Synthesis of Fly Ash Zeolite for Oil Spill Clean- UP

Abstract

Coal is primarily being used for electricity and heat production through a process of combustion. The typical thermal power plant will burn pulverized coal in a furnace with a boiler. The combustion products include fly ash, bottom ash and a boiler slag and flue gas desulfurization (FGD) materials. All these products contain various heavy metals that can create serious danger if released into the environment. Most of these harmful elements are present in the trace or ultra-trace levels, which give rise to significant accumulation of pollutant in the environment on a daily basis. This has attracted more attention within a context of progressively more stringent regulation of hazardous air pollutants (viz. fly ash) discharge from thermal power station. The amount of fly ash generated has been increasing at an alarming rate throughout the world. The disposal of such a huge quantity has become a pressing issue. Several approaches have been made for proper utilization of fly ash, either to reduce the cost of disposal or to minimize the environmental impact. Fly ash was generally released into the atmosphere, but pollution control equipment mandated in recent decades now requires that it be captured prior to release. In most of the power plants, fly ash particles are collected by Electrostatic Precipitators (ESP) or filter bags, in India. The fly ash properties will largely be influenced by the type of coal that is burned. One of the solutions is the conversion of fly ash to zeolites, which has wide applications in the field of an environment. The present study is concerned with the synthesis of zeolite from fly ash and its application in the field of an environment. Fly ash is the finely divided mineral residue resulting from the combustion of coal in thermal power plants. It consists of inorganic, incombustible matter that has been fused during combustion into a glassy, amorphous structure. Fly ash mostly consists of Silicon dioxide (SiO2), Aluminum oxide (Al2O3) and Iron oxide (Fe2O3) and hence is a suitable source of aluminum and silicon. The zeolite synthesis from these fly-ashes produced by the power generation industry is an alternative for environmental management of this type of waste. This can be achieved by a novel method of silica reduction i.e. microwave digestion based on the principle of molecular heating. In the last decade, the use of closed vessel microwave assisted digestion method under high temperature and pressure has become increasingly popular. Compared to the more traditional method, this procedure allows shorter digestion times and good recoveries. Furthermore, it requires smaller amount of acids, reduces risk to external contamination, which in turn, results in improved detection limits and the overall accuracy. Microwave digestion inherited some disadvantages from open air digestion; most of these problems, however, are associated with usage of Hydrofluoric Acid (HF). So far, researchers attempted to optimize the method in many different ways; some research has been done to determine the need for HF. It has been found that for digestion of coal addition, of HF is not necessary and its absence will not result in poorer recovery of trace elements. However, for fly ash, addition of HF proved to be necessary. The objective of this study is to try to understand the microwave digestion methods for fly ash. Based on that modify and further improve the method by attempting various parameters – temperature, time and effect of HF usage. Since, there is no published American Standards for Testing of Materials (ASTM) or Environmental Protection Agency (EPA) method for microwave assisted digestion of fly ash samples, as a starting point we chose two different procedures published in their “Application Notes” handbook that came with the instrument. There is numerous ongoing research efforts focused on optimization and improvement of microwave assisted acid digestion method for fly ash. Most of them are concerned with completeness of digestion procedure, length and time consumption, pretreatment conditions and use of HF. As such, a critical review of these methods and their limitations and superiority over each other becomes necessary. Incidentally, it has also been demonstrated by the researchers that there are several industrial applications for synthetic fly ash zeolite; author has also tried to review industrial applications of synthesized fly ash zeolite for oil spill clean-up. The increasing requirements in the sphere of environmental protection have induced search for more effective, inexpensive and ecologically safe solutions. Given that, the zeolite is aluminosilicate members of the family - microporous solids known as “molecular sieves” and have sorptive and ion-exchange properties; the most important pollution of hydrocarbon (HC) (viz. petrochemical spills), may find applications in the removal of oil spill, using hydrophobic - oleophilic - high-silica content - hydro thermally stable – zeolite; particularly those, prepared cheaply from fly ash; while, simultaneously providing a solution to other environmental problems. The research will be applicable in wide variety of environmental pollution control applications. Since clean up after an oil spill is so ineffective and so difficult, and does not always fully rehabilitate affected areas; “prevention is better than cure” is the most important tool for an environmental researcher. As a challenging task, the author has experimentally investigated the strategy for synthesis and application of fly ash zeolite for oil spill clean-up.