Extraction Behaviour of Fe3+ From Chloride Solution by Technical Grade D2 EHPA: A Comparison with the Results Obtained by Analytical Grade

Abstract

The solvent ex tract ion of Fe3 + from ch lorid e sol uti on by tech n ical grade (t.g) d i-(2-eth y l h exy l ) phosph oric acid , D2EH PA d i ssol ved i n k erosen e has been i nvesti gated over a w id e range of aq u eous acid i ty as a functi on of ph ase con tact ti me, concentrat i ons of Fe3 + , HCI , H + and Cl- i n the aq ueous ph ase, D2EH PA  concentration i n  the organ i c phase an d temperature and the resu l t s h ave been compared to th at reported for anal yt i ca l grade (a.g). Eq u i l i bri u m ti me i       60 m i n , com pared  to 50 mi n  for a.g .   Na t u res of Fe3• cu n cen t rati on  dependen ces Iff t:  not si m i l ar a n d  th e va l u    · of

ex tracti on  ra li    a r c u su a l l y  h Lm d red t i m e   greater for t.g. t h un  for a .g. u nd  r si mi l a r cond i ti on s. Th e H    I depen den ce pl ot   pu ss t h rn u gh  a m ax i m u m  and  a m i n i m u m a t  1 .6 M  and  1 . 1  M  1-!CI , 1·cspec t i vel y, wh ereas, these are at  1 . 2 M  an d

0.3 M H CI , respec t ivel y, for a.g . At [Cl-] = 3 M, the sh ape of 1-1·dependence pl ot for t.g. reagent di ffers w id el y from t h at for th e a . g. The extract i on i s also fou n d to be i mm en esel y dependent on [Cl-] for both th e grades of extractant, b ut t h e extent of dependen ce u n der si m i l ar condition depend s on the grade of extractant u sed. The extractant dependen ces a re lower for t.g. com pared to those for a.g. Reaction s are exothermic i n h i gh er temperatu re  regi on , wh ereas, t h e extract i on i s al most i ndependent of te m peratu r e i n i ts lower region s. The apparent enth a l py change , t.H va l ue i n th e h i gh er tem perature regi on 1s decreased wi th decreas i n g 1-( con cen tration i n the aqu eou s ph ase. But the opposite trend was observed  w i th  a. g. The l oad i n g capacity depends on  the aqueous  acid i ti es an d  grades of  D2EH PA.  It is 13.05 and

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6 83 g ofFe3+ per  I 00 g D2EH PA (t.g.) at [HCI] of 0.1 3 and 3 M, respecti vel y, compared to 8.38 and 3. 1 4 g of Fe3     per

1 00 g D2 EH PA (a.g.) at [HCI] of 0.05 an d  I  M, respecti vel y. Mecha n i sm of extraction  is compl i cated by the si m ul ta­

,

 

neou s extra ction s of Fe3+ , FeCI '+ , Feel;, FeC l

3

H FeCl ,

etc. i n  both  cases.  I t  is observed  t h at  99.4 % of i ron  speci es

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extracted by D2EH PA (t.g.) i n the organ i c phase can be str i pped by 5 M HC I i n three stages at organ ic to aqueou s ph ase

r atio of u n i ty. Organi c phase a fter on e cycl e can be recycl ed after add i n g 0. 72 g dni-3 mono-(2-ethy l hexyl ) phosphoric acid , M2EH PA.