Indian Journal of Chemical Technology Vol. 11, November 2004, pp. 787-792
Flotation-separation of nickel from aqueous media using some hydrazone derivatives as organic collectors and oleic acid as surfactant S E Ghazy*, H A Mostafa, S A El-Farra & A S Fouda Chemistry Department, Faculty of Science, Mansoura University, P.O. Box 66, Mansoura, Egypt Received 25 September 2003; revised received 24 June 2004; accepted 22 July 2004 A simple and rapid procedure was developed for the quantitative flotation of nickel(II) from aqueous solutions. Hydrazone derivatives such as: 4-acetylpyridine-[N-(3-hydroxy-2-naphthoyl)]hydrazone (H2APHNH), thiophene-2-carboxaldehyde-[N-(3-hydroxy-2-naphthoyl)]hydrazone (H2THNH), salicylaldehyde-[N-(3-hydroxy-2-naphthoyl)]-hydrazone (H2SHNH), p-anisaldehyde-[N-(3-hydroxy-2-naphthoyl)]hydrazone (H2-p-AHNH) and ethylacetoacetate-[N-(3-hydroxy-2naphthoyl)]hydrazone (H2EHNH) have been used as organic collectors and oleic acid as surfactant. The different parameters, affecting the flotation process, namely, ligand and surfactant concentrations, foreign ions (which are normally present in fresh and saline waters), pH and temperature are examined. Nearly 100% of nickel ions are floated at a metal:ligand ratio of 1:2, pH ~ 7 and at a temperature ~ 25ºC. The procedure is successfully applied to recover Ni(II) from some water samples. The flotation mechanism is suggested. IPC Code: B03D 1/004, 101:02 Keywords: Flotation, hydrazone derivatives, nickel, surfactant, oleic acid, organic collectors
The most fertile field of nickel technology is the production of a wide variety of alloys (Monel metal, Nichrome, Alinco, etc.). Nickel is quite resistant to the attack by air or water at ordinary temperature and is, therefore, electroplated on other metals as a protective coating1,2. Since nickel reacts slowly with fluorine, the metal and its certain alloys (Monel metal) are used to handle fluorine and other corrosive fluorides1. The finely divided metal is used as a catalyst in the preparations of primary and secondary alcohols, alkanes from alkenes by the Fisher-Tropsch process and in ammonia synthesis3. Nickel is found in certain mineral waters (20 ppm) and its amount in seawater ranges from 0.001 to 0.06 ppm4,5. Hence, the separation and recovery of the economically valuable nickel from natural waters has become a subject of great interest. Numerous techniques6-8 for the removal, separation and/or pre-concentration of metal ions from aqueous solutions and wastes are available. Some of these techniques are tedious, need time and rigid conditions for the preparation of solid adsorbents9. These inconveniences may partly be avoided by the use of flotation technique10 which is the choice for this investigation. Flotation-separation process has recently re—————— *For correspondence (E-mail:
[email protected]; Fax: 020502246781)
ceived a considerable interest owing to its simplicity, rapidness and good separation yields (R > 95%) for small impurity concentrations11 (10-6 - 10-2 mol/L). It is believed that this process will be adopted as a clean technology to treat water and wastewater12. Although several investigations have been carried out for the separation and/or pre-concentration of nickel from aqueous solutions, wastes and natural waters using hydrated oxides of iron13-16, indium17,18, aluminum19, zirconium20 and organic collectors21-25, no attention has been paid towards the use of hydrazone derivatives in this respect. Therefore, the present work aims to separate Ni(II) from aqueous media using some hydrazone derivatives, which have biological importance26, as organic collectors and oleic acid as surfactant under the optimized conditions. Experimental Procedure Reagents and solutions
All chemicals used in this investigation were of analytical reagent-grades. Oleic acid (HOL) was used directly as received. Its stock solution (3.36×10-2 mol L-1) was prepared from food grade with specific gravity 0.895 (J.T. Baker Chemical Co.) by dispersing 20 mL in 1 L kerosene. Nickel sulphate hexahydrate (NiSO4.6H2O) stock solution (1×10-2 mol L-1) was
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INDIAN J. CHEM. TECHNOL., NOVEMBER 2004
prepared by dissolving the calculated amount of the salt in double distilled water. The stock solutions of the hydrazone derivatives, H2APHNH, H2THNH, H2SHNH, H2-p-AHNH and H2EHNH (1×10-2 mol L-1) were prepared by dissolving the required amount of compound in minimum amount of ethyl alcohol and completing the required volume with double distilled water. The hydrazone derivatives (ligands) were prepared as has been described elsewhere27. 3-Hydroxy-2-naphthoic acid (0.01 mol L-1) was added to 0.01 mol L-1 of each of 4-acetyl pyridine; thiophene-2-carboxaldehyde; salicylaldehyde; panisaldehyde and ethylacetoacetate in absolute ethyl alcohol. The mixtures were refluxed on a water bath for 3 h. The product thus obtained was crystallized several times from absolute ethanol and dried in a vacuum desiccator over anhydrous CaCl2. The purity of each compound was checked by elemental analysis and IR spectra. Apparatus
Fig. 1—Floatibility of Ni2+ at different pH values. Ni2+, 1×10-4
The flotation cell (a cylindrical tube of 29 cm length and 1.5 cm inner diameter, provided with a stopcock at the bottom) used was the same as described ealier28. The infrared spectra were recorded on Mattson 5000 FTIR spectrometer using KBr disc. The pH measurements were made using Jeanway pH meter. The low concentration of Ni(II) was determined by using Pekin-Elmer Atomic Absorption Spectrometer with air-acetylene flame at 232 nm while higher concentration was determined by EDTA titration.
mol L-1; ligand, 4×10-4 mol L-1; HOL, 4×10-4 mol L-1.
Recommended method
A suitable aliquot containing known amount of Ni(II), specified for each investigation, was mixed with one of the hydrazone derivatives followed by addition of 3 mL of double distilled water. After adjusting the pH with HCl and/or NaOH to the required value, the solution was transferred to the flotation cell and the total volume was made up to 10 mL with double distilled water. The cell was shaken well for few seconds, to ensure complexation. To this, 2 mL of HOL (with known concentration) were added. The cell was then inverted upside down twenty times by hand. After 5 min standing, for complete flotation, the concentration of Ni(II) in the mother liquor was determined. The floatability (F) of Ni(II) was determined from the relation:
F= (Ci-Cf) / Ci ×100%, where Ci and Cf denote the initial and final concentrations of Ni(II) in the mother liquor, respectively. Results and Discussion Effect of pH
Several experiments were carried out to investigate the relation between the floatability of Ni2+ solution and pH using each of the hydrazone derivatives and HOL. The results obtained are plotted in Fig. 1. It can be seen that, maximal floatabilities of Ni2+ ions (~ 100%) were attained in the pH ranges 2-9, 4-9, 4-7.5, 5-7.5 and 6.5-9 for H2THNH, H2APHNH, H2-pAHNH, H2SHNH and H2EHNH, respectively. This facilitates the application of some of the investigated hydrazone derivatives for the separation of Ni(II) from acidic, neutral and alkaline medium. The pH range in which all the hydrazones give maximal flotation was found to be 6.5-7.5. Hence a pH ~7 was fixed for further experiments. Effect of collecting agent concentrations
The collecting ability of hydrazone derivatives towards Ni(II) was examined. The results of the experiments performed to observe the effect of variable concentrations of the ligands on the floatability of
GHAZY:et al.: FLOTATION-SEPARATION OF NICKEL FROM AQUEOUS MEDIA USING HYDRAZONES
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Ni2+ using HOL at pH ~7 were investigated. The obtained data showed that the floatability of Ni2+ increases abruptly reaching its maximum value (~ 100%) at M:L molar ratio of (1:1) and sometimes (1:2). These data agree well with those previously reported27, in which nickel reacts with ligands according to the following modes: Ni2+ + H2L = [NiHL]+ + H+
… (1)
and/or Ni2+ + H2L = [NiL2] + 2H+
… (2)
The most interesting feature of using hydrazone derivatives as collectors is that the use of excess amounts of collector has no adverse effect on the flotation process which facilitates the separation of Ni(II) from unknown matrices. Therefore, for assured functioning, a concentration of each of the hydrazone derivatives equal to four-folds of Ni(II) was used throughout. Effect of nickel concentration
Attempts to float different concentrations of Ni(II) using each hydrazone derivative and HOL at pH~7 were carried out. The results obtained (Fig. 2) show that the maximum flotation efficiency (~100%) of Ni(II) remains constant for all the investigated hydrazone derivatives whenever the ratio of (Ni:L) is 1:1 for some hydrazones or 1:2 for others and less than 1:2 for both. The flotation begins to decrease when these ratios are larger than 1:1.
Fig. 2—Floatibility of different concentrations of Ni2+. Ligand, 4×10-4 mol L-1; HOL, 4×10-4 mol L-1; pH~7.
Effect of surfactant concentration
Trials were carried out to float Ni(II) with HOL only, but the recovery does not exceed 20%. Therefore, another series of experiments were performed to float Ni(II) in presence of hydrazone derivatives and different concentrations of HOL at pH~7. The results obtained (Fig. 3) show that in the HOL concentration range of 2.5-25×10-4 mol L-1, complete flotation of Ni(II) is achieved, below which the flotation decreases. This may be attributed to the presence of insufficient amounts of surfactant required for complete flotation. At higher surfactant concentration the incomplete separation of Ni(II) may be due to the fact that the surfactant changes the state of the particles, Nihydrazone precipitates, from coagulation precipitation through coagulation flotation to redispertion with an increase in the amount of HOL added29. Moreover,
Fig. 3—Floatibility of Ni2+ in the absence and presence of ligand using different concentrations of HOL. Ni2+, 1×10-4 mol L-1; ligand, 4×10-4 mol L-1; pH~7.
INDIAN J. CHEM. TECHNOL., NOVEMBER 2004
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Table 1—Floatability of Ni2+ in the presence of some selected foreign ions [Ni=~ 5.87 mg L-1(1×10-4 mol L-1); Ligand=4×10-4 mol L-1; HOL=4×10-4 mol L-1 ; pH=~7] Iona) Na+ K+ Mg2+ Ca2+ ClSO4 2HCO3 CH3COO-
H2THNH
H2EHNH
230 390 240 40 35.5 9.6 5.6 5.9
230 390 2.4 40 35.5 96 56 59
Tolerance limit (mg L-1) H2SHNH H2-P-AHNH 23 39 0.24 40.5 35.5 9.6 5.6 5.9
23 39 0.24 40.7 35.5 96 56 59
H2APHNH 23 39 24 40 35.5 96 56 5.9
a)
The cations are added in the form of their chloride or sulfate salts while the anions are added as their sodium or potassium salts.
the poor flotation at high surfactant concentration is caused by the formation on the air bubble surface of a stable, hydrated envelope of surfactant or, perhaps, by forming a hydrate micelle coating on the solid surface30,31. As a result, the hydrophobicity of this surface was not satisfactory for flotation. Therefore, a concentration of 4×10-4 mol L-1 of HOL was fixed throughout. Effect of temperature
Under the recommended conditions, a series of experiments was conducted to float Ni(II) in a wide range of temperature. The obtained results showed that the maximum separation (~ 100%) of Ni(II) was achieved up to 70ºC using H2EHNH and H2APHNH. However, the maximum flotation was attained in the temperature ranges, 15-50, 15-30 and 25-70ºC for H2THNH, H2SHNH, and H2-p-AHNH, respectively. The decrease in separation upon raising temperature may be due to the increase in solubility of the precipitate and the instability of the foam giving rise to partial dissolution of the precipitate and insufficient foam consistency to hold up the precipitate32. Since this parameter has an important and variable influence on the flotation process, it is very interesting to study each particular case, especially for large temperature variation33. Accordingly, all experiments were carried out at a room temperature of ~ 25ºC. Effect of foreign ions
In order to assess the applicability of the proposed method to recover Ni(II) added to water samples, the effect of some foreign ions was investigated. These foreign ions were selected on the basis that they are normally present in fresh and saline waters. Solutions containing various amounts of foreign ions, Ni2+, and
each of the ligands were subjected to the described flotation procedure. The tolerable amounts of each ion, giving a maximum error of ±2% in the recovery, are summarized in Table 1. As can be seen, all the investigated foreign ions with a relatively high concentration (in comparison with that of Ni2+) have no adverse effect on the flotation of nickel. Therefore, the recommended procedure may find its applications on natural water samples. Application
In order to evaluate the capability of the flotation method for the recovery of Ni(II) from water, various types of water samples were selected. The selection of these samples was done in a way to provide a wide variety of sample matrices characterized by different types of interferents. Solutions of pre-filtered water samples (10 mL, each) containing Ni(II) with a concentration of 5 or 10 mg L-1 were floated under the recommended conditions. The data obtained are tabulated in Table 2. It is clear that a satisfactory recovery of Ni(II) was obtained. Flotation mechanism
The flotation mechanism is suggested for the precipitation-flotation of nickel depending on the following facts: (i) Nickel reacts with hydrazone derivatives to give the complexes [Ni(APHNH)(H2O)3], [Ni(HTHNH)2], [Ni(HSHNH)2].H2O, [Ni(H-p-AHNH)2] and [Ni (HEHNH)2(H2O)2].H2O. These formulae were confirmed by elemental analyses, IR and 1HNMR spectral studied of the ligands and the isolated complexes27. These complexes have many sites containing electronegative atoms, such as oxygen and nitrogen, capable
GHAZY:et al.: FLOTATION-SEPARATION OF NICKEL FROM AQUEOUS MEDIA USING HYDRAZONES
791
Table 2—Recovery (Re, %) of Ni2+ added to 10 mL of some water samples Ligand =4×10-4 mol L-1 ; HOL =4×10-4 mol L-1 ; pH=~7 Water samples (Locations)
Ni(II) added, mg L-1
H2THNH
H2EHNH
Distilled water
5 10
99.6 100.0
99.8 99.9
Drinking water (Mansoura City)
5 10
99.6 99.9
Nile water (Mansoura City) Sea water
5 10
(Alexandria) (Gamasah) Underground water (Cinbellaween City)
Re, %a) H2SHNH
H2-P-AHNH
H2APHNH
99.8 99.8
99.8 100.0
100.0 99.9
99.8 100.0
99.8 99.8
99.6 99.9
100.0 100.0
99.8 99.9
99.6 100.0
99.8 99.8
100.0 99.9
100.0 100.0
5 10 5 10
99.8 100.0 100.0 100.0
99.6 99.8 99.8 100.0
99.8 99.6 100.0 100.0
100.0 99.9 100.0 100.0
99.8 99.6 99.8 99.9
5 10
99.8 100.0
100.0 99.9
99.9 99.7
100.0 100.0
99.6 99.9
a)
The mean of three experiments.
of forming hydrogen bonds. (ii) Oleic acid begins to dissociate at pH ≥ 56 and the percent of different forms of oleic acid determined by IR analysis at pH 9 (adjusted by NaOH) are: 13.2% oleic acid, 68.2% oleate and 18.2% sodium oleate34. Therefore, oleic acid can interact with other systems, through hydrogen bonding, either in its undissociated or dissociated form depending on the pH of the medium. (iii) The infrared spectra of the isolated complexes from the float layers (after good washing) have no absorption bands corresponding to oleic acid. This means that oleic acid may combine with nickelhydrazone chelates through hydrogen bonds depending on the solution pH and according to the following schemes34: O || (Ni-hydrazone) — C ═ O … HO ─ C ─ R O || (Ni-hydrazone)—C ═ N … HO ─ C ─ R
(II)
O || (Ni-hydrazone)—C ═ OH … −O ─ C ─ R
(III)
(I)
O || − (Ni-hydrazone)—C ═ NH … O ─ C ─ R
(IV)
(iv) The combination of oleic acid surfactant with the nickel hydrazones gives hydrophobic aggregates that float with the aid of air bubbles (created inside the flotation cell by slight shaking) to the surface of the solution6. Conclusion This investigation presents hydrazone derivatives as organic collectors (which are not pollutant for water media and have biological importance) for the separation of nickel ion. This is accomplished by using the simple, rapid and inexpensive flotation technique. The procedure is successfully applied to the recovery of nickel from different water matrices and the mechanism is suggested depending on the formation of hydrogen bonding between oleic acid surfactant and nickel hydrazone complexes. References 1 Cotton F A & Wilkinson G, Advanced Inorganic Chemistry, 3rd edn (Wiley Eastern Ltd, New Delhi), 1972, 891. 2 Lee J D, A New Concise Inorganic Chemistry, 3rd edn (Van Nostrand Reinhold, London), 1987, 365. 3 Freemantle M, Chemistry in Action (Macmillan Education LID, London), 1987, 259, 709, 7. 4 Ackermann G & Sommer L, in The Determination of trace
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