ABSTRACT
The synthesis and characterization of zeolite and its application in adsorption of nickel from aqueous solution was investigated. Synthesis of zeolite was performed at 90 oC for 8 h. The size of the resulting crystals increased with an increase in the water content of the reaction mixture. The synthesized zeolite was characterized by Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) techniques. Crystal structure of the product was determined as zeolite X by XRD. The concentration of the nickel ion was determined using atomic absorption
spectrophotometer (AA 320 – ON). Removal efficiency of nickel ion was dependent on the pH, contact time, adsorbent dosage and temperature. Batch adsorption studies conducted for the removal of nickel(II) ion at 25, 40 and 50 oC respectively showed that nickel ion adsorption increased with increase in temperature. The effect of adsorbent dosage of 0.5-4.5 g showed that there was an increase in the adsorption capacity when the adsorbent dose was increased from
2.0-4.0 g. The pH values were adjusted to 3.2, 4.3, 5.3, 6.7, 7.9 and 9.5 and it was evident from the result that at pH 5.3, uptake capacity of nickel(II) ion onto zeolite X was maximum. The effect of contact time at 10, 20, 30, 45, 60, 75 and 90 min was analysed and it was evident that adsorption of nickel was rapid in the first 40 min followed by a gradual increase until equilibrium was attained. Adsorption data was interpreted in terms of Langmuir and Freundlich isotherms. It was observed that the experimental data fitted better to Langmuir model with a
correlation factor (R2) value of 0.993 compared to Freundlich with R2 value of 0.980. The
kinetics  rate  were  modelled using  pseudo-first-order and  pseudo-second-order models.  The pseudo-second-order model  explained  the  adsorption  kinetics  most  effectively.  The  result showed that zeolite X was effective in the removal of Ni(II) ion from aqueous solution.
CHAPTER ONE
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 highly- reproducible 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)
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.
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.
This material content is developed to serve as a GUIDE for students to conduct academic research
SYNTHESIS AND CHARACTERIZATION OF ZEOLITE AND ITS APPLICATION IN ADSORPTION OF NICKEL FROM AQUEOUS SOLUTION
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