US2042576A - Smelting sulphide ores - Google Patents

Description

Filed Sept. 26, 1950 mill I a.

lNVENTOR fizz world 1? Bacon ATTO RNEYS Patented June 2, 1936 UNITED STATES PATENT OFFICE 7 Claims.

This invention relates to the blast furnace smelting of pyrites and has for its object the provision of a pyrites smelting process wherein the sulphur liberated is recovered in elemental form.

partly as safety factor in in case of irregularity of than the sulphur dioxide.

As a matter of fact, however, the exit gases in operating the furnace and also as a result of the more or less open top with which the usual smelting furnace is run.

In accordance with the process of my invention, the large such oxidation.

The manner in which I accomplish the same consists in general, in regulating the air fed to the furnace, in slower feeding, in reducing the sulphur dioxide from the combustion zone by the action of the ferrous sulphide (FeS) in the charge, maintaining a non-oxidizing atmosphere in the upper part of the charge to prevent the oxidation of the sulphur so reduced as well as that liberated by volatilization, and operating the furnace with a closed top to prevent the ingress of air above the charge which would result in oxidation of the elemental sulphur. I also prefer to use a hot blast in my process.

It is to be noted, moreover that this is accomplished and the smelting operation carried outas well, with the employment of only the coke or other carbonaceous pyritic smelting; viz. 2 to 6 If reliance were to be placed upon sulphur dinormal amount of materials used in per cent.

my invention is as follows:

A blast furnace smelter of any well known type, for example the common water-jacketed pyritic extending through the water-jackets provide for amount of silica and calclum an iron calcium silicate slag.

To this charge is added a small amount of coke or other suitable carbonaceous material, primarily to impart suitable porosity to the ore to promote dilfusion, and to an extent, to provide a safety factor in maintaining the heat in case of earths to provide irregularity of operation This function can' likewise be served by any material other than coke which will accomplish the same result with- 'the top of the furnace is its variance upon 2 out interfering with the smelting or recovering operations.

The amount of coke used will depend upon the physical nature of the ore and the requirements of the particular operation. In general it will vary between approximately 2 and 6 per cent as in ordinary pyritic smelting, in so far as it is not relied upon to any material extent for fuel value or as a reducing agent for the sulphur dioxide.

The differentiation of my invention from the ordinary pyrites smelting operation, is not concerned particularly with the amount of coke used provided the use of such coke is limited by the dictates of porosity maintenance and the necessity of providing afuel safety factor.

This charge is introduced into the furnace without the ingress of air during such operation, and the desired depth of bedis *contrcillsd i -by periodic additions to the charge as the operation proceeds.

Air is blown in through the tuyeres in the well known manner, and in accordance with my invention the air blast is introduced at such a controlled rate that the oxygen will be substantially entirely consumed in the smelting zone, in order to assure the maintenance of a substantially nonoxidizing atmosphere in the :upper part of the furnace.

.In addition the air blast is introduced atsuch a rate that an elongated hot zone is produced and the temperature of the furnace is higher in the zone above the tuyere zone than is .usual in-pyritic smelting, this for the purpose of accelerating the reduction of thesulphur dioxide by the FeS. To further amplify the thermal resources of the process and to assure virtually completeconsumption .of the oxygen in the combustion zone, it is also zdesirable that a very hot blast be used. If desired the blast may also be dry, to promote .uniformity of operation and .to facilitate the attainment of theelongated focus.

As a resulto'f this iproductiono'f an elongated focus, it is desirable to increase the normal height of the charge, :and where necessaryasuitably higher furnace should be provided for this purpose. Bysodoing, sufliciently prolonged contact of the sulphur dioxide with the :iron sulphide will be provided, and an undulyhigh temperature in the gases escaping from the top of the charge will be avoided. The temperature at desirably: held at' 350 to 450 C. V

The most suitable height of charge for the particular ore and operating conditions can be readily ascertained in each instance by the effect of the operation. The-effect, for example, upon the natureof the slag, the concentration of the matte, and the composition of the exit gases from the furnace, particularly as regards their relative sulphur dioxide and free sulphur contents will serve to indicate the changes which should be made.

'In-any case,'.lhowever, the charge should not be extended to such a height that thesulphur would tend to deposit in the furnace as .a result of :an unduly low top temperature.

'By careful observance of the conditions here- 7 tofore noted, a very high percentage of elemental sulphur will be present in the exit gases from the furnace and the smelting operation will proceed in a markedly .efiectivemanner.

The reactions which take place in the furnace areprobably constituted as follows:

In the intense combustion zone or focus, the iron and a large proportion of the sulphur in the iron sulphide mixture remaining after the volatile sulphur has been driven off, will be oxidized by the hot air blast with the formation of sulphur dioxide, an iron calcium silicate slag, and a matte containing the copper or nickel and other values. This matte and slag will descend to the bottom of the furnace, and may be tapped off in the usual manner.

The hot sulphur dioxide will ascend into the charge, and upon contacting with the hot iron sulphide will be reduced to elemental sulphur with the accompanying production of an iron oxide. This reaction probably proceeds more or less in accordance with one or both of the equations- "In the lower'part of the furnace the first reaction is more likely to take place than the latter, in view of the silica present which .will tend to avidly take up ferrous'oxide at the prevailing high temperature to form a slag.

Furthermore, the higher v temperature: provided in the elongated focus, will'materially accelerate these reactions, which proceed more rapidly at higher temperatures. The removal by the silica of the FeO formed, reduces the possibility of the action reversing, and the same is true of the velocity of the gas current which will carry the elemental sulphur produced to the regions where reversing is less likely to'occur.

Proceeding upwardly through thecharge, the reactions will tend to progress to substantial completion, for a temperature as 'low as'0 'C, is

ordinarily satisfactory for rapid reaction, a requirement amply satisfied by the attendant smelting conditions.

To further assure the substantial completionof this reducing reaction and particularly. asregards the cooler portion of the chargejI have'found an intimate admixture of magne's'i'awith the charge to be peculiarly effective .in catalyzing this reaction, a material reduction in [the necessary temperature being therebyJn'ade possible. In the case where magnesia is added to the chargeJas for instance a dolomitic lime it passes into the slag, whose composition will be modified in accordance with rulesiwell known in the art. 'Lime and iron oxide also act as catalystsifor this reaction, but not as effectively as'magnesia.

In the upper portions of the charge the heat ascending from the focus through the medium of the gases will volatilize the feeble sulphur atom of the pyrites present in the charge.

Due to the regulation of the air blast to assure consumption of practically .all of the oxygen in thecombustion zone, the atmosphere in the upper part of the charge will be non-oxidizing, and the volatilized sulphur and that produced by reduc-.

tion of the sulphur dioxide will not'be subjectto oxidation therein.

Furthermore, upon their escape -at the top of the charge, the provision of the closedtop under which the furnace is operating, -will assure the substantial absence of air at the top of the furnace and the exitgases will retain theirhigh content of elemental sulphur substantially-unaffected. 7

Upon discharge from'the' furnace, the gases may be conducted to ya fsuitable dust col le'ctor,; for example a mechanical dust separator such :aas-ea bafiie chamber, or an electrostatic i precipita'tor such-as the well knownCottrellg and 'the dust free gases subsequently conducted thru a fcatalyzer to form sulphur from gaseous sul hur compounds and then to an apparatus for recovering the sulphur. For this purpose a waste heat boiler or similar cooling means may be utilized to condense the sulphur and its partial separation may be accomplished therein, or subsequently by the use of an electrostatic precipitator.

The gases from the dust separation usually contain appreciable amounts of sulphur compounds which warrant further treatment, to recover the sulphur values or remove noxious constituents.

The sulphur compounds which may be present in these gases would ordinarily consist of S02 and/or H25, and Where carbon wasprovided in the charge for gas diffusion, a slight amount of COS.

These particular compounds are capable of interaction with the production of elemental sulphur according to the equations- These reactions are carried out in a catalytic chamber containing a catalyzer such as porous alumina or bauxite, where they will readily react to yield the additional sulphur in elemental form.

Where insuflicient amounts of sulphur dioxide are present in the gases, supplemental amounts may be added if desired, to carry out the aforenoted reactions, or by slightly increasing the blast the amount of S02 may be increased.

i'he gases remaining after the final sulphur separation may then be discharged into the atmosphere, practically entirely freed of the constituents which ordinarily constitute a very objectionable nuisance in the usual smelting operation.

By proceeding in accordance with the process herein described, many advantages are provided over the processes heretofore available.

An economical and very effective recovery of elemental sulphur as an incident to pyrites smelting, is made possible, thereby opening up a substantial and inexpensive source of this element.

The amount of air necessary calculated on the pyrite is less than half that required in the usual pyritic smelting process; and the noxious gas nuisance ordinarily encountered in the operation is entirely eliminated.

The amount of air used in my process is also much less, calculated on the pyrites charge, than in any process in which coke or coal or other carbonaceous fuel is used in the furnace in relatively substantial quantity, say 9 to 10 per cent or more. Due to this fact the sulphur content of the exit gases is much higher in percentage than in such processes which is a marked advantage of my process, as completely condensing the sulphur vapor from very dilute hot gases adds cost to a process.

The term pyrites as used herein is not intended to be limited to true pyrites, FeSz, but also includes other forms of iron sulphide containing less sulphur than Fesz, for example, pyrrhotite, also iron sulphides containing nickel and/or copper, and likewise manufactlured products, such as mattes, which consist principally of iron sulphides. When a material of the type of pyrrhotite is smelted, there is little or no feeble atom of sulphur to be removed by volatilization, hence the zone of sulphur volatilization is absent; otherwise the operation is much the same as in the smelting of true pyrites by my process with only such usual changes in the smelting operation as will be apparent to one skilled in the art.

I claim:

1. In a process of recovering sulphur from pyrites wherein the pyrites is smelted in a smelting furnace, the steps which comprise, contacting the sulphur dioxide from the combustion zone with the ferrous sulphide from the partially desulphurized pyrites in the presence of a magnesia catalyst to accelerate the reduction of the sulphur dioxide to elemental sulphur by said sulphide.

2. In a process of recovering sulphur from pyrites wherein the pyrites is smelted in a smelting furnace, the steps which comprise, contacting the sulphur dioxide from the combustion zone with the ferrous sulphide from the partially desulphurized pyrites in the presence of dolomitic lime to accelerate the reduction of the sulphur dioxide to elemental sulphur by said sulphide.

'3. In a process of recovering sulphur from pyrites wherein the pyrites is smelted in a smelting furnace, the steps which comprise, intimately admixing magnesia throughout the pyritic charge to catalyze a reaction of ferrous sulphide upon sulphur dioxide to reduce the latter to elemental sulphur, contacting the sulphur dioxide gases from the combustion zone first with the hot molten ferrous sulphide of the partially desulphurized magnesia-containing pyritic charge, and then contacting said gases with the unmelted ferrous sulphide of said magnesia-containing pyritic charge.

4. The process of recovering elemental sulphur from pyrites which comprises, subjecting a charge containing the pyrites to the action of an air blast in a smelting furnace with the blast introduced at such a rate that a smelting temperature is attained in the lower portion of the furnace and the oxygen of the blast is substantially consumed in said portion, passing the sulphur dioxide produced in such combustion zone in contact with the hot iron sulphide in the charge above the combustion zone for a suitable period of time and with the sulphide provided in such amount that substantially all of the sulphur dioxide is reduced to elemental sulphur by reaction therewith, 'exeluding oxidizing atmosphere from above the charge in the furnace, Withdrawing from the furnace the gases issuing from the top of the charge, and separating the elemental sulphur from said gases.

5. The process of recovering sulphur from pyrites which comprises, subjecting a charge containing the pyrites to the action of a hot air blast in a smelting furnace with the blast introduced at such a rate that a smelting temperature is attained in the lower portion of the furnace and the oxygen of the blast is substantially consumed in said portion, passing the sulphur diamount that substantially all of the sulphur dioxide is reduced to elemental sulphur by reaction therewith, excluding air from above the charge during feeding to prevent oxidation of the elemental sulphur, withdrawing from the furnace the gases issuing from the top of the charge, and separating the elemental sulphur from said gases.

6. In a process of recovering elemental sulphur from pyrites wherein the pyrites is smelted in a smelting furnace, the steps which comprise, subjecting the lower portion of a charge within the furnace to the action of a blast of oxidizing gas I5 from pyrites wherein 4 to oxidize the charge and produce sulphur; dioxide and toemelt the resulting oxidized charge, contacting the sulphur dioxide from the combustion zone in-the furnace with the hot iron sulphide in the upper portion of the charge in said furnace in the absence of air, and maintaining a suitable amount of iron sulphide in the furnace and suitably prolonging the period of contact of the sulphur dioxide with said sulphide to substantially completely by reaction therewith reduce the sulphur dioxide furnace, the oxidized charge being withdrawn from the furnace in a molten condition.

.7. In a process of recovering elemental sulphur the'pyrites is smelted in a smelting'furnacathe steps which comprise, com tacting the sulphur dioxide :fromv the combustion zone and in the absence of air first with the hot molten iron sulphide of ized pyritic charge, and then contacting the gases with the unmelted iron sulphide in the upper portion of the furnace, the contact of the sulphur dioxide with said sulphide belng'maintained for a suitably prolonged period of time and with the sulphide provided in sufiicient amount to substantially completely reduce the sulphur dioxide by reaction therewith to elemental sulphur within the furnace.

RAYMOND F. BACON.

the partially desulphur-

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