ABSTRACT
A m o rp h o u s Ғе(ОН)з p ro v id es reac tiv e sites on th e su rface a fte r F e 2+ ad so rb s [28]. T h e F e 2+-F e3+-h y d ro x id e is a s tro n g er red u c tan t co m p ared w ith free F e 2+ o r F e(II)-E D T A , o r F e(II)-c itra te . It is p o ss ib le th a t tran sfo rm a tio n o f ca rb o n te trach lo rid e w as m e d ia ted by Ғе(Ш) red u c in g b a c te ria as w ell as th e F e2+-F e3+-h y d ro x id e su rface . O u r resu lts in d ica ted th a t th e ra te o f ca rb o n te trach lo rid e tran sfo rm atio n in th e p re se n ce o f am o rp h o u s Ғе(ОН)з w as fa s te r th an th e ra tes o b se rv ed in th e F e(III)-c itra te an d F e (n i)-E D T A se ts (T ab le 2). T h e Ғе(Ш) red u c in g co n so rtiu m , h o w ev e r, a lso w as ab le to u se c itra te as a ca rb o n source . A fte r th e c itra te is co n su m ed by th e b ac te ria , F e3+ w ill p rec ip ita te as Ғе(ОН)з so lid fo rm d u rin g F e (III)-re sp irin g p ro cesses. N ev e rth e le ss , Ғе(ОН)з fo rm a tio n is n o t lik e ly to eq u a l th e am o u n t p resen t in th e am o rp h o u s Ғе(ОН)з se ts. M o st o f th e F e 3+ w as red u c ed to F e 2+ an d p rec ip ita ted w ith ca rb o n a te to fo rm ҒеСОз. T h e Ғе(Ш) red u c in g co n so rtiu m d id n o t d eg rad e E D T A . R e d u ce d Ғе(Ш), F e2+, h o w ev e r co m p lex e s s tro n g ly w ith E D T A (co m p lex co n s ta n t a ro u n d 10 16 to 10 18). B ecau se F e(II)-E D T A is a n o t s tro n g red u c tan t, ca rb o n te trach lo rid e tran sfo rm a tio n w as m a in ly m e d ia ted by th e Ғе(Ш) red u c in g co n so rtiu m . C o n seq u en tly , in th e p resen ce o f am o rp h o u s Ғе(ОН)з, ca rb o n
te trach lo rid e tran sfo rm atio n w as m o st lik e ly m ed ia ted b io lo g ica lly by th e F e(IH )-red u c in g co n so rtiu m as w ell as ab io tica lly on th e su rface o f th e F e 2+- F e3+-m in era l ph ase . T ran sfo rm atio n o f ca rb o n te trach lo rid e w as m a in ly m e d ia ted by th e F e(III)-red u c in g co n so rtiu m b io lo g ica lly in th e Ғ е(Ш )- c itra te an d F e(III)-E D T A sets (F e2+-F e3+-m in era l p h ase is ab sen t).
