INTRODUCTION:

Nowadays, the treatment of industrial water waste to remove heavy metal ions represents an acute problem. [1] The key elements contained in water waste discharged by ferrous metals production plants include copper [2]. Copper is one of standardized mineral components. The presence of copper in natural, waste, tap and boiler water is regulated at the rate of maximum allowable concentration (MAC), which MAC amounts to 1.0 mg/l in drinking water. [3].

The application of polymeric sorbents in order to extract Cu²⁺ ions from waste water of hydrometallurgical production would remedy not only the environmental impact caused by copper compounds getting into the environment, but would also allow for avoiding any mass valuable metal loss. For example, over 0.46 thousand tons of copper vanish in waste water of electroplating plants annually [4]. In this regard, creating ion-exchange resins of high sorption and kinetic properties on the basis of any available raw stock is an important task to pursue.

In fact, redox polymers based on polyamines and halide-containing quinones have a high oxidizing capacity [5, 6]. However, there is scarcely any information on sorption capacity of such redox polymers.

Meanwhile, as their structure contains such groups such as amino-, hydroxyl and carbonyl groups, there is a purported possibility that synthesized redox polymers may participate in ionic and donor-acceptor interactions. This provides for a simultaneous occurrence of both redox and sorption processes within the resin phase.

Polystyrene or divinylbenzene-involving styrene copolymers amino-derivatives are usually used as polyamines. Such are obtained by way of nitration and subsequent reduction nitro-copolymers [5, 8]. However, the reactions proceed in corrosive environment at high temperature involving a long process. In order to attribute any specific features (such as ion exchanging, complexing, redox reactions, etc.) to polyamines, such polyamines should be exposed to functionalization. This leads to a multi-stage process.

Such undesirable procedures can be avoided by using polyethyleneimine (PEI) and aminated polyvinylchlorid (APVC) amino-compounds. Being commercially available, they are distinguished by a high capacity for substitution reactions [9]. Furthermore, an inert matrix represented by aliphatic fragments involves high exchange, sorption, and complexing capacities in final products.

We have developed the synthesis of redox polymers based on polyethyleneimine (PEI), aminated polyvinylchlorid (APVC) and tetrachloro-p-benzoquinone (TChBQ). The structure and certain physical and chemical properties thereof have been investigated. The ability to complexing has been studied with respect to copper ions (II).

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 a 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, whereafter the key 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 25⁰С.

In some cases, the process was monitored in view of the change in the intensity of absorption mostly typical for the resulting quinoid-strip polymer. IR-spectra of initial, intermediate and final products were recorded on IR-80 spectrophotometer in KBr tablets or Vaseline oil.

Cu²⁺ ion sorption by way of PEI-TChBQ and APVC-TChBQ redox polymers in OH-form (grain size from 0.5 to 1 mm) was studied at 20 ± 2°C under static conditions at 400 solution/sorbent module. Copper concentration in sulfuric solution ranged from 0.097 to 1.853 g/l. Sorption was studied at pH 1.2-4.6 involving 0.1n of H₂SO₄or NaOH solutions. Sorbent’s contact with solutions lasted from 15 minutes to 7 days. CuSO_4∙(chemically pure) was used to prepare model solutions.

Sorption capacity (SC) was calculated in view of a spread between the values of both initial and equilibrium concentration of the solutions. It was measured by way of classic polarography against 0.5 M NH₄Cl at Cu²⁺ reduction waves (Е_1/2= -0.16V). Polarograms were filmed on PU-1 universal polarograph in a temperature-stabilized cell at 25 ± 0.5⁰С, applying a mercury dropping electrode. Oxygen was removed from the solutions under test by way of argon blowing for 5 minutes. A saturated calomel electrode was used as reference electrode.

RESULTS AND DISCUSSION:

Synthesis of Redox Polymers Based on PEI, APVC and TChBQ:

In order to develop conditions for the synthesis of redox polymers based on PEI, APVC and TChBQ complying with the Green (Sustainable) Chemistry concept [10,11], we have studied various approaches to this process. The following things have been taken into consideration: the nature of solvents, the presence or absence of catalysts, and both the temperature and time modes. Protic and aprotic solvents, and basic type catalysts were tested as to whether such can be used as proper reaction environment, because reactions proceed involving the formation of acid products. Initially, solvents were selected based on the degree of dissolution of the original reactants therein. Thereafter, solvents were assessed from a perspective of Green (Sustainable) Chemistry.

Studying the nature of catalysts (NaAc, NaOH, NH₄OH) showed that the use of sodium acetate appears to be the most efficient. Polymer yield amounts to 50,9% (48,1%); 43,7% (39,0%); and 42,0 (34,5%)^, respectively. The catalyst activity range is: NaAc> NН₄ОН > NaOH.

As for the solvents used (dioxane - DO, ethyl alcohol – EA, mixture of ethyl alcohol and water - EA: W = 1:1, and water W), the output of redox polymer decreases as follows: EA:W> EA > DO > W, and amounts to 75,7% (67,0%); 75,2% (65,3%); 69,2% (62,5%); and 27,7% (16,7%)*, respectively. As can be seen, the transition from dioxane to green solvents promotes enhanced PEI conversion. Apparently, this is explained by its high polarity. Polarization of carbonyl quinone groups in their environment increases the mobility of C-Cl, and the process proceeds quite well even if there are no catalysts (redox polymer yield in EA-W mixture is up to 87,7%). Low polyamine conversion in water is explained by poor TChBQ solubility therein. Thus, the use of protic solvents (such as ethyl alcohol or water) relating to green solvents is preferable, because it complies with the Green (Sustainable) Chemistry concept. Furthermore, they provide for higher yields of final products and catalyst-free. Therefore, EA:W = 1:1 mixture was used as solvent for further syntheses.

The impact of the initial reagents ratio on PEI and TChBQ redox polymers’ yield (Fig. 1) showed that when the amount of TChBQ decreases below the equimolecular level, the redox polymer yield drops significantly. Thus, the optimization of the process of redox polymers production based on PEI, APVC and TChBQ allows for assuming 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, рК_α 6,9.

Fig.1. Influence of a ratio of initial reagents on an yield of redox polymers on the basis of PEI and TChBQ (78^оС, 0,5 ч, EA:W=1:1).

The IR spectra of redox polymers based on PA with TChBQ acquire intrinsic absorption bands (cm^-1) of high intensity relating to valence vibration C=O (1653) and valence vibration–С-С- (1210) of quinoid ring, and >C=C< (1501), =NH- (1580), C-Cl (760), and C-N (1340). This confirms the formation of amino-quinoid structures.

Sorption of Copper Ions (II) by Redox Polymers Based on PEI, APVC and TChBQ

Economic feasibility and efficiency of a purification process are determined by the properties of the solution being treated: primarily, its concentration and acidity. The copper content in the technological solutions and waste water derived from various production plants varies widely. For example, acidic waste water from ferrous plants (metals washing water after etching treatment) contains from 60 to 120 mg/l of Cu [12]; solutions derived from ore leaching by sulfuric acid at the Zhezkazgansky Deposit contain from 1,50 to 6,25 g/l [12]; waste water from plating plants contains 10 g/l (washing water) and from 80 to100 g/l (abandoned etching treatment containers) [4]. Hence, research on the sorption activity of ion exchangers depending on the concentration of metal ions in solutions is important. Cu²⁺ sorption isotherms by new redox polymers based on PEI-TChBQ and PVC- TChBQ are shown in Fig. 2.

Fig. 2. Isotherms of sorption of ions of Cu²⁺ (1) redox polymers PEI-TChBQ and APVC- TChBQ (2). Time of contact of 7 days,

As can be seen from Fig. 2, PEI-APVC redox polymer extracts Cu²⁺ ions far better than APVC- TChBQ. Thus, the highest values of SC are observed when Cu²⁺ ions are extracted from solutions at 1,85 g/l, and for PEI-TChBQ and PVC- TChBQ amount to 211,6 mg/g and 105,6 mg/g, respectively.

When studying the impact of environment’s acidity on the SC of redox polymers (Fig. 3), it has been established that, within the 1,2-4,1 pH range, sorption capacity of PEI-TChBQ remains unchanged, and is gradually increasing for PVC- TChBQ. The optimal pH value at which Cu²⁺ions should be extracted is 4,6 where SC of PEI-TChBQ and PVC-TChBQ reaches the highest values of 466,0 mg/g and 284,0 mg/g, respectively.

Fig.3. Influence of acidity of the sulphatic solutions on sorption of ions of Cu²⁺ redox polymers PEI-TChBQ (1) and APVC-TChBQ (2). Time of contact of 7 days.

Among industrial anion-exchange resins, carboxyl anion exchanger ANKB showed the best results for extracting Cu²⁺ions that, in addition to amino-group, contains carboxyl groups [12]. Sorbent’s SC in relation to copper ions at 4-5 pH amount to 120 mg/g, which is significantly lower than the value showed by the redox polymers we synthesized. Weakly basic anion exchanger AM-7 (SС_Cu2+=3,5 mg-eq/g or 111,2 mg/g [13]) upon its sorption activity is also significantly inferior to redox polymer PEI-TChBQ and APVC-TChBQ.

Redox polymers’ extracting capacity is higher than that of ion exchange resins, which have similar chemical structure. Thus, the Cu²⁺ion SC for anion composed of allyl glycidyl ester and PEI is 6,1 mg-eq/g (193,8 mg/g) [14]. The Cu²⁺ion SC for redox polymer based on vinyl ester of monoethanolamine and chloranilic acid is 8,0 mg-eq/g (254,2 mg/g) [15].

As shown in Fig. 4, PEI-TChBQ and PVC-TChBQ have the same kinetic properties. The equilibrium between redox polymers and CuSO₄solution (pH 4,6; copper content 2,75 g/l) is reached for 5 hours. Consequently, they have quite high kinetic properties. Empirically obtained data show that PEI-TChBQ has higher Cu²⁺ion sorption capacity than APVC-TChBQ. This is probably explained by the presence of, in addition to secondary, tertiary amine groups in the PEI- TChBQ structure.

Fig. 4. Dependence of sorption of an ions of Cu²⁺ PEI-TChBQ (1) and APVH-TChBQ (2) redox-polymers from time of its contact with CuSO₄solutions (рН = 4,6, C_Cu=2,75 g/l).

CONCLUSION:

Thus, by using commercially available aliphatic polyamines and Tetrachloro-p-Benzoquinone, we have synthesized redox polymers subject to certain provisions of Green (Sustainable) Chemistry: the process takes one stage; no catalyst systems requiring further utilization were used; in green solvents. The structure and the properties of polymers so obtained were studied.

The studying of Cu²⁺ion absorption from sulfate solutions showed that new redox polymers have high sorption and kinetic properties. Therefore, such new redox polymers can be recommended for the purposes of extraction and concentration of copper ions from recycled waste water derived from non-ferrous metallurgy plants. It has been shown that the Cu²⁺ion absorption capacity of PEI- TChBQ is significantly higher than that of APVC-TChBQ and industrial anion-exchange resins, such as ANKB and AM-7.

Abbreviations:

MAC	maximum allowable concentration, mg/l
PEI	polyetheleneimine
APVC	aminated polyvinyl chloride
PA	polyamine
TChBQ	tetrachloro-p-benzoquinone
DO	Dioxane
EA	ethyl alcohol
W	Water
IR	infrared spectroscopy
ORC	oxidation-reduction capacity (mg-equ/g)
SEC	static exchange capacity (mg-equ/g)
SC	sorption capacity (mg/g)
ANKB	industrial aminocarboxyl polyampholyte
AM-7	weak-basic anion exchanger

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Received on 07.06.2013 Modified on 25.06.2013

Asian J. Research Chem. 6(7): July 2013; Page 659-662