US3375097A - Reducing to mno the mno2 of a manganese ore - Google Patents

Description

J. YY. WELSH 3,375,097

REDUCING TO MMO THE MmOgOF A MANGANESE ORE 3 sheets-sheet 1 March 2G, 1968 Filed 001;. 18, 1965 -w ATToRNExs March 26, i968 .1. Y. WELSH 3,375,097

HEDUCING TO MmO THE MMOZOF A MANGANESE ORE y Filed Oct. 18, 1965 5 Sheets-Sheet 2 o( v -,420 f @0 #so 0 P so y a] 6o `l00 Oo( BY @mld y Mw Q21 ATroRNEYs J. Y. WELSH March 26, 1968 REDUCING TO MmO THE MmOZOF' A MANGANESE ORE 3 Sheets-Sheet 3 Filed OCt. 18, 1965 INVEN TOR /Hy )4 Wwf-l da@ ATTORNEYS United States Patent O '3,375,097 REDUCING T MnO THE MnO2 0F A MANGANESE ORE Jay Y. Welsh, Catonsville, Md., assignor to Manganese Chemicals Corporation, Baltimore, Md., a corporation of Maryland Filed Oct. 18, 1965, Ser. No. 496,965 12 Claims. (Cl. 751) ABSTRACT OF DISCLOSURE The higher oxide of manganese in a mangan'iferous 'ore material, in which the manganese values are present in the form of a higher oxide of manganese, is reduced to MnO by a method which Vcomprises feeding -an air- This invention relates vto the vart of reducing manganif- `erous ores in which the manganese Vvalues lare present in the form of a higher oxide of manganese, and is particularly concerned with the reduction .to MnO of the MnO2 vvalues of a manganese ore or ore material. e

One of the most difficult problems encountered in the reduction of manganese ores has been `the control of reaction heat. If a stable MnO -product is desired-that is, a product which will not undergo reoxidation under ambient or near-ambient conditions-it is necessary that the reduction temperature be near or slightly above 1300" F. On the other hand, if the reduction temperature is about 2000 F. or higher the reducing ore may soften and bond together producing a sinter which is extremely diflicult to handle or process. 'In an eifort to circumvent the problem of temperature control, current reduction methods have become both expensive and troublesome. f v

It is an object o-f the present invention Ito provide a process by which the manganese ores comprising or consisting essentially of any normal .oxide composition can be reduced in beds, piles o r columns under precise temperature control and -at a much lower cost .than by current methods.

The basic principle of this process consists in feeding an accurately controlled ratio .of air to hydroca-rbonaceous gas (e.g., -natural gas or methane) through a yhot bed of MnO and then causing the issuing gaseous productshaving a net reducing effect-immediately to pass into and through a bed or layer of the raw manganese ore. It is apparent that these conditions are realized if 4the air-gas mixture is passed upwardly or outwardly through a bed .of reducing ore, `the surface of which lis being fed with raw ore. Under these conditions the hot bed of MnO is supplied by the ore which has lundergone reduction and of course the issuing Vreducing gases Ifrom the MnO ybed .pass directly into the raw ore layer on the surface .of the MnO bed. The hot bed of MnO serves as a catalyst to promote a reaction Ibetween the air and the hydrocarbonaceous gas. MnO is a very effective lcatalyst in ,this `regar-d, vand .virtually Aany `gas-air mixture can be made to react .to its theoretical products yeven at temperatures as low as 700 to 800 F.

The advantages of this process over other methods can be fully understood only Vby a detailed discussion of the mechanical and thermodynamic .factors involved. Such 3,375,097 Patented Mar. 26, 196s ICC a discussion will be shown in terms of a metallurgical grade p yrolusite ore containing MnQ-2 yits raw state and 84% MnO in its reduce-d state. The hydrocarbonaceous reducing gas will be considered as CH4, with CO and H2 as special cases. The following discussion will refer to one or another of the appended drawings, in which:

FIG. 1 is a schematic representation of zones possibly existing in a manganese ore bed undergoing reduction;

FIG. 2 is a graph showing the heat o f reaction `of air and methane as a function of air-to-methane ratio and also vas affunction of temperature;

FIG. 3 is a graph showing the heat of reaction of higher oxides of manganese.;

FIG. 4 is a curve correlating the heats of reaction with the heat capacity of the product gases, in .terms vof temperatures attained; and

FIG. 5 is a simplified diagrammatic representation .of `gases and solids flow in an ore bed.

I n FIG. l various zones which can or do exist in a reducing ore bed 'are schematically indicated.

Case l. As it stands FIG. 1 represents the zones -ideally `operating in the process of the present invention.

y Case 2. 4If .the reducing gas Lis methane only, zones 1 and II do not exist.

Case 3. If ythe primary reducing gas is either CO or H2 (plus inert gases) or a combination o f CO and H2 instead ,of an air-methane mixture, -zones I and II do not exist. Further, lin the event of an .exceessive overblow of this reducing gas mixture zones IV and V are combined and zone VI is virtually non-existant.

FIG. 2 shows the heat of .reaction of air and methane as a function of air to methane ratio, and also asa function of temperature. The l500 F. curve represents the net heat ofireaction taking place under the catalytic inlluence of Mn'O in zone I and III in a bed operating in `proper thermal balance.

,-FgIG. 3 `shows the heat of reaction of MnO2, Mn2O3 and Mn3O4, respectively with the gaseous products of Athe catalytic air-methane reaction, as a functioin of air-tomethane ratio. It is to be noted that the curves in both FIG. 2 and FIG. 3 show abrupt changes at an air-tomethane ratio of 2 .4/1.'Thi s can be understood in terms of Ithe products of the air-methane reaction at a temperature of 1500" F. or over. Ata |`ratio of 2.4/ l the reaction products are essentially CO and H2 only. Below a ratio of v2.4/1 increasing amounts of unreacted methane exist and yabove 2.4/1 increasing amounts of CO2 and H2O vare produced. In :the case of FIG. 2 yt-he high iheat of formation of carbon dioxide and water account for the abrupt increase of heat of reaction above the 2.4/1 ratio. Applied to FIG. 2, the heat of reaction increases as the ratio of CO and H2 to CH4 increases. At the 2 .4/ 1 ratio ythe reducing components remain CO and H2 only, vtherefore the heat of reaction remains essentially the same.

Balancing the heatsof reaction are four heat-consuming processes, viz:

(1)-.the heat required to raise the temperatures of the various gaseous components up to the temper ltures existing vin the bed;

(A2) the ,hea-t required to raise the various solid components up to temperatures existing in the bed (the volatilization of free or chemical water contained in the ore is to be vincluded in these values);

(3) .the heat .required to thermally `decompose MnO2 vtci Mn203; and (4) Yheat removed from the system by radiation, convection, articial cooling, etc.

In any bed process the above thermal processes must algebraically balance the reaction and gas transfer heats under steady state conditions, and-as mentioned previously-they must balance in such a way that the reduction zone temperature is controlled within the approximate temperature limits of about 1300 to 2000 F.

COMPARISON OF OTHER REDUCTION METHODS A. Kiln Before proceeding with a detailed discussion of bed, pile or column reduction systems, the reduction of ore in a rotating kiln will be considered for comparison. Basic in the operation of a kiln are the following features which distinguish from bed processes:

(l) The size of the ore particles must be small to permit complete reduction during the retention time of a kiln of practical length.

(2) A heat balance of the reacting materials does not have to be strictly maintained between the reactants themselves because heat can be artificially removed or added through the walls of the kiln to maintain the temperatures desired.

(3) Any movement of gas through the kiln in conjunction with a moving bed of finely divided solid material gives rise to the necessity of expensive dust collecting equipment.

(4) As opposed to bed reduction, coal or charcoal can be effectively used in kiln reduction providing an excess is employed.

(5) Expensive alloy tubes and troublesome mechanical maintenance are inherent.

(6) Gas permeability and heat transfer factors limit the depth of bed and tube size and therefore limit the rate of production per kiln.

It is apparent that the features characterizing kiln operation vs. bed operation are disadvantageous with possibly two exceptions, namely, the versatility with respect to heat balance and the ability to employ a solid fuel. Since the latter is often more expensive than natural gas and in addition leaves an undesirable residue, the option of its use is not attractive. And, since the proposed process provides a simple and practical method of controlling reaction temperatures (or heat balance) within a bed, kiln reduction methods appear to have no advantageous features.

B. Column reduction with producer gas The reduction of a bed of ore with producer gas represents a special case of gas mixtures containing CO, H2 and N2. The use of producer gas in bed reductions will be analyzed at this point for comparison also. A typical gas would be represented -by the following composition:

Percent H2 5 CO2 2 N2, (by volume) 61 The gaseous reaction products will be:

Percent CO2 34 H2O 5 N2 61 Consider a peak reaction zone temperature of l860 F. The average mean heat capacity to this temperature is 0.0226 B.t,u./cu. ft. for the above product gases.

The reaction.-Mn2O3-l2.7 (.32 CO-l-.OS H2f)- 2 MnO 2.865 COz-l-.135 H2O.produces 41,400 B.t.u/#' mole (2MnO).

The reaction.-2MnO2-}5.4 (3.2 CO-l-.OS H2)- 2 MnO-i-1.73 CO2-|-.27 H2O produces .-124,000 l 3,t.u/# more (zMno).

4 Heat Balance calculations: (based on 2 moles of MnO product) Input: B.tu./# mole ZMnO Heat transferred to cold ore by hot inert 5 gas at 1860 F., based on the reduction of M1'1203 Heat of reduction Mn2O3 -41,400

Total transfer and reaction heat 81,000

Required:

Heat required to raise 2 moles of MnO as raw ore from 60 to 860 F. 28,600 Heat required to thermally decompose 2MI102 t0 Mn203 (860 Heat required to raise 2 moles of MnO plus gangue from 860 to 1860 F. 27,400

Total heat required 90,400

A similar calculation at a peak reaction temperature of 1360 F. gives:

B.t.u. Input 68,600 Required 77,900

These data indicate that a sufficiently high reaction temperature cannot be maintained if all of the MnO2 is thermally decomposed to Mn2O3 before the reduction 90 takes place. In practice, however, the thermal decomposition lreaction is not complete and net heat is added to the system in two ways, (l) from the direct reduction of a portion of the MnO'2 which produces (see reaction heat ofthe two reduction equations) about three times as much heat per unit of MnO produced as does the re- D duction of Mn2O3, and (2) by a corresponding reduction of the endothermic heat of decomposition of MnO2 and Mn2O3. Fortunately, the proportion of MnO2 -undergoing thermal decomposition to the MnO2 undergoing direct reduction is largely self-regulating. Thus, if the reaction zone temperature (zone IV, FIG. 1) is high, more heat will be transferred to the pre-heat and thermal decomposition zone (zone V, FIG. 1), giving rise to a greater degree of thermal decomposition. The converse is equally true.

Two factors effect the ability of the system to regulate itself in the manner described. (l) As the gas flow rate is increased, a point will be reached when increasing l amounts of reducing gas will pass through the reduction zone and enter the pre-heat and thermal decomposition zone creating an ever widening intermediate zone labeled zone (IV-i-V) in FIG. 1. This in turn leads to an excessive proportion of direct MnO2 reduction and excessive temperatures. (2) As the screen size of the ore is increased, both the rate of reduction and of thermal decomposition are decreased. The combined effect of these rate factors is again to broaden the intermediate zone (IV-l-V) and cause more direct reduction of MnO2, leading to excessive temperatures.

One extreme set of `operating conditions should also be mentioned in connection with reduction of ore beds with producer gas. If very high gas ow rates are imposed, reaction zones IV and V (FIG. 1) merge into one composite zone and zone VI (FIG. 1) virtually disappears. Under these conditions the excessive heat of the direct MnO2 reduction (which now comprises nearly 100% of the reduction processes) is removed from the top of the bed, thus permitting the temperature of the composite reaction zone to be controlled. This sheer brute force method requires about twice the amount of reducing gas.

It is apparent then that even though it is both feasible and practical to carry out the reduction of ore in a bed with producer gas, rather restrictive conditions must be imposed with respect to gas flow rate and/ or ore particle size in order to avoid excessive temperatures within the ore bed. Further, producer gas inherently contains ob jectionable sulfur impurities as well as being unfavorable with respect to cost, convenience and maintenance. In the special case of ore containing oxygen corresponding to an Mn3O4 level only, insuicient reaction heat is available even under the most ,favorable conditions to permit fedacffm by producer se@ It willbe shown in the subsequent heat balance analysis of ore reduction, by the use of air-methane mixtures thatunlike producer gas reduction-wide latitude is possible with Irespect to reduction rates (gas iiow) as well as particle size range. Further, adjustments can be made which would even permit the reduction of ores containing manganese oxides at the Mn'3O4'oxidation level. l

-DISCUSSION OF PROPOSED PROCESS As one varies the air-to-methane ratio two extremes of course are evident. As the air-to-gas ratio approaches 9.6/1 (the theoretical `ratiofor complete combustion) it is self-evident that bed temperatures will be excessive (over 3000 F.). In FIG. 2 and FIG. 4 it is readily apparent that air-to-gas ratios approaching 5/1 or even 4/1 would represent a practical upper limit, even zone I would approach or exceed 2000-o F. The thermal characteristics ,of a reducing bed Vfor which the air-to-gas ratio is zero (that is, pure methane) yare not obvious and since this extreme has an important bearing on the overall concept, it will, in the following, be analyzed carefully and compared with experi-mental results.

A peak reaction zone temperature of 1860 F. and 100% direct reduction of MnOz will be assumed. The average mean heat capacity of the CO2 and H2O emerging from the reduction' zone is 0.0255 B.t. u./cu. ft.

Heat balance calculations (based on 2 moles of kMnO product) Heat required to raise t-he raw ore and reactions products from 60 F. to 1.8609 F. raw ore from 60 -F. to 860 F.

=(174/.75`)(.16)(800) 29,600 MnO plus gangue from y860" F. to 1860 Total heat required 56,600

Thus, hypothet-ically, if 100% of the MnO2 were reduced directly by methane an excess of 85,300-56,600 or 28,700 B.t.u. of heat would be produced for each two moles of MnO product. The assumed .temperature of l860 F. could therefore Ynot representa stable condition and the reaction zone temperature would increase. Experimental data have shown the converse yto be the ac-tual result. In fact, if pure methane is used as the reducing Agas the reduction zone temperature drops so low that the reduction can cease. The reason for this paradox has already ybeen mentioned, namely, that the ,transfer of heat to the unreacted ore by the hot, inert gaseous reduction products is sufficient to thermally decompose a .substantial portion of the Mn02 to Mn2O3. .Calculations indicate that a theoretical balance would zbe reached if about 30% ofthe Mn02 lthermally decomposed to Mn2O3 before actual-reduction took place, but since experiment indicates that a heat balance does not exist, appreciably more than 30% thermal decomposition must occur in the pre-heat and thermal -decomposition zone (zone V, FIG. 1).

Accordingly, somewhere between an air-to-methane ratio of 0/1 and 4/1 -there should exist a ratio of air-to- -methane which gives the thermal balance required. This h as in fact been found to be true and, further, the range has been found to be suiciently broad to lrender the process extremely practical. One of the reasons for Va relatively broad range of operation has already been discussed in terms of the se1f`regulating control of the degree of thermal decomposition of MnOg' to Mn2O3. To the previous discussion in this regardy one additional note should be added, namely, that ahot reduction Azone not only transfers more heat to the thermal decomposition`zone by virtue of the temperature of the'issuing gases but also because there is a greater volume of them. That is, any MnOz undergoing directreduction, which is of course the source of the v'additional heat, also produces twice the volume of gaseous products as'does Mn2O3 per rnole of MnO produced.

The air-to-methane ratio for reduction of a normal metallurgical pyrolusite or'e by the present process has been found to fall within a range of about 2/ 1 to about 3.5/ 1. If exceptionally high production rates are desired per unit of .bed surface or if exceptionally coarse ore is involved, ratios approaching 2/1 or even less may be required. The factors involved here have been discussed in connection with producer gas reduction. Conversely, low "gas flow rates in conjunction with a finely divided ore `or an ore with exceptionally low oxygen content may require air-to-me'thane ratios approaching 3.5/1 or even higher. Since an air-to-methane ratio of 2.4/ 1 falls well within the normal process range, and because of the simplicity of the equations involved, a complete thermal analysis will be made for this air-gas ratio. Conclusions concerning air-to-methane ratios falling on either side will be made when appropriate.

The yreaction and heat effects taking place within the MnO zones, I, II and III (FIG. 1) are not only high relevant to the overall process but uniquely adapted to it. It has already been mentioned that MnO acts as a catalyst to promte air-methane reactionsat low air-tomethane ratios and further will permit these reactions to take place at temperatures as low as 700"to 800 F. It is a very important ancillary fact that air-methane reactions can be established in a bed of MnO the temperature of which has fallen to as low as about 400 F. The process by which this is accomplished is two-fold in nature. (1) A n air-to-methane Aratio somewhat higher than normal should be chosen to reactivate such a cold MnO bed, a ratio of about 3.5/1 for example. (2) When .the gas blow is started, the initiating reaction is between .the lair and the MnO since the lcatalytic air-methane reactions are largely inactive at temperatures as low as 400 F. The MnO reaction, however, produces heat which readily raises the advancing heat band to the temperature necessary to initiate the air-methane reactions; in fact, blowing air alone through such a bed can `develop enough heat for fusion.

Once the catalytic air-methane reactions are initiated, no furtheroxidation of MnO will take place, and the reaction -herat will be characteristic of the particular ratio. A l3.5/1 ratio o f air-to-tnethiane produces product gases ,at about l550 F. (see FIG. 4). These gases as they` move upwardly or outwardly .th-rough the bed will progressively Vbring the entire bed to 15509 F. level `and will re-establish the reduction process if raw ore is placed on ythe surface. The air-methane ratio is then adjusted to a normal process level.

Thermodynamic analysis of the air-methane reactions ltaking place in zones I and III (FIG. l) .prove to be uniquely applicable to .the process of the present invention. At an air ratio of 2.4/ 1, i.e., l/ z mole of O2 per `mole of methane, the following lreactions are possible:

A free energy analysis `indicates that reaction (1) is very minor between 800 and .1000 F. and that reaction (3) is somewhat predominant over reaction (2). At 1200 F. reactions (1), (2) and (3) are of about equal importance. At 1500 F. reactions (2) and (3) are both minor, and (1) is dominant. v

FIG. 2 shows the heat produced by the above reactions (suitably weighted in Aaccordance with their importance) as a function of air-to-methane ratio at various temperatures. The curve of FIG. 4 correlates the heats of reaction with the heat capacity of the product gases in terms of the temperature the product gases attain. The curve sections of FIG. 4 labeled A, B and C are of special significance to the reduction process under discussion. Curve section A is indicated as a solid line since the heat of reaction is ydominated by reactions (2) and (3) which do not change appreciably in importance over the temperature range covered. Curve section B is indicated as a dotted line since it covers a temperature range which represents a transition from the dominance of reactions (2) 4and (3) to Ka dominance of reaction (l). Since the heat of reaction (1) is quite low-about 1sth that of reactions (2) and (3)- the curve falls off sharply below l400 F.

Coincidential with the temperature level which permits the predominance of reaction (1) two additional (or sequential) reactions develop negative free energies and therefore take place:

Both reactions (4) and (5 have very high endothermic heats of reaction. These endothermic reactions proceeding concurrently (or predominately) from the products of reactions (2) and (3) stabilize the reaction gas temperature producing plateau line, section C. Beyond section C the excess CO2 and H2O in the combustion products of the higher air-to-methane ratios cause a rapid rise in temperature of the resulting gaseous products.

Two additional reactions should be mentioned:

(6) 1/2 (z+1/2 Copco (7) 1/2 C 21/2 H20-W2 Co 21/2 H2 These react-ions (6) and (7) both show negative free energy changes above about 1300 F., both are endothermic but less so than are (4) and (5).

These data can now be applied to zones I, II and III (FIG. 1). It is apparent from FIG. 4 that within the normal air-to-methane ratio range, the temperature in zone I is relatively constant at about 1250" to 1350 F. Further, since reactions (6) and (7) go within this temperature range, any carbon produced by reaction (3) is substantially removed from the surface of the ore particles. The temperature in zone II (1250 to 1350 F.) will maintain the same as the temperature generated in zone I. The gases moving through zone II are largely CO2, H2O and unreacted CH4.

In the specific case being analyzed, a 2.4/1 air-tomethane ratio, no extra reaction heat is available to cause endothermic reactions (4) and (5) to proceed. However, in zone III the air-methane reaction gases may encounter MnO higher in temperature. In fact the temperature of the upper part of zone III is very close to the temperature of the reduction zone, zone IV. Experimental measurements indicate zone IV may range in temperature from as low as 1200 to as much as 1900 F., depending on the rate of gas blow and the ore particle size. If a high zone 1V temperature exists, the MnO inA zone III represents a heat reservoir from which heat is supplied yfor the endothermic reactions (4) and (5 Calculations indicate that if the temperature drop between zone IV and zone II is 400 F. for higher, suiiicient sensible heat will be supplied to complete reactions (4) and (5) before the reducing gases reach zone IV. Because of the endothermic reactions taking place, the temperature gradient in zone III (if one exists) will be relatively sharp. For the same reason the temperature of the gases entering zone IV may be little above their temperature before entering zone III.

In zone IV active reduction of manganese oxides is taking place and reaction heat is produced. As indicated, zone IV may have a temperature range of 1200 to 1900 F. For the present analysis a temperature of 1800 F. will be used for the upper range and 1200 F. for the lower range. (A temperature as low as 1200 F. is extreme and would 'be avoided in practice.)

If as a first approximation it be assumed in both instances that Mn203 is the only oxide undergoing reduction, then the reduction equation will be:

1800 F. case Input 1 (based on 2 moles of MnO produced):

1 The aver-age mean Iheat capacity of the product gases from 60 to 1800" F.=.0236 B.t.u. per cu. ft.

B.t.u./# mole (2MnO) Heat transferred to zone V from zone IV by the hot product gases=(1740) (.0236) The calculations indicate that if all of the reduction in zone IV is based on Mn2O3, thermal balance cannot be maintained at 1800 F. The imbalance indicated is 32,100 B.t.u. for each 2 moles of M110 less input than is required.

As a second approximation assume 25% of the product MnO is reduced in zone (IV-i-V), FIG. 1 from MnOZ. The remaining of the product MnO is assumed to be reduced in zone IV from Mn203.

The reduction equation of MnO2 s:

Heat transferred to zone V from zones IV and (IV plus V)=(1740)(.0236)(378) (1.63-1- .25) 31,600 Heat of reaction 32,200 .75) 110,

Total heat transferred and produced 83,200

Required:

Total heat required=89,600 (34,400)

Thus, if slightly more than 75 of the Mn() undergoes thermal decomposition in zone V and slightly less than 25% still remains to be reduced directly in zone (IV plus V) a heat balance will be established.

1200o F. case Input: B.t.u./# mole (2MnO) Heat transferred by hot product gases 19,000 Heat of lreduction 30,200

Total heat tranfserred and produced 49,200

Required:

Heat to raise raw ore to 860 F 29,800 Heat to decompose MnO2 to Mn2O3 34,400 Heat to raise product MnO to 1200 F. 9,200

Total heat required 73,400

In this instance the thermal deficiency is 24,200 B.t.u. instead of 32,100, and it would appear that about 19% of direct MnOg reduction is required to give a thermal balance. l

The difference in the degree of thermal decomposition indicated above is `obviously the reason for the low ternperature of the reduction Zone instead of the result. A higher (more efficient) degree of thermal decomposition occurs in the event of a low rate of gas blow in conjunction with a finely divided ore, which leads to low reduction zone temperatures. Further, the heat balance calcu lations for the 1200 F. case should be qualified. If the reduction zone is at 1200 F. no extra bed heat is available for endothermic reactions -(4) and (5 and this heat must either be supplied by the reduction reaction (that is, more direct reduction of MnO2 would be necessary than the 19% indicated, and such an indicated percentage may not exist) or by additional air in the air-methane mixture. In practice the latter is preferred (in fact is necessary for efiicient operation). Thus, if a fine ore bed is to be reduced at a relatively low rate, higher air-tomethane ratios are needed, preferably sufficiently high to raise the reaction zone temperature to at least 1400 F.

Assume a reduction bed has been brought to a suitable thermal balance by an adjustment of the air-to-methane ratio. The proper ratio, as indicated, falls into a range either below 2.4/1 or above 2.4/ 1. At air-to-methane ratios between 2.4/1 and 2/1 little change will be observed in the conditions in zones I, II and III. The reduction heat generated in zone 1V will drop significantly, however (see FIG. 3), thus compensating for a lower degree of thermal decomposition of M1102 to Mn203. At air-to-methane ratios less than 2/1 there will be a significant drop of the temperature in zone I with corresponding shifts up through the bed and a slight carbon deposit may also develop on the ore particles. Below an air-to-methane ratio of 1/1 the catalytic air-methane reaction will not function smoothly, and Mn3O4 cycling may occur.

At air-to-methane ratios between 2.4/1 and slightly over 3/ 1, zones I and II will not change greatly with respect to temperature. However, more and more of the endothermic heat for reactions (4) and (5) will have been supplied by the airmethane reaction itself, zone III will be broader and the exit gases will pass into Zone IV somewhat nearer to the zone IV temperature. Since the heat of reduction remains unchanged above the 2,4/1 ratio, it is apparent that the additional heat of the airmethane reaction compensates for the loss of reaction heat due to a greater degree of thermal decomposition of MnOZ to Mn2O3. Above a ratio of 3.5/1 the temperature throughout the bed will rise rapidly and at about 4/1 even zones I, II and III will approach the limiting ternperature of 2000 F. exclusive of the additional reduction heat. Gas-methane ratios within this range would be ernployed for ores very low in oxygen content.

Additional notes-There are several comments (not included in the previous discussion) which are of importance: l

(1) Of major importance is the fact that over one half of the reduction is carried out with hydrogen in the present process. This has an advantage when coarse ore is reduced since the rate :of diffusion of hydrogen to the center oa lump .of ore is about 31/2 times that of carbon monoxide. The result is a narrower reduction zone and a more efiicient heat interchange between Zones IV and V. This fact in addition to the ability to adjust the heat of reduction downward by as much as 40% permits the reduction of coarse ore at high rates without danger of overheating.

(2) The gas entering the reduction zone contains a high percentage of reducibles: even the highest air-tornethane ratio of the normal operating range contains about 50% reducibles. This means relatively low gas flows per unit of production. High gas blows through an ore bed `are generally undesirable because the fine ore particles are moved with the gas stream and tend to collect in pockets using poor gas distribution.

(3) The process once initiated in a proper bed is virtually efficient with respect to methane utilization, and since some 75 to 80% of the reduction is from the Mn203 level instead of from the Mn02 level the process is very economical.

(4) The surface of the reacting bed is cool which minimizes operating hazards.

(5) The equilibrium temperature in the MnO bed due to the air-methane reaction is generally sufiicient in itself to produce stable MnO regardless of the reduction zone temperature.

(6) It is normally desirable to limit the peak temperature to avoid partial fusion or sintering. There are applications, however, for which partial fusion of an MnO product is desirable. It is important to note therefore that with higher air-to-methane ratios sintering can be produced, and--more important-that the degree of sintering can be controlled. i

S umlmnry Before proceeding with a discussion of types of reduction beds and the operational parameters involved, it is desirable to put the various factors which correlate with the proper choice of aiuto-methane ratio in table form, as follows.

Factors which suggest a lower range of air to methane ratios:

' (1) Ore exceptionally high in MnOz content.

(2) Ore with large mesh size.

(3) High pro-duction (or, gas flow) rate.

(4) Continuous processes in which all of the M110 lcorresponding to zones I land II (FIG. l) is continuously removed.

(5) Desirability of a reactive MnO.

-Factors which suggest a higher range of lair to methane ratios:

(1) Ore with a high proportion of lower oxide.

(2) Ore with low mesh size.

(3) Low production (or, gas flow) pate,

(4) Batch processing.

(5) When a product is desired which is completely free from traces of carbon.

(6) Excep-tionally wet ore.

(7) Desirability of very .Stable Ore.

APPLICATION OF PROCESS Introduction The versatility of the proposed method of reduction has been stressed and it will be evident that this versatility can vbe transposed to the type of equipment in which the reduction process is carried out. Since the problems of heat balance `and temperature control VWithin the reducing ore bed are inherently solved by the process itself, the design of equipment for an overall process is concerned almost entirely with three problems:

( 1) proper gas flow pattern-s within the bed;

(2) suitable ore fow patterns (correlation between (l) rand (2) is normally necessary); and

(3) a means of cooling the product MnO `subsequent `to its participation in the reduction process.

Background factors The movement of gas through a finite ore bed is inuenced by the following:

(1) the container-bed interface. There is a marked tendency for higher gas flow rates at this interface than within the bed proper.

(2) the distribution of the ore particle size within the bed. If the feeding pattern is such that particle size segregation occurs, the `gas flow will tend to bypass areas containing a higher proportion of fines.

(3) the temperature `distribution in the bed. The gas flow, in terms of weight of ygas per unit time, will tend to be highest through the colder tareas of the bed.

(4) the length of path. It is obvious but important that the highest ow of gas will tend to be through the shortest bed path.

Thermal stability of MnO in air The stability of MnO in air will vary greatly depending upon the tempenature -at which it was reduced. -Even the most 'stable MnO cannot be handled in lau open system, however, unless it is tirst cooled to a suitable temperature level. In general, MnO should 'be cooled to at least 300 F. before exposure to an open atmosphere.

Ore movement in a bin or cone-There is a marked tendency for any particulate material to flow muc-h more rapidly from the center of the bin or cone than from the peripheral areas.

DISCUSSION OF VARIOUS TYPES OF ORE BEDS Stationary The most simple type of bed from the point of view of the operational parameters is a stationary one. For the process of the present invention, stationary beds offer several unique advantages. `One special case, namely, of a simple pile on la tiat surface, is of particular interest and will be discussed in detail.

PILE REDUCTION Applications of the process of the present invention to reduction in a pile of ore requires only very simple and inexpensive apparatus, and is ideal for yapplication to a manganese ore in the physical form in which i-t customarily moves in trade, namely, material varying in size from particles as large as one inch (or even larger) in diameter down through Ia progression of smaller and smaller sizes to lines. It is a batch process. It can be, and preferably is, carried out right on the ground. To prepare for carrying out the process a shallow hole is dug in the ground and in it a distribution chamber is constructed by placing on the earth floor of the hole bricks or blocks in two parallel rows and bridging the two rows with a row of bricks or blocks to form a grating over the distribution chamber. 'l'lhe `bricks are laid up without mortar, and purposefully are spaced apart to provide plenty of inerstices. An inlet pipe, partly buried in the ground, has its discharge end in this distribution chamber whilst its other, outer, end is branched and communicates with sour-ces of ya plurality of gases, as more specifically described 'hereinbelow If a round pile of ore is to be built up, the distribution chamber and hole Ifor the same are square or rectangular with the longer axis not very much longer than the shorter laxis. If an elongated pile, or windrow, of ore is to be built up the hole is an elongated ditch, and the distribution chamber wit-hin this ditch is correspondingly elongated. In either event, the hole is dug to suoh a depth that the top of the grating is at a level about opposite the level of the adjacent earth. Advantageously, a distribution chamber about eighteen inches in cross-section is adequate for an ore pile about twelve feet in cross-section.

To the branched outer end of the inlet pipe there are led -a plurality of valved conduits leading, respectively,

from (l) a source of air under slight pressure, (2) a source of the selected lhydrocarbonaceou-s iiuid and (3) a source of an inert relatively cool cooling gas (which latter will be further described hereinafter).

To begin a batch operation, a small amount of the manganese ore material to be reduced is placed in a small pile over (eg, on) the grating and heated to an elevated temperature (e.g., between about 800 F. and about l200 F.) at which reduction of higher oxide of manganese to MnO proceeds at a desirable rate. This initial heating m-ay be performed by burning in situ in the `small pile of ore a combustible mixtureof fluid fuel and air introduced into the ore by way of said distribution chamber. However, I prefer to effect this initial heating by forming the aforesaid small pile of ore about (i.e., over) a still smaller pile of charcoal lying on the aforesaid grating, lighting the charcoal, and blowing into the burning charcoal a controlled amount of cornbustion-supporting air (introduced by way of said distribution chamber) whilst slowly covering the pile of burning charcoal with successively applied individually very thin layers of the ore material. Application of ore to the pile advantageously is done, ya shovelful at a time, by an operator who rspreads out the shovelful over the top or over the sides of the pile in such thin layer.

It is an important featu-re of the process that the addition of ore material to the sides of the pile shall be in relatively thin layers and that the thin layer of ore be applied in such manner that the ore material cascades over a portion of a side of the pile, in order that the ore particles -segregate (size-wise) at the pile surface, with the coarsest particles rolling faster and farther than the smaller particles whereby the particles adjacent the earth are relatively very coa-rse and hence their larger interstices influence ready passage of gases therethrough.

By the time the underlying charcoal has been consumed (burned), the covering of ore material will have grown so that a sizeable although still small pile of ore will have been formed. The layers of ore material overlying the burning charcoal tend to prevent complete combustion of the fuel, and the burning fuel gives oif CO gas which--since it is hot and is an active reducing agent-in passing radially outwardly through the overlying ore heats the ore (thereby driving off the customarily present absorbed water) and raisesits temperature to, say, l000-1l00 F. and simultaneously reduces the higher oxide of manganese present in the ore to MnO. Since this reduction is strongly exohermic, the temperature of the ore undergoing reduction usually rises to about 1700-1800o F. In consequence, a red-hot layer or zone of active reduction is maintained only a few inches beneath the surface of the pile, and the gases moving radially outwardly through this highly heated layer carry the heat along into the outermost layers of fresh ore material.

As soon as there has been formed a sizeable but still small pile of ore material in the interior of which reduction is taking place, the operator feeds to the aforesaid distribution chamber a stream of gaseous mixture containing a gaseous carbonaceous'fuel. Advantageously, this mixture may be a mixture of natural gas rich in methane, CH4 (and hereinafter sometimes referred to simply as methane), and air, in controlled amounts relative to each other and in an aggregate amount controlled with due regard to the rate of progress of reduction in the ore pile. Since hot MnO is an active cracking agent the air-natural gas mixture as it becomes heated by contact with hot ore is cracked to a mixed gas-reducing in net effect-consisting essentially of CO, H2, CO2 and N2 (together with some uncracked CH4). The relative amounts of air and natural gas thus mixed and cracked are adjusted to about the ratio of 3-t0-l. During the building up of the pile the operator uses a thermocouple stuck into the pile to determine the temperature pattern, and adjusts the relative amounts of natural gas vusual amount of absorbed water the -air-natural gas vratio may be altered in the direction of a 4:1 ratio.

As was mentioned abve, the ore is so delivered onto the sides of the pile as to induce segregation of particles to bring it about the particles nearest theground are the largest particles of the ore. Whilst continuing to furnish the aforesaid mixed gas of net reducing eifect the operator continues to add ore-in the manner-'above described-the additions being made with strict Aregard to the temperature distribution pattern within the ore pile. This temperature pattern can--in effect-ehe visually ascertained, in the sense that wherever-the radially outwardly moving gas mixture tinds a zone of readiest egress that zone will become highly heated fastest and the zone of maximum temperature within the pile will lie nearest the exterior surface ofthe pile.r Since the waste gases exiting from the pile contain much water vapor, the pile steams visually. Those spots onthe surface where the emerging steam is the densest are the hottest spots. Whenever and wherever the operatorsees an unevenness in the density of the emerging steam he feeds layers of ore to such a hot spot at an enhanced rate and until the denseness of steam emanating from such hot spot has become the same as that in the areas surrounding such spot. In the ideal situation, steam emanates from the pile at a uniform intensity throughout the entire surface of the pile, Since conditions are never ideal for any length of time, the operator keeps watch over the steaming pile and applies his next shovelful or so where more steam is seen. In other words, he feeds (ore) to the hot spots.

All during this procedure, the natural gas and air entering the pile from the distribution chamber quickly. become highly heated by the hot reduced ore which` the mixture first contacts, and the mixture is cracked to a reducing gas mixture of CO, H2, CO2, N2 and some uncracked CH4. Simultaneously with the cracking, the gases are highly heated to about'or above 1000 F. These hot reducing. gases pass radially outwardly,

through the pile, into the overlying layer of highly heated unreduced ore which they encounter and drive oli Water from, and heat, and reduce the same` to MnO. With proper operation the gasesactually emerge from the exterior surface of the pile containing no or only a little CO or H2, and simply are water vapor, carbon dioxide. and nitrogen.

The reduction which proceeds radially outwardly as the pile grows occurs in a layer which is only two or three inches, under the actual surface of the pile: lif the operator pushes the ore away with the tip of his shovel he can see the red-hot layer of the freshr ore just".'der the surface.

As the pile of ore continues to grow, it inherently changes its general shape, and becomes yless and less spread out over the ground. When the angle of the layer under-going active. reduction (or, differently expressed, where the angle of the zone of maximum temperature) has reached the steepness of the angle of repose of the ore, it is time to stop feeding Qreto the pile. The product pile at this stage consists of the,4 ore with a thin"ski n (outermost layer) of unreduced or incomplete-,ly reduced ore on the surface. Continuance of ore feedwould simply bring it about that theheatpattern no longer couldbe followed with the ore pattern and the base of thel ore layers would be too thick to reduce.` In a one-man operation this stage 'may be reached in` about l2Q hours. However, the operator continues to supply natural gas through the distribution chamber for-some time, (say, onehalf hour). after he has stopped feeding ore to the sides of the pile, whereby to provide enough reducing gas to fnishfthe reduction of Vthe final outer layer of ore. Just as soon as ycooled Vdown to a temperature at which the MnO of the reduced ore will not reoxidize in the presence of air. As soon as this has been accomplished, the -batch process is at an end, and the reduced ore can be picked up (e.g., with a power shovel) and moved to a point of further use. Then the batch procedure may 'be repeated.

The above-,mentioned cooling gas may be any gas which is non-oxidizing to MnO. Thus, it may be roomtemperature nitrogen or carbon dioxide from any suitable source. In lieu thereof, a cool reducing gas such as CHr, CO, H2, etc. probably could be used. Advantageously, an operable cool' neutral gas economically may be produced at the site ,by (l) burning natural gas in an amount of air yielding oxygen in a stoichiometric amount with respectv to the combustibles content of the natural gas, thereby producing a neutral gas, and (2) cooling the cembustion gases as, for example, by passing said gases through a water spray, and then blowing the so-cooled inert gas through the aforesaid inlet pipe and into and through said distribution chamber into and through the reduced ore pile. Presumably, steam might be used as pooling agentalthough steam does re-oxidize a small proportion of the MnO. The worst aspect of cooling with steam is that steam hydrates the MnO-once it has cooled down to a lower temperature near the boiling point of water-and the manganous hydrate is unstable in air, even at room-temperature. Accordingly, steam is not an industrially feasible cooling agent in this connection.

It is believed that the process is operable using crushed ore material of any normal size distribution (e.g., with the largest lumps not larger than 2-3 inches in diameter and the greater part falling within the minus 1/2 inchfiues range). Presumably, it would not be economically feasible to crush finer than all minus one-half inch. Crushingiujaj'aw crusher gives a desirable particle size distribution (not too large a proportion of tines).

SPECIFIC EXAMPLE In `one specific reduction to practice of the process of ther-present invention, applicant used amanganese ore which, Vas received,` had been crushed to minus threeeighths inch diameter,` which material contained particles in allszes vdown to (and including considerable) fines. It analyzed 4850% Mn, mostly as MnO2, with the remainder beingA the usual gangue constituents A1203, SiO2, Fe203, H2O and alkaline and alkaline earth metal oxides. This material could not be reduced in a shaft-type reduction; apparatus because the considerable amount of fines in the material created an intolerably high back pressure; nor could it be reducedv in an indirectly heated reduction tube furnace of practieal length and normal feed rate, because some of the material was too coarse. As will appear, applicants reduction process successfully handled a'` raw material which neither of the present-day con- Ventional processes could tolerate. v

- In this instance when using the above ore, and working with a round pile (of ore.) over a distribution chamber about 48 inches by 18 inches by four inches, the operato-r fed through the. distribution chamber about 25 c.f.m. of natural gas and c.f.m. of air. The. temperature maintained inythezone of reduced ore was 1300'-1400 F., andyin the zone of. active reduction (the red-hot layer only an inch or so beneath the exterior surface of the pile) the temperature` was about 1800'o F. The operator progressively fed fresh-ore, shoveful-by-shoveful, to the dry (hot) spotseto maintain a uniform heat pattern and uniform diffusion (steaming) pattern. The end of the growth of the pile wasl reached when about 17 tons of fresh ore had been fed to it: at that stage, the height of the pile was about 4.5v feet and the sides ofv the pile were at the anglepf` repose of the oreyThe operator stopped feeding ore after 19 hours, and then continued to feed the gas mixture for about one (1) hour. Cool gaseous cornbustion products (derived from burning natural gas with a neutral flame and cooling Iby passing the gaseous combustion products through a water spray) were then passed into the distribution chamber and from thence radially through the bed. This cooling step was continued until the temperature of the ore was lowered to a point, e.g., about 300 F., at which the ore was stable in air.

In all, the batch required about 50 hours.

The material in the so-treated pile was sampled in an approved manner and was analyzed for its content of Mn2O3 and MnOz. The material two inches and more below the surface was found to contain none of its manganese values in a state of oxidation higher'than MnO.

The identical process can be Operated employing an elongated windrow type of pile, over a correspondingly elongated distribution chamber.

If producer gas were used in lieu of natural gas, the reduction might be carried out without adding air (or other oxidizing gas); however, by so doing one would lose the great economic advantage resulting from cracking the natural gas-air mixture in situ in the hot reduced ore. On the other hand, if one were to generate CO, only, in situ within the pile by blasting burning coal with air, the resulting very high temperature of combustion would fuze everything in the immediate vicinity whilst underheating the outer portions of the pile, with resulting formation of extensive masses of clinker worth less than nothing.

The process of the present invention, as practiced on manganese ore, is attended by a further economic advantage, as follows: The customary uses or applications of MnO (i.e., of reduced manganese ore) call for a uely ground product, eg., 98% minus 200 mesh. In the conventional tube furnace process the ore is crushed, ground to final size, and finally reduced. According to the present process the ore is only coarsely crushed (c g., to all minus three-eighths inch) and then reduced and finally ground to desired nal size. The reduced ore is relatively very friable, and hence is a great deal easier to grind than is the raw ore. The diiference in grinding costs is very significant.

Relative to reduction in the pile, the following quali fications and additions should be mentioned:

(a) All of the -bed zones which have been discussed hereinabove, along with the corresponding interplay of chemical reactions, are applicable to pile reduction; also, the changes in thermal balance as a function of gas velocities and ore particle size.

(b) Special consideration must be given to the change of gas velocities through the reduction and preheat zones in the case of pile reduction. If a constant gas-air feed is introduced into a pile, it is evident that as the pile grows in size the gas ow per unit area through the outer zones decreases. In accordane with the preceding discussions, the ratio of air to methane should increase accordingly, in order to preserve a suitable reaction zone temperature. An alternate, of course, is to correlate the gas iiow rate with the surface area. In practice it is generally more convenient to change the gas-air ratio than the gas feed rate.

(c) The segregation of ore fed to the side of the pile (as described under Pile Reduction. above) is much more pronounced as the upper screen size of the orefis increased. The limiting cross section of a pile, therefore, increases as a direct function of the ore particle size.

Cone reduction horizontal plane surface at any vertical level within the cone. This offers a simplification with respect to feeding the raw ore.

Other parts of the structure indicated in FIG. 5 include the following: At its apex 13 the vessel 10 projects into a catalyzer which latter may (as is suggested in the drawing) take an inverted cone form 15 `akin to the form of vessel 10. The top 16 of the catalyzer has an opening 18 into which the apex outlet 20 of vessel 10 projects, said top having a horizontal dimension such that particulate solids gravitationally descending from vessel 10 into catalyzer 15 can take an angle of repose directly beneath the top or roof of 15, leaving above the angle of repose a free space 19 into which an air-methane gas mixture may be introduced via conduit means 21.

Catalyzer 15 is superimposed above a cooling vessel 25, and particulate solids gravitationally descending from catalyzer 15 into cooler 25 make this transition out of access of air, the apex discharge outlet 26 of catalyzer 15 having an air-tight fit with an opening 27 in the upper surface of cooler 25.

(b) Once the cone 10 is filled to the desired level the reaction is allowed to proceed to the ore surface 12 and the reduced MnO can be drawn olf through any type `of conventional controlled atmospheric cooling mechanism as suggested at 25. In practice a heel ofthe hot MnO is left in the lbottom of the cone which provides the catalytic zone for a fresh batch reaction.

Moving or continuous beds If the MnO is drawn off continuously from the cone just described, then a mechanical compensation must be made for the fact that the gas iiow pattern does not correlate with the ore flow pattern. The rate of reduction, as pointed out above, is essentially uniform over the entire (at) surface of the bed while the ore tends to move down through the center. If new raw ore were fed to the center only, to replace the ore withdrawn, the reducing gas emerging through the outer areas of the bed would not be productive land the reducing gas emerging through the center area would be insufficient to reduce the raw ore fed.

One solution to this problem is to feed raw ore to the periphery of the bed only and progressively to move it toward the center by a series of simple rotating plows. This procedure is illustrated in simple embodiment in FIG. 5 wherein at the upper right hand edge of vessel 10 there is suggested the raw ore be fed to the periphery of the charge bed and be gradually swept inward (over the bed) toward the center of the beds surface. This permits productive -utilization of the reducing gas emerging over the entire surface of the bed while at the same time compensating for the uniform ore ilow.`

I claim:

1. Process of reducing to MnO the content of higher oxides of manganese in a manganese ore, which comprises passing a methane-rich hydrocarbonaceous gas-air mixture, in which the ratio of air to methane is within the range of about 2:1 and about 4:1, into and through a body of reduced manganese ore whose oxide of manganese content is in the form of MnO, said reduced ore being at an elevated temperature of from about 10'00" F. to about 2000 F., whereby to form in the gaseous mixture a substantial content of active reducing gas including CO and H2, and passing the resulting hot reducing gas-containing mixture into and through a layer of initially unreduced manganese ore contiguous to said body of reduced ore whereby to reduce to MnO the higher oxides of manganese in said layer.

2.Process of reducing to MnO the content of higher oxides of manganese in a manganese ore, which comprises passing a methane-rich hydrocarbonaceous gas-air mixture, in which the air-methane ratio is from about 2.411 to about 3.5:1, into and through a body of reduced manganese ore whose oxide o f manganese content is in the form of MnO, said reduced ore being at an elevated temperature of from about 1250" to -about 1350 F., whereby to form yin the gaseous mixture a substantial content of active reducing gas including hydrogen and CO, passing the resulting hot reducing gas-containing gaseous mixture into and through a layer of initially unreduced manganese ore contiguous to said body of reduced ore whereby to enlarge the body of reduced ore, and thereafter cooling reduced ore in that part of said body which is remote from said layer to a temperature at which MnO is relatively stable by passing therethrough a current of relatively cool non-oxidizing gas.

3. Process of reducing to MnO the content of higher oxides of manganese in a manganese ore, which comprises passing a methane-rich hydrocarbonaceous gas-air mixture, in which the air-methane ratio is from about 2.0:1 to about 4.0:1, into and through -a body of reduced manganese ore whose oxide of manganese content is in the form of MnO, sai-d reduced ore being at an elevated temperature of from about 1250o to about l350 F., whereby to form in t-he gaseous mixture a substantial content of active reducing gas including hydrogen and CO, passing the resulting hot reducing gas-containing gaseous mixture into and through a layer of initially unreduced manganese ore contiguous to said body of reduced ore thereby enlarging the body of reduced ore and to develop a zone of maximum temperature.

4. The process defined in claim 2, in which the ratio of air to methane is so adjusted within the range 2.0-4.0:1 as to maintain the temperature within the layer wherein reduction of higher oxide of manganese to MnO is progressing within the range 13002000 F.

5. The process dened in claim 4, in which said body is progressively enlarged by successive additions of fresh layers of unreduced ore to said body as the higher oxide content of the ore in the underlying layers becomes reduced to MnO.

6. The process dened in claim S, in which the size of said body is maintained within predetermined limits by progressively withdrawing reduced ore from said body in amounts equivalent to t-he amounts of unreduced ore added to said body.

7. -Process of reducing a manganese ore whose manganese content is mostly in the form of a higher oxide of Mn which ore is substantially free from pieces larger than 3 inches in diameter and has a normal size distribution, which process comprises establishing a gas distribution chamber covered by a grating;

forming a small initial pile of t-he ore on top of the grating covering said chamber;

heating the small initial pile of ore with heating gases passing outwardly from the vicinity of the chamber by burning a carbonaceous fuel with air adjacent said chamber, the heating being continued until at least the interior of said initial pile has attained a temperature of at least 800 F.;

progressively feeding ore in relatively thin layers to the Y top and to the sides of the pile in a manner to establish and maintain a substantially uniform temperature pattern over the peripheral portion of the pile while simultaneously outwardly passing through the pile from adjacent said distribution chamber a reducing gas mixture rich in CO and H2 whereby to create and maintain a zone of active reduction of the higher oxide of manganese to MnO;

continuing the passage of said reducing gas mixture while continuing feeding of the ore to maintain substantially uniform the thickness of the layer of relatively unreduced ore exterior to the zone of active reduction,

the ore being fed to the top and to the sides of the pile in cascading thin layers and in a manner which in- `duces particle size segregation as the ore cascades over the surfaces of the pile;

terminating the feeding of ore when it no longer is possible to maintain substantial uniformity in the thickness of the layer of unreduced ore exterior to the zone of active reduction;

substituting a relatively cool non-oxidizing gas for the reducing gas whereby to cool the material of the pile from the center outwardly, and continuing such passage of said relatively cool non-oxidizing gas until the temperature of substantially all of the material of the pile has been lowered to a temperature at which the reduced material is `substantially .stable to air.

8. `Process of reducing a manganese ore whose manganese .content is mostly in the form of a higher'oxide of Mn which ore is substantially free from pieces larger than 3 inches in diameter and has a normal size distribution, which process comprises establishing -a gas distribution chamber covered by a grating; forming a smalll initial pile of the ore on top of the grating covering said chamber; heating the small initial pile of ore with heating gases passing outwardly from the vicinity of t-he chamber by burning a carbonaceous fuel with air adjacent said chamber, the heating being continued until at least the interior of said initial pile has attained a tempearture of at least 800 F.;

progressively feeding ore in relatively thin layers to the top and to the sides of the pile in a manner to establish and maintain a substantially uniform temperature pattern over the peripheral portion of the pile while simultaneously outwardly passing through the pile from adjacent said distribution chamber a reducing gas mixture rich in CO `and H2 whereby to create and maintain a zone of .active reduction of the higher oxide of manganese to MnO;

continuing the passage of saidreducing gas mixture while continuing feeding of the ore to maintain substantially uniform the thickne-ss of the layer of relatively unreduced ore exterior to the zone of active reduction,

the ore being fed to the top and to the sides of the pile in cacsading thin layers and in a manner which induces particle size segregation as the ore cascades over the surfaces of the pile;

terminating the feeding of ore when it no longer is possible to maintain substantial uniformity in the thickness of the layer of unreduced ore exterior to the zone of active reduction;

continuing the passage of reducing gas until the aforesaid unreduced ore layer has been substantially reduced;

substituting a relatively cool inert gas for the reducing gas whereby to cool the material of the pile from the center outwardly, and continuing such passage of said relatively cool inert gas until the temperature of substantially `all of the material of the pile has been lowered to a temperature Iat which the reduced material is substantially stable in air.

9. The process defined in claim 8, in which the reducing gas mixture is produced in situ within said pile by catalytically cracking an air-natural Igas mixture introduced into the pile by way of said distribution chamber.

10. The process -dened in claim 9, in which the zone of catalytic cracking is maintained at from about 1250 to about 1400 F., while the zone of `active reduction is maintained at from about 1400 to about l900 F.

11. The process defined in claim 8, in which the relatively cool inert gas consists essentially of non-reducing gaseous products of the combustion of natural gas in a stoichiometrically equiv-alent amount of air.

.19 12. Process of reducing to MnO the content of higher oxides of manganese in a manganese-containing material the manganese content of which is in the form of oxides Whose oxygen contents lie between Mn2O3 and MnO,

which comprises passing a methane-rich hydrocarbonaceous gas-air mixture, in which the air-methane ratio is from about 3:1 to about 5:1, into and through a body of reduced manganesecontaining material Whose manganese content is in the form of MnO, said reduced material being at an elevated temperature of from :about 140`0 to about l800 F., whereby to form in the gaseous mixture a substantial content of active reducing gas including hydrogen and CO, passing the resulting hot reducing gas-containing gaseous mixture into Iand through a layer of said References Cited UNITED STATES PATENTS 1,951,342 3/1934 Bradley et al 23-145 2,310,258 2/ 1943 Riveroll 75-80 l2,745,730 5/1956 De Vaney 75-1 v3,149,961 9/1964 Moklebust 75-80 BENJAMIN HENKIN, Primary Examiner.

DAVID L. RECK, Examiner.

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