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t h e

glass researcher

G la s s - C e r a m ic s M a n u f a c t u r in g f r o m S lu d g e

a n d A n o d iz e d W a s t e

Feasibility of manufacturing ceramic-tile from sludge ash from a city wa ter-treatment

plant and from anodized aluminum process water fram lacal industries has been

studied to reuse both residues and prevent their disposal.

M a . P .   Har o Va zqu ez B.C. Alcdntar Vaz que z E.G. Carrillo Cedillo Ma .E. Villafuerte Castrejon an d G.C. Diaz Trujillo

A great problem faced by constantly developing cities, such

  s  Tijuana (the most populated municipality in the state of Baja

California. Mexico, with more tha n one million inhabitan ts), is

the high amount of wastewater generated. This generates

increasing amounts of activated sludge produced by the waste-

water-treatment plant. The sludge is disposed of in an outdoor

confinement area in the Punta Bandera area. This sludge con-

tains a high amount of organic material and humidity (70%),

which generates bad odors and leaching. The city's climatic

conditions make this confinement area a potential source of

infectious disease. Also, in the industrial sector, anodizing

processes generate a significant amount of aluminum-rich waste.

It is important to introduce the possihility of applying

ceramic processes as a new alte rnative to disposal of corpo rate

inorganic industrial waste, because its metal content might be

highly toxic in otherwise inert materials. Currently, many

countries have prioritized research on (cement, ceramic, glass

and glass-ceramic) matrix development that can guarantee the

removal of inorganic industrial waste. The matrix must pres-

ent chemical and thermodynamic stability and must be easily

produced and manipulated.' '

In some countries—such  s  Japan—recent legislation limits

transportation and dumping of heavy-metal-containing ash

(such as those generated by incinerators). As a result, a tech-

nology called sludge fusion or vitrifica-

tion has developed. Tliis process also is

used in the United States to permanently

encapsulate harmful chemicals in a solid

block of a material similar to glass, which

prevents their release into the environ-

ment. This process can he conducted

underground or over a surface.

The activated sludge process is the most

frequently used worldwide. It is estimated

that the amount of sludge produced in the

European Union was between 15 and 20

Tlie major means of eliminating generated sludge has be

its transport to dumps, its dispersion on the ground, its use

compost, its dumping into the sea or its incineration.^ T

most attractive option is to spread the sludge on agricultur

lands to recycle the nutrie nts. Th is is useful from an agronom

ic point of view. However, this application is limited to trea

ed water. Untreated water can co ntain traces of heavy m et

and organic compounds that are barely hiodegradable. Th

may cause concern hecause ofthe possibility of environmen

risks, which intensifies the sludge elimination issue.

An important factor to take under consideration is that t

chemistry of sludge is not constant. It varies according to t

characteristics of plant design and type of sewage water to

treated.

Dumping toxic influents into sewage municipal water tre

ment plants inhibits the biological activity of the activat

sludge, which generally contains protozoan, rotiferous a

bacteria. If the sludge activity decreases, the volume of gen

ated sludge increases, because the organic matter does n

degrade.

Because of the problem caused by the great amount

sludge, studies have been made to create incinerators th

allow easy handling of this residue by considerably decreasi

its volume, which decreases disposal and treatment costs.

T a b l e   1   C o m p o s i t i o n   o f   G l a s s - C e r a m i c  M a t e r ia l s

M a t e r i a l  SiO

  n o i z e

r e s i u e

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These ashes can be used as raw material for the manafac-

cure of various products, such as construction materials,' ^

concrete,'' ceramics^''' and glass-ceramics. ^

Materials and Methods

Three systems were selected for study:

SiO,-Al .Oj-MgO and SiO,-Al ,O)-Lip . S ludge (bio-sol id)

was dried at 105°C for 5 h and bumed'at 700°C for 3 h. Six

glass-ceramic materials was prepared (Table 1), where sludge

ash and aluminum-containing residue were incorporated In

the form of salts as a replacement for A1,O, In each system.

Two series of tiles were prepared: the first used industrial

grade AljO^ the second used aluminum-salt residues. Both

series contained

  iO

sludge ash.

Pieces of ti le ( 5 x 5 x 1 cm) were obtained by applying a

biaxial pressure of 5000 lb/in.^ Subsequently, die tile was sin-

tered and crystallized: the SiO2-Al2O,-CaO and

^ P j i p at 1000°C for 5 h and at

 900°C

  4 h .

Material Characteristics

The gla-ss-ceramic materials obtained possess diverse tex-

tures, aspects and colors because of the variety of properties

offered by the oxides used in their preparation. Nevertheless,

they .share particle-size homogeneity. However, weight loss

and compression increase when aluminum-salt residues are

added. Because of tbe nature of the waste, the mixture of alu-

minum salts (predominantly sulfates and hydroxides) permits

a better interactiiin with the raw material, which contributes

to diminished porosity. Therefore, the weight loss is increased

(Table 2).

A similar effect occurs for density and water absorption.

The materials obtained using aluminum-salt residues present

greater density, which is attributed to the greater compression

of the material. This also presents better thermal reaction and

decreases porosity because of decreased presence of pores

and/or micropores. It might be tbat, in the materials that con-

tain anodizing waste, the water abstirption capacity decreases

while the density increases. An exception is the material that

contains lithium, as evident when material 4 (which c ontains

Li,O) is compared with material 6 (which contains MgO). In

the latter material, water absorption occurs within the range

determined by the norm (10-18%).

Tbe predominant crystalline pbases in eacb system have

been identified using X-ray diffrac tome try (XR D). T he

SiOj-Al^Oi-CaO material contains predominantly anortbite

(Ca (Al ,S ip3)) as well as quartz (SiO^). The S iO .- A ip , -

MgO material contains cordierite (Mg,(Al^SiP|j,)), enstatite

(MgSiO,) , anorthlte (Ca(Al,SiPs)) and quartz (SiOp. The

S i O n - A i p , - L i p m a t e r i a l c o n t a i n s s p o d u m e n e

(Li(AISiPj,)) and quartz (SiO^.

In all cases (Fig. 1), an increment in the vitreous phase is

observed when aluminum-salt residues are added TTiis is

attributed to the greater melting effect of the residue that

li ^

  W

A

  A

Q

  A

A Q Q QA 0

Q a

A 0

E A E E Q Q E

26  deg)

Fig.

  1 XRD patterns of gloss-ceramic moterials Q is qua rtz , S is

spodumene, A is onorthite, C is cordierite and

  E

 is ensta tite).

  T a b l e  2

Maletial

1

2

3

4

5

6

Physical Properties of Glass-Ceramic Materials 1

Compression

  { }

2.20

 

5.08

10.67

7.37

9.28

Weight

loss

  { )

7.06

7.25

4.0

10.49

11.86

8.98

Water

absorption

 { )

27.01

26.22

1S.3

2.54

19.75

13.3

Density

2.5212

2.6147

2.5884

1.8184

2.6295

2.6454

originates in solubility of SiO^.  A different effect is observed

for the SiO ,- A ip ,- M g O material. The presence of alu-

minum -salt residue pennits the solubility of cordierite and the

presence of calcium, which favors the formation of an anor-

thite phase.

The morphology of the materials has been studied using

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Glass-Ceramic Manufactur ing

scanning electron microscopy (SEM). The materials to

which aluminum-salt residues have been added as a replace-

ment of Al^Oj present greater homogeneity. Fewer pores

occur, and an increment in tbe vitreous phase occurs

hecause of the melting effect of the mixture of aluminum-

salt residues that perm its the solubility oft he system compo -

nents.

Similarly, elementary chemical analysis bas been con-

ducted using energy-dispersive spectroscopy (EDS ). Th e ele-

ments silicon, aluminum, calcium, magnesium, iron, potas-

sium and oxygen, which conform to each one of the identi-

fied phases, are recognized. A series of photomicrographs

that permit the observation of the microstructure of tbe

materials has heen studied (Fig. 2).

Was te Useful for Tile Man ufacture

The objective of this study was to assess the mineralogi-

cal, physical and microstructural properties of a glass-ceram-

ic material made using residues of industrial processes.

Analysis of the determ ined properties shows tha t it is possi-

hle to consider the residues as a replacem ent for raw materi-

als in the fahrication process of ceramic-tile materials. All of

the tested materials present crystalline phases (spodumene,

anorthite, cordierite, enstatite and quartz) in their composi-

tions that are needed for the specific heat treatment temper-

atures for sintering and crystallizing to promote the crys-

talline phase.

Introduction of aluminum-salt residues does not itibibit

the formation of the phases. However, it slightly promotes

the presence of

 

vitreous phase, hecause the aluminum salts

act as melting agents, which promotes decreased porosity.

This results in materials that present better physical proper-

ties.

 The SiO2-Al2O3-Li,O material presents a greater propor-

tion of vitreous phase because of the double presence of flux,

lithium and hydroxides. The SiOi-Al^O^-MgO system con-

tains the phases enstatite, cordierite and quartz. Introduction

of residue during the melting action tends to make the

cordierite phase soluble. •

Acknowledgment

The authors thank Ing. Leticia Barios L6pez, Carlos Flores

Morales and Dr. Jose Guzman oft he Institute) de Investigacion

en Materiales, UNAM for assistances in XRD and SEM meas-

urements. This work is the product of a study supported hy

Universidad Autonoma de Baja California (UABC) in 9th

Internal Program Research and collaboration of the Applied

Chemical group.

About the Authors

Ma.P.

 Haro Vazquez, B.C. Alc antar Vazquez., E.G. Carrillo

Cedillo and G.C . Diaz Trujillo are faculty members of Ciencias

Fig.

  2 SEM micropholographs of glass-ceramic ma terials.

Qui micas e Ingenierfa (U AB C) M exico and participate in

Applied Che mistry Gro up. Ma .E. Villafuerte Ca strejon

member of Instituto de Investigaciones en Materia

(UNAM) Mexico in the Metallic and Ceramic Dept.

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