Clay Minerals (1994) 29, 87-92
T H E F O R M A T I O N OF G R E E N R U S T A N D ITS
TRANSFORMATION
TO L E P I D O C R O C I T E
U. SCHWERTMANN
ANO H . F E C H T E R
Lehrstuhl fiir Bodenkunde, Technische Universitiit Miinchen, 85350 Freising-Weihenstephan, Germany
(Received 20 January 1993; revised 28 May 1993)
A B S T R A C T : The formation of Fe n,m hydmxy salts (green rusts) from Fe n sulphate and chloride
solutions and their transformation to lepidocrocite, 7-FeOOH, was studied at ambient temperature,
constant pH of ~7.0 and under controlled air flow. The formation of green rust and its subsequent
transformation to lepidocrocite could be distinguished by the reaction rate and solution chemistry. The
SO42- and CI- concentrations in solution attain a minimum at the break between the two reaction steps and
are completely restored to their initial values after complete transformation to lepidocrocite. While the
green rust is being formed, its FeU/FOn ratio shows a minor decrease and its Fern/anion ratio a minor
increase. These ratios, however, deviate from the ideal pyroaurite-type s t r u c t u r e (M2+/M 3+ = 3 ; M3+/A =
1; M: metal; A-: anion) and possibilities to accommodate this deviation are discussed. A period during
which no protons were produced (i.e. no base consumed) was found to separate the two reactions in the
chloride, but not in the sulphate system. During this period a partial solid state oxidation of the green rust
took place, leading to its destabilization and eventual decomposition.
G r e e n - b l u e iron h y d r o x i d e c o m p o u n d s occur
u n d e r reducing a n d weakly acid to weakly alkaline conditions as i n t e r m e d i a t e phases in the
f o r m a t i o n of Fe oxides (goethite, lepidocrocite,
m a g n e t i t e ) . B e c a u s e these g r e e n c o m p o u n d s
were first discovered in c o n j u n c t i o n with corrosion of steel in e a r t h surface e n v i r o n m e n t s , they
were called g r e e n rusts. T h e i r well-known structure is of a p y r o a u r i t e type. It consists of sheets of
F e n ( O H ) 6 o c t a h e d r a (called h y d r o x i d e layer in
this article) in which some of t h e Fe n is replaced
by Fe m, creating a positive layer charge which is
b a l a n c e d by anions located b e t w e e n the layers
( F e i t k n e c h t & Keller, 1950; B e r n a l et al., 1959;
Stampfl, 1969; B r i n d l e y & Bish, 1976). C h l o r i d e
a n d sulphate are the most c o m m o n interlayer
anions, b u t a c a r b o n a t e form of g r e e n rust also
exists (McGill et al., 1976; Stampfl, 1969; T a y l o r
& M c K e n z i e , 1980; Taylor, 1980) a n d m a y b e the
form occurring in n a t u r e . Recently, B e n d e r K o c h
& Mc~rup (1991) h a v e identified g r e e n rust in an
o c h r e sludge in D e n m a r k .
T h e oxidation of F e ( O H ) 2 to F e O O H via g r e e n
rust in u n b u f f e r e d chloride a n d sulphate systems
was extensively studied by D e r i e & G h o d s i (1972)
a n d D e t o u r n a y et al. (1974, 1976). T h e y monit o r e d the overall d e g r e e of oxidation, pH, Eh, C1a n d SO42- c o n c e n t r a t i o n in solution a n d the 0 2
c o n s u m p t i o n . D u r i n g the reaction, the p H
d r o p p e d from 8 to below 4 and the Eh rose from
--0.5 V to + 0 . 4 V with strong i n t e r m e d i a t e
buffering at p H --6 a n d an Eh of --0 V. A b r e a k in
the rate of oxidation was c o m b i n e d with a
m i n i m u m of [SO42-] ([] d e n o t e s c o n c e n t r a t i o n )
( D e t o u r n a y et al., 1974) a n d [CI-] ( D e r i e &
G h o d s i , 1972) in the s u p e r n a t a n t . F o r the chloride system, these a u t h o r s divided the r e a c t i o n
into t h r e e parts: F e ( O H ) 2 ~ FeII g r e e n rust I --~
F e m g r e e n rust I ~ lepidocrocite.
Solcova et al. (1981) recognized rate of oxidation, type a n d c o n c e n t r a t i o n of anion, t e m p e r a ture a n d particularly p H as i m p o r t a n t factors t h a t
d e t e r m i n e the n a t u r e of the oxidation product. In
a later study, t h e r e f o r e , t h e same g r o u p (Vins
et al., 1987) as well as T a y l o r (1984a,b) k e p t the
pH constant during the reaction and measured
the base c o n s u m p t i o n as a q u a n t i t a t i v e indicator
for the e x t e n t of hydrolysis of Fe. T h e a u t h o r s
noticed a p l a t e a u in the base c o n s u m p t i o n - t i m e
curve a n d T a y l o r (1984a) f o u n d t h a t this p l a t e a u
was a c c o m p a n i e d by a d r o p in Eh.
T h e e x p e r i m e n t s described in this p a p e r were
a i m e d at gaining f u r t h e r insight into the r e a c t i o n
m e c h a n i s m during the f o r m a t i o n a n d t r a n s f o r m a tion of g r e e n rust. A closely m o n i t o r e d sytem was
used in a n a t t e m p t to i m p r o v e s e p a r a t i o n of the
9 1994 The Mineralogical Society
88
U. Schwertmann and H. Fechter
various reaction steps by analysing the solution
and the nature and composition of the precipitates during the process.
0.02~ step. During the scans the samples were
either purged with N 2 (Philips) or covered with a
Mylar film (Guinier).
METHODS
The standard oxidation experiment was as
follows: 370 ml aliquots of a solution of 0.1 M
FeSO4 or 0.1 M FeC12, freshly prepared from
reagent grade FeSO4"7H20 and FeCI2.4H20 and
purged with N2, were placed in a reaction vessel
equipped with a magnetic stirrer, a gas and base
inlet and a p H electrode, and connected to a
R a d i o m e t e r titrator TTF80. The solution was first
titrated with 1 M N a O H to p H 7.0 (sulphate
system) and p H 6.8 (chloride system). This p H
range guarantees green rust formation with no
interference by magnetite (at higher pH). The
nitrogen gas was then replaced by CO2-free air at
a rate of 7.1 ml/min While stirring, and the p H was
kept constant (0.1 pH) by adding 1 M N a O H as
needed through a magnetic valve. The gas flow
was monitored with a calibrated gas flow apparatus. To analyse the solution and the precipitate
during the reaction, 5 ml aliquots were taken
intermittently. In a series of rapid steps, these
were centrifuged under N2 with N2-treated water
and dissolved in 2.5 ml 2.5 M HCI or H2SO4. Both
the supernatant and the dissolved precipitate
were analysed for Fe u, total Fe, and SO42- or C I with o-phenanthroline, suiphosalicylic acid and
with
an
ion
chromatograph
(Dionex),
respectively. The Fe In was taken as the difference. Prior to anion determination, Fe had to be
r e m o v e d from the solution and this was achieved
by passing the solution through a column with a
strong acid cation-exchange resin.
A total o f 30 separate runs were performed. To
determine the analytical error of the solid phase
analysis in the SO4 system, the oxidation was
quenched in three separate experiments at 25.9,
53.6 and 68.1% of total base consumption by
cutting off the air supply. Four 5 ml aliquots were
taken from each of the suspensions. The average
FeU/Fe Ill and Feln/so4 mole ratios of the precipitate were 1.98 + 0.05 and 1.42 + 0.08 (n = 12),
respectively.
X-ray diffraction ( X R D ) step scans were run
f r o m 5-35~
(Co-Kct) with a Philips vertical
g o n i o m e t e r (PW 1050)equipped with a diffracted
beam m o n o c h r o m a t o r or with a H u b e r Guinier
diffractometer. T h e counting time w a s 1 s per
RESULTS
General observations
A f t e r the p H of the solution was brought up to
7 (6.8) at the start of the experiment, the solutions
had a green colour with a slight turbidity,
indicating traces of Fe IIl even in the initial
solutions. As soon as air was introduced, N a O H
was consumed to neutralize protons resulting
from Fe hydrolysis and a heavy green precipitate
started to form. A t an air flow of 7.1 ml/min,
complete oxidation of the initial 37 mmol Fe 2+ at
p H 7 (sulphate system) took ~ 140 min. A f t e r this
time, 8.5 mmol O2 had been passed through the
system, with which 34 mmol of Fe 2+ can theoretically be oxidized, close to the initial amount. In
this experiment, the rate of oxidation was thus
determined by the air flow as in the experiments
by Vins et al. (1987).
Visual observation indicated the reaction to
take place in two parts. In the first part the
amount of green precipitate increased steadily,
whereas in the second part it turned gradually into
the final orange Fe In oxide. No more base was
consumed once the bright orange product was
obtained, and in all runs the total base consumption corresponded to the theoretical value, i.e. 2
mole O H - per mole Fe 2+. This means that the
oxidation was complete.
Sulphate system
Figure 1 (upper left) shows a typical example of
the changes of [Fe] and [SO42-] in the supernatant solution with time. The loss of Fe and
SO42- from solution is linearly related to base
consumption. A t --80% base consumption the
decrease of [SO42-] ceased and began to increase
at a rate equivalent to the reduced base consumption, the rate of which dropped from 0.74 + 0.04
mmole/min before the break to 0.014 ___ 0.002
mmole/min after the b r e a k (n = 3). A t the end o f
the reaction, all Fe was in the precipitate, whereas
all SO42- had reappeared in solution.
X-ray diffraction of the quickly freeze-dried
precipitate during the first part of the reaction
taken at three r e a c t i o n stages showed only the
sharp peaks at 1.10, 0.565 and 0.370 nm corres-
Formation o f green rust and transformation to lepidocrocite
p o n d i n g to t h e 001, 002 a n d 003 spacings of
s u l p h a t e g r e e n rust b a s e d on a h e x a g o n a l cell
( B e r n a l et al., 1959). This was, t h e r e f o r e , the sole
product. A t t h e e n d of the r e a c t i o n the precipitate
consisted of lepidocrocite, occasionally with a
trace of goethite.
In all runs the FeU/Fe m ratio d e c r e a s e d gradually from a b o u t 2.4 to 2.0 b e f o r e the b r e a k , a n d
m o r e rapidly after the b r e a k , finally r e a c h i n g zero
(Fig. 1, u p p e r right). T h e F e m / S O 4 2 - ratio was
r a t h e r c o n s t a n t and close to 1.0 b e f o r e the b r e a k ,
a n d increased rapidly after the b r e a k .
Chloride system
Similar to the sulphate system, [CI-] in the
chloride system w e n t t h r o u g h a m i n i m u m a n d
r e a t t a i n e d its initial value at the e n d of the
reaction. In the first p a r t of t h e reaction the Fell/
Fe u[ ratio of the g r e e n rust gradually d e c r e a s e d
f r o m 3.0 to 2.2 a n d t h e Fetn/Cl - t ratio increased
slightly f r o m a b o u t 0.8 to 1.0.
T h e m a i n difference b e t w e e n the C I - a n d the
SO4 z- system was t h a t , in the f o r m e r , the two
reaction steps were s e p a r a t e d by a p e r i o d w h e r e
no O H - is c o n s u m e d , i.e. n e t H + p r o d u c e d
(Fig. t, lower left). This p l a t e a u , which has also
b e e n described by T a y l o r (1984a,b) a n d Vins et al.
(1987), was paralleled by a slight increase in
[Fe 2+] a n d [C1-] in the solution. A d r o p in Eh
similar to t h a t f o u n d by Taylor (1984b) was also
o b s e r v e d (not shown). T h e precipitate did not
noticeably c h a n g e colour d u r i n g the plateau
period, a n d its X R D p a t t e r n uniformly s h o w e d
(as b e f o r e the p l a t e a u ) a chloride g r e e n rust
p a t t e r n with spacings at 0.809 (003), 0.404 (006)
a n d 0.269 n m (102) b a s e d on a r h o m b o h e d r a l cell.
Only a trace of lepidocrocite was p r e s e n t . A t t h e
same time t h e FeIVFe m ratio of t h e solid decr e a s e d drastically, from 2.25 to 0.78 a n d the FeHV
C I - ratio increased f r o m a b o u t 1.0 to 3.0 (Fig. 1,
lower right).
To e n s u r e f o r m a t i o n of lepidocrocite only, the
100.
~
O~4.0
..~ 80,
.E
0.0.
aoH consumpuo.
60.
2.0,
o ;~ 40-
.~; %
2o-
a~o 0
1
0
~ 1.0'
/
-~.~, ~ %~ata,~
-
40
8~0
Time (rn~)
0
1
~
~
~
,
,
89
=-~=
0
120
~
_==~..
_
4"0
0
Fe"~/S042-
gO
120
Time (min)
~
4.0,
-=........_.,==.~=
~
FeC
"/t
i
6o
,;'Ol
/\
Ir ~ I ~
0
20
~c 2.0
-~
"~cOtinsupematant
40
60
Time (rain)
80
~. 1.0'
100
0
0
~o
4'o
go
~o -16o
Time (min)
Fro. 1. Upper left: Relative change of iron and sulphate concentration in solution as a function of time. Upper right: Change
of the mole ratios Fell/Fe In and FeIWSO42 in the precipitate as a function of time. Lower left: Relative change of iron and
chloride concentration in solution as a function of time. Lower right: Change of the mole ratios Fell/FenI and FeIn/CI- in
the precipitate as a function of time.
90
U. Schwertmann and H. Fechter
air flow h a d to b e increased b e y o n d the p l a t e a u
(e.g. from 7.1 to 40 ml/min) b e c a u s e otherwise
m a g n e t i t e was f o r m e d , i.e. the oxidation was
i n c o m p l e t e . This agrees with earlier o b s e r v a t i o n s
t h a t slow oxidation leads to c o m p l e t e d e h y d r a t i o n
a n d only partial oxidation of the g r e e n rust to
Fe304, w h e r e a s o n fast oxidation t h e g r e e n rust is
completely oxidized a n d only partially dehydr a t e d to lepidocrocite ( B e r n a l et al., 1959; Taylor
& S c h w e r t m a n n , 1974; Solcova et al., 1981).
DISCUSSION
T h e f o r m a t i o n of lepidocrocite by oxidation of
Fe n chloride and s u l p h a t e solutions at a b o u t p H 7
a n d a low air flow rate clearly p r o c e e d s via two
different reaction steps. T h e first reaction
involves the f o r m a t i o n of green rust. Because
g r e e n rust contains structural Fe m, its f o r m a t i o n
from a p u r e Fe II solution requires some oxidation
b e f o r e the f o r m a t i o n can begin. T h e bluish-green
precipitate t h e r e f o r e does n o t form b e f o r e air is
i n t r o d u c e d into the system. If oxidized at a b o u t
p H 7, F e m ions once f o r m e d will i m m e d i a t e l y
hydrolyse a n d precipitate as a hydrous, poorlyo r d e r e d F e m oxide (2-1ine-ferrihydrite). This is
sufficiently active to react quickly with dissolved
Fe z+ at this p H to form g r e e n rust, t h r o u g h the
reaction:
x " F e ( O H ) 3 "1 + yFeSO4 + 2(y - z) N a O H
FeynFe., -m (OH)3x+2y 2::($04)~+ (y - z) Na2SO4
This reaction gains s u p p o r t from a s e p a r a t e
e x p e r i m e n t in which freshly precipitated 2-1ineferrihydrite was completely c o n v e r t e d to green
rust by a d d i n g dropwise a solution of 0.1 M FeC12
at p H 7.
T h e rate of g r e e n rust f o r m a t i o n a p p e a r s to be
limited by the rate of ferrihydrite f o r m a t i o n
which, u n d e r the conditions chosen, is determ i n e d by the rate of 0 2 supply. T h e f o r m a t i o n of
green rust ceases w h e n a certain m i n i m u m [Fe 2+]
is r e a c h e d , which may be close to t h a t in
equilibrium with the g r e e n rust. O n f u r t h e r
lowering of [FEZ+], the solution eventually
b e c o m e s u n d e r s a t u r a t e d with respect to g r e e n
rust a n d it begins to d e c o m p o s e . A t this point, the
1 For simplicity, this formula is used for the poorlyordered Fe m oxide because the exact composition of a 2line-ferrihydrite is not known.
values for [Fe 2+] were 2-3 x 10 3 M/I for t h e
s u l p h a t e form a n d 13-14 • 10 .3 M/1 for t h e
chloride form. T h e t r a n s f o r m a t i o n to lepidocrocite can b e described by:
FeyllFexlil(OH)3x+2),_2z(So4)z
+ 0.25yO2 + 2 z N a O H ~ (x + y) F e O O H
+ zNa2SO4 + (x + 0.5y) H 2 0
D u r i n g this reaction, base is c o n s u m e d to
c o m p l e t e the h y d r o x y l a t i o n of Fe, i.e. to replace
SO42 or C1 for O H - .
W i t h regard to t h e c o m p o s i t i o n of g r e e n rusts,
two aspects should b e discussed: the F e n / F e Iu a n d
the F e r n / a n i o n ratios. If the f o r m u l a of p y r o a u r i t e
is t a k e n as the ideal c o m p o s i t i o n of this g r o u p of
an FeWFe m ratio of 3, and F e n q a n i o n ratios of 1
for the chloride a n d 2 for the s u l p h a t e form would
b e expected.
F e i t k n e c h t & Keller (1950) suggested an ideal
FeU/Fe ul ratio as high as 3 for the chloride form
but n o t e d t h a t the structure tolerates a ratio as
low as 0.78 b e f o r e it b r e a k s down. Vins et al.
(1987) p r o p o s e d a general r a n g e of 0.43-1.5 for
b o t h the h a l o g e n i d e (CI, Br, I) and s u l p h a t e
forms. F r o m the intensity ratio of the Fe II a n d
Fe TM doublets of M 6 s s b a u e r spectra, t h e s e
a u t h o r s e s t i m a t e d FeU/Fe m ratios of 0.78, 0.59
and 1.14 for t h r e e s e p a r a t e samples. Using the
same m e t h o d for a s u l p h a t e g r e e n rust, C u t t l e r
et al. (1990) f o u n d a ratio of 2.25, similar to t h e
value of --2 of T a m a u r a et al. (1984). A wide
r a n g e of 0.82-3.0 was r e p o r t e d for chloride g r e e n
rust by D e t o u r n a y et al. (1976), b u t a ratio of 3
was t a k e n as t h a t of an unoxidized green rust.
Finally, for c a r b o n a t e g r e e n rusts, ranges of 0 . 5 3.0 were r e p o r t e d by M u r a d & Taylor (1986) o n
the basis of M 6 s s b a u e r spectra and 1.86-2.06 by
H a n s e n (1989) using chemical analysis. T h e
f o r m a t i o n of g r e e n rust requires a m i n i m u m of
F e m t h a t most p r o b a b l y lies close to 25% of total
Fe for the chloride form a n d close to 33% for the
s u l p h a t e form. O n c e f o r m e d , h o w e v e r , the structure tolerates m u c h higher p r o p o r t i o n s , possibly
up to more t h a n 5 0 % , before b r e a k i n g down.
T h e F e n / F e m ratios for t h e two different forms
found in the p r e s e n t e x p e r i m e n t s are well within
the range r e p o r t e d in the literature. H o w e v e r ,
additional i n f o r m a t i o n was o b t a i n e d t h a t during
the f o r m a t i o n p h a s e of g r e e n rust, its F e n / F e nl
ratio is on the high side of t h e possible r a n g e ( 2 . 5 3.0) a n d not very variable. A drastic d e c r e a s e in
Formation o f green rust and transformation to lepidocrocite
this ratio only takes place w h e n the [Fe 2+] in
solution has d r o p p e d to a value t o o low for f u r t h e r
g r e e n rust f o r m a t i o n .
W i t h r e g a r d to t h e interlayer occupancy, deviations to b o t h sides of the ideal value h a v e b e e n
r e p o r t e d ( F e i t k n e c h t & Keller, 1950; Stampfl,
1969; H a n s e n , 1989). In particular, an Fern/C1 ratio of 0.85 (instead of 1), close to t h a t r e p o r t e d
in this p a p e r , was f o u n d by F e i t k n e c h t & Keller
(1950). T a m a u r a et al. (1984) gave a ratio of 1
(instead of 2) for SO4 g r e e n rust, a n d D e t o u r n a y
et al. (1976) f o u n d a r a n g e of 1-2 for the chloride
g r e e n rust. E v e n higher ratios of 1.1-5.8 were
r e p o r t e d by Vins et al. (1987). L a r g e variations of
MIu/CO3 2- w e r e also r e p o r t e d for o t h e r
m e m b e r s of the p y r o a u r i t e g r o u p ( H a n s e n &
Taylor, 1990, 1991). T h e s e data a n d the fact t h a t
in o u r e x p e r i m e n t s the F e n q S O 4 2 - ratio is
relatively c o n s t a n t o v e r the time span of g r e e n
rust f o r m a t i o n m a k e it likely t h a t deviations from
the theoretical ratio are real.
T h e a p p r o x i m a t e bulk f o r m u l a of o u r sulphate
g r e e n rust during m o s t of its f o r m a t i o n p e r i o d is
F e n z F e l n ( O H ) 5 ( S O 4 ) . This surplus of 8 0 4 2 - may
b e e i t h e r explained by cations t h a t are located
b e t w e e n the layers such as in w e r m l a n d i t e ,
a n o t h e r p y r o a u r i t e - t y p e mineral (Rius & Allm a n n , 1984) or, m o r e p r o b a b l y , by an O 2 or
8 0 4 2 - sharing a n O ligand with an Fe of the
h y d r o x i d e layer.
T h e c o r r e s p o n d i n g a p p r o x i m a t e bulk f o r m u l a
for the chloride form would b e Fenlz.yFO ll(0H)7.6C10. s. In c o n t r a s t to the sulphate form,
this would indicate a 20% deficiency in C1. This
could b e a c c o u n t e d for by some O 2- replacing
OH
in the h y d r o x i d e layer ( T a m a u r a et al.,
1984), leading to Fell2.yFelll(OH)7.400.1oCln.8o.
A n o t h e r possibility, suggested by Vins et al.
(1987), is the p r e s e n c e of some O H b e t w e e n the
layers. A pure hydroxyl i n t e r l a y e r e d form of a
p y r o a u r i t e c o m p o u n d (meixnerite) was described
by Mascolo & M a r i n o (1980).
T h e plateau separating the f o r m a t i o n of g r e e n
rust from its d e c o m p o s i t i o n p h a s e has b e e n
o b s e r v e d for the CI system by Taylor (1984b)
and in o u r e x p e r i m e n t s , and in the SO42- system
by Solcova et al. (1981). D u r i n g this period, the
Eh in the solution (Taylor, 1984b) and the Fell/
F e m ratio of the g r e e n rust decreases (the latter
from 2.25 to 0.78). W e also o b s e r v e d a m i n o r b u t
significant increase of [Fe 2+] a n d [CI ] in solution, with an [Fe2+]/[Cl - ] ratio of --0.5 (1.40 vs.
91
3.07 m m o l , respectively). T h e increase in [Fe 2+]
would explain the d e c r e a s e in Eh. X - r a y diffraction of the p r o d u c t at the plateau s h o w e d g r e e n
rust with only a small b u t slightly increasing
p r o p o r t i o n of lepidocrocite.
B a s e d o n these data it is suggested t h a t the
m a i n r e a c t i o n taking place at the plateau is a
solid-state oxidation of the g r e e n rust (Solcova
etal., 1981) to form w h a t D e t o u r n a y (1976) called
"ferric g r e e n rust". Progressive oxidation eventually destabilizes the g r e e n rust, leading to a
slightly e l e v a t e d solubility, as seen from the small
b u t significant increase in [Fe 2+] a n d [C1-].
N e i t h e r the dissolution n o r the solid-state oxidation of the g r e e n rust a n d the f o r m a t i o n of
lepidocrocite affect the pH. This explains why n o
O H - is c o n s u m e d .
ACKNOWLEDGEMENT
We thank Dr H.C.B. Hansen, Chem. Dept., Royal Vet.
Agric. Univ. Copenhagen very much for his critical
comments to an earlier version of this paper, Dr E. Murad
from this institute for revising the text and Dr R. M. Taylor,
CSIRO Div. Soils, Adelaide, for improving the final
version.
REFERENCES
BENDERKocu C. & MORUPS. (1991) Identification of green
rust in an ochre sludge. Clay Miner. 26, 577-582.
BERNALJ.O., DASGUPTAD.R. & MACKAYA.L. (1959) The
oxides and hydroxides of iron and their structural
interrelationships. Clay Miner. Bull. 4, 15-30.
BRINDLEY G.W. & BISH D.L. (1976) Green rust: a
pyroaurite type structure. Nature 262, 353.
CU'ITLERA.H., MAN V., CRANSHAWT.E. & LONGWORTHG.
(1990) A M6ssbauer study of green rust precipitates: I.
Preparations from sulphate solutions. Clay Miner. 25,
289-301.
DERIE R. & GHODSIM. (1972) Contribution ~_l'6tude de la
formation des sesquioxydes de Fe(III) monohydrates par
adration de gels d'hydroxyde de Fe(ll). Ind. Chim. Belg.
37, 731-740.
DETOURNAY J., GHODSI U. & DERIE R. (1974) t~tude
cin6tique de la formation de goethite par a6ration de gels
d'hydroxyde ferreux. Ind. Chim. Belg. 39, 695-701.
DETOURNAYJ., DERIE R. ~; GHODSI M. (1976) Etude de
l'oxydation par aeration de Fe(OH)2 en milieu chlorure.
Z. anorg, allg. Chem. 427, 265-273.
FEH'KNECHT W. & KELLER G. (1950) Uber die dunkelgrtinen Hydroxylverbindungen des Eisens. Z. anorg.
allg. Chem. 262, 61-68.
92
U. Schwertmann and H. Fechter
HANSENH.C.B. (1989) Composition, stabilization and light
absorption of Fe(II)Fe(llI)hydroxy carbonate ('green
rust'). Clay Miner. 24, 663~70.
HANSON H.C.B. & TAYLOR R.M. (1990) Formation of
synthetic analogues of double metal-hydroxy carbonate
minerals under controlled pH conditions: I. The synthesis of pyroaurite and reevesite. Clay Miner. 25, 161-180.
HANSEN H.C.B. & TAYLOR R.M. (1991) Formation of
synthetic analogues of double metal-hydroxy carbonate
minerals under controlled pH conditions: II. The synthesis of desautelsite. Clay Miner. 26, 507-525.
McGILL I.R., MCENANEYB. & SMITHD.C. (1976) Crystal
structure of green rust formed by corrosion of cast iron.
Nature 259, 200-201.
MURAO E. & TAYLOR R.M. (1986) The oxidation of
hydroxycarbonate green rusts. Pp. 585-593 in: Industrial
Applications of the MOssbauer Effect (G.J. Long & J.G.
Stevens, editors). Plenum Publ. Co., New York.
MASCOLO G. & MARINO O. (1980) A new synthesis and
characterization of magnesium-aluminium hydroxides.
Mineral. Mag. 43, 619-621.
RIUS J. & ALLMANN R. (1984) The superstructure of the
double layer mineral wermlandite [Mg7(A10.57,Fe0.433+)(OH)1812+.[(Cao.6, Mg0.4)(SO4)2(H20)12]2-. Z.
Krist. 168, 133-144.
SOLCOVAA., StJaRXJ., VINSJ., HANOUSEKF., ZAPLETALV.
t~. TLASKALJ. (1981) Oxidation of ferrous sulphate in
neutral and weakly alkaline so|utions. Coll. Czech.
Chem. Commun. 46, 3049-3056.
STAMPFLP.P. (1969) Ein basisches Eisen-(lI)-(IIl)-Karbonat in Rost. Corr. Sci. 9, 185-187.
TAMAURA Y. YosnIDA T. & KATSURE T. (1984) The
synthesis of green rust II (FemrFen2) and its spontaneous transformation into Fe304. Bull. Chem. Soc.
Japan 57, 2411-2416.
TAYLORR.M. (1980) Formation and properties of Fe(II),Fe(IIl) hydroxy-carbonate and its possible significance in
soil formation. Clay Miner. 15, 369-382.
TAYLORR.M. (1984a) Influence of chloride on the formation of iron oxides from Fe(II) chloride. I. Effect of [CI]/
[Fe] on the formation of magnetite. Clays Clay Miner. 32,
167-174.
TAYLORR,M. (1984b) Influence of chloride on the formation of iron oxides from Fe(II) chloride. II. Effect of [CI]
on the formation of lepidocrocite and its crystallinity.
Clays Clay Miner. 32, 175-180.
TAYLOR R.M. & McKENZ~ER.M. (1980) The influence of
aluminum on iron oxides. VI. The formation of Fe(II)Al(IIl)hydroxychlorides, -sulphates, and -carbonates as
new members of the pyroaurite group and their significance in soils. Clays Clay Miner. 28, 179-187.
TAYLOR R.M. & SCHWERTMANNU. (1974) Maghemite in
soils and its origin. II. Maghemite syntheses at ambient
temperature and pH 7. Clay Miner. 10, 299-310.
VINS J., ZAPLETALV. • HANOUSEKF. (1987) Preparation
and properties of green rust type substances. Colt.
Czech. Chem. Commun. 52, 93-102.