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Ind. Eng. Chem. Res. 2002, 41, 2948-2952
SEPARATIONS Recovery of Chromium and Nickel from Industrial Waste Bina Gupta,* Akash Deep, and Shiv N. Tandon Department of Chemistry, Indian Institute of Technology (IIT), Roorkee, 247667 Uttaranchal, India
The paper embodies an analytical approach to the recovery of chromium and nickel from different kinds of industrial wastes, namely, a Cr(III)-Ni(II) plating sludge, a Ni(II) plating mug, and a tannery effluent. The proposed methods employ precipitation, solvent extraction, and electrowinning steps. A toluene solution of Cyanex 923 is used as an extractant for the separation of Cr(III) and Ni(II) from some commonly associated metal ions such as Al(III), Fe(III), Mn(II), Co(II), Cu(II), Zn(II), and Pb(II). The experiments conducted up to 10 cycles indicate a negligible loss in extraction efficiency. The electrodeposition of Cr(III) and Ni(II) offers average cathode efficiencies around 40 and 75%, respectively. The recovered metals are 99.9% pure. The proposed procedures will be helpful in saving the wastage of metals and protecting the environment from metal pollution. 1. Introduction Chromium and nickel find extensive applications in the electroplating industry. Chromium salts are also widely used in the tanning sector while nickel compounds are important as catalysts. In India a large-scale industrial utilization of these metals is resulting in their ponderous discharge in the open environment. It is not only damaging the environment but also leading to a substantial monetary loss. Solvent extraction-electrowinning is a well-established technique for the recovery of chromium and nickel from complex matrixes. However, the majority of extractants such as oximes,1 high molecular weight amines,2 and alkylphosphorus compounds such as mono(2-ethylhexyl)phosphoric acid,3 bis(2-ethylhexyl)phosphoric acid,4 and tri-n-octylphosphine oxide5 used for the extraction of these metal ions generally suffer from the drawback of poor selectivity and or extractant loss. Cyanex 301 [bis(2,4,4 trimethylpentyl)dithiophosphinic acid] has been reported for the recovery of Cr(III)6 and Ni(II)7 from some industrial wastes. Cyanex 301 is associated with a foul smell even in dilute solutions. Also, the removal of copper from the extractant phase is difficult, and at times a slow phase separation is experienced. Lately, Cyanex 923 (a mixture of four trialkylphosphine oxides, namely, R3PdO, R2R′PdO, RR2′PdO, and R3′PdO, where R is an n-octyl chain and R′ is an n-hexyl chain) has been reported as an extractant free from most of the above shortcomings. With this view in mind, it is proposed to develop Cyanex 923 for the recovery of chromium and nickel from industrial wastes. As a first step the partition data in Cyanex 923 has been used for attaining separations of chromium and nickel from metal ions commonly associated with them in some of the industrial wastes. The stability and recycling capac* Corresponding author. E-mail:
[email protected]. Fax: 091-1332-73560. Phone: 091-1332-72537.
ity of the extractant is assessed. The developed extraction steps have been employed for the recovery of pure chromium and nickel from a Cr(III)-Ni(II) electroplating sludge, a Ni(II) plating mug, and a tannery effluent. The purified solutions obtained after extraction are used in electrolytic baths for the recovery of metals. 2. Experimental Section 2.1. Reagents and Materials. Cyanex 923 was received from Cytec Inc. (Canada) and used as such. All of the chemicals were analytical-grade reagents from E. Merck/T. Baker (India). The metal solutions were prepared by dissolving their suitable salts in a known volume of double-distilled water containing a minimum concentration of the corresponding mineral acid. These solutions were standardized by the usual complexometric titrations. The industrial waste samples, namely, a Cr(III)Ni(II) electroplating sludge, a Ni(II) plating mug, and a tannery effluent, were collected from different industrial units situated in Uttar Pradesh (India). The Cr(III)-Ni(II) electroplating sludge is the waste of a large size plating shop involved in coating the metal bodies of flashlight batteries. Prior to discharge, Cr(VI) used for plating is reduced to Cr(III) by using sodium metabisulfite. The combined waste contains an effluent from Cr and Ni plating units and washing and deelectroplating operations. The effluent is converted into a sludge by precipitation with sodium hydroxide using polyelectrolytes. The typical composition of this sludge (dried at 110 °C) is 21% Cr, 10% Ni, 4.2% Cu, 0.83% Fe, 0.52% Pb, 0.98% Zn, 0.24% Al, and 0.13% Mn. The nickel plating mug is the mud left in the nickel plating bath after prolonged operations. The mug (dried at 110 °C) contains 34% Ni, 4.1% Fe, 1.2% Al, 0.34% Cu, 0.29% Pb, 0.23% Mn, and 0.12% Zn. The tannery effluent is a composite waste from activities such as pickling and chrome tanning. The concentration (mg L-1) of metal ions in the effluent is as follows: Cr, 550; Fe, 32; Cu, 7.9; Pb, 4.3; Mn, 2.7; Ni, 0.21; Al, 0.12.
10.1021/ie010934b CCC: $22.00 © 2002 American Chemical Society Published on Web 05/17/2002
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2.2. Procedure. 2.2.1. Dissolution of Cr(III)Ni(II) Electroplating Sludge and Ni Plating Mug. About 250 g of a Cr(III)-Ni(II) electroplating sludge or a Ni plating mug was repeatedly leached with 5 × 100 mL of 6 mol L-1 H2SO4. The solution was decanted, and the final volume was 500 mL (6 mol L-1 H2SO4). The solutions of plating sludge and mug were marked as AI and BI, respectively. To get a representative value, five different samples of each waste were processed by the proposed methods. 2.2.2. Liquid-Liquid Extraction. Organic and aqueous solutions having an O/A ratio of 1:1 (v/v) were shaken at room temperature (25 ( 3 °C) for 5 min to ensure complete equilibration. The two layers were separated, and the metal concentration in the aqueous phase was assayed by an atomic absorption spectrometer (GBC Avanta, Australia) or an inductively coupled plasma-atomic emission spectrometer (Labtum Ltd. 8440, Australia). The experimental conditions of different studies are mentioned along with the corresponding data. 2.2.3. Electrodeposition Studies. The chromium(III) electrodeposition cell consists of a rectangular Pyrex glass trough (500 mL) with a sintered crucible (50 mL; G4 disk of 1.2 mm thickness) fixed to one of its sides. The crucible constitutes the anodic compartment, and it was filled with dilute sulfuric acid. The anode was a silver cylinder of surface area ) 20 cm2. The remaining part of the trough (cathodic compartment) was filled with a mixture of chromium(III) sulfate and sodium sulfate in dilute sulfuric acid, and a circular copper disk of surface area ) about 5 cm2 was employed as the cathode. The pH of both the anodic and cathodic solutions was maintained at 1.4-1.5. The nickel(II) deposition apparatus employs a lead anode and a copper cathode (dimension 12 × 8 cm). These were immersed in a 500 mL solution of nickel sulfate and sodium sulfate (pH 2.6-2.8). The power supply in the above circuits was regulated by a dc rectifier (0-10 V and 10 A) properly assorted with an ammeter and a voltmeter.
Figure 1. Extraction behavior of metal ions (1.0 × 10-3 mol L-1) from 1 to 8.0 mol L-1 H2SO4 using 0.5 mol L-1 Cyanex 923 (toluene).
3. Results and Discussions
Figure 2. Extraction behavior of metal ions (1.0 × 10-3 mol L-1) from 1 to 8.0 mol L-1 HCl using 0.5 mol L-1 Cyanex 923 (toluene).
3.1. Extraction Studies. 3.1.1. Extraction Behavior of Metal Ions (1.0 × 10-3 mol L-1) in a 0.50 mol L-1 Toluene Solution of Cyanex 923. Figures 1 and 2 depict the data on the extraction of Cr(III) and Ni(II) along with some commonly associated metal ions such as Al(III), Fe(III), Mn(II), Co(II), Cu(II), Zn(II), and Pb(II) from 1 to 8.0 mol L-1 H2SO4-HCl media. The extraction of Cr(III) and Ni(II) is negligible (
