.I PORTIOS OF T H E PTSTEXI, FERRIC' OXIDE-C'I'PRIC OXIDE-Pt7LPHV'R TWIOSIDI~-\\~ATER
Introduction The investigation of the system, ferric oxide-cupric oxide-sulphur triositlewater, was undertaken primarily to gain some knon-ledge of the processes which take place and the equilibria which may be a t t n i n r d during the natural oxidation of the disseriiinnted iron and copper hulphicte ore bodies in altered porphyry. Since thesr processes presumably take pl:i re in the neighborhood of surface temperatures and in not very concentrated solutions, the investigation was restricted to these conditions a s i large amount of time to work out the quaternar
Experimental Methods For the preparation of the initial mixtures, besides riorinal cupric sulphate and normal ferric sulphate, a basic f m i c sulphate and a specially prepared suspension of cupric oxide together with the required amount of water were used. The hasic ferric sulphate )vas obtained .mne years ago from the firm of J. T. Baker and an analysis (33.61 per c m t Fe,20:j.4 2 . 1 2 per cent PO3, ani1 by difference 2 4 . 2 7 per cent H20)was fuiintf to :rpproach the composition of the basic salt ?Fe20:,.;W3.~ jHl.O. It, ivas rxtreniely fiiir-grained and for that reason could not be definitely identified niicroscopicnlly. The su5pension of finely tiividrd cupric oxide w:is prepared by adding a dilute solution of sodium hydroxide to a fairly concentrated warn1 solution of cupric sulphate, with constant stirring, until it became just alkaline. The greenish-blue precipitate first formed changed at this point to a brownish-black one which vas cupric oxide :is \vas evidenced by its X-ray clifr'raction pattern. The precipit:ite \viis washed by shaking it u p with hot water and throwing it clown by centrifuging. This was continued until the finely diyicled cupric oxide began to form a suspensicn which was no longer precipit:ited by ordinary centrifuging (approximately a relative centrifugal force of I 1 0 0 times gravity). The suspension prepared in this way \vas found by :in analysis to Le pr:tctieally free from sodium. Froni appropriate amounts of the 1ii:itc'ri:il- described above mixtures of definite total composition were prepared which, on reaching equilibrium, furnished sufficient amounts of liquid and solid phases for their identification. 'The total amounts of the mixtures ranged from about 40 to about I O O grams. l h c h mixture \vas sealed in a Jena combustion tube, which it about twothirds filled. Thrse t u b Xvere placed in an air thermostat at 50' in which the variation of temperature \vas limited to about + I O , The time the tubes viere kept in the thermostat ranged. from about one t o about three years and during this time they TverP shaken up :ilinost every day to promote thr establishment of equilihrium.
930
0.TUXELL AXD E. POSNJAK
After the tubes were taken out of the thermostat they were quickly opened and the solid separated from the liquid phase by suction filtration through a dense Jena glass filter. A sample of the solid with adhering mother liquid was examined microscopically for control. The rest of the solid was washed with a mixture of water and alcohol and finally with alcohol or acetone. The air-dry solid was subjected to careful microscopical examination and X-ray analysis to establish the nature of the phase or phases present. Despite the extreme fineness of the precipitates representing the solid phases, it was in all cases possible to establish definitely their crystallinity and crystal individuality even when more than one solid phase was present in the precipitate. The liquid, or a portion thereof, was weighed and analyzed. The following procedure was used: The copper was removed first by electrolysis of the solution, and weighed. The remaining solution, largely increased in volume due to washing of the copper precipitate, was partially evaporated and at the same time the iron which was reduced during electrolysis was re-oxidized by the addition of a few drops of “perhydrol” to the solution. A double precipitation of the iron with ammonia in the usual way followed and the iron on ignition was determined as oxide. I n the combined filtrates the sulphate was finally determined, also gravimetrically, as barium sulphate. This method had been tried out with a mixture of standard solutions of copper and iron sulphat,es and was found in the absence of nitric acid to give accurate results. Water in all cases was taken by difference.
The Crystalline Phases Geometrical and optical crystallographic descriptions of all of the compounds found in the portion of the quaternary system investigated have already been published.‘ I n this paper the mode of occurrence of all these in the quaternary system will be described and X-ray powder diffraction patterns will be given for two of them, Fe203.H20 (goethite) and 3Fe~O3. 4S03.9H20,the patterns of the others having already been published.2 Fe203.H20(Goethite).28KO single faceted crystals of goethite formed in the quaternary system at 50’ (the only temperature a t which experiments I E. Posnjak and H. E. hlerwin: The Hydrated Ferric Oxides, Am. J. Sci., 47,320 (1919); E. Posnjak and H. E. Merwin: The System, FegOa-$03-HzO, J. Am. Chem. Soc., 44, 1977 (1922); E. Posnjak and G. Tunell: The System, Cupric Oxide-Sulphur Trioxide-Water, Am. J. Sci., 18, 12-23 (1929). 2Am. J. Sci., 18, 1 2 (1929).
2 8 The usage of the term goethite in this paper is the same as that in earlier papers from this Laboratory; the term goethite is thus, used as a synonym of a-Fe20a.HzO. It may be added that in this Laboratory the term lepidocrocite is used as a synonym of y-Fe?Oa.H10. These usages are consistent with those of most other authors. Unfortunately, however, by WiUmann (Cbl. Min., 1921, 673) and in “Gmelins Handbuch der anorganischen Chemie” (8.Aufl., Teil A, S.147 (1929)) the term goethite has recently been applied to y-FezOa.Hg0. For a clear statement of the hstory and present usages of the terms see “Handbuch der anorganischen Chemie” (Vierter Band, dritte Abteilung, zweiter Tea, B, Lieferung I , S. B224, B225 (1930)) by R. Abegg, Fr. Auerbach, and I. Koppel. These authors use the terms goethite and lepidocrocite in the same sensea in which they are used in the Geophysical Laboratory. Abegg, Auerbach, and Koppel ive a good summary in tabular form of the geometrical optical, and X-ray cvstaUograpfic properties, the densities, and some other physical pdperties of the dimorphc forms of Fe20J.H20 (S. B226).
FERRIC OXIDE-CUPRIC OXIDE-SULPHUR TRIOXIDE-WATER
93 1
were carried out in the quaternary system), or in the ternary system, Fe203-S03-H20, a t 50' or at any other temperature. Spherulites of goethite, single and in aggregates, were formed in one ternary solution a t 50' and in other ternary solutions a t higher temperatures. All of the goethite preparations formed in solutions containing all four components a t 50' consisted of fibrous or optically amorphous aggregates. I n all cases, however, their crystallinity and identity were established by the X-ray powder diffraction method. The apparatus used was one made by the General Electric Company in which the K, radiation of molybdenum is used and the distance between sample and photographic film is eight inches. As a standard of comparison well-crystallized goethite from Pribram, Bohemia (Harvard
I
?Fe,O,.450,
1
PY~O
I
FIG.I Diagrams of X-ray powder diffraction patterns of F e ? 0 3 . H Z 0(goethite) and 3Fe2O3.qSO8.gHZ0.The relative intensities are visual estimates with ten representing the maximum in each case.
Museum KO. 80927), was utilized, of which the measured spacings of the diffraction lines and their estimated relative intensities are given in Table I.3 3Fez03.4S03.9Hz0. Faceted crystals of 3Fe203.4S03.9H20and aggregates of fine anhedral grains formed in ternary solutions of Fe203-S03-H20 a t 50'. I n solutions containing all four components no faceted crystals formed but only fine-grained (crystalline) aggregates of anhedral, equant grains which were identified microscopically and by means of their X-ray powder diffraction pattern. Crystals of 3FezO3.4S03.gHzO1precipitated in a ternary solution of Fe203-S03-H20were used to obtain the standard X-ray spectrum of this substance. The measured spacings of the lines in the standard spectrum and their estimated relative intensities are given in Table I. ~
~
The diffraction pattern obtained from this specimen was identical with that obtained from one of goethite from El Paso County, Colorado, the analysis of which was KO.5 in Table I and the specific gravity No. 5 in Table VI1 of "The H drated Ferric Oxides" (Am. J. Sci., 47, 316 (1919)). Powder from the specimen from &l Paso County, Colorado, was examined under the microscope by Merwin and by Tunell. No impurities were found. The powder consisted of brown, transparent to translucent grains some of, whmh were perceptibly pleochroic between slightly different shades of brown. Grains lying approximately parallel to the erfect cleavage exhibited the characteristic green interference color already mentioned by herwin and these also showed a biaxial optical figure. 4 Identified optically. The optical properties of anal zed crystals formed in the system, Fe2O8-SO~-HZ0, had been established previously by Sosnjak and Merwin. 3
G . TUXELL AND E. POSSJAK
93 2
TABLE I Planar Spacings and Estimated Relative Intensities of the X-ray Diffraction Lines of Fe203.H20 (Goethite) and 3Fe201.qS03.gH20 Fe?O:3.H,O (Goethite) Spacing Intensit)
4.0
2
5.1
3Fe203.4S03.gH20 Spacing Intensity
3 5 7
4.25
IO
3.42
3
3.07
0.5
5.7 5 15 3 09
2 . 7 2
0 4
3 54 3 .IO
3 9
3.00
1
2.475
2.84
2.325
0 .j
2 .
,i4
3 4
2.275
7
2.27
3
2.220
h
2.110
0
1.99 1.93:
2
2.040
0.j
2.61 2 . 5 2
,
5
1,940 1.820
3 8
1.732 I . 704
-5:s 470
840 I . 780
0.j
3
I .
,
I.520 I .
,890
1.745 1.6j1 1.595
3
,675 1.613 I
I.
I
I
(broad)
1,431 1 ,403
-I I
jio
1 1
IO
> 1 I
1
2 2
2 1
I
54.5 1.503
3
1.441 1.39'
3
1.35'
2 2
3
1
1.372
>
I 320
.32.?
2
I .2j2
I ,301
0.5
I .230
1
I.2jI
1
I .2 0 0
I .208
I
I .
I .1 ;;.
2
1.134
3 3 3
1.131
2
I . IO0
I
1.075
0.5
1
I .Oj;
1
1.033 I . 018
I
Further weak lines prrsent
I
I60
Further weak lines present
G. TUNELL AND E. POSNJAK
93 4
TABLErr The Saturation Surface of the System, Ferric Oxide-Cupric Oxide-Sulphur Trioxide-Water, a t 50' inside and just outside the Limited Portion of the Tetrahedron Expt.
8A
FezOs
70
1''
< o . 001
gA I o . : {
Liquid Phase
CuO
%
sos %
H,Oz
0.06
0.06
99.88
0.14
0.15
99.71
SA'
0.05
0.08
0.39
99.48
6.4'
0.17
0.15
0.74
98.94
0.61
0.64
98.75
IIh
{'o
