INTRODUCTION:

Extraction of Mo (VI) as MoO₄^- can be done by liquid ion exchange method from HCl medium. The stoichiometric investigation of probable structure of extracted complex was [BG⁺][HMoO₂Cl₄], especially for the λ_max=620nm. This method was applied for spectrophotometric determination of Mo (IV) in various samples¹. Extraction of Cr(VI) as Cr₂O₇⁼ and Mn(VII) as MnO₄^- from HCl solutions was accomplished by using Janus green B, that investigates the finest conditions for extraction determination. 0.1M and 0.05M of HCl have been suitable for extraction efficiency of Cr(VI) and Mn(VII) respectively in existence of 50μg Mn(VII) or 20μg of Cr(VI) with 0.8mL 1% TritonX-100 for Cr(VI) as well as 0.5mL for Mn(VII) under 95°C at 15 minutes. It was appropriate for formation of cloud point layer. This method was applied to determine Cr(VI) and Mn(VII) in different samples².

2-[(4–formyl phenyl)azo]-4,5-diphenyl imidazole as complexation agent has been used to form ion association complex with Tungsten at pH=8. The extracted complex has λ_max of 460nm. The study shows that the extracted ion pair complex has a structure of 1:1, and thermodynamic investigation with an extraction method of WO4˭ was endothermic³. Solvent extraction was carried out to investigate the selectivity of some extractants such as TOPO and Alamine 308 towards Mo and Co from synthetic acidic chloride⁴. Cloud point extraction method has been used for extraction of Mg(II) as [Mg(OX)_з‾] by using Rhodamin–B⁺ as a complexing agent under basic conditions⁵. Separation and determination of Mg(II) and Ca(II) were performed after combination with EDTA (H₃Y^-) to form (MgHY^-) and (CaHY^-) after preparing ion pair complexes according to liquid ion exchange method by using Cinchonine (CK) in HCl medium⁶. Extraction of Pt(II) as PtCl₄⁼ with cloud point extraction method has been used Triton X-100 from HCl solution with Janus green B and 1% Triton X-100⁷. Membrane filtration processes used in the gas and oil production for wastewater treatment, with focus on microfiltration, nanofiltration, ultrafiltration, reverse osmosis, forward osmosis, membrane distillation, and electrodialysis⁸. Review fouling-resistant membranes with focus on the membrane fouling phenomena; enhancement of interfacial polymerization procedures and assortment of new initiating monomers; modifying the membrane surface using physical and chemical methods⁹.

Experimental procedure:

A biochrom double beam UV-Visible Spectrophotometer model (Biochrom libra S60) (Cambridge UK), and Electrostatic water bath (G, Gerhardt, Germany) were employed in this study. All chemicals were used as received from the commercial company without any further purification. All solutions were prepared with double distilled water. The standard molybdenum solution was prepared by dissolving 0.1830g from (NH₄)₆Mo₇O₂₄ (Merck 99.8%) in 100mL distilled water, and Tungsten was prepared by dissolving 0.1794g from Na₂WO₄ (Merck 99.5%) in 100mL distilled water. On the other hand, Manganese was prepared by dissolving 0.2877g from KMnO₄ (Aldrich 99.9%) in 100mL distilled water. Any other working solutions have been prepared by dilution with doubly distilled water for an appropriate volume.

Principal method:

10mL aqueous solution has 50µg from oxyanion of metals under study, Mo(VI), W(VI) and Mn(VII). Each one is in the presence of the finest concentration of HCl with sufficient optimum volume of non-ionic surfactant Triton X-100 as well as 1×10^-4 M Safranin. These solutions are heated in electrostatic water bath at 90°C for 15min. Until complete formation of cloud point layer, isolate the CPL from aqueous solution, then dissolve CPL in 5mL ethanol and determine the absorbance of ethanolic solution at λ_max for each ion against blank prepared in the same manner in absence metal ion¹⁰.

RESULTS AND DISCUSSION:

Spectrophotometric study:

The λ_max for each ion pair complex of Mo(VI),W(VI) and Mn(VII)as MoO₄⁼, WO₄⁼ ,MnO₄^- with Safranin has been extracted to cloud point layer. 10mL aqueous solution has been prepared that contains 50µg of Mo(VI) or W(VI) or Mn(VII)with 1×10^-4 M of Safranin and 1M HCl, 0.5mL of Triton X-100. Heat this solution at 90°C for 15min. After formation of cloud point layer, separate this layer and dissolve it in 5mL ethanol. Then, take the spectrum of this layer against blank prepared in the same manner in the absence of metal ion. The spectra were depicted in Fig. 1.

Figure (1): UV-Vis. spectra of ion pair association complexes for MnO₄^-, WO₄⁼ and MoO₄⁼

The study illustrated that the wavelengths for maximum absorbance λ_max were 536nm for Mo(VI), 533nm for W(VI) and 534nm for Mn(VII).

Variation of HCl concentration:

Extraction of 50μg for each metal ion Mo (VI),W(VI) and Mn(VII) as oxyanion, from 10mL aqueous solution, has rising concentration of hydrochloric acid HCl of 0.5mL with 1% Triton X-100 and 1×10^-4M of Safranin. Heat this solution at 90°C for 15 min and up to formation of cloud point layer separate this layer from aqueous solution and dissolve it in 5mL ethanol. Then, measure the absorbance of ethanolic solution against blank prepared in the same manner without metal ions. The results show (1.0,1.0 and 0.6) M HCl for Mo (VI), W(VI) and Mn (VII) respectively. More suitable concentrations of HCl will give higher active extraction as stable ion pair association complexes. The results clearly show that at these concentrations of HCl, a maximum extraction efficiency has been reached by getting better thermodynamic and kinetic equilibria to form higher concentrations of ion exchanger. Ion pair association complex with better stability and any concentrations of HCl less than optimum value would not allow favorable equilibrium with decreasing in ion exchanger concentration. Consequently, ion pair association complex will decrease stability. But at HCl concentration more than optimum value, it will decrease extraction efficiency. Correspondingly, because of increased backward direction of equilibrium relation, an increased dissociation equilibrium has appeared with declined ion exchanger concentration formation. In high concentrations of HCl, more stable compound such as MnO₃Cl may form and change Mn²⁺ to form MnCl₂. These species cannot be extracted as ion pair complexes for other metal ions¹¹.

Variation of metal ion concentration:

By following the principal method as detailed previously, extracted metal ions under study from 10mL aqueous solutions contains rising quantities of each metal ion alone. The results were presented in Fig. 2.

Figure (2): Effect of Mⁿ⁺ ions concentration on formation of ion pair complex extracted and stability

We can predict from the results that the concentrations of 50μg for Mo(VI),W(VI) and Mn(VII) were the optimal magnitudes that give higher extraction efficiency constantly. Another parameter for an equilibrium is listed below:

Concentrations of metal as oxyanion less than optimum value to reach the suitable equilibrium, decline the extraction efficiency as well as metal ion concentration more than optimum value. Also, they have effects to fall off extraction efficiency according to mass action law by predominant dissociation equilibrium.

Effect of Triton X–100 volume:

By the application of principal method, extracted metal oxyanion has been made in the presence of increasing the volume of 1% Triton X–100. The results demonstrated that the volume of Triton X–100 was (0.8, 0.8 and 0.6)mL for Mo(VI),W(VI) and Mn(VII) respectively. Optimum volume helps to obtain higher extraction efficiency. This volume’s thermodynamic applicability is sufficient to reach favorite thermodynamic and kinetic equilibria to form the best cloud point layer and replenishment. Reaching the critical micelle concentration (CMC) less than this value would not allow equilibrium of formation of CPL so that volume more than optimum effect can increase diffusion and prevents realization of good CPL.

Effect of Temperature:

10mL aqueous solution has 50μg of Mo(VI),W(VI), and Mn(VII) under 1×10^-4M Safranin at optimum HCl concentration and 1% Triton X-100. Heat these solutions at different temperatures (70–90)°C for 15min. After that, the CPL is separated and dissolved in 5mL ethanol. The absorbance is measured at λ_maxagainst blank organized in the same manner without metal ions. The results were shown in Fig. 4.

After plotting logK_exagainst 1/T K, there is possibility of giving straight line as in Fig. 3 from the slope of a straight line and determined thermodynamic relation¹²below with data of extraction:

Figure (3): Effect of temperature change on extraction constant

*ΔG_ex =ΔH_ex –T∆S_ex*	*ΔG_ex= -R T ln K_ex*		Ions
161.44	- 58.52	0.08396	Mo(VI)
131.66	- 47.70	0.09186	W(VI)
196.08	-71.13	0.04879	Mn(VII)

The results demonstrate that the extraction method was endothermic and the positive small value of ΔH_ex determines the proximity of the ions of pair association complex to each other so that the high positive value of ΔSex exemplifies the dependence of extraction method on entropy.

Effect of heating time:

Extracted metal ions under study are according to the principal method at the different periods of heating. The optimum time of heating for all ions was 15min. At this time, it reaches the best thermodynamic and kinetic equilibria for formation of ion pair association complex of Mo(VI),W(VI) and Mn(VII) that were extracted by cloud point extraction method. The time of heating represents the kinetic side of extraction, which helps to reach the advantageous energy quantities in solution for aggregation micelles to form CPL with smaller volume and higher density with good dehydration as well as better equilibrium for CPL partition. Each time less than optimum is not suitable to reach the best equilibrium and drops extraction efficiency. Thus, any time more than optimum value has effect to decrease extraction efficiency by the effect of increased diffusion of micelles and decreases dehydration and partitioning concerning the CPL.

Stoichiometry:

By this application, dual spectroscopic methods of slope analysis and slope ratio have been employed for determining most probable structures of extracted ion pair complex for metal ions under study. The results are shown in Figs. 4 and 5.

Table (1): effect of electrolyte salts on extraction efficiency of Mo (VI), W(VI) and Mn (VII)

*Mn (VII)*		*W(VI)*		*Mo (VI)*		*Electrolyte salt*
D	*Abs.at λ_max=534nm*	D	*Abs.at λ_max=533nm*	D	*Abs.at λ_max=536nm*	*Electrolyte salt*
40.30	1.430	21.50	1.654	30.40	1.460	*LiCl*
35.60	1.120	14.30	1.421	28.60	1.380	*NaCl*
37.80	1.250	19.80	1.473	28.90	1.420	*MgCl₂*
32.90	1.080	17.30	1.371	23.80	1.300	*AlCl₃*

Table (2): interference effect on extraction efficiency

*W(VI)*		*Mn (VII)*		*Mo(VI)*		*Interferences*
D	*Abs.at λ_max= 533nm*	D	*Abs.at λ_max=534nm*	D	*Abs.at λ_max=536nm*	*Interferences*
22.5	0.930	25.70	0.750	17.97	0.856	*Zn²⁺*
20.2	0.852	27.20	0.810	18.70	0.934	*Ni²⁺*
13.1	0.671	22.40	0.655	13.11	0.653	*Fe³⁺*
16.7	0.755	19.70	0.513	17.53	0.889	*Cd²⁺*

Effect of interferences:

By application of this method according to principal method, extracted metal oxyanion under investigation from 10mL aqueous solution in presence of 0.1M from another foreign ion has been prepared. The results are presented in Table 2.

The results demonstrate that there is an interferences for all foreign ions, which means that these ions participate in extraction method and formed ion pair association complexes extracted to the CPL¹⁵. With different efficiencies according to the nature of affinity of each ion as well as this participation, it decreases the extraction efficiency of metal oxyanion by decreasing ion pair association complexes formation to metal ions under experimentation.

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Received on 14.10.2021 Modified on 21.01.2022

Research J. Pharm. and Tech. 2022; 15(8):3685-3689.

DOI: 10.52711/0974-360X.2022.00618