TABLE
OF CONTENTS
Title
Page i
Approval Page ii
Certification iii
Dedication
iv
Acknowledgement v
Table
of Contents vi
List
of figures xi
List
of tables xiii
Abstract xiv
1. Introduction
1
1.1
The Solvent Extraction Process 2
1.2 Kinetics of Extraction 3
1.3 Properties of Liquids
4
1.4 Thermodynamics of Solutions 5
1.4.1 Ideal Mixtures and Solutions: 5
1.4.2 Non-Ideal Mixtures and Solutions 6
1.4.3 Scales of Concentration 7
1.5 Solubility in Binary Systems 8
1.5 Measures of Effectiveness 9
1.6.1 Distribution Law 9
1.6.2 Distribution Ratio 11
1.7 Extraction Factor (D,) 12
1.8 Quantitative Treatment of Solvent Extraction Equilibria 14
1.9 Extraction Methods in Solvent Extraction 18
1.9.1 Batch-Extraction Process 18
1.9.2 Continuous Extraction 23
1.9.3 Discontinuous Counter Current Extraction 24
1.10 Classification of Inorganic Extraction System 25
1.10.1 Metal Chelate 25
1.10.2 Ion Association Complexes 30
1.10.3 Additive Complexes 31
1.11 Factors that Influence Stability and Extractability of Metal Chelate Complexes 33
1.11.1 Effect of Acidity (pH) 33
1.11.2 Effect of Organic Chelating Agent 34
1.11.3 Effect of Masking Agent 34
1.11.4 Effect of Variation of the Oxidation State of Metal 35
1.11.5 Effect of Salting-Out Agent 35
1.11.6 Effect of the Stability of the Metal Chelate 36
1.11.7 Influence of Organic Solvent 36
1.12 The Features of Ligand that Affects Chelate Formation 37
1.13 Applications of Solvent Extraction 38
1.14 Drawbacks on Solvent Extraction 38
1.15 Scope of Study 39
1.16 Aims and Objectives 39
2.0 Literature Review 41
2.1 History of Solvent Extraction 41
2.1.1 Early Models on Solvent Extraction 44
2.2 The Solvent Extraction of Zinc 44
2.2.1 Previous Works on Solvent Extraction of Zinc 46
2.3 The Solvent Extraction of Cadmium 50
2.3.2 Previous Works on Solvent Extraction of Cadmium 52
2.4 The Chemistry of Ligand Formation 57
3.0 Methods and Materials 59
3.1 Description of Apparatus 59
3.2 Preparation of Metal Stock Solution 59
3.3 Synthesis of 4-Amino Antipyrine-Pyrogallol 60
3.4. Complexes of the Ligand 61
3.4.2 Stiochiometry of the Complexes 61
3.5 Extraction Procedure 61
3.5.1 Extraction from Buffer Solution 62
3.5.2 Extraction from Acid Media 62
3.5.3 Extraction in Salting-Out Agent 63
3.5.4 Extraction in Complexing Agent 63
3.6 Measurement of Distribution Ratio 64
3.7 Spectrophotometric Analysis of the Metal Ion 64
3.7.1 Cadmium (II) Analysis 64
3.7.2 Zinc (II) Analysis 64
3.7.3 Calibration Curve 65
3.8 Separation Procedures 65
3.9 Extraction from the Industrial Material 65
4.0 Results and Discussions 67
4.1 Electronic Spectra 67
4.2 IR Spectra
71
4.3 Metal-Ligand Mole Ratio 77
4.4 The Molecular Formula of the Ligand and the Complexes 77
4.5 The Properties of the Ligand and the Metal complexes 78
4.5.2 Solubility Test Data 79
4.5.3 Dissociation and Protonation Constant of the Ligand 79
4.6 Equilibration Time 81
4.6.1 The Effect of pH Buffer on Extraction of Zn(II) and Cd(II) 82
4.6.2 Effect of Acidity
84
4.6.3
Effect of Salting-Out
86
4.6.4 Effect of Masking Agent 89
4.6.5 Metal Separation 91
4.6.6 Determination of Metal from Real Material 92
4.7 Quantitative Treatment of Solvent Extraction Equation 93
Conclusion 94
REFERENCE 95
ABSTRACT
The azo-ligand, 1,5-dimethyl-2-phenyl-4-[(E)-(2,3,4-trihydroxylphenyl) diazenyl]-1,2-dihydro-3H-pyrazol-3-one (H3L) and its Zn(II) and Cd(II) complexes have been synthesized and characterized based on stoichiometric, molar conductance, electronic and infra-red spectral studies. The results showed that H3L reacted with the metals in 2:1 ratio. H3L coordination was through the hydroxyl, azo and carbonyl groups to form [Zn(H2L)2]2+ and [Cd(H2L)2]2+ respectively. Solvent extraction studies on Zn(II) and Cd(II) using 1,5-dimethyl-2-phenyl-4-[(E)-(2,3,4-trihydroxylphenyl) diazenyl]-1,2-dihydro-3H-pyrazol-3-one were carried out with CHCl3. Effects of other extraction variables like, pH, salting-out agent, masking agent and acids were also investigated. Cd(II) was quantitatively extracted in 0.001 M HCl up to 100%; and 0.001 M of either thiocyanate, or 0.001 M tatrate masked Cd(II) up to 90%, under five minutes. Extraction of Zn(II) with H3L/CHCl3 was quantitative in 0.001 M HCl up to 96% under seventy minutes. In the same vein, 1 M cyanide and 1 M thiocyanate masked it up to 79% and 67% respectively. Cd(II) was successfully separated from Zn(II) following four-cycle extraction up to 96.5% in 0.001 M HCl using H3L/CHCl3 in the presence of 1 M cyanide. Recovery of Zn(II) and Cd(II) from rubber carpet was up to 90% and 85% respectively under the established parameters. The extraction constant was established for both Zn(II) and Cd(II) complexes from the results obtained from pH, where the slope was 0.141 and 0.0516, and the extraction constant 7.316 and 3.899 respectively. Hence, H3L is a promising extractant for Zn(II) and Cd(II) ions.
CHAPTER ONE
- INTRODUCTION
During the years 1900 to 1940, solvent extraction was mainly
used by the organic chemist for separating organic substances. Since in these
systems, the solute, (desired component) often exist in only one single
molecular form, such system are referred to as non- reactive system1.
However, it was also discovered that mainly weak acids could complex metals in
the aqueous phase to form complex soluble in organic solvent. This is an
indication that organic acid may be taken from the aqueous or the organic
phase; such system is referred to as reactive system. This has become a tool
for analytical chemist, when the extracted metal complex showed a specific
colour that could be identified spectrometrically.
Solvent extraction is a process whereby two immiscible liquids are vigorously shaken in an attempt to disperse one in the other so that solutes can migrate from one solvent to the other2. When the two liquids are not shaken the solvent to solvent interface area is limited to the geometric area of the circle separating the two solvents. However as the two liquids are vigorously shaken the solvents become intimately dispersed in each other. The dispersal is in the form of droplets. The more vigorous the shaking the smaller the droplets will be. The smaller the droplets are, the more surface area there is between the two solvents. The more the surface area between the two solvents, the smaller the linear distance will be that molecules will travel to reach the other solvent and migrate into it. The shorter the linear distance travelled by the molecules, the more rapid will be the extraction. The fundamental reason for molecules to migrate from one phase into another is solubility. The molecules will preferentially migrate to the solvent where they have the greatest solubility. If the molecules are very polar they will generally favour the aqueous phase. If the molecules are non-polar they will favour the organic phase. The key concept to take away at this point is that the process of solvent extraction requires that the chemist adjust the solution conditions so that the radionuclide of interest is in the proper oxidation state and the solution pH is adjusted so that the appropriate complexing agent will form a neutral complex that will easily migrate into the organic phase based on those chemical conditions1.
Solvent extraction has been used
predominantly for the isolation and pre-concentration of a single chemical
species prior to its determination3; it may also be applied to the
extraction of group of metals or classes of organic compounds, prior to their
determination by techniques such as atomic absorption or chromatography.
Solutes have differing solubilities in different liquids due to variation in
the strength of the interaction of solute molecules with those of the solvent.
For this reason, the choice of solvent for extraction is governed by the
following4:
- A high distribution
ratio for the solute and a low distribution ratio for undesirable impurity.
- Low solubility in the
aqueous phase.
- Sufficient low viscosity
and sufficient density difference from the aqueous phase to avoid the formation
of emulsion.
- Low toxicity and
flammability.
- Ease of recovery of
solute from the solvent for subsequent analytical processing. Thus the boiling
point of the solvent and the ease of stripping by chemical reagents merit
attention when a choice is possible. Sometimes, mixed solvent may be used to improve
the above properties; and salting-out agent may also improve extractability.
1.1 The Solvent
Extraction Process
SOLVENT EXTRACTION STUDIES ON Zn(II) AND Cd(II) COMPLEXES OF 1,5-DIMETHYL-2-PHENYL-4[(E)-(2,3,4-TRIHYDROXYPHENYL)]DIAZENYL-1,2-DIHYDROXYL-3H-PYRAZOL-3-ONE
