Determination of Chromium in Chromite Rocks by Different Methods

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Determination of chromium in chromite rocks by different Methods

A thesis Submitted by Buthaina Abdullah Abdel Mageed In fulfillment of the award of the Degree of the Master of Science in Chemistry

Department of Chemistry

Faculty of Science

August Ϯ Ϭ Ϭ ϰ

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DEDICATION

To My Parents and Family.

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ACKNOWLEDGEMENT

I would like to express my sincere appreciation and gratitude to my supervisor Dr. Tag El Sir Abass Ahmed for his supervision, persistent, and help throughout this work. I am greatly indebted to Dr. Hassan Abdul Aziz A. Allah who started the supervision of this work before his immigration to Europe. I am greatly indebted to the Geological Resource Authority of the Sudan (G.R.A.S), for finance of the research. Lots of thanks to the staff of chemical laboratory of the Geological Resource Authority of the Sudan. Special thanks to Mouawia El Asum and Abdul Monem Basheer for their help. I would like to thank Dr. Elsheikh Mohamed Abdul Rahman for his support. My sincere thanks also are due to my friends in the chemistry department, (university of Khartoum) with special appreciation to Ustaza Iman Elidrisi Great appreciation to my husband Mr. Hussein Elgoni, my sons Loai and Allaa Eldeen for their support, encouragement, understanding and patience. Thanks are also extended to Mr. Sharaf Eldeen Hassan for his professional typewriting.

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Abstract

Samples of chromite rocks were collected from different parts of the Sudan, namely Hamassana, Onib Region North East of the Red Sea Area, Gebl Rahib, North West of the Sudan, Oshib North West the Red Sea mountains and Jam area Blue Nile Region. The samples were treated by fusion with sodium peroxide to bring about all raw chromium into chromium (VI). The chromium content was determined by different methods, namely the classical titration method where barium diphenyl sulphonate was used as indicator, the direct spectrophotometry using diphenyl carbazide as chelating complex, and the indirect spectrophotometry, by extraction with N-phenylbenzohydroxamic acid. Through comparison of the different methods it was found that all the results are close to each others; however, the results of the spectophotometric method (with some exceptions) are generally the best of them.

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Table of contents

Dedication………………………………………………………………….. i Acknowledgement…………………………………………………………. ii Contents…………………………………………….. ……………………..iii

Abstract in English …………………………… …………………………...iv

Abstract in arabic ………………………………………………..v

Chapter one

Introduction………………………………… ………………………………1

1.1.Chromium…………………………………… ………………………….1

1.1.1. History………………………………………………………………...1 1.1.2. Occurrence……………………………………………………………2 1.1.3. Distribution in the world……………………………………………...2 1.1.4. Distribution in the Sudan……………………………………………..2 1.1.5. Chemical and physical properties of chromium……………………...4 1.1.6. Oxidation .States……………………………………………………...5 1.1.7. Usage in life…………………………………………………………..5 1.1.8. Economical Importance………………………………………………7 1.1.9. Environmental Impact……………………………………………...... 8

1.1.10Effect innutrition……………………………………………………...8

1.1.11.Chromium Deficiency Effect………………………………………...9

1.1.12Metal Carcinogenesis and toxicology…………………………….....10

1.2. Analytical Separation………………………………………………..10 1.2.1. Solvent Extraction …………………………………………………..11

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1.2.2. Selectivity of solvent extraction…………………………………...... 13 1.2.3. Method of increasing selectivity of Solvent extraction……………..13 1.2.4. Advantages of Solvent Extraction ………………………………….15 1.2.5. Sensitivity of Spectrophotometric Methods…………………………15 1.3. Hydroxamic Acids ………………………………………………….17 1.3.1. Structure of Hydroxamic Acids……………………………………..17

1.3.2. Detection ofhydroxamic……………………………………………..19

1.3.3. Preparation of Hydroxamic Acids…………………………………...19

1.3.4. Properties of Hydroxamic Acids…………………………………….21

1.4. Biological Activity………………………………………………….....22

1.4.1.Analytical applications……………………………………………….24

Chapter two

2. Experimental………………………………………………………...25

2.1. Sample Collection………………………………………………….25

2.1.1. Instruments ……………………………………………………... 25

2.1.2. Chemicals ………………………………………………………..25

2.2. Preparation of N-phenylbenzohydroxamic acid…………………. .26

2.2.1. Preparation of b phenythydroxylmine ………………………….26

2.2.2. Coupling Reaction between b -phenyl hydroxylamine and Benzoyl Chloride…………………………………………………………………27

2.3. Analysis of chromium (VI) in chromite ore ……………………...28

2.3.1 Treamentof chromium reference material and samples…………..28

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2.3.2 Preparation of reagents…………………………………………...28

2.3.3. Volumetric determination of chromium (VI)…………………….29

2.4. Costruction of calibration curves…………………………………..29

2.4.1. Construction of calibration curve for chromium (VI) using diphenyl carbazide …………………………………………………….29

2.4.2. The effect of sulphuric acid on extraction of chromium (VI) with N-phenylbenzohydroxamic acid ……………………………………….30

2.4.3 The effect of sulphuric acid on extraction of chromium (VI) with N- phenylbenzohydroxamic acid…………………………………………..30

Chapter three

3. Results and Discussion ………………………………………………31

Chapter four

4. Reference……………………………………………………………54

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Chapter one

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INTRODUCTION 1.1. Chromium:

Chromium is a hard lustrous silvery-white metal, with atomic number of 24, atomic weight of 52.01 and electronic configuration of 3 d5 4s1. It is one of the most familiar transition metals. It is widely distributed in soil and vegetation although the concentration is very low. Chromium is also widely distributed in human tissues in extremely low and variable concentrations[1- 4].

1.1.1. History:

In 1766 Lehman [5] referred to a new red mineral from Siberia. Its bright red- orange colour made it very interesting to the chemists of the day. He determined this mineral to be lead salt.

In 1797, Vauquelin and Klaproth [1] both established that the mineral, later named crocosite, was lead salt of an acid derived from a new element that Vauquelin called chromium from the Greek word Chroma for colour since all the compounds of the new element appeared to be coloured [1].

Vauquelin isolated the crude metal by reducing chrome oxide by carbon. Commercially the insoluble chromate, which are of an analytical importance were made as pigments by Kurtiz 1816 [5]. The application of chromium coordinator appeared in 1820 [5].

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1.1.2. Occurrence:

Chromium occurs principally as mineral chromite, a spinel having the [5] idealized composition FeCr2O4 . It occurs naturally as chrome iron stone, [6] [7] (iron (II) chromate (III)FeO,Cr2O3 . It forms 0.02% of the earth crust . It is very widely diffused and it is almost wholly confined to the femic (ferromagnesium) rocks, especially those which are high in magnesia and low in silica [8]. It substitutes easily for magnesium in the silicates of very basic rocks [9].

Chromium does not occur free in nature. Traces of it may occur in minerals like emerald [10].

1.1.3. Distribution in the world:

The chief sources of supply of chromite, in order of production are Russia, Turkey, Nameebia, South Africa, Cuba, Yougoslavia, New Caledonia, India, Greece, Japan, and Republic of Philipines [11]. It was found that production of the world in 1998 exceeded ten million tons . Turkey, Russia, Republic of Philipines, and Nameebia Produced 78% of the estimated world output [12].

1.1.4. Distribution in the Sudan:

Chromium is an important metal found distributed in different areas in the [13] Sudan It was firstly reported in Sudan in 1930. Small scale mining of the ore has been started since 1950. One of the most Important areas are the Ingessena Hills area. The ore is generally massive, compact, and consists of chrome spinel, sometimes ferruginous with

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minor chromium chloride and chromium garnet. Chemically, the ore is of metallurgical grade is the one with a high Cr-Fe ratio. Low-grade banded

chromate ores are also common in this area, with up to 25% Cr2O3. New discoveries are being reported every now and then in the area [13]. In Gala Elnahal area, chromite has been reported from areas north east of the Blue Nile: Dinder, Rahad River and Um Saqata. The ores body varies in length, thickness, and unknown down dip extension. It is generally massive with

Cr2O3 concentration ranging between 25% to 37.8%. The eastern part of Nuba Mountains [14] in the central Sudan is covered by low-grade chromate,

where analysis indicated that the ore consists of 30% of Cr2O3, 22% Fe2O3. About 26 occurrences have been recorded [14]. At the red sea hills region of Eastren Sudan the most important occurrence is found in Wadi Hamissana

area. Assay result gave an average of 28% Cr2O3 with 2.5% Cr-Fe ratio. Jabel Rahib area is located in northern Darfur State where the ore is very

compact, massive and coarse grained. Average Cr2O3 content is about 55%. The ore reserve, though promising is not yet determined.

Chromate in southern Sudan has been reported from two different areas,

Juba area and Kapoeta-Nagishot region where Cr2O3 is 48-50%. Northern Sudan Chromium oxide samples from Wadi Akasha area reached up to 31% [13]. The overall production in Sudan was 10.000 tons in 1999 [13]. Chromium exploration in the Sudan, showed that the occurrences, discovered by Chinese program were developed by identifying the ore quality and quantity and evaluating economically the actual calculated reserve of these occurrences [14].

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1.1.5. Chemical and physical properties of chromium:

Chromium rock is massive, granular and compact having the colour of brownish black. Chromium itself is a silver- white metal. It has the second highest melting point of 1890c0, boiling point of 2300c0 and density of 7.19 g/cm3 [15]. It is hard, good thermal and electrical conductor. It occupies an intermediate position in the electrochemical series [7]. It does not corrode in air at normal temperature; it forms chromic oxide when heated strongly in air [7].

4Cr(s) + 3O2 (g) =2Cr2O3.

It does not react with water under normal conditions, but when heated to red hot with steam it gives chromic oxide and hydrogen

2Cr+3H2O=Cr2O3+3H2.

It dissolves in dilute mineral acids to give chromium salts and hydrogen as well.

+ 2+ Cr+2H = Cr + H2(g).

Concentrated hydrochloric or sulphuric acid reacts with chromium metal more vigorously than dilute acids. Dilute nitric acid does not react easily with metallic chromium. Hot concentrated sulphuric acid attacks the

metal to give chromic sulphate. Chromium combines with several other elements to give chromic salts such as its reaction with hot chlorine [15].

2Cr + 3Cl2(g) = 2CrCl3

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1.1.6. Oxidation States:

Chromium has a number of oxidation states. Chromium (VI) is an oxidizing reagent, chromium (III) is the most stable one, whereas chromium (II) is a powerful reducing reagent and has the least oxidation state [15]. Solutions containing chromium (II) ions are readily oxidized by air so it is only preserved in an inert atmosphere [15]. This is demonstrated by shaking an acidified solution of potassium dichromate with zinc amalgam. The colour changes from orange to green to blue, respectively. Chromium of zero [16] oxidation state occurs in Cr (CO) 6 and Cr (C6H6) .

Another oxidation state (IV) is known only in few compounds. Chromium

tetrafloride CrF4 is known but easily hydrolyzed by water. Oxidation state

(V) is not very widely known. Chromium pentafloride CrF5 is known but very easily hydrolyzed. It is made by passing fluorine over chromic oxide [16]. Chromium gives rise to three series of compounds; chromous, chromic, and chromate corresponding to valences of (II), (III) and (VI), respectively [16].

1.1.7. Usage in life:

Industrially most Chromium consumption is closely related to metallurgical industry where the ore is used by both refractory and chemical industry as well [12]. Distribution of chromite ore consumption in the U.S.A shows that 56% used in ferro-alloy manufacture, 33% in refractors, and 11% was used in chemical production. Most of the chromium refractors are used by the metallurgical industry for lining and patching furnaces. A fair percentage of

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the chemical is used for metal treating, plating and the manufacture of chromium metal [12].

A large portion of chromium produced is used in production of steel alloy which is a very hard and strong stainless steel. This alloy usually contains chromium and nickel and is used in cutlery because of its corrosion resistance [17]. Alloys that do not contain iron are used in various heating devices. Chromium is a protective decorative coating for other metals [9], such as plumbing fixtures. It is also widely used in plating because it is very resistant to atmospheric corrosion [17]. Chromium alloy used in jet aircraft, gives good resistance to high temperature, corrosion, and fatigue which is important in those passing the sound barrier [18]. Furthermore, it makes a high polish, which lasts because of the formation of an invisible self- protective oxide coat [19].

Chromium trioxide, “chromic anhydried”, is a very good oxidizing agent and is used extensively in preparing organic compounds [20]. Suspension of chromium oxide in sulphuric acid is frequently used as a cleaning solution for glass equipment in labrotaries. Cleaning action is due to the oxidation of grease [21]. Setllite, which is an alloy of chromium, cobalt,

molydbenum and tungsten,that find use in high speed tools and cutlery [1]. Chromium is employed as a refactory material for linning and repairing basic hearth furnace [1]. Chromous solutions are used in direct potentiometry of certain metals.

Nonferrous chromium alloys include nichrome (chromel) (nickel and chromium) are used in various heating devices because of their electrical

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resistance properties [17]. Chromium compounds such as potassium

dichromate (K2Cr2O7 )and potassium chromate (K2CrO4 ) are used as oxidising agents [21]. Potassium dichromate is largely used as oxidising agent in the manufacture of other chromium compounds. Chromium alum and lead chromate are used in dyeing industry and manufacture of inks. Dichromate solution in concentrated sulphuric acid are used in degreasing and cleaning laboratory glassware [9].

1.1.8. Economical Importance:

Minerals related to ultra - basic rocks such as platinum and magnesite are found in prospecting and exploration of chromate. In Gam mining area (Blue Nile area) analysis of samples has indicated the presence of

Platinum-group elements mainly rhodium, iridium, osmium, palladium, and platinum [13]. The components of platinum group elements increase with the increase of chromium oxide contents thus the platinum metal is usually associated with the mineral chromite[18].

The Geochemical behavior of the platinum group elements during partial melting and crystallization is used to define the conditions of formation of chromite and platinum elements concentrations [20].

Radiochemical modification of neutron activation analysis is used to study the platinum and gold distribution in different rocks and minerals. The concentration of palladium and platinum are comparatively high [22].

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1.1.9. Environmental Impact:

Chromium is widely distributed in soil, water and biological materials. In small amount it is an essential element, but more often its toxicity is of general concern in the environment [23].

It is one of the contaminants present in water system around mining areas and industries using metal [24]. Chromium (III) is essential to mammals, whereas chromium (VI) is toxic to human [25]. Chromium (VI) is toxic to animals although less so to plant [3]. Chromium (VI) and chromium (III) enters the environment as a result of effluent discharge, electroplating, tanning industries, and oxidative dyeing. The metal may also enter the drinking water in distribution system from corrosion inhibitors used in water pipes and containers. Hence this metal poses a serious threat to human health due to environmental pollution [25].

1.1.10. Effect in nutrition:

Chromium is an essential material found in concentrations of 20 ppb of blood. It has functions in both animal and human nutrition [26]. The World Health Organization European Standard quotes a limit for chromium (III) in potable water of 0.05 mg/1, and European Community Directive concerning the required of surface waters intended for abstraction of drinking water, quotes a total chromium limit of 0.05 mg/l [27].

Chromium is widely distributed in human tissue in extremely low and variable concentrations. (Total body contents < or = 6mg). Toxic level is considered to be 200mg/day. Chromium in plasma is bound to the

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transferring components of the ß-globulin fraction of the plasma proteins. Biological activity of chromium is dominated by the trivalent state Chromium (III). 5ppm is the recommended limit for irrigation water while 100 ppm is the recommended limit for fisheries [4]. Chromium stimulated the activity of enzymes involved in the metabolism of glucose for energy and the synthesis of fatty acids and cholesterol [26]. It also appears to increase the effectiveness of insulin, thereby facilitating the transport of glucose in the cell [26]. Chromium may be involved in the synthesis of protein through its binding action with RNA molecules. Sources of chromium include corn oil, clams, whole grain cereals, and meat [26]. Chromium is used not only in industrial processes, but in its trivalent state (III) is also an essential nutrient [28].

The mechanism of absorption of chromium from the intestine has not been clearly identified but it apparently involves processes other than simple diffusion. It has been found that chromium absorption is elevated by chemically induced diabeters and depressed by aging [26].

1.1.11. Chromium Deficiency Effect:

Chromium deficiency is characterized by disturbance in glucose, lipid and protein metabolism [26]. Even a very slight chromium deficiency will have serious effect on the body. This deficiency may be a factor that will upset the function of insulin and results in depressed growth rates and severe glucose intolerance in diabetics [26]. Chromium deficiency may be due to the fact that the soil does not contain an adequate supply and thus chromium cannot be absorbed by the crops or reach the water supply. The refining of natural

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carbohydrate is another possible cause of chromium loss [12]. Signs of chromium deficiency have been found in three women who were receiving long-term total parental nutrition with infusate low in chromium. It has been found that a patient receiving total parenteral nutrition for years exhibited impaired glucose tolerance and glucose utilization, weight loss, neuropathy, elevated plasma free fatty acids, and depressed respiratory quotient and abnormalities in nitrogen metabolism. All were alleviated by chromium supplementation [29].

1.1.12. Metal Carcinogenesis and toxicology:

Metals are important emerging class of carcinogen [30]. There are in fact,

Several metals that are known to be carcinogen including nickel, chromium, and arsenic [31]. The evidence of these metals is considered sufficient to classify these metals as human carcinogen [32]. A more than normal incidence of lung cancer has been noted among workers in plants where chromate has been produced for many years [5]. It has not yet been established what class of compounds may be responsible for close control of hygiene in modern plants is believed to have either eliminated this hazard or [5] reduced it to a point of minor concern .

1.2. Analytical Separation:

For a completely unknown sample to be analyzed, first requirement is to decide what impurities are present or what are absent. This is called qualitative analysis. Then the analyst can confirm how much of each component is present. The solution of such problem lies within the province

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of quantitative analysis [33]. Quantitative methods of chemical analysis are several; some are traditional such as, gravimetry, titrimetry and solvent extraction while others are advanced such as, atomic spectroscopy [34].

Separation techniques are several, and they are often used when element or a compound is not easily identified or quantitatively determined by simple measurement [34].

1.2.1. Solvent Extraction:

Solvent extraction is a traditional separation technique [36]. It is based on the distribution between two immiscible phases. One of these two phases (usually water) is brought into contact with a second solvent (usually organic) in order to bring about a transfer of one or more solutes into the second one [36]. This method is preferable because it is simple, clean, rapid, and convenient and can be applicable to trace levels or large amount of materials [37].

The extraction of a solute by this method is governed by Nernest’s distribution law which states that, at equilibrium, a given solute will always be distributed between two essentially immiscible liquids in the same proportions. This law can be expressed as [38]:

KD =[ Ao/ AW]

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Where KD is constant called the distribution or partition coefficient, and AO ,

AW are the concentrations of a solute A distributed between the two immiscible phases, the subscripts o and w stand for organic and aqueous phases, respectively.

In practical applications of solvent extraction the interest is in the fraction of the total solute in one or other phases, regardless of its mode of dissociation, association or interaction with other dissolved species, so it is convenient to introduce the term the distribution ratio D:

D = [CA] O / [CA]W

Where C represents the total concentration of the solute A in all of its forms. If D is large i.e. about 100 or, more single extraction may be enough for removing a solute quantitatively from the solution.

If Vw is the volume of an aqueous solution containing Wi gram of solute to be extracted (n) times with Vo volume of a given solvent, the weight of a solute Wr remaining in the aqueous phase is given by the expression:

Wr = Wi Vw n Vw +DVo

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The efficiency of an extraction depends on the magnitude of D and on the relative volumes of the liquid phases. The percentage extraction (% E) is given by:

% E = 100Wo /(Wo+Ww)

% E = 100CoVo /(Co Vo+CwVw)

Dividing by CwVo

%E = 100D/ [D+(Vw / Vo)]

When the two volumes are equal, the expression can be reduced to:

%E = D / (D+1)

1.2.2. Selectivity of solvent extraction:

The selectivity of colour reaction and corresponding spectrophotometric reactions depends on the method and nature of the reagents used [39]. To achieve adequate selectivity in analytical work it is necessary to make use of the differences in physical and chemical properties among reaction products. Most common properties are [34]: a- Differences in solubility. b- Production of characteristic colour. 1.2.3. Method of increasing selectivity of Solvent extraction: Various methods have been applied to increase selectivity of solvent extraction such as [40]:

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(i) Oxidation state: This involves modification of the interfering ions present in solution in order

to prevent the formation of their extractable metal complex.

(ii) pH:

Metal chelate extraction depends mainly upon proper pH control. Increase of

selectivity can be achieved in the extraction of acidic or basic organic

substances by addition of buffer solution [41].

The extraction behaviour of the substituted hydroxamic acid indicates

general increase of the amount of metal extracted with an increase of pH [42].

(iii)Masking

For efficient extraction of metal pairs that are difficult to separate, masking

agents such as cyanide, tartarate, citrate and ethylinediaminetetra acetic acid

(EDTA), are introduced to improve separation [40].

(iv) Back wash: This technique is used with batch extractions to affect quantitative separation of elements. It is similar in many aspects to the precipitation step in gravimetric procedure in which most of impurities can be removed without affecting the total amount of the component [43].

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1.2.4. Advantages of Solvent Extraction: Advantages of solvent extraction can be summarized as follows [44]: 1- ease and speed of accomplishment. 2- general applicability due to the great number of complexing agents, solvents and mixed solvents availability. 3- the ultimate overall selectivity which can be obtained. 4- reproducibility regardless of different solute proportions or presence of

impurities.

5- apparatus are simple and cheap.

1.2.5. Sensitivity of Spectrophotometric Methods:

Spectrophotometric determination of metals is one of the most important applications of solvent extraction. Many organic reagents form coloured chelates with metal which can be determined in the visible region. Most of these chelates are insoluble in water and soluble in organic solvents and can be extracted [45]. Such solutions show differential absorption of light of different wavelength [46].This is quantitatively expressed by the well known Beer-Labert’s law [ 47 ].

The numerical expression of the sensitivity of spectrophotometric method is the molar absorptivity (e) at the wavelength of maximum absorbance.

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A e= C L

Where:

A = absorbance.

C = concentration (mole/L).

L= the light path length. (cm) e = is expressed in cm-1. mol-1

It is suitable to express and compare sensitivities of pectrophotometric methods in terms of specific absorptivity (a) [44] ,which is obtained by dividing e by atomic weight of the element and 1000.

e a = atomicweight´1000

The sensitivity of spectrophotometric methods is often expressed by sensitivity index given by Sandell [44], which represents the number of micrograms determined per ml of a solution having an absorbance of 0.001 for a pathlength of 1cm. The sensitivity (S) according to Sandell is expressed 3 10-3 in mg/cm and therefore, is equal to a . The sensitivity of spectrophotometric measurement depends on the monochromaticity of the radiation. The molar absorbtivity is diminished as the bandwidth increases [48].

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1.3. Hydroxamic Acids:

Hydroxamic acids are important chelating agents having extra -ordinary complexing ability towards a very great number of metal ions [49]. They have been known for more than a century. They belong to a group of organic compounds, which are derived from hydroxylamine [50]. They are known compounds having the bidentate functional grouping. They form a family of chelating reagents, which are used as colourimetric and gravimetric reagents. Hydroxamic acids are weak organic acids used as commercial flotation reagents in extractive metallurgical, inhibitors for copper corrosion [51]. 1.3.1. Structure of Hydroxamic Acid:

Hydroxamic acids are known ato have the bidentate functional group [52].

O OH

C N

This functional group makes complexes with different metal ions and form a family of chelating agents. They have the general formula [53]:

O OH

R C N R

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Where R and R` could be hydrogen, alkyl or aryl group. Hydroxamic acids are found into two forms: Keto (1) and enol (II) form

H N OH N OH

R C O R C OH (I) (II) Keto enol

Unless the structure is hindered, most hydroxamic acids will be hydrogen bonded and exist in the keto form bonded to a transition metal through the oxygen atom. They have been classified into three groups [54-55]: 1- Primary hydroxamic acid with the general formula H N OH

R C O

2- Secondary hydroxmaic acid with general formula.

R N OH

R ` C O

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3- Cyclic hydroaxamic acid with the general formula.

N OH

C O

1.3.2. Detection of Hydroxamic Acids: A simple method for detection of small amount of hydroxamic acids was described by Agawal [52], who assumed that a chloroform soluble, violet coloured vanadium(V) complex is formed between hydroxamic acid and vanadium, allows the detection of small amounts as little as10-20µg of hydroxamic acid. Also one of the most characteristic reaction is between hydroxamic acid and Fe (III) ion which gives a red blood color in weak acid media [52]. Characteristic bands associated with hydroxamic acid functional grouping such as (O–H), (N-O) can be shown using infrared (IR) spectroscopy. Frequencies are generally assigned in the region of 3200, 1600, and 910cm-1, respectively [56].

1.3.3. Preparation of Hydroxamic Acids: Several methods of preparation of hydroxamic acids have been described by Yale [57]. They were first prepared from carboxylic acids using their methyl or ethyl esters or anhydride by reaction with hydroxylamine in alcohol or alkali [58].

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N-phenylbenzohydroxamic acid is prepared by acid chloride method in which hydroxylamine is acylated with an acid chloride or ester [59].

R N OH R N OH + R C O + HX R C O H X

Where: x = Cl, OCOR-OR

3. The reaction between primary amines and oxidizing agent: The product obtained depends on oxidizing agent and nature of alkyl group. [59]

( O2 ) 2 RCH2NH2 RCH2NH2 +RCOHNOH Dutta has synthesized qunalidine hydroxamic acid and nicotine hydroxamic acid using sodium ethoxide instead of sodium hydroxide[60]. Recently Tandon prepared many new N- substituted hydroxamic acids by acylation of N – arylhydroxylamine with the appropriate acid chloride at low temperature in ethereal solution containing a suspension of sodium bicarbonate [61].

RNHOH+RCOCl+ NaOH R-N-OH R-C= O + NaCl +H2O

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In Blatt method an alkyl or aryl ester (RCO2 R*) reacts with hydroxylamine in the presence of alkali [60-61]. The reaction is carried out in absolute alcohol and at room temprature.It is rapid particularly in presence of equimolar quantity of sodium alkoxide. In absence of the alkaline reagent longer time is needed. The free acid is obtained by the addition of acid (HX) in the appropriate quantity in cold solution [62].

RCO2ET +NH2OH+KOH RCONHOK+ETOH+H2O

RCONHOK+HX RCONHOH+KX

Brand and Wise used different technique, in which the pure acid was recovered by passing the methanol solution of potassium benzohydroxamate through hydrogen from cation exchanger (R-H) and removing the excess solvent under vacuum [58].

RCONHOK+ RH RCONHOH+RK

1.3.4. Properties of Hydroxamic Acids Generally they are white solids [63] except for the nitro-substituted and iodo- substituted derivatives, which are pale yellow, and pale pink, respectively [64- 65]. They are weak acids but stronger than phenol [52]. The acidity of hydroxamic acids is mainly due to the OH group which causes supression of intermolecular hydrogen bonding [66]. They are insoluble in water, sparingly soluble in carbon tetrachloride and in cold benzene but readily soluble in hot

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benzene, diethyl ether, dioxane, chloroform, and ethanol. They have low melting point. The reactions of hydroxmaic acids resemble those of acid amides in many aspects but they are more acidic than amides. However, the presence of a second oxygen atom in the O =C-N-O chain of hydroxamic acid alters both of substitutions compared to amides [63, 67]. All hydroxamic acids give characteristic blood red colouration in aqueous media according to the equation.[68]

3RCONHOH + FeCl3 = Fe (RCONHO) 3 + 3HCl Monohydroxamic acids reduce Fehling’s solution to give blue green in soluble copper salts when reacted with cupric acetate [69]. Benzohydroxamic acid on heating gives:

2C6H5 – CONHOH C6H5-NH2 + CO2 + C6H5- N = C = O + H2O

The resultant product C6H5-N=C=O is due to the migration of the phenyl group from the carbon atom to the nitrogen atom, that obeysLoosen rearrangement in which the group attached to carbon migrate to the nitrogen. [ 70] .

1.4. Biological Activity: The importance of Hydroxamic acids in biology and medicine is now well recognized, and much of their biological activity seems to be related to their ability to chelate iron Fe (III) in particular. The trihydroxamic desferroxamine is currently being used for the treatment of Fe (III) overload disease and aluminium intoxication. They are used therapeutically in

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hepatic comma [71], anti-fungal reagents, pharmaceutical food additives and nuclear fuel due to the possession of the bi-dentate functional group [72]. Their characteristic reactions are known in chemistry, biology and medicine. Recently great interest has been shown in compounds containing hydroxamic acid moieties. It is found that they are very active as antibiotic growth factor, antibiotic antagonists, tumours inhibitors cell division factors, antifungal agent and food additives [72, 73]. Hydroxyurea containing the functional group (-COHOH) of hydroxiamic acid [69], is a well known anticancer drug. It inhibits the DNA synthesis in Hela cells, while RNA or protein synthesis was not affected. Hydroxy urea and a few of other hydroxamic acids inhbit DNA synthesis by impairing the activity of enzyme ribonucleotide reductase, though it is clinically used as anticancer reagent [74]. Hydroxamic acids have not only been shown to be mutagenic and carcinogenic but they have also been useful in the treatment of certain cancers [75]. The influence of 5-bromosalicylohydroxamic acid on serum cholesterol- level studies showed that the level of cholesterol was reduced in average by 20%. They are also used as antitubercular agents such as salicylic derivatives [ 76]. A series of tetra phthalohydroxamic acids and other dicarbohydroxamic acids have been investigated as potential antimalarials [77].

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1.4.1. Analytical applications: Hydroxamic acids have received considerable attention as analytial reagents [78]. They have great value in solvent extraction and spectrphotometric determination of metals [79]. These reagents are also useful in analysis of trace elements by flow injection [80] and high performance liquid chromotography (H.P.L.C) [81]. Hydroxamic acids show good complexing behavior with abroad range of metal ion [82]. Complexation of metal ions by hydroxamic acid is a basis of a number analytical determinations [68 ,83].The best known of these complexes is that formed with Fe (III) whose purple colour forms the basis for sensitive qualitative and quantitative determination of carboxylic acid,amino acid and their derivatives [82,86 ] The complex formation of hydroxamaic acids with metal ions usually takes place with the replacement of the hydroxlamine hydrogen by the metal ion and the ring closure takes place by participation of the carbonyl oxygen [ 86] . The hydroxamic acids have important analytical applications. due to their ability to form very stable metal complexes such as vanadium and molybdenum complexes. These complexes are highly coloured and so can be colourimetrically determined.[87] Chelating ion exchange resins such as polyhydroxamic acids are used for separation of metal ions [88]. Because of their high selective adsorpation capacity for metal ions. Hydroxamic acids are known for their chelation ability with heavy metals [89]. The extractability of hydroxamic acid chelate depends upon the nature of the reagent.Hydroxamic acids with aromatic substituents are commonly soluble in organic solvents while those of with aliphatic substituent are commonly soluble in aqueous phase. [ 79 ] .

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N-benzylbenzohydroxamic acid has been reported to be a highly selective reagent for determination of vanadium (V) in biological material such as, blood tissue and urine [90]. Hydroxamic acids are widely used for organic and inorganic analysis including pharmaceutical and food additives, such as the spectrophotometric determination of molybdenum (VI) in vegetal tissues, soft and pharmaceutical compounds [45].

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Chapter two

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2. Experimental: 2.1. Sample Collection: The samples of chromite rocks anaysed in in this study were collected from different locations in the Sudan. Hamassana at Red Sea Reagion North West of the Red Sea Hills, Gebell Rahib North West Darfor, at the north west of the Sudan some are from Osheip Area East of the Sudan, and Jam at eastren part of the Blue Nile state. The samples collected in a fresh clean polyethylene bags with labels showing the locality of the samples.

2.1.1. Instruments: 1- UV/VIS Spectrophotometer Milton Roy spectronic 1001+. 2- I.R Spectrophotometer Perkin Elmer model 1330. 3- Metter Melting point apparatus.

2.1.2. Chemicals: All reagents used are of analytical grade unless otherwise stated. The water used is distilled. Nitrobenzene, ammonium chloride, zinc powder, sodium hydrogen carbonate, sodium chloride, benzene, diethyl ether, sodium peroxide, ammonium ferrous sulfate, potassium dichromate, barium diphenylaminosulphonate, and phosphoric acid were purchased from BDH, UK. Standard reference materials (CRM.) were purchased from South Africa prepared by Council for Mineral Technology

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2.2. Preparation of N-phenylbenzohydroxamic acid: 2.2.1. Preparation of b- phenylhydroxylamine:

0.45 moles of nitrobenzene were mixed with 0.47 moles of ammonium chloride in 800 cm3 of water. The mixture was placed in a two-litre beaker with a thermometer and mechanical stirrer. The mixture was heated to about 55oC with vigorous stirring. Then 60.0 gm of zinc dust was added during a period of 15 minutes. The temperature was kept between 60o-65oC until all of the zinc dust has been added. Stirring was continued till temperature began to decrease. The warm mixture was filtered under suction to remove the zinc oxide and washed with 100 ml of hot water. The filtrate was placed in a conical flask, 300 g of sodium chloride was added (till saturation) with vigorous stirring, then cooled in an ice-bath for at least one hour and half. The mixture was filtered and the needle-shaped pale yellow crystals obtained were recrystallized from benzene [56]. (Yield 23.0 gm.86%)

E K Ϯ E , K ,

ϲ Ϭ -ϲ ϱ

н Ϯ Ŷ н , Ϯ K н Ϯ Ŷ K

NHϰ Cl

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2.2.2.-Coupling Reaction between b -phenyl hydroxylamine and Benzoyl chloride: 27.0g of freshly prepared b-phenylhydroxlamine were dissolved in 200 cm3 of diethyl ether and placed in a 600-cm3 beaker. 0.45 mole of sodium hydrogen carbonate was dissolved in 50.0cm3 distilled water and added to the mixture in the beaker. The mixture was cooled to 0Co or below using ice- bath. 0.25 mole benzoyl chloride were dissolved in 15 cm3 diethyl ether, placed in a separatory funnel and added drop-wise to the cooled reaction mixture during a period of one hour. After the addition of benzoyl chloride has finished, the stirring was continued for further 30 minutes. The white precipitate was filtered under suction. The ethereal layer of the filtrate was separated and distilled under reduced pressure. The residue was added to the product. The product was mainly N-phenylbenzohydroxamic acid contaminated with di-substituted derivatives. The Nphenylbenzhydroxamic acid was extracted from the crude with concentrated ammonia using mortar and pestle. The ammonia extract was diluted with water, cooled and acidified until just acidic with 20% sulphuric acid. The hydroxamic acid produced was filtered off recrystallized from water (m.p 1180C yield26 %). H O

NHOH COCL N C

+ OC ether +HCl

NaHCOϯ /HϮ O

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2.3. Analysis of chromium in chromite ore: 2.3.1.Treatment of chromium reference material and samples 0.50gm of the very powdered ore was weighted into 30-35 cm3 zerconium crucible, 4.0 gm of soduim peroxide was mixed thoroughly by means of a thin glass rod. The adhering powder was removed by stirring 1.0gm of sodium peroxide with it. The curcible was covered in fume cupboard until the mass was quite liquid. The sample was kept fused for further ten minutes at a dull red heat and then allowed to cool. When crust had formed 4.0g of sodium peroxide was added and then fused again for ten minutes. The crucible was allowed to cool and placed in a 600 cm3 beaker containing little amount of water. The beaker was covered with a clock glass and a little warm water was added. After the violent reaction had subsided, the crucible was removed after being washed throughly. The mixture was boiled for 30.0 minutes to decompose sodium peroxide keeping the beaker covered, 250.0 ml of boiling water was added and allowed to settle. The resultant solution was filtered off through handeren filter paper or sintered glass filtering crucible, washed thoroughly with boiling water until free of chromium. The filtrate was evaporated to about 200.0cm3, cooled, transferred to 250.0 ml volumetric flask and completed to the mark.

2.3.2. Preparation of Reagents: 0.1gm of Barium diphenylsulphonate was dissolved in 50.0 ml of water, transfered to 500 ml volumetric flask. 450.0 ml of 50% phosphoric acid was then added and the volume was completed to the mark.

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2.83g of potassium dichromate was taken from a dried sample, dissolved in small amount of water and transferred to 1000 cm3 volumetric flask and then completed to the mark to give 1000 ppm. Working solutions were prepared serially by dilution from the stock solution. 39.25gm of Mohr salt (ammonium ferrous sulphate) was dissolved in a small amount of water transferred to one litre volumetric flask. 87.25ml of 50%

H2SO4 was added and completed to the mark.. 4.903gm of dried potassium dichromate were dissolved in water, transferred to one litre volumetric flask and completed to the mark to give 0.1N solution of potassium dichromate. 2.3.3. Volumetric determination of Chromium (VI): The Mohr slat (ammonium ferrous sulphate) was standardized against potassium dichromate. 25.0 ml of the sample solution was pipetted into 600.0ml beaker. Then 25.0 ml of 0.1N ammonium ferrous sulphate were added followed by 10.0 ml of barium diphenylsulphonate indicator. The colour changed to pale green. The mixture was then titrated against 0.1N standard solution of the potassium dichromate. At the end point the colour changed to violet red.The standardization factor was used in calculations.The percentage of chromium (VI) oxide was calculated and the results are shown in table (4) and figure (4). 2.4. Construction of calibration curves: 2.4.1. Construction of calibration curve for chromium (VI) using diphenyl carbazide. A calibration curve was constructed by transfering 1,2,3,4,5, cm3 of 10 ppm chromium stock solution into 50.0 ml volumetric fask. . 5.0ml of 1M

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sulphuric acid were added to each flask, and 1 cm3 of 1% of diphenylcarbazide was introduced. The solutions were completed to the mark with water to give 0.2, 0.4, 0.6, 0.8 and 1.0 ppm of chromium standard solutions respectively, and left for about 5 minutes to complete colour development. The absorbance was measured at 540nm. The results are shown in Table (1) and Fig (1 ). 2.4.2:The effect of sulphuric acid concentration on the extraction of chromium (VI) with N-phenylbenzohydroxamic acid. 5.0 ml of 10.0 ppm Chromuim (VI) standard solution was pipetted into 100. volumetric flask, 5.0 of 1M sulphuric acid was added, and completed to the mark with water to give 5.0 ppm standard solution of chromium. 5.0 ml of the above standard solution was transferred to a set of four 125.0 ml separatory funneles. 5.0ml each of 1M, 2M, 3M and 4M sulphuric acid was added and 10.0 ml of 0.5% hydroxamic acid was introduced, respectively.The solution mixture was shaked gently for two minutes and left to stand to allow the two layers to separate. The organic layer was separated and the absorbance was measured at 540nm. The results are shown in Table (3) and Fig ( 3). 2.4.3:Construction of calibration curve of chromium (VI) extractedwith N-phenylbenzohydromic acid in 3M sulphuric acid. 5.0ml of 1.0, 2.0, 3.0, 4.0 and 5.0 ppm standard solutions were transfered into a set of 125.0ml separatory funnels 5.0ml of 3M sulphuric acid were added, then 10.0ml of 0.5 %N-phenylbenzohydroxamic acid were introduced. The mixture was shaked gentlely for two minutes. The organic

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layer was separated and the absorbance was read at 540nm.The results were shown in Table (2) and Figure (2) The samples were treated the same way using the three methods. The chromium (VI) oxide percentage was calculated and the results were shown in tables (4), (5), (6) and figure (4), (5), (6) respectively.

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Chapter three

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Discussion & Conclusion

The techniques used in this work are volumetric analysis, direct colourimetric analysis using diphenylcarbazide and indirect one using solvent extraction.

All methods are subjected to systematic and random errors. Both can be corrected by using certified reference materials (CRM) purchased from South Africa prepared by Council for Mineral Technology. The highly refractory mineral chromite was brought about into solution by dry ashing and this was carried out by fusing with sodium peroxide at high temperature on flame burner, followed by wet digestion. The stock solution obtained was used for all methods. The certified reference materials (CRM) received the same pretreatment as the rock sample. When these certified reference materials were studied for chromium, the results obtained were almost identical with certified values, and this was taken as a sign of the accuracy of the three methods used in this study. In volumetric analysis the amount of chromium measured by converting chromium into dichromate, reduced by ammonium ferrous sulphate.

The results were convenient compared to the result of the standard samples. The spectophotometric method showed best results by using chelating agent diphenylcarbzide at wavelength 540 nm which is one of the best methods to determine chromium [45].The results compared to volumetric method is much better with some exceptions.

Hydroxamic acid prepared was verified by the characteristic colour test with acidic solution of vanadium (V) in chloroform and iron (III) in aqueous

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solution to give violet and red blood colours respectively[87]. The extraction of chromium was obtained at 1, 2, 3 and 4 molar solutions of sulphuric acid. The maximum extraction was obtained at the 3M sulphuric acid.This is because of high selectivity of the acid. [90]

The best results of those methods were obtained using diphenylcarbazide This was expected as spectophotometric technique are more accurate than volumetric methods as the literature show[91] ,while the extraction method is prone to error because of it is more laborious and the study of organic layer increases the source of error due to the volatility I the solvent.

Samples of chromite rock were collected from deferent parts of the Sudan namely Hamassana ,Onib Region North East of the Sudan.Oshib North West of the Red Sea mountains and Jam area Blue Nile Region .In all of these chromite rocks are found in considerable amount. In this study Hamassana area showed the least amount of chromium contents, whereas the other areas are relatively have amount of chromium contents similar to each other, with some exceptions. The chemical analysis done in this study and results obtained showed considerable between this study and work done in The Geological Research Authority of the Sudan [93]

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Table (1): Concentration of standard solutions of Chromium (VI) by diphenyl carbazide

Concentration in (ppm) Absorbance

0.00 0.000

0.20 0.133

0.40 0.262

0.60 0.389

0.80 0.514

1.00 0.634

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Table (2): Concentration of standard Chromium solution extracted with N-henylbenzohydroxamic acid indiferent molarities.

Morality Absorbance

1M 0.029

2M 0.036

3M 0.064

4M 0.043

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Table ( 3 ): Standard solutions of Chromium (VI) extracted with hydroxamic acid in 3 M H2SO4.

Concentration Absorbanc

1.0 0.041

2.0 0.064

3.0 0.086

4.0 0.104

5.0 0.126

6.0 0.144

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Table (4): Percentage of Chromium (VI) by Volumetric Analysis.

Sample Concentration 1 48.65

2 46.62

3 50.68

4 54.73

5 56.76

6 58.78

7 48.65

8 44.59

9 42.57

10 40.54

11 54.73

12 50.68

13 52.71

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Table (5 ):

Percentage of Chromium (VI) by colourimetric method

Sample Concentration ϭ ϰ ϵ ͘ ϲ ϵ Ϯ ϰ ϲ ͘ ϳ ϲ ϯ ϱ Ϭ ͘ ϴ ϲ ϰ ϱ ϰ ͘ ϵ ϱ ϱ ϱ ϱ ͘ ϱ ϰ ϲ ϱ ϲ ͘ ϭ Ϯ ϳ ϰ ϴ ͘ ϱ Ϯ ϴ ϰ ϱ ͘ Ϭ Ϯ ϵ ϰ Ϯ ͘ Ϭ ϵ ϭ Ϭ ϰ Ϭ ͘ ϵ Ϯ ϭ ϭ ϱ ϰ ͘ ϯ ϳ ϭ Ϯ ϱ Ϭ ͘ ϴ ϲ ϭ ϯ ϱ Ϯ ͘ Ϭ ϯ

ϯ ϳ

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Table ( 6 ):

Percentage of Chromium (VI) by N-phenylbenzohydroxamic acid

Sample Concentration

1 447.1 2 45.30 3 48.68 4 53.46 5 55.90 6 56.60 7 45.30 8 42.71 9 40.20 10 39.50 11 52.00 12 48.20 13 50.70

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Figure (1)

Construction of Calibration curve for Chromium (VI) using diphenyl carbazide

Ϭ .ϳ

Ϭ .ϲ

Ϭ .ϱ e c n a

b Ϭ .ϰ r o s b Ϭ .ϯ A

Ϭ .Ϯ

Ϭ .ϭ

Ϭ Ϭ Ϭ .Ϯ Ϭ .ϰ Ϭ .ϲ Ϭ .ϴ ϭ ϭ .Ϯ

Concentration in ppm

ϯ ϵ

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Figure (2)

The effect of Sulphuric acid concentration on the extraction of Chromium (VI) with N- phenylbenzohydromic acid

Ϭ .Ϭ ϳ

Ϭ .Ϭ ϲ

Ϭ .Ϭ ϱ

Ϭ .Ϭ ϰ

e c Ϭ .Ϭ ϯ n a b r

o Ϭ .Ϭ Ϯ s b A Ϭ .Ϭ ϭ

Ϭ Ϭ ϭ Ϯ ϯ ϰ ϱ

Morality

ϰ Ϭ

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Figure (3)

Construction of Calibration curve of Chromium (VI) extracted with N- phenylbenzohYdroxamic acid in 3M sulphuric acid

Ϭ .ϭ ϲ

Ϭ .ϭ ϰ

Ϭ .ϭ Ϯ

Ϭ .ϭ e c

b Ϭ .Ϭ ϴ r o s

b Ϭ .Ϭ ϲ A Ϭ .Ϭ ϰ

Ϭ .Ϭ Ϯ

Ϭ Ϭ ϭ Ϯ ϯ ϰ ϱ ϲ ϳ

Concentration in ppm

ϰ ϭ

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Figure (4)

Percentage of Chromium (VI) by volumetric method

ϳ Ϭ

ϲ Ϭ

ϱ Ϭ

n o i t a

r ϰ Ϭ t n e c

o ϯ Ϭ

Ϯ Ϭ

ϭ Ϭ

Ϭ Ϭ Ϯ ϰ ϲ ϴ ϭ Ϭ ϭ Ϯ ϭ ϰ

Sample

ϰ Ϯ

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Figure (5)

Percentage of Chromium (VI) using colourimetric method

ϲ Ϭ

ϱ Ϭ

ϰ Ϭ o

n ϯ Ϭ e c n o

C Ϯ Ϭ

ϭ Ϭ

Ϭ Ϭ Ϯ ϰ ϲ ϴ ϭ Ϭ ϭ Ϯ ϭ ϰ

Sample

ϰ ϯ

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Figure (6)

Percentage of Chromium (VI) extracted with

N- henylbenzohydroxamic acid

ϳ Ϭ

ϲ Ϭ

ϱ Ϭ

ϰ Ϭ

n o i t

a ϯ Ϭ r t n e

c Ϯ Ϭ n o C

ϭ Ϭ

Ϭ Ϯ ϰ ϲ ϴ ϭ Ϭ ϭ Ϯ ϭ ϰ

S ample

ϰ ϰ

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Figure (7)

Percentage of Chromium (VI) by volumetric colourimetric & extraction by N-phenybenzohydromic acid

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Chart (1)

Construction of Calibration curve for Chromium(VI) by Colourimetric Method using diphenyl carbazide

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Chart (2)

The effect of Sulphuric acid concentration on the extraction of Chromium (VI) with N- phenylbenzohydromic acid

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Chart (3)

Construction of Calibration curve of Chromium (VI) extracted with N- phenylbenzoHYdroxamic acid in 3M sulphuric acid

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Chart (4)

Percentage of Chromium (VI) by volumetric method

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Chart (5)

Percentage of Chromium (VI) using using colourimetric method

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Chart (6)

Percentage of Chromium (VI) extracted with N-phenylbenzohydroxamic acid

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Chart (7)

Percentage of Chromium (VI) by volumetric colourimetric methodsand extraction by hydroxamic acid

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Chapter four

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REFERENCE

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