The solvent extraction of cadmium(II) from nitrate medium was studied. The using extractants were quaternary ammonium-based room temperature ionic liquid Aliquat 336 in either the chloride [(C 8H 17) 3 CH 3N +·Cl -], thiocyanate [(C 8H 17) 3CH 3N +·SCN -] and hydrogenophosphate forms, diluted in the kerosene. The effects of different parameters such as equilibration time, initial pH, O/A molar ratio (n extractant/n Cd), initial extractant concentration and ionic strong on extraction of cadmium(II) were investigated. The extraction yields of cadmium(II) increase with increasing initial pH and initial extractant concentration. The stoichiometry of the extracted species was determined on the basis of slope analysis. The effect of various salts such as KSCN and NaNO 3 in the feed solution within the concentrations of 10 to 100 mM on extraction of cadmium(II) was studied at optimal initial pH = 6.2. The relation between the percentages of the extracted species ( ) and the extraction yields were investigated by a calculation program using CHEAQS V. L20.1. The results showed that the decrease of the extraction yield of Cd(II) was related with the decrease gradually of percentage of cadmium(II) free and the increase of percentage of and species with the addition of KSCN. More the hydrophobic character of the extractant is high, more the extraction is better. The metal ion was stripped out satisfactorily using nitric acid as stripping agent, in one step.
Industrialization has led to a substantial increase, especially in natural concentrations of the heavy metals in the environment all over the world. Since heavy metals cannot be biodegradable and tend to accumulate in living organisms, their removal from wastewaters is required prior to discharge [
Cadmium is known to be both extremely toxic, is present in wastewaters from various industries and ubiquitous in natural environments; however, human activities have greatly increased these levels [
The critical organ for chronic cadmium exposure has long been considered to be the kidney and the main site of cadmium accumulation is in the proximal tubular cells of the renal cortex. The so called critical effect, the first adverse effect that occurs as the dose increases, is renal tubular dysfunction detected as increased urinary excretion of low-molecular-weight proteins and intracellular tubular enzymes [
The International Agency for Research on Cancer (IARC) has classified cadmium as a human carcinogen because of the large incidence of lung cancers in occupationally exposed populations [
Liquid effluents containing cadmium can be treated using conventional physical and chemical techniques such as, precipitation [
It has been demonstrated that task-specific ionic liquids have advantages compared to common solvents used as separation media in liquid-liquid extraction processes achieving high efficiencies and selectivities of separation. The physic-chemical properties of ionic liquids (ILs) such as the negligible vapor pressure, the miscibility with other solvents, and good solubility of organic and inorganic compounds, are in a medium of choice for solvent extraction techniques [
Application of ILs in separation of cadmium and their mechanisms have been investigated by several research groups in the past few years. De Los Ríos has studied the extraction of Zn, Cd, Cu and Fe by methyltrioctylammonium chloride [MTOA+∙Cl−] and 1-methyl-3-octylimidazolium tetrafluoroborate
A fundamental study assessed the potential of ionic liquids based on quaternary ammonium cations for future applications in advanced sewage treatment and the removal of metals, lanthanides and metalloids like Cu, Rh, Eu, Ce, Ag, As, Cd, Cr and Hg [
In the present study, the extraction of Cd(II) in nitrate solution using quaternary ammonium-based room temperature ionic liquid Aliquat 336 in either the chloride, thiocyanate or hydrogenophosphate forms are studied. The effects of equilibration time, initial pH (pHi), extractant concentration, O/A molar ratio (nextractant/nCd), and ionic strong on the extraction systems were studied. Stripping of the metal ion from the organic phases was also investigated.
All chemicals and reagents used were analytical reagent grade. Cadmium nitrate, ammonium thiocyanate, potassium thiocyanate, sodium hydrogenophosphate, sodium nitrate, 4-(2-pyridylazo) resorcinol (PAR) and kerosene were provided from Fluka. Buffer solution at pH = 9.0 and nitric acid were supplied from Riedel-Dehaen AG. Aliquat 336 chloride was purchased from Merck.
Analytik Jena SPECORD 210 Double Beam UV-VIS was used for spectra recording and absorbance measurements.
Spectra were recorded in the range from 400 to 800 nm with 0.2 nm resolution in 10 mm quartz cells. Data were processed with WinLab software.
pH measurements for all solutions were taken on a potentiometer Consort C831, with combined glass electrode, that was calibrated at pH 4.00, 7.00 and 10.00 with buffer standards.
The synthesis of ILs was performed using published procedure [
Hydrophobic character of extractants was evaluated by the logarithmic n-octanol/water partition coefficients (Log P), calculated with Clog P program of the commercial available software ChemDrawultra8.0 (Cambridge Soft).
Ionic liquid phase in kerosene solvent was mixed and shaken with aqueous solution of cadmium(II) for few minutes which was sufficient for equilibrium. The mixtures were then centrifuged to enhance phase separation. For stripping of metal ion, different concentrations of nitric acid were contacted with the loaded organic phase at an O/A phase volume ratio of 1:1, followed by vigorous shaking to reach equilibrium.
The cadmium concentrations in the aqueous phase were spectrophotometrically determined using 4-(2-pyri- dylazo) resorcinol (PAR) as a chromogenic reagent at pH 9.0 [
The extraction yield Equation (1), the distribution ratio D (2) and stripping percent S (3) were defined as follows:
where [Cd]i,aq and [Cd]f,aq denoted the initial concentration and the equilibrium concentration of cadmium ion in the aqueous phase respectively; [Cd]f,strip is equilibrium concentration of cadmium in stripping acid and [Cd]i,org is initial concentration of cadmium ion in organic phase, respectively.
Vaq represented the volume of aqueous phase; Vorg represented the volume of organic phase.
All the extraction and stripping experiments were carried out at room temperature (20˚C ± 1˚C). Every experiment was three times repeated.
To study the effect of mixing time on the extraction of Cd(II), an aqueous nitrate solution (pHinitial = 6.2) containing 1 mM of Cd(II) and an organic phase of 10 mM and 50 mM Aliquat 336 in kerosene in the forms of chloride [R3CH3N+∙Cl−], thiocyanate [R3CH3N+∙SCN−] and hydrogenophosphate
For a lower concentration of extractant ( 10 mM ), the extraction efficiency was found to increase slowly to reach a maximum value after 20 min. Subsequently, the effects of different parameters on the extraction were carried out at 30 min.
The extraction of Cd(II) was studied from aqueous nitrate solutions containing 1 mM metal ion by 50 mM [R3CH3N+∙Cl−], [R3CH3N+∙SCN−] and
The extraction yield of cadmium is higher for [R3CH3N+∙SCN−] and
From
The effect of Aliquat 336 in the different investigated forms, on the extraction of Cd(II) from aqueous nitrate solution was studied with different extractant concentrations 10 - 100 mM. It was observed that the extraction yield increased with increase of extractant concentration (
The hydrophobic character of extractant can be determinated calculating log P, log P is definited as the partition coefficient between two phases of a substance, generally n-octanol and water. This parameter developed by Hansch [
and reactivity in phase transfer Heck reaction [
The experimental data for log D versus log different extractants concentrations were plotted in
The extraction equation of cadmium in nitrate medium with different Aliquat forms diluted in kerosene can be represented by the proposed equilibrium equations:
The molar ratio of organic to aqueous (O/A) in solvent extraction process plays important role for the extraction of metals from solutions. Therefore, the studies were made by varying O/A molar ratio between 1 and 100, for the extraction of Cd(II) from the aqueous feed solution containing 1 mM of metal ion (A/O volume phase ratio = 1). As shown in
As the nitrates and alkali ions frequently accompany metal ion in industrial solutions, it is worthwhile to know if
they affect the extraction process efficiency. To study the effect of salts such as KSCN, NaNO3 on the extraction of Cd(II) from the nitrate solution, extractions were carried out with 1mM metal ion at equal phase ratio. The concentrations of the salts in the aqueous solution and Aliquat 336 in the different investigated forms were varied within the range 10 to 100 mM . From
The results in
The results found by calculation program using CHEAQS V. L20.1 are summarized in
The results of
In the case of the extractant [R3CH3N+∙SCN−], the increase in concentration of KSCN from 0.0 (without addition) to 100 mM , in the same experimental conditions, increases the extraction yield from 57.5% to 94.9%. This increase is related with the decrease gradually of percentage of
The results given in
[KSCN] (mM) | Extraction yield (%) | Species (%) | |||||
---|---|---|---|---|---|---|---|
[R3CH3N+∙Cl−] | [R3CH3N+∙SCN−] | Cd2+ | Cd(SCN)2aq | ||||
0.0 | 55.1 | 55.9 | 57.5 | 100 | 0.0 | 0.0 | 0.0 |
10 | 87.7 | 63.2 | 90.1 | 0.2 | 34.6 | 58.3 | 0.6 |
50 | 87.6 | 88.3 | 91.6 | 0.0 | 7.5 | 85,0 | 7.3 |
100 | 89.7 | 89.6 | 94.9 | 0.0 | 3.3 | 80.5 | 16.1 |
[NaNO3] (mM) | Extraction yield (%) | Species (%) | |||
---|---|---|---|---|---|
[R3CH3N+∙Cl−] | [R3CH3N+∙SCN−] | Cd2+ | |||
0.0 | 55.1 | 55.9 | 57.5 | 100 | 0.0 |
10 | 75.5 | 35.0 | 32.5 | 97.6 | 2.3 |
50 | 77.0 | 64.4 | 76.7 | 93.0 | 6.8 |
100 | 80.6 | 61.6 | 78.8 | 89.1 | 10.5 |
Stripping studies were carried out on organic solution consisting of 50 mM of ionic liquid in kerosene after extraction of 1 mM of Cd(II) from nitrate media of initial pH = 6.2. The loaded organic was stripped using nitric acid. Different concentrations of nitric acid were contacted with the loaded organic phase at an A/O phase ratio of 1:1(v/v) and the results are given in
The solvent extraction of cadmium in nitrate medium by quarternary ammonium-based ionic liquids has been studied and following conclusions may be drawn from the above studies.
- The percentage cadmium extraction with these three extractants follows the order
- More the hydrophobic character of the extractant is high, more the extraction is better.
- The stoichiometry of the complex between extractant and Cd(II) in the liquid-liquid extraction system was confirmed by the results of slope analysis.
- It has been demonstrated that the yield of Cd(II) extraction with quarternary ammonium-based ionic liquids from nitrate solutions containing NaNO3 or KSCN depends mainly on the ionic strength of the aqueous phase.
- In the stripping studies, the stripping efficiency of Cd(II) increased with the increasing of the concentration of HNO3. Quantitative extraction of Cd (II) was obtained in one stage at equal phase ratio from the loaded [R3CH3N+∙Cl−] and [R3CH3N+∙SCN−] with nitric acid 100 mM and 500 mM respectively.
- The liquid/liquid extraction demonstrated that we can achieve good levels of extraction of Cd(II) with ionic liquids based on quaternary ammonium.
We gratefully acknowledge the ATRST (Agence Thématique de Recherche en Sciences & Technologie-Algérie) (ex. ANDRU) for this financial support.
BrahimGuezzen,Mohamed AmineDidi, (2015) Highly Efficient Extraction of Cadmium(II) in Nitrate Medium by Quarternary Ammoniums. American Journal of Analytical Chemistry,06,898-910. doi: 10.4236/ajac.2015.611085