COMPARATIVE STUDY OF LOPHIRA ALATA SAWDUST AND ACTIVATED CARBONIZED SAWDUST IN ADSORPTION OF HEAVY METAL CONTAMINATED WATER

COMPARATIVE STUDY OF LOPHIRA ALATA SAWDUST AND ACTIVATED CARBONIZED SAWDUST IN ADSORPTION OF HEAVY METAL CONTAMINATED WATER

ABSTRACT

The lophira alata wood sawdust that was obtained was washed with distilled water, dried, and divided into two portions. The first portion was used as the unmodified sawdust sample while the second portion was first carbonized at a temperature of 600C for 4 hours and later activated using 2M KOH for 24 hours at room temperature. The two samples were used as adsorbent to adsorb Nickel and Cadmium ions from aqueous solution. The effect of contact time, sawdust dosage, and the PH, of heavy metal ions removal has been studied. The physiochemical properties of the two adsorbents used have also been computed. The results obtained shows that an increase in sawdust dosage, contact time, and the PH, all resulted in an increase in the adsorption rate. The results obtained indicated that the activated-carbonized sawdust adsorbs more than the unmodified sawdust. The selectivity order of adsorption in terms of adsorption rate is: Activated-Carbonized sawdust > Unmodified sawdust. From these results, it is concluded that the lophira alatawood sawdust is a very good and effective low-cost adsorbent for the removal of heavy metal ions from contaminated water and the activated-carbonized form of this sawdust is most preferred for removing toxic contaminants from waste water.

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TABLE OF CONTENT

TITLE PAGE …………………………………………………….. i

CERTIFICATION ….……………………………………………. ii

DEDICATION ……………………………….………………….. iii 

ACKNOWLEDGEMENTS …………………………..…………. iv

ABSTRACT …………………………………………...………… v

TABLEOFCONTENTPAGE

CHAPTER ONE                                                    1

1.1. INTRODUCTION…………………………………………….1

1.1.2 SCOPE OF STUDY…………………………………………..2

1.1.3 OBJECTIVE OF STUDY…………………………………….2

1.2 LITERATURE REVIEW…………………………...…………..3

1.2.1 HEAVY METALS……………………………………………3

1.2.2 SOURCES OF HEAVY METALS..………………………….4

1.2.3EFFECTS OF HEAVY METALS………...…………...……..5

1.3 VARIOUS CONVENTIONAL METHODS FOR THE 

REMOVAL OF HEAVY METALS………..…………………9

1.3.1 CHEMICAL PRECIPITATION……………………………...9 

1.3.2 ELECTRODIALYSIS...………………………………………9 

1.3.3 COAGULATION/ FLOCCULATION…………………….....10

1.3.4 ULTRA-FILTRATION……………………………………….10

1.3.5 REVERSE OSMOSIS...………………………………………11

1.4ADSORPTION………………………………………………….12

1.4.1 PHYSIOSORPTION………………………………...….……..13

1.4.2 CHEMIOSORPTION…………………………………….……13

1.4.3 LOW-COST ADSORBENT……………………………….…..13

1.4.4 FACTORS AFFECTING ADSORPTION……………...…..…14

1.4.5 ADSORPTION EQUILIBRIUM……………………………...16

1.5 THEORETICAL MODELS……………………………………..16

CHAPTER TWO20

2.0 MATERIALS AND METHODOLOGY.......……………………20

2.1 APPARATUS…………………………………………………….20

2.2 REAGENTS…..………………………………………………….20

2.3 EQUIPMENTS…………………………………………………...21

2.4 METHODOLOGY……………………………………………….21

2.4.1 COLLECTION OF SAMPLES.………………………………..21

2.4.2 PREPARATION OF SAMPLES……………………………….22

2.4.3 PREPARATION OF CARBONIZED SAWDUST…………….22

2.4.4 ACTIVATION OF CARBONIZED SAWDUST………………22

2.5 CHARACTERIZATION OF THE UNMODIFIED SAWDUST

AND THE ACTIVATED-CARBONIZED SAWDUST...………………23

2.5.1 MOISTURE CONTENT...……………………………………..24

2.5.2 ASH CONTENT.………………………………………………24

2.5.3 BULK DENSITY..…………………………………………..…25

2.5.4 PH..……………………………………………………………..26

2.5.5 CONTACT TIME.……………………………………………..27

2.5.6 SAWDUST DOSAGE…………………………………………27

2.6 PREPARATION OF STOCK SOLUTION...……………………28

2.7ADSORPTION EXPERIMENT...……………………………….28

CHAPTER THREE29

3.1 RESULTS……………………………………………………….29

3.1.1 RESULTS OF THE PHYSIOCHEMICAL PROPERTIES OF 

         UNMODIFIFED SAWDUST...…….........................................29

3.1.2 RESULTS OF THE PHYSIOCHEMICAL PROPERTIES OF 

         ACTIVATED-CARBONIZED SAWDUST..............................29

3.1.3 RESULTS FOR THE ADSORPTION OF NICKEL…..………30

3.1.4 RESULTS FOR THE ADSORPTION OF CADMIUM..…...…37

3.2 DISCUSSION.……………………………………………………45

3.3 CONCLUSION..………………………………………………….47

REFERENCES..………………………………………………………48

APPENDIX..………………………………………………………….52

CHAPTER ONE

1.1 INTRODUCTION

The Lophira Alata sawdust which is also known as theAzobe wood sawdust, locally called Ekki or Red iron wood Sawdust, is specie of plant in the ochnaceae family. Its natural habitat is sub-tropical or tropical moist lowland forests. The timber is extremely hard and used for railroad ties and bridge planking. (Tih et al., 2006; Murakami et al., 1992) 

      The LophiraAlatawood has some unique sorptive properties which are very useful for adsorption. For example, the timber is strong and resistant thereby making it useful for demanding construction outdoors. (Tih et al., 2006) The timbers also have better electrical properties than other wood making it possible to use it in poles for electric fences without separate insulators. The color is reddish brown and the wood is abrasive, dulling tools rapidly.

      Because of its hardness and resistant properties, the Lophira Alatawood is well appreciated for heavy construction work for extreme conditions including hydraulic works, marine construction, bridges, decks, ship building, industrial floors, staircase, wooden frame houses, and railway sleepers.(Tih et al., 2006;Murakami et al., 1992)

                                                                   1           

       It also has a high energy value. It is a good fuel wood and yields excellent charcoal. The wood is very heavy with a density of 1010-1150 kg/m3 at 12% moisture content, and very hard. It also has excellent mechanical properties, being both flexible and resistant to bending and very resistant to shock and abrasion.

       I would like to state too that the Lophira Alata wood is very difficult to work with hand tools because of its hardness and high density. It is normally processed by sawing and is not suitable for peeling or slicing for veneer. But with appropriate heavy duty machine tool, it saws well. The blunting effect on saw teeth and cutting edges is relatively small as it does not contain silica.

1.1.2SCOPE OF STUDY

In view of the unique sorptive properties of the Lophira Alata wood, its sawdust form shall be used as a low-cost adsorbent for the removal of Heavy metals from solutions. Using this particular sawdust in adsorption of Heavy metals appreciates the enhanced effectiveness of a low-cost adsorbent in the removal of toxic metals.

1.1.3OBJECTIVE OF STUDY

The objective of this research study is as follows:

⦁ Use the Lophira Alata wood sawdust and the activated-carbonized form of this sawdust to adsorb Heavy metalsfrom contaminated water and compare which form of these sawdust adsorb more Heavymetalion from contaminated water.

⦁ Determination of the adsorption rate of the unmodified sawdust and the activated-carbonized sawdust.

⦁ Find out the optimum condition for removing Nickeland Cadmium from aqueous solution through adsorptionof sawdust.

1.2LITERATURE REVIEW

1.2.1HEAVY METALS

Heavy metals are elements having atomic weight between 63.5 and 200.6 and a specific gravity that is greater than 5.0(Suciu etal., 2008). They can also be chemical elements with a density that is greater than 4g/cm and is found in all kinds of soil, rocks, and water in fresh water and terrestrial ecosystem 

(Aelekan and Abegunde). Heavy metals can also refer to any element that has a relatively high density and is toxic or very poisonous even at a low concentration (Lanntech, 2010). Therefore, Heavy metals are at least five times the specific gravity of water. The specific gravity of water is 1 atm. Another school of thought puts Heavy metals as having a density of 60g or more (much more higher than the average particle density of soil which is 2.65) and they occur naturally in rocks, but concentrations are frequentlyelevated as a result of contamination (Asio, 2009). They can also be said to be intrinsic,natural constituents of our environment (Aderinola etal., 2009). Therefore, they can be said to be a group of metals and metalloids with atomic density greater than 4g/cm or five times greater than water (Obodai etal., 2011).

1.2.2SOURCES OF HEAVY METALS

       Heavy metals are the major pollutants in marine, ground, industrial, and even treated water. These heavy metals are often discharged by a number of industries, such as metal plating facilities, mining operations and tanneries, and this lead into contamination of fresh water and the marine environment(Low and Lee, 2000; Bailey etal., 1999).

       Heavy metals exist naturally in the soil from the soil forming processes of disintegration of parent resources at rare levels (<1000mg kg-1) and infrequently poisonous (Kabata-Pendias and Pendias, 2001; Pierzynski et al., 2000). Heavy metals comes from man-made sources trying to be more moveable in the soil, thereafter biologically available than soil forming phenomenon (Kuo et al., 1983; Kaasalainen and Yli-Halla, 2003). Metal-containing solids at polluted places can originate from an extensive variation of man-made sources in terms of metal mine stake outs, Lead (Pb) gasoline and paints that are Lead (Pb) based, application of fertilizers, discarding high metal wastes in inappropriately protected landfills, animal manures, bio solids (sewage sludge), coal combustion remainders, compost, petrochemicals, pesticides, and decomposition in atmosphere (Khan et al., 2008; Zhang et al., 2010; Basta et al.,2005).

1.2.3EFFECTS OF TOXIC HEAVY METALS

Heavy metals are not bio-degradable and can lead toaccumulation in living organisms thereby causing variousdiseases and disorders (Bailey etal., 1999). Some metals areseverely harmful to life. Examples of such metals are antimony,chromium, copper, lead, manganese, mercury, cadmium, nickel, e.t.c., and they are significantly toxic to human beings and ecological environments (Dorris etal.,2000). Most of the heavy metals that are discharged into the waste water are found to be toxic and carcinogenic and they cause a serious threat to the human health (Srivastava etal., 2006). The release of large quantities of these hazardous materials into the environment has resulted in a number of environmentalproblems and because these hazardous materials are not biodegradable and are persistent, they accumulate in theenvironment elements such as food chain, and this poses a significant danger to the human health. The table at the next page highlights the sources and toxic effect of some heavy metals. These metals have been extensively studied and their effects on human health are regularly reviewed by international bodiessuch as the WHO.

Table 1: Sources and toxicological effects of some heavy metals: (Alluriet al.,2007).

HEAVY METAL SOURCES EFFECT

Copper

Water pipes; Copper water heaters;

Frozen greens and canned greens

using copper to produce an ultra-green color; Alcoholic beverages

from copper brewery equipment;

Instant gas hot water heaters;

Hormone pills; Pesticides,

Insecticides, Fungicides; Copper

Jewelry; Copper cooking pots. Mental disorders; Anaemia;

Arthritis/rheumatoid arthritis;

Hypertension; Nausea/vomiting;

Hyperactivity; Schizophrenia;

Insomnia;Autism;Stuttering;

Postpartum Psychosis;

Inflammation and Enlargement of

Liver, Heart problem, Cystic Fibrosis.

Chromium Steel and Textile Industry Skin Rashes; Respiratory problems;

Haemolysis; Acute Renal failure;

Weakened Immune Systems;

Kidney and Liver damage;

Alteration of Genetic material; Lung Cancer; Pulmonary Fibrosis.

Nickel Effluents of Silver Refineries;

Electroplating; Zinc Base Casting

and Storage Battery Industries. Dermatitis;Myocarditis;

Encephalopathy; Pulmonary

Fibrosis;Cancer of Lungs, Nose and

Bone;Headache; Dizziness; Nausea

and Vomiting;Chest Pain; Rapid

Respiration.

Lead Industries such as Mining, Steel,

Automobile, Batteries and Paints;

Pollutants arising from increasing

Industrialization Nausea;Encephalopathy;

Headache and Vomiting;Learning

Difficulties;Mental Retardation;

Hyperactivity;Vertigo; Kidney

Damage;Birth defects; Muscle

Weakness;Anorexia; Cirrhosis of the Liver;Thyroid dysfunction;

Insomnia;Fatigue;Degeneration

of Motor Neurons; Schizophrenic-like

Behaviour.

Cadmium Phosphate Fertilizer; Sewage Sludge; Industrial uses like Batteries, Plating, Pigments and Plastics Chills, Fever, Muscle aches (Cadmium Blues); Trachea-bronchitis; Pneumonitis; Pulmonary Edema; Respiratory Tract and Kidney problems; Damage to Liver and Kidneys.

Mercury Industries like Chloro-alkali, Paints,

Pulp and Paper, Oil Refining, Rubber

processing and Fertilizer, Batteries,

Dental Fillings, Adhesives, Fabric

Softeners, Drugs, Thermometers,

Fluorescent Light Tubes and High

Intensity street Lamps, Pesticides,

Cosmetics and Pharmaceuticals Tremors; Birth defects; Kidney damage; Nausea; Loss of Hearing

or Vision; Gingivitis;

Chromosome damage; Mental Retardation; Tooth Loss; Seizures;

Cerebral Palsy; Blindness and

Deafness; Hypertonia; Muscle Rigidity; Minamata disease.

To avoid the aforementioned health hazards, it is therefore essential to remove these toxic heavy metals from waste water before they aredisposed. The various techniques used for removing heavy metals includes precipitation, ion-exchange, filtration, electro dialysis, adsorption, reverse osmosis (Rao etal., 2000).

However, most of these techniques do not give a satisfactory depollution, especially when you consider the operational costs (Marchetti etal., 2000). Precipitation methods, for example, are particularly reliable but they require large settling tanks for the precipitation of voluminous alkaline sludge and a subsequent treatment is needed. In addition, the effluents after such a treatment usually have an unacceptably high total dissolved solid and when applied to dilute metal waste or lower concentrations, these processes are either ineffective or not cost-effective and they require high level of expertise, hence, they are not used by many end-users. Ion-exchange has the advantage of allowing the recovery of metallic ions, but the problem with this method is that it is very expensive and sophisticated.

       For these reasons, Adsorption technology has gained a wider application due to its inherent low cost, simplicity, versatility, and robustness. Adsorption is operative in most natural, physical, biological, and chemical systems, and is widely used in industrial applications such as activated charcoal, synthetic resins, and water purification. Adsorption is also currently considered to be very suitable for waste water treatment because of its simplicity, and cost effectiveness 

(Yadanaparthi etal., 2009; Kwon etal., 2010). Adsorption is a commonly used technique for the removal of metallic ions from various industrial effluents (Gottipati, R. and Mishra, S., 2012)

1.1 VARIOUS CONVENTIONAL METHODS FOR THE REMOVAL OF

HEAVY METAL 

1.3.1CHEMICAL PRECIPITATION

Chemical precipitation processes involves the addition ofchemical reagents, followedby the separation of the precipitated solids from the cleaned water. Precipitation ofmetals is achieved by the addition of coagulants such as alum, lime, iron salts andother organic polymers. Gopalratnamet al. (1988) found 80% removal of Zn, Cu, andPb, and up to 96.2% removal of oil from industrial waste water by using a jointhydroxide precipitation and air floatation system.

1.3.2ELECTRODIALYSIS (ED)

Electro Dialysis (ED) is a membrane process whereby ions are transportedthrough semi-permeable membrane but under the influence of an electric potential. Themembranes are cat ion- or anion-selective, which basically means that either positiveions or negative ions will flow through. Cat ion-selective membranes arepolyelectrolytes with negatively charged matter, which rejects the negatively charged ionsand allows only the positively charged ions to flow through.

1.3.3COAGULATION/FLOCCULATION

      Coagulation and flocculation are an essential part ofdrinking water treatment as wellas wastewater treatment. Coagulation is the chemical reaction which occurs when achemical or coagulant is added to the water. The coagulant encourages the colloidalmaterial in the water to join together into small aggregates called “flocs”.  Suspendedmatter is then attracted to these flocs. Flocculation is a slow gentle mixing of the waterto encourage the flocs to form and grow to a size which will easily settle out. Randtkeet al.,(1997) reviews the basic mechanisms involved in the removal of organiccontaminants by coagulation. Kuoet al.,(2001) studied theeffects of initial pH andadsorption of Heavy metalsand reviewedturbidity, alum and pre-ozonation doses, and flocculation time on the removal of dissolved organic matter during alum coagulation.

1.3.4ULTRA-FILTRATION

Ultra-filtration is a separation process which involves using membranes with pore sizes in the range of0.1 to 0.001 microns. Typically, ultra-filtration will remove high molecular weightsubstances, colloidal materials, and organic and inorganic polymeric molecules. It is apressure-driven purification process in which water and low molecular weightsubstances permeate a membrane while particles, colloids, and macromolecules areretained. The primary removal mechanism is size exclusion, although the electricalcharge and surface chemistry of the particles or membrane may affect the purificationefficiency.

1.3.5REVERSE OSMOSIS

Reverse Osmosis is when a pressure is applied to the concentrated side ofthe membrane forcing purified water into the dilute side, the rejected impurities fromthe concentrated side being washed away in the reject water. Applications that havebeen reported for Reverse Osmosis processes include the treatment of organic containingwaste water, wastewater from electroplating and metal finishing, pulp and paper,mining and petrochemical, textile, and food processing industries, radioactivewastewater, municipal wastewater, and contaminated groundwater (Slater et al., 1983;Cartwright,1985; Ghabriset al, 1989; Williams et al., 1990).

1.4ADSORPTION

       Adsorption is a process whereby a gas or liquid solute accumulates on thesurface of a solid or a liquid (called the adsorbent). (Piero, 2005) It is the capability of all solidmolecules to attract to their surfaces, molecules of gases or solutions with which they are in contact with. Solids that are used to adsorb gases or dissolved substances are called adsorbents,whilethe adsorbed molecules are usually referred to collectively as the adsorbate.It should be noted that adsorption is quite different from absorption. Absorption is the process through which a substance, originally present in one phase is removed from that phase by dissolution in another (typically a liquid), as opposed to the accumulation at the interface as in the case of adsorption. (Piero, 2005)Adsorption can either be physical adsorption (physiosorption) or chemical adsorption(chemiosorption).

1.4.1PHYSIOSORPTION

This type of adsorption depends mainly on the physical or van der waals forces of attraction between the solid adsorbent and the adsorbate molecules. There is no chemical specificity in physical adsorption.

1.4.2CHEMIOSORPTION

       In this type of adsorption,gases are held to a solid surface by chemical forces that are specific for each surface and each gas. Chemical adsorption usually occurs at a higher temperature than those at which physical adsorption occurs, and like most chemical reactions, it usually involves energy of activation.

1.4.3LOW-COST ADSORBENT

       As earlier noted, adsorption technology has gained a widerapplication for the removal of Heavy metals due to its inherent low cost, simplicity, versatility, and robustness. Other conventional methods for heavy metals removal are either very costly or require high level of expertise. Low cost adsorbents used in adsorption are derived from agricultural by-products and industrial wastes and are exploited to remove recalcitrant wastes from synthetic wastewater. Conversion of these materials into adsorbents for wastewater treatment helps to reduce the cost of waste disposal. The adsorption of toxic wastes fromindustrial wastewater using agricultural waste and industrial by-products has beenmassively investigated (Basuet al., 2006; Srivastava et al., 2006). The technicalfeasibility of the various low-cost adsorbents for heavy metal removal from contaminatedwater has been reviewed (Babel et al.,2003).Instead of using very expensive materials as adsorbents for heavy metals removal, wood sawdust which is considered largely as wastes and is locally available, is an inexpensive material and an effective low cost adsorbent for the removal of heavy metals from waste water.

1.4.4FACTORS AFFECTING ADSORPTION

       The most important factors affecting adsorption are:

1. Surface Area of Adsorbent:The larger the size of the surface area of the adsorbent, the greater the adsorption capacity. (Piero, 2005) In this research work, the surface area of the sawdust will be increased by carbonizing the sawdust and then activating the carbonized sawdust. Activating the adsorbent will cause it to have a very high degree of micro porosity which is a useful property in adsorption.

2. The Particle Size of Adsorbent: Smaller particle size reduces internal diffusion and mass transfer limitation to the penetration of the adsorbate inside the adsorbent. In other words, equilibrium is more easily achieved and nearly full adsorption capability can be attained. However, waste water drops across columns packed with powdered materials are too high for use of this material in packed beds. Addition of powdered adsorbent must be followed by their removal. (Piero, 2005)

3. Contact Time: The longer the time, the more complete the adsorption will be. However the equipment will be larger. (Piero 2005)

4. PH: The degree of ionization of specie is affected by the pH (e.g. a weak acid or a weak base). This in turn affects adsorption. (Piero, 2005)

5. Degree of Ionization of the Adsorbate Molecule: More highly ion molecules are adsorbed to a smaller degree than neutral molecules. (Piero, 2005)

6. Solubility of the Solute (Adsorbate) in Liquids: Substances that are slightly soluble in water will be more easily removed from water that is, adsorbed than substanceswith high solubility. In addition, non-polar substances will be more easily removed than polar substances since the latter possesses a great affinity for water. (Piero, 2005)

7. Number of Carbon Atoms: For substances in the same homologous series, a larger number of carbon atoms are generally associated with a lower polarity and therefore a greater potential for being adsorbed (e.g. the degree of adsorption increases in the sequence: Formic – Acetic – Propionic – Butyric acid) (Piero, 2005)

8. Size of the Molecule with Respect to Sizes of the Pores:Large molecules may be too large to enter small pores and this may reduce adsorption independently of other causes. (Piero, 2005)

9. Affinity of the solute of the Adsorbent (Carbon): Thesurface of the activated carbon is only slightly polar. Hence, non-polar substances will be more easily picked up by the carbon than polar ones. (Piero, 2005)

1.4.5ADSORPTION EQUILIBRIUM

        Upon contacting an amount of the unmodified sawdust and the activated-carbonized sawdust with waste water containing an adsorbate substance, adsorption will take place. Adsorption will continue until equilibrium will be established between the substance in solution and the same substance in the adsorbed state. At equilibrium a relationship exist between the concentration of the species in solution and the concentration of the same species in the adsorbed state (that is, the amount of species adsorbed per unit mass of the adsorbent). (Piero, 2005)

1.5THEORETICAL MODELS

There are several models for predicting the equilibrium distribution.  However, the following four models are most commonly observed

i. Linear Isotherm

ii. Langmuir Isotherm

iii. Freundlich Isotherm

iv. Brunauer, Emmet, and Teller (BET) Isotherm

However, for the application of activated carbon in water and waste water treatment, the most commonly used isotherms are the Freundlich and Langmuir adsorption isotherm.

LANGMUIR ISOTHERM: Langmuir was the first to point out that in the chemical adsorption of a gas on a solid surface, a layer single molecule in thickness is formed (Sharma and Sharma, 2004). This theory assumes the process:

A + Surface Site ↔ A(adsorbed) 

We assume that only a single layer of molecules (a monolayer) can be adsorbed on the surface sites (Robert, 2008). The Langmuir Isotherm assumes

1. Monolayer coverage,

2. Equilibrium model,

3. All adsorption sites are equally probable,

4. A second order reaction

Image

Fig.1:Langmuir Adsorption Isotherm

FREUNDLICH ISOTHERM: To show the variation of the amount of gas adsorbed per unit mass of the adsorbent with pressure at constant temperature, Freundlich suggested an empirical equation (Sharma and Sharma, 2004). This equation is very widely used:

 qe =  KfCe1/n   

Where Kf = Freundlich Constant, indicating the adsorption capacity.

 n = A Constant characterizing the affinity of the metal ion towards

adsorbent.

q = Amount of heavy metal ions adsorbed per weight unit of heavy metal.

C = Heavy metal concentrations at equilibrium.

Image

Fig.2:Freundlich Adsorption Isotherm