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Extraction of acid and iron values from sulphate waste pickle liquor of a steel industry by solvent extraction route
Hydrometallurgy 88 (2007) 58 – 66 www.elsevier.com/locate/hydromet
Extraction of acid and iron values from sulphate waste pickle liquor of a steel industry by solvent extraction route Archana Agrawal a,⁎, S. Kumari a , B.C. Ray b , K.K. Sahu a a
Metal Extraction and Forming Division, National Metallurgical Laboratory, Jamshedpur-831007, India b Department of chemistry, Jadhavpur University, Kolkata, India Received 28 February 2007; received in revised form 2 April 2007; accepted 2 April 2007 Available online 13 April 2007
Abstract The extraction of sulphuric acid from the actual solutions generated during the process of pickling of steel from a local tube company dealing with the processing of iron and steel tubes using Alamine 336 has been studied in detail. Various parameters were optimised for the maximum extraction of acid such as concentration of organic extractant, time for equilibration, O/A ratio, acid concentration in the feed, temperature for extraction was varied from 30 to 60 °C. Stripping of loaded acid was done with distilled water at 60 °C. Stripping parameters studied were, temperature and time effect on equilibration, O/A ratio, multiple contact of the same strippant with fresh loaded organic. The effects of the numbers of extraction and stripping stages on the extraction and stripping of sulphuric acid recovery are discussed. After the extraction of acid from WPL, iron values in the raffinate were extracted with a binary solvent mixture consisting of MIBK and D2EHPA which shows a synergistic effect on iron extraction. © 2007 Elsevier B.V. All rights reserved. Keywords: Sulphuric acid extraction; Alamine 336; Iron extraction; Methylisobutyl ketone and Di-2-ethylhexylphosphoric acid extractant; Synergism; Waste pickle liquor
1. Introduction Pickle liquors from the primary metal and metal finishing industries comprise a major source of toxic industrial wastes. Pickling is a method used in sheet and wire mills or metal fabricating plants to remove oxide and scale from the surface of the metal sheet, strip, wire, or parts before another operation, such as galvanizing, electroplating, or painting, by passing the metal products through an acid bath. Steels are usually pickled in 15– 20% HCL or H2SO4 at temperature up to 100 °C. During pickling the scale oxides dissolve to give iron(II) ⁎ Corresponding author. E-mail address: [email protected] (A. Agrawal). 0304-386X/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.hydromet.2007.04.001
sulphates/chloride and repeated pickling in the same liquor lead to the generation of pickle liquor containing mineral acids along with various metals such as iron, Zn, Cr, Ni etc depending upon the type of steel treated. This pickle liquor then becomes unacceptable for further use and is bled off as spent pickle liquor. Due to the corrosive nature and presence of the high amount of dissolved iron (II) this WPL cannot be disposed off without pretreatment. In industrial processes, such spent pickling solutions are usually treated with lime to neutralise acid and the sludge generated is dumped. Alternatively SPL is evaporated and cooled to 5 °C, and then to 0 °C to crystallize iron(II) sulphate as its heptahydrate. To recover and reuse the acid and the dissolved iron(II) in the spent pickling solutions as valuable materials and to
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obtain an environmentally benign effluent, an alternative method for treating spent pickling solutions is essentially required. Studies have been reported on the use of Tri-butyl phosphate (TBP) for the extraction of acid (Petkovic et al., 1992; Ritcey and Ashbrook, 1984a,b; Cox, 1992; Eyal et al., 1993). The extraction of mineral acids by Cyanex 923 (Alguacil and Lopaz, 1996) was also investigated and reported. This study deals with the extraction of acid using Alamine 336 a tertiary amine. Similarly selective and quantitative separation of iron (III) from the waste pickle liquor can be effected through solvent extraction. A considerable amount of work has been reported (Demopoulos and Gefvert, 1984; Alguacil and Amer, 1986; Islam and Biswis, 1979; Chen et al., 1992; Sekine et al., 1976; Roddy et al., 1971; Alguacil et al., 1987; Sytefanakis and Monhemius, 1885) either on the removal of iron(III) as an impurity from leach solution or its extraction from dilute solutions. No systematic work has been reported on the solvent extraction of iron(III) from the concentrated sulphate solutions. Several solvents such as methyl isobutyl ketone (MIBK) (Chiba and Kimura, 1989), tri-n-butyl phosphate (TBP), (Majumdar and De, 1960; Roddy et al., 1971), di(2ethylhexyl) phosphoric acid (D2EHPA), (Sato et al., 1985; Roddy et al., 1971; Hirato et al., 1992; Kimura et al., 1984; Agatzini et al., 1986) and amines (Alguacil and Amer, 1986; Alguacil et al., 1987; Sahu and Das, 2000; Sahu and Das, 1997), are used for extracting iron (III). Metal recovery from liquid effluents has been studied by Andersson and Reinhardt (1983), Haines et al. (1973) and Tunley et al. (1976) mentioned the use of ion exchange resins to separate Fe(II) and Zn followed by Zn extraction by D2EHPA. Good and Bryan (1960, 1961) have extensively studied the extraction of some base metals including Fe(II) and Fe(III) in sulphate and chloride medium. Sanad et al. (1982, 1992) have studied iron extraction from chloride and bromide medium using tri-butyl phosphate. But these systems are found to have some disadvantages such as low extraction and difficult stripping, hence binary solvent mixtures have been tried. Though the literature on binary extraction of iron is very less, an attempt has been made to develop a suitable synergistic extraction process with mixed extractants that achieves improved iron(III) extraction from a concentrated iron solution in a sulphate medium.
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2. Materials 2.1. Sample collection, solutions and reagents 10 L of sulphate waste pickle liquor was collected from Tata Tubes Ltd, Jamshedpur. The chemical analysis of this waste is given in Table 1. The organic reagent used for the recovery of acid and iron in this study was Alamine 336, D2EHPA, MIBK. Alamine 336 (R3N) was kindly supplied by Henkel and used as extractant without further purification. Alamine 336 is a mixture of saturated and straight chain trialkylamines with carbon chains C8 and C10, in which the proportion of the carbon chain C8 is about 2 to 1. It is a pale yellow liquid practically insoluble in water (b 5 ppm) with an average molecular weight of 392 g/mol, a density of 0.81 g/cm3, and a viscosity of 11 mPas (30 °C). Other solvents used as diluent and phase modifier are: distilled kerosene, MIBK, TBP, Benzene, Hexane. Chemical analysis of the WPL, acid after extraction, iron and zinc in the solutions were done volumetrically by standard methods as mentioned in Vogel (1989). Mass balance gives the amount of acid extracted by the solvent. Trace metal analysis was done by atomic absorption spectro-photometer (Thermo SOLAAR S-2). 2.2. Experimental Acid extraction from waste pickle liquor (WPL) of the steel tubes industry was done with 35% Alamine 336 (0.723 M) in kerosene. 10% of isodecanol was used as phase modifier. The loading capacity of the solvent for WPL containing 91.9 g/L was performed at 30 °C, 45 °C and 60 °C by multiple contact method at O/A ratio of 1:1. The organic and aqueous solutions were contacted for a period of 5 min to ensure complete extraction in a separatory funnel. The mixture was then allowed to separate into organic and aqueous layers and the acid loaded organic was separated from the aqueous phase with residual acid. The same organic was shaken again with the fresh aqueous feed till the organic is completely loaded with the acid, which is indicated by the chemical analysis of the aqueous phase after each shaking. Various other parameters such as mixing time, O/A ratio, mixing
Table 1 Chemical analysis of the WPL of Tata Tubes Ltd, Jamshedpur Constituents
H2SO4
Fe(T)
Fe(II)
Zn
g/L Composition
91.88
Cu
Co
Ni
Mo
Mn
Cr
5.8
9.8
1
162
6.8
ppm 78.1
73.75
5.15
2.7
60
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Fig. 1. Effect of phase modifiers on % extraction of acid from WPL 35% Alamine 336 [O/A: 1/1, time: 5 min, temp: 30 °C, [H2SO4] wpl: 91.9 g/L].
temperature, aqueous and organic concentration etc. were studied to optimise the amicable for acid extraction. After the extraction of acid by the organic phase stripping of the loaded acid was performed to recover the pure and concentrated acid and iron solution which could be recycled to the pickling bath and iron could be used to prepare pure iron oxide.
Fig. 3. Effect of Alamine concentration on the extraction of acid from WPL. O/A: 1/1, time: 5 min, temp: 30 °C, [H2SO4] wpl: 91.9 g/L.
With the use of nonyl phenol, acid extraction not only decreases (Fig. 1) from 50.6% to 38.0%, but also phase separation become slower. Therefore, 10% (v/v) isodecanol was used as phase modifier with kerosene as diluent in the further study. 3.2. Rate of extraction of acid with Alamine 336
3. Results and discussion Sulphuric acid extraction from waste sulphate pickle liquor containing 91.9 g/L acid and 78.1 g/L Fe(T) along with traces of other metals was performed with different concentrations of Alamine 336.
In order to observe kinetics of acid extraction, both aqueous and organic phases were contacted for different time intervals (Fig. 2) up to 8 min. Beyond 2 min of equilibration percentage extraction remains the same and therefore shaking time in all the experiments was maintained at 5 min to ensure complete extraction.
3.1. Effect of phase modifier 3.3. Effect of Alamine concentration on acid extraction A few preliminary experiments were done with different phase modifiers to examine their effect on acid extraction keeping all other parameters constant. It was observed that though percentage acid extraction remains the same with tri-n-butyl phosphate and isodecanol, but phase separation time was much better in the latter case.
The result on extraction of acid with different Alamine concentrations is shown in Fig. 3. Solvent concentration was varied from 10% to 35% (v/v) in kerosene using 10% isodecanol as phase modifier. An increase in the concentration of Alamine resulted in an increase in the acid
Fig. 2. Effect of time on acid extraction from WPL with 35% Alamine 336. ([H2SO4: 91.9 g/L], O/A:1, temp: 30 °C, no. of contact: 1).
Fig. 4. Plot of log D vs log Alamine 336 concentration O/A1, temp: 30 °C, [H2SO4] aq = 91.9 g/L.
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Fig. 7. Effect of O/A on the extraction of acid by 35% Alamine 336. H2SO4: 91.9 g/L], temp: 30 °C, no. of contact: 1. Fig. 5. Extraction of acid in different contacts and Alamine 336 concentration on the extraction of acid from WPL. [H2SO4: 91.9 g/L], O/A:1, temp: 30 °C.
extraction. Thus extraction increased from 17 to 37 g/L with the increase in solvent concentration from 10 to 35% with O/A phase ratio of 1 in a single contact. Further increase in solvent concentration creates phase separation problem, therefore, 35% Alamine(0.723 M) was used for optimisation experiment. Plot of log D vs log Alamine 336 concentration (Fig. 4) gives a slope of 0.94 indicating the requirement of 1 mol of Alamine for 1 mol of acid. 3.4. Saturation loading capacity of different concentrations of Alamine for multiple contacts Saturation loading capacity of different concentrations of Alamine was determined by using multiple contacts (Fig. 5). With the aqueous acid concentration of 91.9 g/L, saturation loading was achieved in 4 contacts
Fig. 6. Effect of initial sulfuric acid concentration in WPL on the loading of acid to 35% Alamine 336 extraction.
of the same organic solvent with the fresh aqueous phase maintaining O/A of 1. Thus in the 4th contact the loaded acid concentration increases from 40.5 g/L to 80.8 g/L with the increase in the Alamine 336 concentration from 10% to 35%. In terms of percentage about 88.3% of acid is taken up by the 35% Alamine as compared to 44.1% with 10% Alamine. 3.5. Effect of initial sulphuric acid concentration in the waste pickle liquor for the loading of acid on 35% Alamine 336 The effect of initial sulphuric acid concentration in the waste pickle liquor for the loading of acid on to 35% Alamine 336 is represented in Fig. 6. It was found that with the increase in acid concentration from 45 to 200 g/L, loading increases from 26 to 41 g/L in one contact with the O/A phase ratio of 1. A linear plot was obtained up to 120 g/L of acid indicating that the distribution ratio and species do not change with the increase in acid concentration of the said range. Beyond this the extractant
Fig. 8. Mc Cabe Thiele plot for sulphuric acid extraction with Alamine 336. [H2SO4] aq: 91.9 g/L.
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Fig. 9. Stripping of acid from the loaded organic of different concentration with fresh distilled water in different contacts.
Fig. 11. Effect of O/A on stripping of loaded acid from 35% Alamine 336, organic feed: loaded 35% Alamine 336 (81.98 g/L H2SO4), stripping agent: distilled water, time: 5 min, temp: 45 °C.
becomes saturated and the loading plateaus. It is concluded that 35% Alamine 336 can hold up to 40 g/L H2SO4, However, the percentage extraction decreases from 60 to 20% with the increase in initial acid concentration. The saturated loading capacity determined in different contacts as shown in Fig. 5 was 80.8 g/L.
requirement of 3 stages for the maximum extraction of acid at O/A ratio of 2 from an aqueous acid concentration of 91.9 g/L with 35% Alamine removing about 90% of the acid. The acid left in the aqueous feed along with the iron can be neutralised during the synthesis of iron oxide.
3.6. Effect of variation in organic to aqueous phase ratios on percent acid extraction
3.7. Stripping of acid from the loaded Alamine 336 in multiple contacts
Variation in organic to aqueous phase ratios shows that the percentage acid extraction increases from 11 to 88% with the increase in O/A ratio from 0.2 to 5. Thus at O/A of 5 the organic phase contains 81.1 g/L of acid leaving about 10.8 g/L in the aqueous phase (Fig. 7). The McCabe Thiele plot represented in Fig. 8 shows the
Saturation loading of 35% Alamine was done by a multiple contact of the waste pickle liquor with acid concentration of 91.9 g/L. The concentration of acid in the loaded solvent (35% Alamine 336) was found to be 82 g/L. Stripping of acid from the above loaded solvent was performed with hot distilled water at 60 °C so that it could be recycled back to the system. It was found that 25% of acid is stripped in the 1st contact at O/A ratio of 1:1 and in the fourth contact it reached only up to 40.6%. Beyond that acid stripping was found to be difficult (Fig. 9).
Fig. 10. Stripping of loaded organic by multiple contact of aqueous feed with fresh loaded organic each time, organic feed: loaded 35% Alamine 336 (81.9 g/L H2SO4), aqueous feed: distilled water, time: 5 min, temp: 30 °C, O:A: 1.
Fig. 12. Rate of stripping of loaded acid by DW, organic feed: loaded 35% Alamine 336 (81.9 g/L H2SO4), temp: 45 °C.
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Fig. 13. Effect of temperature on the stripping of acid, organic feed: loaded 35% Alamine 336 (81.9 g/L H2SO4), time: 5 min, O:A: 1.
3.8. Stripping of loaded acid with the multiple contact of fresh loaded organic and same aqueous feed Since the concentration of acid obtained after stripping was not suitable for recycling, the same aqueous feed was contacted with the fresh loaded organic and the final strip solution obtained after 5 contacts contained 65.9% concentrated acid (Fig. 10). However, out of the 91.9 g/L of acid in the WPL, only 60.7 g/L of acid was recovered.
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Fig. 15. Effect of MIBK concentration with and without D2EHPA on the distribution coefficient (D) of Fe(III) in H2SO4 medium. [Fe]: 60.88 g/L, H2SO4: 53.9 g/L, time: 5 min, O:A: 2:1, temp: 30 °C.
is sufficient to strip maximum acid in one contact, hence the solutions were shaken for 3 min in each experiment. 3.11. Effect of temperature on stripping of loaded acid
Effect of time on stripping of loaded acid by hot distilled water was also studied. Fig. 12 shows that 3 min
Fig. 13 shows the effect of temperature on stripping of loaded acid and it was found that 28% of acid was stripped at 60 °C as compared to 25% at 30 °C. Hence, all the stripping was done with hot distilled water at 60 °C. Since iron was in the reduced form in the WPL, the stripped acid was free of iron contamination and other impurities present in the WPL. After the maximum stripping of acid by distilled water, the solvent with the residual acid could be treated with the dilute alkaline solution to regenerate the solvent for recycling. Analysis of iron content shows that its extraction was negligible, probably ferrous iron as sulphate has very less affinity for Alamine 336. Thus iron extraction was tried with a mixed solvent system comprising of D2EHPA and MIBK. The acid free ferrous sulphate was oxidised to ferric form by treating it with the required amount of nitric acid and during oxidation the
Fig. 14. Effect of D2EHPA and MIBK on the distribution coefficient of Fe(III) extraction from H2SO4 medium. [Fe]: 60.88g/L, t:5 min, O/A 2:1, T 30 °C.
Fig. 16. Effect of D2EHPA concentration with and without MIBK on D values of Fe(III) extraction from H2SO4 medium. [Fe]: 60.88 g/L, time: 5 min, O/A 2:1, temp: 30 °C.
3.9. Effect of O/A variation on stripping of acid Thus, O/A variation was tried to get a concentrated acid in the strip solution. Fig. 11 shows that about 66.8 g/L of acid could be obtained at O/A ratio of five in a single contact. 3.10. Rate of stripping of loaded acid by hot distilled water
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Fig. 17. Comparison of D values for the Fe extraction in varying concentrations of D2EHPA + 40% MIBK and MIBK + 40% D2EHPA from H2SO4 medium. [Fe]: 60.88 g/L, time: 5 min, O/A 2:1, temp: 30 °C.
concentration falls from 78.2 g/L of Fe(total) to 60.9 g/L of Fe(total). However it is always possible to maintain almost similar iron concentration. Studies were conducted with the oxidised solution for the extraction of iron by the aforesaid mixed solvent system. 3.12. Extraction of iron by a mixed solvent system Effect of D2EHPA and MIBK concentration individually on the distribution coefficient of Fe(III) extraction from the sulphate waste pickle liquor containing Fe: 60.9 g/L was studied at O/A 2:1, T 30 °C with a mixing time of 5 min. The raffinate was analysed for the remaining iron by volumetric titration with potassium dichromate in the presence of BDS as indicator. Fig. 14 shows a plot between solvent concentration vs D values for D2EHPA and MIBK. It was found that D2EHPA is more effective than MIBK for iron extraction with D values varying from 0.05 to 0.286 with the increase in solvent concentration from 20 to 40% and that for MIBK, D varies from 0.009 to 0.019 for the concentration variation from 20 to 40%. Therefore mixtures of these two solvents were tried to see the effect on iron extraction. Thus Fig. 15, a plot between solvent concentration vs D values in the single and mixed solvent shows that when MIBK alone was varied from
20% to 40% the D values varied from 9.0 × 10− 3 to 1.9 × 10− 2. When a fixed amount of D2EHPA was mixed with a varying amount of MIBK the values of D varied from 2.7 to 3.13. Similarly, by varying the D2EHPA concentration from 20 to 40% the D values were found to vary from 0.05 to 0.286 and in addition of a fixed amount of MIBK i.e. 40% to different concentration of D2EHPA (Fig. 16), values of D increase from 0.47 to 3.13. A comparison of D values of D2EHPA + 40% MIBK and MIBK + 40% D2EHPA as depicted in Fig. 17 shows that, iron extraction increases with the increase in concentration of MIBK at a constant concentration i.e. 40% D2EHPA and is more than the mixture of different concentration of D2EHPA at 40% MIBK. Thus with a mixture of 40% MIBK, 40% D2EHPA in kerosene a maximum amount of iron is loaded. This enhancement in extraction percentage is due to the synergistic effect of MIBK on D2EHPA by the formation of adduct. Synergism can be quantified by the synergistic coefficient (SC), which is defined as
DD2EHPAþMIBK Sc ¼ log DD2EHPA þ DMIBK
where DD2EHPA + MIBK is the distribution coefficient obtained with the mixture of D2EHPA and MIBK. The terms DD2EHPA and DMIBK are the distribution coefficients obtained for the individual extractants D2EHPA and MIBK, respectively. Synergism was observed at all mixed extractant compositions studied. Keeping the concentration of D2EHPA constant at 40%, it was observed that SC increased with the increase in concentration of MIBK from 20 to 40% (Table 2). Similarly a constant MIBK concentration of 40% SC value increased with the increase in D2EHPA concentration from 20 to 40%. However the increase in SC was more pronounced in the former case with the maximum synergistic coefficient values at the solvent mixture consisting of 40% each solvent. Since the basicity of MIBK
Table 2 Iron(III) distribution coefficient, D, with D2EHPA, MIBK, D2EHPA(40%) + MIBK(20 to 40%), MIBK(40%) + D2EHPA (20–40%), and synergistic coefficient value Solvent MIBK 40%
D2EHPA 40%
D2EHPA20% D2EHPA 30% D2EHPA 40% MIBK20% MIBK30% MIBK40%
DD2EHPA
DMIBK
DD2EHPA + DMIBK
D(D2EHPA + MIBK)
D
SC
0.048 0.106 0.286 0.286 0.286 0.286
0.019 0.019 0.019 0.009 0.014 0.019
0.067 0.125 0.305 0.295 0.299 0.305
0.473 0.934 3.13 2.71 2.9 3.13
0.406 0.81 2.83 2.42 2.60 2.83
0.85 0.88 1.01 0.96 0.99 1.01
Aqueous feed: [Fe]: 60.88 g/L, time: 5 min, O/A 2/1, temp: 30 °C.
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extraction in three counter-current stages at the A: O = 1:2 phase ratio. Although Alamine 336 is a good extractant for sulphuric acid, the acid could not be stripped completely from the loaded organic with water. After the extraction of acid the raffinate was oxidised and Fe(III) in the solution was then extracted with the appropriate mixture of D2EHPA and MIBK behaving as a binary extractant. MIBK was found to enhance the D value showing a synergetic effect. Acknowledgements Fig. 18. Stripping of loaded iron from 40% D2EHPA and 40% D2EHPA + 40% MIBK with different concentrations of HCl.
is low due to the weak donor properties of the oxygen in MIBK (Sanad et al., 2002), a number of organic molecules get attached loosely to the Fe(III) present in the mixture leading to an adduct formation with D2EHPA– Fe(III) complex. D and SC values for iron(III) are shown in Table 2. A comparison of SC values for D2EHPA (40%)–MIBK (20–40%) and MIBK (40%)– D2EHPA (20–40%) shows higher SC values for the former mixture. 3.13. Stripping of iron from the loaded organic Thus after the extraction of iron in a mixture of 40% D2EHPA and 40% MIBK the stripping was tried with different concentrations of HCl and the percentage of iron(III) stripped from loaded D2EHPA40% + MIBK40% was found to increase with the increasing initial HCl concentration up to 3.25 M after this concentration the stripping decreases(Fig. 18). Such a decrease may be due to the formation of chlorocomplex(es) of iron(III) with the HCl, which is easily re-extracted by MIBK. However stripping of loaded iron from 40% D2EHPA increases in the whole range of acid studied since there is no back extraction of any complex by this single solvent system. 4. Conclusions Solvent extraction of sulfuric acid from the actual waste pickle liquor from Tata tubes company Jamshedpur was carried out using Alamine 336. The extraction of H2SO4 increased with the increase of solvent concentration. The log D vs. log extractant plot was straight lines with slope values of 0.94 indicating that 1 mol of the extractant was involved with 1 mol of the extracted acid. For Alamine 336, the McCabe–Thiele construction indicated the possibility of about 90% H2SO4
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lurgical and Materials Transactions. B, Process Metallurgy and Materials Processing Science 28B (2), 181–189. Sahu, K.K., Das, R., 2000. Mixed solvent systems for the extraction and stripping of iron(III) from concentrated acid chloride solutions. Metallurgical and Materials Transactions. B, Process Metallurgy and Materials Processing Science 31B (6), 1169–1174. Sanad, W., Flex, H., Haggag, A., 1982. Kinetics of iron(III) chloride extraction with n-tributyl phosphate. Journal of Radioanalytical and Nuclear Chemistry, 75 (1–2), 121–128. Sanad, W., Flex, H., Marei, S.A., 1992. Kinetics of iron(III) bromide extraction with n-tributyl phosphate. Journal of Radioanalytical and Nuclear Chemistry, 157 (1), 185–192. Sanad, W.A., Tadros, N.A., Abdel-Fattah, A.A., 2002. Equilibrium and kinetics of Zn(II) bromide extraction with Amberlite LA-2 and methyl isobutyl ketone. Journal of Radioanalytical and Nuclear Chemistry 252 (1), 151–156. Sato, T., Nakamura, T., Ikeno, M., 1985. The extraction of iron(III) from aqueous acid solutions by di(2-ethylhexyl)phosphoric acid. Hydrometallurgy 15 (2), 209–217. Sekine, T., Horida, H., Zeniya, Y., 1976. Kinetic studies of solvent extraction of metal complexes VI. Equilibrium and rate of solvent extraction of iron(III) perchlorate with trioctylphosphine oxide in hexane. Journal of Inorganic & Nuclear Chemistry 38, 1347–1350. Sytefanakis, M.I., Monhemius, A.J., 1885. Determination of organic phase complexes formed on extraction of iron(III) from aluminium nitrate solutions with versatic 10. Hydrometallurgy 15 (1), 113–139. Tunley, T.H., Kohler, H., Sampson, T.D., 1976. Journal of the South African Institute of Mining & Metallurgy 77, 473. Vogel, A.I., 1989. A Textbook of Quantitative Chemical Analysis, 5th edn. ELBS Longman, UK, p. 376.
Extraction of acid and iron values from sulphate waste pickle liquor of a steel industry by solvent extraction route Archana Agrawal a,⁎, S. Kumari a , B.C. Ray b , K.K. Sahu a a
Metal Extraction and Forming Division, National Metallurgical Laboratory, Jamshedpur-831007, India b Department of chemistry, Jadhavpur University, Kolkata, India Received 28 February 2007; received in revised form 2 April 2007; accepted 2 April 2007 Available online 13 April 2007
Abstract The extraction of sulphuric acid from the actual solutions generated during the process of pickling of steel from a local tube company dealing with the processing of iron and steel tubes using Alamine 336 has been studied in detail. Various parameters were optimised for the maximum extraction of acid such as concentration of organic extractant, time for equilibration, O/A ratio, acid concentration in the feed, temperature for extraction was varied from 30 to 60 °C. Stripping of loaded acid was done with distilled water at 60 °C. Stripping parameters studied were, temperature and time effect on equilibration, O/A ratio, multiple contact of the same strippant with fresh loaded organic. The effects of the numbers of extraction and stripping stages on the extraction and stripping of sulphuric acid recovery are discussed. After the extraction of acid from WPL, iron values in the raffinate were extracted with a binary solvent mixture consisting of MIBK and D2EHPA which shows a synergistic effect on iron extraction. © 2007 Elsevier B.V. All rights reserved. Keywords: Sulphuric acid extraction; Alamine 336; Iron extraction; Methylisobutyl ketone and Di-2-ethylhexylphosphoric acid extractant; Synergism; Waste pickle liquor
1. Introduction Pickle liquors from the primary metal and metal finishing industries comprise a major source of toxic industrial wastes. Pickling is a method used in sheet and wire mills or metal fabricating plants to remove oxide and scale from the surface of the metal sheet, strip, wire, or parts before another operation, such as galvanizing, electroplating, or painting, by passing the metal products through an acid bath. Steels are usually pickled in 15– 20% HCL or H2SO4 at temperature up to 100 °C. During pickling the scale oxides dissolve to give iron(II) ⁎ Corresponding author. E-mail address: [email protected] (A. Agrawal). 0304-386X/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.hydromet.2007.04.001
sulphates/chloride and repeated pickling in the same liquor lead to the generation of pickle liquor containing mineral acids along with various metals such as iron, Zn, Cr, Ni etc depending upon the type of steel treated. This pickle liquor then becomes unacceptable for further use and is bled off as spent pickle liquor. Due to the corrosive nature and presence of the high amount of dissolved iron (II) this WPL cannot be disposed off without pretreatment. In industrial processes, such spent pickling solutions are usually treated with lime to neutralise acid and the sludge generated is dumped. Alternatively SPL is evaporated and cooled to 5 °C, and then to 0 °C to crystallize iron(II) sulphate as its heptahydrate. To recover and reuse the acid and the dissolved iron(II) in the spent pickling solutions as valuable materials and to
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obtain an environmentally benign effluent, an alternative method for treating spent pickling solutions is essentially required. Studies have been reported on the use of Tri-butyl phosphate (TBP) for the extraction of acid (Petkovic et al., 1992; Ritcey and Ashbrook, 1984a,b; Cox, 1992; Eyal et al., 1993). The extraction of mineral acids by Cyanex 923 (Alguacil and Lopaz, 1996) was also investigated and reported. This study deals with the extraction of acid using Alamine 336 a tertiary amine. Similarly selective and quantitative separation of iron (III) from the waste pickle liquor can be effected through solvent extraction. A considerable amount of work has been reported (Demopoulos and Gefvert, 1984; Alguacil and Amer, 1986; Islam and Biswis, 1979; Chen et al., 1992; Sekine et al., 1976; Roddy et al., 1971; Alguacil et al., 1987; Sytefanakis and Monhemius, 1885) either on the removal of iron(III) as an impurity from leach solution or its extraction from dilute solutions. No systematic work has been reported on the solvent extraction of iron(III) from the concentrated sulphate solutions. Several solvents such as methyl isobutyl ketone (MIBK) (Chiba and Kimura, 1989), tri-n-butyl phosphate (TBP), (Majumdar and De, 1960; Roddy et al., 1971), di(2ethylhexyl) phosphoric acid (D2EHPA), (Sato et al., 1985; Roddy et al., 1971; Hirato et al., 1992; Kimura et al., 1984; Agatzini et al., 1986) and amines (Alguacil and Amer, 1986; Alguacil et al., 1987; Sahu and Das, 2000; Sahu and Das, 1997), are used for extracting iron (III). Metal recovery from liquid effluents has been studied by Andersson and Reinhardt (1983), Haines et al. (1973) and Tunley et al. (1976) mentioned the use of ion exchange resins to separate Fe(II) and Zn followed by Zn extraction by D2EHPA. Good and Bryan (1960, 1961) have extensively studied the extraction of some base metals including Fe(II) and Fe(III) in sulphate and chloride medium. Sanad et al. (1982, 1992) have studied iron extraction from chloride and bromide medium using tri-butyl phosphate. But these systems are found to have some disadvantages such as low extraction and difficult stripping, hence binary solvent mixtures have been tried. Though the literature on binary extraction of iron is very less, an attempt has been made to develop a suitable synergistic extraction process with mixed extractants that achieves improved iron(III) extraction from a concentrated iron solution in a sulphate medium.
59
2. Materials 2.1. Sample collection, solutions and reagents 10 L of sulphate waste pickle liquor was collected from Tata Tubes Ltd, Jamshedpur. The chemical analysis of this waste is given in Table 1. The organic reagent used for the recovery of acid and iron in this study was Alamine 336, D2EHPA, MIBK. Alamine 336 (R3N) was kindly supplied by Henkel and used as extractant without further purification. Alamine 336 is a mixture of saturated and straight chain trialkylamines with carbon chains C8 and C10, in which the proportion of the carbon chain C8 is about 2 to 1. It is a pale yellow liquid practically insoluble in water (b 5 ppm) with an average molecular weight of 392 g/mol, a density of 0.81 g/cm3, and a viscosity of 11 mPas (30 °C). Other solvents used as diluent and phase modifier are: distilled kerosene, MIBK, TBP, Benzene, Hexane. Chemical analysis of the WPL, acid after extraction, iron and zinc in the solutions were done volumetrically by standard methods as mentioned in Vogel (1989). Mass balance gives the amount of acid extracted by the solvent. Trace metal analysis was done by atomic absorption spectro-photometer (Thermo SOLAAR S-2). 2.2. Experimental Acid extraction from waste pickle liquor (WPL) of the steel tubes industry was done with 35% Alamine 336 (0.723 M) in kerosene. 10% of isodecanol was used as phase modifier. The loading capacity of the solvent for WPL containing 91.9 g/L was performed at 30 °C, 45 °C and 60 °C by multiple contact method at O/A ratio of 1:1. The organic and aqueous solutions were contacted for a period of 5 min to ensure complete extraction in a separatory funnel. The mixture was then allowed to separate into organic and aqueous layers and the acid loaded organic was separated from the aqueous phase with residual acid. The same organic was shaken again with the fresh aqueous feed till the organic is completely loaded with the acid, which is indicated by the chemical analysis of the aqueous phase after each shaking. Various other parameters such as mixing time, O/A ratio, mixing
Table 1 Chemical analysis of the WPL of Tata Tubes Ltd, Jamshedpur Constituents
H2SO4
Fe(T)
Fe(II)
Zn
g/L Composition
91.88
Cu
Co
Ni
Mo
Mn
Cr
5.8
9.8
1
162
6.8
ppm 78.1
73.75
5.15
2.7
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Fig. 1. Effect of phase modifiers on % extraction of acid from WPL 35% Alamine 336 [O/A: 1/1, time: 5 min, temp: 30 °C, [H2SO4] wpl: 91.9 g/L].
temperature, aqueous and organic concentration etc. were studied to optimise the amicable for acid extraction. After the extraction of acid by the organic phase stripping of the loaded acid was performed to recover the pure and concentrated acid and iron solution which could be recycled to the pickling bath and iron could be used to prepare pure iron oxide.
Fig. 3. Effect of Alamine concentration on the extraction of acid from WPL. O/A: 1/1, time: 5 min, temp: 30 °C, [H2SO4] wpl: 91.9 g/L.
With the use of nonyl phenol, acid extraction not only decreases (Fig. 1) from 50.6% to 38.0%, but also phase separation become slower. Therefore, 10% (v/v) isodecanol was used as phase modifier with kerosene as diluent in the further study. 3.2. Rate of extraction of acid with Alamine 336
3. Results and discussion Sulphuric acid extraction from waste sulphate pickle liquor containing 91.9 g/L acid and 78.1 g/L Fe(T) along with traces of other metals was performed with different concentrations of Alamine 336.
In order to observe kinetics of acid extraction, both aqueous and organic phases were contacted for different time intervals (Fig. 2) up to 8 min. Beyond 2 min of equilibration percentage extraction remains the same and therefore shaking time in all the experiments was maintained at 5 min to ensure complete extraction.
3.1. Effect of phase modifier 3.3. Effect of Alamine concentration on acid extraction A few preliminary experiments were done with different phase modifiers to examine their effect on acid extraction keeping all other parameters constant. It was observed that though percentage acid extraction remains the same with tri-n-butyl phosphate and isodecanol, but phase separation time was much better in the latter case.
The result on extraction of acid with different Alamine concentrations is shown in Fig. 3. Solvent concentration was varied from 10% to 35% (v/v) in kerosene using 10% isodecanol as phase modifier. An increase in the concentration of Alamine resulted in an increase in the acid
Fig. 2. Effect of time on acid extraction from WPL with 35% Alamine 336. ([H2SO4: 91.9 g/L], O/A:1, temp: 30 °C, no. of contact: 1).
Fig. 4. Plot of log D vs log Alamine 336 concentration O/A1, temp: 30 °C, [H2SO4] aq = 91.9 g/L.
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Fig. 7. Effect of O/A on the extraction of acid by 35% Alamine 336. H2SO4: 91.9 g/L], temp: 30 °C, no. of contact: 1. Fig. 5. Extraction of acid in different contacts and Alamine 336 concentration on the extraction of acid from WPL. [H2SO4: 91.9 g/L], O/A:1, temp: 30 °C.
extraction. Thus extraction increased from 17 to 37 g/L with the increase in solvent concentration from 10 to 35% with O/A phase ratio of 1 in a single contact. Further increase in solvent concentration creates phase separation problem, therefore, 35% Alamine(0.723 M) was used for optimisation experiment. Plot of log D vs log Alamine 336 concentration (Fig. 4) gives a slope of 0.94 indicating the requirement of 1 mol of Alamine for 1 mol of acid. 3.4. Saturation loading capacity of different concentrations of Alamine for multiple contacts Saturation loading capacity of different concentrations of Alamine was determined by using multiple contacts (Fig. 5). With the aqueous acid concentration of 91.9 g/L, saturation loading was achieved in 4 contacts
Fig. 6. Effect of initial sulfuric acid concentration in WPL on the loading of acid to 35% Alamine 336 extraction.
of the same organic solvent with the fresh aqueous phase maintaining O/A of 1. Thus in the 4th contact the loaded acid concentration increases from 40.5 g/L to 80.8 g/L with the increase in the Alamine 336 concentration from 10% to 35%. In terms of percentage about 88.3% of acid is taken up by the 35% Alamine as compared to 44.1% with 10% Alamine. 3.5. Effect of initial sulphuric acid concentration in the waste pickle liquor for the loading of acid on 35% Alamine 336 The effect of initial sulphuric acid concentration in the waste pickle liquor for the loading of acid on to 35% Alamine 336 is represented in Fig. 6. It was found that with the increase in acid concentration from 45 to 200 g/L, loading increases from 26 to 41 g/L in one contact with the O/A phase ratio of 1. A linear plot was obtained up to 120 g/L of acid indicating that the distribution ratio and species do not change with the increase in acid concentration of the said range. Beyond this the extractant
Fig. 8. Mc Cabe Thiele plot for sulphuric acid extraction with Alamine 336. [H2SO4] aq: 91.9 g/L.
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Fig. 9. Stripping of acid from the loaded organic of different concentration with fresh distilled water in different contacts.
Fig. 11. Effect of O/A on stripping of loaded acid from 35% Alamine 336, organic feed: loaded 35% Alamine 336 (81.98 g/L H2SO4), stripping agent: distilled water, time: 5 min, temp: 45 °C.
becomes saturated and the loading plateaus. It is concluded that 35% Alamine 336 can hold up to 40 g/L H2SO4, However, the percentage extraction decreases from 60 to 20% with the increase in initial acid concentration. The saturated loading capacity determined in different contacts as shown in Fig. 5 was 80.8 g/L.
requirement of 3 stages for the maximum extraction of acid at O/A ratio of 2 from an aqueous acid concentration of 91.9 g/L with 35% Alamine removing about 90% of the acid. The acid left in the aqueous feed along with the iron can be neutralised during the synthesis of iron oxide.
3.6. Effect of variation in organic to aqueous phase ratios on percent acid extraction
3.7. Stripping of acid from the loaded Alamine 336 in multiple contacts
Variation in organic to aqueous phase ratios shows that the percentage acid extraction increases from 11 to 88% with the increase in O/A ratio from 0.2 to 5. Thus at O/A of 5 the organic phase contains 81.1 g/L of acid leaving about 10.8 g/L in the aqueous phase (Fig. 7). The McCabe Thiele plot represented in Fig. 8 shows the
Saturation loading of 35% Alamine was done by a multiple contact of the waste pickle liquor with acid concentration of 91.9 g/L. The concentration of acid in the loaded solvent (35% Alamine 336) was found to be 82 g/L. Stripping of acid from the above loaded solvent was performed with hot distilled water at 60 °C so that it could be recycled back to the system. It was found that 25% of acid is stripped in the 1st contact at O/A ratio of 1:1 and in the fourth contact it reached only up to 40.6%. Beyond that acid stripping was found to be difficult (Fig. 9).
Fig. 10. Stripping of loaded organic by multiple contact of aqueous feed with fresh loaded organic each time, organic feed: loaded 35% Alamine 336 (81.9 g/L H2SO4), aqueous feed: distilled water, time: 5 min, temp: 30 °C, O:A: 1.
Fig. 12. Rate of stripping of loaded acid by DW, organic feed: loaded 35% Alamine 336 (81.9 g/L H2SO4), temp: 45 °C.
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Fig. 13. Effect of temperature on the stripping of acid, organic feed: loaded 35% Alamine 336 (81.9 g/L H2SO4), time: 5 min, O:A: 1.
3.8. Stripping of loaded acid with the multiple contact of fresh loaded organic and same aqueous feed Since the concentration of acid obtained after stripping was not suitable for recycling, the same aqueous feed was contacted with the fresh loaded organic and the final strip solution obtained after 5 contacts contained 65.9% concentrated acid (Fig. 10). However, out of the 91.9 g/L of acid in the WPL, only 60.7 g/L of acid was recovered.
63
Fig. 15. Effect of MIBK concentration with and without D2EHPA on the distribution coefficient (D) of Fe(III) in H2SO4 medium. [Fe]: 60.88 g/L, H2SO4: 53.9 g/L, time: 5 min, O:A: 2:1, temp: 30 °C.
is sufficient to strip maximum acid in one contact, hence the solutions were shaken for 3 min in each experiment. 3.11. Effect of temperature on stripping of loaded acid
Effect of time on stripping of loaded acid by hot distilled water was also studied. Fig. 12 shows that 3 min
Fig. 13 shows the effect of temperature on stripping of loaded acid and it was found that 28% of acid was stripped at 60 °C as compared to 25% at 30 °C. Hence, all the stripping was done with hot distilled water at 60 °C. Since iron was in the reduced form in the WPL, the stripped acid was free of iron contamination and other impurities present in the WPL. After the maximum stripping of acid by distilled water, the solvent with the residual acid could be treated with the dilute alkaline solution to regenerate the solvent for recycling. Analysis of iron content shows that its extraction was negligible, probably ferrous iron as sulphate has very less affinity for Alamine 336. Thus iron extraction was tried with a mixed solvent system comprising of D2EHPA and MIBK. The acid free ferrous sulphate was oxidised to ferric form by treating it with the required amount of nitric acid and during oxidation the
Fig. 14. Effect of D2EHPA and MIBK on the distribution coefficient of Fe(III) extraction from H2SO4 medium. [Fe]: 60.88g/L, t:5 min, O/A 2:1, T 30 °C.
Fig. 16. Effect of D2EHPA concentration with and without MIBK on D values of Fe(III) extraction from H2SO4 medium. [Fe]: 60.88 g/L, time: 5 min, O/A 2:1, temp: 30 °C.
3.9. Effect of O/A variation on stripping of acid Thus, O/A variation was tried to get a concentrated acid in the strip solution. Fig. 11 shows that about 66.8 g/L of acid could be obtained at O/A ratio of five in a single contact. 3.10. Rate of stripping of loaded acid by hot distilled water
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Fig. 17. Comparison of D values for the Fe extraction in varying concentrations of D2EHPA + 40% MIBK and MIBK + 40% D2EHPA from H2SO4 medium. [Fe]: 60.88 g/L, time: 5 min, O/A 2:1, temp: 30 °C.
concentration falls from 78.2 g/L of Fe(total) to 60.9 g/L of Fe(total). However it is always possible to maintain almost similar iron concentration. Studies were conducted with the oxidised solution for the extraction of iron by the aforesaid mixed solvent system. 3.12. Extraction of iron by a mixed solvent system Effect of D2EHPA and MIBK concentration individually on the distribution coefficient of Fe(III) extraction from the sulphate waste pickle liquor containing Fe: 60.9 g/L was studied at O/A 2:1, T 30 °C with a mixing time of 5 min. The raffinate was analysed for the remaining iron by volumetric titration with potassium dichromate in the presence of BDS as indicator. Fig. 14 shows a plot between solvent concentration vs D values for D2EHPA and MIBK. It was found that D2EHPA is more effective than MIBK for iron extraction with D values varying from 0.05 to 0.286 with the increase in solvent concentration from 20 to 40% and that for MIBK, D varies from 0.009 to 0.019 for the concentration variation from 20 to 40%. Therefore mixtures of these two solvents were tried to see the effect on iron extraction. Thus Fig. 15, a plot between solvent concentration vs D values in the single and mixed solvent shows that when MIBK alone was varied from
20% to 40% the D values varied from 9.0 × 10− 3 to 1.9 × 10− 2. When a fixed amount of D2EHPA was mixed with a varying amount of MIBK the values of D varied from 2.7 to 3.13. Similarly, by varying the D2EHPA concentration from 20 to 40% the D values were found to vary from 0.05 to 0.286 and in addition of a fixed amount of MIBK i.e. 40% to different concentration of D2EHPA (Fig. 16), values of D increase from 0.47 to 3.13. A comparison of D values of D2EHPA + 40% MIBK and MIBK + 40% D2EHPA as depicted in Fig. 17 shows that, iron extraction increases with the increase in concentration of MIBK at a constant concentration i.e. 40% D2EHPA and is more than the mixture of different concentration of D2EHPA at 40% MIBK. Thus with a mixture of 40% MIBK, 40% D2EHPA in kerosene a maximum amount of iron is loaded. This enhancement in extraction percentage is due to the synergistic effect of MIBK on D2EHPA by the formation of adduct. Synergism can be quantified by the synergistic coefficient (SC), which is defined as
DD2EHPAþMIBK Sc ¼ log DD2EHPA þ DMIBK
where DD2EHPA + MIBK is the distribution coefficient obtained with the mixture of D2EHPA and MIBK. The terms DD2EHPA and DMIBK are the distribution coefficients obtained for the individual extractants D2EHPA and MIBK, respectively. Synergism was observed at all mixed extractant compositions studied. Keeping the concentration of D2EHPA constant at 40%, it was observed that SC increased with the increase in concentration of MIBK from 20 to 40% (Table 2). Similarly a constant MIBK concentration of 40% SC value increased with the increase in D2EHPA concentration from 20 to 40%. However the increase in SC was more pronounced in the former case with the maximum synergistic coefficient values at the solvent mixture consisting of 40% each solvent. Since the basicity of MIBK
Table 2 Iron(III) distribution coefficient, D, with D2EHPA, MIBK, D2EHPA(40%) + MIBK(20 to 40%), MIBK(40%) + D2EHPA (20–40%), and synergistic coefficient value Solvent MIBK 40%
D2EHPA 40%
D2EHPA20% D2EHPA 30% D2EHPA 40% MIBK20% MIBK30% MIBK40%
DD2EHPA
DMIBK
DD2EHPA + DMIBK
D(D2EHPA + MIBK)
D
SC
0.048 0.106 0.286 0.286 0.286 0.286
0.019 0.019 0.019 0.009 0.014 0.019
0.067 0.125 0.305 0.295 0.299 0.305
0.473 0.934 3.13 2.71 2.9 3.13
0.406 0.81 2.83 2.42 2.60 2.83
0.85 0.88 1.01 0.96 0.99 1.01
Aqueous feed: [Fe]: 60.88 g/L, time: 5 min, O/A 2/1, temp: 30 °C.
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extraction in three counter-current stages at the A: O = 1:2 phase ratio. Although Alamine 336 is a good extractant for sulphuric acid, the acid could not be stripped completely from the loaded organic with water. After the extraction of acid the raffinate was oxidised and Fe(III) in the solution was then extracted with the appropriate mixture of D2EHPA and MIBK behaving as a binary extractant. MIBK was found to enhance the D value showing a synergetic effect. Acknowledgements Fig. 18. Stripping of loaded iron from 40% D2EHPA and 40% D2EHPA + 40% MIBK with different concentrations of HCl.
is low due to the weak donor properties of the oxygen in MIBK (Sanad et al., 2002), a number of organic molecules get attached loosely to the Fe(III) present in the mixture leading to an adduct formation with D2EHPA– Fe(III) complex. D and SC values for iron(III) are shown in Table 2. A comparison of SC values for D2EHPA (40%)–MIBK (20–40%) and MIBK (40%)– D2EHPA (20–40%) shows higher SC values for the former mixture. 3.13. Stripping of iron from the loaded organic Thus after the extraction of iron in a mixture of 40% D2EHPA and 40% MIBK the stripping was tried with different concentrations of HCl and the percentage of iron(III) stripped from loaded D2EHPA40% + MIBK40% was found to increase with the increasing initial HCl concentration up to 3.25 M after this concentration the stripping decreases(Fig. 18). Such a decrease may be due to the formation of chlorocomplex(es) of iron(III) with the HCl, which is easily re-extracted by MIBK. However stripping of loaded iron from 40% D2EHPA increases in the whole range of acid studied since there is no back extraction of any complex by this single solvent system. 4. Conclusions Solvent extraction of sulfuric acid from the actual waste pickle liquor from Tata tubes company Jamshedpur was carried out using Alamine 336. The extraction of H2SO4 increased with the increase of solvent concentration. The log D vs. log extractant plot was straight lines with slope values of 0.94 indicating that 1 mol of the extractant was involved with 1 mol of the extracted acid. For Alamine 336, the McCabe–Thiele construction indicated the possibility of about 90% H2SO4
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