US1603710A - Process of producing pure iron from its ore - Google Patents

Description

Patented Oct; 19, 1926.

UNITED STATES PATENT OFFICE.

CHARLES E. PARSONS, OF NEW YORK, N. Y., AND SAMUEL I'EACOCK, OF WHEEIIING WEST VIRGINIA, ASSIGNORS TO METAL RESEARCH CORPORATION, OF NEW YORK N. Y., A CORPORATION OF DELAWARE.

PBOCESSOF IRODUCING PURE IRON FROM ITS ORE.

80 Drawing.

its Ob ect to improve the procedure of making the same, over What has been heretofore known. (I

With these and other objects in View the invention consists in the novel steps and combinations of steps constituting the process,.all as will be more fully hereinafter disclosed and particularly pointed out in the claims.

The process of this invention makes pure iron by employing a temperature of reduction which does not permit the iron ore to sinter, and therefore, it does not collect impurities, such as slag, silica, etc. As is Well known, should these impurities .lbecome embedded in the fused mass of the iron, the subsequent step of separating out the pure iron from the gangue would fail to remove all the impurities, and therefore, upon the later fusion of the pure iron, after passing the magnetic separator,'such impurities would .remain with the metal andlater cause more or less matalloids to form and thus lessen the purity of the resulting product. It is also known that unless pure iron is produced above a given temperature, it will constitute when formed what is known as pyrophoric iron, which is chemically very active, and therefore, not suitable for the purposes in hand. It is therefore necessary in carrying out this ,process, to heat the iron oxide above 1500 F. which will prevent the presence of pyrophoric properties in the iron; and it is also necessary to so control the temperature that it will not go above 1800 F., for otherwise its purity will be decreased.

In order that the invention may be the more clearly understood it'should further be said that the metallurgy of iron and steel as usually practiced at this time, consists in reducing iron oxideusually with carbon or carbon monoxide, producing a crude iron carbide and treatlng such crude metal by various methods to remove impurities. Such refinin rocesses consist lar el in uddling or kneading the crude metal to separate out the relatively low melting point impurities, or in burning with air, and slag- Application filed October 17, 1923. Serial No. 669,111.

ging out the metalloids. All these processes are costly and are not technically effectual. The puddling process does not clear the metal of slag, but gives a product containing relatively very small quantities of occluded gases and oxidation products, nitrogen compounds, etc. The air processes of the Bessemer and open hearth type of furnace are capable of removing more or less slag and the metalloid impurities forced into the metal by the blast furnace process, but in doing so they charge the metal with dissolved gases, iron oxidation products in solid solution in definite'proportions, and undetermined forms of nitrogen compounds. It is possible, it is true, with elaborate and costly refining operations, to greatly minimize the objectionable effects of these refining treatments, but a positively-homogenous metal is substantially never realized, thus givingrise to an inevitable uncertainty as to the performance of such refined iron when used industrially.

By the process to be objections are removed as will presently appear. Further, the so-called pig iron or blast furnace smelted iron varies considerably in composition, depending upon the ores and coke employed and the method of working the furnace. An approximate general analysis showing the impurities in such iron, may be stated as follows Per cent. Iron carbide tem furnace such as a blast furnace, and.

the whole mass, exclusive of fuel carbon, is melted down together. All components of this furnace mixture, together with the necessary fuel, are charged into the furnace disclosed below, these concerned. Unfortunately, elemental iron readily forms compounds with metalloids, hence silicon from the silica, and carbon from thecoke together with the highly objectionable sulphur and phosphorus in the furnace charge tend to ultimate in the crude iron. Iron ore generally contains very little sulphur, but the coke necessarily employed contains from one to two percent, and of thetotal sulphur in the furnace charge, about 90% .comes from coke. This sulphur must be as completely removed as possible, and this is usually done by adding a relatively large proportion of lime to the furnace charge, which requires still morecoke for its conversion to a fusibleslag, so that at best, sulphur elimination is never more than partial. By the procedure of this invention, these objections are likewise eliminated as will presently appear.

In addition to the foregoing objections,-

' the fuel 'proportion' is greatly augmented,

- under the prior procedures, because to form and melt a pound of slag requires seven times as much coke as is necessary to rediice from the oxide and melt apound of iron. The inefliciency of the blast furnace process is indicated by the fact that while somewhat-less than one third of, a pound of coke is technically suflicient to reduce and melt a pound of iron from iron oxide, more than one pound is required in actual prac- Again, although tice andthe result is a very crude iron product of v minor industrial value, unless it is further refined.

Theselast named objections are likewise obviated by the procedure disclosed below. pig iron refined by the kneading or puddhn process gives av moderately uniform pro uct, yet, the operation.

volumeof gases which highvtemperatures.

is entirely too costly for general industrial application. And thp Bessemer and open hearth processes, while almost universally employed, give ,a very uncertain product.

'In fact, Sir-Roberts Austin experimentally determined that steel made by such methods, contains from six to eight times its alone will not remove, and ample evidence supports the belief that these dissolved gases are seriously objectionable, althou h elaborate and costly processes have; been evised for thelr removal as an industrial procedure. It results that most of these methods involve adding further impurities, and none of them are positive in effect. Also in these smelting processes, from the blast furnace through the open hearth furnaces or converters, a considerable proportion of rejected materials are produced, which gen erally contain too much iron to discard as waste and which must be reworked in the blast furnace. In fact, it is safe to say that practically over 25% of the total iron smelted in a blast furnace connected with steel making is reworked metal which must bear again and again the cost and losses of smeltmg.

The process of this invention again avoids these objections as will appear more fully hereinafter.

According to this invention, on the other hand,pure iron may be produced direct from the ore by the following procedure which consists simply in reducing iron oxide at about 1500 F. in a stream of reducing gas which has previously been desuleffected in a closed system with a large ex cess of reducing gases flowing in a counter current to the movement of the ore. By using the reducing gases in excess and maintaining in the reducing chamber a partial pressure of carbon dioxide, or water vapor, never in excess of 5 centimeters, practically a quantitative reduction of iron oxide may be realized. The ore prior to reduction is thoroughly dried and passed through rolls to evenly size the particles of mineral and prevent clumping.

It-is aiot practicable to completely reduce ferric oxide, or the magnetic oxide with a theoretical quantity of carbon monoxide only in the presence of the catalytically reacting pyrophoric elemental iron in contact with carbon monoxide, because there will result the following reaction on the metal, pyrophoric metal, if present,

and it would be difficult to later remove it But, if once deposited and not removed. thecarbon would ultimate as iron carbide when the iron is melted thus destroying its puversion of the pyrophoric properties of the iron commences. Butthere is always possible, a momentary temperature drop which may deposit carbon upon the reduced pyrophoric metal and thus upon fusion, introduce iron carbide into the end product of iron. But, this is avoided by providing in the apparatus a positive temperature control which prevents the iron from reaching a point below a predetermined degree. Probably equally undesirable is the presence of a small, even minute quantity of ferrous oxide which may accompany the carbon deposition, and which would dissolve into the iron upon fusion. Therefore, to avoid these objections the temperature ranges employed must be strictly maintained Within narrow limits not above 1800 F. and not below 1500 F.

Coal gas may be used as. a reducing agent containing about 47% hydrogen. A gas of this type contains by volume approxis matelyr CO 8% CO 3% 7' CH 232% C H 5% H 247% N 4% The gas and ore are preheated to any desired temperature. and reducing agents may be kept above the temperature at which pyrophoric iron can exist and at which bon.

If hydrogen is used as a reducing agent, the reaction is strongly endothermic requiring about 347 B. t. u. per pound of iron thus formed, and allowance is made for such heat. The heat produced by reducing ferric oxide with carbon monoxide at 1500-F. amounts to about 139 Ht. u. per pound of iron thus .made, and does not constitute a thermal obstacle to theprocess.

Average Lake Superior iron ore has approximately the following composition 1:

Volatile matter 5 The iron oxide of this ore may be se arated out by an 011 separation, or by other well known ore treating operations, produc- By this means, the ore the CO can deposit car- ,.temperature such .as 4000 F.

with pure carbon will take up nearly 10% ing asan end product, iron oxide of a purity exceeding 99.9%; or the crude iron oxide may be reduced to elemental iron, and such iron removed from the gangue material by a magnetic separation. After treatment with reducing gas, as described above, if crude ore is employed, I

there remains in the solid form from 100 pounds of such ore, 56 pounds of elemental iron and 14 pounds of gangue material, the latter having passed through the reducing chamber unchanged. The solid matter is conveyed out of the reducing chamber by any suitable means, and, after cooling below the magnetic transformation point or substantially below 1400 .F. is passed through a magnetic separator by means of which,

in two'or more passes, the elemental iron is completely separated from .the gangue matter and is physically in the form of a fine powder and substantially chemically pure as it has not been in contact with carbon or metalloid oxides at a higher temperature than about 1500 F. The iron powder is then suitably delivered into an electric furnace of the induction. or similar type, by means of which it is melted into a mass without contact with carbon electrodes, or in anyway subjected to carbonaceous material; The molten product is pure iron.

Its positive freedom from gaseous occlusions, metalloid solutions and slag inclusions of any kind preclude the resence of alloy eutectics or eutectoids, and constitutes this metal as a composition or state of matter never heretofore known in mass as an industrial product.

Its industrial usefulness iswide and varied; it has a low corrosion factor, is easily worked without strain hardening, and may be shaped as readily as zinc or tin. Its chief use, however, is in making steels free of gaseous occlusions and metalloideuteetoids.

For such purposes it is only necessary that a suitable alloying metal or compound be added in the desired proportions to the molten pure iron. Any desired alloy effect may be an positively and exactly duplicated at wil accomplishment uite impossible under the present method of making special steels.

For making straight iron carbides for carburizing iron and steel without adding impurities, this metal, brought to a high in contact of carbon. An alloy of iron and carbon of this nature enables the manufacturer to produce a wide range of iron carbon steels of exceptional purity and of positive physical properties. There can be no blow holes in an ingot made of such materials, and practically no lamination a. reducing gas, at a low temperature. Illustrating with carbon monoxide and with hy-- drogen, the reactions may be stated thus For every pound of iron reduced with carbon monoxide, 139 B. t. u. are liberated; reduced with hydrogen; 347 B. t. u. disappear. As the reaction product for the manufacture of one pound of pure iron with carbon monoxide. consists solely of one and one-fifth pounds of carbon dioxide, assuming a radiation loss of producing iron by this means is a heating 'eiiect and must be supplied in the heating chamber to regulate the combustion of the gases used for heating the charge, to avoid too high temperatures. If the hydrogen is employed as the'reduction reagent, heat is absorbed and there is no danger of objectionably high temperatures in the reducing chamber.

According to the theory of allotropy, all allotrppic substances are complex, and if ferric oxide is reduced at a temperature different from that at which the oxide was formed originally, a metallic phase different from the original metallic state will be ob-- tained. WVhen iron oxide is reduced very slowly at about 750 F. the elemental iron thus obtained, has very different physical properties from those of ordinary iron at 750 F. The elemental iron produced at such low temperature consists possibly of ferrous ions exclusively, and constitutes substantially the state of iron usually known as pyrophoric. Pyrophoric iron is extremely active, as above stated. and its presence in elemental iron produced by gaseous reducing reagents, very markedly lowers the efiiciency of reduction. because the partial pressure proportion of the gaseous reaction product is enormously reduced. That is, the reaction reverses at vastly lower partial pressures of carbon dioxide or water vapor than is usually observed in studying reactions with ordinary iron. ously involves the commercial application of reducing pure iron bv gaseous reducing agents; and means must be found for the elimination of the pyrophoric state in such reduced elemental iron.

In fact, pyrophoric iron maintained at 600 F. for 48 hours, loses most of its ac,- tive tendency, and at 650 F. for 24 hours,

the pyrophoric state entirely disappears;-

. but, holding a charge of such iron for 24 hours under narrow temperature limits, is adifiicult' and costly industrial operation.

The general proposition has been confirmed that the well known iron alpha-beta transformation point, about 1420 F. (770 (l), is not an ordinary transition iphenomenon, andthat at such temperature, an'inner equilibrium is established with great veloc- It is obvious This, of course, serithe magnetic separation to fail, the reducing temperature must not exceed 1800 F. Pure ferric oxide melts at 2854 Rand sinters readily at 2300 F. The crude oxide .as it occurs in iron ore, sinters' appreciably at 1850 F. Therefore, for efliciency in the operation of our process, theiron oxide under treatment in the reducing phase should nevenfall below 1500 En er exceed 1800 F.; also in drying the ore i and driving out water and organic matter,.the maximum temperature employed should not exceed 1800 F.

that after reduction to elemental iron the material must be cooled below the magnetic transition point, 1420 F.

I inorder to enable magnetic separation. The

cooling of the finely divided elemental iron under such conditions does not restore the pyrophoric state. As a further means of preventing the formation of pyrophoric iron, thus enabling quantitative reduction of iron oxide at low temperatures, a negative catalyst maybe mixed with the 0xidc, such as arseneous acid in very small proportion; or afew hundredths of one percent ofchlorine may be added to the reducing gases, While such practice enables lowering the temperature of reduction, it

does not enable the .pse of temperatures in the preparatory I higher than 1800 F. stages' p In the practical operation of our process, the iron oxide is thoroughly dried and organic matter burned out, when present. The ore is then passed through a reducing apparatus, the temperature being positively maintained between 1520 and 1800 F. The reducing apparatus may conveniently consist of the well known constructions to which no claim is made but involving three or more reducing decks upon which the ore is slowly delivered at a point on the outer circumference of the uppermost deck. Revolving arms having plow shaped stirrers attached, slowly move the ore in successive circular ridges, from the circumference of the deck to a central aperture, when the charge falls to the deck below. On this deck the plows attached to the revolving arms, work the charge in successive ridges to the circumference of the deck, where apertures suitably placed, enable the ore to fall to the next lower deck; this treatment of successive ridging is continued on as many decks as the for heating the ore when required, by burninga portion of the reducing gases within such chamber or chambers. The reducing gases enter the reducing furnace at the bottom deck and pass through and over the successive decks, in counter current to the flow of the furnace charge. The discharge from the reducing furnace, passes over magnetic separators to eliminate gangue, and the pure iron powder is discharged 1nto an induction furnace for fusion. The whole system, from the reducing furnace to the induction melting furnace is sealed in a closed system.

The performance of the'reducing furnace is the controlling factor in the process. It is known that the efficiency of deoxidation of iron oxides by means of reducing gases is .less a function of fineness of subdivision than of surface contact between the oxide and the reducing reagent. By means of a plow stirring effect, fresh surfaces are constantly being exposed to gas contact; i

What is claimed is 1. The process of making substantially pure iron directly from iron oxide which consists in reducing said oxide free from carbonaceous material in the presence of a stream of sulphur free reduclng gas at a temperature between 1500 F. and 1800-F.

2. The process of making pure iron directly from iron oxide ore free from carbonaceous material which -consits in subjecting said ore to a stream sulphur free reducing gas in excess at a temperature above 1500 F. and below 1800 F.

3. The process of making pure iron directly from its ore which consists in subjecting said ore free from solid carbon to the action of a sulphur free'stream of prov ducer gas at a temperature between 1500 F. and 1800.F.

4. The process of making substantially pure iron directly from iron oxide which consists in reducing said oxide while in motion in the presence of 'a stream of reducing gas flowing in a direction opposite to the movement of said ore, said gas being free from sulphur and at a temperature sufficient to prevent the formation of, iron carbide.

5. The process of making-pure iron directly from iron oxide ore which consists in subjecting said 'ore-to a stream of a reducing gas in excess at a temperature suiticient to prevent the deposition of carbon, and preventing the partial pressure of any carbon dioxideor water vapor that may be present from exceeding five centimeters of mercury.

6. The process of making pure iron directly from iron oxide ore which consists in subjecting said ore toastream ofa reducing gas free from sulphur and in excess at a temperature suflicient to prevent the deposition of carbon, and positively maintaining said temperature throughout the pe- I riod of reduction.

7. The process of making. pure iron directly from iron oxide ore which consists in subjecting said ore mixed with a negativecatalyst to a stream of a reducing gas in ex-- cess at a temperature sufiicient to prevent the deposition of carbon.

In testimony whereof we atiix our signatures.

CHARLES E. PARSONS.

SAMUEL PEACOCK.