Synthesis and characterization of zeolite and its application in adsorption of nickel from aqueous solution

Thesis Overview

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