Elsevier

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Volume 80, Issue 5, April 2001, Pages 739-745
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Synthesis of zeolites from a lagoon ash

https://doi.org/10.1016/S0016-2361(00)00135-6Get rights and content

Abstract

The amount of ash, and its hazardous impact on the environment, produced from the coal fired thermal power plants is continuously increasing. This poses a very challenging task of safe handling, proper disposal and utilisation of the ash. A very common method of disposal of the ash is the wet disposal, in a slurry form, in the lands nearby thermal power plants, known as lagoons. During the process of wet disposal, the ash interacts with water and looses its original physical as well as the chemical properties. The ash–water interaction may also lead to the formation of zeolites over a period of time, which may be used for various industrial applications. This paper deals with the effect of water interaction, and hence the formation of zeolite, on a typical Class ‘F’ lagoon ash, from India.

Introduction

The growth in industrial development in any developing country needs a sustained supply of electrical energy. Major source of this electrical energy in India (as well as the world-wide) is the thermal power, constituting almost 70% of the total energy production, which is responsible for the production of enormous amount of the ash from these power plants. In India, the current production of ash from coal based thermal power plant is about 80 million tonnes per year and is expected to increase to more than 100 million tonnes in the near future. This requires a proper strategy for ash handling, its disposal and utilisation. At present, only 5–10% of the ash disposed is being used for various purposes viz., as a stabilizer of sub-grade and sub-bases in pavement construction, as a filler material, filling of mines, constituents of cement, treatment of polluted water, treatment of unsuitable soil for agriculture and to improve foundation soils.

Proper utilization of ash depends on its handling, collection, storage and the method of disposal viz., wet or dry disposal. Researchers [1], [2], [3] have highlighted the advantages and disadvantages of these disposal methods and have concluded that the ash properties (in particular, the chemical and mineralogical properties) change, to a great extent, when wet disposal of the ash is adopted. During wet disposal, and subsequently its impoundment in the lagoons, the ash interacts with water and alkalies present in it (Na2O and K2O) react with major constituents of the ash (SiO2 and Al2O3) to form different zeolites [4].

Some efforts have been made, in the recent past, to synthesise zeolites from the fly ash [5], [6], [7], [8], [9], [10], [11], [12], [13]. These zeolites have been used for preventing the degradation of the environment and for different industrial applications such as removal of heavy metals from the industrial sludge [14], [15], [16], flue gas and ammonia removal [17], [18], replacement of phosphate in detergent [19], removal of radioactive waste [20], [21] etc.

However, it has been noticed that the researchers have not attempted synthesis of zeolites, from the lagoon ash. In order to achieve the same, controlled thermo-chemical treatment has been given to the ash. This simulates prolonged interaction of ash with water. Effect of such interaction, along with formation of ash zeolites, on the lagoon ash has been investigated and the details are being presented herein.

Section snippets

Experimental

The lagoon ash from Koradi Thermal Power Plant (KTPP), Nagpur, India, is taken for the present study. Sampling of the ash has been done randomly from the slurry disposal site of the power plant, the lagoon. To minimize the effect of heterogeneity, samples have been collected in four batches during a span of seven days. Later, these batches were mixed together to form the representative sample of the ash. The ash sample has been characterised and its properties are mentioned below:

Results and discussion

Results of various tests conducted on the Original Lagoon Ash (OLA) and the Activated Lagoon Ash (ALA) samples are being presented in the following. ALA1, ALA2, ALA3 and ALA4 are the ash samples undergoing alkali activation for 12, 24, 36 and 48 h, respectively.

Conclusions

Based on the experimental investigations conducted in the present study, on the OLA and the alkali activated lagoon ash (ALA1–ALA4) samples, the following generalised conclusions can be drawn:

  • 1.

    Alkali activation causes a decrease in silica content of the lagoon ash. It has also been observed that alkali activation is responsible for etching (and hence dissolution) of the silica present in the ash. This process leads to creation of more fines (fraction) in the ash for its particle size ≤0.152 mm.

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