US1744174A - Process of obtaining lead from its ores or other compounds - Google Patents

Description

20 (sometime later) other ways.

Patented Jan. 21, 1930 PATENT OFFICE GEORGE LESLIE OLDRIGHT, OF SALT LAKE CITY, UTAH PROCESS OF OBTAINING LEAD FROM ITS ORES OR OTHER COMPOUNDS No Drawing.

to various by-products which in certain regions furnish a commercial, although comparatively small, supply of lead.

The process of obtaining lead varies slightly, depending upon the. characteristics of the particular source of supply thereof. If the lead is not in a readily reducible form (and possibly the major portion thereof is not) it is first thoroughly oxidized so as to make it readily reducible. In the oxidizing step the ore is agglomerated, since the agglomerate material can be more readily treated, and in addition is not apt to be carried up through a chimney, as would happen if there were a substantial portion of fines present.

It is the prevailing practice after the ore is obtained in a readily reducible form to mix it with a comparatively large percentage of coke and charge it in, a blast furnace. In this furnace the oxidized lead is reduced and liquated, and the gangue is slagged and drawn off. The lead of course is drawn in the usual manner and after refining, molded in the form of pigs.

The oxidizing of the ore is accomplished in either a McDougal furnace or in a Dwight- Lloyd sintering machine. are used, in which case the roastlng and oxidizing step is carried out in the McDougal roaster, and the partially oxidized material then charged into a Dwight-Lloyd'sintermg machine where it is further oxidized and sintered to an agglomerate cake,-or a part of the ore may have the entire oxidizing and sintcring of the sulphide ore to take place in the Dwight-Lloyd sintering machine.

Recently great strides have been made n concentrating lead ore by flotation and in Since these very lead-rich prod- .ucts are now rather common, attempts have not resist corrosion.

Sometimes both Application filed November 22, 1926. Serial No. 150,164.

been made to metallize more directly so as to avoid the diificulties in connection with the old processes. The Scotch hearth has been introduced into this country and employed with comparatively cheap cost for operation on these products but the fuming on the Scotch hearth is also bad and losses result both as to health of operatives and also loss of metal. Moreover, it is difficult to get workmen because the Scotch hearth requires rather well trained and skilled operators and it is difiicult to obtain skilled operators who are willing to perform the arduous labors in connection with the operation of the Scotch hearth and at the same time accept the obvious health hazard.

One difliculty encountered in all of the methods heretofore used is that the preliminary steps in the recovery of lead from its ores had to be carried on in. a brick or similar refractory container, since aniron or steel container under oxidizing conditions would The use of brickwork is objectionable whenever a reducing atmosphere is employed because the ore readily adheres thereto, and whatever liquated lead is present is likely to run between portions of the brickwork and behind the same, thus giv ing rise to frequent delays.

The prior art having been outlined in a general way and the difficulties in connection therewith pointed out, the objects of the present invention as will now be pointed out will become readily apparent.

Among the objects of the invention is the provision of a more direct method for recovering lead from sources of supply thereof. Under favorable circumstances this may be accomplished without great alteration of the gangue products, from which the lead may be separated, without great expense.

Another object of the invention is the production of metallic lead without appreciable vaporization thereof.

Still another object is the provision of a method whereby the lead-bearin material may be treated in a metallic lined rnace.

Still another object is to introduce lead ore to a smelting dition, thereby decreasing the amount of furnace in a reduced conheat and fuel required in the final process.

A further object is the production of a smeltable lead-producing mass substantially free from oxides, and in such condition that it can ,readily be introduced into a smelting furnace and the metallic lead extracted therefrom with a minimum amount of heat.

A still further object is to obtain metallic lead rich in'precious metals. &

The above outlined objects are accomplished by in improved method which briefly stated is as fbllows:

A lead ore is selected which is of such a nature that it may be directly reduced. The lead ore so selected may be a natural product or may have been preliminarily treated by an complished in two oxidation or similar step. The selected ore is heated at a temperature similar to a socalled roasting temperature, namely, a temperature under 1000 C. in a reducing atmosphere. A practical way of carrying out this ste is the inclusion of bituminous coal or a re ucing gas in the furnace, say a kiln, admixed with the lead ore. 1y all of the lead compounds have been reduced, the heating is discontinued and the reduced ore may be treated inon'e of two general ways. The metallized lead may be separated from the gangue directly, as for instance by liquation, pressing while still warm, or by cbncentration methods. The other treatment is to charge the reduced ore into a smelting furnace where the lead is separated from the slagged gangue constituents. The residue obtained from the first method of separation after the direct metallizing of the lead may also be charged in a blast furnace and tgeated'substa-ntially in the normal way therea ter.

It will be observed that the process as developed by, me comprises a number of distinct steps which may be set out as follows:

(1) Selection of the.soure of lead.

(2) Treatment in a reducing atmosphere to largely metallize the lead.

Separation of the metallic constituents from the gangue.

The separation after metallization is acgeneral ways, namely,

(a) Direct separation after metallization of the valuable metals in the ore;

(b) Separation and completed metallization in a smelting furnace.

In order to make clear applicants process and to permit those skilled in the art to readily practice the same, the various features and practices to be observed in connection with eaclDone of the steps therein will now be referred to in detail.

(1) Selection of the ore Under the term fore is included any material, natural or artificial, from which lead may be obtained. Y

step of the When substantialf The lead ore selected should be such that it can bereadily'and directly reduced in the following step of the process. If the metal is present in the ore in the oxide form, the natural ore may be charged without preliminary treatment into a reducing furnace. Other forms of lead ores may also be used directly such as the carbonate or the sulphate forms when properly mixed. Possibly the only common lead ore of natural origin that could not be used directly would be a pure galena, since the sulphide form could not be readily broken up by heat alone. To treat this ore in accordance with my process, it would have to be preliminarily subjected to a treatment to put it in a readily reducible form. The usual step would be an oxidizing roast which could be accomplished by means of a great variety of apparatus, for example, either a McDougal type roaster, or even a Dwight-Lloyd sintering machine if properly controlled. c

It is contemplated that the sulphide ore could also be orms of ore containing a substantial supply of oxygen in a combined form, in which case sufficient chemical activity could be made to take place within the ore itself so that good results could be obtained.

The source of lead supply either natural or artificial having been selected, the selected I source is then ready to subject to the first heating step of the process.

(2) Treatment in a reducing atmosphere The reducing step can be carried on at a comparatively temperatures as low or lower than the socalled roasting temperatures. The lead oxide may be reduced at a temperature under 400 C. although tov obtain reaction speed I have found it advisable to operate at higher temperatures. During the heating the reducing atmosphere may be maintained in a variety of ways. 7

Among the means for maintaining reduc; ing atmosphere is the passing of producer gas through the charge during the heating thereof, or the use of a modified reverberatory type of furnace wherein the gases coming in contact with the ore are charged with carbon or other reducing compounds. The ore can also be mixed with coke breeze or with bituminous coal, or other carbonaceous event no precautions need be taken in directing reducing gases through the charge. In connection with the use of producer gas the well known method of employing this gas can be resorted to. I have also thought of the possibility of operating a coke oven or gas producer in connection with my process, so that much of the gas now being wasted in coke and'gas producing operations, could be utilized to good advantage in heating the lead-bearing charge and in reducing the lead low temperature, for example,

fuel, in which partially mixed with other too compounds, as the percentage of carbon monoxide in the gas necessary for the reduction of the metal is low, and the other gases either inert or not, will transfer heat as long as they are above the temperature of the charge.

Possibly the preferred means for controlling this step of my process, is the admixture with the ore of a fairly generous proportion of bituminous coal. In this event the gases distilled from the coal together with the tar and other similar products will be sufficient as a rule to accomplish the reduction of the ore. The reducing atmosphere will prevent thorough burning of the coal so that this material will be converted into a cheap supply of coke which can be employed in a Subsequent smelting operation, as will be more fully described under the proper sub-headin g.

The reactions which will take place in the ore during the reducing step will vary considerably, depending upon the type of ore present. The oxides present are likely to be directly reduced by combination with the carbon monoxide etc. produced from the coal, the oxygen from said oxides thereby being carried out through the fine as carbondioxide. Lead carbonate if present would probably be converted rather readily into lead oxide and carbon dioxide, or carbon monoxide, if the carbon dioxide reacted with the carbon of the coal. The oxide would then be reduced directly by the carbonaceous gascharged atmosphere produced by the coke or other carbonaceous fuelpresent.

If lead sulphate is present it will probably reduce in part to lead sulphide which will react with some of the unreduced lead sulphate to form lead oxide and some of this lead sulphide may react with lead oxide to produce metallic lead. These reactions will continue until only lead sulphide and metallic lead are present if there is an insufficient supply of oxygen. However, if the oxygen is present in just sufficient quantities, it is obvious that the entire charge may be reduced to metallic lead (admixed of course with the usual gangue).

. The invention contemplates the provision of a substantially reducing atmosphere during the reducing step whereby ores having substantially proper proportions of sulphur and oxygen in combination may be autogenously reduced. Independent of exactly what conditions are maintained during the reducing treatment of the ore it is. obvious that most of the sulphur contained therein is carried off in the gas formed as sulphur dioxide.

By means of the reducing step of the process I aim to have a material consisting mainly of a mixture of metallic lead and gangue (with a'percentage of coke admixed therewith where the reducing atmosphere is maintained by means of coal). -When the ore is obtained inthis form it is then ready for the next step of the process.

(3)8eparati0n of the lead from the gangua (a) Separation after direct metatlization of R the reduced ore The metal may be recovered directly after the reducing step by pressing the mass of ore while still warm, thereby causing an exudation from the mass of a substantial portion of the liquid lead; or the metal may be recovered by direct liquation, that is, by tapping the bottom of acontainer, and all of the liquid lead which has naturally sought the bottom of the container can thereby be removed. The amount. obtained, however, will not be as great as when the pressing operation is employed because obviously small portions of lead are readily trapped in the cup-like interstices between the agglomerated portions of the gangue. Still another possibility is to cool the reduced lead ore and recover the lead therefromby the usual concentration processes.

It would be very difficult to obtain all of the lead from theore by such direct methods, and accordingly the residue material can be further treated if found economically desirable. The further treatment of this residue material will be discussed hereinafter under the following subheading:

(6) Separation after the metallization in a smelting furnace The reduced lead ore obtained from the first heating step of my process may all be charged directly into a smelting furnace such as a blast furnace without any preliminary direct recovery of any portion of the lead.. The reduced material can be charged into the usual form of blast furnace but it will be unnecessary to employ the usual large amounts of coke, because the coal employed in the reducing step of the process has resulted in the production of a by-product coke which is now present in the reduced lead-bearing charge. If sutficient coal was mixed with the unreduced ore, the reduced ore will have such a large percentage of coke that no additional supply of coke need be added. This so far has not been found entirely practical although of course it is possible. The best results seem to be obtained by employing a somewhat smaller percentage of coal, and then supplyingithe deficit in the blast furnace the yield of lead is smaller.

by the admixture of an additional amount of could be used, and since no oxidation of the coke. ore takes place, corrosive action due to slagfurnace, it is now ready for treatment therein. The cokein the charge is ignited and combustion is carried on by supplying a normal air draft which is carried through the charge. The charge will become heated more quickly than in the ordinary blast furnace practice because there is no endothermic reaction such as is necessary when the de-oxidation takes place in the blast furnace. The usual slagging operation is carried out, and the lead and slag are recovered in their respective containers.

When the lead ispartially metallized by direct liquation or in a similar manner, in the reducing step, the residue material is treated in substantially the same way in the blast furnace. The only difference is that Under certain circumstances it may be considered economically undesirable to recover the lead from this residue material. The improved methods being worked out continually for the concentration of ores, makes it seem possible that within a comparatively short time suflicient lead can be recovered directly by means of my process so that it will not be necessary to employ a blast furnace at all. Concentration is 1possibly not the best means for recovering ad directly when employing my process with the present technique because the resulting residue material is in finely divided form and would have to be agglomerated in some way before it could be properly treated in a blast furnace. This does not rule out the use of a concentration process in this connection, however, since the particular means employed throughout my process depends upon technique and may be modified considerably.

Among the advantages of my invention is the fact that the precious metals have a tendency to flow from the ore with the first lead removed therefrom. As a result, the lead obtained by direct liquation or other direct means Wlll be found rich in silver and whatever other precious metals may be present. By segr ating the first portion of the lead obtained y direct metalllzation, a lead very rich in silver and other precious metals can be obtained. Oxides of arsenic and antimony and some other impurities are known to be very volatile if so present, or otherwise will be unaltered under the reducing conditions used, so that these objectionable im urities will be present to a lesser extent in t e bullion, than when the leadsintering process is employed under oxidizing conditions. Thus a portion of the lead may be roduced which is nearly ure. Still anot er advantage, which has een indicated heretofore, is that by my process it is feasible to emplo "a metal lined furnace directly in contact wit the ore. For example, a steel container, say a kiln.

The charge having been placed in a blast -cient to sinter and ging would be avoided. Experiment has shown that corrosion from sulphurous compounds and other similar sources is very small, and usually can therefore be disregarded. The use of a steel shell (which should of course be protected on the outside for exter} nally fired furnaces) next to the ore insures against the stickin of this material to the brickwork of the urnace, or other difliculties such as molten lead running behind or into crevices in the brickwork in the furnace.

Throughout the above description reference has been made to many details which may be'observed in the practice of the invention. This has been necessary for a proper understanding thereof, and so that those I skilled in the art may readily understand how the various steps of the process may be modified, depending upon conditions present, and the result desired. However, I do not wish to limit myself by this descriptive matter since it is apparent thatthe details of the process may be changed to a very great extent'without departing from the spirit and scope of the invention which is defined by the appended claims.

What I claim asnew and desire to secure by Letters Patent of the United States is as follows:

1. The process for obtaining lead from lead bearing ore, which comprises heating the ore in a reducing atmosphere to a sintering temperature, whereby lead isreduced to elemental form as molten metal and the residual ore particles are agglomerated, removing a part of the molten lead from the agglomerated re sidualore, and leaving said residual ore in a nodulized form for a subsequent smelting process.

2. The process for obtaining lead from lead ore which comprises heating the ore under reducing conditions to a temperature suflia glomerate the ore particles and reduce lead to its elemental form, but insufiicient to cause complete fusion, removing at this stage the molten metallic lead that is freed from the residual sintered ore, and subjecting the residual sintered and agglomerated ore to a smelting process.

3. The process of obtaining lead from lead bearing ores which comprises heating the ore in a reducing atmopshere, before its introduction to a blast furnace, to a temperature at which lead is reducedto elemental form, and agglomerating the ore particles in said atmosphere whereby the ore is nodulized preparatory for the subsequent smelting process.

4. The process of obtaining lead from lead bearing ores which comprises charging the ore into a reducing furnace, heating the ore therein to a temperature at which lead is reduced to elemental form, agglomerating the ore particles in said furnace, charging the agglomerated ore with a small amount of coke into a smelting furnace, and smelting the ore therein.

In witness whereof, I hereunto subscribe my name this 16th day of November, 1926.

GEORGE LESLIE OLDRIGHT.