL and geomembrane double layer.

A similar multibarrier system has to be constructed for the cover sealing. The dif-

ference is expressed in the type of GCL and the drainage layers. The GCL should not

contain expanding 2:1 clay minerals, such as montmorillonite or vermiculite, because

they tend to dry out and form desiccation cracks. Therefore non-swelling 1:1 clay

waste

drainage

geomembrane

clay liner

geologic

barrier

drainage

clay liner

(a)

(b)

Fig. 11.3.4. (a) Base liner system for inert waste. Two CCL without geomembrane (b) Base

liner system for domestic waste. Three CCL combined with a geomembrane.

11.3.4. Conclusions 699

30cm 30cm

75cm

150cm

Base Liner System

Domestic waste

German regulation

Industrial waste

German regulation

Category I

Category II

Multimineral barrier

Waste

Drainage layer 30cm

Mineral barrier 50cm

Geologic barrier

Geo-

membrane

Sorption

layer

Clay,

Na-bentonite

optimized

Clay,

kaolinite

optimized

pervious

layer

Fig. 11.3.5. Comparing different base liner systems. The multibarrier system consists of two

clay units: an adsorbing bentonite unit and a sealing kaolinite unit.

(a)

(b)

Fig. 11.3.6. Environmental Protection Agency (EPA) recommendation for surface liner sys-

tems in the USA. Clay barriers are combined with geomembranes (a) The optional system (b)

comprises additional ﬁller systems: a biotic ﬁlter on top of the sealing unit and a gas collection

layer below.

Chapter 11.3: Clay Liners and Waste Disposal700

minerals (e.g., kaolinite) or tectosilicates (e.g., zeolites) should be the index minerals

for the sand–silt–clay surface GCL. In case of untreated household waste, a gas

drainage layer has to be provided in order to divert the methanol that develops as the

waste decomposes.

REFERENCES

Bradshaw, A.D., Southwood, R., Warner, F., 1992. The Treatment and Handling of Wastes.

Chapman & Hall, London.

Caldwell, J.A., Reith, C.C., 1993. Principles and Practice of Waste Encapsulation. Lewis

Publishers, Boca Raton, FL.

Czurda, K.A., 1992. Deponie und Altlasten. EF-Verlag fu

r Energie- und Umwelttechnik

GmbH, Berlin.

Deponieverordnung, 2002. Verordnung u

ber Deponien und Langzeitlager, Bun-

desministerium fu

r Umwelt, Naturschutz und Reaktorsicherheit, Berlin.

Drescher, J., 1997. Deponiebau. Alphabet KG, Berlin.

EU-Richtlinie, 1999. Richtlinie u

ber Abfalldeponien, Rat der Europa

ischen Union. Amtsblatt

der Europa

ischen Union, Bru

ssel.

Gassner, E., 1991. Gesamtfassung der Zweiten allgemeinen Verwaltungsvorschrift zum Ab-

fallgesetz 1. Teil. Verlag Franz Rehm, Mu

nchen.

Hiltmann, W., Stribrny, B., 1998. Tonmineralogie und Bodenphysik. Springer-Verlag, Berlin.

Huttenloch, P., Roehl, K.E., Czurda, K.A., 2001. Sorption of nonpolar aromatic contam-

inants by chlorosilane surface-modiﬁed natural minerals. Environmental Science and

Technology 35, 4260–4264.

Rowe, R.K., Quigley, R.M., Booker, J.R., 1995. Clayey Barrier Systems for Waste Disposal

Facilities. Chapman & Hall, London.

TA Siedlungsabfall, 1993. Technische Anleitung zur Verwertung, Behandlung und sonstigen

Entsorgung von Siedlungsabfa

llen, Ministerium fu

r Umwelt, Rheinland-Pfalz. Bundesan-

zeiger, Ko

ln.

References 701

Handbook of Clay Science

Edited by F. Bergaya, B.K.G. Theng and G. Lagaly

Developments in Clay Science, Vol. 1

703

Chapter 11.4

CLAYS AND NUCLEAR WASTE MANAGEMENT

R. PUSCH

Geodevelopment AB, Ideon, S-22370 Lund, Sweden

Eliminating the risk of transportation of radionuclides from radioactive waste

stored underground to the biosphere is the goal set by all countries that make use of

nuclear power. Different countries plan ‘‘geologic disposal’’ in rocks, salt and clay

sediments. The design principle is that highly rad ioactive waste, like burnt-out fuel

and products from processed waste, is enclosed in containers—canisters—isolated by

smectitic (smectite-rich) clay. These canisters are placed in vertical boreholes or long

horizontal bored or blasted tunnels at a depth of 300–800 m. Low- and medium-level

waste has shorter lifetimes and can be stored at smaller depth with less effective

isolation.

Selection of smectitic clays with suitable bulk density to embed the canisters, is

based on the fact that this type of ‘‘clay buffer’’ has the following valuable prop-

erties: (i) very low hydraulic conductivity; (ii) very low anion diffusion capacity and

fairly low transport capacity of positively charged radionuclides; (iii) a high swelling

potential for self-sealing of gaps and openings in the buffer and its contacts with the

rock and canisters; (iv) favourable rheological properties, such as sufﬁcient bearing

capacity to minimise settlement of the heavy canisters, and sufﬁcient softness to

avoid transfer of high tectonically induced shear stresses to the canisters; (v) suf-

ﬁcient thermal conductivity to transfer heat caused by the radioactive decay to the

rock without being too hot; (vi) colloid ﬁltering capacity; and (vii) capacity to ﬁlter

microbes.

The optimum bulk density at ﬂuid saturation should be in the region of

1900–2100 kg/m

to meet the criteria; this density cannot be achieved by on-site

compaction. Instead, very dense blocks of highly compacted smectitic clay powder

are placed around the canisters, embedding them tightly. The required tightness is

attained when the clay material swells after taking up water from the surrounding

rock. Suggested design principles for repositories are illustrated in Fig. 11.4.1. The

design of a repository for low- and medium-radioact ive waste is illustrated in

Fig. 11.4.2. This type of repository is located about 150 km north of Stockholm and

has been in operation for 15 years (Pusch, 1994).

DOI: 10.1016/S1572-4352(05)01023-8