RARE METALS Vol. 28, No. 3, Jun 2009, p. 209 DOI: 10.1007/s12598-009-0041-3
Solvent extraction of vanadium from sulfuric acid solution WANG Mingyu, ZHANG Guiqing, WANG Xuewen, and ZHANG Jialiang School of Metallurgical Science and Engineering, Central South University, Changsha 410083, China Received 6 May 2008; received in revised form 21 October 2008; accepted 12 November 2008
Abstract The behaviour of vanadium(V) extracted from sulfuric acid solution was investigated using Cyanex 923 as an extractant. The effects of the concentration of Cyanex 923 and the pH of the solution were studied. The extraction of vanadium(V) increases with the increase of Cyanex 923 concentration and shaking time. Cyanex 923 can extract vanadium(V) from sulfuric acid solution at low pH conditions, and the best pH conditions for extraction of vanadium(V) are at pH 1.0-2.0. The species extracted into the organic phase is VO2HSO4 with one molecule of Cyanex 923. Equilibrium studies were used to assess the extraction efficiency of vanadium(V) recovery from the sulfuric acid solution. Keywords: solvent extraction; vanadium(V); Cyanex 923; sulfuric acid solution
1. Introduction There are many well-established applications of vanadium: as an alloying element in steel and iron, as an additive to titanium alloys, and as catalysts (for the chemical and polymer industries). The principal commercial use of vanadium is as an alloying element in steel and cast iron. Vanadium consumption in the iron and steel industry represents about 85% of the vanadium-bearing products produced worldwide [1]. With the ceaseless exploitation of resources in the world, high grade ore is exhausted day by day, primary sources are presently insufficient to supply demand, and low grade ore is being increasingly exploited. As a result, a mass of vanadium bearing dilute solution is produced. To extract vanadium from the dilute solution, the solvent extraction technique has attracted increasing attention. Zeng et al. [2-3] studied the extraction mechanism of vanadium(IV) from a sulfuric acid medium by primary amine N1923. Liu et al. [4] studied the extraction process of vanadium(IV) by P538. Shen et al. [5] used P507 to extract vanadium(IV). Using P204 (D2EHPA) to extract vanadium was also studied in detail [6-8]. Lozano and Godinez [9] studied the process of
vanadium solvent extraction from a sulphate solution by Primene 81R and Alamine 336. Navarro et al. [10] studied solvent extraction using Aliquat 336. Most of the aforementioned studies have mainly been aimed at the extraction of vanadium(IV) and vanadium(V) protonated polyanions, and the study of extraction of vanadium(V) under strong acid conditions has not been sufficient. The purpose of the present work is to study the behavior of Cyanex 923 for the extraction of vanadium(V) in a sulfuric acid medium to obtain a more economic and effective extraction reagent.
2. Experimental 2.1. Reagents and solutions A vanadium aqueous solution was prepared by leaching no-salt-roasted stone coal with 0.6 vol.% sulfuric acid, and the main ingredients of the vanadiferous leaching solution are given in Table 1. Cyanex 923 (TRPO), supplied by Cytec, Canada, was used without further purification. Its composition and properties have been described elsewhere [11]. As diluent of the organic phase, sulfonated kerosene was used during the process. All other chemicals used were of (g⋅L−1)
Table 1. Main ingredients of the vanadiferous leaching solution V2O5
Mg
Al
Fe
Si
K
Ca
Na
Zn
Ni
2.20
0.018
0.045
0.003
0.083
0.065
0.21
0.16
0.11
0.003
Corresponding author: WANG Mingyu
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RARE METALS, Vol. 28, No. 3, Jun 2009
analytical reagent grade. 2.2. Experimental procedure Vanadium extractions were carried out by mechanical shaking in separatory funnels at room temperature for the time necessary to achieve equilibrium. After phase separation, the concentration of vanadium left in the aqueous phase was analyzed by ammonium ferrous sulfate titration. The concentration of vanadium in the organic phase was computed by material balance. The extraction yield R was taken as the ratio of the content of vanadium in the organic phase to that present in the raw vanadium aqueous solution. Equilibrium pH was adjusted by the addition of 2 mol/L NaOH.
cient factor. Organic phases ranged between 10 vol.% and 70 vol.% of Cyanex 923 using sulfonated kerosene as diluent. The results of the linear regression shows a slope of 1.14 (with r2 = 0.9917), indicating the ratio of the extractant to the metal species at this pH value.
3. Results and discussion 3.1. Influence of pH value The extraction yield of vanadium (R) from the leaching solution with organic phases made up of Cyanex 923 (60 vol.%) and kerosene (40 vol.%) using an organic/aqueous (O/A) phase ratio of 1:2 is shown in Fig. 1. The shaking time used in these experiments was 10 min.
Fig. 2. Effect of Cyanex 923 concentration on vanadium(V) extraction.
In acidic media (pH between 0 and 3), the major species is the pervanadyl ion VO 2+ . According to Rakib and Durand [12], vanadium(V) mainly exists in the form of VO 2SO 4− in the sulphate medium. Based on the extraction equilibrium of titanium(IV) with Cyanex 923 (TRPO) [13], the extraction equilibrium of vanadium(V) with Cyanex 923 (TRPO) is given by the following expression: VO 2SO 4− + H+ + xTRPOorg ⇔ VO2HSO4 (TRPOorg)x
(1)
The slope obtained from the linear regression shown in Fig. 2 ensures that the ratio of Cyanex 923 (TRPO) to vanadium(V) is around 1, which confirms x = 1. The extraction equilibrium constant Kext is expressed as [VO 2 HSO 4 TRPO] (2) K ext = [VO 2SO 4− ][H + ][TRPO] Fig. 1. Effect of pH on the extraction yield of V(V).
The effect of pH on vanadium extraction yield is not obvious in pH range of 0 to 1.0, and the vanadium extraction yield is about 70%. With an increase in pH, the vanadium extraction yield obviously increases and shows an optimum range (pH between 1.0 and 2.0). When the pH values are beyond 2.0, the vanadium extraction yield decreases sharply. 3.2. Effect of extraction concentration The effect of Cyanex 923 (TRPO) concentration on vanadium(V) extraction has been studied at constant vanadium concentration, and the results are shown in Fig. 2. The extraction of vanadium(V) increases with an increase in extractant concentration. The graph of lg E versus lg [TRPO] shows a linear relationship. Here, E is the extraction coeffi-
3.3. Effect of shaking time Fig. 3 shows the effect of shaking time on the extraction yield of vanadium(V). The organic phases were made up of Cyanex 923 (60 vol.%) and kerosene (40 vol.%). It is clearly shown that the vanadium extraction yield increases with an increase in shaking time, and after about 10 min, the increase trend in vanadium extraction yield is no longer obvious with prolonging shaking time. 3.4. Extraction isotherms Equilibrium curves at room temperature at pH 1.5 are shown in Fig. 4. Data were obtained by shaking volumes of organic and aqueous phases at O/A ratios ranging from 1/1 to 1/4 and initial concentration of vanadium in aqueous liquor at 2.08 g/L. It can be seen from the shape of the vana-
Wang M.Y. et al., Solvent extraction of vanadium from sulfuric acid solution
dium(V) extraction isotherm that Cyanex 923 diluted with kerosene is a low efficiency system for the extraction of vanadium(V). However, Cyanex 923 can extract vanadium from the low pH sulfuric acid solution.
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Foundation of Central South University (No. 76112037) and the Postdoctoral Science Foundation of Central South University.
References
Fig. 3. Effect of shaking time on the extraction yield of vanadium(V).
Fig. 4. Extraction isotherm for Cyanex 923 (40 vol.%).
4. Conclusions The results obtained with Cyanex 923 dissolved in kerosene indicate that this reagent can be used to extract vanadium(V) from sulfuric acid media at low acid pH values. Experimental data obtained confirms that the extracted species for vanadium at pH 1.5 is one molecule of Cyanex 923 with VO2HSO4 extracted into the organic phase. Extraction isotherms confirm low loading capacity for Cyanex 923. This fact and the broad pH range, especially low pH conditions, lead this reagent to be used economically only for the extraction of vanadium(V) from high acid conditions.
Acknowledgements This work was financially supported by the Science
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