US2772153A - Roasting pyrites - Google Patents

Description

Nov. 27, 1956 J. R. WEST Erm. 2,772,153

RoAsTI'NG PYRITES 2 JAMES 2.

FREDE RIC/f GORMLE f NOV. 27, 1956 J, R, WEST ETAL ROASTING PYRITES Filed Aug. 4, -1955 2 lSheets-Sheet 2 ok Now (ONDNSEIZ u? Sv N2 E l PDEHEATER llal N HQ .POI

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United States Patent ROASTING FSZRLTES James R. West, Pittsburgh, Pa., and Frederick Gormley, Vera Cruz, Mexico, assignors to Texas Gulf Sulphur Company, New York, N. Y., a corporation of Texas Application 'August 4, 1955, Serial No. 526,460

7 Claims. (CL75- 9) This invention relates to the roasting of pyrites, and a major object is Yto provide a method of'roastmg 1t to produce elemental sulfur (S) and ferrie oxide (P ezOs):

Another object is to provide such a method 1n which inert gas 'is used to 4free the labile sulfur as the iirst step, or stage, yof roasting with production of a rmmrnal amount of sulfur dioxide (SO2).

Yet another object is to provide a method of the foregoing types in which roasting of the sulfur contained in pyrites is eifected chiey by means Vof sulfur dioxide.

As special object is to provide a method 1n accordance with the foregoing objects in which pyrrhotite (FeS) 1s reacted with sulfur dioxide to produce magnetite (Fe304) and elemental sulfur, and in which the sole source of sulfur dioxide is produced by reacting ferrie oxide with pyrrhotite to producemagnetite and sulfur dioxide.

Still another object is to eect roasting of pyrites 1n accordance with the foregoing objects to produce ferrie oxide containing less residual sulfur than has been the case with prior roasting methods.

A still further object is to effect roasting of pyrites in accordance with the foregoing objects under fluidizing conditions.

The invention will be `described with reference to the accompanying drawings in which:

Fig. 1 is a schematic representation or" one mode of practicing the invention;

Fig. 2 is a iiow sheet representing one embodiment of the invention as practiced with uidization;

Fig. 3 is a flow sheet illustrating another embodiment of the invention using ui'dization; and

Fig. 4 is still another ow sheet representing yet another uidized embodiment.

We have discovered, and it is upon this that the'invention is largely predicated, vthat the stated objects of the invention are attained by treating pyrites with an inert gas that is non-oxidizing to sulfur, and preferably comprising essentially at least one member lofthe group consisting of nitrogen (N2) and sulfur dioxide at a temperature at which the labile sulfur atom is drivenfrom the pyrites with formation of pyrrhotite, treating the resultant pyrrhotite with at least one member of the group Vconsisting of oxygen (O2) and sulfur dioxide at a temperature to convert it to magnetite, vheating the magnetite with an oxygen-containing gas at a temperature'to convertit to ferrie oxide, and recovering the sulfur produced and the Vferric oxide produced.

Having reference now to the drawings, Fig. 1 shows schematically a reactor i inthe form of a vertical moving bed shaft furnace into the upper end of which, as indicated in the drawing, pyrites is introduced through suitable ,feeding mechanism, not shown. The pyrites may suitably 2,772,153 aented Nov. =27, 1956 The pyrrhotite thus formed reacts, in `moving'downthe shaft, with sulfur dioxide toV produce magnetite-according to the following reaction Pyrrhotite likewise reacts with any oxygen remaining'in the upmoving gases in accordance with the ,following The magnetite formed by either lor both ofRea'ctions 2 and 3 then reacts with the oxygen of the air introduced into the bottom of the reactor, asshown, accordingtothe following reaction 4portion being passed at 4 to a stack. In the '.pra'c'tice'of this embodiment of the invention the air suppli'edtothe reactor is controlled in an amount such as to' eect Reaction 3 yand to avoid having any 'substantial excessof oxygenpassing into the upper portions'of the reactor, whereby oxidation of the vsulfur of the 'pyr'ites andpyrrhotite is avoided. `In this way the maximum amount 'of sulfur is recovered as such.

Various modications of the embodiment of Fig'lof the invention are permissible. For instance, thefern'c oxide from reactor 1 may be passed 'to a chloridizing reactor into which common salt, air and fuel are introduced for conversion of non-ferrous metals, such las nickel. and" copper, present in the ore into soluble chlorides. Similarly, the excess sulfur dioxide from condenser 2 that is-'not required for circulation in the system maybe passed 'toa liquefaction plant to recover sulfur dioxide for Vdesired use. In this latter embodiment it Amay be'preferable tto supply oxygen instead of air to the bottom-of shaft furnace lfwhereby there is no necessity for separating nitrogen from the sulfur dioxide'that is to be liquefied.

In the preferred embodiment of the invention the various stages of the'process are carried out under uidizing conditions, as illustrated in Figs. 2 to 4. Referring lto Fig. 2, pyrites in a form adapted to be uidized is passed to a preheater 5 where it is uidized by a stream of hot gas composed of nitrogen and sulfur dioxide from 'a heater 6, the temperature of the gas being such as to drive the labile sulfur atom from the pyrites and form pyrrhotite in Jaccordance with Reaction 1. The pyrrhotite passes into reactor 7 where it is uidized with a gas composed chiey of oxygen and nitrogen at a temperature such as to cause Reactions 2 and 3 to occur. The resulting magnetite then passes to a reactor 8 where it is fluidized with air "ata temperature to effect Reaction 4, with the olfg`as'(largely O2 and N2) being passed to reactor v7.

lyrites is fed likewise to a preheater 5a Where it *is uidlzed with hot gas from heater 6 with production of pyrrhotite according to Reaction 1. The pyrrhotite thus produced passes to a reactor 7a where it is uidized with the mixture of sulfur dioxide and nitrogen from reactor 7, land by sulfur dioxide from heater 6, with production of magnetite and elemental sulfur. The magnetitefrom reactors 7 and 7a is then passed to reactor `8, where it is fluidized by air and from which ferric oxide, per Reaction 4, is withdrawn.

The mixture of sulfur dioxide, sulfur vapor and fuitrogen fromreactors and Sa is passed-to a sulfurJcondenser 9 of any desired type from which the :sulfuris recovered, with the residual gas being passed to a stack `or Ato a sulfur dioxide liquetaction plant.

The mixture of sulfur dioxide, nitrogen and sulfur vapor from reactor 7a is likewise passed to sulfur condenser 9a for recovery of its content of sulfur, the residual sulfur dioxide and nitrogen then being passed to heater 6Yfor recirculation inthe system in the manner described.

Although preheater 5, reactor 7 Yand reactor 8 are shown in the ow sheet as separate units, it will be understood that the three stages may be combined in a single uidized reactor with the top, middle and bottom zones being represented, respectively, by preheater 5, reactor 7 and reactor 8. Likewise, the same thing applies 'to preheater 5a and reactor 7a.

If desired, all or a portion of the ferrie oxide from reactor 8 may be passed to a chloridizing reactoril in Y the manner and for the purpose described in connection with Fig. 1.

Having reference now to Fig. 3,.here again pyrites of appropriate size is fed to aV preheater 11 where it is Y uidized with an inert gas from generator 12 at a temperature sufficient to drive the labile sulfur atom from Ythe ore and form pyrrhotite. The inert gas supplied from generator 12 may be flue gas composed largely of nitrogen and carbon dioxide, or it may be blast furnace gas, or other gas that is substantially free from oxygen and nonreactive with sulfur under the roasting conditions. A portion of the pyrrhotite from preheater 11 then is uidized in a reactor 13 with sulfur dioxide under conditions in accordance with Reaction 2, thus forming magnetite and elemental sulfur. Another portion of the pyrrhotite formed in preheater 11 is passed to a reactor 13a where it is uidizcd with sulfur dioxide at a temperature* to cause Reaction 2 to proceed, likewise with production of magnetitie and sulfur vapor. VThe magnetite from reactors 13 and 13a then passes to a reactor 14 where it is treated at a temperature such that with oxygen or a gas containing a high'percentage, say 85 to 95 percent, of oxygen, preferably in an amount such that the ott-gas, if any, is substantially oxygen-free and consists essentially of nitrogen. Y

An important feature of this embodiment of the Yinvention is the recirculation, asY shown, of a portion of the ferrie oxide from reactor 14 Vto reactor 13 where the following reaction occurs Reaction 5 constitutes in this embodiment the sole source of the sulfur dioxide used in this embodiment, which is important and desirable in that oxidation of sulfur in reactors 13 and 13a and preheater 11 is avoided Ferrie oxide from reactor 14 is withdrawn and passed Y to use or storage, and the mixture of inert gas and sulfur vapor from preheater 11 is passed to a suitable sulfur condenser 15 from which sulfur is withdrawn, with the inert gas being wasted. Similarly, the mixture of sulfur dioxiderand sulfur vapor from reactors 13 Vand 13a are v passed to a condenser 15a for recovery of the sulfur content, the sulfur dioxide from the condenser being passed to a heater 16 for recirculation to reactors 13 and 13a, as described.

As in the case of Fig. 2, the separate stages of pre- Vheater 11 and reactors 13 and V14 may be combined in a single fluidized unit. Y

The embodiment of Fig. 4 is generally similar to that kof Fig. 3 in that pyrites of appropriate sizeA is iluidized Reaction 2. The magnetite from the two reactors is then Vfiuidized with air in a reactor 19 at a temperature to convert the magnetite Vto ferrie oxide in aodlle with Reaction 4. In this embodiment the air is preferably supplied to reactor 19 in such an amount that the product gas consists essentially of nitrogen which is passed as the inert gas to preheater 17. Preferably, a portion of the ferric oxide leaving reactor 19 is recycled to reactor 18, as shown, for the purpose described in connection with Fig. 3. The mixture of sulfur dioxide and sulfur vapor from reactors 18 and 18a is passed to an appropriate condenser 21for recoveryV of the' sulfur, with the separated sulfur dioxide passing to a heater 22 whence it is fed to reactors 18 and 18a. Here, also, preheater 17 and reactors 18 and 19 may be combined in a single uidized unit.

Although in various embodiments two sulfur condensers have been shown and described, it will be understood that all of the sulfur vapor-carrying gases Vmay be treated in a single condenser. Likewise,'in all instances the ferric oxide may go to a chloridizer, per Figs. 1 and 2.

According to the provisions Yof the patent statutes, We have explained the principle of our invention and have illustrated and described what we now consider to represent its best embodiment. However, we desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

We claim:

l. That method of roasting pyrites to produce sulfur and ferric oxide comprising V'fluidizing one portion of pyrites with nitrogen-containing gas substantially free from oxygen at a temperature to drive off the labile sulfur atom and form pyrrhotite, separately tuidizing a second portion of pyrites in the same manner, recovering the sulfurY from said treatments, liuidizing the pyrrhotite from said one portion with an oxygen-containing gas at atemperature to convert it to magnetite and'produce sulfur dioxide, uidizing the pyrrhotite from said second portion with sulfur dioxide, including that from said one portion, at a temperature to convert the pyrrhotite to magnetite with production of a mixture of sulfur dioxide and sulfur vapor, condensing sulfur from said mixture and passing part of the residual sulfur dioxide to treat said one portion and passing another part to treat the pyrrhotite from second portion, uniting the magnetite thus produced and uidizing it with an oxygen-containing gas at a temperature to convert it to ferric oxide, and

pyrites with nitrogen-containing gas substantially freeV from oxygen at Ya temperature to driveV ot the labile sulfur atom and form pyrrhotite, separately uidizing a second portion of pyrites in the same manner, recovering the sulfur from said treatments, uidizing the pyrrhotite from said one portion with an oxygen-containing gas ata temperature to convert it to magnetite and produce sulfur dioxide, treating the pyrrhotite from said second portion with sulfur dioxide, including that from said one portion, at a temperature and with uidization to convert it to magnetite with production of a mixture of sulfur dioxide and sulfur vapor, condensing sulfur from said mixture and passing part of the residual sulfur dioxide to treat said one portion and passing another part to treat the pyrrhotite from second portion, uniting the magnetite thus produced and fluidizing it with an oxygen-containing gas to convert it to ferric oxide, returning a portion of said ferrie oxide to the combined pyrrhotite, whereby the treatmentA of pyrrhotite is the sole source of sulfur dioxide in the system, and recovering ferric oxide. v

3. That method of roasting pyrites to produce sulfur and ferrie oxide comprising uidizing one portion of pyrites with nitrogen-containing gas Substantially free from oxygen at a temperature 'to drive off the labile second portion of pyrites in the same manner, recovering the sulfur from said treatments, iiuidizing the pyrrhotite from said one portion with an oxygen-containing gas at a temperature to convert it to magnetite and produce sulfur dioxide, treating the pyrrhotite from said second portion with sulfur dioxide, including that from said one portion, at a temperature and with uidization to convert it to magnetite with production of a mixture of sulfur dioxide and sulfur vapor, condensing sulfur from said mixture and passing the residual sulfur dioxide to a heater, passing sulfur dioxide 1rom the heater to treat said one portion and another part to treat the pyrrhotite from said second portion, uniting the magnetite thus produced and uidizing it with an oxygen-containing gas to convert it to ferrie oxide, and recovering the ferrie oxide.

4. That method of roasting pyrites comprising the steps of uidizing pyrites with non-oxidizing gas at a temperature to drive oiiC the labile sulfur atom and form pyrrhotite, recovering the sulfur thus produced, dividing Said pyrrhotite into two portions, fluidizing one of said portions with sulfur dioxide at a temperature to form magnetite and a mixture of sulfur dioxide and sulfur vapor, recovering sulfur from said mixture and passing part of the sulfur dioxide to treat said one portion and another part to fiuidize the other of said portions at a temperature to produce magnetite and a mixture of sulfur dioxide and sulfur vapor, recovering sulfur from said lastnamed mixture, combining the magnetite thus produced and uidizing it with an oxygen-containing gas at a temperature to convert it to ferrie oxide, and recovering the ferrie oxide.

5. That method of roasting pyrites comprising the steps of uidizing pyrites with non-oxidizing gas at a temperature to drive off the labile sulfur atom and form pyrrhotite, recovering the sulfur thus produced, dividing said pyrrhotite into two portions, uidizing one of said portions With sulfur dioxide at a temperature to form magnetite and a mixture of sulfur dioxide and sulfur vapor, recovering sulfur from said mixture and passing part of the sulfur dioxide to treat said one portion and another part to uidize the other of said portions at a temperature to produce magnetite and a mixture of sulfur dioxide and sulfur vapor, recovering sulfur from said lastnamed mixture, combining the magnetite thus produced and udizing it with an oxygen-containing gas at a temperature to convert it to ferrie oxide, and supplying said sulfur dioxide solely by returning a portion of said ferric oxide to the combined magnetite to react with pyrrhotite with production of magnetite and sulfur dioxide, andv recovering the ferric oxide.

6. That method of roasting pyrites comprising the steps of fiuidizing pyrites with non-oxidizing gas at a temperature to drive oi the labile sulfur atom and form pyrrhotite, recovering the sulfur thus produced, dividing said pyrrhotite into two portions, uidizing one of said portions with sulfur dioxide at a temperature to form magnetite and a mixture of sulfur dioxide and sulfur vapor, recovering sulfur from said mixture and passing part of the sulfur dioxide to treat said one portion and another part to uidize the other of said portions at a temperature to produce magnetite and a mixture of sulfur dioxide and sulfur vapor, recovering sulfur from said last- .nanied mixture, combining the magnetite thus produced and uidizing it with air at a temperature to convert it to ferrie oxide and in an amount such that the oli-gas is substantially oxygen free, passing said off-gas to iiuidize said pyrites, and recovering the ferric oxide.

7. That method of roasting pyrites comprising the steps of uidizing pyrites with non-oxidizing gas at a temperature to drive off the labile sulfur atom and form pyrrhotite, recovering the sulfur thus produced, dividing said pyrrhotite into two portions, uidizing one of said portions with sulfur dioxide at a temperature to form magnetite and a mixture of sulfur dioxide and sulfur vapor, recovering sulfur from said mixture and passing part of the sulfur dioxide to treat said one portion and another part to uidize the other of said portions at a temperature to produce magnetite and a mixture of sulfur dioxide and sulfur vapor, recovering sulfur from said lastnamed mixture, combining the magnetite thus produced and uidizing it with air at a temperature to convert it to ferrie oxide, said air being in an amount such that the ot-gas is substantially oxygen free, passing said oft'- gas to uidize said pyrites, supplying said sulfur dioxide solely by returning a portion of said ferric oxide to the combined magnetite to react with pyrrhotite to form magnetite and sulfur dioxide, and recovering ferrie oxide.

References Cited in the tile of this patent UNITED STATES PATENTS 1,941,592 Bacon etal Jan. 2, 1934

Claims (1)

1. THAT METHOD OF ROASTING PYRITES TO PRODUCE SULFUR AND FERRIC OXIDE COMPRISING FLUIDIZING ONE PORTION OF PYRITES WITH NITROGEN-CONTAINING GAS SUBSTANTIALLY FREE FROM OXYGEN AT A TEMPERATURE TO DRIVE OFF THE LABILE SULFUR ATOM AND FORM PYRRHOTITE, SEPARATELY FLUIDIZING A SECOND PORTION OF PYRITES IN THE SAME MANNER, RECOVERING THE SULFUR FROM SAID TREATMENTS, FLUIDIZING THE PYRRHOTITE FROM SAID ONE PORTION WITH AN OXYGEN-CONTAINING GAS AT A TEMPERATURE TO CONVERT IT TO MAGNETITE AND PRODUCE SULFUR DIOXIDE, FLUIDIZING THE PYRRHOTITE FROM SAID SECOND PORTION WITH SULFUR DIOXIDE, INCLUDING THAT FROM SAID ONE PORTION, AT A TEMPERATURE TO CONVERT THE PYRRHOTITE TO MAGNETITE WITH PRODUCTION OF A MIXTURE OF SULFUR DIOXIDE

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