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

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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

  1.                                                     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:

  1. A high distribution ratio for the solute and a low distribution ratio for undesirable impurity.
  2. Low solubility in the aqueous phase.
  3. Sufficient low viscosity and sufficient density difference from the aqueous phase to avoid the formation of emulsion.
  4. Low toxicity and flammability.
  5. 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