Biosorptive Potential of Vigna radiata Biomass for Removal of Copper (II) and Cadmium (II) from Aqueous Medium

TABLE OF CONTENTS

LIST OF FIGURES

LIST OF TABLES

LIST OF ABBREVIATIONS

ABSTRACT

CHAPTER 1: INTRODUCTION
1.1 Water pollution
1.2 Heavy metal pollution
1.3 Toxicity of heavy metals in waste water
1.3.1 Nickel
1.3.2 Lead
1.3.3 Chromium
1.3.4 Mercury
1.3.5 Manganese
13.6 Zinc
13.7 Arsenic
1.4 Emission of heavy metals
1.5 Chemistry of heavy metal pollution
1.6 Methods for removal of heavy metals
1.6.1 Biosorption
1.6.2 Chemical Precipitation
1.6.3 Membrane Processing
1.6.4 Adsorption
1.7 Factors affecting rate of adsorption
1.7.1 Amount of Adsorbent
1.7.2 Effect of temperature
1.7.3 Effect of pH
1.7.4 Effect of Time
1.8 Adsorption isotherm models
1.8.1 Langmuir adsorption isotherm
1.8.2 Freundlich isotherm model
1.8.3 Tempkin Isotherm Model
1.8.4 Dubinin-Radushkevich Model
1.9 Kinetic modelling
1.9.1 Pseudo first order model
1.9.2 Pseudo second order model
1.9.3 Elovich model
1.9.4 Intra particle diffusion model
1.10 Thermodynamic parameters of adsorption
1.11 Removal of cadmium from aqueous medium (Adsorbate)
1.12 Removal of copper from aqueous medium (Adsorbate)
1.13 Vigna radiata as an adsorbent
1.13.1 Applications of Vigna radiata
RATIONALE
OBJECTIVES

CHAPTER 2: LITERATURE REVIEW

CHAPTER 3: EXPERIMENTAL
3.1 Analytical technique
3.1.1 Atomic absorption spectrophotometer
3.1.2 Instrumentation
3.1.3 Working
3.1.4 Types of atomic absorption spectrophotometer
3.1.4.1 Single beam atomic absorption spectrophotometer
3.1.4.2 Double beam atomic absorption spectrophotometer
3.2 Experimental work
3.2.1 Apparatus and chemicals
3.2.2 Apparatus used
3.2.3 Chemicals used
3.2.4 Instrument/ Equipment used
3.3 Methodology
3.3.1 Sample collection
3.3.2 Sample preparation
3.3.3 Preparation of solutions
3.3.3.1 Preparation of stock solution of copper
3.3.3.2 Preparation of stock solution of cadmium
3.3.3.3 Preparation of standard solutions of cadmium
3.3.3.4 Preparation of standard solutions of copper
3.3.4 Factors affecting the adsorption process
3.3.4.1 Amount of dosage
3.3.4.2 pH factor
3.3.4.3 Contact time
3.3.4.4 Temperature
3.3.5 Adsorption isotherm models
3.3.6 Vigna radiata regeneration

CHAPTER 4: RESULTS
4.1. FTIR analysis of adsorbent
4.2 Factors affecting the adsorption process of copper
4.2.1 Effect of adsorbent dose on adsorption of copper
4.2.2 Time factor
4.2.3 pH factor
4.2.4 Temperature factor
4.3 Adsorption isotherm
4.3.1 Langmuir isotherm model
4.3.2 Freundlich Isotherm
4.3.3 Tempkin isotherm model
4.3.4 Dubinin-Radushkevich Model
4.4 Kinetic study
4.4.1 Pseudo 1st order kinetics
4.4.2 Pseudo 2nd order kinetics
4.4.3 Elovich model
4.4.4 Intra particle diffusion model
4.5 Thermodynamic study
4.6 Factors affecting the adsorption process of cadmium
4.6.1 Dose factor
4.6.2 Time factor
4.6.3 pH Factor
4.6.4 Temperature Factor
4.7 Models
4.7.1 Langmuir isotherm model
4.7.2 Freundlich Isotherm
4.7.3 Tempkin Isotherm Model
4.7.4 Dubinin-Radushkevich Model
4.8 Kinetic study
4.8.1 Pseudo 1st order kinetics
4.8.2 Pseudo 2nd order kinetics
4.8.3 Elovich model
4.8.4 Intra particle diffusion model
4.9 Thermodynamic study
4.10 Desorption of Vigna radiata

CHAPTER 5: DISCUSSION

CONCLUSION

LIMITATIONS

RECOMMENDATIONS

REFERENCES

ACKNOWLEDGMENT

Whatever I am today is just because of ALLAH ALMIGHTY. One thought always motivated me to walk alone through a road full of hurdles and hardship is that He is always with me who can change these hardships into happiness whenever He wills and all the rewards are given by ALLAH. Special praises and regards for His last prophet HAZRAT MUHAMMAD (PBUH) who is forever a tower of knowledge and guidance for humanity.

I want to express my gratefulness to our respected principal Dr. Rukhsana David for providing me an opportunity to do research. I want to thank Dr. Shahnaz Choudhary, Dean of Natural, Formal and Applied sciences for providing me all the guidance to do my research work.

I am also obliged to Ms. Rahila Tariq, Head of Chemistry Department for her cooperation, guidance and support. I want to thank Ms. Almas, Head of Environmental Sciences for providing me research facilities and Sir Haseeb for his cooperation. I am very grateful to my supervisor Ms. Khalida Naseem for her guidance, care, unlimited time and for giving me the topic of my interest. I am very thankful to my other department teachers especially Ms. Anum Khaleeq for making me what I am today.

I am very thankful to my father Muhammad Shahbaz for believing in me and being a perfect role model for me. I am blessed to have a mother like Khalida Shahbaz for being my best friend and biggest support system. I am very thankful to my elder sister Kiran Shahbaz for being so supportive and caring. I am thankful to my elder brother Ali Shahbaz for always fulfilling my demands and standing by me through thick and thin. I would love to acknowledge the efforts of my friends Rida, Mahnoor, Ramsha, Sehrish and Memoona which they put in me to become a better person. Their pure love, support, genuine concern, sisterly behavior, care and guidance made this journey so joyous for me. I am very thankful to Lab attendants for helping me throughout my research work. At the end, I would like to thank myself for never giving up.

LIST OF FIGURES

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LIST OF TABLES

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LIST OF ABBREVIATIONS

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ABSTRACT

This study is based on investigation of biosorptive potential of Vigna radiata for removal of copper (II) and cadmium (II) from aqueous medium. Effect of different parameters like amount of dosage, agitation time, pH and temperature of the medium on adsorption process was studied. It was observed that Vigna radiata showed maximum adsorption potential for copper and cadmium at pH 5 and 7, respectively. Different models like Langmuir, Freundlich, Tempkin and DR were employed to analyze the insight of adsorption process of heavy metals. Maximum adsorption capacity for copper and cadmium were found to be 2.426 mg/g and 6.82 mg/g respectively. Biosorption process of Vigna radiata for removal of heavy metals followed pseudo 2nd order kinetics. Thermodynamic parameters of adsorption process indicated the feasibility and spontaneity of adsorption process. Desorption of Vigna radiata biomass was also done using HCl solution as eluting agent and adsorption potential of recycled adsorbent was also studied.

CHAPTER 1

INTRODUCTION

Heavy metals present in the surroundings are deleterious for living organisms especially humans. Many toxic pollutants are present in the environment but toxic heavy metals are non-biodegradable and they become intensive through food chain 1.

1.1 Water pollution

Water is polluted due to accumulation of heavy metals by different sources like industries, metal fishing and plating operations. It is used as the main cooling system for industrial purposes. Some of the sources of trace metal pollution in river and ocean include thermal power plants which accumulate toxic heavy metals like Hg and Se. Water is polluted due to wastewater effluents like arsenic, chromium, copper, manganese and nickel and is contaminated due to the presence of many pollutants like non-conservative materials, conservative pollutants and heavy metals [2, 3].

1.2 Heavy metal pollution

An undesirable alternation in the chemical, physical or biological attribution of air, land or water due to the presence of heavy metals which can have deleterious effects on living organisms is known as heavy metal pollution 4. All the circumstances which encircle a group of organisms for their survival, growth and development is known as environment and pollutant is any substance which is present in environment and become harmful for the environment and causes objectionable effects. A pollutant must be removed from an environment or it should be present in an optimal limit. Therefore, toxic heavy metals should be removed from water to make it pure 5. Water is contaminated because of toxic heavy metals in water. They accumulate in water due to different processes such as mining and agriculture etc. 6.

For the last three decades, the most important subject of interest among chemists and eco-toxicologist is the behaviour of heavy metals. Huge amount of data has been collected from water or soil samples which indicates the existence of high concentration of heavy metal in them 7. Any chemical element having specific gravity five times greater than specific gravity of water is referred to as heavy metal and it is malignant in higher concentrations 8. Heavy metals are often described as a group of metals and metalloids which are usually linked with toxicity and contamination. Heavy metals exist naturally in air environment and cannot be degraded or destroyed. They enter in human body through different mediums like water we drink and food we eat and they have tendency to accumulate in living material [9-11]. Heavy metals are deleterious for human body, aquatic animals and environment. Up to certain level they are important for human body as well 8. Most common heavy metal pollutants are lead, chromium, zinc, copper and nickel which are found in industrial effluents. These heavy metals are harmful even in minute concentrations 12.

1.3 Toxicity of heavy metals in wastewater

Heavy metals present in effluents are a serious problem because of its toxicity and ability to gradually gather in living tissues 13. Due to increase in industrial wastes and accumulation of heavy metals in sea water, life of sea creatures is at risk. Due to their toxic nature, heavy metals have always been a source of threat for living organisms. Many scientists focused on this topic to find out better way of their removal from aqueous medium 14. Metal toxicity depends upon different factors like their concentration, chemical reactivity, exposure to living organisms, age of the individual and way of exposure 15. Metal toxicity depends upon their chemical forms more than their total elemental content 16.Toxicity of some of the heavy metals are described as follows:

1.3.1 Nickel

Nickel is very toxic and it is widely present in the environment. In industries such as plating, alloys, stabilizers nickel is widely used 17. Nickel in less quantity is not dangerous for human body but in higher quantity it could be fatal for human health. Higher concentration of nickel is very toxic for human body because it can cause several diseases like skin rashes, headache, dizziness, and vomiting, nausea and lung diseases. It also causes coughing, skin rashes and shortness of breath. Nickel is usually present in the air because of burning of fuel oil, tobacco smoke and contaminated waste 8.

1.3.2 Lead

Lead present in even minute quantity is harmful for human body as it causes blood disorders and gastrogenital track disorders in human body especially in children because children can absorb 50% more lead as compared to adults. Lead also affects the nervous system 18. Lead is used in storage batteries and gasoline additives from where it enters in water 19.

1.3.3 Chromium

Chromium is present in different oxidation states. Among different oxidation states of chromium, Chromium (III) and chromium (IV) are important because they possess different characteristics and properties. Its deleterious effects depend upon its oxidation state. From the food, chromium is being ingested in the body. Major source of chromium is from leather tanning industries. Chromium causes diseases of gastrointestinal and respiratory diseases [20,21]. More toxic form is hexavalent chromium which is produced due to human activities. Chromium is harmful for plant growth as it stops plant root development. 22. The optimal limit of chromium in water is 0.05mg/L which is set by World Health Organization (WHO) 13.

1.3.4 Mercury

Even in low concentrations, mercury is harmful for microorganisms. Concentration of mercury up to 5µg/L in water is acceptable. Mercury affects the aquatic plants and even minute concentration is harmful for aquatic life 23.

1.3.5 Manganese

Up to certain limit, manganese is essential for human body and below this limit body can suffer from different diseases like nausea, weight loss and vomiting 24. Permissible contaminant level of manganese in water is 0.05 mg/L 25. It is found in groundwater because of disintegration of manganese bearing minerals. Manganese concentration in living organism is regulated by the mechanism of homeostasis which shows a high rate of presystemic elimination which is done by liver and also due to low absorption level of manganese 26. Red color of ground water is due to the presence of manganese. This color appears due to the precipitation of manganese and oxidation of ground water appears when ground water is exposed to air 27.

1.3.6 Zinc

Zinc in 0.4 mg/day is permissible for human body but in higher concentrations it becomes toxic. Zinc intake in higher amount can cause nausea, vomiting and several diseases 28. Zinc toxicity in water depends upon pH of the medium. Higher concentrations of zinc effect the life span of aquatic animals 29.

1.3.7 Arsenic

Arsenic in drinking water is acceptable within 10-50 mg/L and above this limit arsenic is very toxic and can be carcinogenic 3.

1.4 Emission of heavy metals

Heavy metal pollution is due to mining of metals, industrial waste, geochemical structure. Heavy metals can cause ecological damage under certain conditions 30. In developing countries, the waste matter containing toxic metals from coal mining, smelting of metals, dyeing, electroplating, paper mills, electro-osmosis, plastic industries, chemical industries, fertilizers, metallurgy, batteries, refining process enter into water streams or in the environment which brought up serious environmental pollution problems which results in threatening of living organism and when this water enters into human body, many diseases occur which can lead to death 31.

Due to natural and anthropogenic causes, heavy metals are emitted in the environment. By anthropogenic sources like mining operations, heavy metals are emitted in both compound and elemental form. Other sources of emission of mercury is through cosmetic products and during the manufacture of sodium hydroxide. Sources of lead is automobile exhausts, mining and smelting. From zinc refining, cadmium is released. Heavy metal pollution is very noticeable in areas of mining. These heavy metals drained out from where they are carried away by acid water and they run into sea 32. Toxic metals are accumulated in aquatic environment from plastic manufacturing, fertilizers and metallurgy processing. This waste water causes big threat for ecosystem and causes environmental pollution 33.

1.5 Chemistry of heavy metal pollution

Generation of acid mine drainage is due to mining activities and geochemical processes. Acid mine drainage (AMD) is usually a phenomenon which is linked with the mining activities and it is being produced when pyrite, sulphide mineral and water containing bacteria are exposed to air, and it oxidises and produces metal ions along with acidity and sulphate.

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Heavy metals when combine with organic matter in the presence of bacteria yields monomethyl mercury and dimethyl cadmium which are highly toxic compounds 5.

1.6 Methods for removal of heavy metals

Different methods have been adopted for removal of heavy metals such as reverse osmosis, precipitation, ultra-filtration, solvent extraction, electrochemical treatment, evaporation and adsorption 34.

1.6.1 Biosorption

Removal of metalloid species from aqueous solution by using biological material is called as biosorption. Biosorption process includes physical, chemical and biological interactions to remove heavy metals from wastewater. The process of biosorption depends upon functional groups which are present on the cell 35.

1.6.2 Chemical Precipitation

Chemical precipitation is the conventional process which is used to remove heavy metals from wastewater. From inorganic waste materials, heavy metals have been removed by using this method. This process can be described by using an equation

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M2+ shows the dissolved metal ions and hydroxyl ions(OH-) shows the precipitant. While M(OH)2 shows that metal hydroxide which is still insoluble 36.

Heavy metal removal by the using chemical precipitation method can be improved by adjusting pH of the aqueous medium. In many countries, most commonly used precipitants are lime and limestones. Lime precipitation method is cheap, easily handled and effective method. This method required large availability of chemicals to remove metals. Other disadvantages included sludge disposable and poor settlement 37.

1.6.3 Membrane Processing

Several industries produced wastewater which contain cadmium and copper. Their removal from wastewater can be done by reverse osmosis and nanofiltration. High removal of copper and cadmium can be obtained by reverse osmosis. In this process, ethylenediaminetetraacetic acid (EDTA) is used as a chelating agent for the removal of Zn2+ and Cu2+. In this process, alumina composite membrane is manufactured and used to remove copper ions. By using this process, wastewater containing copper ions can be reduced to concentration below 1 mg/L 38.

1.6.4 Adsorption

Adsorption is an effective and economical technique. It is a process by which substance is poured from liquid state to the surface of solid. Adsorption takes place with the help of chemical or physical interactions on surface by a mass transfer method 39.

1.7 Factors affecting rate of adsorption

Rate of adsorption is controlled by different factors which are described below.

1.7.1 Amount of adsorbent

Metal adsorption capacity increases with increase in adsorbent dose.

1.7.2 Effect of temperature

Process of adsorption can increase or decrease with increase in temperature and it depends upon the nature of metal and the adsorbent.

1.7.3 Effect of pH

pH is an important factor for adsorbent-adsorbate interactions. Metal adsorption capacity differ at different pH. Adsorption capacity of metals increases with increase in pH but up to certain optimum level and above that its value starts decreasing 40.

1.7.4 Effect of time

Efficiency of adsorbent to remove heavy metals depends upon the amount of metal adsorbed at a specific time or its efficiency depends upon the agitation time of adsorbate and adsorbent 18.

1.8 Adsorption isotherm models

Adsorption isotherms are used to explain how adsorption takes place. These models describe how the atoms and molecules of the adsorbents interact with those of the adsorbate and are important for defining the optimum conditions for adsorption 41. Adsorption isotherms helps to understand the adsorption process. Different isotherm models are used to describe the adsorption process like Langmuir, Dubinin-Radushkevich, Tempkin and Freundlich isotherm. These models have been study to check the equilibrium between adsorbent and adsorbate at constant temperature 42.

1.8.1 Langmuir adsorption isotherm

This model describes the formation of a single layer of metal onto the surface of adsorbent. This is the equilibrium process after that no further adsorption takes place. It can also be described as an equilibrium process which involves the distribution between liquid and solid phase of metal ions. This model is suitable for single layer adsorption and for those surfaces which contains many identical sites.

Linear form of Langmuir equation is written as,

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Where, Ce shows the equilibrium concentration of metal which is expressed in mg/L , qe shows the amount of adsorbate per gram of the adsorbent, qm is the maximum capacity of monolayer which is expressed in mg/g and KL shows the Langmuir isotherm constant which is expressed in L/mg 43.

1.8.2 Freundlich isotherm model

Freundlich adsorption isotherm is the oldest known adsorption model which is used to describe the reversible, multi-layered adsorption process Currently, this model is being applied to a wide range of systems especially to explain the adsorption of organic compounds on molecular sieves or activated carbon 44. This model commonly describes adsorption on heterogeneous surfaces. This model has also been used for adsorption onto single layer which contain many same sites. 43. Freundlich proposed an isothermal model for adsorption. The linear form of that model is as follows:

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KF indicates the adsorption capacity of an adsorbent while 1/n tells the strength of adsorption 45. If 1/n is less than 1 then adsorption is normal, if it is above 1 then cooperative adsorption occurs while 1/n = 1 shows that the adsorption process is independent of concentration of adsorbate 46.

1.8.3 Tempkin isotherm model

Tempkin and Pyzehev studied the effects of indirect interaction of adsorbent on adsorption isotherms and they found out that due to indirect interactions of adsorbent, heat of adsorption of all the layers would be affected in a way that it will decrease with coverage 47. The rate equation can be expressed as following:

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Graph is plotted between qe (mg/g) and ln Ce (mg/L) which shows the analysis of adsorption data and it determines the constant A. Constant b is associated with heat of adsorption 48.

1.8.4 Dubinin-Radushkevich model

This model has been used to describe biosorption process. This model does not require same surface for the adsorption process to occur. The linear D-R isotherm model can be represented as,

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In this equation,

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Where, Ce= equilibrium concentration of metal in solution (mol/L), qe= equilibrium concentration, R= gas constant (JK-1mol-1) [49,50].

1.9 Kinetic modelling

1.9.1 Pseudo first order model

Rate equation for pseudo first order is expressed as:

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Where, refers to equilibrium capacity of this biosorption process and refers to the capacity of biosorption at any time and k1 is the rate constant of the pseudo-first rate constant. This model is used to explore the sorption kinetics of the divalent metal ions which takes place by the adsorbent 8.

1.9.2 Pseudo second order model

Its rate equation is expressed as:

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The graph between t and 1/qe is linear which shows good bonding between experimental and calculated qe values 52.

1.9.3 Elovich model

The equation for Elovich model is given as:

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Where, α = initial adsorption rate and its units are mg g-1 min -1 and β = desorption constant (mg/g) 53.

1.9.4 Intra particle diffusion model

The equation for intra particle diffusion model is expressed as:

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Where Ki= Rate constant (mg/g) 54.

1.10 Thermodynamic parameters of adsorption

The equation for studying thermodynamics parameters is as follows:

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Where, ΔG˚= Free energy, ΔS˚= Entropy, ΔH˚= Enthalpy 42.

If the value of ΔG is negative, then it shows that reaction is spontaneous and adsorption is favourable. If the value of ΔS is positive, then it shows increase in randomness of the surface [55, 56].

1.11 Removal of cadmium from aqueous medium (adsorbate)

It is a naturally occurring element which occurs in the form of ores with other heavy metals like zinc and lead. In phosphate fertilizer, cadmium is present as a pollutant. Cadmium intake in body through air has increased since 20th century due to increased consumption of fossil fuels. Environment is being contaminated by dumping cadmium with household garbage which causes environmental pollution 32. In environment cadmium contamination is of serious problem because cadmium can cause bioaccumulation through food chain which become a threat for human being 57. During the last century, cadmium concentration has been increased in agricultural soil and in wheat. Every year at about 0.2% cadmium increases in soil. Cadmium exposure is through industrial emissions, sewage sludge and cigarette smoke 58. Cadmium is very toxic to aquatic life as well. Aquatic life is being affected by cadmium through the leaching of lead-zinc smelters in sea water 59.

Major sources of cadmium emissions are fuel combustion, non-ferrous metallurgy, from fertilizers, sewage sludge and cigarette smoke. One of the major sources of cadmium is cigarette smoke. It may cause notable increase of cadmium in blood which has adverse effects on human body. one of the most important source of cadmium is through food therefore, its concentration in human body varies from person to person 32. Cadmium compounds have many applications like they are used as stabilizers in PVC products. They are used in cadmium-nickel batteries and also for making several alloys 32. Cadmium causes kidney damage, kidney stones, cancer, skeletal damage, acute pulmonary effects. It also causes cardiovascular diseases. Cadmium may cause skeletal damage, prostate cancer and lung diseases. Even inhalation of fumes of cadmium can cause several diseases and can lead to death too if concentration becomes very high 32. Cadmium intake may cause cancer as it is considered as a carcinogenic metal 60.

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