INTRODUCTION:

Rhenium is among the rarest trace metals. It is one of the rarest elements in the Earth's crust: its Clarke value constitutes 7х10^-8%. Among the most expensive metals, Rhenium takes the eighth place. Molybdenite of copper and molybdenum deposits are the minerals richest in Rhenium. Significant Rhenium resources are contained in the ores of the Dzhezkazgan deposit in which Rhenium exists as a mineral called “dzhezkazganit” [1]. Rhenium is indispensable as a component of superalloys in aerospace engineering, efficient Platinum-Rhenium catalysts in the production of high-octane gasoline, etc.

When molybdenum and copper concentrates are exposed to oxidative roasting, Rhenium is removed, together with furnace gas, as Re₂O₇. To remove it from dust and sludge, diluted H₂SO₄leaching is applied. Rhenium is removed from the solutions so produced and from wash sulfuric acid by way of extraction or sorption. Associated extraction of Rhenium can be arranged during in-situ leaching of uranium ore by sulfuric acid solutions.

At large scale production, the efficiency of associated extraction of valuable components from raw materials rises sharply. Sorption and ion-exchange methods can assist in extracting metal ions almost to the fullest extent [2-4]. In alkaline, neutral and acidic solutions, Rhenium exists as a simple anion ReO₄^-, while in highly acidic solutions (200 g/L Н₂SО₄) cationic complexes may be formed [4].

The purpose of the work constitutes the synthesis of a redox-polymer based on Polyethyleneimine and Chloranil and the study of the sorption of perrhenate ions by synthesized Polyaminoquinone.

MATERIALS AND METHODS:

A redox-polymer based on Polyethyleneimine (PEI) and Chloranil (CA) was obtained by condensation of PEI with CA at weight ratio equal to 5.0-5.5:1, in the presence of 10-15% (mass) of sodium acetate in a mixture of ethanol and dioxane (volume ratio 1:1) at the temperature of 80°C for five (5) hours. The final product was washed with ethanol in a Soxhlet extractor for sixteen hours. The sample was then cut small, and a polymer with particle sizes of 0.5-1.0 mm was obtained. As a result, a new redox anion-exchanger was synthesized. It has a spatial structure with static exchange capacity of 0.1 N solution HCl 11.8-12.8 mg-eq/g. Such redox anion-exchanger can be used in hydrometallurgy for the purposes concentration and separation of rare metals. Elemental analysis (calculated / found), %: 44.27 / 44.48 C; 1.86 / 2.14 H; 6.45 / 6.28 N; 32.67 / 32.21 Cl; 14.76 / 14.89 O.

The change in the nature of IR-spectra in original PEI (Figure 1a), as compared with the condensation product, shows that the process is running as designated. The IR-spectra in redox-polymer based on PEI and CA (Figure 1b) acquires featured absorption stripes of significant intensity that relate to stretch vibrations C=O (1,653 cm^-1) and stretch vibrations of a –С-О- phenol (1,206 cm^-1) quinoid ring, as well as links > C=C< (1,501 cm^-1), = NH- (1,580 cm^-1), C-Cl (756 cm^-1) and C-N (1,340 cm^-1). As observed, the frequencies of absorption of stretch vibrations NH increase from 3,280 cm^-1 in PEI up to 3,404 cm^-1 in redox-polymer, which is apparently associated with a change in the nature of the surrounding structure, namely the occurrence of a strong electron-acceptor substituent in polyamine units. The aforesaid confirms the formation of an aminoquinoid polymer.

Fig. 1 IR-spectra in original PEI (a) and redox-polymer based on PEI and CA (b).

For the purposes of thermal gravimetric analysis of the sample on the basis of CA, in a dynamic mode, a thermal gravimetric module of thermal analytical Mettler TA-3000 System was used. The sample was heated at 5 deg/min within a temperature range from 30°C to 300°C in the air (1) and in the inert atmosphere (2) (for comparison, N₂). The results are shown in Figure 2. As can be seen from the Figure, at almost up to 200°C, the mass losses do not exceed 5%. Notably, such losses occur at the start-up step (up to 80°C). Within the range of 80°C to 200°C the samples barely show any losses of weight. When the temperature reaches 200°C, a rapid change in weight is observed in all samples, which remains as such up to 300°C. The sample though maintains 75% of its weight. Inert environment has virtually no effect on the thermal stability of PEI-CA (Curves 1 and 2).

Fig. 2 Curves for losses of mass in redox-polymer according to the dynamic thermal gravimetric data in the inert atmosphere (2) and in the air (1).

The temperature range of a low-temperature effect is apparently conditional upon dehydration (i.e. water evaporation). Based on experiments, the water content in a sample does not exceed 5%. The second effect is apparently caused by irreversible chemical processes (i.e. release of active groups and destruction of polymer matrix). When heated in the air and the inert atmosphere up to 300°C, the losses of mass in redox-polymer hardly differ. This allows to assume that thermal breakdown runs similarly in both cases.

The sorption of Rhenium ions by PEI-CA redox-polymer in OH-form (the size of a grain is 0.5-1 mm) was studied under static conditions at a solution/sorbent module, which equals 400, and at a room temperature of 20±2⁰C. The concentration of Rhenium С_Re varied within the range of 0.102-1.024 g/L. The acidity of solutions varied within the range of pH 1.2 ÷ 6.2 adding 0.1 N solutions H₂SO₄ or NaOH. The duration of contact between the sorbent and the NH₄ReO₄ solution was within the range of fifteen (15) minutes to 168 hours (or seven days). NH₄ReO₄salt of “chemically pure” quality was used for the preparation of model solutions.

The sorption capacity (SC) was calculated based on the difference between the initial density and the equilibrium density of the solutions. Such density was determined through classical polarography at 0.5 M NH₄Cl background upon the recovery waves Re⁷⁺ (Е_1/2 = −0.50 V).

Polarograms were filmed with a universal polarograph PU-1 in a thermostatic cell at a temperature of 25±0.5⁰C using a mercury dropping electrode. Oxygen was removed from the solutions under analysis by blowing argon for five (5) minutes. A saturated calomel electrode served as a reference electrode.

RESULTS AND DISCUSSION:

The sorption of perrhenate ions by redox-polymer based on PEI-CA was studied given such factors as concentration and pH of NH₄ReO₄ solutions; the duration of their contact with the ion exchanger is shown on Fig. 3-6. Fig 3 shows the isotherm of sorption of ReO_-4 ions by PEI-CA redox-polymer. As can be seen, with an increase in the concentration of Re in NH₄ ReO₄ solutions, the SC increases and reaches 3.5-4.2 mg/g when they are removed from a solution containing 1.02 g/L of Rhenium.

Fig. 3 Isotherm of sorption of ReO^-₄ ions by PEI-CA redox-polymer (contact time 7 days).

The rate of recovery of perrhenate ions by PEI-CA redox-polymer within the range of concentrations 0.1-0.7 g/L of Rhenium remains virtually constant and amounts to 92% (Fig. 4). Where the content of Rhenium is 1.02 g/L (pH=6.2), the rate of recovery drops slightly and amounts to 86%.

Fig. 4 Dependence of the rate of recovery of perrhenate ions by PEI-CA redox-polymer on the concentration of NH₄ReO₄solutions (contact time 7 days).

The research into the impact of the acidity of NH₄ReO₄solution on the sorption properties of PEI-CA showed that the SC values within the range of pH 1.2-5.1 change from 349.2 mg/g to 368.4 mg/g (Fig. 5). The maximum rate of recovery (98.1%) is observed at pH 5.1.

Fig. 5 Dependence of the sorption of ReO^-₄ ions by PEI-CA redox-polymer on the acidity of NH₄ReO₄solution (C=0.94 g/L; contact time 7 days).

Figure 6 shows the dependence SC of PEI-CA redox-polymer on the time of contact with NH₄ReO₄ solution (С_Re=0.94 g/L; pH 5.1). As can be seen from the Figure, the equilibrium condition is reached within 3 hours. For the first fifteen minutes, 86% of perrhenate ions is recovered.

Fig. 6 Dependence of SC on the duration of sorption of perrhenate ions from NH₄ReO₄solutions by PEI-CA redox-polymer (С_Re= 0.94 g/L, pH=5.1).

When Rhenium is absorbed from sulfuric acid solutions by active coal, the rate of recovery does not exceed 65% [5]. The exchange capacity of Rhenium, when it is absorbed by industrial anionites AN-21 from a solution containing 0.93 g/L of Rhenium, reaches 1.29 mg-eq/g (in terms of 343 mg/g) [6, 7]. Balance is reached within 45 hours.

The redox-polymer that we synthesized showed higher sorption characteristics than those of known industrial adsorbents. It has a higher exchange capacity which allows considering it as a promising element in the processes of concentration and recovery of Rhenium from waste water produced by various production plants.

REFERENCES:

1. Snurnikov AP. Kompleksnoe ispol'zovanie syr'ja v cvetnoj metallurgii. M.: Metallurgija. 1977: 272 (In Russian).

2. Abisheva ZS, Zagorodnjaja AN, Ospanov NA i dr. Issledovanie sorbcii renija iz proizvodstvennyh rastvorov promyvnoj sernoj kisloty Balhashskogo medeplavil'nogo zavoda na anionite A170. Cvetnye metally. 7; 2012: 57-61 (In Russian).

3. Zagorodnyaya AN, Abisheva ZS, Sharipova AS aa. Sorption of rhenium and uranium by strong base anion exchange resin from solutions with different anion compositions. Hydrometallurgy. 131/132; 2013: 127–132.

4. Lebedev KB, Kazancev EI, Rozmanov V.M. i dr. Ionity v cvetnoj metallurgii. M.: Metallurgija. 1975: 352 (In Russian).

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6. Abisheva ZS, Zagorodnjaja AN, Sadykanova S.Je. i dr. Vlijanie soderzhanija DVB v anionite AN-21 i krupnosti ego zeren na sorbciju renija i urana iz individual'nyh rastvorov i rastvorov ih sovmestnogo prisutstvija. Kompleksnoe ispol'zovanie mineral'nogo syr'ja. 4; 2011: 16-23 (In Russian).

7. Zagorodnjaja AN, Lebedev KB. Vlijanie koncentracii i vneshnego rastvora, temperatury i diametra zerna anionitom AN-21h16 na kinetiku sorbcii renija. Trudy Kazmehanobra. Alma-Ata. 3; 1970: 101-112 (In Russian).

Received on 09.01.2017 Modified on 27.01.2017

Asian J. Research Chem. 2017; 10(1):.41-44

DOI: 10.5958/0974-4150.2017.00008.6