1. INTRODUCTION:

Waste water containing high toxic vanadium compounds are formed in iron, steel and metal processing industry, where vanadium is used for steel alloying [1], in chemical production of vanadium-oxide catalysts [2], etc. Its content is also high in the oils of the Caspian Sea region [3].

Vanadium (V), in the media of different pH and solutions of dissimilar concentration, form both cationic and anionic monomeric or polymeric complexes [4]:

Vanadium ion	VO₄^3-	HVO₄^2-	V₃O₉^3-
рН	<13.0	8.0-3.0	8.0-6.6

V₁₀O₂₈^6-	HV₁₀O₂₈^5-	H₂V₁₀O₂₈^4-	VO²⁺
6.5-6.0	6.0-3.5	3.2-2.0	<2.0

This is why its extraction is considerably complicated. Therefore, all of the completeness of vanadium recycling out of vanadium-containing raw materials, high quality of the product, and environmental cleanliness of production are often challenging.

Analysis of the existing methods of vanadium removal from waste and sewage water shows that extraction-and-sorption methods are the most promising at the stage of hydrometallurgical processing of vanadium-containing raw materials [5-6].

In view of the aforesaid, it is of immediate interest to create efficient adsorbents to have vanadium ions extracted from solutions and purified from waste water up to sanitary standards, and to obtain V₂O₅ of high quality. Quite a wide variety of vanadium ionic forms may provide for various adsorbents suitable for vanadium sorption [6-10].

This paper pursues the aim of researching and analyzing the sorption of vanadate ions by way of aminoquinoid redox polymers based on tetrachloro-p-benzoquinone (TChBQ) and aliphatic polyamines, such as polyethyleneimine (PEI) and amidated polyvinyl chloride (APVC) [11-12]. Sorption of vanadate ions was studied and analyzed in view of sample solutions of NH₄VO₃ by way of polarographic analysis.

New redox polymers, due to the presence of, within their structure, such groups as >C=O, >NH, >N=>, and C-Cl, show, in addition to redox capacity, high sorption features with respect to heavy metal ions [12].

MATERIALS AND METHODS:

The synthesis of redox polymers based on PEI, APVC and TChBQ was carried out in various solvents within a period from half an hour to three hours, at various mole ratios of initial PEI (APVC): TChBQ reactants, and at various temperature and time modes. The pH level was adjusted by adding ammonia, sodium hydroxide or sodium acetate. As soon as the reaction terminated, the polymer was separated, cleaned with methyl (ethyl) alcohol in a Soxhlet extractor, treated by 4% NaOH, washed until the wash water showed neutral reaction. Thereafter, main physical and chemical properties were identified.

The progress of the reaction was assessed in view of the data obtained by way of elemental analysis and IR spectroscopy, as well as by referring to redox capacity (RC) and static exchange capacity (SEC) upon the main groups of final products, and the values of potentiometric acid-base and redox titration measured by DL50 titration apparatus Mettler Toledo at 25⁰.

Sorption of vanadate ions was carried out in static conditions. Initial and equilibrium solutions of ammonium and sodium metavanadates were determined by way of polarographic analysis, with background 0.1n HCl. Polarograms (i.e. graphs of current versus potential) were recorded by PU-1 polarography device within a temperature-controlled cell at 25±0.5⁰C, applying a capillary-flow dropping mercury electrode (DME) at open circuit: m^2/3 t^1/6 = 4.28 mg^-2/3sec^-1/2. Saturated calomel electrode had the function of a reference electrode. Oxygen was removed from the solutions by argon blowing for 5 minutes. It was found that, within the range of 10^-4-10^-3 mol/L concentration, the diffusion current is in direct proportion with the concentration. On the 0.1N HCl background, Е _1/2 = -0.85 V for NН₄VО₃, and Е_1/2 = -0.95 V for NаVО₃.

results and DISCUSSION:

Redox Polymers on the basis of PEI, APVC and TChBQ:

are produced in the following conditions: polyamine (PA): TChBQ = 1:1, solvent – ethyl alcohol and water (1:1 vol.), T =78°C, duration from 0.5 to 1 hrs. Redox polymer capacity of 0.1N Fe₂(SO₄)₃ is up to 6,0-7,5 mg-eq/g; and anion-exchange capacity of 0.1N HCl is up to 6.3-12.1 mg-eq/g, pK_a 6.9 [12].

Analysis of the sorption of vanadium ions by aminoquinoid polymers has shown that vanadium concentration in a solution has significant impact on the sorption capacity (SE) of redox polymers (Fig.1), because the degree of ion condensation depends on SE. Thus, within the range of 10^-1 – 10^{-4 gram atom/L vanadium concentration, its ions exist
in the form of mononuclear particles only under acidic (pH<2) or highly
alkaline (pH>13) solutions [5].}

Fig.1. Sorption isotherms of vanadium ions (V) by redox polymers PEI-TChBQ (1) and APVC-TChBQ (2). Time of contact of 7 days.

As it follows from Fig.1, a sharp increase in the sorption isotherm at low equilibrium concentrations of vanadium (V) ions by polymer PEI-TChBQ (curve 1) indicates that redox polymer PEI-AQ can extract such ions sufficiently, while APVC-TChBQ (curve 2) is inefficient [6], because this type of isotherm is most likely conditional upon physical sorption only. The degree of extraction of vanadium (V) ions by redox polymer APVC-TChBQ from solutions with 0.19-0.51 g/L concentration reaches 94-95%.

Along with metal concentration, the ion composition of vanadate solutions depends significantly on their acidity. Н₆V₁₀О₂₈ decavanadic acid exists in the pH 2-6 range and easily removes, in aqueous solutions, 4 protons, thus forming ions Н₆V₁₀ О₂₈^4-[5]. In the pH 5-7 range, deca-vanadate ions co-exist with meta-vanadate ions. The authors [7] argue that quintavalent vanadium, having amphoteric properties, forms ions of three kinds: VО₃^-, VО₂⁺, VО₂³⁺, notably, VО₂⁺ и VО₂³⁺cations exist in highly acidic solutions, and VО₃^-anion exists in low acidic solutions. In the pH 0.2-4 range, vanadate ion exists in two forms VО₃^- and VО₂⁺which are in equilibrium as determined by the concentration of hydrogen ions.

Fig. 2. Impact of acidity of NH₄VO₃(C_V=1.92g/L) solutions on sorption of vanadium (V) ions by redox polymer PEI-TChBQ. Time of contact of 7 days.

As follows from Fig. 2, which shows the dependency of SE of PEI-TChBQ polymer relating to vanadium ions on the acidity of NH₄VO₃solutions, it appears that, in the рН 4-6.6 range, its absorption capacity is the same. When рН is reducing from 4 to 1.7, SE of redox polymer PEI-AQ relating to vanadium ions is increasing reaching the maximum value of 331.2 mg/g, which applicable to V₂O₅ is 591.25 mg/g, i.e. 1.3-1.5 times higher than industrial ionites “АN-31” (450 mg/g) and “EDE-10P” (400 mg/g) [5]. The degree of extraction of and the SE of copolymers derived from allyl derivatives of 1,4-benzoquinone, and 4-vinylpyridine with respect to vanadium ions at pH 1 are 82% and 221.5 mg V₂O₅/g, respectively [8]. SE of redox polymers synthesized out of mono- and disubstituted derivatives of vinyl ether of monoethanolamine (VEMEA) and 1,4-benzoquinone by copolymerization with 4-vinylpyridine equals to 173.2 mg V₂O₅/g [5]. They have high kinetic properties because the equilibrium between ionites phase and NH₄VO₃ solvent occurs within 10 minutes. It appears from the analysis of sorption of vanadate ions from 0.05М of NH₄VO₃(рН 6.4) by chlorine-containing redox polymers on the basis of VEMEA [9] that vanadate ions are better absorbed by a redox polymer synthesized out of VEMEA and chloranilic acid (SЕ=386.6 mg V₂O_5,extraction 85%), slightly lower than that of redox polymers based on VEMEA and TChBQ, VEMEA and dichloro-napthoquinone, which do not exceed 96.8 and 88.2 mg V₂O₅/g, respectively.

It appears from Fig. 3, which shows kinetic curve of sorption of vanadium ions, that the equilibrium between redox polymer PEI-TChBQ and NH₄VO₃ containing V 2.04 g/L V and having рН 1.8 can be reached within 18 hours.

Fig.3. Kinetic curve of sorption of vanadium ions (V) by redox polymers PEI-TChBQ from NH₄VO₃(pH 1.8, C_V=2.04 g/L)

Therefore, redox polymer PEI introduced into the structure significantly enhances its sorption properties in relation to vanadate ions. Redox polymer PEI-TChBQ can be applied in practice in various industries for the purposes waste water treatment to remove toxic vanadium compounds.

ABBREVIATIONS:

PEI	Polyetheleneimine
APVC	Aminated polyvinyl chloride
PA	Polyamine
TChBQ	Tetrachloro-p-benzoquinone
EA	Ethyl alcohol
W	Water
ORC	Oxidation-reduction capacity (mg-equ/g)
SEC	Static exchange capacity (mg-equ/g)
SC	Sorption capacity (mg/g)
AN-31	Industrial weak-basic anion exchanger
EDE-10P	Industrial polyfunctional anion exchanger

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Received on 21.02.2014 Modified on 15.03.2014

Asian J. Research Chem. 7(4): April 2014; Page 401-403