Note: Descriptions are shown in the official language in which they were submitted.
Process for converting, into an easily removable form, metallurgi-
cally harmful components present in mainly sulfidic complex and/or mixed ores
and concentrates.
The process according to the present invention relates to the con-
verting of sulfidic complex and mixed ores into a form technically easy to
refine. These ores and concentrates usually contain as their main components
copper, nickel, cobalt and iron. These components are usually combined into
complicated complex sulfides containing arsenic, antimony and bismuth. Owing
to their manner of formation, these ores quite often contain rare and there-
fore valuable heavy-metal compounds, some of their components being Se, Te,
Ga, In, Tl, Ge, Sn, Pb, Zn, Cd, Hg, Mo, Mn, Re, Ag, and Au.
The process is used for removing, as principal impurity metals,
As, Sb and Bi, and as great a part as possible of the said volatile heavy
metals from ore or concentrate powder. If the amount of the said impurities
is very high, the aim is to convert according to the process these impurities
into such a form that they can be easily evaporated as pure sulfide minerals
in the actual refining process of the main components.
It is generally known that the impurity components As, Sb, and Bi
are very harmful in, for example, pyrometallurgical refining processes. Some
of the heavy trace element components -- e.g., Hg, Cd and Te -- being highly
poisonous substances, constitute a great harm~ul factor in terms of environ-
mental protection. The numbers of a great many of the trace elements are also
high in the periodic system and therefore, being rare substances, they are
very valuable both technologically and economically.
Arsenic, antimony and bismuth cause very great problems in the
metallurgy of copper and nickel. In pyrometallurgical processes the compounds
of these components, which easily dissociate into metals, are present through-
out the processing of the principal metals. An attempt is made to remove
B -1-
7~7
these components during each processing stage because, when left in the raw
metal, they complicate its purification and, when left in the final product
even in very small contents, spoil it ~the content per component should be
in conductive copper, for example, less than 0.001% by weight).
The impurities under discussion are usually combined with the
principal metal into complicated complex compounds so that a pretreatment of
the ore or concentrate by evaporating annealing or selective froth flotation,
for example, does not produce any results. Neither are the processes for a
selective dissolving of the components successful, either for the above
reasons or for thermodynamic reasons due to the impurity metals themselves.
There are few patented or otherwise recently published processes
comparable to that according to this new invention, i.e., removal of im-
purities directly by a pretreatment of the ore or concentrate. Some of the
latest pyrometallurgical processes for copper and nickel are discussed below
to illustrate the current methods developed for the removal of the impurities
discussed and the technological level involved in these methods.
When copper is produced by conventional methods (reverberatory
smelting, sulfide converting, electrolysis), part of the arsenic, antimony
and bismuth present in the copper concentrates can be removed, but not to a
sufficient degree to obtain a satisfactory end result. In colmection with
a thermal agglomeration of the concentrate before the melting, for exampie,
approx. 20% of the antimony can be transferred into the flying dusts. Approx.
another 20% of the antimony is transferred into the slags and flying dusts of
the reverberatory melting. In the sulfide matteconverting process, approx.
40-50% of the original antimony amount present in the feed concentrate is
transferred into the flying dusts. Although approx. 80-90% of the antimony
can thus be removed during the process, the antimony content of converter
copper can still be 0.5-2.0% by weight so that the problems involved in the
~ - 2 -
copper electrolysis are very great.
Attempts have continuously been made to improve the techniques of
removing impurities at different processing stages. In connection with the
production of sulfide matte , the removal of the impurity components under
discussion can be affected by the selection of suitable smelting techniques.
In shaft, reverberatory and electric furnace smelting, approx. 50% of the said
impurities present in the feed are left in the sulfide phase. In suspen~sion
processes, especially when producing sulfide mattes rich in valuable metals
(strong suspension oxidation), results considerably better than those mentioned
above are obtained, especially regarding arsenic and bismuth. The processes
according to U.S. Patents 3 754 891, 2 506 557, 3 555 164 and 3 687 656) and
processes analogous to these should be mentioned among the suspension
processes.
By the development of recent years it has been possible to improve
the separation, per apparatus at the converting stage, of the impurities under
discussion from the conventionalvalues (70-75%) to above 90%. The separation
has been improved by, for example, combining the impurities by oxidating them
with alkali or iron oxides into stable compounds separating from the melt.
An example of these processes is that according to U.S. Pat. 3 744 992,
wherein antimony is combined with iron into mixed spinel lattices. Nowadays
the aim is to remove the metals As, Sb, Bi, Pb and Zn from the valuable-metal
sulfide melt after the iron blast stage of the converting process. The recent
development is illustrated by, for example, the selective chlorination of
nickel sulfide melt by the process according to GFR Pat. 2 056 001 (appli-
cation of process also: M.C. Bellym, 103rd AIM~ Ann. Meet., Feb. 24-28, 1974,
Dallas, Texas). Great efforts have also been made to develop the removal of
impurities by a vacuum treatment of sulfide melt (e.g., H. Kametani et al: Trans
JIM, 14, 1973, pp. 218-223).
3 -
7~
In the prepurification of raw metal in an anode furance, the same
technique is used as in converting. Some examples Gf the various processes
are the selective oxidation of impurities with earth-alkali oxides, the
double-slag processes (GFR Pat. 1 137 223) and vacuum processes (e.g., J.
Bocle et al.: Erzmetall, 24, 1971, pp. 480-485; A. Yazawa et al.: Can. Met.
Quart., 8, 1969, pp. 257-261). It should be noted that the activity con-
ditions of the impurity metals under discussion in metal melts are highly
disadvantageous so that the removal of impurities which have reached the
metal melt is highly uneconomical by current processes.
The purification of calcines of pyrites and chalcopyrite, comprising
a great number of different methods, should also be mentioned. The aim is to
remove sulfur, arsenic, and antimony, as well as valuable metals, from the
calcine, whereby the treated calcine can be used as raw material in iron
production. The processes are usually one- or two-stage oxidation and
reduction processes to which a sulphating, chlorinating or evaporating
rOasting is almost always linked. Fluidized-bed furnaces are generally used
for carrying out the processes. The processes according to U.S. Pat. 3 649 245,
Canadian Pat. 890 343, 876,030, 885 378 and 882 585 can be mentioned as
examples of the latest technology.
The object of the present invention is to provide a process by
which complex and mixed ores can be treated advantageously in terms o both
economy and technology.
By the process according to the invention, the ore or concentrate
is brought, through simulation by modern technological methods, into con-
ditions in which they presumably were before the condensation of the volatile
impurity components and their reaction with the melts or solid sulfide phases
which are pure at a high temperature. According to the invention this is
achieved by decomposing and then rearranging the mineral crystals formed by
10S7~~
the elements constituting the main components -- Cu, Ni, Co, Fe -- at a suf
ficiently high temperature, i.e., 500-900C, and under a sufficiently high
partial pressure of elemental sulfur vapor, into stable simple compounds
corresponding to the altered conditions. The rearranging is made possible
within the said very low temperature range by the strongly increased
velocity of metal diffusion in the sulfide matrix, catalyzed by the non-
stoichiometry of compounds caused by sulfur vapor. In connection with the
rearrangement, both impurities and trace elements are detached from the
complicated complex structures into which they have combined during the
formation of the ores in the course of millions of years as the conditions
have changed. In this case, part of the impurities can be removed already
when realizing the process, while part of them remain in the product in a
new structural form that allows their easy removal when the obtained con-
version concentrate is refined further by conventional methods.
Accordingly, the present invention provides a process of working
up sulfidic complex ores and concentrates into a form suitable for refining
by conventional methods, starting with a raw material consisting of sulfide
complex ores and concentrates containing at least one of As, Sb, Bi, Se
and Te as an impurity difficult to remove, comprising converting said impurity
into a removable form by decomposing and rearranging the raw material at a
temperature of ~rom about 500C to about 900C, and in an atlnosphere whercin
the part~al pressure of elemental sulfur is at least 0.2 atmospheres.
The conversion process can be carried out in conventional static
or continuous-working metallurgical apparatuses with an advantageous heat
economy. For example, a conventional, tight periodic-working or continuous-
working cylindrical furnace used for the drying of concentrate is suitable for
the purpose.
According to the process, the operation conditions of the process
~ _ 5 _
~C)S~7~
can be controlled in many ways, in accordance with the mineral content of the
material to be treated, and likewise the amounts of impurities and trace
elements in the final product can be regulated.
Ad~antageously, the converted impurity can be at least partly
evaporated in the decomposing and rearranging stage. Furthermore, `after the
decomposition and rearrangement , the temperature of said impurity can be
raised to remove the converted volatile components.
Preferably, said impurity present in the raw material is decomposed
and rearranged in an atmosphere containing substantially only elemental
sulfur. Preferably the raw material is kept for about 1/2 - 2 hours at a
temperature of 650-750C.
The invention under discussion thus consists of a process for
decomposing the complicated mineral present in sulfidic complex and mixed
ores and concentrates and for simultaneously rearranging these compounds into
new and simple mineral structures. According to the process, part of the
elements which are present in the complex ores and greatly complicate their
- 5a -
~V5'7S~
treatment can, when carrying out the process according to the invention, be
removed entirely or partially from the ore matrix, and part of the elements
can be rearranged into such mineral crystals as facilitate the removal of
these substances when the ores are refined by conventional methods. The bulk
of these elements, which are combined into sulfides of copper, nickel, cobalt
and iron as complicated and stable complex structures, consist of arsenic,
antimony and bismuth. In addition to these, the process covers a great
number of elements which independently form complex minerals or are present
in the crystals of others. Such elements include Se, Te, Ga, In, Tl, Ge,
Sn, Pb, Zn, Cd, Hg, Mo, Mn, Re, Ag, and Au.
According to the process, the rearrangement of the minerals is
effected by very strongly catalyzing the solid-state diffusion of metals, and
also sulfur, by means of a high partial pressure of elemental sulfur within
the temperature range 500-900C, preferably 600-800C. The minerals compound
into stable sulfides corresponding to the new conditions. Depending on the
temperature and the amounts of material, some of the impurity substances (as
such very valuable and partly rare elements) are evaporated either as sulfides
or in a pure form, according to their vapor pressures.
In the process according to the invention, the usually very com-
plicated mineral structures of mainly sulfidic complex and mixed ores andconcentrates are decomposed into their elemental components and these are
rearranged into synthetic and at the same time simple mineral structures.
Simultaneously, with the rearrangement of the minerals of the main components
(Cu, Ni, Co, Fe, etc.), many substances (As, Sb, Bi, Se, Te, Ga, Ge, Cd, Hg,
Re, etc.) which are combined into complex structures and are often counted
as impurities in regard to the main components are decomposed and rearranged
into mineral phases which facilitate a simultaneous or subsequent removal
of the same. Some of these impurities are evaporated totally or partially,
s~
depending on the treatment temperatures and amounts of material and the
vapor pressures of the components.
The decomposition and rearrangement of the complex minerals is
preferably carried out within the temperature range 600-800C, using the
"catalytic" acceleration of metal diffusion (also sulfur diffusion) which
occurs in the sulfide phase under a high vapor pressure of elemental sulfur.
A rapid transport of metal in the system makes possible those activity con-
ditions of the sulfidic compounds of the main components which are advantag-
eous for the process and are caused by the diffusion, and it also makes
possible the direct evaporation of part of the components.
The ores covered by the process have mainly been created as a
result of late magmatic differentiation. Some of the mineralizations (e.g.,
magnetic pyrite-pentlandite paragenesis, stable arsenic and antimony minerals
of platinoids, etc.) segregated under the effect of the melt-melt solubility
gap of the latter stage of the early magmatic phase are covered by the pro-
cess. The greater part of the ores within the range of the method are, how-
ever, created by the differentiation of the rest eutectic of the latter
phase and, in addition, as a mineralization by the low temperature and
pressure of that phase (i.e., the slowly crystallized, well-mineralized
complex and mixed ores, etc.). In this case, those ores that are involved
are, in the order of importance, pegmatitic te.g., molybdenum and copper
glances), pneumatolytic (e.g., copper and arsenic pyrites, lead glance, zinc
blende, and pyrites), contact metasomatic (e.g., copper and arsenic pyrites,
pyrite, lead and iron glances, zinc blende, and selenium and bismuth mi.nerals
of noble metals), and hydrothermal deposits.
Most of the ore mineralizations covered by the process appear
specifically as hydrothermal deposits. Some of these groups and some minerals
of the groups are discussed below by classifying them mainly on the basis of
B _ 7
105751~
their composition.
a. Pyritic and arsenic-rich groups: the following general-form minerals
are given as examples:
(Fe, Co, Ni) (S, Se, Te)2
(Fe, Co, Ni)As2
(Fe, Co, Ni)(As, Sb)S
Cu(Fe, Ga, In)S2
(Cu, Ag)Fe2S3
Cu3(Ge, Fe, As, Sb)S4
10 Cu5FeSn; Cu2S, CuS
b. Lead, zinc, silver groups: the following forms are given as examples:
(Cu, Ag)20(Fe, Zn, Hg, Ge, Sn)4(As, Ab, Bi)8S26
(Zn, Cd, Hg)(S, Se, Te)
Pb(S, Se, Te)
c. Tin, zinc, silver groups
Cu3(As, Sb, Fe, Ge, V)S4
Cu2(Ag, Fe, Zn, Sn)S4
d. Cobalt, nickel, silver, bismuth, uranium groups
(Co, Ni, Ag, U)(As, Bi)3
e. Groups of arsenic, antimony, bismuth complex ores: the :Eollowing mineral
types are mentioned as examples:
Ag3(As, Sb)S3
Cu3BiS3
Cu(Sb, Bi)S2
Ag(As, Sb)S2
(4 Te, llg)(As, Sb)4S8
Pb, Cu(As, Sb, Bi)S3
etc.
- 8 -
~(3S751~
In addition to the natural minerals, the process naturally also
covers the precipitates containing synthetic parts of the above mineral
groups, produced as by-products of industrial processes.
It was noted above that most of the ores that can be treated by
the process according to the invention belong to pneumatolytic and hydrothermal
deposits. In such cases the ore mineralizations have been separated from the
hydrothermal solutions mainly below the temperature and pressure range 400-
500C and 220-250 kg/cm2. Elements which represent the high o~dinal numbers
of the periodic system and which move easily and have high vapor pressures
have then been concentrated in both the liquid and the gas phases. When the
conditions of the separation system (pressure, temperature, concentration,
grain size, etc.) gradually change, the phases of the already separated
compounds become unstable and the atom and ion structures corresponding to
the changed conditions are created (i.e., metasomatic metamorphosis), while
the compositions of both the liquid and the gas phases are changed simultan-
eously. Of the elements covered by the new process, arsenic, for example, is
separated to a considerable degree already at the pegmatitic stage, bismuth
from hot hydrothermal solutions, and antimony and mercury at temperatures
lower than the former. The composition of the gas phase of the segregation
system can be deduced from, for example, volcanic exhalation products, which
in addition to superheated water vapor usually contain sulfur, arsenic,
selenium, tellurium, mercury, zinc, lead, etc. These substances participate
in the geochemical exchange and other reactions in mineral formation.
The starting point of the new process was the reversal, by tech-
nological methods, of the metamorphosis which has taken millions of years in
nature. According to the process, the rearrangement of the mineral lattices
of the ore or concentrate is carried out by creating, by means of an external
gas phase and thermal excitation, the conditions under which volatile heavy
~ r~i _ 9 _
l(lS7S10
metals form new minerals of their own or are transferred into the gas phase.
Of course, the conditions corresponding to those before the pneumatolytic or
hydrolytic separation phase cannot be obtained economically, but in terms of
technology the low sulfur content and high total pressure of the thermal
waters can be simulated by using for ~he rearrangement a greater sulfur
pressure and temperature gradient and shorter diffusion distances than
previously (the particle size, i.e., diffusion distance, of ground con-
centrate is of the order of only some hundredths of millimeters; in the
natural metamorphosis the diffusion distance may be tens of kilometers).
The invention is described below in more detail with reference to
the enclosed drawings, in which
Fig. 1 shows electrograms and roentgenograms of a Cu-Co-Fe-As-S
concentrate, 500 x enlarged,
Fig. 2 shows similar graphs of a partially reacted CoSAs grain,
Fig. 3 shows similar graphs of a partially reacted Cu-Co-Fe-As-S
concentrate,
Fig. 4 shows a linear analysis of a partially reacted CoSAs grain,
Fig. 5 shows an equilibrium diagram of the system Co-As-S,
Fig. 6 shows the scheme of reactions of the rearrangement of cobalt
arsenide,
Fig. 7 shows graphs of a partially reacted Ni~Fe,Co)SAs grain,
300 x enlarged,
Fig. 8 shows a linear analysis of a NitFe,Co)SAs grain,
Fig. 9 shows graphs of a (Ni,Co,Fe)(As,Sb) concentrate, 300 x
enlarged,
Fig. 10 shows graphs of a partially reacted Ni(Co,Fe)SAs(Sb) grain,
500 x enlarged,
Fig. 11 shows a linear analysis of a Ni~Co,Pe)SAs(Sb) grain,
- 10 -
~0575~
Fig. 12 shows graphs of a partially reacted (Ni,Co,Fe)~As,Sb) grain,
500 x enlarged,
Fig. 13 shows a linear analysis of a ~Ni,Co,Fe)(AsJSb) grain,
Fig. 14 shows graphs of a partially reacted Cu3AsS4 grain, 500 x
enlarged,
Fig. 15 shows a linear analysis of a Cu3AsS4 grain,
Fig. 16 shows graphs of a partially reacted Cu3AsS4 grain, 500 x
enlarged~
Fig. 17 shows a linear analysis of a Cu3AsS4 grain
Fig. 18 shows the vapor pressures of metal sulfides as functions
of temperature, and
Fig. 19 shows a cylindrical furnace designated for the application
of the process according to the invention.
A theoretical discussion on the process according to the invention
is greatly complicated by the lack of both the balance diagrams and the
thermodynamic functions of the various systems, and therefore a mathematical
quantitative illustration of the rearrangement possibilities of minerals can
be given only in a small number of cases.
A chalcopyrite-cobalt-glance-pyrite concentrate is taken as the
first object of discussion. The main components according totllo analysis
(~ by weight) were as follows: 9.6-10.0 Cu, 2.8-3.0 Co, 35.8-38.4 Fe, 35.1-
38.4 S, and 3.4-6.1 As. The cobalt glance of the concentrate, CoAsS, was in
the form of large, well-formed crystals. The structure of the concentrate can
be seen from the series of electrograms and roentgenograms of Fig. 1. The
roentgenograms corresponding to the pyrite (1), chalcopyrite ~2) and cobalt
glance (3) of the electrogram indicate a very clear distribution of arsenic
in the CoAsA phase. Cobalt and arsenic were not present in the other minerals
of this specimen.
- 11 -
1~5~7~
To decompose and rearrange the minerals of the concentrate specimen,
it was annealed at 700C under a sulfur pressure of one atmosphere. The
annealing period was 30 minutes. The average atomic number of the molecules
of the sulfur vapor was then 2.48. The temperature of the experiment was
above the boiling point of arsenic sulfide (vapor: As4S6) so that the arsenic
was removed from the reaction area when the crystal decomposed. During the
annealing the arsenic content in the specimen decreased from 4.3% to 0.24% As.
Fig. 2 shows a series of electrograms and roentgenograms taken of a
partly decomposed CoAsS structure. The size of the initial cobalt glance
granule and the rearranged zone of the boundary areas of the granule can be
well seen in the electrogram. The roentgenograms show that while cobalt covers
the entire area of the initial granule, arsenic has completely disappeared
from the zone of transformation but is obviously fully left in the core of the
grain. Sulfur has concentrated in the transformation zone of the grain in a
far greater quantity than there is in the unreacted part. The strong filtra-
tion of iron into the zone of transformation is noteworthy. The chalcopyrite
granules of the concentrate remain unchanged. Fig. 3 illustrates a specimen
corresponding to Fig. 2, but on a smaller scale. The figure shows, in addition
to the concentration phenomenon, the behavior of pyrite and chalcopyrite.
Fig. 4 shows a roentgenographic linear analysis of a partially re-
arranged cobalt mineral corresponding to Fig. 2 in regard to the various
components. The rearrangement reactions mentioned above can be seen in the
figure as measured percentages of the components. The analysis of the cobalt
glance in the core of the grain (figure: measured at approx. 30-70u from the
original grain boundary) corresponds to a stoichiometric iron-alloyed
Co(Fe)AsS composition, i.e., (% by weight): 33.4 Co, 2.0 Fe, 45.1 As, and
19.3 S. According to Fig, 4, great changes in the percentages have taken
place in the phase boundary area between the rearranged and the original
. - 12 -
i(~5'75~0
mineral ~figure: distances 20-30~ and 80-90~). A very sharp decrease takes
place in the arsenic concentration in these areas of transformation, i.e.,
from concentrations corresponding to cobalt glance (45% As) to values close
to zero. According to the linear analysis, the cobalt concentration begins to
apparently decrease long before the change in the arsenic concen~ration, and
this is due to the alloying of the created new sulfide by iron. The sulfur
concentration rises very strongly in the transition area. The sulfur con-
centration according to the analysis corresponds to ~he sulfide composition
CoS2 8 3 o(60.4-62.0% by weight S). After the area of transformation the
sulfur concentration decreases to correspond to the sulfur concentrations of
pyrite (FeS2) and cattierite (CoS2) ~i.e., 53.5% and 52.1% S). It should be
mentioned that the three minerals under discussion have cubic lattices, the
lattice constants (aO,A/MeS) being as follows: 5.42/FeS2, 5.52/CoS2, and
5.61/CoAsS.
The equilibrium diagram of the Co-As-S system is not known. Fig. 5
shows the positions of the binary intermediary compounds of the system as
functions of the composition. The free energy of the formation of correspond-
ing compounds (calculated from pure metals) per S2(g) mol and As4(g) mol is
indicated in the figure as corresponding to the temperature 700C. The thermo-
dynamic values of cobalt thioarsenide are not known. On the basis of thevalues of iron glance, the value of react:ion (10)
(10) 2Co (s) * S2 (g) * 1/2 As4 (g) ', 2CoAsS (s)
can be estimated:
-QGT/RTlnlO = log kp = 19050/T - 10.695
At the observation temperature, the value QG = 39540/cal/mol S2 (g)
is obtained for CoAsS. When the QG values of the thermally stable compounds
CoS (s) and CoAs (s) of Fig. 5 (melting points 1150C and 1180C) are compared
with the value according to the equation (10), it can be noted that there are
~S7Sl(~
no considerable differences in stability between the compounds (~G9730K/~ey: -
39540/2CoAsS,- 39240/2CoS and - 38116/4CoAs).
The following equilibrium constants are obtained thermodynamically
for the rearrangement reaction of cobalt glance:
Equilibrium reaction log kp = A/T-B.
A B
(11) 2Co (s) + S2 (g) '-7 2CoS (s) 15758 7.376
(12) Co (s) + S2 (g) ~7 CoS2 (s) 13867 9.197
(13) As4 (g) + 3S2 (g) '7 As4S6 (g) 27550 23.486
(14) As4 (g) + 2S2 (g) ~'7 As4S4 (g) 27550 23.664
(15) 4CoAsS(s) + 4S2(g) '~ 4CoS2(s) + As4S4(g) 44910 39.062
(16) 4CoAsS(s) + 5S2(g) ~-7 4CoS2(s) + As4S6(g) 44910 38.884
(17) 2CoAs2(s) + 5S2(g) '7 2CoS2(s) + As4S6(g) 39060 31.177
(18) 4CoAs(s) + 7S2(g) ~7 4CoS2(s) + As4S6(g) 64820 50.146
Fig. 6 shows the rearrangement reaction series of cobalt arsenide,
calculated on the basis of the above values. The numbers in the figure cor-
respond to the results of the reactions. In the following table the free
energy values of the equations corresponding to the reaction series, indicated
in the figure (temperature 700C), are given as functions of temperature.
Reaction equations ~GT = -A + BT
-A B
1/2 4CoAsS(s) ', 4CoS(s) + As4(g) -30140 -30.36
1/5 4CoAsS(s) ~ 4CoS(s) + As4S6(g) 95830 77.04
3/4 4CoAsS(s) ~7 2CoS2(s) + 2CoAs2(g) 26740 35.25
3/2 4CoAsS(s) + 2S2(g) ~7 4CoS2(s) + As4(g) 79400 70.42
3/5 4CoAsS(s) + 5S2~g) ~ 4CoS2(s) + As4S6(g) 205360 177.82
3/6 4CoAsS(s) + 4S2(g) '7 4CoS2(g) + As4S4(g) 205360 178.63
At the temperature 700C, the most advantageous of the rearrange-
ment reaction series of cobalt glance in terms of energy is that shown by the
~ - 14 -
10575~
equation 3/5 (~G = -32348 cal). According to the linear analysis, the com-
position of cobalt sulfide is CoS2 ~ 3 0 at the phase boundary. The actual
rearrangement mechanism is thus obviously mediated by CoS3, i.e., according
to Fig. 6 the phase bounday mechanism is:
Initial reaction: 10CoAsS(s) + 12.5S2(g) C7 lOCoS2~g) + 2.5As4S6(g)
Concentration: lOCoS2(g) + 5S2(g) ~, lOCoS3(s)
Phase boundary: 4CoAsS(s) + lOCoS3(s) ~7 14CoS2(s) + As4S6(g)
Total: 14CoAsS(s~ + 17.5S2(g) ~7 14CoS2(s) + 3.5As4S6(g)
or 4CoAsS(s) + 5S2(g) ~7 4CoS2(s) + As4S6(g)
According to literature (Gmelins Handbuch, Co 58, T.A. Erg., Verlag
Chem., 1961, 742) it has been possible to synthetize the sulfide CoS2 8 3.
It is assumed that the compound is a mixed crystal of CoS2 and S. The S2
molecule is concentrated at the lattice points as S2 groups and respectively
the Co 2 sites are left free. The thermodynamics and stability ranges of
this compound are, however, unknown.
As a second example of the rearrangement of a natural mineral the
behavior of high-grade nickel thioarsenide concentrate under conditions cor-
responding to the previous example is discussed. The anaylsis of the nickel
concentrate (% by weight) was as follows: 1.3 Cu, 1.4 Co, 11.0 Fe, 22.5 Ni,
19.4 S, 39.9 As, and 0.21 Si02.
The rearrangement of the min0rals of the concentrate (700C, PS =
1.0 atm) took place in as few as 15 minutes, and at the same time the arsenic
content of the specimen decreased to practically zero. Similarly to the
previous example, a cubic pyrite (FeS2: aO = 5.42 A) - vaecite (NiS2: aO =
5.67 A) mixed crystal was formed to replace the gersdorffite crystal (NiAsS:
aO = 5.71 A).
The electrogram and roentgenogram series of an only partially
reacted NiAsS granule found in the specimen and the linear analyses of the
- 15 -
:1~5~51(~
components are given in Figs. 7 and 8.
The rearrangement stages fully analogous to the previous example can
be seen in Fig. 7. The sharp changes in the concentrations of the components
(As, S) in the transition zone of the phase boundary can also be seen from the
linear analyses in Fig. 8. The sulfur concentration in the nickel sulfide at
the phase boundary corresponds to the composition NiS2 8.
In the case illustrated by this example, a rearrangement mechanism
completely corresponding to the previous one was observed. The intermediary
was a sulfide with a high sulfur content. According to literature (Gmelins
~andbuch, Ni 57 B, Verlag Chem., 19, 675-676), nickel sulfides corresponding
to the composition NiS3 4 4 are known at low temperatures. The stability
ranges of these sulfides are not known.
As a third example, a concentrate with the following composition
(% by weight) is discussed: 0.03 Cu, 1.1 Co. 3.5 Fe, 31.0 Ni, 4.2 S, 52.0 As,
5.0 Sb, and 0.62 SiO2. The structure of the concentrate can be seen in the
electrogram and roentgenogram series in Fig. 9. Especially noteworthy in the
figure is the concentration of antimony in arsenic-poor ullmanite (NiSbS).
When the concentrate specimen was treated with sulfur vapor
~2h, 750C, PS = 1.0 atm), the rearrangement of the minerals took place
analogously to the previous cxample. The arsenic content in the specimen
decreased from 52% to 0.1% As and its antimony content respectively from 5%
to 0.01% ~b.
The roentgenogram series of the small As-Sb-containing phase area
observed in the specimen and the corresponding linear analyses of the com-
ponents are given in Figs. 10 and 11. Fig. 10 shows a Ni-As-Sb phase with a
very low sulfur content and outside it, in a porous, rearranged zone, an
Sb2S3 phase as pure segregations. On the basis of the performed analyses and
roentgenographic studies it can be assumed that the rearrangement in the
~ 16 -
~)S'7~
specimen has taken place after an anticipatory rearrangement of arsenic.
Antimony has been removed from ullmanite and has concentrated as pure sulfide,
which is further transferred into the gas phase as a function of its vapor
pressure. Owing to the lack of mathematical values the mechanism cannot yet
be proven thermodynamically.
Figs. 12 and 13 show roentgenograms and linear analyses of a
specimen of a concentrate corresponding to the previous one, treated under the
same conditions for 30 minutes. The specimen represents a partially reacted
nickelin in which antimony has originally been present together with arsenide.
Both the roentgenograms and the linear analyses clearly indicate the changes
in the concentrations at the phase boundary and in the transition zone. The
linear analyses also indicate the formation of a separate sulfide mineral of
antimony when the phase boundary moves towards nickelin. In this case a con-
siderable amount of arsenic is still present in the sulfide. The composition
of a sulfur-saturated, almost iron-free nickel sulfide phase can also be seen
just at the phase boundary.
In the following example, an enargite concentrate with the following
composition (% by weight) is discussed: 20.5 Cu, 21.8 Fe, 0.02 Ni, 0.03 Co,
36.5 S, 7.0 As, and 1.2 Sb.
Already in 15 minutes a rearrangement in a sulfur atmosphere at
700C caused a complete removal of arsenic and a decrease in the amount of
antimony to 0.4% Sb. The analysis sample taken from the treated concentrate
is shown as a roentgenogram series and linear analyses in Figs. 14 and 15.
It can be noted on the basis of the analyses that the rearrangement obviously
takes place in connection with antimony-containing enargite (Cu3AsS4) through
a complete stibic enargite (Cu3SbS4). Result (% by weight): 44.5 Cu, 4.5 Fe,
23.7 Sb, 3.0 As, and 28.2 S.
A rearrangement test which was carried out at 600C and lasted 15
~S7S~q~
minutes (the roentgenograms and linear analyses of the components are given
in Figs. 16 and 17) illustrates the effect of iron filtration in the decom-
position of enargite. The figures show the analyses of undecomposed and
decomposed enargite crystals side by side. Arsenic has been removed from the
reacted enargite crystal, and under the effect of the filtrated iron the
remaining crystal has mineralized into chalcopyrite (mainly the final product
even in the specimens illustrated in Figs. 14 and 15).
The discussed examples illustrate the rearrangement and the
rearrangement mechanism of the minerals of some typical complex ores. The
micromechanism of the rearrangement is a very complicated process and is
naturally a function of the quality of the components present in the minerals
and of the stabilities of the intermediary compounds of these components,
these stabilities being for a great part unknown in terms of energy. Special
attention has been paid in the examples to glance grains containing arsenic
and antimony, which are very stable minerals, because their treatment is
generally very difficult technologically. In natural sulfide minerals As, Sb
and Bi are usually present in the ratio 1000:8:2 so that the proportionate
quantities of the latter two are usually low.
The minerals covered by the process contain, owing to their manner
of formation, a great deal of volatile compounds of heavy metals in particular.
When the main components of the minerals are rearranged, the same takes place
in regard to the heavy metal components. It should be noted in particular
that since the previous mineral structure is usually totally changed, even
substances lying deep in the crystals are revealed and removed even if they
are present in small concentrations. Depending on the temperatures of the
rearrangement and the extents of the gas phases used, these volatile impurities
either remain in the final product or are evaporated and then recovered from
the gas phase. The vapor pressures of the most common volatile sulfides
10~7~
covered by the process are given in Fig. 18. ~E.g., at 700C are evaporated
in the order of their pressure Re2S7, HgS~Hg), Asx, As4S4~ Se6, As4S6, GeS~
Te2, GeS2, Sb4S6, T12S, Bi2S3, Sns, Pbs, Ga2SJ CdS, In2S, Sb4, Bi2, ReS2,
In2S3, ZnS.)
Selenium and tellurium, which are often combined with noble metals,
are taken here as examples of the rearrangement of volatile substances. The
rearrangement reactions of silver selenide and silver telluride are
(19) Ag2Se~s) + 1/2 S2~g) ~7 Ag2S~s) + 1/2 Se2~1)
[1/6 Se6~g)]
~20) Ag2Te~s) + 1/2 S2~g) ~7 Ag2S~s) + Te~l)
[1/2 Te2~g)]
At the evaporation temperatures 600 - 800C, the equilibrium
constants of the reactions are
~19) log kp = 6074.2/T - 3.079
~20) log kp = 6964.9/T - 3.663
The values of theequilibrium constants are high; e.g., at 700C:
~l9)/kp = 1460 and ~20)/kp = 3120.
The equilibrium constant ~log kp = 3846.3/T - 4.531) of the
rearrangement reaction of copper selenide corresponding to the equation ~19)
is much lower than the previous ones within the operation range. The re-
arrangement reactions are still rerllized because, out of the reaction
products, Cu2S is dissolved in the other sulfi.de matrix ~-~ CuFeS2, whereby
the Cu2S activity decreases). Also noteworthy in this connection is the
formation of a ~Se, S)x~g) molecule, whereby the equilibrium conditions
obviously move in a di:rection more advantageous than that mentioned above.
The alloying effect mentioned above is very important when the
process is applied to the treatment of simple arsenides, antimonides, etc.
created as byproducts of very high-grade and pure natural minerals or
- 19 -
1(~5751~
industrial processes. Thereby the actual equilibrium equations of the re-
arrangement of the minerals are usually thermodynamically advantageous, but
the low melting and sintering ranges of the initial minerals or reaction
products constitute an obstacle to a rapid realization of the process. The
melting or sintering of the grain of the matrix causes a growth of the
diffusion distances and also causes technical problems in the realization
of the process. The following reactions can be mentioned as examples:
Reaction ~G, cal/mol As4-Sb4
(21) 4Cu3As(s)+6S2(g) ~-7 As4S6(g) + 6Cu2S(s) -203880
(22) 2Cu5As2(s) ~ 5.5S2(g) S As4S6(g) + 5 Cu2S(s) -103090
(23) 2Co5As2(s) + 13S2(g) '-~ As4S6(g) + lOCoS2(g) -207090
(24) 4Cu2Sb(l) + 5S2(g) '7 Sb4S6(s) + 4Cu2S(s) -135970
(25) 4Ag3Sb(l) + 6S2(g) ~ Sb4S6(s) + 6Ag2S(s) -243920
The melting points of the initial minerals corresponding to the
equations (C/No.) are: 830C/(21), 710C/(22), 918C/(23), 585C/(24), and
559C/(25). It is therefore advantageous to use as additives in connection
with the rearrangements sulfides of iron, cobalt or nickel, for example,
whereby the problems of molten phases and sintering are eliminated by
alloying.
In the above examples, the rearrangement of the minerals has been
performed in the vicinity o 700C. Ilowever, 500-900C can be regarded as
the temperature range for the realization of the process.
The realization of the rearrangement process under normal pressure
and at a high temperature causes technical difficulties. Pyritic sulfur is
usually present in the ores to be treated. The pyrite decomposes, as a
function of the temperature, according to the equation
(26) 2/(1-x)FeS2(s) '7 2/(1-x)FeSl+x(s) + S2(g)
In an open system the sulfur pressure is obtained from the equation
- 20 -
i(lS'7S~
log PS = -16291/T + 16.947
According to the equation the sulfur pressure reaches atmospheric
pressure at 688C. In literature the respective values are within 697-743C.
At the initial stage the decomposition of pyrite follows the
kinetic law
dNF S /dt = -3.33 x 10 NFeS exp~-50900/RT), (t, min)
At the temperatures 600, 700 and 800C, the half times of the
reaction, derived from the velocity law are 117, 5.7, and 0.5 min. It was
observed in experiments that under the sulfur pressure of one atmosphere at
800C, the pyrite of sulfide mixtures did not decompose when the process was
realized. On the other hand, when using the sulfur pressure of iron pyrite,
the sulfides of the other metals did not concentrate, at least to a sufficient
degree.
The properties of sulfur-rich sulfides of metals, important in
regard to the process are not known well enough in science. It has, however,
been observed that FeS2 decomposes peritectically at approx. 800C and under
the pressure 25 atm., the reaction products being liquid sulfur and pyrrhotite.
Pyrite can obviously also melt congruently at a temperature above 1000C.
The exact pressure and temperature are not, however, known. It is clear that
the rearrangement of minerals according to the invention can be performed
even at high temperatures ti.e., 800C) if an elevated pressure is used in
the system (a question of economy and technology).
The velocity of the rearrangement is naturally determined by the
diffusion velocity of the components in the sulfides. The temperature
dependence of diffusion is exponential, and therefore as high temperatures
as possible should be used in the process. The diffusion cannot, however, be
analyzed here because the diffusion constants are not known well enough in
the sulfide system. As an example of diffusion constants it can be noted
- 21 -
lOS7Sl(~
that the diffusion velocities of iron and sulfur, the sulfide composition
being FeSl 03 at 600C, are DFe = 9 7 x lO 9 and DS = 6.6 x 10 25cm2/s.
Thus, the diffusion velocity of sulfur in a sulfide lattice is negligible
and consequently the transport function of the system is determined almost
alone by the metal diffusion. An atmospheric pressure of sulfur has
obviously an especially catalytic effect on the rearrangement of the minerals
under discussion. At least partly this can be deduced (as could be noted
regarding the linear analyses already) from the great disorder and nonstoich-
iometry prevailing in the crystal in the process of rearranging. Concerning
metal oxide systems it is already known that their diffusion velocities are
at minimum when the structure is stoichiometric. Thus it can be assumed
that in the mineral systems under discussion the diffusion velocities of the
metals are very high. When trials were carried out under a lowered sulfur
pressure (that is, with the H2S/H2 system), some rearrangement was noted to
occur, but the velocities were then very low. The realization of some very
essential parts of the process naturally depends on the diffusion velocities
of the system~ in both the solid and gaseous phases. A sufficient diffusion
velocity even at low temperatures can be achieved according to the new
process by using high partial pressures of sulfur.
A pilot furnace apparatus according to Fig. 19 was used in the
rearrangement and evaporation experiments of complcx concentrate. The
diameter of the furnace cylinder provided with a control of the slant and
the number of revolutions was 1.00/0.75 m and its length 12 m. To compensate
for heat losses, an electric heating apparatus had been installed in the
furnace outside the gas-tight reaction chamber.
Preheated concentrate was fed pneumatically through the feeding
end (2) of the furnace (1) by means of a feeder. The sulfur vapor phase
used in the experiments was prepared from elemental sulfur granules by
~ - 22 -
~(~5'75~0
evaporation and fed into the furance through a gas pipe ~3). The gas phase
was directed out of the cylinder through another gas pipe (4). Before the
sulfur gas was condensed it was purified of dusts by means of a hot cyclone.
Volatile substances were separated from the sulfur by conventional methods
and the sulfur was reevaporated. The product concentrate flo~ed through the
discharge end (6) of the furnace into a tight cooling cylinder ~5).
The elemental sulfur could also be fed into the apparatus together
with the concentrate, in which case it was evaporated in the furnace system.
The capacity of the system was then lower than usual.
The experiment cylinder could be operated during experiment run
either continuously, periodically or statically in regard to the feeding.
Of the performed experiment series, one performed with mixed con-
centrate is described in this connection. A synthetic concentrate was
prepared by mixing three different kinds of natural concentrate. Sulfide
compounds of bismuth and antimony were also added together with copper and
noble metals. The greater part of the trace elements of the concentrate
mixture originated in an enargitic copper concentrate. The thioarsenide and
thioantimonide concentrates of cobalt and nickel did not contain trace
elements in great quantities. The analysis of the main components of the
concentrate mixture (% by weight) was as follows: 15.00 Cu, 2.91 Ni, 2.01 Co,
25.49 Fe, 37.13 S, 9.60 As, 1.40 Sb, and 0.23 Bi. Tlle analysis of the
secondary components o~ the mixture ~ppm) was respectively: 225 Se, (7.5 Te),
10 Ga, (7.5 In), (7.5 Tl), 20 Ge, 250 Sn, 1200 Pb, 1050 Zn, 150 Cd, 100 ~Ig,
25 Mo, 25 Mn, (7.5 Re), 1230 Ag, and 24 Au.
The particle size of the concentrate was approx. 50%/-250 mesh.
In the experiment run according to the example, the temperature was
approx. 725C. The elemental sulfur was fed into the cylinder in the form of
- 23 -
1()57510
vapor at 900C, whereby its excess heat was used to cover the heat deficiency
of the system. The quantity of elemental sulfur was 250 kg per one ton of
concentrate. The post-treatment concentrate was finely-divided and dry.
The material balance corresponding to the example, calculated per one ton of
concentrate, is given in Table 1 and the heat balance in Table 2. The flying
dust of the gas phase has been included in the product concentrate of the
material balance; on the average the flying dust constituted 4% of the
quantity of the product concentrate. According to the material balance,
the rearrangement of the complex concentrate had been very successful. Of
the main impurities, arsenic had been removed entirely. The other impurities
and trace elements had been removed almost as functions of their vapor
pressures. A study of the conversion concentrate showed that pyrites and
chalcopy~ite were its main minerals. Antimony and bismuth had formed in-
dependent sulfide minerals which were present as segregations in the very
porous matrix formed by the main minerals.
It can be noted from the heat balances of Table 2 that the addition-
al heat of the process corresponding to the example (Balance I) was only 50
kWh per one ton of concentrate.
Example II
The experiment run according to this example corresponded exactly
to that of Example I. ~or the evaporation, the temperature of the final part
of the cylinder (that is, 4/12 m) was raised by extra resistor elements
so that the temperature of the products rose to approx. 900~C.
It can be noted from the material balance of Table 1 that with the
exception of a small quantity of antimony the conversion concentrate was
devoid of impurities. The noble metals, zinc, manganese, and molybdenum
were naturally left. ~;
According to the heat balance of Table 2, the amount of heat
- 24 -
57510
required for covering the heat losses had risen only slightly (78 kWh) when
compared with the value of the previous example.
Example III
A mixture of two concentrates have been used in the experimental
runs of this Example, whereby part of the rare impurities of previous
Examples are not present.
Rearrangement of the minerals of the concentrate mixture have been
effected by using different sulfur pressures of the feed gas phase. Both the
concentrate mixture and the gas phase have been preheated to a temperature
of about 500C. Each feed component was heated to the reaction temperature,
i.e. 725C, in an electric furnace (Fig. 19). The reaction time and the
capacity of the furance were maintained constant in the various experimental
series and corresponded to Example I.
In the experiments, the value of 2,5 ~Ps ) was taken as the
average atom number for the sulfur molecule. The values Ps = 0.20, 0.50
and 0.75 atm were selected as the sulfur pressures of the experimental runs.
As carrier gas for the sulfur vapors technical nitrogen gas was used. It
should, however, be noted that also oxygen containing gases may be used as
the carrier gas. According to the experiments the partial pressure of the
SO2 in the gas phase may rise to (700C) Pso = 0.60 wlthout detrimental side
effects as to the rearrangement. The material balances of the experimental
series (III~ 2, and -3) corresponding to Example III with analyses are
given in Table 3.
As to the results, it should especially be noted that the initial
mineral structure of the concentrate is most decisive for its rearrangement
rate. In the concentrate used arsenic was attached to the readily decomposing
enargite lattice as well as to thioarsenides of nickel and cobalt hard to
decompose. For the concentrate mixture used the rearrangement rate, when
- 25 -
1~)57S10
using the arsenic content as label material, is approximately potential
function of the partial pressure of the elemental sulfur of the feed gas
phase. The exponential values were of the order of from 0.50 to 0.55. A
slight increase in these exponential values is expected when the temperature
decreases and the atom number of the sulfur gas molecule increases
correspondingly.
The feed amounts of sulfur in Table 3 may suffer from some in-
exactness. The simultaneous condensation of the volatile components and
sulfur was not very exact in full-scale. The condensation result corresponds
to the condensation temperature of a mixture of S-As-polymers containing
about 30% by weight As. In view of the results of Example III it seems that
the rearrangement can be effected with a relatively low Ps -partial pressure.
At low sulfur pressures, however, the reactions are substantially retarded.
Even a radically extended reaction retention time does not result in suf-
ficiently low arsenic contents in the end product. This is apparently parti-
ally due to a decrease in the sulfur content top created at the phase boundary
contemplated in the above specification.
The results of Example III does not differ from the results of the
previous Examples in any other respects. According to Table 3 the behaviour
of antimony is somewhat anomalous as the sulfur pressure of the gas phase
decreases. This is probably due to the dissociation of Sb trioxide to Sb
monoxide having a higher vapor pressure.
In the experiments it has been noted that the exponential relation-
ship of the rearrangement with the sulfur pressure is true also for concen-
trates having oxidized grain surfaces. Then effective rearrangement of the
concentrate is preceded by an incubation time required to remove the oxygen.
This oxygen removal is partly covered by the rearrangement process but appears
as a remarkable increase in the reaction time.
- 26 -
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