US3671197A - Treatment of pyrites - Google Patents

Abstract

PROCESS FOR TREATING PYRITES WHEREIN THE PYRITES IS DIRECTLY CONTACTED WITH AN INERT GAS UNDER CONDITIONS TO PRODUCE PYRROHTITE BY FREEING THE LABILE SULFUR FROM THE PYRITES, THE INERT GAS PROVIDING THE HEAT REQUIREMENTS FOR THE SULFUR DISTILLATION. THE SULFUR IS RECOVERED FROM THE INERT GAS AND THE INERT GAS INDIRECTLY HEATED BY AN OFF-GAS PRODUCED IN ROASTING THE PYRROHTITE FOR SUBSEQUENT PASSING TO THE SULFUR DISTILLATION.

Description

June 20, 1972 N. E. MAsclo 3,671,197

TREATMENT OF PYRITES Filed Feb. 5, 1970 ATTORNEYS United States Patent O 3,671,197 TREATMENT OF PYRITES Nicholas E. Mascio, Verona, and Robert F. Burke, Riverdale, NJ., assignors to The Lummus Company, Bloomfield, NJ.

Filed Feb. 5, 1970, Ser. No. 8,837 Int. Cl. C21b 1 04 U.S. Cl. 23-200 13 Claims ABSTRACT F THE DISCLOSURE Process for treating pyrites wherein the pyrites is directly contacted with an inert gas under conditions to produce pyrrohtite by freeing the labile sulfur from the pyrites, the inert gas providing the heat requirements for the sulfur distillation. The sulfur is recovered from the inert gas and the inert gas indirectly heated by an off-gas produced in roasting the pyrrohtite for subsequent passing to the sulfur distillation;

This invention relates to the treatment of pyrites and more particularly to a new and improved process for producing sulfur and iron oxxide from iron pyrites.

The Imineral pyrite is generally characterized as FeS2, though the stoichiometry is not exact. Numerous processing schemes have been developed in an attempt to economically produce iron oxide and sulfur from pyrites, but such schemes have met with little success. In general, these processes involve a first step for freeing labile sulfur from the pyrites as represented by the following equation:

and the resulting pyrrohtite is then roasted with an oxygen containing gas to produce the iron oxide, as represented by the following equation:

The processing step for freeing labile sulfur is endothermic and therefore the high fuel requirements for this step have made the overall process unattractive.

In an attempt to reduce the fuel requirements for the initial processing step numerous schemes were developed wherein the hot sulfur dioxide-containing gas generated in the roasting step is employed to directly heat the pyrites for removal of labile sulfur. These processing schemes have also met with little success as a result of poor yields of sulfur and/or iron oxide and/or the presence of unacceptable amounts of sulfur in the iron oxide product.

Accordingly, an object of this invention is to provide a new and improved process for producing iron oxide and sulfur from pyrites.

Another object of this invention is to provide a process for treating pyrites which produces sulfur and iron oxide of acceptable quality in acceptable yields.

A further object of this invention is to provide a process for treating pyrites which lowers overall fuel requirements.

These and other objects of the invention should be more readily apparent from reading the following detailed description of the invention with reference to the accompanying drawing wherein:

The drawing is a simplified schematic ow diagram of an embodiment of this invention.

The objects of this invention are broadly accomplished by heating an inert gas by indirect heat transfer with the hot off-gas from the pyrrohtite roaster and directly contacting pyrites with the heated inert gas to remove the labile sulfur therefrom, thereby meeting at least a portion of the heat requirements, and preferably essentially all of the heat requirements, of the endothermic sulfur distillation step with the heat generated in the exothermic pyrrohtite roasting. In this manner, fuel requirements are reduced and the sulfur distillation steps and pyrrohtite roasting may be separately regulated to produce sulfur and iron oxide, respectively, of acceptable quality and in acceptable yields.

The removal of labile sulfur from pyrites is effected by directly contacting the pyrites with the inert gas which is provided at a temperature and in a quantity suicient to meet the heat requirements of this reaction. In addition, the temperature of the inert gas must be at a value to insure that the vapor pressure of sulfur in the gas stream, if any, is slightly less than that in equilibrium with the pyrites at the operating temperature and pressure. In general, the labile sulfur is removed from the pyrites at temperatures from about 600 C. to about 1000 C., preferably from about -600 C. to about 650 C. and pressures from about -10l H2O to about +10" H2O, with respect to atmospheric pressure, and preferably at a pressure of about 0" H2O (atmospheric pressure). The inert gas employed may be any gas which does not adversely aifect the sulfur distillation; i.e., inert with respect to the oxidation of sulfur, and as representative examples of such gases, there may be mentioned: nitrogen, sulfur dioxide and the like.

The pyrrohtite roasting is generally effected with an excess of oxygen; i.e., an excess of the stoichiometric roasting requirements, at bed temperatures from about 11000 C. to about 1050 C., preferably from about 1020 C. to about 1035 C., and at pressures from about 5" H2O to about 0" H20, with respect to atmospheric pressure. The use of temperatures within the hereinabove noted narrow temperature range and an excess of oxygen, results in an acceptable production rate of an iron oxide cinder low in sulfur.

The invention isfurther described with respect to an embodiment thereof illustrated in the accompanying drawing, but it is to be understood that the scope of the invention is not limited by this embodiment. It is further to be understood that various equipments, such as pumps, valves, heat exchangers, etc. have been omitted from the drawing to facilitate description thereof, and the placing of such equipment at appropriate places is within th scope of those skilled in the art.

Referring now YAto the drawing, a drying gas, such as air, in line 10 is passed through heat exchanger 11 wherein the air is heated by indirect heat transfer with a roaster off-gas, as hereinafter described. The heated air from heat exchanger 11 in line 12 is introduced into oneiend of a suitable drier 13, such as a rotary lkiln or fluidized unit, with a kiln being preferred, along with moisture containing pyrite in line 14. The pyrite introduced into the drier 13 generally has a moisture content in the vicinity of about 10% and as a result of the direct cocurrent contact between the pyrite and heated air, the moisture content of the pyrite is reduced to about 0.1

be an ore or a concentrate, suchas tailings from a copper concentrator. If in the form of an ore, the size of the feed is generally from about 1-2 mm. and if in the form of a concentrate the size of the feed is generally from about 22S-325 mesh.

Moisture laden drying air is withdrawn from drier 13 through line 14, introduced into a cyclone separator 15 to separate pyrite dust therefrom and the moisture laden air is released to the atmosphere through line 16.

The dried pyrite is withdrawn from drier 13 through line 17, combined with dust removed from cyclone separator 15 through line 18, and introduced into a pyrite sublirnator 21 such as a rotary kiln or fluidized unit, with a kiln being preferred, to separate labile sulfur therefrom. A heated inert gas, such as nitrogen, which may also contain uncondensed sulfur, is introduced into sublimator 21 through line 22 and countercurrently contacts the pyrites therein. The inert gas is introduced at a temperature and in a quantity to both provide the heat requirements for freeing labile sulfur from the pyrite and maintain a reaction bed temperature within the hereinabove described range. In addition, if the inert gas contains uncondensed sulfur, the temperature at which the inert gas is introduced should be at a value at which the vapor pressure of such sulfur is less than the vapor pressure of the sulfur in equilibrium with the pyrites in the sublimator 21 at the prevailing temperatures and pressure. It should be readily apparent that the quantities and temperatures of both the inert gas and pyrites may be varied to provide the desired operating conditions for the sublimator. As a result of the countercurrent contact between the pyrites and the hot inert gas, the labile sulfur is freed from the pyrites (approximately 85-98%) producing pyrrohtite.

The inert gas, now containing sulfur vapor, is withdrawn from the sublimator 22 at a temperature above the dew point of the sulfur contained therein and introduced into a cyclone separator 24 to separate any pyrrohtite dust contained therein. The sulfur containing inert gas is withdrawn from cyclone separator 24 through line 25 and passed to sulfur recovery, as hereinafter described.

Solids, containing mainly pyrrohtite and some unreacted pyrite, is withdrawn from sublimator 21 through line 26, combined with any dust recovered from cyclone separator 24 through line 27, and introduced into a roaster 28, preferably a fluid bed roaster, along with a molecular oxygen-containing gas, such as air in line 31. The roaster 28 is operated at the temperature and pressure conditions hereinabove noted and preferably with an excess of oxygen, to produce sulfur dioxide and iron oxide, as hematite (Fe203).

The iron oxide cinder is withdrawn from roaster 28 through line 32 and a hot sulfur dioxide-containing gas is withdrawn therefrom through line 33. The sulfur dioxide-containing gas in line 33 is introduced into cyclone separator 34 to separate any iron oxide contained therein which is withdrawn through line 35 and combined with the iron oxide in line 32. The sulfur dioxide containing gas from cyclone separator 34 in line 36 is passed through heat exchanger 37 to indirectly heat the inert gas being passed to sublimator 21 as hereinafter described. The cooled sulfur-dioxide containing gas from heat exchanger 37 in line 38 is passed through heat exchanger 11 to indirectly heat the drying air in line and then passed to further recovery through line 39, e.g., reaction with hydrogen sulfide, if available, to produce sulfur; production of sulfuric acid, or the like.

The inert gas, containing elemental sulfur, from cyclohe separator 24 in line 25 is passed through heat exchanger 41 to effect cooling thereof by indirect heat transfer with an inert gas from a sulfur recovery zone, as hereinafter described, and the cooled gas in line 42 is introduced into a sulfur recovery zone, schematically designated as 43. 'I'he sulfur recovery zone 43 may include any one of a wide variety of processing techniques for separating sulfur from a gas, including, for example, sulfur scrubbing, or sulfur absorbing, and the like. These processing techniques are generally known in the art and therefore no detailed description thereof is deemed necessary for an understanding of the invention.

An inert gas, containing minor amounts of sulfur, is Withdrawn from sulfur recovery zone 43 through line 44 and passed through heat exchanger 41 to effect heating thereof by indirect heat transfer with the sulfur-containing inert gas in line 25. The heated inert gas from heat exchanger 41 in line 45 is passed through heat exchanger 37 to effect heating thereof by indirect heat transfer with the sulfur dioxide-containing gas in line 36 and the heated inert gas is passed through line 22 to sublimator 21, aS hereinabove described.

Numerous modications of the hereinabove described embodiment are possible within the spirit and scope of the invention. Thus, for example, in some operations total heat recovery may not be economical and, therefore, a portion of the heating requirements for maintaining the inert gas at the proper operating temperature may be provided by supplemental heating, i.e., the sulfur dioxide offgas does not provide all of the heating requirements for maintaining the inert gas at the proper operating temperature.

The process of the invention is extremely effective for providing iron oxide and sulfur from pyrites. The use of an inert gas to transfer heat evolved from the exothermic roasting of pyrrohtite to the endothermic iron pyrites distillation to free the labile sulfur reduces overall fuel requirements. In addition, this transfer of heat is effected in a manner such that the processing conditions for freeing labile sulfur, roasting pyrrohtite and providing heat to the inert gas are each independently Variable and therefore may be separately regulated. Thus, the roasting operation,V unlike prior art processes, may be operated at conditions particularly suited for producing iron oxide in acceptable quality and at acceptable yields, i.e., an excess of oxygen and temperature control within a narrow range. Similarly, the temperature, heat content and quantity of the inert gas may be controlled in a manner to provide the optimum conditions for the freeing of the labile sulfur of the pyrites.

In addition, the processing scheme should include provisions for supplying make-up inert gas at an appropriate place to offset inert gas leakage.

Furthermore, the inert gas and pyrites may be contacted cocurrently instead of countercurrently as particularly described, although countercurrent contact is preferred. As still another modification, the drying of iron pyrites may be effected in a manner other than as particularly described or with a drying gas other than air, provided the gas is inert with respect to the pyrites. The above modifications and numerous other modifications should be apparent to those skilled in the art from the description herein.

The following example is illustrative of conditions for the process of the invention and it is to be understood that the scope of the invention is not to be limited thereby.

EXAMPLE The processing conditions tabulated below may be employed for producing 540 short tons per day (st./d.) of Fe203 and 191 short tons per day of sulfur. The pyrites is supplied through line 14 at the rate of 1000 short tons per day (10 Wt. percent moisture) and is dried With 30,000 s.c.f.m. of air in line 12 to a moisture content of 0.1 wt. percent.

The composition and rate of flow in each of the major streams are Ias below.

l P.s.i.g.

Numerous modifications and variations of the invention are possible in light of the above teachings and therefore the invention may be practiced otherwise than as particularly described.

What is claimed is: 1. In a process for producing 1ron oxlde from iron pyrites by freeing labile sulfur from the iron pyrites to thereby produce pyrrohtite and roasting the pyrrohtite to produce iron oxide, the improvement comprising:

(a) directly contacting the pyrites with a hot inert gas which is inert with respect to the oxidation of sulfur to provide heat requirement for removing labile sulfur from the pyrites, thereby producing pyrrohtite;

(b) introducing the pyrrohtite into a roasting zone wherein the pyrrohtite is contacted with a molecular oxygen-containing gas at a temperature from about 1000 to about 1050 C. to produce a gaseous stream containing sulfur dioxide and iron oxide;

(c) separating sulfur from the inert gas recovered from step (a);

(d) passing the inert gas in an indirect heat transfer relationship with the sulfur dioxide containing gas from step (b) to effect heating of the inert gas; and

(e) passing heated inert gas to step (a).

2. The process as defined in claim 1 wherein the contacting of step (a) is effected at a temperature from about 600 C. to about 1000 C.

3. The process as defined in claim 2 wherein the roasting is effected with an excess of oxygen.

4. The process as defined in claim 3 wherein the roasting zone is maintained at a temperature from about 1020 C. to about 1035 C.

5. The process as defined in claim 1 wherein the contacting of step (a) is effected at a temperature from about 600 C. to about 650 C.

6. The process as defined in claim 1 wherein the inert gas is nitrogen 7. The process as defined in claim 1 wherein the molecular oxygen-containing gas is air.

8. A process for producing sulfur and iron oxide from iron pyrites, comprising:

(a) introducing pyrites into a first zone wherein the pyrites is directly contacted with an inert gas which is inert with respect to the oxidation of sulfur, said inert gas being introduced at and in a quantity to maintain a temperature from about 600 C. to about 1000 C. and to provide a vapor pressure of sulfur in the inert gas which is less than that which is in equilibrium with the pyrites at the conditions in the first zone, said inert gas providing heat requirements to free labile sulfur and produce pyrrohtite;

(b) introducing the pyrrohtite into a second reaction zone with a molecular oxygen-containing gas, said gas being introduced in an amount to provide oxygen in excess of stoichiometric requirements, said second reaction zone being maintained at a temperature from about 1000 C. to about 1050 C. to produce a gaseous stream containing sulfur dioxide and iron oxide;

(c) withdrawing inert gas, containing gaseous sulfur, from the reaction zone and introducing the inert gas into a sulfur recovery zone wherein sulfur is recovered therefrom;

(d) passing inert gas from the sulfur recovery zone in an indirect heat transfer relationship with the gaseous stream, containing sulfur dioxide, withdrawn from the second reaction zone to effect heating of the inert gas; and

(e) passing the heated inert gas to the first reaction zone.

9. The process as defined in claim 8 wherein the process is a continuous process and the pyrites and inert gas are countercurrently contacted in the first reaction zone.

10. The process as defined in claim 8 wherein the first reaction zone is maintained at a temperature from about 600 C. to about 650 C. and the second reaction zone is maintained at a temperature from about 1020 C. to about 1035 C.

11. The process as defined to claim 8 wherein the inert gas is nitrogen.

12. The process as defined in claim 8 wherein the pyrites is dried prior to introduction thereof into the first reaction zone by direct contact with a hot drying gas, said hot drying gas being heated by indirect heat transfer with the gaseous stream, containing sulfur dioxide, after the heat transfer step with the inert gas.

13. The process is defined in claim 8 wherein the pressure in said first zone is maintained at from about 10" 7 H2O vto about +10 H2O with respect to atmospheric pressure.

References Cited UNITED STATES PATENTS Jukkola 23-1177 X Heath 23-224 Fogh 23-227 Aanerud 23--227 Bacon et al 75--9 Clark 23-227 X 8 1,971,815 8/ 1934 Halvorsen 23-200 2,785,050 3/ 1957 Swaine et al 23-200 X FOREIGN PATENTS 5 731,527 Y 6/ 1955 Great Britain 75-9 OSCAR R. VERTIZ, Primary Examiner G. O. PETERS, Assistant Examiner 10 U.s. c1. X.R.

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