US 2660525 A
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Patented Nov. Z4, 1953 METHOD oF EXTRACTNG LEAD Faoin Irs sULrmEsl Charles B. Foster, Mankayan, Mountain, Republic of the Philippines Application January 22, 1952, Serial No. 267,557 y12 claims. (ol. `75 77 This invention relates to an improved method of reducing lead from its sulfide, and is a continuation in part of my copending application, Serial No. 787,286, filed November 21, 1947, now abandoned.
Lead ore most frequently appears in nature in the form of a sulfide (PbS) termed Galena. At present the mined ore usually undergoes certain concentrating processes whereby a good proportion of the impurities in the ore are re moved and the ultimate product is a high-grade, iinely divided concentrate having a lead sulfide content of between 63% to nearly 100%.
Metallurgists have long known that introducing air or oxygen into molten lead causes a chemical reaction with considerable evolution of heat:
2Pb-l-O2=2Pb0 (exothermic) resulting in a hot molten mixture of lead and lead oxide. If Galena is introduced into this bath, the lead oxide reacts with the lead suliide, producing sulphur dioxide gas and molten lead,
The heat which is evolved by the partial oxidation or combustion of the lead is of such intensity that no outside fuel or other heating agent need be added or employed to complete the double decomposition process. The socalled yScotch hearth, Newman hearth, and ore hearth processes, for example, utilize to a slight extent the reaction to furnish heat for the double decomposition reactions. Heat is also evolved by the primary reactionsof ore oxidation as follows:
mass is rabbled (agitated) to break up fused p pieces and crusts. Fresh lead sulde ore is then introduced on top of the burning mass. This fresh ore and, to some extent, the hot carbon particles and evolving carbon monoxidegas, re-
actv with vthe partially oxidizedore .to produce v The metallic lead so formed trickles down through the mass to form a pool on which the charge floats andthe sulfur dioxide 'and carbon dioxide rise as gases out of the charge. Molten metallic lead is periodically tapped, slag particles are periodically removed from the surface of the molten lead and fresh charge is added as required.
The Scotch hearth process, although taking some advantage of the natural reducing and c-aloriilc powers of the sulfide ore, has been proven unsatisfactory in several respects, among which are namely:
The process generally involves use of an open hearth, 'and even though mechanical instead of human operating means are employed to skim the 'floating slag from the top of the bath, and even though the iiues are so arranged as to carry olf most of the gases and dust, a considerable amount of such volatile material escapes into the surrounding air, making it an extremely unpleasant neighborhood in which to work and also an extremely dangerous one because of the likelihood of lead poisoning to human beings who may inhale the escaped fumes.
No completely satisfactory means of accurately regulating the proper amount of air and therefore the subsequent amount of oxidation taking place within the bath has been devised.
The high-grade, finely divided lead concentrates which are available `commercially today are not entirely suited to be employed in the Scotch hearth process because the blast of air through the ore causes the finely-divided partioles' of ore to be lost up the flue or in the surrounding air as a dust loss.
lThe necessity of forcing air under pressure through the hot ore charge also causes an important proportion of the lead and a large proportion of the silver usually associated with lead ores to volatilize and be carried away as fumesv in the evolved gases. This results, unless elaborate precipitation equipment is installed, in a serious loss of lead and such a low recovery of silver that the process is not applicable to ores having an important content of this metal.
. A great' deal of hand labor is generally neoessary to operatea conventional Scotch hearth.
and because of inaccurate mechanical means so far developed to control the chemical reaction, successful operation, of the plant is considerablyy dependent upon the personal skill and judgment of its operators.
In the instant invention I have provided amethod wherein the chemical reaction as above set forth. takes place entirely within a closed circuit, wherein all dust, fumes, and gases are captured without the possibility of any of them escaping from without the enclosure into the open air. Thusy not only have yI greatly minimized the risk and danger of lead poisoning for personnel working within the neighborhood o1 the plant, but I have also provided a means whereby the costly dust and silver loss is reduced to a minimum. Furthermore, because 'I am able to mechanically control with great accuracy the chemical reactions taking place in the process, I am not so dependent upon the personal slzill and judgment of the plant operator as is the case in operating a Scotch hearth.
Although recovery in a blast furnace is the most commonly employed means of extracting lead from its ores, there vare inherently multiple disadvantages attendant in employing this system, which my invention as presently described will entirely abrogate or greatly minimize.
In conventional and current lead-blast furnace practice, a Quantity of the ore, Galena, is roasted at a reduced heat in the sintering plant. This process. is not only costly, but results in a considerable dust loss. Furthermore, the actual sulfide of the ore combines with the oxygen in the air to form primarily lead oxide (PbO) and sulphur dioxide (SO2) along with smaller amounts of lead sulphate (PbSOi). Thus, the elimination of the sulphur existing `inthe form of a suliide during sintering Wastes the natural reducing power and caloric 'power of the Galena, thus making necessary the later use of carbon in some form to serve as a reducing agent and also as a `fuel during the actual smeltering of the ere in the blast furnace at a high temperature.
The extreme neness of present day high-grade ore concentrate is not suited for use in a blast furnace because of increased dust loss aswell as clogging of the blast furnace when such finelydivided concentrate is subjected to the air blast in the furnace. One of the objects in sintering the ore is to provide a coarse, porous product suitable for use within the blast furnace.
Although currently available lead ore concentrates are very high-grade, it has been found economically and practically expedient to ex cessively dilute this concentrate before considering it suitable for introduction into a blast fur nace.
Furthermore, the sulphur dioxide gas which is evolved at the sintering plant is so highly diluted with surplus air that even after removal of dust and volatile impurities it is not generally considered commercially feasible to utilize this gas in acid manufacture.
Further disadvantages attendant with blast furnace operations are that the initial installation involves. a large capital investment generally contemplating additional detached plants for the manufacture of intermediate and by-products, and also the fact that the starting and shutting down of blast furnaces is costly and results in a considerable time loss.
The instant invention is designed speciilcally to overcome these objections applicable to bla-st furnace operation. For example, sintering Vthe ore is both unnecessary and undesirable in practicing my method. Therefore, the natural reducing and caloric power of the sulde ore is not lost by sintering, but is fully preserved and utilized to the utmost extent as hereinabove pointed. out. Furthermore, the fineness of present day ore concentrate is especially suited for use in my process as the more nely divided the particles of ore, the more readily and completely will they react with the molten lead oxide. Again. the current high-grade ore concentrate may be employed without .dilution in practicing my process, and furthermore the relatively undiluted Sulphur dioxide gas which is given off during the reaction may "be 'subsequently recovered for suitable acid manufacture. It should also be pointed `out that both the initial installation cost and the cost of starting and stopping my apparatus is much less than the installation and/or operating cost for a conventional type blast furnace.
A principal object of this invention is to provide a new and practical method of lead reduction which utilizes to great advantage currently available, relatively high-grade quality, lead ore concentrates in the reduction process without the necessity of excessively diluting the said con centrates.
Another object of this invention is to provide a-continuous, thermally self-sustaining method of metal reduction which requires no application 'of external heat to `accomplish the reduction of metal from its concentrate after operations have been commenced, as will more fully appear hereinafter.
Another object of my invention is to provide a method which utilizes the natural self-contained calorific properties and the natural reducing power of simple sulfide ore concentrates to accomplish the reduction of metal therefrom.
Another object of this invention is to provide a method which takes full advantage of currently1 available, high-grade sulde ore concentrates by introducing them into a reaction chamber without expensive dust loss and/or without the necessity of providing for large and expensive installations for dust recovery.
Another object of the invention is to provide a method vwhich may be practiced in an apparatus which is relatively inexpensive to install and to operate as compared to cost of installation and operation of known types of apparatus in more or less common usage today, as above men tioned.
Another object of my invention is to produce as a by-product a highly concentrated sulphur dioxide gas suitable for acid manufacture.
Further objects of my invention will become apparent upon the reading of the specification and referring to the accompanying drawings in which similar characters of reference represent corresponding parts in each of the several views.
In the drawings:
Fig. 1 is a schematic view of a suitable ap paratus in which the process may be practiced.
Fig. 2 is a sectional View taken on line 2 2 of Fig. l.
Fig. 3 is an enlarged perspective view of the impellor incorporated in the apparatus.
Fig. 4 is a top plan View of a preferred em bodiment of the apparatus.
Fig. 5 is a sectional View taken on line 5--5 of Fig. 4.
Fig. 6 is a sectional view taken on line i5 of Fig. 4.
In accordance 'with the present invention I Standards, part il, Non-Ferrous Metals, page .1.016, published in 195o. The iinely-divided ore or concentrate, red into reaction chamber I3 by screw feeder l5, mixes with and chemically unites with the lead oxide carried along as a part of the molten mixture, as hereinabove clescribed. Baines is, similar to baiiies Il, are provided to insure a thorough mixing of the molten mass and lead sulfide together and thereby insure a more complete chemical reaction between the lead sulde and the lead oxide. This latter chemical reaction is violent and produces metallic lead and sulfur dioxide gas as illustrated in the following chemical equation:
PbS+2PbG=2Pb+SOz [is above ind ated, the screw feeder permits the finely-divided PbS to be fed into the reaction chamber at a predetermined regulated rate of flow, The amounts PbS continuously introduced into the reaction chamber for reaction with the PbO should, of course, preferably be substantially in proportions for a balancedv equation in a reaction between the lead suliide contained in the ore and the lead oxide. It will be recalled that the PbO carried along in the molten stream was itself produced through controlled oxidation oi a predetermined fractional part of the original metal bath, and, therefore, the total amount of PbO available for reaction with the PbS is readily ascertainable.
It is also preferable to introduce into the reaction chamber along with the lead sulde concentrate, relatively small quantities ci a suitable ux, such as limestone, lime, or soda ash, for
example, which will react with contained silica impurities in the concentrate to form relatively fusible slag. Increased fusbility of the slag will, of course, minimize metal loss through its inclusion within slag ultimately removed from the bath.
Residual diluent gases from the oxidizing chamber and evolved sulphur dioxide, intermixed with hot molten metallic lead and nongaseous impurities, leave reaction chamber i3 through discharge conduit ll' and are introduced into the vortex of a closed impellor, such as indicated at la, which is adapted to operate within roof enclosed agitation chamber I9. Violent intermixing created by agitation of the irnpelloi` favors the completion of the reactions in the reaction chamber and the formation of a clean and fluid slag. The agitation also causes the intermixed gases to rise through the molten lead contained in chamber i9. The escape of these gases is prevented by means of a hood which covers the agitation chamber.
The impellor, heretofore indicated at it, may be of generally conventional constructionA and is shown as being of a type commonly used in ore notation process apparatus. More specifically, this type of impellor comprises a pair of oppositely disposed, spaced, circular plates Z and 2l housing a plurality of radial iins 22. An upper tubular casing 23 dening an enlarged inlet mouth 2o in flow communication with the interior of the impellor provides an opening through which drive shaft 2.5, which is. anchored at 26 to bottom plate 2l, may project. upwardly. Shaft 25, in turn, may be rotated by means of a motor 2l, or other driving means, located outside of agitation chamber I9.
Rotation of the impellor will continuously centrifugally force outwardly the molten mass and contained gas introduced into mouth 24. of
the impellor from conduit Il. The impellor functions to continuously suck downwardly into agitation chamber i9 the materials from reaction chamber I3 and prevent back-pressure from building up in the system by virtue of the SO2 gas produced in chamber I3. Moreover, as above suggested, the impellor creates a turbulent agitation within chamber I9 and thus serves to insure a thorough mixing and reaction between any unreacted PbO and PbS iiowing from the reaction chamber I3. A suitable flue 30 supported by hood 3| conducts the gases to a point of suitable disposal. The sulfur dioxide concentration in these gases is exceptionally high, and it may therefore be inexpensively recovered for use in the manufacture of sulfuric acid, liquid sulfur dioxide, or other commercial by-products.
The agitation chamber is provided with a port 32 through which solid particles of slag may be removed from the surface of the bath at such intervals or under such conditions as this may become necessary. This port is provided with a hinged gas-tight door 33 so that under normal operating conditions no gas can escape through said port.
From the agitation chamber the liquid mixture oi molten lead and molten slag together with suspended solid particles is conducted through a suitable conduit 34 into storage reservoir 2.
The lead reservoir tank 2 is a quiet zone which permits the separation by gravity of the molten lead from its molten and solid impurities. At one side of this reservoir is a lead well 35 in communication with the reservoir via opening 35i and from which molten lead may be continuously or intermittently withdrawn, as through port 31, at a rate substantially equivalent to the rate of entry into the system of the contained lead in the sulde ore. The reservoir is likewise provided wtih a slag tap hole 38 through which accumulated slag may be perodically tapped from the surface of the lead. Within this reservoir and taking its feed therefrom, is variable-speed, centrifugal pump 4, heretofore designated. This pump continuously pumps molten lead to the oxidation chamber, thus closing the circuit and making this a cotninuous cyclic process.
As heretofore stated, it is a principal object of the present invention to teach and to provide a continuous and thermally self-sustaining cycle-process of metal reduction. In the cyclic process just described, and as stated heretofore, the exothermic oxidation reaction:
y no extraordinary, elaborate, or unusual precautions need. be taken to maintain the necessary heat. balance betwen the reactions sufcient to maintain a caloriiic self-sustaining continuous process.
Although it is not essential to use any particular type of material in constructing the instant apparatus, other than a material which can suitably withstand the various temperatures and chemical reactions taking place during the process as above enumerated, I prefer to use as my construction materials. ceramic rerractories for reaction chamber linings and heavy cast iron, similar to that used in common lead refining kettles, for the reservoirs and pump parts. Not only can cast iron ci this type endure the temperatures, pressures and chemical reactions pron duced during the process, but such material upon once being brought up to proper temperature has a marked tendency to hold and retain the heat imparted to it. ribis tendency is especially valuable in my process for the reason that the apparatus may be stopped or shut down for a period of several hours while retaining sufficient heat to prevent the molten lead from cooling and solidiiying. Shouldthe lead solidify in the tanks or conduits during a shut-down, it is only necesary to heat the equipment by oil burners and blow-torches as earlier described, until the meta-l assumes a molten forni. The pump and inipellor may then be started and when the lead is freely circulating within the system, the procinay be cotninued oeiore and as above described.
Although l have described the present invention in come detail for purposes of illustration and example, it is understood that various changes modifications may be practiced within the spirit or' the invention scope of the appended claims.
l. in method of reducing lead from relatively h" .li-grade undiluted lead sulfide ore, the successive steps comprising, forming a molten of relatively pure lead, continuously cir- 'ng said molten bath of lead from a startet oxygen in an amount substantially will oxidize the entire quantity or said molten bath, whereby a molten lnixture c iprising predetermined amounts of molten lead and lead oxide formed, during continuous circulation through a second chamber introducing into said molten mixture for reaction w i said lead oxide amounts of ne i relatively high-grade, undiluted lead Cdilation in reaction between said predeter-mined amount of lead oxide and the lead sulcontained in said ore, whereby there ene. chemical reaction resulting in the production of a rcolten mixture of molten lead and sulphur diox le gas, removing said sulphur di.. o'ficle said rnoltel'l niixture, and then dating part csaid lead back to said first chamber recirculation baci through said of chambers and removing a part of said metal for recovery.
fl method or reducing lead from relatively undilute1 sulfide ore according to claim l and wherein the amount oi oxidizing gas than the arncunt of said gas one-half ci entire quantity circulating through said iirst 5. Amethod of extracting lead from its sulde which comprises; providing a mass of lead in la molten condition, providing also a mass of predominantly lead sulfide, introducing the moltenA lead into an oxidation zone, and also introducing in said oxidation zone an oxidizing agent in quantity suicient to oxidize a substantial proportion of the lead to its oxide according to the exothermic reaction 2Pb+O2=2PbO, introducing the molten mass of lead and oxidized metal to a reduction zone; adding said lead sulde to the molten 'mass in the reduction zone in quantity sufficient to reduce substantially all of the lead oxide according to the endothernlic reaction PbS+zPbO=3Pb+Oz; separating sulphur olioxide from the reduced mass; and returning a surliclent quantity of molten metal from the reduction Zone to the oxidation zone to maintain a body or" molten, circulating and reaction medium lor continued operation of the process; said quantity of oxmlzing agent being sufficient to provide the heat absorbed in said endothermic reaction and to also maintain the mass in molten condition Without input of heat from an external source.
6. lhe method of claim 5 wherein the said oxidizing agent introduced into said oxidation zone comprises molecular oxygen, and wherein the amount or' lead sulllde introduced into said reduction zone is in substantially stoichiometric proportion to the quantity of molten lead oxidized in said oxidation zone Jfor the said reaction PoS+2PbO=3Pb+SOa 7. The method oi' claim 5 wherein the mass of predominately lead sulliue contains from about 55 U/U to 85% by weight of lead and which is line enough to all pass through a standard No. 2O sieve.
8. A continuous method of extracting lead from its suliide which comprises: providing a mass or' lead in a molten condition; providing also a mass of predominantly lead sulfide; continuously circulating the molten lead into an oxidation zone, and also continuously introducing molecular oxygen into said zone in quantity suiicient to oxichze a substantial proportion or' the lead to its oxide according to the exothermic reaction 2Pb+O2=ZPbO; continuously circulating the fluid mass of molten lead and oxidized lead to a reduction Zone; continuously adding said lead sulde to the molten mass 1n the reduction zone in quantity sufficient to reduce substantially all of the lead oxide according to the endothermic reaction PbS+2PbO=3Pb+SO2g continuously separating sulphur dioxide from the reduced mass and withdrawing a portion of the lead for recovery and continuously recirculating a sufu cient quantity of said lead from the reduction Zone to the oxidation zone to maintain a body of molten circulating and reaction medium for continued operation of the process; said quantity of oxygen being sucient to provide the heat absorbed in said endothermic reaction and to also maintain the mass in molten condition Without input of heat from an external source.
9. The method of claim 8 wherein the amount of lead sulfide introduced into said reduction zone is in substantially stoichiometric proportion to the quantity of molten lead oxidized by said molecular oxygen in said oxidation zone for the said reaction PbS+2PbO=3Pb|SOa lo. The method of claim 8 wherein the mass of predominately lead sulfide contains from about 55% to 85% by Weight of lead and Which is ne 11 enough to all pass through a 'standard No. 20 sleve.
11. The method of extracting lead from its sulfide which comprises: providing a mass of predominantly lead sulfide containing not more than about 37% of impurities; providing a mass of molten lead; continuously introducing said molten lead into an oxidation zone; continuously introducng molecular oxygen into said oxidation zone in quantity sufcient to react With not more than 50% of molten lead to form a molten mass of lead and oxidized lead, continuously circulating said molten mass into a reduction zone and continuously introducing into said zone said lead sulfide in a proportion approximately stoichiometrioally related to the oxygen introduced into the oxidation zone so 'as to approximately bal'- ance the reactions: 12 @mth ferr-F1142)..21Ebir02ll0y continuously removing sulfur dioxide resulting from Reaction 2; and continuously recirculating a suiiicient quantity of molten lead from the reduction zone to the oxidation zone to maintain a continuous, cyclic ilow of molten metal; out under conditions to utilize tll'ehe'at evolved ln action 1 the quantity of oxygen introduced into said oxidation Yzone being 'such that the heat -generated in Reaction 1 Ais sufficient t'o supply the heat absorbed by Reaction 2 and also to maintain the mass in molten condition Without input of heat from an external source. v
12. The method of `claim 11 wherein the mass of predominately lead sulfide contains from about 55% to 85% by Weight of lead and which is fine enough to all pass through a standard No. 20 sieve.
c'HARLEs B. FOSTER.
Referenes cited in the file of this parent UNITED 'STATES PATENTS