Reductive stripping of Fe(III)-loaded D2EHPA with the aqueous solutions containing sulfur dioxide
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I.
INTRODUCTION
FERRIC ion is generally extracted more strongly with acidic extractants than all common metal ions. The stripping of Fe(III) extracted with acidic extractants such as D2EHPA, Versatic acid, Lix reagents, etc., is often difficult. For example, Fe(III) in aqueous solution is readily extracted with Versatic 10 above a pH value of around 1.2. However, while 6 N HC1 can strip Fe(III) from the organic phase, 6 N H 2 8 0 4 cannot.~ Also, D2EHPA is an excellent extractant for Fe(III), but again stripping is known to be very difficult. In regard to this, Nishimura and Watanabe developed a novel process to extract Fe(III) and unreacted acids from a spent pickling liquor by means of a solvent extraction process in which D2EHPA is used as an extractant for Fe(III).-' In their process, Fe(III) is recovered from an organic phase by adding NH4HF to avoid the difficulty of stripping of Fe(III), and crystalline (NH~)3FeF6 is produced from the strip liquor. Monhemius and Thorsen developed the technique called hydrolytic stripping which involves reacting an iron-loaded carboxylic acid solution with water at 423 to 473 K. Iron is precipitated directly as hematite, and the carboxylic acid solution is regenerated and can be recycled to extractionfl Burkin and Burgess have studied the production of metal powders by direct reduction of loaded extractants with hydrogen at elevated temperature. Iron-loaded Versatic 911 could be reduced to form metallic iron on colloidal carbon seeds when ammonia was present in the autoclave. 4 Since the stripping of Fe(II) is far easier than that of Fe(III), it may be possible to improve the stripping if Fe(III)-loaded in organic phase can be reduced to Fe(II). Alternately, if Fe(II1) stripped from the organic phase can be quickly reduced to Fe(II) in the aqueous phase, the stripping reaction may be greatly improved as expected by the Le Chatelier rule. In this study, the authors investigated the reductive stripping of Fe(IlI)-loaded D2EHPA by various acid solutions (including HC1, HC104, and H2S04) in the presence of sulfur
HIROSHI MAJIMA is Professor. Department of Metallurgy, Kyoto University, Kyoto, Japan 606 TOSHIO IZAKI, Professor and Dean, and SUMIKO SANUKI, Instructor, are with the Department of Metallurgy, T,oyama Umverslty, To3,ama, Japan 930. Manuscript submitted October 24. 1983.
METALLURGICAL TRANSACTIONS B
dioxide. Stripping was greatly accelerated in the presence of SO,. This paper provides details of the results obtained.
II.
EXPERIMENTAL PROCEDURES
A kerosene solution of D2EHPA whose concentration was 10 or 30 pct was used for the extraction of Fe(IlI) from an aqueous solution. Ferric nitrate or ferric perchlorate of reagent grade was used to prepare Fe(III)-loaded D2EHPA. Aliquots (150 mls) of organic solution of Fe(III)loaded D2EHPA and aqueous stripping solution were taken into a 1000 m18 glass autoclave, and the solution temperature was adjusted to the required level, in some stripping experiments, oxygen gas originally contained in the solution as well as the re
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