ABSTRACT

 

 

Clay which is one of the most abundant raw materials in nature is a very rich source of alumina and iron oxide. The direct application of this mineral in the dissolution process yields very poor result due to small surface area. This research was directed towards the modification of the clay mineral from Ozoro and investigating the thermodynamics and kinetic model of their dissolution. The clay relatively 33.90% alumina and 12.0% iron oxide. The raw and modified clay was characterized using the X-Ray florescence (XRF) for chemical composition, the Fourier Transform Infrared spectroscopy (FTIR) for the determination of effect of heat treatment and SEM for determination of surface area. In order to determine the best calcinations temperature and period in the thermal activation process, temperature range of 400 to 900oC and period of 30mins to 180mins were investigated. The calcined samples were ground to particle size of 0.045mm and leached with 3M H2SO4 for 90mins and the best calcinations conditions were found to be 700oC at 1hr since this gave the highest yield for the two metals. For the leaching kinetics of the clay using HCl, H2SO4 and HNO3, the clay was subjected to the best calcinations conditions. The resulting samples was ground to different particle sizes, and at different concentrations of the solvents, liquid to solid weight ratio, stirring speed and leaching temperature, the dissolution kinetics were investigated. The dissolution kinetic data were analyzed using the various forms of the shrinking core model. The values of K were calculated and the activation energy, the order of reaction and thermodynamic data were obtained. The Response Surface Methodology (RSM) based on the central composite rotatable design (CCRD) was used to optimize the leaching of both alumina and iron oxide from the clay.

 

The characterization showed that Ozoro clay is kaolinitic in nature. Analysis of the dissolution data showed that the process increased with increased calcinations temperature, leaching temperatures, stirring speed, liquid-solid ratio and solvent concentration but with decreased particle size. Results showed that alumina dissolution in HCl and HNO3 conform to the liquid film diffusion model, but in H2SO4, product layer diffusion model and the activation energies were respectively 35.32, 25.43 and 31.44KJ/Mol. Iron dissolution in HCl and HNO3 conform to the liquid film diffusion model, but in H2SO4, product layer diffusion model and the activation energies were respectively 34.003, 32.60 and 38.88KJ/Mol. Maximum yield of alumina of 90.48% was achieved in leaching with H2SO4 at calcinations temperature 582.33oC; leaching temperature 67.92oC; concentration 1.92mol/dm3; liquid-solid ratio 10.78cm3/g and stirring speed289.54rpm. Maximum iron yield of 84.91% was achieved in leaching with H2SO4 at calcinations temperature 662.72oC; leaching temperature 59.76oC; concentration 2.06mol/dm3; liquid-solid ratio 9.99cm3/g and stirring speed 373.60rpm. The results from this study showed that heat treatment of the Ozoro clay increased both alumina and iron yield. Hence, application of the simple and low cost modification techniques employed in this study has shown that Ozoro clay is a rich source of both alumina and iron.


 

 

 

 

 

 

 

 

 

 

 

 

 

 

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CHAPTER ONE

 

 

INTRODUCTION

 

 

 

 

 

 

1.0 Background of the study

 

 

There has been increased demand for aluminum and iron in recent times. Alumina is produced from bauxite as the raw material and iron from iron ore, but these materials are not found in sufficient quantities in Nigeria to meet up with the increasing demand. Also, due to the high volume of waste generated from bauxite in the production of alumina from bauxite, there is need to replace bauxite with alternative raw materials with less environmental hazards. To make provision for this increased demand of these metals, there must be a search for alternative local raw materials with sufficient quantity of these metals. Clay is one of the raw materials that have much of alumina and iron. Most clay contain about 25-40% alumina and up to about 30% iron (Ajemba and Onukwuli, 2012).

 

One of the numerous raw materials distributed on a large scale in the country is clay (Igbokwe and

 

Ogbuagu, 2003). Clays are essentially alumina silicates which have resulted from weathering of rocks

 

and aluminum silicates. Some of these clays have weathered under conditions which have concentrated the alumina. These are called high alumina clays. The critical characteristics of alumina silicates, including clays as far as treatment to obtain alumina is concerned is the inherent quality of alumina in its persistent affinity for silica. Because of its affinity for silica, it is difficult to separate alumina from silica and this presents the big problem in treatment of clays. Chemical processes to

 

 

 

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accomplish the separation are well known and have been carried out on a laboratory scale in many places.

 

Most researchers have used different sintering and acid-extraction processes for the leaching of alumina and iron from clays. For example, Hydrochloric acid has been used by most researchers and it has been found to have some advantages over other acids in terms of alumina production. It is reported in the literature that some of the most important advantages of using hydrochloric acid over other acids for leaching alumina are the ease of filtration of slurries, the ease of iron removal and the insolubility of titanium dioxide which is present in many clays (Al-zarhani and Abdul, 1996). The most serious problem connected with the use of hydrochloric acid is the severe corrosion, however, the development of corrosion-resistant plastics and rubber have partially solved this problem so that the corrosion is no longer a prohibitive factor (Peters et al., 1962). Both hydrochloric acid and tetraoxosulphate (vi) acid extract approximately the same quantity of alumina from each ton of clay (Schoenborn et al., 1979). It has been reported also that the silica residue is easily separated from the chloride solution which filters rapidly and a number of procedures have been proposed for eliminating iron from aluminum chloride solution (Park et al., 1992).

 

Different concentrations of sulfuric acid were reported for extraction of alumina and iron from calcined clays. It was reported that, in general, the extraction of alumina and iron from calcined clays increases with increasing duration of extraction at a fixed temperature and also increases by increasing temperature at a fixed duration of extraction (Abdul et al., 1956; Al-Zarhani and Abdul, 1996).

 

In the chemical processes of extracting alumina and iron from clay, it has been reported that calcinations temperature and the period of calcinations affect the yield of alumina and iron from the clay ( Al-zharani and Abdul, 1996). It is not the purpose of this research work to proceed to detailed


 

 

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economic analysis of the viability of clay processing for the extraction of alumina but it should be mentioned here that the raw clay heat treatment represents a significant proportion of the capital and operating cost (Bailey and Chapman, 1987). Most researchers have identified temperature and time or duration of calcinations as the conditions controlling the heat treatment of clay. Some have suggested

that a temperature of 600OC for 20minutes have produced the best leaching condition for some forms of clays. Other investigations report that the amount of alumina and iron extracted increase with

 

increasing the calcinations temperature from 500OC to 750OC but decreases at 850OC. At 900OC and

 

1000OC, the amount of extracted alumina and iron ore decreases sharply (Al-Zarhani and Abdul, 1996). Based on an analogy with cement clinker kilns, three kilns of 5.4m diameter per 175m long would be required for a calcinations process. The elimination of the clay heat treatment from the process could therefore significantly improve the economics of the process (Claude et al., 2005), but from investigations, calcinations temperatures appear to be the most important parameter affecting the

 

leaching process of alumina from clay. As earlier stated, below calcinations temperature of 450OC

 

represents a negligible extraction zone but an active zone exists between 500OC and 600OC and another

 

inert zone exists after about 650OC (Al-Zarhani and Abdul, 1996). Al-Zarhnai and Abdul (1996) reported that the alumina extraction yield increases from 17.02% to 62.94% over the range of 400-

 

600OC for a calcinations period of 60minutes. The decrease in the extraction beyond a calcinations

 

temperature of 600OC may be attributed to a total dehydration of clay samples at 600OC and to the solid

 

phase transformation of alumina beyond 600OC. for this reason, the extraction yields of alumina and iron begin to increase after some certain temperature after which the yields decrease (Ozdemir and Cetisli, 2005). The release of water modifies the crystalline structure of clay and probably creates cracks in the clay particles allowing the leach liquor to reach the alumina and iron embedded into


 

 

 

 

 

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particles. The heat treatment of clay remains however demanding process that if possible should be eliminated despite possible losses of alumina and iron recovery.

In order to maximize the extent of alumina and iron from the clay, the effects of process variables like the particle size of clay, concentration of the leaching acid or base, temperature of leaching, calcinations temperature, stirring speed and liquid-solid weight ratio have been investigated by researchers ( Plilips et al., 1982; Saddique and Kurny, 2009).

 

There is much deposit of clay in Nigeria and in view of its high alumina and iron contents; it is very attractive for producing the alumina and iron. However, despite the huge quantity of the clay in Ozoro, no work has been done on it. This research is therefore centered on evaluating the viability of Ozoro clay for alumina and iron production.


 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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1.1 Aims

 

The aim of the project is to characterize the local clay obtained from Ozoro to ascertain its viability in the leaching of alumina and iron oxide using tetraoxosulphate (vi) acid, hydrochloric acid and trioxonitrate (v) acid. To increase leaching result, the clay will be subjected to calcinations process and the calcined clay will be leached using the three acids to study the kinetics. The process will be optimized using one-factor-at-a-time and experimental design based on the central composite design to develop a statistical model equation of the process.

 

1.2 Objectives

 

To characterize the local clay obtained from Ozoro using the X-ray fluorescence (XRF), Fourier Transform Infrared (FTIR) spectroscopy and Scanning Electron Microscope (SEM) to ascertain its economic importance as a viable source of alumina and iron.

 

To ascertain how thermal treatment of the clay will improve performance.

 

To evaluate how process parameters affect yield of alumina and iron from the clay.

 

To obtain thermodynamic data (enthalpy, entropy, and Gibb’s free energy) that can be suitable for design of metallurgical plants.

 

 

 

 

1.3 Scope of the research

 

This research covers the following areas:

 

Characterization of the clay using the X-ray fluorescence (XRF), Fourier Transform Infrared (FTIR) spectroscopy and SEM.

 

Thermal activation of the clay.

 

Kinetics study of the process parameters that affect alumina and iron yield from the clay. Optimization of the leaching process.


 

 

 

 

 

 

 

 

 

 

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