US1573013A - Process of smelting ores of volatile metals - Google Patents

Description

Feb. 16 1926.

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:dii/sys more particularly Patented F eb, 16,)1926.l

WILLIAM A. OGG', OF NEWTON, MASSACHUSETTS.

PROCESS or SMELTING omas or votATILF METALS.

Applica/c1011 mea February 7, 1925. sei-iai No. 7,561.

To/ all whom il? may concern/f Be it known that I, lVILiiIAM A.' OGG, a

citizen of the United States, and a' resident of Newton, county of Middlesex, State of l\Ia'ssacl1-usetts,have `invented an Improvement in Processes of Smelting Ores of Vlatile Metals, of which the followingl description, in connection with the accompanying drawings, 'is a specification, like characters on the drawings representing like parts.

y My invention relates to the smelting of material bearino' volatilizable metals, particularly but notexclusively natural or concentrated ores of zinc, and has among its objects the accomplishment of an increased recovery of the metal values' at low cost by an improvement in thatprocess of smelting practiced with retorts and condensers. My

improved method, which may be so .prac-4 tjced as to increase the oretreating capacity'- of a`given,f urn ace, securing a higher percentage recovery of themetal values,an increased yield of spelter" per'retort, and in addition to@L produce 'directly' the zinc bearing/ore productsA of, high economic value hitherto produced only by"mor\e costly processes involving-'the treatmentof vmetallic zinc, will be best understood. from the following description when read in .light of the accompanying drawingsV showing one form of Y,apparatus for practicing my invention, while the scope of my invention will be pointed out inthe appended claims. j y In the dravfing:-` l Fig. 1 shows more or less diagrammatically anf arrangement of apparatus for prac'- ticing my inventiony-and y Fig. 2 is afsection on the line'Q-QOR Fig. l. The furnace commonly used for thereduction of Zinc ores'or ores. of `1ikevo1atil izable 'metals includes tiers of 'cylindrical I retorts commonly made lof fire clay or other suitable refractory material, which retorts are removably supported in the combustion i' chamber of the furnace. The ore which may be natural oxides, or sulphides converted t oxides by roasting,' is mixed Lwith reduction fuel,usually coal or coke free as far as pos- .crease 'the coo `above that of the condenser now .commonlyo i, liquefy t sible from sulphur, and the mixture c argedl into the retort. Injpracticewhen sm l-tin zincbearing ores the retortsare subjected `to a temperature of about 1300 degrees centigragle, which reduces vthei ore, and being above the boiling point ofzic volatilizes the metal which passes out of'the retort in the form of a vapor andi is condensed -to a lip'uid in a condenser, the latter consisting o `a shortI frustoconical continuation of the -retort projecting from the combustion chamber and being commonly detachably. connected with the retort,

In practicing the smelting rocess now commonly employed with existing apparatus the re ulation of the .amount of retort charge an temperature is av matterfof great nicety. The limitations ofthe material used for making the condensers, initial cost, and handling chargesmake it im ractical to ining surface o the condenser employed. The. limitation to thef'use of .a condenser with ya relatively small cooling surface therefore makes it necessaryin 'practice to limit the charge yin the retort to a value which willgproduce a rate of Vapor discharge into: the condensernot in excess of the ca acity of the condenser veiiiciently to lie metal. This charge is materially below vthefull cubical capacity of thev retort the practice of; the process by the condenser reduce the-output of the furnace, and in addition" make 1t necessary closely to regu- -and consequently the limitationsplaced on late the temperature to reduce to a' minimum y the losses. due .to escaping vapors from the mouth of the condenser. With existing apparatus the metallurgist isconfronted with two alternatives, that of running with the condensers too' cold with consequent production of a high percentage of blue powder which will have to be redistilled with further losses, or thatof runningwith the condensers too hot with consequent loss of vapor from the mouth of the condenser.

By way of an example of goodc practice with the prior. method the retort is loaded with mixed gre and fuel to roughlyf'percent of its cubic'al capacity. The recoveryv of metal contentis about 89.5p`percen'tin f' of air the form of spelter, and of the remainder about 7.75 percent is in the residue, about lpercent is absorbed by the walls of the retort and condenserkfand the remaining loss of 1.75 percent is principally inthe form of escaping vapors from themouth ofl thecondenser whiehvvit is uneconomical to attempt to recover. The4 recovery of 32 pounds per twenty-four hour day of metal value in the formof spelter may be considered the maximum capacity of the condenser in itsV normal operation with thel prior method.

Because of the increasing.,r prices of coal and labor and increasing overhead charges necessary to the performance of the prior method the expense ofproducing the product has increased greatly and one object of the present invention is both to permit more ore to be treated atone time and to increase the percent/recovery of metal values, thus minimizing the expense per unit of commercially available metal produced. In accordance with the invention the retort is deliberately substantially overcharged beyond 'the capacity of the condenser to con-v dense eiciently, and as a purpose of the invention is to secure a large recovey of (spelter the condenser is operated at full conensing capacity for the given operating conditions. Suicient heat is applied to the retorts. substantially to^reduce all the metal which is in oxidized form and a substantial fraction of the metal values -is intentionally caused .to escape from the condenser land is recovered by othermeans.'v By this deliberate overcharging of the retort so that a substantial percentage of the metal values vaporizedis passed out from the condenser an increased recovery of spelter per lretort is obtained, while the remaining metal values as will be pointed out later are collected as highly valuable products. A

Referring to the drawing I- have shown a furnace 1 of the regenerative type in which are formed gas passages 3 connected .by means of suitableV flues 5 andjports 7 to combustion chambers 9. In the combustion chambers are arranged tiers jof retorts 11 each of whichJ is provided with a condenser 13 projecting beyond the front of the furnace. The furnace described is of'a common type and per se forms lno part of my invent1on. A. .Y

-In practicing my invention I attach to the front of the fur-naceop osite the condensers suitable hoods 15 Whic -may be supported in any suitable manner as for example by providing them Awith the flanges 17 fitting a channel 19 carriedby the front of the furnace. .Each`hood is provided with observation holes v21\-vlfhich may be 'provided with dampers 22 for regulating the amounts dmitted. h `hood is connected bjy means of a pipe 23 having a gate valve 25' to a main suction pipe 27 leading to an exhaust fan or blower 29 so that the vapors escaping from the condensers maybe conveyed froxm the furnace to suitable collecting means for the vapors, and for this purpose I have shown the dischargev pipe 31 of the fan leadingr to cooling chambers 33 discharging into a bag house 35 in which are suspended cloth bags `37 releasably closed at their lower ends by any suitable means 39, as for example a cord. i Conveniently the vapors escaping from the condensers.v are burned in the hood to provide zinc oxide, and as the vapors are burned in a relatively cool atmosphere due to the excess of air, the zinc oxide is sud-- denly chilled to roduce a very fine powder easily handled by the conveying means and having in itself a high commercial value.

Preferably the condenser mouths arc plugged with a mixture of screened anthracite dust with enough ore to give it body which provides a porous plug for the condenser mouths acting as a filter which frees the vapors from dust and other solid impurities and further acts to materially prevent the escape of heavy vapors such as the lead content of the ore.

In operation if the ore charged'has an appreciable cadmium content .the same largely may be `segregated from the bulk of the zinc content discharged from the] condensers due to the fact that the cadmium ore reduces at -a lower ktemperature and consequently more rapidly than the zinc, which makes it possible first to pass olf vapors rich in cad-4A miumand then after it has been determined that the most active reduction of cadmium is completed to open the bottom of the bags in the bag house and shake them to recover a product rich in cadmium, or if desired this high cadmium bearing fume may be collected in a separate bag house or settling chamber. .Isls the lead content of the ore .at ter reduction is less volatile than the zinc practically all the lead is collected in the sov ico

condensers resulting inthe production of zinc roxide low in discoloring lead impurities, and if an ore low 1n cadmmm be pro# vided because of the substantlal elimlnatlon lof the lead content and the 'burning of the vapors in a large excess of air the zinc oxide, after a subsequent treatment if necessary to remove carbon, will be analogous or equal in quality to thezinc oxide produced by the so called Fre lch process consisting of burning metallieziinc.

It will be noted that my improved process A avoids the previously mentioned alternative of running the condenser so cool compared to the rate of vapor How fromthe retortsas to produce la substantial portion of the metalvalues `as blue powder, and that as a consequence it-is not necessary to use` the same degree of care in lcarrying out my same time Ithe current of air induced by Jthe exhaust fan is directed over the conden'sers which it is believed keeps them cool enough as compared to the increased rate of vapor flow to function tocondense an increased amount ofspeltcrper retort'as compared with the prior process. As an example of my yimproved method without limitation thereto I have found 'that M a retort furnace having 405 retorts, using v280 retorts for roasted oreand 125 rctorts 3() pounds of reduction fuel consisting of.

, approximately 5 pounds of anthracite coal f and pounds of coke breeze, the nine content' of the roasted ore averaging 69,4 pounds per retort. If Athe return products resulting from the smelting operation given as an example are assumed to be equal in metal value to the return products charged from the next preceding operation, which assumption I have found toy be approximated in practice, then @the total production of metal values represents the recovery from the ore charged, which means that the spelter recovery` averaged 57.7 pounds for each. retort/charged with ore. This spelter -recovery represents 83.1 percent of the metal values charged in the form of ore, and at the' same time there was recovered in the bag house a productrepresenting 3.1 pounds `of zinc per retort of the total 405, retorts or 4.5 pounds per retort charged with ore, rep

resenting 6.5 percent of the metal' values of the .ore charged. The total recovery of not'returned tothe furnace. a

As an example of the' prior method I have -found on the same basis of computation lnrthe example given above, thatawith the same retortsv and furnace. a retort' charged with/'7 pounds of roasted ore of the same composition having a metal content of 52.2y

pounds mixed `with 28v pounds of the same kind of reduction fuel produced 46.7 pounds of spelter, the latter`represent'i"ng 89.` per cent ofithe metal values of the ore charged.

'fhus it will be noted that-not`only does my imp rovedprocessO increase the furnace output but it also secures an increased recovery.v

of the metal values with' a smaller ratio of reduction fuel to theroasted ore charged,

`all of whichwill be'iapp'arentfrom an inspection of the following table summarizing` the results of the above examples of my in- ,proved method and thel prior method.

Improved Prior method. method.

Number of retorts charged with ore. i 280 280 Number of retorts chargedwith return prodi ucts 125 125 Ore charged per retort charged with ore 98. 2# f 75# Fuel charge per retort charged with ore 30# 28# etai value of ore per retort charged with ore. 69. 4# 52. 2# Spelter recovery from ore per retort charged.l

with ore 57.7# 46. 7# Percent metal recovery from ore in bag house 6. 5 None Total percent recovery of metal values of ore charged 92 89. 5

i In the above example of my improved erage atotal :volumetric capacity of 1.41 cubic Dfeet, and the charge per cubic foot of charging the retorts with tore` and reductionV fuel to theirfull cubical capacity, in which vcase the output of fume and spclter will be correspondingly increased 4without it being4 necessary materially to increase. the reduction temperature. Conveniently this may be ldone by briquetting the ore and fuel, in which case a'mixture of ore and reduction fuel mixed with a suitable binder will .be formed into briquettes under pressure, thus increasing the amount of metal values that may be charged Linto a retort of given cathis total retort capacity amounted to 69.7

pacity. As As'uitablefor this purpose I may use a mixtureof 70 coke breeze,fand 5 ercent of pitch, which ercent of roasted ore, 5 percent of anthracite coal, 2O percent of mixture can be briquetted in'any suitable briquette making machine.

The amount of zinc oxide` produced by my' method can be varied by varying either the charge or temperature or both, but preferably by varying the charge. In the above example of hny method the temperature was raised gradually fromA about 1000 degrees centri` grade, at which temperature. the reduction prccess will begin, to a maximum of 1450 degrees centigrade, reaching the` latter teinperature after the operation had continued for about 14 hours, and was maintained at thatI maximum temperature for about 5 hours, or until jhe operation was completed.

By reducing this maximum temperature pr' furnace, but the proposedprocess has been y escaping from the condenser, which losses are necessarily low as heretofore explained, and the proposed'process is not pract-ical as the cost would be greater than the returns. \Vith my improved method, on the contrary, I. p'ropose deliberately to overcharge the retorts as compared to the condenser capacity and to collect an economically material proportion of the metal charged to the retort after it has passed through the condenser as a sublstantial and intentional factor in the process. At the same time spelter recovery is an important object and -the con-` densers are operated under such conditions as will secure a maximum production of that product. f

l/Vhile the process as described has some aspects of fractional distillation, especially in the selective recovery of lead and cadmium if present, itcis primarily a smelting process of treating ore or other crude zinc bearing material With reduction fuel.

An import-ant feature of the invention is the possibility of production in substantial quantity of a high grade. zinc oxide although in a sense as a by-product of spelter production, and it Will be observed that in'absence of a market for thezinc oxide the same may be charged to the retorts as a concentrated product rich in zinc.

The invention is applicable to existing installations of retort furnaces and is exceedingly simple, requiring only amoderate installation charge lfor alteration of the usual existing plant arranged for carrying out the prior method of 'spelter recovery. As a larger amount of ore may be treated in each retort at one time, an economy of expensive heating fuel per` amount of ore treated is realizedfor it Will-be observed that furnace heat losses are substantially independent of, the amount of ore charged. v.Also .as a greater amount of ore is heated at one time the overhead and labor charges ire correspondingly reduced. The maximum effective production of metallic spelter is provided for, yet a considerable'fraetion of the metal values is lrecovered exterior-ly of the condenser. .y

Although I have. described for purposes of illustration one specific manner of carrying out my improved method it is to be understood that I am notlimited thereby to its particular details as deseribed,but that Within the scope'of my invention wide deviations may b'e made therefrom Without departing from the spirit of my` invention.

1 That method of smelting crude zinc bearing material utilizing aretort furnace and condenser, which consists' in charging the retort 'with )a mixture of said material and reduction fuel in amount to produce and condenser, which consists in charging the retort with a mixture of said materialv and reduction fuel in amount to produce .a volume of metal vapors in substantial excess of the capacity of the condenser fully to condense .the same and ,conducting the vapors discharged from the condenser, which .comprise a considerable fraction of the metal values in the material treated by a current of air, for recovery by deposit of the metal values therein while obtaining a recovery of spelter in the 'condenser to the full capacity thereof.

3. That method of smelting crude zinc bearing material utiliz-ing a retort l. furnace and condenser, which consists in charging the retort with a mixture of said material and reduction fuel in amount to produce a volume of metal lvapors in substantial ex` cess of the capacity of the condenser fully to' condense jthe same and conducting the vapors discharged from the condenser, which comprise a considerable fraction of the metal `values in the material treated by a current of air directed against the condenser, for

recovery by deposit of the metal values therein while obtaining a recovery of spelter in the condenser to the full capacity thereof. LL That-.method oi smelting crude zinc bearing material utilizing a retort furnace and condenser, which consists fin .charging the retort with a mixture of said material and reduction fuel in amount to produce a volume' of metal vapors in substantial excess of the capacity of the condenser fully Y to condense the same and burning in an excess of air the vapors discharged from the condenser, which vapors comprise a. considerable fraction of the metal values inthe materialv treated, to produceatinely divided oxide While obtaining a recovery of spelter in the condenser to the full capacity thereof.

5. That method of smelting crude zine bearing material utilizing a retort ,furnace and con-denscr, which consists iii/charging the retort with' a mixture of sai/d materiali and reduction fuel-` in amount t produce a volume of metal vapors 1n sul stantial excess l.of the capacity of the condenser fully to condense the same and burning inan excess of air the vapors discharged from the condenser, which vapors comprisel a con.- siderable fraction of themetal values in the mascia material treated, to produce a finely divided least 2.5 percent of thev metal vvalues to be 05 oxide While obtaining a recovery of spelter in the condenser to the full capacity thereof discharged yin the form of vapor from the condenser mouth, directing a current of air and conducting the oxide by a current `of air against the condenser toI increase its spelter for recovery therefrom by deposit.

6. That method of smelting crude zinc bearing material utilizing a retort furnace and condenser, which .Dconsists in charging the retort with a mixture of said material and reduction fuel in lamount vto produce a volume of metal vapors. in substantial excess of the capacity of the condenser fully to condense the same, directing a current of air against the condenser to Vincrease the spelter-produ'cing capacity thereof, burning in said current of air nthe' vapors discharged from the condenser, which comprise a considerable fraction of the metal values in the material treated to'produce a finely divided oxide and conductm'g the oxide by saidn current of air for recovery therefrom by de osit. Thatmethod of smelting zinc bearing material utilizing a retortv furnace and condenser, which consists in charging the retort with a mixture of said material and reduction fuel in subst-antial excess of the capacity. of the condenser to condense fully the resulting metal vapors, burning the vapors discharged from the condenser in a current of air to produce a finely divided oxide, and collecting the oxide from said air by deposit in successive fractions to recover a fraction high in cadmium and a `second fraction lower in cadmium While recovering spelter in the condenser to the full capacity thereof.

with condensation therein of substantially all the lead content of the material. l

8. That method of smelting zinc b aring material utilizing a retort furnace an condenser, which consists in charging the retort with a mixture ofnsaid material and reduction fuel suficient lin amount to cause at least 2.5 percent `of the metal values' to be .discharged in )the form of vapor from the condenser moutii, and entraining said vapor by an air current flowing past the condenser mouth for vrecovery from said air by deposit.' 9. That method of smelting zinc bearing material utilizing a retort furnace and condenser, Which consists in chargingthe retort with a mixture of said material and reduc tion fuel sufficient in .amount to cause at least 2.5 percent of the metal values to be discharged in the form of vapor` from the condenser mouth, burning said vapor to proddee an oxide, and entraining said oxide a current ofy air for recovery from said air by deposit. s

.10. That method of smelting zinc\bearing material utilizing a retort furnace and condenser, Which consists in charging the retort with a mixture of said material and reduction fuel ,sufficient in amount to cause at material utilizing a retort furnace and conl denser, Which'consists in charging the retort -to substantially its full lcubical capacity With a mixture of said material and reduction fuel suiiicient effectively to reduce the metal values'and 'to produce Aa volume of metal vapors inl substantial excess of the capacity of the condenser fully to condense the same, burninginfair the vapors discharged from the condenser mouth, which comprise a considerablev fraction of the metal values in the material treated, entraining the resulting oxides in a current of air, and recovering the oxides from said current of air by deposit.

l2. That method of smelting zinc bearing material utilizing a retort furnace and condenser, which consists in charging the retort to substantially its fullcubical capacit'y with a mixture of said material andl reduction fuel sufficient effectively to reduce the metal valuesand'to produce a volume oft'metal vapors in substantial excess of the capacity of the condenser fully to condense the same, directing a current ofair against the condenser to increase the spelter producing capacity of said condenser, burning the vapors discharged from the condenser mouth in a current 'ofl a1r, and recovering the resulting oxides from said air by deposit.

,' 13. That method of smelting zinc bearing material utilizing -a retort furnace and condenser, Which consists in charging the retort `With a mixture of said material and reduction fuel in substantial excess of the capacity of the condenser to condense fully the reslting metal vapors, converting the vapors' discharged from the condenser pound in a current of air, and separating the compound from said air by deposit.

. 14. yflhat method of smelting zinc bearing material utilizing a retort furnace/- and com denser, vhich consists in charging the retort with a mixture of "said material and reduction fuel insubstantial excess of the capacity of the'condenser to condense fully the resulting metal` vapors, converting the vapors discharged from (the condenser mouth and which lcomprise a considerable kfraction of the metal values treated to a pulverulent solid compound by treating them with a gaseous substance Which Will '.retort to substantially its full cubical capacity with a mixture consisting of reduction fuel and a relatively large proportion of said material, heating the. retortby progressively raising the A temperature to a maximiun, maintaining said temperature at substantially said maximum until the yreduction is vsubstantially completed to produce during the reduction step a volume of fmetal vapors in substantial excess. of the capacity of the condenser fully to condense the same, burning in an excess vapors discharged from the condensers, comprising a considerable fraction of the `metal values treated, and recovering the metal values from the air by deposit.

16. That method -of smelting zinc bear.

ing material: utilizing a retort furnace and condenser, which cuonsistsi` in charging the retort to substantially Iits full cubical capacity with a mixture of said material and reduction fuel, heating the. retort by pro` gressivelyJ raising thetemperature to` a maximum, .maintaining said temperature at substantially said maximum until the reduc'- tion isA substantially completed to produce during the reduction step a Volume of metal vapors in substantial excess of the capacity of the condenser Ffully to condense th same, burning in an'excess of air the vapors discharged from theconden'sers, ,comprising a considerable fraction of the metal values treated, and recovering the metal values from'the air by deposit.

17. That method of smelting inc bearing material utilizing a retort furnace and condenser, Which consists in charging the -retort to substantially its full cubical capacity with a` mixture of said materiahand reduction fuel, heating the retort by slovifly raising the temperature to a maximum, maintaining said temperature at substantially said maximum Yuntil the reduction ismsubstantially'completed to produce durif"iz"the reduction step a volume of metal Avapors in substantial excess of the capacity of the condenser fully to condense the same, burnl ing 1n an excess of air the vapors discharged from the condensers, comprising a con--` Siderable --fraction of the metal values treated, land recovering 'the metal values froml the airby deposit.

y 18. That method of smelting zinc bearing denser, which consists in compressin material utilizing a retort furnace and condenser, Which consists inchargin'g the retort to substantially its full cubical capacity with a.mixture of reduction fuel and said 'material, heating the retort by starting at substantially .the temperature at which reduction will begin, progressivelyraising this temperature to a maximum materially in excess of thev starting temperature and maintaining said temperature at substan-A from the condenser mouths, comprising a" considerable ,fraction of the metal values' treated, and recovering the metal values from said air`by deposit. 19. That method of smelting zinc bearing material utilizing a retort furnace and con-d of air the denser, Which consists 1n compressingl1 a mixture of said material and reduction l, charging the retort With the compressed mixture in amount-to producea rate of vapor flow in excess of the. capacity of the condenser efiiciently to condense said vapor, burning in an excessof air the .vapordischargedy from the condenser mouth, comprising a considerable fraction of the metal values treated, and drecovering the metal values from said'air by deposit. l

20. That method of smelting zinc bearing materiahutilizing a retort furnace and cona mixture `of said material and reduction nel, charging the retort with the compressed mixture to substantially the full cubical capacity of said retort to produce a rate -of flow of metal vapoiry in substantial excess of the' capacity of the condenser fully toI condense the same, burning in an excess of air the vapor discharged from the condensery mouth, comprising a considerable fraction of the metal values treated, and recovering the metal values from said air by deposit. d

21.- That method of smelting zinc bearing material utilizing a retort furnace and condenser, Which consists in briquettingA a mixture of said material and reduction fuel,

charging the retorts With the briquettes in amount to produce a rate of vapor flow in substantialgggexcess of` the capacity of the condenser efficiently to `condense said' vapor, burning in an excess` of air the vapor discharged from the condenser mouth comprising a considerable fraction of the metal values treated, and recovering the metal values from said airl by deposit.

22. That method of smelting zinc bearing material utilizing a retort furnace and con-l denser, which consists 1n brlquettlng a mlxture -of said material and reduction fuel, vapor"dischargefrom the condenser gzouth, charging the retorts with the vbriquettesto comprsing'a considerable fraction bf the substantially the full cubieal capacity of metal ,values treated, and recovering the l0.

saidretort to producel a rate o flow ofmetal values from said air b deposit.

5 metalA vapor in substantial excess of the `In testimony whereof, I ave signed my capa ty of the condenserfully Ato condense name to this specification. v the same, burning in an excess ofv airthe A

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