CA1113258A - Method for controlling the heat content and evening out temperatures in various sulfidizing processes - Google Patents

Abstract

METHOD FOR CONTROLLING THE HEAT CONTENT AND EVENING OUT
TEMPERATURES IN VARIOUS SULFIDIZING PROCESSES

ABSTRACT OF THE DISCLOSURE

The dissociation and recombination energies of sulfur molecules is utilized to control the heat content and maintain the temperature between 400°C and 900°C in a sulfur atmosphere wherein the partial pressure of sulfur is 0.1-1 atm by controlling the partial pressure of the sulfur in sulfidizing process.

Description

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OUTOKUMPU OY, Outokumpu Method for controlling the heat content and evening out temperatures in various sulfidizing processes , The present invention relates to the control of various sulfidizing processes. The invention relates primarily to the control of sulfidizing processes in which the object is a sulfidizing treatment, mainly in solid state, of polymorphous complex minerals which contain metals Cu, Ni, Co, Zn, Pb and Fe as principal components and also metals which constitute impurities with regard to these. The purpose of the sulf;dizing is in this case the decomposition of the original complex minerals and the simultaneous conversion of their principal metals and impurities to stable, independent sulfides. Such a conversion based on sulfidizing requires a sufficient reaction velocity and, in order to produce stable sulfides usually with ?
a high sulfur content, the use of high partial pressures of sulfur. On the other hand, many complex minerals melt at very low temperatures, and therefore the sulfidizing must be carried out under conditions in which the melting points of the mineral matrices are not surpassed and/or ~n which the use of high sulfur pressures raises the temnerature ranges of the breaking-down and rearrangement of mineral matrices. The sulfidizing processes of the said type are usually performed within the .

temperature ran~e 700-1200K (427-927C) and within the sulfur vapor pressure range 0.1-1.0 atm.

When using high sulfur pressures, the heat required by the process must be introduced into the system indirectly,since the use of, for example, a fossil fuel in the reaction space causes the partial pressure of sulfur to decrease, and since the combustion gas reactions cause losses of sulfur. The in~
direct heating of the sulfidizing systems for its part easily causes the complex minerals to melt and sinter since, owing to the poor heat transfer caPacities of mineral powders, a large temperature gradient must be used in the transfer.

The method according to the invention re~ders unnecessary both the external heat transfer of sulfidizing systems and the internaL
use of fossil fuel.

The method according to the invention can also be used in high-temperature sulfidizing processes, melt refining, etc.
The method according to the invention is to a high degree independent of the equipment and other technology used in the process. By the new method, the elemental sulfur can easily be cycled, no polluting gases are produced, and both the solid and the gaseous phases are obtained as powders or in forms which condense as sulfur polymers. Therefore, in many sulfidizing processes the new method is not only economical as regards energy but also almost indispensable in terms of both safety at work and environmental protection.
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In the process a~ccording to USP 3,459,535 the solubility of the copper present in Cu-Fe-S minerals is improved in an acid, oxidizing leach in an autoclave. This is performed by treating the said minerals within the temperature range 300-600C in contact with elemental sulfur and its vapor. The treatment is performed in an externally heated retort. It can be shown that below 501C chalcopyrite and bornite sulfidize to idaite (Cu5FeS6) and pyrite. Above 501C, bornite again becomes stable, and above 508C, both bornite and chalcopyrite are stable.

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The process according to USP 3,817,743 is analogous to the above. In this process the chalcopyrite is sulfidized within the temperature range 460-500C to X-bornite (Cu3FeS2 phase in which there is an excess of sulfur, about 0.5% by weight) and to idaite at a sulfur pressure of PS = 200 mmHg.
Processes older than those described above are represented by that according to USP 1,523,980 (Colcord or Hulst process), in which the copper present as an impurity in molten lead is removed by sulfidizing it as solid digenite by means of (solid or vapor) elemental sulfur. In the process according to DRP
497,312, sulfur or sulfur-yielding material is added to molten metal or a molten metal alloy (an alloy of Pb, Sn, Sb, etc.) in order to remove the copper in sulfide form. The reducing agents used in the process are pitch, tar, etc. In the process according to DRP 431,984, impurity metals, Zn, Pb, Cu, etc.,are removed as sulfides from raw antimony by adding sulfur and by smelting.
The use of elemental sulfur vapor for the determination of phase-equilibriums is a commonly used, although difficult, method.
Various applications of the process are described in the followin3 publications: H.E. Marwin, R.H. Lombard: Econ. Geol., 32, 1937, 203-284; T. Rosenqvist, T. Harvig: ~eddelelse Nr. 12 fra Metallurgisk komité, Trondheim, Norway, May 1958. 21-52.
The objective of reduction-sulfidization processes is to reduce oxide ores at a low temperature and to recover, either as metal alloys or sulfide matte, the valuable metals present in them in low concentrations. This group includes numerous processes for the refining of limonitic and/or serpentinitic laterite ores which contain Ni, Co and Cu. The valuable metals are reduced and sulfidized out from the ores, and the obtained product i9 separated from the gangue by conventional methods ~leaching, magnetic separation, smelting, etc.). The reduction and the sulfidization are performed within the temperature range 700-1100C
using a tubular furnace or a fluid-bed reactor (e.g. USP 3,004,846;

3,030,201; 3,272,616) and the sulfidizing agent is usually the reduction qas (H2S, COS, etc.). The sulfidization can in this ~ -case be performed using many sul~ur-yielding materials, pyrites, injection of sulfur into the combustion gases, SO2 fed to the reduction zones, S-bearing raw oil, etc. (e.g. USP 3,388,870;
3,535,105; 3.772,423; 3,819,801).

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What the said sulfidizing processes have in common is that, in aiminq at producing as a solid or a molten phase a metallized or conventional sulfide matte, the sulfur pressure required for the sulfidization is usually very low. The following sulfidizing reactions of nickel are mentioned as examnles:
NiO ~ Ni ~ Ni ~ Ni3S2 + x 700C PS2 ~ 10 -3.7x10 atm.
matte: 20.6-21.8 S by weight;900C: Ps2 ~ 1.5x10 8_10 2 atm.
matte: 19.2-30.3 S by weight.

The cate~ory of processes in which the aim is to vaporize the impurities of concentrates and ores or to convert them to an easily separable form includes, as does the former one, a large number of patented and/or otherwise published methods. In the process according to USP 1,762,~67 the impurity components are removed by fractional distillation from primarily complex concentrates of copper and from technical intermediate products in such a manner that the sulfides of the metals Hg, As, Sb, Sn, Cd are vaporized, within the temperature range 600-1200C, and finally the sulfide of zinc is vaporized, the remaining product phase being a Cu-Fe sulfide matte. When the process is carried out in, for example, a tubular furnace, sulfur or sulfur-yielding compounds, iron, and lime (to eliminate the effects of the low melting point of sulfides) are, when necessary added to the batch in àddition to coke. The batch is heated by means of combustion gases flowing countercurrently to it. Using these gases the volatile sulfides can be oxidized before they are discharged from the furnace.

The process according to DRP 504,487 (Skappel) for the treatment of complex ores is very well known. In one embodlment of the process, impure concentrates or industrial intermediate products are smelted or sintered together with sodium sulfide (Na2$, Na2SO4 + C, etc.), whereby suitable eutectics and Na2S-MeS binary salts are produced. The product obtained is broken up ~ .
with a flow of water to produce a powder-slurry mixture containing separate sulfides, and the separate sulfide phases can be recovered from this mixture by conventional methods.
When the batch is heated or smelted, a portion of the impurities vaporizes and a portion is removed during the aqueous wash stage : ~ . , - ,, , . , -:
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(e.q. As). The temperature ran~e of the application of the process is hetween 600C and 1600C, depending on the raw material.

In the process according to Finnish Patent 49 186, serpentinic laterites are subjected to a reduction-sulfidization at a low tem~erature. The metallized sulfide produced by sulfidization is "filtration-smelted" by exploiting the melt solubility gap of the Me-MeS system to form sufficiently lar~e particles (the oxide matrix remaining solid). sy long annealing performed at a temperature decreasin~ from the ran~e of the solubility ~ap the metals of the Me-MeS system are divided in such a manner that Ni, Co, Pt-metals, (Fe), etc., are concentrated in the metal phase and metals Cu, Cr, Mn, etc., are concentrated in the sulfide layer surrounding this phase. The Me-MeS system is separated from the oxide matrix of the product, and the Me phase is separated from the MeS phase, both by conventional methods.

In the above processes the heat required by the process is introduced into the batch by means of fossil fuel in the reaction space. irhereby the sulfur potential of the system remains low.
Ca~a~/~a~ ~af~n~ /~0 IJ ~S~J5/o In the process according to F~ h ~atcnt ~pplication l~l~/74, the components of complex concentrates are rearranged from their complex compounds into stable, independent sulfides corresponding to the new conditions, both as re~ards the principal metals (Cu, Ni, Co, Pb, Zn) and the impurities (As, Sb, Bi, Se, Te, Ga, In, Te, Hg, Ge, Sn, etc.). Some of the impurities vaporize quantitatively under the treatment conditions (600-800C, Ps = 0.25-l.00 atm) and some can be separated by conventional means after the processin~. Usually the process does not require the introduction of additional heat into the sulfidization furnace. Another example of processes operating with external additional heat is the process, which is still subject to much research, in which arsenic, for example, is separated from its compounds by heating them (Fe-, Cu-, Ni-, Co-based sulfldes or arsenides) to~ether with pyrite. However, the quantities of pyrite required are lar~e. The decomposition of the pyrite in . .. : ; . . : ~

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order to make sulfur available for the reactions also requires large amounts of energy (e.g. Il-W. Loose: Chemismus der Entfernung von Arsen aus seinen Verbindungen mit Eisen, Kupfer, Nickel und Kobalt durch Erhitzen in Anwesen-heit von Pyrit, Dissertation Arbeit, Breslau 1931, 1-73).
According to the present invention there is provided a method for controlling the heat content and evening out the temperatures in sulfidizing processes, in which the sulfidizing is performed in a sulfur atmosphere, com-prising regulating the partial pressure of sulfur in the sulfur atmosphere in order to utilize the energy of dissociation and recombination of sulfur molecules, the temperature of the sulfur atmosphere being 400-900C and the partial pressure of sulfur being 0.1-1 atm.
The control method according to the invention utilizes the very high dissociation-recombination energies linked with changes in the atomic number of sulfur-vapor molecules within the temperature and pressure ranges specified below. These amounts of energy which are freed or bound are functions of both the temperature and the partial pressure of sulfur vapor.
The amounts of dissociation-recombination energy are so large that in many low-temperature sulfidizing processes they suffice to cover the amounts of energy required for the sulfidizing reactions, impurity vaporiz-ation, and the heat losses of the apparatus. Thus the sulfidizing processescan be made self-sufficient in terms of heat economy by regulating only the temperature and/or partial pressure of the sulfur vapor to be fed into the sulfidizing system.
The new method for regulating and controlling sulfidizing processes operates within the temperature range 400-900C and within the elemental sulfu~ vapQr pressure range 0.1-1.00 atm.
The invention relates primarily to the treatment of predominantly sulfidic complex ores which contain, as their principal metal, copper, zinc ~3' . ' ' . ~ ' . ~ .

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lead, nickel, cobalt and iron and which have been produced by low-temperature and low-pressure pneumatolytic and especially hydrothermal minerali~ation.
The technological utili~ation of these ores is effectively prevented by a large quantity o heavy elements usually present as impurities in these ores.

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One of the things common to these complex minerals is that they are both ~ormed and dissociated and/or melt at very low temperatures. In order to separate the sulfides of both the impurities and the principal components from each other to form separate phases, the sulfidization of these minerals must be controlled as regards the order of phenomena, velocity, degree of sulfidization and other factors. This must be done in such a manner that there are hardly any molten phases formed.

The method according to the invention makes it ~ossible to perform the sulfidization process so that it is self-sufficient as regards heat. In this case the heat yielded by the actual exothermal mineral sulfidization must be sufficient to cover the heat losses of the processing apparatus, the vaporization enthalpies, and the heat required for heating the sulfidizing agent and the concentrate from the pre-heating temperature to the reaction temperature. Thus no additional heat is fed into the sulfidizing system by using fossil fuel in the reaction chamber or by heating the processing equipment externally.
The feeding of such additional heat would usually be very difficult to implement because of the low melting-temperature range of the material being processed or because of the high sulfur potential required.

In the new method under discussion the realization of the thermal - balance of the sulfidizing system is regulated as follows:
the ore is pre-heated to a temperature below that at which any chemical or physical changes detrimental to the process take place, and the amounts of heat are regulated, taking the exothermal nature of sulfidizing processes into account, by means of the considerable dissociation-recombination heat amounts linked with the change in the atomic number of the sulfur vapor molecules. These amounts of heat are exploited by regulating the feeding temperature and partial pressure of sulfur vapor and the point at which the sulfur vapor and other components are essentially fed into the system.

By the method according to the invention it is possible, in sulfidizing processes, to control not only the heat balance f.. .1 . . , , , ' ' . . ~ , . .
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_ 8 of the system but also the melting temperature ranges of complex minerals, the velocity of the sulfidizing reactions, the structurs of the product matrix, and the structures of both the impurity sulfides remaining in the matrix and the impurity compounds vaporizing under the conditions o the process. The method makes it possible to use a more versatile and simultaneously less complicated sulfidizing technique, which is hiqhly economical and usually independent of the technical equipment used. The method also makes it possible to carry out sulfidizing processes which require high sulfur potentials and have not been previously feasible.

By the method according to the invention, various sulfide processes are thus regulated by utilizing the great changes in the heat content of the gas phase in connection with the dissociation and recombination of molecules. The following is an example of the proportions of the heat amounts: At a pressure of one atmosphere, at the temperature T = 700K, the average atomic number o~ the molecules of sulfur vapor is V = 6.97 and its enthalpy values are ~kcal/kg S): ~as enthalpy ~H700_298 = 62.82 and heat of formation ~H298 =
170.36. At the temperature T = 1100K the respective values ' 1100-298 = 96.58 and ~H298 = 575 14 Thus within the temperature range involved,the heat available for process control, ~(~He+f) = 404.78 kcal/kg S. In this case the proportion of conventional thermal gas enthalpy is only 8.3~ -and the proportion of dissociation-recombination energy 91.7%.
This dissociation ener~y is not only a function of the tempera- ~.
ture but also a function of the partial pressure of sulfur vapor and in such a manner that the change in energy corresponding to a chan~e in the atomic number of the molecules occurs at different temperature ran~es, depending on the different partial ; pressures. The suitability of sulfur vapor for the control of sulfidizin~ processes thus has a very wide range of operation, `~ especially in processes in which the partial pressure of sulfur i~ vapor varies within the range Ps = 0.1-1.00 atm and within ;~ ~ the temperature range T = 700-1200K. Utilizing the peculiarbehavior oif sulfur vapor it is possible to control not only the temperature of the processes but also the final states, , . .

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composition and cooling of the reaction products, the order of the sulfidizing phenomena, eXcit~tign, etc.

The method according to the invention is especially suitable for performing sulfidizing processes which re~uire high partial pressures of elemental sulfur. Because of the poor heat conductivity of the concentrate and ore powders and because of the melting of the complexes, indirect transfer of external heat is usually difficult in the processes involved. On the other hand direct heating of the reaction chamber using, for example, combustion gases, is not suitable because of the resulting decrease in th~ partial pressure of sulfur and the formation of detrimental, sulfur-consuming gas components (COS, H2S, etc.).
The use of combustion cases in the processes would also result in pollutant gases technically difficult to handle, as well as in dust problems with increasing amounts of gas. It is evident that the method is also applicable to many high-temperature sulfidizing processes.

Some sulfidizing processes falling within the sphere of the method accordin~ to the invention are listed briefly below:
.
- The br~ d~wn of impure complex ores and the ~rearrangement Ca~al/~7 P~l*~7f QJo . /~ ~S;~
D of the matrix (e.g. innish Patont .~p~lication Mo lgl2,~7l).
- The sulfidization of impurities to separate nonvolatile minerals (partial-melt processes) and multi-stage sulfidizing processes (Examples 4 and 5).
- Low-temperàture sulfidizi~g processes in which the preheating, ignition, and extinguishing of the concentrate are carried out with elemental sulfur (Examples 1-3).
- Colcord and similar processes (USP 1,523,980).
, - The refining of antimony and tin alloys (DRP 431,984, British Patent 1,348,278).
- Constant-temperature sulfidizing processes.
- Matrix changes of copper concentrates prior to leaching in continuous processes (USP 3,459,535).
- High-temperature zone reduction-sulfidization processes, in the control of zone temperatures (USP 3,754,891; 3,900,310).

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The method accordin~ to the invention is highly aoplicable -to the treatment o~ predoninantly sulfidic complex ores which contain as their urincipal metals Cu, Zn, Pb, Ni, Co, Fe, etc., and which have been formed partly through pegmatitic-pneumatolyti~
and esoecially hydrothermal mineralization. Hence, heavy elements representin~ the high ordinal numbers of the periodic system, which are very mobile and have high vapor pressures within the range of operation o the process (but are to be considered harmful impurities as regards the principal metals) have concentrated in the mineral-forming "solutions" (temperature ~400-450C, pressure 225-250 kg/cm2). The structure of such ore minerals can be altered by a suitable sulfidizing treatment so that the impurities and the principal metals form separate, independent sulfides which can be separated ~rom each other by conventional methods.

The following include some of the mineral categories involved, grouped according to their composition: -Pyritic and arsenic- and antimony-rich groups:
(Fe,Co,Ni)(S,Se,Te,As)2, (Fe,Co,Ni)(As,Sb)S; Cu(Fe,Ga,In)S2, Cu3(Ge,Fe,As,Sb)S4,etc. -~

Lead, zinc and silver groups:
(Cu~Ag)20(Fe~Zn~Hg~Ge,Sn)4(As,Sb~Bi)8S26, (Zn,Cd,Hg)(S,Se,Te), Pb(S,Se,Te).
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Tin, zinc and silver groups:
Cu3(As,Sb,Fe,Ge,V)S4, Cu2(Ag,Fe,Zn,Sn)S4.

Cobalt, nickel, silver, bismuth, and uranium groups:
(Co,Ni,Ag,U)(As,Bi)3.
. . :
Arsenic, antimony and bismuth complex minerals:
Ag3(As,Sb)S3, Cu3NiS3, Cu(Sb,Bi)S2, A~(As,Bi)S2, (Pb,Cu)(As,Sb, Bi)S3, etc.
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In addition to natural minerals, many high-temperature technical intermediate products which contain respective ~""~, .

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impurities but are not complex also fall within the sphere of the method according to the invention.

The control method according to the invention is thus based on the exploitation of the dissociation-recombination energy of molecules in connection with the change in the atomic number of sulfur vapor molecules as a function of the partial pressure and the temperature.

It is known that sulfur vapor has a very complex structure.
The detailed structure of individual vapor molecules is almost unknown. Also, the quantitative proportions of the different vapor molecules in the gas phase are under dispute. The heats of formation of the categories of molecules, as well as their specific heats, are at least technically known with sufficient precision, and so the total enthalpies of the separate components of the gas phase can be calculated with relatively g~eat precision.

The invention is described below in more detail with reference to the accompanying drawings. Fi~ures lA and lB in the drawings depict the molar proportions and enthalpy of the sulfur vapor as functions of temperature. Figure 2 depicts the total pressure of sulfur vapor as a function of the average atomic number of its vapor molecules and the temperature, Figure 3 depicts part of the apparatus developed for applying the method according to the invention, Figure 4 depicts a side elevation of the entire apparatus, and Figure 5 depicts an equilibrium diagram ~ -of the minerals as a function of the sulfur activity and the temperature.

Figure lA shows the molar proportions of sulfur vapor Sv (v= 2-8~ as a function of the temperature. Of special note is that the sulfur molecule S4,used in conventional calculations, is almost completely absent in the ga~s phase. Figure lB shows the calculated total enthalpy of sulfur vapor (in comparison with solid rhombic sulfur3, corresponding to vapor pressures Ps =
1.0 and 0.1 atm. The average change in the atomic number x of the gas phase molecules as a function of the temperature ~

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is also indicated in the figure. The figure also shows, as a parameter, the change in the total vapor pressure at different partial pressures of vapor dissociated to a molecule of atomic number two.

The dissociation energy used for the control of the sulfidization is seen qualitatively in Figure lB. At 1100 K (827C) the total heat of sulfur vapor at one atmosphere is ~He+f = 575.1 kcal/kg. ~ -The average atomic number of the vapor molecules in this case is v = 2.07.

When the gas phase cools to a temperature of 700K (427C), a heat amount of 404.7 kcal/kg is released by the recombination of the sulfur molecules, while the sulfur remains in vapor state (700K, ~He+f = 170.4 kcal/kg, v = 6.97~. The released ~
heat is thus 240% of the heat required for smelting the sulfur -and for vaporizing it to 700K. As can be seen f~om Figure lB, ~-the partial pressure of sulfur vapor has an important effect on the temperature range of the dissociation-recombination energy.

The amount of reIeased or bound energy within à wide temperature and partial~pressure range of sulfur vapor allows a versatile technical use of the phenomenon in many sulfidizing processes, especially at low temperatures.

For example, the approximate isobaric equations of the following -form can be caiculated for the sulfur vapor enthalpy change as a function of the temperature:

S = 1.0 atm, T = 800-1000K, ~He+f, kcal/kg S =

exp10(-159.568 + 184.577 x 10 3T - 69.002 x 10 T + 46727~T) PS = 0.1 atm, T = 700-900K, ~He+f, kcal/kg S =

exp10(-198.922 + 257.952 x 10 3T - 108.538 x 10 6T2 + 51673/T).

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Similar approximate equations can be calculated for all partial pressures by determining the gas composition. It should be noted that the equation in itself does not exactly correspond to reality, since in the actual process the consumption of sulfur results in a change in its partial pressure, a fact which is not in itself taken into consideration in the equation.

Dissociation of sulfur vapor by thermal excitation: -The mutual balancing between the different types of molecules of sulfur vapor is a very slow process, especially at low temperatures. In the balancing, sulfur represents an intermediate case between or~anic and inorganic compounds. The vaporization temperature of sulfur and its heat of vaporization are lower than those of other inorganic materials and yet only a little hi~her than those of most organic compounds (sublimation energies, ~H298, kcal/g at: 2.87-2.97/S, 19.2/Te, 29.0/As, 49.3/Sb, etc.). Most organic compounds, including their vap,ors, are thermodynamically metastable. The slow settling of the equilibrium is obviously another reason for some of the many allotropes of sulfur.
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The activation energy of the balancing of sulfur vapor is in proportion to the energ~ of the S-S bond in ring molecules, a form in which all sulfur molecules appear to be present. All molecules of sulfur apparently have a double bond. The dissociation ener~y of molecules increases only slightly with increased atomic number: D298, kcal/atom: 50.8S/S2, 54.40/53, 54.73jS4, 60.56/S5, 61.90/S6, 62.31/S7 and 63.06/S8. Selenium, which is in many respects analogous to sulfur, does not show conditions of inequilibrium at low temperatures. Its bond energy and its vaporization temperature show, respectively, lower and higher values than those of sulfur.

Owing to the behavior of sulfur vapor, it is advan*ageous to produce this vapor at a lowered pressure ahd using a suitable catalyst. In the present method, sulfur vapor is produced using a carrier ga5, which is saturated in molten sulfur and directed to a preheatin~ apparatus.
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The vapor pressure of molten sulfur is of the form:
Log ~P~atm) = -6109.6411/T + 16.64157 -17.05358 x 10 3T + 7.9769 x 10 6T2 The partial pressure of the sulfur vapor obtained is regulated by controlling the temperature of the molten sulfur bath. For example, when a temperature of 427C is used for the sulfur bath, the partial pressure of the vapor obtained is PS = o~757 atm a~d the average atomic number of its molecules corresponds to v = 6.62. Thus the following gas phase is obtained from the pre-heating apparatus at 600C: PS = 0.845 atm, v = 4.o5, and at lo 700C: PS = 0.891 atm, v = 2.65.
A ther.~ally stable general sulfur catalyst is a suitable equilibr-ium catalyst of sulfur vapor. A chromite catalyst is especially appropriate for this purpose slnce in addition to its excellent catalytic capacity it has good heat conductivity, thermal stability and, compared with other cat-alysts, a small but effective surface area per unit weight (the space require-ment of the catalyst is small since its denslty is high).
Figure 3 shows an apparatus for sulfur vapor production used in the new process. me apparatus works under atmospheric pressure. me vapor-izer 2 consists of two electricaIly-heated tanks, one inside the other. The ;20 temperature of the outer tank 15 provided With a stirrer 23 is far below the vaporization point of sulfur, and so elemental sulfur can be fed into this tank throu~h inlet 24 in solid state. ~he inner tank 16 is an electric vaporizer, thermally insulated on the outside. It forms a oommunicating vessel with the outer tank 15. m e sulfur 22 is vaporized and carried out of the tank 16 by means of pre-heated nitrogen 4. The sulfur vapor and the carrier gas flow from the vaporizer into an electric pre-heater 3 filled with a chrcmite catalyst. In the pre-heater 3 the sulfur vapor is brought to the desired tem~erature and the respective e~uilibrium. From the pre-;,., . , , ., .
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Figure 4 shows one embodiment of the apparatus for oarrying out suLfid:Lzing processes. The system comprises a concentrate pre-heating device 6 with its feeding and heating devices 7, a sulfidizing devioe 1 with its feeding and discharging devices ~sulifidized product concentrate 8, gas phase 9, suLfur polymer 10) a vaporizer 2 corresponding to Figure 3, a vapor dis-sociating pre-heater 3, and nitrogen vaporizer 5.
Utilization of the thenmal dissociation-recombination energy of sulfur vapor for controlling sulfidizing processes:
~he new control method is applicable primarily to sulfidizing pro-cesses which are carried out at a high partial pressure of sulfur vapor and often at low temperature. mese processes are usually very complicated as regards their mechanism and the technological operations required. For this reason the examples to be discussed contain essential pa~sages relating to the theoretical grounds of the control method. me examples cover only part of the sphere of application of the new method. It should also be noted that some of the sulfidizing processes falling within the sphere of application of the method, perforned using a high sul~ur pressure, are currently imposs-ible to oarry out by other procedures, and therefore the control method is crucial, being almost the only method for controlling the prooesses.
To illustrate the control method Or the sulfidizing processes under discusslon, the stability ranges of the initial and product materials and the gas phases of the embodiments given as examples have been calculated as a function of the temperature and the sulfur activity and are shown in Figure 5. The aotion of the sulfur processes in reality can be observed from the temperature and sulfur pressure values given in the examples.

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F~2mple 1 This example illustrates the processin~ of a sulfidic ~ -cobalt arsenide concentr~te. In this process the complex mineral present in the concentrate is decomposed and sulfidized to a compound more stable than previously. The arsenic present in : .

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the concentrate leaves the system together with sulfur vapor.
Thus the partial pressure of sulfur in the vapor phase must be sufficient both to maintain the stability of the volatile arsenic sulfide and to maintain the mineral composition of the sulfide concentrate obtained as a product close to that correspondin~ to the mineral equilibrium: (Co, Fe)S2 + FelOS12.
According to the equilibrium diagram of Figure S, at 1000K
(727C) the partial pressure of sulfur vapor, both before and after the sulfidization, must be over 0.1 atm (stability range COS2-FeSl+Xi As4S6(g) boils a The calculated heat balance and balance of materials corresponding to Example 1, the bases of calculations used, and the explanations are compiled in Table 1. The partial pressure of sulfur vapor in the feed gas phase was PS = 0 50 atm and that in the product gas phase, respectively, PS = 0.255 atm and so, according to the equilibrium diagram, the system is within the correct range of operation both before and after the sulfidiza-t on ( roduct gas phase, atm: PS2 = 0.255, PAs4S6 0.064, The temperature of the suIfur bath in the vaporization of sulfur was 630K and the average atomic number of the vapor molecules was v = 6.88. The total enthalpy of sulfur vapor at the vaporization temperature was 160.1 kcal/~g S. The saturation pressure of sulfur vapor was PS = 0.233 atm, i.e. PS2 = 0.50 atm, calculated as the S2 pressure of the equilibrium diagram.

The heat of formation of the concentrate corresponding to Example 2 was AH298 = -259.8 Mcal/t and that of the sulfidiæed concentrate respectively ~H298 = -337.3 Mcal/t. The decomposition and rearrangement of the complex concentrate is thus a strongly exothermal process in the case under discussion. The heat-consuming factors in the process are the heating of the con-centrate and the sulfur vapor (and the carrier gas) from the feed temperature to the reaction temperature and the heat losses o the processing apparatus. It can be seen from the balances of Table 1 that when the concentrate is fed into the system at the temperature Tl = 473K (200C), the feed temperature of the gas phase must be T2 = 950K (677C). When the pre-heating .... , ,. , .: . : ~'' . ' .-,, . ~ -17 ~h3Z5~d temperature of the concentrate is raised to the value T1 =
773K (500C), the gas phase must be fed into the system at T2 = 869K (596C). In each case the -total enthalpy of the sulfur vapor is still far below the value corresponding to the reaction temperature (1000K). In this case the exothermal heat obtained from the sulfidization is used for the heat of dissociation required by the sulfur vapor (within the range T2 ~ 1000K) and for realizing the other parts of the heat balance. The temperature of the feed phases of the sulfidization can thus be varied within a rather wide range, which is crucial for control of the velocity of the sulfidization, the melting of the complexes, and other factors.

The heating of the feed concentrate mentioned in Example 1, usinq the heat of recombination (polymerization) yielded by the sulfur vapor from the drying temperature of the concentrate to the excitation point of the sulfidization reactions are discussed below in order to illustrate the change in the enthalpies in the control method.

The enthalpy of the feed concentrate corresponded to the following Equation (01):

(01) ~He = 110.263 x 10 3T + 22.857 x 10 6T2 _ 26.820 Mcal/t concentrate The quantity corresponding to the example, i.e. 291.2 kg, is taken as the quantity of elemental sulfur. The total enthalpy of this quantity of sulfur (~He+f, Mcal) is in accordance with Equation (02):

(02) log~He+f = -160.1033 + 184.5768 x 10 3T - 62.0020 x 10 6T + 46726.5/t 400K (127C) is taken as the temperature of the concentrate fed into the sulfidizing system; this temperature corresponds to the temperature of the product obtained from a conventional drying cylinder. The elemental sulfur is vaporized to 1000K
(727C), at which t1-e the avera~e atomi- number of its vapor . "' "' ' .

: , 18 ~ Z5~

molecules is v = 2.17 and its enthalpy AHe+f'= 157.7 Mcal.

When the concentrate and the sulfur vapor meet each other, the temperature and the enthal~ of the vapor decrease, while the atomic number of the vapor molecules increases, and, respectively the temperature and enthalpy of the concentrate increase under the effect of the heat released by the polymerization of the sulfur vapor. In this case the heat balance of the system co~responds to the following Equation (03):

(03) 205.523 = 110.263 x 10 3T + 22.857 x 10 6T2 +
exp10 [ ~He+f / Sv]

The value obtained for the equilibrium temperature from Equation (03) is T = 872K (599C). The average atomic size of the sulfur vapor molecules increases from the initial value, v = 2.17, to v = 4.18, while the volume of the qas decreases from 94 Nm3 to 49 Nm3, respectively.

Equation (04) is obtained or the thermal enthalpy of sulfur vapor (~He~ heat of formation, not included), kcal/kg S:

(04) ~He = -161.567 + 470.813 x 10 3T - 214.667 x lQ 6T

The values in the following table are obtained for the change in the enthalpy of sulfur vapor (Mcal/291.2) from Equations (02) and (04):

H 1000K 872KDifferenceDifference, %
~He 27.54 24.972.57 3.93 ~Hf 130.19 67.3162.88 96.07 He+flS7.13 92.2865.45 100.00 It'can be seen from the table that, when cool'ing from 1000K
to 872K, the sulfur vapor yields 62.88 Moal as recombination energy for the heating of the concentrate from 400K to 872K.
The proportion of the thermal ~as enthalpy of the sulf~r vapor of the total heat transfer of the ~as phase is only 3.93%
[~(~He) = 3.93 Mcal l. If the vaporization point of sulfur (717.8K) is'taken as the reference state, the sulfur vapor '.. ~, , , , , , 7 , .. . ..
: . , . : . . . ~ -:

~ , . . .: . . . . . ,.: , . ".. .
:: : . : ''1' : .. : . .. ;~

h~Z~3 yields only 64.9~ of its recombination ener~y in the reaction observed. It should be noted that the final temperature, 872K, reached by the concentrate and the sulfur vapor is quite sufficient for the ex.citation of the exothermal sulfidization reactions. If, as the result of these reactions, the temperature of the system tends to rise too much, the sulfur vapor begins to re-dissociate, whereby the temperat-ure is buffered.

It can be observed from the calculations that the amounts of heat produced by the changes in the atomic number of sulfur vapor molecules are large, and on the other hand, the control of these heat amounts is very easy, a fact which makes the control method highly advantageous technologically.

Exam~le 2 ~ ~ .
Example 2 illustrates the structural changes in a cobalt concentrate corresponding to Example 1 and the formation and vaporization of arsenic sulfides when part of the sulfur required by the process is added to the system in the form of pyrite.

The decomposition of pyrite corresponds to reaction (equilibrium as in Example 1):
., ~
2--~ FelOS12 + (1/1-25 X)Sx(g) The quantity of sulfur required for structural chan~es in the concentrate and for the formation of the vaporization sulflde is 182.12 kg S (851.80 k~ FeS2) per one tonne of concentrate.
The free elemental sulfur of the arsenic polymer is added to the system by means of the feed gas phase, whereby the sulfur pressure in the gas phase is that corresponding to Example 1, i.e. PS = 0 50 atm. If only a proportion, Z, of the amount of pyrite mentioned above is fed into the system, the additional sulfur required is fed in a gaseous form ~P5 = 0.50 atm).

Example 2 with its balance of materials and heat balance is illustrated in detail in Table 2.

: ~ -. .

..
:~ ' - -: .

~3Z~3 It can be seen from Table 2 that, when the total sulfur quantity required for the structural chan~es in the concentrate (65.24%
of the total sulfur) is fed in the form of pyritic sulfur, the temperature of the feed ~as phase rises beyond technical control (5616C). In reality this temperature is somewhat lower, since part of the S2 molecules used in the calculations have dissociated into Sl molecules, in which case the heat of polymerization obtained is ~reater than that calculated (the pressure of monoatomic sulfur vapor at 2500K is, however, only 10 5 atm).

When sulfur,vapor is fed ~to the syste~ at 1000K (727C), the quantity of sulfur to be obtained from pyrite is only 45.95 kg. Howe~er, this corresponds to only 15.8% of the feed of sulfur.

It can be concluded from these results that the use of pyritic sulfur for producing structural changes in a process into which heat is introduced only by pre-heating the concentrate and the gas phase is of no si~nificance. It must be noted in particular that introducing heat into the system with combustion gases (i.e., the use of fossil fuel) lowers the partial pressure of elemental sulfur so much that the process is not realized.

The result obtained is, of course, due to the act that the decom~ositlon of pyrite is a highly endothermal process (and also requires a high excitation tem~erature). The basic heats ~ -of formation (~H29~) have been calculated for the following table, using the heats of formation of the feeds and the products (Mcal) per one tonne of the feed mixture according to the casesdlscussed above:
Proportion SFeS2 feed product Z kg Mcal Mcal Mcal 0 0 259.8 328.3 68.6 0.252 45.95 274.3 310.6 36.4 1.000 182.12 297.5 282.3 -15.1 It can be seen from the table that when only cobalt concentrate (Example 1) is processed the structural change is strongly exothermal. The addition of pyrite to the system makes thè
process endothermal.

Z~

Thus, when an exothermal process is involved, the excess heat of the system and a temporary rise in the temperature can easily be prevented by a pyrite spray into the reaction chamber, since pyrite rapidly binds the-excess heat by endothermal reactions.
~xcess heat is easily produced when the pre-heating temperature of the feed concentrate has been raised above that required in the process so as to enable the excitation of the exothermal reaction when the pre-heating temperature rRquired by the processing of the concentrate is far below the éxcitation point of the sulfidization reactions of the concentrate. A conventional product processed to a high level of sulfur concentration can be used advantageously for lowering the temperature. In this case this product discharges its excess sulfur endothermally (the use of such a product also prevents the precipitation of the reaction product with iron). For cooling, the temperature of the sulfur vapor can, of course, also be lowered (use of energy ~f dissociation), provided that this is possible without causing the vapor to condense.

Example 3 The feed concentrate corresponding to Example 3 is the same as that in Exam~le 1. However, the sulfidizin~ process is operated within the stability range of cobalt-iron pyrite [(Co,Fe)S2].
The amount of cobalt present in the concentrate is sufficient for raising the dissociation pressure of the Ca pyrite formed to the range of the sulfidization temperature (1000 - 900K).
The heat of formation of the product concentrate (~H298, Mcal), per one tonne of feed con`centrate, grows from the value corresponding to Example 1, ~Hf = -302.~, to ~Hf = -3-32.6, i.e. the increase in the exothermicity of the process is very ~reat (78.9 Mcal).

.
The great difference (113.5 Mcal/t) between the heats of formation of the feed and product concentrates of the sulfidization requires very low feed temperatures for both the concentrate and ~as phases. In the reaction chamber of the furnace the feed components can no longer react without excitation. For this reason it is advantageous to feed a portion of the elemental sulfur required for sulfidization along with : . .

~ .3~
the concentrate, whereby the temperature and partial pressure of the sulfur fed in gaseous state can be maintained at such high level that, when the sulfur ~as cools in the reaction chamber to the point oE excitation of the sulfidization of the concentrate, it yields, while polymerizing, the heat required for the excita-tion, whereafter the exothermal reactions realize the heat balance of the process. Momentary rises in the processing temperature can be rectified by intermittent dilution of the sulfur gas phase of the system, whereby the dissociation of the sulfur vapor and the heating of the dilution gas rapidly cause a lowering in the temperature of the system.

The calculated balance of materials and heat balance corresponding to Example 3 are given in Table 3.
It should be noted that the carrying out of the sulfidizing process in a manner corresponding to Example 3, instead of that corresponding to Example 1, increases the sulfur requirement, but on the other hand it eliminates the unit for pre-heating the concentrate from the process apparatus.
Example 4 In the case corresponding to Example 4, a nickel-antimonide concentrate mineral (NiSb) is sulfidized so as to obtain pure minerals as final products, i.e. sulfides of nickel and antimony.
The balance of materials and the heat balance illustrating the various processing stages of the example are given in detail in Table 4.
Nickel antimonide mineral is sulfidized usin~ the following steps a) The nickel-antimonide mineral is sulfidized at approx. 1000K, using a sulfur-vapor partial pressure of PS = 0 35 atm. The temperature of the feed concentrate is 429K (156C) and that of the feed gas phase, respectively, 750K (477C). On the basis of the analyses performed, the reaction products obtained are a solid nickel sulfide phase devoid of antimony and a molten antimony sulfide phase devoid of nickel.
The heat of formation of the initial concentrate (~H298, Mcal/t) is QH = -110.8 and that of the product obtained, respectively, ~H ~ -180.3 (i.e. ~H = -260.4 per 1.444 t of product. The .
' ,, - . .

23 ~ z~ ~

exothermal heat released by the process is used for pre-heating the concentrate (429--~ 1000K) and for heating the sulfidiz~ing ~as (750--~1000K). The sulfur vapor of the sulfidizing gas phase dissociates, and its enthalpy (~He+f, kcal/kg) increases from ~EIe+f = 208.4 to ~He+f = 549.4. The heat required for the dissociation, ~(~He~f) = 341.0, is taken from the exothermal sulfidizin~ reactions. In the sulfidization,the partial pressure of the sulfur vapor in the ~as phase decreases ~PS = 0 35 PS = 0.10 atm). In this case, with the decrease in the partial pressure, the unreacted part of the sulfur vapor dissociates further so that at 1000K the heat of dissociation required is 17.9 kcal/k~ S.

b) The products of reaction and the gas phase pass from the sulfidizing process to the cooling furnace. It can be observed from the equilibrium dia~ram in Figure 5 that, when the product cools down, the operation moves within the stability field to the area of nickel pyrite (NiS2), while the antimony sulfide remains liquid LSb2S3(1)]. The bulk of the sulfur contained in the gas phase then becomes stacked on the surface of nickel monosulfide so that when the ~as phase discharges from the furnace its sulfur content is only about one percent by volume (890K). The antimony sulfide present in the gas phase becomes condensed in the reaction chamber of the coolin~ furnace. The thermal losses of the coolin~ furnace are obtained from the increase in the exothermicity of the reaction ~roducts (NiS 7 NiSX ~ NiS2, ~He+f = -29.8 Mcal/1.444 t of feed mixture) and from the change in the heat content of the gas phase (cooling:
1000K-~890K). It should be noted that the quantity of the final reaction products obtained from one tonne of antimonide concentrate i3 1 . 545 tonnes. The respective increase in the exothermicity of the reaction products is 179.4 Mcal/t feed concentrate.

By regulating the amount of sulfur in the sulfidization product in the cooling furnace it can be determined whether the antiomny sulfide is at the bottom of the tank or on the surface in the cooled product, or whether or not the sulfides of antimony and nickel are mechanically mixed with each other. Since the ~ .

,, . " . . . ............ . . . .

:
:' ' : , : . ~:: : ::

~Lh~ ~Z~r~3 concentrates also often contain iron, this control is simple.

c. From the cooling furnace the sulfur- and antimony-low gas phase is fed to the feeding end of the sulfidizing apparatus, where elemental sulfur arrives from the sulfur vaporizer.
When sulfur is vaporized at 700K, its heat content is ~He+f =
170.4 kcal/kg Sv (v = 6.97). The temperature of the sulfur fed i~to the sulfidizing process is 750K and its heat content is ~He+f = 208.~ kcal/kg S. The thermal energy required for the dissociation of the sulfur, 3-8.1 kcal/kg S, is yielded by the gas phase obtained from the cooling furnace.

E~ample 4 illustrates clearly the versatile ways in which the dissociation-recombination energy of sulfur vapor can be utilized in sulfidizing processes.

Example 5 The behavior during sulfidization in order to obtain structural changes, of technologically highly important co~plex minerals containing a high amount of impurities and belonging to the Cu-As-S basic system is reported below in greater detail than the behavior of the minerals discussed above.
, The fahlerz series, of the general form (Cu, Ag)l2(Cu,A~, Fe, ;~
Hg, Ge,Sn)l2(As, Sb, Bi)8S24S2, which is structurally analogous to zinc sulfide of the sphalerite type (ei~ht-fold elementary cell volume), and the enargite series, of the general form Cu3 (As, Sb)S4, which is analogous to zinc sulfide of the wurzite type, are discussed below as a technologically important group of minerals.
' ' , , With some exceptions, these groups of hydrothermal minerals usually appear in the same ore deposits.

Tennantite (Cu24As8S26) of the fahlerz series and enargite (Cu6AsS4) of the enar~ite series a~pear as compounds of the ; basic system Cu-As-S. This system also includes sinnerite (Cu6As4Sg) and lautite (CuAsS), both ra~e ih nature, as well p (Cu24Asl2S31), which participates in the phase reactions but is unknown in nature. The sulfidization of the ...... . . . .
~ ` ` , ' : ' , , ~ .3Z~`B

compounds mentioned above is encumbered by the low melting ranges of the compounds and the phase r~actions between the same.
For this reason, special sulfidizing conditions are usually required.

The following are some examples of the melting conditions of the compounds and the reactions:

- sinnerite melts incongruently to liquid and compound A at - enargite reacts with compoul~ A to tennantite and iquid at 573C, and compound A decomposes to tennantite and liquid at - tennantitè having the composition Cul2 31As4S13 melts at 665 C
- enargite for its part decomposes to an enargite about 2% atomic ~ -As-poorer (~Cu3Aso 84S4) and liquid at 666C. The maximum melting temperature of enargite compositions is not known.

The Cu-As-S system has never been studied under a controlled sulfur pressure, and so the melt phase ranges and melting points corresponding to the above and any other reactions may deviate substantially from the values measured at low total pressure. In sulfidizing experiments it has been observed that -tennantite can be converted to enargite at temperatures >700C, and the enargite, for its part, when the arsenic vaporizes as a sulfur polymer, can be converted to digenite and/or chalco-pyrite and kernite, depending on the iron amount present or added. Sintering of the concentrate or visible appearance of melt phases cannot be observed during treatment. The equilibrium constants (numbered) relating to the sulfidizing of tennantite-enargite systems, calculated according to the avallable thermodynamic values (imprecise~, correspond to those given in the table on the following page. ~he stability ranges of the compounds most important considering this discussion are indicated in the equilibrium diagram in Figure 5 as a function of the sulfur pressure and the temperature.

` .` ' ' .., ~ . ' ' .

.. .: : . ... :
: - , ::: .. ~ , - :: . - . .

~$~3Z5~3 ~r '`D~ O N Ln 1` ~ O
CO ~ n ~r ~ o ~9 ~ Ln00 ~ o Ln co ~r r~ ~ ~ Ln ~ o co ~r r 00 ~ ~D ~ ~J ~ N
O Ln ~ OD O
m I , ~ ~ o ~
~ a~ co ,~ ~ ~ Ln O ~ O U:~N~r O r~
er Ln ~ O ,~ ~ ~D O
o ~ Ln ~ ~
o ~O ~ ~ ~ oO
Ln1~ ~ ~I N
~_) I . I . .
V~ t ~ N ~r Ln OD ~ 0 ~ r oo Ln ~r Ln tJ~ ~ ~ OD ~ ~ 1-- Ln Ln O Ln O ' ~ + ~ +
m +

tn ~
. . _ P ~ U~
K --o _ D +
U~ +
U~ ~1 ~ _ + +
+ ~ ~
~ a) -- ~ _ ~ ~ ~o U~
U U~
;r + ~ +

Q ~ 3 + V~
~ +U~ ~
oK _ ~ _ 3 + +
o S
o _ LD ~ Q) I` + S ~
o ~ U~ ~
~ : ~ +
+ + + ~ ~

h ~ ~ U ~1 ~ ~1 ~rl .
æ ~1 ~ ~ ~ Ln ~ ,~

ZSB

Reactions 1-9 in the table:
It can be observed from the extrapolated equilibrium values of Reaction 1 that enargite becomes stable at 1000K at a sulfur pressure above PS = 3 49 x 10 2 atm.

According to Reaction 2, the enargite dissociates to digenite and ~aseous arsenic sulfide. At a sulfidization temperature of 1000K the free energy of Reaction 2 is positive. When a high partial pressure of sulfur is used, a digenite phase (Cu2 ~S), short of the full capacity of the metal,is formed in place of chalcocite (Cu2S), whereby the activity of chalcocite decreases to one advantageous to the equilibrium reaction. The equilibrium constant of the reaction )Cu2s(ss) + (~/2)S(ss) = Cu2 ~S
and the activities of sulfur and chalcocite can be calculated `
from known measured values. Within the temperature ranqe 823-1023K (550-750C) and with ~ values of ~ = 0.14-0.24, both the ~ and aCU S functions are of the form aCu2S 2~ + 1.3222 - 2C3.7/T
(~/4/log PS = 0 3335 ~ 460.0/T - (1 - ~)log aCU S

When the sulfur pressure corresponding to the tennantite-enargite equilibrium, PS = 3-49 x 10 2 (1000K), is used, the equilibrium digenite obtained from the equations corresponds to the composition Cul 86S and the chalcocite activity obtained i5 acu S = - 81. In this case the vapor pressure of arsenic PAs4S6 0.56 atm so that Reaction (2) proceeds advantageously. Owing to the positive nature of the free energy of the reaction, the vapor pressure of arsenic sulfide dëcreases when the partial pressure of the vapor of sulfidizing sulfur is raised. On the other hand, the lowering of the partial pressure of sulfur results in that the arsenic is not removed from the system, since when the sulfur amount in the digenite ?
decreases the solid solubility of arsenic in it increases (e.g. 500 C, composition (Cu, As)l 92S, where As2O3 ~0.70% by .. ~ - . .- . . , : .
, : : . - . : . ~:

28 ~ zSB

wei~ht). It is of particular interest that melt phases which encumber the process are also produced if the sulfur amount in digenite decreases, i.e. if the partial pressure o~ sulfur in the system is lowered. The same observations apply to Reaction 7 as to Reaction 2. However, it should also be noted that in the tennantite-digenite equilibrium the solid solubility of digenite and arsenic is even greater than under the conditions of Reaction 2. In performing the vaporization sulfidization, sulfur pressures above those of the tennantite-enargite conver-sion are thus effective.
.
Each of Reactions 3, 4, 5, and 6 is realized. When iron sulfide or iron is added to enargite, the products of the reaction are bornite and/or chalcopyrite. It can, however, be observed in carrying out the sulfidization that Reaction 3 proceeds poorly. Results are not obtained from Reactions 4,

5, and 6 at the computed limit pressure of sulfur, since under these conditions the sulfide of arsenic is not stable. It should also be noted that, when low sulfur pressures are used, the reactions proceed slowly and there is a risk of the appearance of stationary melt phases. The above observations apply to tennantite~chalcopyrite reactions according to Reactions 8 and 9.
:
Table 5 shows the calculated balance of materials and heat balance for sulfidizing processes of conventional iron-bearing enargite concentrate (~ by weight: 30.5 Cu, 11.8 As, 0.3 Sb, 35.7 S, and 15.8 Fe), in which both the arsenic and the antimony vaporize as sulfides and the original enargite matrix is rearranged to correspond to the chalcopyrite-bornite-(digenite) equilibrium.

Values easy to achieve technically have been placed in the general outcome of the balances for the partial pressure of sulfur vapor and for the arsenic concentration in the arsenic-sulfur polymer, i.e. PS = X = 0.8 atm and Y = 0~4 (40% by weight As). In the case of the concentrate under discussion, the sulfidizing process is endothermal, and therefore additional heat is introduced into the system by burning part of the sulfur . ,~ .

.

L3Z5~3 :

~eed. Owing to the endothermal character of the process, the concentrate is fed into the system at a high degree of pre-heating, i.e. in this case at 500C. The significance of a high sulfur potential for the quantitative and kinetic removal of arsenic and for the elimination of the formation of melt phases has already been discussed above (the solid solubility of arsenic in the chalcopyrite-enargite equili~rium is equal to or ~reater than in a corresponding digenite equilibrium).

In the technical implementation of the sulfudizing process, the high sulfur pressure is of crucial importance, especially as regards endothermal sulfidizing reactions. This point is discussed briefly in the summary below:

a) It can be observed by a differential-thermal analysis that '~-enargite concentrate is excited in a sulfur atmosphere to produce a reaction sufficiently rapid technically at 570C
(the speed at which the temperature increased was 6C min 1 and the corresponding increasing negative temp,erature gradient of the endothermal reaction was -1.4C min 1).
.
b) The entha,lpy of the enargite concentrate (Mcal/t)' was ~He = 145.989 x 10 3T - 39.323, and the enthalpy including the heat of formation, respectively, QHe+f = 145.989 x 10 T -219.898. The total enthalpy of the products of sulfidization (product sulfide + arsenic sulfide) was~He+f = 194.570 -10 3T - 24,3.709.

c) The values obtained for the enthalpy of the vapor (~He~f, '-kcal/kg S) from the temperature functions of the total enthalpy of sulfur vapor at temperatures 1100, 1000, anq 845K are 575.1, 541.7, and 276.1, respectively. ~t the same temperatures the total enthalpies of vapor corresponding to a pressure of P' = 0.i atm are 582.6, 567.3, and 492.1, respectively.
Sx According to the balance of materials in Table 5~, the sulfur feed requirement'of the process per one tonne of concentrate is 33.73 kg and this'plus the sulfur quantity required for providing additional heat total 95.49 kg. The heat yielded into the system ' .. . .

. . : .

,~ , . ~ , . : ~: ::
-: : , . , - , ., ~ 3Z~3 by the polymerization of the sulfur vapor, when the temperature of the vapor decreases from the feed temperatures 1000K and 1100K to the excitation point of the concentrate, is in accordance with the following table, calculated from the values given:

PS ~ atm ~T, K ~He+f~ Mcal 33.73 kg S 95.49 kg S
0.8-1.0 1100-845 10.09 28.55 1000-845 8.96 25.36 0.1 1100-845 3.05 8.64 1000-845 2.54 7.17 It can be seen from the table that,when the operation is carried out at a high partial pressure of sulfur, the heat of polymerization of the pre-heated sulfur vapor provides the heat required for heating the concentrate from the pre-heating temperature, 773K (500C), to the excitation temperature of the reactio~s, 845K (572C). According to point b) this heat is ~EIe = 10.15 Mcal. Thus a large amount of the heat of poly-merization remains unused. When the operation is carried out at a low pressure, the heat of polymerization is not sufficient even for heating the concentrate.

d) Within the range of the excitation temperature of the feed concentrate, arsenic-antimony sulfide is formed as a molten pure phase which separates from the matrix. When using the total enthalpy values given in point b), the value obtained for the enthalpy of the concentrate a~ 7?3K is ~He+f = -107.05 and that obtained for the enthalpy of-the products at 845C is ~He+f = -79.30. The heat required for both the heating of the concentrate and for satisfying the heat requirement of the endothermal reactions ~excluding the heat losses of the system) i9 thus 27.75 Mcal. It can be observed from the table in point c) that the heat yielded by the polymerization of sulfur with a high partial pressure is approximately sufficient for realizin~
the sulfidization at a low temperature. When the operation is carried out at a low partial pressure of sulfur, the releasing o~ the polymerization energy of the vapor does not fall within .

. , ~ :
:: - :: -, ~ . .
:. ..
~ .

--~ 31 ~ ~ ~3Z5~ ~

the range applicable in the process, but within a temperature range approx. 100K lower.

e) The (As,Sb)2S3(1) phase formed within the excitation temperature range o sulfidization must be vaporized in the process. The temperature of the system must therefore be raised in order to reach the vaporiza-tion temperature. The heat required both for covering the thermal losses of the furnace and for the vaporization enthalpy is appropriately obtained for the process by burning part of the sulfur vapor.

The utili~ation of the heat of polymerization of sulfur vapor in the manner described above also makes it possible to burn the sulfur vapor only after the sulfidization reactions have started, whereby the ore matrix which is now at least partly rearranged tolerates (without sintering or melting) the temperature of the flame and the combustion gases.

Some cases (A, B, C, and D) of various sulfidizing methods have been calculated for the sake of comparison in addition to the general case in Table 5.

In cases A and Al the enar~ite concentrate is sulfidized conventionally with pure sulfur vapor. In case A the feed temperature of the sulfur vapor is 900K, and in case Al it is 1000K (i.e. the same as the temperature of the products).

In case A the change in the total enthalpy of the gas phase from the feed temperature to the product temperature is ~He+f = 163.05 kcal/kg, of which the proportion of gas enthalpy He) is only 4.61%. The dissociation energy required for raising the temperature of the sulfur (95.99 kg) of the gas pha~e within the temperature range 900 - 1000K is thus ~Hf = 14.85 Mcal. In case Al this amount of energy is not required and so the amount of sulfur used for burning is respectively (15.09 Mcal) less than in case A.
.
In cases B and Bl, iron powder has been added to a concentrate corresponding to the previous case in such a quantity that .. . . . , ~ -.. ' , . ~ ' , ~ ' . ... , . ' !

~.3Z~3 all of the sulfide obtained as a product is chalcopyrite. It can be observed from the corresponding balance of materials and heat balance that the consumption of sulfur has increased sharply in comparison with the previous case. Out of the sulfur vapor fed at a temperature of 1000K, however, only 15.26 kg is burned for the heat required by the endothermal reactions, this amount being 3.6 times smaller than in case A. This is, of course, due to the increased endothermicity of the system (the iron is sulfidized). In case C, the additional heat required by case B has been introdu~ed into the system by burning iron corresponding to the equilibrium FeSl 27. The amounts fed were 49.99 kg Fe and 36.45 kg S. The outlet gases are thereby obtained devoid of sulfur dioxide.

In case D the iron required for obtaining the chalcopyrite of the final product was added to the system as pyrrhotite (FeSx).
In this case the amount of sulfur to be burned in order to produce the heat required for the endothermal reactions (and heat losses) has increased from the value corresponding to case B, 15.26 kg, to 44.37 kg. This is due to the increased endothermicity of the process, since the exothermal heat of the sulfidization of the iron phase is complete~ly absent.

The sulfidization of pure enargite mineral to the bornite stage under conditions corresponding to the above examples (X = 0.8; Y = 0.4) is discussed briefly below:

Corresponding to reaction 5Cu3AsS4 + 3Fe ~ 3Cu5FeS4 + 5/4As4S6(g) + 1/4S2 an amount of 85.09 kg of iron and 180.92 kg of sulfur must be fed per one tonne of enargite. The sulfur released according to the reaction amounts to 8.14 kg. Out of the total sulfur feed, 25.82 kg of sulfur must be burned in order to produce additional heat~
: .
When the iron is replaced with pyrrhotite, the amount of sulfur fed is 154.55 kg, QUt of which 48.30 kg of sulfur must be "! burned in order to realize the heat balance. The quantity of .

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Z~3 sulfur released in the reactions i5 57.00 kg S. When the required iron is added in the form of pyrite, the sulfur feed amounts to 126.53 k~, out of which the share of sulfur to be burned is 69.13 kg. In this case the amount of sulfur released in the reactions is 105.85 kg.

When the additives are fed into the system at 773K and the products [Cu5FeS4ts) + As4S6(~)] are withheld from the system at 1000K, the followin~ values are obtained for the endo-thermicity of the reactions per one tonne of enargite when using various additives: 29.99/Fe, 59.68/FeS, and 85.25 Mcal/
FeS2. At 1000K the heats of formation of the product compounds ~-and enargite (Mcal/t) are as follows: -73.06/Cu5FeS4, -117.74/CuFeS2, and -27.40/Cu3AsS4.

I~ can be observed from the examples that the sulfidization of enargite or its concentrates to chalcopyrite or bornite by adding the lackin~ amount of iron in the form of iron or its suIfides is usually not advanta~eous, since the amounts of sulfur feed easily increase with increased endothermicity of the reactions (in spite of the fact that the final s~lfide products are more stable than the inltial products).

To summarize, the utilization of the heat of dissociation-recombination of sulfur vapor is crucial in the treatment of the endothermal process under discuss~ion. It is self-evident that, when the mineral composition of the ore chan~es, the conditions, temperatures and partial pressures of the sulfidizing ;~
process must also be changed according to need.

Example 6 This example illustrates the chlorination of molten copper .
sulfide matte in order to va?orize, in the form of chlorides, the impurities present in it. The molten matte o the example corresponds to the so-called converter matte, from whi¢h the iron has already been sla~ged.
;~
` The converter matte is in equilibrium with metallic copper (aCU ~0.99), and it usually already contains a large amount of metallic copper, both dissolved without char~e (Cu) or in inequillbrium. It can be assumed -that a large amount of impurities adhere to this copper. Accordin~ to measurements, the dlstribution of impurity components as regards copper sulfide and the copper in equilibrium with it at 1250C is as follows (% Me in Cu2S/~ Me in Cu): 0.57/Zn, 0.12/Pb, 0.10/Sn, 0.06/Sb, and 0.15/si. When an attempt is made to chlorinate the melt as such, the copper chlorinates well and the impurities chlorinate poorly. When elemental sulfur is added to such a melt before chlorination or during it, the melt takes it in in excess when compared with the stoichiometric chalcocite (Cu2S), e.g. in the case under discussion: PS = 0.8 atm, CuxS:X = 1.902. Thereby the copper activity of the copper in the sulfide melt decreases taCU ~10 ), and the impurities can be chlorinated selectively.

The impurity chlorides formed during the chlorination are so stable that in spite of heat-binding vaporization the total process is strongly exothermal and the temperature of the melt usually rises drastically. Using the large amount of energy required by the dissociation of sulfur vapor molecules, the speed and amount of the increase in the temperature of the melt can be buffered to the desired values, by feeding in the gaseous sulfur at a minimal temperature. The excess of sulfur which perhaps ~is used can be recovered and returned to the process when condensing the chlorides.

Table 6 shows in detail the above chlorination process for converter matte.
' -' .
When the converter matte of the example is maintained unchanged during the chlorination process (1500K), the heat bound by the sulfur vapor is 24. a Mcal (700K-~1500K). When the melt temperature is allowed to increase by 50K, the heat bound by the dissociation is I7.8 Mcal. These amounts of heat are very great, for they represent, respectively, 33.2% and 25.3% of the potential total heat of the heat balance.

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Claims (5)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for controlling the heat content and evening out the temper-atures in sulfidizing processes, in which the sulfidizing is performed in a sul-fur atmosphere, comprising regulating the partial pressure of sulfur in the sul-fur atmosphere in order to utilize the energy of dissociation and recombination of sulfur molecules, the temperature of the sulfur atmosphere being 400-900°C
and the partial pressure of sulfur being 0.1-1 atm.

2. The method of Claim 1, in which the sulfur atmosphere is diluted with an inert gas in order to lower the partial pressure of sulfur in the sulfidizing process so that the sulfur molecules dissociate and bind heat in the sulfur atmo-sphere.

3. The method of Claim 1, in which elemental sulfur is vaporized in the sulfidizing process in order to bind heat in the sulfur atmosphere.

4. The method of Claim 1, in which the sulfur atmosphere is diluted with sulfur dioxide by combusting sulfur in a trailing part of the sulfidizing process.

5. The method of Claim 1, in which sulfur vapors withdrawn from the sul-fidizing process are recycled to the sulfidizing process after heating or cool-ing to a temperature of from 400-900°C.