REMOVAL OF CHROMIUM FROM SIMULATED AQUEOUS SOLUTION USING INTERCALATED AHOKO KAOLIN

ABSTRACT

This study investigates the removal of chromium from simulated aqueous solution of potassium chromate using intercalated Nigeria Ahoko kaolin.  One of the most important problems of contamination at present is the existence of heavy metals owed to their toxicity and cumulative properties. Adsorption process was used for the removal of chromium in this study. The adsorbent was initially refined to remove the quartz content. The adsorbent was intercalated with potassium dihydrogen phosphate for effective Chromium removal. Both batch and column studies were investigated. The conditions for the experiment were effect of pH of the adsorbate, concentration of the adsorbate, time and adsorbent dose for the batch adsorption studies and effect of flow rate for the column adsorption studies. The coefficient of determination for the Langmuir, Freundlich, Temkin and Dubinin-Radushkevich Isotherms were low, this might be as a result of the process condition e.g temperature that was not considered. However, Langmuir adsorption still gave the best fit. For the column study, the breakthrough occurred faster and the breakpoint time decreased at a higher flowrate. The result showed that Nigerian Ahoko Kaolin intercalated with potassium dihydrogen phosphate is effective adsorbent in chromium removal from aqueous solution. Generally, Nigeria Ahoko kaolin can be utilized as potential adsorbent.

CHAPTER ONE

1.0 INTRODUCTION

1.1 Background of the Study

One of the major problem of contamination at present is the existence of heavy metals owing to their toxicity and cumulative properties (Monika, Garg and Kadirvelu, 2009). Pollution of water with toxic substances is of major concern for human health as well as for the environmental quality. A large quantity of wastes containing chromium has been directly discharged into the environment in recent years (Bhattacharya and Gupta, 2008). Trivalent chromium (Cr) compounds are considered to be less toxic than the hexavalent compounds and are neither irritating nor corrosive under normal conditions as well. All forms of Cr are however, toxic when they exist at high levels. Through a large number of activities like tannery industry, metal finishing industry, inorganic chemicals production, steel industries, electroplating etc., chromium can be released into the environment. At high acidic medium (pH=1.0), Cr (VI) ions mostly exist as H2Cr2O4. There is equilibrium between Cr2O72- and HCrO4- species at a pH of 2-6. Cr can enter the air, water and soil mostly in form of Cr (III) and Cr (VI). Health effects may occur immediately or shortly after exposure to high levels of Cr particles, it also causes skin irritation and allergic reactions, kidney damage, liver damage after eating food or drinking water contaminated with hexavalent Cr (Abbas, Farooq, Ilyas, 2010).

A good number of technologies are available for removal of Cr from aqueous solution, namely reverse osmosis, chemical precipitation, ion exchange and solvent extraction among others. These methods are either uneconomical or inefficient, but adsorption has become a preferred method for removal of metals from aqueous solution due to its simplicity, easiness in handling, availability of various adsorbents and more efficiently in the removal of heavy metals at lower concentration (Abbas et al., 2010). Kaolin clay [a layered silicate mineral, Al2Si2O5(OH)4], is one of the adsorbents which is rarely used due to its low cation exchange capacity and its small surface, which is not more than 20 m2/g (Suraj, Iyer and Lalithambika, 1998). Kaolin exhibits low absorption and adsorption properties which are directly related to the low surface charge on the particle and must be modified to improve its adsorption property. Intercalation is a surface modification method in which there is insertion of a material between the layers of another material. In this case, a chemical will be inserted into the clay substrate.

Chemicals modification methods have been used to improve the adsorption capability of kaolin. Chemicals such as sulphate, phosphate, humic acid, hydrazine, formamide and dimethylsulphoxide can effectively improve the cation adsorption capacity of kaolin. Studies have described the adsorption of Cr (VI) from aqueous solution. Talokar (2011) studied the removal of Cr from waste water by adsorption using low cost agricultural biomass as adsorbent. Also, Guerra, Helen, Paulo, Rubia and Claudio (2010) have also studied adsorption of Cr (VI) ions on Brazillian smectite, but no work has been carried out on the intercalation of Ahoko kaolin for adsorption studies.

1.2 Statement of the Problem

Pollution of water with toxic substances poses major challenge to human health as well as for the environmental quality. Also different methods for the removal of Cr have been reported but these methods are either expensive or inefficient, hence, a low cost adsorbent material which can perform the same function should be investigated.

1.3 Aim and Objectives

The aim of this project is to remove Chromium from simulated aqueous solution using intercalated

Ahoko Kaolin. The followings  are the objectives of this project:

1.   To analyze the characteristics of intercalated and non-intercalated Ahoko kaolin.

2.   To determine the adsorption capacity of the intercalated Ahoko kaolin.

3.   To investigate and evaluate the influence of adsorption parameters on the adsorption proficiency of the intercalated and non-intercalated Ahoko Kaolin.

4.   To investigate and evaluate the adsorption performance of the intercalated Ahoko kaolin using batch and continuous adsorption processes.

1.4 Scope of the Study

The scope of this research work is set to remove chromium from simulated aqueous solution through Ahoko kaolin intercalation. Kaolin exhibits low absorption and adsorption properties, reason why it needs to be modified. This can effectively be improved by chemicals such as sulphate, phosphate, humic acid, dimethylsulphoxide and formamide.  This research work is limited to modification of Ahoko kaolin through a process called “Intercalation” (a term which indicates the insertion of a material between the layers of a clay substrate) by phosphate.

Also, few studies have been reported on the modification of kaolin but to our knowledge, no work has been carried out in the use of Ahoko kaolin. The work will be experimental; Scanning Electron Microscope (SEM) will be used for micro structural characteristics of the clay compounds, Fourier

Transform  Infra-Red  (FTIR) for determination  of the functional  groups  present  in  the clay compound, X-ray Diffraction (XRD) for structural characteristics of the samples and Atomic Absorption Spectrophotometer (AAS) for metal analysis.

Related Project Topics :