Thesis Abstract

Thesis Overview

1.0 Introduction
Zeolites are porous crystalline alumino-silicates of regular skeleton structures formed
by alternating silicon-oxygen and aluminum-oxygen tetrahedrons. Although only natural
zeolites were initially used, synthetic zeolites, due to their well-tailored and highlyreproducible
structures, have been used extensively as ion exchangers, adsorbents, separation
materials and catalyst1.The negative charges in aluminum-oxygen tetrahedron, which are not
rigidly fixed to the skeleton of zeolites, are compensated with cations, so they are capable of
interchanging. Silicon-oxygen and aluminum-oxygen tetrahedrons in the zeolites of the type
A, X and Y form a complex structural unit of cubooctahedron. The combination of such units
forms the structure of type A, X and Y [fig 7].. The difference between them consists in the
fact that they are interconnected by means of different number of member rings (i.e., eight
member rings (A), twelve member rings (X, Y). The chemical difference of zeolite is defined
by the ratio of Si/Al. For zeolite A this values is in the range of 0.95-1.051-3. Zeolites A, X
and Y are the most important ones to be used in pharmaceutical, petrochemical and detergent
industries.
Zeolites with different structure are known to be obtained by synthesis 2-7. They are
either synthesized from alumino-silicate hydrogel or by conversion of clay minerals. The
hydrogel can be prepared from different sources of silica and alumina, but the types of
starting materials and the method of mixing determine the structure of the resulting gel.
Moreover, the nature of the gel influences the rate of the subsequent crystallization, which
affects the particle size distribution, and the formation of impurities8. The general pathway
for zeolite synthesis follows a specific temperature gradient at low temperatures (<60 oC)
2
where the sources of aluminum, silicon and water are placed in solution and mixed until a gel
is formed9.
Figure 1: Structure of zeolite framework
1.1 Background of Study
The extremely fast growth of the world population in the last century, in addition to
the industrial revolution, reflected in a considerable rise in both fresh water consumption and
waste water production. Fresh water demand has already exceeded supply; and currently
special treatment is more and more often required in order to obtain drinking water of high
quality as well as to produce environmentally acceptable effluents.
Species of toxic heavy metals cause serious damage to the ecosystem and as a result
of this fact, there is an increase in research on processes for wastewater treatment3. Many of
the wastewater treatment processes are based on adsorptive properties or ion exchange of
some of these materials which immobilize the heavy metal species. Recently, various
materials of natural or synthetic origin, such as bagasse, coal ash, carbonates, phosphates and
zeolite have been tested for their sorption capacity.4 Zeolite are commonly used for sorption
of heavy metals due to their physical and chemical properties (thermal stability, defined
molecular structure and ion exchange capacity.
3
1.2 Statement of Problem
The presence of large quantities of toxic metals such as mercury, lead, cadmium,
zinc, nickel and others in water poses serious health risk to humans, and this threat puts the
scientific community under pressure to develop new methods of detecting and removing
toxic contaminants from wastewater in efficient and economically viable way. The
production of zeolite from chemical sources (Al and Si ) are expensive but have the
advantage of producing zeolites of high purity with highly engineered chemical and physical
properties suitable for some specific applications in pharmacy, electrochemistry,
photochemistry, nano technologies, industries as well as for academic research purposes. The
greatest challenge now is the need to develop low cost and efficient adsorbents for nickel ion
removal from wastewater.
1.3 Objectives of the Study
The objectives of this study are:
i. To synthesize zeolite from analytical grade chemical.
ii. To characterize the synthesized zeolite using spectroscopic techniques such as
XRD, SEM and AAS.
iii. To use the synthesized zeolite to adsorb nickel ion from aqueous solution.
iv. To study the effect of pH, temperature, contact time and adsorbent dosage in
nickel metal removal.
1.4 Justification of the Study
The wide range of zeolite applications and the need to synthesize zeolite with high
purity motivated this work.The study has proffered cheaper routes of making zeolite with
high purity and thereby showed that zeolite is a good adsorbent for wastewater treatment