US3090686A - Recovery of metal by use of lead - Google Patents

Description

United States Patent 3,090,686 RECOVERY OF METAL BY USE OF LEAD John Simon Nachtman, 2801 Quebec St. NW., Washington, D.C., and Henry Gordon Poole, 1000 16th St, Golden, C010. No Drawing. Filed Feb. 19, 1958, Ser. No. 716,033 15 Claims. (Cl. 75-84) This invention relates to methods of beneficiating metallic compounds and recovery of metals therefrom as well as the resulting products, and includes the production of novel types of metals having unique properties and methods for producing such products. This application is a continuation-in-part of application Serial No. 429,674, filed May 13, 1954, now Patent No. 2,834,671, and of application Serial No. 642,377 filed February 26, 1957, now US. Patent No. 3,020,151.

The present commercial process for producing molybdenum by the hydrogen reduction of sublimed and recrystallized molybdenum trioxide makes it diificult to control oxygen without additions of carbon or aluminum during the arc-melting operation, resulting in detrimental effects of oxygen nitrogen and carbon upon the physical properties of for example, molybdenum.

One rather obvious approach would be the direct reduction of moly-bdenite (MoS l0] metal in a controlled atmosphere. This might be accomplished by at least four direct methods.

I. Thermal decomposition II. Hydrogen reduction III. Carbon reduction IV. Silicon reduction Thermodynamically silicon is a most desirable reduction agent since it forms a volatile sulfide at say a temperature of 1227 C. (1500 K.) However, silcon reacts with molybdenum to form a refractory silicide. Carbon also forms a refractory carbide with molybdenum, and this method also is found wanting. Further an examina tion of the equilibria for either thermal decomposition or hydrogen reduction indicates a slow reaction rate at 1500 K. particularly with the former method.

For this type of metallurgical process substantially a complete reaction is needed, circa 100% reduction.

Accordingly prior art methods of producing certain metals from their ores or other compounds, such as molybdenum from molybdenite, involve needless repetitive processing, and also result in the production of contaminated metal.

Among the objects of the present invention is the production of metals by thermo-chemical treatment of their compounds utilizing reducing agents which result in metals free from contamination with impurities commonly pres- 'ent in such metals produced by prior art processes.

Further objects include the production of such metals free from oxygen, chlorine or other halides, sulfur, hydrogen, itrogen, carbon, silicon, and alkali metals.

Further objects include methods of decontamination of metals produced by other processes. I

Further objects include metals resulting from these processes which metals have unique compositions and exceptionally high standards of purity.

Still further objects and advantages of this invention will appear from the more detailed description set forth below, it being understood that such more detailed de- 'scription is given by Way of illustration and explanation only, and not by Way of limitation since various changes therein may be made by those skilled in the art without departing from the scope and spirit of the present invention.

In accordance with the present invention, metals are 3,090,686 Patented May 21, 1963 produced by thermochemically treating a sulfide of the metal desired, particularly metals having an atomic number of 27, 28 and 42 with lead, the treatment being carried out in a non-oxidizing atmosphere, desirably in the presence of hydrogen, helium or argon, or mixtures thereof at a temperature generally above about 1100 C. sulficient to produce a beneficiated metal.

The process permits the production of molybdenum metal shapes by one stage reduction, compaction, pressure welding and sintering, without atmospheric contamination.

The process will be illustrated by the production of high purity molybdenum and reduced cost free from undesir- .able contaminants and by methods utilizing lead which thus make it possible to avoid needless repetitive processing heretofor required in prior art processes. It has thus been found that, sulfides of molybdenum may be subjected to direct reduction by lead in a non-oxidizing atmosphere, as for example in the presence of a nonoxidizing gas e.g. hydrogen, helium or argon, or mixtures thereof at temperatures above about 1100 C. Lead, which is a high boiling point metal, forms a volatile sulfide and thus makes it feasible for the stated purposes. Since plumbous sulfide at the order of temperatures stated, has a vapor pressure that greatly exceeds the vapor pressure of molybdenum sulfide ores, its thermal decomposition products, and molybdenum, vacuum systems may be utilized to accelerate the desulfurization reaction, and rapidly to purify the molybdenum residue, including direct reduction by lead in the presence of for example hy drogen.

In the reduction of molybdenite for example by lead in the absence of hydrogen, the probable major reactions are Other reactions, probably of minor character are:

In the presence of hydrogen, the latter enters the reactions for desulfurizing molybdenum in two ways. One is aiding the decomposition of molybdenite to the sesquisulfide and the other is in decomposing the lead sulfide. These uses can best be summarized in the following series of reactions.

But actually the use of hydrogen alone is unsatisfactory because of equilibria factors. A comparison with lead, shows that in a 12 hour period with H of S is removed while a 2 hour period with lead removes: of S Further excessive quantities of hydrogen sulfide are avoided.

The fact that hydrogen reduces the plumbous sulfide during the regular run subsequent to the desuhiurizing of molybdenum, despite less favorable equilibrium data, is kinetically sound since this latter reaction is a gas-gas reaction to produce a gas and a liquid rather than a gassolid to produce gas-solid.

In an actual run at 1250 C. with lead reacted with molybdenite, M08 under atmospheric pressure, using stoichiometric amounts of lead, namely 30 parts by weight of M05 and 77.6 parts of lead, there were obtained 20 parts of molybdenum plus M0 8 90 parts of lead sulfide, PbS, and 8 parts of lead, the resulting pellet having an unreacted core of M0 8 By using 20% excess of lead over the stoichiometric amount, namely, 30' parts of MOS 3 with 93 parts of lead, there was obtained 18 parts of molybdenum, 90 parts of PbS, and 15.5 parts of lead, and the resulting pellet showed no unreacted core.

After completion of the reduction of molybdenite to metal, a vacuum system at the reaction temperatures permits the volatilization and removal of any excess metallic lead, if desired, leaving the metallic molybdenum free of both sulfur and lead.

During reaction in an atmosphere of hydrogen, lead sulfide formed, is reduced in the presence of dry hydrogen to return lead to the reaction. Also lead sulfide which is carried over may be reduced by known procedures and the recovered lead returned to the system. Accordingly the lead process can be carried out in hydrogen with the following advantages:

(1) The metallic lead is not consumed since it is readily regenerated with hydrogen.

' (2) The carbon content is controlled by hydrogen without the use of oxide additions other than low partial pressures of water for fixed carbon.

(3) The cost for vacuum equipment can be eliminated for molybdenum powder production. This also simplifies retort design.

(4) The circulating hydrogen can be desuliurized by cold traps or other methods and recirculated.

(5) The reaction rates and temperature requirements are maintained at readily attainable levels.

The reactions may be carried out over a wide range of temperatures and periods of time. The temperature employed should at least be about 1100" C. and may be as high as 1450 C. or even higher, the temperature being pressure dependent since it is desired to retain lead in the liquid phase; but from 1200 to 1300 is preferred. The time may be from about 1 to 4 hours, but two hours is a preferable time period. Pressures may vary. The basic lead reduction is not materially affected by the atmosphere. Helium, hydrogen and argon are desirably utilized at atmospheric pressures. The time may vary with temperature and rate of flow of the non-oxidizing gas present. In hydrogen-lead reduction 3.0 is a desirable lead to molybdenite ratio whereas the stoichiometric ratio is 2.59. The rate of gaseous flow may vary. For example, hydrogen may be used for an 8 hour run at a rate of 1 cu. ft./hr.; for 4 hours at 2 cu. ft./hr.; or 4 cu. ft./ hr. for 2 hours.

The following considerations apply to the control of purity of the molybdenite concentrate. Some of the highest grade products on the market, advertised at 99+% molybdenite actually contained 1.16+% carbon resulting from cracking of petroleum oils during their distillation from raw concentrate. The processing of raw materials has become a very important phase of this work since some of the commercially available materials seem to have been inadvertently contaminated with carbon. One concentrate obtained by prior art methods appears to be of two qualities.

(1) Grade I, 7.5% oil, .34 insolubles, .12% Fe., .01% cu. Grade (distilled) II, 1.06% C., 37% SiO +Al O .13% Fe, .01% Cu Grade (leached) III, 1.16% 0., .01% sio +A1 o,,

.16% Fe, .01% Cu (2) Regular grade-5.0% oil, 5.5% insolubles, 1% Fe Another source shows concentrates with three nominal grades and little or no hydrocarbons.

(1) High grade:

85% MoS 0.15% Cu 85% M08 0.50% Cu 80% M08 1.25% Cu A sample of high grade No. 1 shipped 7/7/53 analyzed as follows: 92% M08 5.00% insolubles, 0.120% Cu.

The procedure desirably used for preparing molybdenite for reduction processes desirably uses the following procedures:

(1) Solvent extraction or distillation of oils in H (2) Leaching with hydrofluoric+hydrochloric acids to remove oxides and allied impurities.

(3) Washing and drying.

While the oils may largely be removed by solvent leaching, as by organic solvent such as acetone, distillation in H is more desirable. Molybdenite particle size is not critical. 2Sizes available in commercial products average for example 5-7 microns, 13-17 microns, etc. No diflierences have been experienced. Lead has been used for example at 200 mesh, 30 mesh, and 20 mesh; also as a molten bath. No difference have been detected but for operations on a laboratory scale, minus 20 mesh is preferred.

As illustrative for beneficiated molybdenite products which are obtainable by the preferred process to control purity of the molybdenite concentrate, the following is given, in tabulated form; the feed being the initial molybdenite material, the retort product being that after the heat treatment of the initial material in an atmosphere of hydrogen to give a roasted concentrate, and the final leach product being the molybdenite material ready for H -Pb reduction to produce molybdenum metal.

MOS: H20 011 SiO2+Al20a Fe Feed, percent 70-80 10-15 5-6 4-6 0. 2-1. 0 Retort product, percent 89-94 0 0 5-7 0. 3-1. 2 Final leach product,

percent 99. 5 0 0 0. 05-0. 1 0. 05-0. 07

The product is substantially free of carbon, iron and associated impurities. The small amounts of SiO+Al O may be beneficial.

THE ADVANTAGES CHEMICAL ANALYSES OF PRODUCTS Sample No. Percent 0 Percent S Percent Percent Fe acid insol.

This final leach product may be compared with prior art commercial products prior to the present invention and which show:

PRESENT COMMERCIAL PRODUCTS 98.5% M08 1.16% C, 0.05% Swe l-A1 0 .16% Fe While small quantities of the alumina and iron remain, some of the silicon is removed as silicon monoxide, the remaining quantity being silica. Iron can also be. controlled by special treatment. Most of the copper and tin report in distilled lead sulfides.

It would appear that most of the market available concentrates may be treated for producing metal without using the special high grade.

The wet HF leaching is satisfactory in plastic containers. There is no need for heating the mixture, prolonged washing with acid helpsv remove iron.

The preparation of materials for reduction in the furnace may use various techniques. Loosely mixed granular lead and molybdenite will react, however, it is preferred and recommended that the materials be briquetted. This briquetting may for example be carried out as follows:

(a) Mixture of M03 and granular lead is briquetted. For example, in small scale operations both /2 inch and 1 inch round dies have been employed with pressures of 8000-25300 pounds per square inch.

(b) The M08 may be briquetted and partially or wholly immersed in liquid lead. Under conditions so far employed the M08 and lead should be in contact. The molybdenite briquette is not normally wetted by molten lead at atmospheric pressures and low temperatures.

Consideration should be given to vapor pressures. Lead boils at 1750 C. and at the boiling point of lead sulfide (1250-80 C.) has a vapor pressure of 20 to 30 mm. Hg. The lead may boil off at the reaction temperature, so that at least 20% excess lead is desirable. Furthermore the molten lead does not wet the decomposing molybdenite as did the tin, therefore it is desirable to enclose the reacting pellet partially so that the lead does not run away. This may be done by placing the pellet of 20 mesh granulated lead plus molybdenite compressed at 10,000 to 20,000 lbs. per sq. in. in a molybdenum boat.

The molybdenum metal briquettes when produced are sponge like and capable of re-compression. Thegrain size of the reduced molybdenite is very small and approximate 2-3 microns. However it will vatry with source of raw materials.

Various additives for any of the pure metals obtained under this process or otherwise may be included in the methods set forth above for special effiects or results. These additives may be conveniently considered in two general classes:

I. Inert during sulfide reduction stage:

(a) Elemental W, Co, Ni, Nb, Ir.

II. After reduction to pure molybdenum powder:

(a) Ni, Cr, Zr, Ti, Hf, Co, Ta, Th, W, Al, C-b,

Be, Ir.

(b) Oxides and oxygen bearing compounds of the metals enumerated in II(a) such as zirconates, titanates, alurninates, aluminides, etc. and also the rare earths.

The above additions as set forth in I and Il may be added to the Mo powder and mixed, then sintered or briquetted. The briquetted materials may be extruded or rolled. The sintered materials may be melted, hotpressed, extruded, cold-pressed or rolled. The sintering and mechanical operations should desirably be carried out under non-oxidizing conditions.

Since in the processes of the present invention, it is desired to make ductile metal, i.e. molybdenum, substantially free from oxygen, hydrogen, and nitrogen, the addition of oxides or oxygen containing compounds is only for the purpose of obtaining certain desirable physical properties and also to a controlled extent the oxidation of molybdenum at elevated temperatures. Thus certain oxides and oxygen bearing compounds are added to control grain size or to clean up grain borders.

The metal and alloy additions are also for the purpose of obtaining certain desirable physical properties in the metals. The amounts of the additions may vary with the additives and the metal to which added. In general, oxides or oxygen bearing compounds may be added in amounts by weight of about 0.1 to on the weight of the metal to which they are added. The amounts of metal or alloy additives may vary much more Widely. Nor are the various additives equivalents in their actions since, for example, oxides and oxygen bearing; compounds have different eifects upon the pure metal to which they are added, depending on the addition made.

While the invention has been particularly described with respect to reduction of molybdenum, cobalt, or nickel containing sulfide ores by use of lead, in many instances it is desirable to use an alloy of lead with tin for reduction, desirably in eutectic ratios. Not only may economies be secured in this way, but by the use of such alloys, the amount of excess lead desirably used may be reduced by keeping the lead in place. And when an atmosphere of dry hydrogen is employed during reduction, a leadtin alloy in the correct proportions gives much better control of the amount of metal required, for reduction of the sulfides.

The following example will illustrate the invention, parts being by weight unless otherwise indicated.

Example Molybdenite-lead pellets were made by mixing 20 mesh granulated lead with powdered molybdenite in the ratio of 93 parts to 30 parts and compressed at 20,000 lbs/sq. in. into cylindrical pellets of /i diameter. The pellets were placed in a molybdenum boat and subjected in a furnace to a temperature of about 0 C. for about four hours. A tube furnace was used large enough to permit gas passage. 18 parts of molybdenum metal sponge were recovered after completion of the reaction. The reaction is facilitated by sweeping PbS away from the pellet by flow of a non-oxidizing gas such as argon at a rate of approximately 2 cu. ft/min. using a 1 /2 (inside diameter) reaction tube in a globar furnace.

Cobalt or nickel containing sulfides may be reduced in an analogous manner using amounts of such sulfides in ratios equivalent to the amounts of molybdenum sulfide ore. Both cobalt and nickel sulfides form low melting eutectics with metal at 600900 F. If the reactions are started at low temperatures and are increased to 1200-1300 C., nickel and cobalt sulfides may be retained as solid phase. If the reactions start at 1200 to 1300 0, natural cobalt and nickel sulfides may be liquids until the composition is less than 10% sulfur for nickel and less than 20% sulfur for cobalt. In some cases, therefore, depending on the nature of the sulfides and reacting conditions the sulfides may be liquid during reduction and may be solids in other cases and this applies to molybdenite as well as nickel and cobalt sulfides.

The following examples further illustrate the invention.

By increasing-the hydrogen flow, over 50% of Sn and Pb will be reduced from sulfides, thus increasing H 5 production.

Briquette The'l'eadreduction of M08 should be carried out in a reflux type system. Hence the lead which boils 011? will return, thus eliminating need for 20% excess in briquette. Furthermore, carrying out this reaction in H will permit even smaller proportions than stoichiometric lead to be used in the briquette. It is relatively simple to distil off excess lead from finished molybdenum metal sponge.

These examples may be carried out under the general operation as in the first example set forth above with such changes as the individual examples indicate. In general where nickel or cobalt containing sulfides are used, equivalent amounts may be substituted for the molybdenum sulfide.

The following data is of interest in connection with the operations set forth herein.

Melting points, C.

Ores, particularly sulfide ores, useful for treatment in connection with this invention include: for cobalt, cobaltite CoAs S linnaeite (Ni, Co) S for molybdenum, molybdenite MoS for nickel, pentlandite (Fe, Ni)S, millerite NiS, linnaeite (Ni, Co) S etc.

Since different metals have difierent effects upon the molybdenum, in many cases it is desirable to reduce molybdenite with zinc, cadmium, antimony or bismuth, and mixtures thereof, with or without lead and/ or tin. The reduction will desirably take place at the temperature between 1100" C. and 1450 C. and the amounts may desirably be in stoichiometric proportions. The reduction may-be carried out under non-oxidizing conditions, such as in the presence of hydrogen, helium or argon, and if desired under vacuum, a hydrogen atmosphere being preferred.

Having thus set forth our invention, we claim:

1.-In the method of producing a metal selected from the group consisting of cobalt, nickel, molybdenum and alloys thereof from the corresponding metal sulfides, heating the metal sulfide with lead in a non-oxidizing atmosphere at a temperature of from about 1100 C. to below about 1450 C. whereby a reduction reaction takes place between the metal sulfide and lead to produce the purified metal.

2. The method of claim 1 in which the metal sulfide is molybdenum sulfide. 3. The method of claim 1 in which the metal sulfide is nickel sulfide. v4. The method of claim 1 in which the metal sulfide is cobalt sulfide.

5. The method of claim -1 in which the reduction is carried out in the presence of hydrogen.

6. The method of claim 5 in which the sulfide is molybdenum sulfide.

'7. The method of claim 5 in which the sulfide is nickel Jsulfide. V V V V V 8. The method of claim 5 in which the sulfide is a'co balt containing sulfide.

9. The method of claim 1 in which the reduction is carried out in the presence of helium.

10. The method of claim 9' in which the sulfide is molybdenum sulfide.

11. The method of claim 9 in which the sulfide is nickel sulfide.

12. The method of claim 9 in which the sulfide is a cobalt containing sulfide.

13. The method of claim 1 in which the reduction is carried out in the presence of argon.

14. The method of claim 13 in which the sulfide is molybdenum sulfide.

15. The method of claim 13 in which the sulfide is nickel sulfide.

16. The method of claim 13 in which the sulfide is a cobalt containing sulfide.

17. In the method of producing a metal selected from the group consisting of cobalt, nickel, molybdenum and alloys thereof from the corresponding metal sulfide comprising heating the metal sulfide with lead in a non-oxidizing atmosphere at a temperature of from about 1200 C. to about 1300 C. to reduce said metal sulfide with lead to produce the corresponding purified metal.

18. The method of claim 17 in which an adjuvant metal selected from the group consisting of W, Co, .Cb, Ir and Ni is added in the reduction zone in a form which gives a resultant alloy upon reduction.

19. In the method of producing molybdenum from its ores heating solid phase molybdenite while in a solid phase with a metal selected from the group consisting of zinc, cadmium, antimony and bismuth lead and the mixtures thereof at a temperature of from 1100 C. to below about 1450 C.

References Cited in the file of this patent UNITED STATES PATENTS 855,157 Becket May 28, 1907 1,022,595 Rossi Apr. 9, 1912 1,096,464 Schwarzkopf May 12, 1914 1,175,693 Bosch et a1. Mar. 14, 1916 1,221,873 Ladofi Apr. 10, 1917 1,373,038 Weber Mar. 29, 1921 2,665,474 Beidler et a1. Jan. 12, 1954 2,678,268 Ham May 11, 1954 2,678,269 I-Iam May 11, 1954 2,834,671 Nachtmann May 13, 1958 OTHER REFERENCES Metal Progress, July 1961, pp. 86-88.

Claims (1)

1. IN THE METHOD OF PRODUCING A METAL SELECTED FROM THE GROUP CONSISTING OF COBALT,NICKEL,MOLYBDENUM AND ALLOYS THEREOF FROM THE CORRESPONDING METAL SULFIDES, HEATING THE METAL SULFIDE WITH LEAD IN A NON-OXIDIZING ATMOSPHERE AT A TEMPERATURE OF FROM ABOUT 1100*C, TO BELOW ABOUT 1450*C.WHEREBY A REDUCTION REACTION TAKES PLACE BETWEEN THE METAL SULFIDE AND LEAD TO PRODUCE THE PURIFIED METAL.