1.1 Introduction
Rice grows on every continent except Antarctica, covering about 1% of the earth’s surface. Rice husk is the residue generated on the processing of rice. In this process, called rice milling, the paddy or rough rice is treated to remove the husk and the bran layers, producing a white rice kernel free of impurities. On average, it is estimated that about 20% of the rice paddy is husk, the internal bran layer constitutes about 11% and the finished rice is therefore 69% of the initial product. Since rice is the most produced cereal all over the world, totalising about 720 million tons of paddy annually (equivalent to 482 million tons of milled rice) (FAO, 2011), the resulting husk constitutes a high volume waste material with costs for the companies.
As a prelude to other parts of this study, this chapter will discuss the background upon which this study was initiated, the statement of problems that led to this study, the Aim and Objectives of the study. Others are Significance of the study, Scope of work, Research hypothesis and questions, Limitations of the Study and Definition of technical terms.
1.2 Background of Study
Several components of the rice husk are interesting concerning its potential valorisation, namely energetic for the organics (about 75-80wt%, essentially cellulose, hemicellulose and lignin) and materials valorisation for minerals (about 15-20wt%, mainly silica). The rice husk has no commercial value due to its hardness, fibrousness and abrasive nature, being an underused biomass resource. However, it is normally used because of its high caloric content (about 16 720 kJ/kg), as an alternative source of heat to generate hot gases for the drying of the cereal itself. This corresponds to 50% of thermal capacity of a good quality bituminous coal and about 33% of thermal capacity of the oil (Anwar et al., 2000).
Besides thermal valorisation above referred, there are several options of materials valorisation to produce a silica-rich ash by calcination (rice husk ash, RHA) for use in construction materials, insulation or ceramics (Chandrasekhar et al., 2003). Other applications include catalyst support, fillers (e.g. in paper, paint, rubber, polymers) and other several types of additives, abrasives, insulators and pollutant absorbers/adsorbents. Silica ash, with amorphous nature, has high value as cement replacement or additive (Givi et al., 2010), in the zeolites production (Ali et al., 2011) and other ceramic applications (Chandrasekhar et al., 2006). Under appropriate conditions, an ash containing porous/activated carbon can also be produced (Malik et al., 2003).
Although various research studies concerning the production and application of RHA have already been made, there are still gaps regarding the optimization of treatment conditions and its relationship with the properties of the final RHA. In this sense, for producing high reactive and pure silica, some conditions are crucial in order to obtain an amorphous structure and the absence of unreacted carbon.
The silica in the ash undergoes structural transformations depending on the temperature regime it undergoes during combustion. The analyses showed that the highest amount of amorphous silica is present in RH char combusted at a range of 500–700°C, and at greater temperatures, crystalline silica is formed (Nair et al., 2008). However, under controlled burning conditions of RH, amorphous silica with high reactivity, ultra fine size and large surface area is produced. This micro silica can be a source for preparing advanced materials like SiC, Si3N4, elemental Si and Mg2Si. Due to the high pozzolanic activity, this RH silica also finds application in high strength concrete as a substitute for silica fume. The possibility of using this silica as filler in polymers has been mentioned by Chandrasekhar and co-workers (Chandrasekhar et al., 2003).
Therefore, in Nigeria where the research was carried out, the activities that was conducted is to know the Preparation of Amorphous White Silica from Waste Materials and Its Application in Environmental Remediation.
1.3 Statement of Problems
In the absence of a regular and efficient solid waste collection system, waste is dump in open spaces in access roads and along water courses, which constitute health hazards. In most parts of urban areas, there are no public facilities for disposing refuse within reasonable distance. Dumping sites or waste bins are non-existence and where dumps are sited overflows with refuse constituting health fire hazard.
Leaching has a variety of commercial applications, including separation of metal from ore using acid and sugar from beets using hot water. Chloride can also be leached from food. The main theory of leaching neglects mechanisms for holding the material on the solid. Although adsorption and ion exchange can bind materials tightly to solids, we will simplify the analysis and consider only dissolving a soluble constituent away from an insoluble solid such as removing salt from sand by extraction with water.
1.4 Aim and Objectives of Study
The aim of the study is to determine the Preparation of Amorphous White Silica from Waste Materials and Its Application in Environmental Remediation. In achieving this aim, the following specific objectives were laid out as follows:
- To assess the preparation process of Amorphous White Silica from Waste Materials
- To find out the application of Environmental Remediation in waste material
- To contribute a better knowledge about the appropriate conditions to achieve a good quality product.
1.5 Significance of Study
This study will be of immense benefit to researchers who intend to know more on this study and can also be used by non-researchers to build more on their research work. This study contributes to knowledge and could serve as a guide for other study.
1.6 Scope of Study
The study focuses on the Preparation of Amorphous White Silica from Waste Materials and Its Application in Environmental Remediation in Nigeria.
1.7 Limitations of the Study
During the course of this study, many things militated against its completion, some of which are:
- Time Constraint: The time frame given to accomplish this project was very short due to school academic calendar and it was carried out under pressure which made the researcher not to implement some necessary features.
- Research material: availability of research material is a major setback to the scope of the study.
- Frequent power failure: This made the researcher append more money on fuel to ensure sustainable power.
- Financial Constraint: Insufficient fund tends to impede the efficiency of the researcher in sourcing for the relevant materials, literature or information and in the process of data collection (internet).
1.8 Definition of Terms
Aquifers: These are underground layers of porous rocks or sand that allows the movement of water between layers of non-porous rocks (sand stone, gravel or fractured lime stone or granite).
Waste Prevention: It is the method of eliminating waste at source and reducing the demand on natural or origin resources.
Waste Re-Use: It is the method of using a waste product from one process as a raw material to form another.
Waste Recycles: This is the method of breaking down the waste items into raw material.
