Resources, Conservation and Recycling, 10 (1994) 341-347 341 Elsevier Science B.V.

Production of Fe203 from FeSO4"xH20 formed in galvanizing works

Mustafa Arslan, Cihan Alkan, Mehmet Cici and Mehmet Kaya Chemistry Department, Ftrat University, Elazz~, Turkey

ABSTRACT

FeSO4-xH20 is generated in large amounts in galvanizing workshops. It can be reutilized by con- version to Fe203. In this study, the recovery of Fe203 from FeSO4-xH20 formed in the galvanizing process has been examined. The experimental work was carried out at various temperatures and times in the oxidizing medium. The reaction temperatures and times were selected as 450, 500, 550, 600, 650, 700, 800 and 900 ° C, and 15, 30, 45, 60, 90 and 120 minutes, respectively. In order to determine the amount of Fe203, a titrimetric method was applied. The reaction products were characterized by means of IR and XRD techniques.

The extent of conversion is low at temperatures below 650 ° C. Almost all of the iron (II) sulfate in the original sample was converted to iron(III) oxide at 650°C ( 120 rain), 700°C (90 rain), 800°C (60 rain) and 900°C (45 min).

INTRODUCTION

The first important treatment in the galvanization process is the removal of the surface oxides from metals such as iron and steel. For this purpose, the pickling bath which is usually a dilute solution of H 2 S O 4 ( 5 - 2 0 % ) or HC1 (5-25%) is used. Sulfuric acid is used extensively. The metal either is dipped into the pickling bath for the requisite time or the acid is sprayed on it (Bruns, 1967; Yonar, 1979; Considine, 1974). As the result of the cleaning process, FeSO4-xH20 is precipitated in the acid solution.

The utilization of this by-product, which is produced in the galvanizing works, is important from an economic perspective. It can be reutilized via production of F e 2 0 3 which is widely used as a pigment. Iron oxide pigments were probably the first inorganic coloring material used by man. Almost all types of paints and protective coatings require synthetic iron oxides because of their lightfastness, chemical inertness, high opacity and pleasing color tones either alone or in combination with organic pigments (Kirk-Otmer, 1967).

Correspondence to: M. Arslan, Chemistry Department, F~rat University, 23169 Elazt~, Turkey.

0921-3449/94/$07.00 © 1994 Elsevier Science B.V. All fights reserved.

342 M. ARSLAN ET AL.

Recently, Fe203 (hematite) has been used as a photoanode and a catalyst in the production of hydrogen by means of photochemical, photocatalytic and thermochemical methods (Getoff, 1988; Khan, 1984, Harutyunyan, 1988; Ohta, 1979).

Iron (III) oxides may be prepared synthetically by oxidizing iron ( II ) disul- fide, by calcination of iron (III) hydroxide or other iron salts, and by the elec- trolysis of a solution of sodium sulfate in a diaphram cell with a wrought iron anode (Kirk-Otmer, 1967). In this study, the production of Fe203 from FeSO4-xH20, which is a by-product of the galvanizing process, and the pro- duction conditions have been investigated.

EXPERIMENTAL

FeSO4 oxH20 that has been used throughout the experimental work was ob- tained from the galvanizing workshop of the Ere~li Iron-steel Plant in Turkey. The iron (II) sulfate content of this waste is 54.2%. Thirty grams of sample were put in a porcelain crucible to carry out the conversion of FeSOa.xH20 into Fe203. It was heated in an oxidizing condition at various temperatures in a thermostatic oven. The reaction temperatures selected were: 450, 500, 550, 600, 650, 700, 800 and 900°C. The effect of time on the reaction has also been studied at these temperatures for the periods: 15, 30, 45, 60, 75, 90 and 120 rain. In order to determine the amount of Fe203 in the reaction prod- uct, 0.4 gram ( + 0.0002) of product was weighed and 2 ml of concentrated HC1 was added and heated until the product was dissolved. Three ml of H2SO 4 ( 1 : 1 ) was added to the solution, and heated until a fume of SO3 was ob- served. The sample was then cooled and 20 ml of water was slowly added. The solution was passed through a 'Jones reductor'. After 16 ml of concen- trated H2SO4, 50 ml of water and 6 ml of H3PO 4 (85%) were added to the filtrate~ passing through the reductor, it was titrated with standard 0.1 N KaCr207 solution; diphenylamine sulfonate was used as an indicator (Skoog, 1976; Giindiiz, 1975 ). Then the amount of iron in the reaction product was calculated. In the calculation of Fe203 amounts below the incidence of 100% conversion, the reaction product was assumed as iron (III) oxide and iron (II) sulfate.

For the characterization of the reaction products and to follow the reaction, XRD and IR techniques have been used. A Philips Diffractometer was used in this investigation. It was equipped an iron tube to generate monochromatic Fe K~ radiation. The counting and scanning rates and the speed of recording paper were chosen as 400 cps, 1 ° /min and 600 mm/h, respectively.

DISCUSSION

The variation of the weight loss (%) of sample with reaction temperature for 15 min for the 90-700°C range is shown in Fig. I. The elevation of the weight loss is quite high: between 90 °C and 200 °C and above 600 ° C.

PesO3 FROM Fe2SO4.xH20 IN GALVANIZING WORKS 343

20

15 v

o,

~ I o

~o

o 5

i

2~o .~o 600

Tem~reture (°C)

800

Fig. 1. Loss of weight at var ious temperatures .

Q I 5 r f l l r l

90 * 30 rain • 45 fain

80 o 60 rain • 90 rain

70 a 120 rain

6O

5O

40 400 500 6O0 7'00 8GO 900 1000

Temperature (°C)

Fig. 2. Variat ion of Fe203 (%) con ten t of product with temperature .

'°°Tt , 4 s o , c

90 -I * 500°C + 550~C

80 • 600 • 650~

70 x 700 ~C N • 800

~" 60 A 900

5O

4O o 2'o io o'o ~'o ,oo ,~o

Reaction time (rnin)

Fig. 3. Variat ion of Fe203 (%) conten t of product with react ion time.

344 M.ARSLANETAL.

_/ 120 min

120 rain

120 min

650°C

70000 45 rain

BO0°C

r " ~ - 900°C , , • l,

~ooo 3ooo 2ooo 14oo looo 600

Waver, umber (cm -1 )

Fig. 4. IR spectra of the reaction products at various temperature (time indicates the maximum converting time).

Fe203 FROM Fe2SO4"xH20 IN GALVANIZING WORKS 345

Original.

120 rain 40oo 360o 26oo obo soo

Wavenumber (cm--1)

Fig. 5. IR spectra of the reaction products at various time.

The analysis of iron in the product has been carried out by titrimetric method and the variations of Fe203 formed with reaction periods and tem- peratures are given in Figs. 2 and 3. The amount of Fe203 is approximately the same at temperatures below 650°C for the periods of 15, 30, 45 and 60 rain.

In order to investigate effects of temperature and time on the reaction, IR spectra of the products were taken (Figs. 4 and 5 ).

When IR spectra are examined, it is observed that there is not an important difference until 650°C; however, the formation of Fe203 is completed at 650°C. It is also understood from IR spectra that the optimum reaction time

346 M. ARSLANETAL.

650°C / 120 min h~ ~h

., h A h .h h

700°C/90 min | h f] flh

h,,hematite , i

a'o 7'0 6'0 s'o 4'o 30

28

Fig. 6. X ray diffractograms of the reaction products.

is 120 min at 650 °C at which the reaction is almost completed. The increase in temperature decreases the reaction time. It was found to be 90 min at 700°C, 60 min at 800°C and 45 min at 900°C. By comparing the IR data obtained from original and reacted samples, the strong peaks observed at 1000-1200 and 1600 cm-] in the IR spectrum of original sample have dis- appeared and the intensity of the peak between 3500 and 3000 cm-1 de- creased considerably.

During the convertion of FeSO4-xH20 into Fe203, a small amount of Fe304 may be formed. It is known that Fe203 converts to the form Fe304 above about 1400°C (Greenwood, 1984). The understanding of the formation of Fe304 is very difficult by IR technique because the vibration frequencies of both oxides (Fe203 and Fe304) are almost the same. In order to distinguish the iron oxides in the reaction products, an XRD technique has been used. For this purpose, the X-ray diffractograms of the products at 650°C (120 min), 700°C (90 min) and 800°C (60 min), at which the characteristic IR peaks of FeSO4-xH20 disappeared, have been taken (Fig. 6 ).

The X-ray diffractograms show that almost all of the reaction product is Fe203 at these temperatures for these reaction times.

Fe~O3 FROM Fe2SO4.xH20 IN GALVANIZING WORKS 347

CONCLUSIONS

The experimental results indicate that important factors of economic value in converting FeSO4-xH20 into Fe203 are the roasting temperature and the reaction time. In order to increase the conversion rate of FeSO4-xH2) into Fe203 at low temperatures (above 650°C), the reaction must be continued for a long time. The conditions for 100% of conversion are considered opti- mum reaction conditions. For complete conversion, the reaction temperature must be 650°C for 120 min, at 700°C for 90 min, at 800°C for 60 min, and at 900°C for 45 min. It is observed that the increase in temperature decreases the reaction time. It may also be emphasized that the amount of the oxidizing agent (air was used in this study) affects the completion conversion ratio.

REFERENCES

1 Bruns, R.M. and Bradley, W.W., 1967. Protective Coatings for Metals, 3rd edition. Rein- hold, New York.

2 Yonar, I.K., 1979. Galvano Teknik. Milli Egitim Baslmevi, Istanbul, pp. 42-43. 3 Considine, D.M., 1974. Chemical and Process Technology Encyclopedia. McGraw-Hill,

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Hydrogen Energy Progress, VII. Proc. 7th World Hydrogen Energy Conf., Moscow, Vol. 1, pp. 235-256.

6 Khan, M.M. Taqui, Jadhav, C.M. and Bhardwaj, R.C., 1984. Hydrogen production by nat- urally occuring hematite electrode using visible light. Adv. Hydrogen Energy, 4 (Hydrogen Energy Prog. 5, Vol. 3), pp. 1067-1073.

7 Harutyunyan, V.M., Sarklssyan, A.G. and Arakelyan, V.M., 1988. Water electrolysis by use of semiconductor oxide anodes. In: Hydrogen Energy Progress, VII. Proc. 7th World Hy- drogen Energy Conf., Moscow, Vol. 1, pp. 579-594.

8 Ohta, T. and Sastri, M.V.C., 1979. Hydrogen energy research programs in Japan. Int. J. Hydrogen Energy, 4: 489-498.

9 Skoog, D.A. and West, D.M., 1976.Fundamentals of Analytical Chemistry, 3rd edition. Holt, Rinehart and Winston, New York, pp. 741-742.

10 Gtindiiz, T., 1975. Kantitatif Analiz Laboratuvar K.itabl. Ankara Oniversitesi Fen FakiJl- tesi Yaymlan, Ankara, pp. 109-122.

11 Greenwood, N.N. and Earnshaw, A., 1984. Chemistry of the Elements. Pergamon, Oxford, pp. 1254-1255.