US3634069A

US3634069A - Tin smelting

Info

Publication number: US3634069A
Application number: US805503A
Authority: US
Inventors: Howard Knox Worner
Original assignee: Conzinc Riotinto Ltd
Current assignee: Conzinc Riotinto of Australia Ltd; Conzinc Riotinto Ltd
Priority date: 1969-03-10
Filing date: 1969-03-10
Publication date: 1972-01-11
Anticipated expiration: 1989-01-11

Abstract

Method for continuously smelting in a low-shaft blast furnace pelletized iron-containing tin ores and concentrates in the form of composite carbonized pellets by tapping tin-iron alloy and slag into an elongated launderlike refining furnace operatively connected the blast furnace, continuously separating alloy and slag in the furnace, injecting an oxidant into the separated alloy forming molten tin and slag, tapping tin and slag separately from the furnace. A low-shaft blast furnace for continuously smelting composite carbonized pellets of tin ores and concentrates with cooperating means for pelletizing, carbonizing and feeding the composite pellets into the furnace, a common taphole for continuously tapping tin-iron alloy and slag into an elongated launderlike refining furnace operatively connected to the blast furnace and having an alloy and slag entry point, separate tin- and slag-tapping ends, means for separating alloy and slag, means for injecting oxidant into the alloy, means for continuously separating alloy and slag in the furnace and separate tin and slag tapholes.

Description

United States Patent Howard Knox Worner North Balwyn, Victoria, Australia [72] Inventor [21] Appl. No. 805,503 [22] Filed Mar. 10, 1969 [45] Patented Jan. 11, 1972 Conzinc Riotinto of Australia Limited Melbourne, Victoria, Australia [73] Assignee [32] Priority May 2, 1966 [33] Australia [31 4934/66 Continuation-impart of application Ser. No. 634,938, May 1, 1967, now abandoned. This application Mar. 10, 1969, Ser. No. 805,503

[54] TIN SMELTING 13 Claims, Drawing Figs.

75/41, 266/11 [51] Int. Cl C22b /02 Field of Search /23, 36,

Primary Examiner-L. Dewayne Rutledge Assistant Examiner.l. Davis Attorney-Pierce, Scheffler and Parker M ABSTRACT: Method for continuously smelting in a low-shaft blast furnace pelletized iron-containing tin ores and concentrates in the form of composite carbonized pellets by tapping tin-iron alloy and slag into an elongated launderlike refining furnace operatively connected the blast furnace, continuously separating alloy and slag in the furnace, injecting an oxidant into the separated alloy forming molten'tin and slag, tapping tin and slag separately from the furnace. A low-shaft blast furnace for continuously smelting composite carbonized pellets of tin ores and concentrates with cooperating means for pelletizing, carbonizing and feeding the composite pellets into the furnace, a common taphole for continuously tapping tin-iron alloy and slag into an elongated launderlike refining furnace operatively connected to the blast furnace and having an alloy and slag entry point, separate tinand slag-tapping ends, means for separating alloy and slag, means for injecting oxidant into the alloy, means for continuously separating alloy and slag in the furnace and separate tin and slag tapholes.

BENEFICATlON Greater Bulk FINE COAL RETURN FINES PELLETISATION r FLUXES BLAST FURNACE SMELTING TlN-lRDN ALLOY PLUS SLAG AIR SLAG

LAUNDER LIKE FURNACE TiN PATENTED JAN] 1 1572 SHEET 3 [IF 3 TIN ORE BENEFICATION GANGUE LOW T0 MEmuM TlN OXlDE T0 DUMP RKLH GRADE CONOCENTRATE MATERAL (z 35*55/0 5n) es-707cm) Gvemev Bulk FlNE COAL FLUXES RETURN FINES PELLET\SATION CARBONiSATlON BLAST FURNACE smu'rmo AIR TIN-\RON ALLOY PLUS SLAG SLAG LAUNDER LIKE FURNACE TIN SMELTING tially pure tin metal and a low tin content slag. Higher grade tin concentrates or fume material may also be utilized.

Existing tin-smelting methods, including reverberatory, blast furnace and electric furnace methods, are normally designed to operate on highly beneficiated concentrates in which the iron content is low and the percentage of tin is preferably greater than 55 percent. This present invention makes possible economic smelting of many concentrates with less than 50 percent tin and in some cases even below 35 percent tin, and with relatively large amounts of iron-bearing minerals present, including a limited amount of iron sulphides. Such concentrates would usually not be acceptable as feed to a conventional tin-smelting furnace unless further beneficiated by methods such as roasting and magnetic separation or flotation and magnetic separation. This extra beneficiation, apart from adding to treatment charges, usually leads to further losses of valuable tin and lower overall recoveries.

The invention according to one general form comprises a method for smelting tin ores and/or concentrates containing iron, which includes the steps of continuously smelting agglomerated particulate tine ores and/or concentrates in a lowshaft blast furnace forming and substantially continuously tapping a molten tin-iron alloy and a liquid slag from said blast furnace into a second furnace and refining the alloy therein by introducing into the molten alloy at least an oxidant, forming a molten tin product and a liquid tin-bearing slag, continuously or semicontinuously separating molten tin from the slag in the second furnace, and tapping molten tin and liquid low tin content slag separately from the second furnace.

According to another aspect of the method of this invention the agglomerated particulate tin ores and/or concentrates are fed to said blast furnace in the form of composite pellets containing carbon along with tin ores and/or lowto mediumgrade tin concentrates, and in which said second furnace is in the form of an elongated launderlike furnace which is operatively connected to the blast furnace and in which the tin-iron alloy is refined by injecting at least an oxidant into the molten alloy thereby forming said molten tin product and said liquid tin-bearing slag.

The present invention also envisages the case where the molten tin-iron alloy or hardhead product is tapped from the blast furnace but is reserved for subsequent refining to tin metal in a separate refining furnace either at the same site as the blast furnace or at another location.

Preferably however, both molten tin-iron alloy and liquid slag are tapped from the blast furnace through a common taphole directly into the second or launderlike furnace for refining to tin metal.

According to another variation of the method of this invention where the slag from the blast furnace is ofa very low tin content, the slag is tapped separately from the blast furnace and molten tin-iron alloy or hardhead is then tapped from the blast furnace into the second furnace.

Such separate withdrawal of the blast furnace slag may suit particular operating conditions, or practices, for instance:

i. the slag may be of very low tin content and therefore not merit further treatment for tin removal ii. the slag volume may be too great for convenient handling in the second furnace,

iii. the slag may contain undesirable impurities which cannot be readily removed in the second furnace.

The tapping of molten slag as well as of molten tin-iron alloy from the blast furnace into the second furnace is generally advantageous because this slag transfers heat to the refining stage of the process, particularly to the slag well, and provides extra bulk for mass flow of the slag in the second furnace. Furthermore in this way the blast furnace slag can be treated for tin removal by fuming simultaneously with the countercurrent slag from the refining zone.

Preferably the oxidant includes an oxygen-containing gas. In the second furnace, material of higher SnO content than that processed in the first furnace is advantageously injected into the molten tin-iron alloy simultaneously with the oxygencontaining gas, which also serves as an entraining medium for the said higher SnO material. The velocity of momentum or injection must be sufficient to cause vigorous mixing and stirring of incoming higher SnO; material and the tin-iron alloy in the second furnace.

The above method preferably also includes the steps of agglomerating particulate tin concentrates or other tin-containing material, by pelletizing or briquetting a blend of tin concentrates and coal and then carbonizing the pellets or briquettes and charging the carbonized pellets or briquettes, preferably hot, into the blast furnace.

More particularly finely comminuted tin concentrates are pelletized or briquetted using caking coal and caking coal and lime and the pellets or briquettes are then carbonized before smelting in the low-shaft furnace.

Alternatively the concentrates may be pelletized or briquetted with coke fines, char or noncaking coal and a binder or mixtures of binders or other suitable caking material. Fluxing agents may also be included in the pellet or briquette blend.

Preferably the ratio of coal or other solid carbonaceous component to the tin concentrates in the composite pellets or briquettes will usually be between 0.25 and 0.5 on a weight ba- $15.

In one preferred form of the method the pellets are rapidly carbonized on a belt, grate or moving hearth carbonizer with a final carbonizing temperature within the range of about 500- to 800 C. and within an optimum temperature range of between 650and 700 C.

In another aspect of the invention the tin-iron alloy formed in the blast furnace contains above 10 percent of iron, preferably above 18 percent by weight of iron. The slag leaving the blast furnace has a low tin content preferably below 1.2 percent tin. It has been found that this is readily achieved when the iron content of the alloy being tapped is above 20 percent.

In a further aspect of the method according to the invention the slag formed in the second or elongated launderlike furnace is flowed countercurrently to the tin-iron alloy along a substantial proportion of the length of the furnace.

Preferably molten tin product and a low tin content slag are each separately tapped continuously from opposite ends of the second furnace.

The molten tin-iron alloy and liquid slag may conveniently both be tapped from the blast furnace through a common taphole directly into the second or elongated launder like furnace at a point of entry along the length of the second furnace preferably between 10 and 40 percent of the distance from the slag-tapping end.

In the process of the invention during the substantially continuous injection of an oxygen-containing gas and tin oxide concentrates or return fume or other material richer in SnO and of appropriate fluxes, into the tin-iron alloy as it flows towards the metal-tapping end of the launderlike furnace, reactions of the following general type occur:

O +2 SnFe 2 Sn+2 FeO Sn0 +2 Fe (in tin alloy) Sn+2 F e0 The FeO formed immediately reacts with silica and other slagforming fluxes to produce a slag which is caused to flow countercurrent to the tin-iron alloy towards the slag taphole end of the launderlike furnace.

In effect, the smelting is achieved in two stages. The first stage, preferably carried out in a low-shaft blast furnace, is deliberately designed, contrary to conventional blast furnace tin smelting, to produce a tin alloy relatively rich in iron rather than tin metal itself. The iron in this alloy is then used in the closely integrated second stage operation in the launderlike furnace both to produce heat (by its oxidation) and to reduce more tin oxide to metal. It may be said that the first-stage reduction is deliberately overshot in order to produce a bath fuel and reducing potential for the second stage.

This novel approach to tin smelting has the following advantages:

a. It is not necessary to remove as much of the ferruginous gangue minerals from the tin concentrates as would be the case with conventional smelting methods, thus saving beneficiating costs and usually permitting a significantly greater overall recovery of tin.

b. As irony tin alloy is considered desirable rather than a disadvantage in the first-stage smelting, the blast furnace may be driven hard" with consequent high productivity. The use of hot composite pellets or briquettes also greatly accelerates the first-stage smelting rate.

c. The presence of considerable percentages of iron in the tin tapped from theblast furnace contributes to low tin losses in slags.

In the experimental work upon which this invention has been based, it was found that the tin-in-slag values were in the vicinity of 1 percent or lower when the iron content of the alloy tapped from the blast furnace was approximately percent.

The iron in the alloy flowing into the launderlike secondstage smelting unit is capable of stripping tin out of the slag flowing countercurrent to it. The reaction can be represented as SnO in slag Fe in alloy Sn+FeO (enters slag). This has the effect of maintaining relatively low tin values in slag, irrespective of whether the slag is generated in the blast furnace or in the launderlike furnace.

It should be understood that maximum thermal efficiency is attained in the process of this invention, if the operations of pelletization or briquetting including carbonization, blast furnace production of hardhead and refining in the launderlike furnace are combined, that is, carried out successively on one and the same site. However, under certain circumstances it may be convenient and economic to carry out the pelletization or briquetting operations together with the blast furnace operation at, say, mining sites, and the refining at other geographically distant locations. Adoption of this latter course cannot be considered to depart from the spirit and scope of this invention which includes every novel feature and combination of features herein described.

The invention also includes apparatus for producing tin-iron alloy from iron-containing tin ores and/or concentrates and which, according to one general form, comprises a blast furnace including means for agglomerating iron-containing tin ores and/or concentrates, means for feeding said agglomerates into said furnace and means for tapping molten tin-iron alloy and low tin content slag from the furnace. The blast furnace is preferably also adapted to substantially continuously deliver molten tin-iron alloy and low tin content slag for refinement to tin metal in a second or refining furnace which, as previously stated, is preferably an elongated launderlike furnace.

According to one embodiment which may be preferred the assembly comprises a low-shaft blast furnace, a hot grate type carbonizer adapted to feed hot carbonized agglomerates of particulate tin ore and/or concentrate into the furnace, and means for continuously collecting and tapping molten tin-iron alloy and slag from the furnace. Preferably the means for tapping molten tin-iron alloy and slag from the blast furnace comprises a common vertical slot type or other suitable taphole.

In one preferred embodiment the blast furnace is also provided with a separate charging chute for feeding additional tin-containing material in the form of cold scrap or the like into the charge stream.

In another aspect of the invention a hot screen is interposed between the carbonizer and the blast furnace to remove fines from the pelletized and carbonized feed entering the furnace.

The blast furnace may also be advantageously provided with a row of auxiliary tuyeres in the upper sections of the furnace.

According to another general form the invention includes apparatus for refining tin-iron alloy and comprises a refining furnace, preferably in the form of an elongated launderlike furnace, which is adapted to receive and continuously or semicontinuously process molten tin-iron alloy delivered from a blast furnace and which includes means for introducing at Ieast an oxidant into the molten tin-iron alloy so as to form a molten tin product and a tin-bearing slag, means for continuously or semicontinuously separating molten tin from the slag and means for tapping molten tin and liquid low tin content slag separately from the refining furnace. The refining furnace also preferably includes means for withdrawing hot combustion gases formed during smelting.

In a preferred embodiment the launderlike furnace has separate tapping points for molten tin and slag situated at or near the opposite ends of the furnace and an entry launder for molten alloy situated between the tinand slag-tapping points. The launderlike furnace is preferably provided with means for promoting vigorous reaction and countercurrent flow of the molten tin-iron alloy flowing mainly towards the tin-tapping point and the molten tin-bearing slag flowing mainly towards the slag-tapping point.

The launderlike refining furnace preferably includes means for introducing higher grade tin concentrates or other material of high tin content into the molten bath.

The invention also includes in combination apparatus for carrying the above methods into effect in one operation and which in a general form comprises a low-shaft blast furnace for continuously smelting agglomerated particulate tin ores and/or concentrates to form molten tin-iron alloy and slag, including means for tapping said alloy and slag into a second furnace integrated with or operatively connected to the blast furnace, means in said second furnace for introducing at least an oxidant into the molten tin-iron alloy forming a molten tin product and a liquid tin-bearing slag, means for continuously or semicontinuously separating molten tin from the liquid slag, and means for tapping molten tin and liquid low tin content slag separately from said second furnace.

One form of apparatus for carrying out the invention which is shown diagrammatically in the accompanying drawings will now be described. The drawings and appertaining description are illustrative only and not to be regarded as limitative of the invention. In the drawings like reference numerals denote like parts. Referring to the drawings:

FIG. 1 is a partial sectional elevation of one embodiment of the invention.

FIG. 2 is a sectional elevation through one form of the launderlike second furnace.

FIG. 3 is a sectional plan view of the launderlike furnace shown in FIG. 2.

FIG. 4 is a sectional elevation through a modified form of the furnace of FIGS. 2 and 3.

FIG. 5 is a flowsheet showing one method of smelting tin concentrates according to this invention.

Referring now to FIG. 1, concentrates 5a, finely ground caking coal 5b and return fines 6 together with any necessary fluxes are formed into composite pellets 22 in pelletizer 7 and delivered via belt feeder 8 to the grate-type carbonizer 9. The volatiles given off from the coal in the composite pellets 22 are burned with hot air blown in through ports or jets 10, the air having been heated in a recuperator 11 associated with the main gas offtake 12. The heat generated by the burning of the volatiles in the carbonizer 9 is usually sufficient to make this operation entirely autogenous. This heat may be supplemented by the hot CO-bearing gases leaving the top of the low-shaft blast furnace 13. The combustible carbon monoxide in the blast furnace gases may conveniently be burnt by jets of hot air blown in at 14. Alternatively, the blast furnace gases may be withdrawn through stack 15 and used for other heating purposes about the smelter.

The hot, partially coked pellets 22 delivered from the hot end of the grate-type carbonizer 9 may contain a small proportion of fines and for this reason it is advantageous to interpose a hot screen 16 between the carbonizer 9 and the blast furnace 13. The hot fines 17a are collected in sealed bin 17 which is conveniently p urged with steam or fully combusted furnace gases before opening periodically for removal of the fines and their return to the grinding and pelletizing circuit.

The blast furnace 13 is preferably provided with a separate charging chute 18. By this means cold pellets or other furnace charge components, as for example, slag and tin-rich scrap material from about the smelter, may be added in addition to the hot pellet charge.

The general aim is to keep the solids at the top of the shaft at about dull read heat (say 500700 C.). This temperature is low enough to minimize volatilization of tin from its compounds but high enough to ensure reasonably good elimination into the furnace gases of the usual impurities such as sulfur, arsenic, antimony and lead. Indeed, it has been found that considerable proportions of these undesirable impurities are eliminated in the pellet-carbonizing stage.

The hot blast for the blast furnace 13 enters the tuyeres 20 from the bustle pipe 19. It is sometimes advantageous with side charging as shown to have a row of auxiliary top tuyeres 21. These help to burn some of the top CO-rich furnace gases and also to achieve a more uniform temperature in the rilling feed of pellets 22.

In the embodiment of the invention shown in FIG. 1 the tiniron alloy and slag both leave the blast furnace via the one taphole 23, which may be in the form of a vertical slot, and pass directly via the covered entry launder 23a, to the launderlike refining furnace 24, entering 24 at a position along the length of the furnace preferably between 10 and 40 percent from the slag-tapping end of the furnace 24.

Referring to FIGS. 2 and 3 the launderlike furnace has a bottom 25, sidewalls 26,

end walls

27a and 27b and roof 28. The oxygen-containing gas is fed in via

lances

29a, 29b, 296 which may enter the furnace through the roof 28 as shown or through the sidewall(s) 26. The floor may be designed with slopes as shown to provide a deeper bath in the region where the oxygen-containing gas is injected via lances 29 into the slowly flowing tin-iron alloy.

The molten tin 31 forming from the tin-iron alloy being slightly lighter than the hardhead tends to accumulate nearer to the top of the bath and immediately below the slag and is tapped substantially continuously via a conveniently located notch 32 in the end wall 27b into a holding chamber 33. Alternatively with slag may be dammed back by an internal or external refractory dam, not shown. From 33 the tin may be tapped continuously or intermittently via spout 34 for casting or other refining treatments. If desired other refining treatments may be given to the tin in chamber 33.

Hot gases and any entrained fume may leave the furnace through one or more gas offtakes. Only one gas offtake is shown in FIG. 2 located near to a position over the entry point ofthe molten tin-iron alloy and slag.

It is highly desirable that the molten tin-iron alloy entering the launderlike furnace 24 via spout 230 be vigorously mixed with the tin-bearing slag flowing back from the refining operations nearer to the tin-tapping end of the furnace 24 to ensure ample opportunity for the tin stripping reaction Fe-i-(SnO)- FeO+Sn to occur. This mixing can be effected partly by the cascading of the tin-iron alloy into a restricted region provided by the refractory banks 35. Alternatively, the tin-iron alloy can be caused to flow with momentum into a circular bowl mixing chamber (not shown) in the launderlike furnace. During the circulation of the tin-iron alloy and slag in this bowl the aforementioned reaction between SnO in slag and Fe in alloy helps to reduce the tin in the slag.

In any case the launderlike furnace 24 design and operation should be such as to achieve the maximum opportunity for reaction between the incoming tin-iron alloy and the slag flowing back from the refining end ofthe furnace.

Apart from the oxidation effected by gaseous oxygen, it is advantageous if some concentrates of higher SnO content or fume etc., are injected or otherwise impelled into the bath via one or more of the lances 29, e.g., lance 29c or otherwise fed into the bath near such lance or lances. Additional tin oxide bearing material may be added to the bath through a port 36 in the roof near the tin tapping end. These additions richer in the tin oxide serve to cool the bath near the surface both by the absorption of sensible heat and by the endothermic reaction SnO +2(Fe)'Sn+2FeO. The cooling of the slowly flowing alloy helps to throw further iron out of solution in the tin and so enrich the tin before: it flows out through taphole or notch 32.

To provide maximum opportunity for any prills of tin to settle from the slag which has flowed countercurrent to the irontin alloy, a slag well 37 is advantageously located between the point of addition of tin-iron alloy and slag from the blast furnace 13 (via launder 23a, and the lip-type slag taphole 38.

An air-cooled slag weir or ridge 39 conveniently divides the more quiescent slag well 37 from the more turbulent liquids flowing immediately under the discharge from the launder 23a.

If desired, further carbonaceous or other reductants and slag conditioners such as lime can be added to the launder furnace via the port 40 to the slag in the well 37.

Alternatively, it may be advantageous to reduce the tin content of the slag by a fuming treatment. This may be achieved by blowing into the slag in the slag well a little particulate coal and sulphur or coal and iron pyrites or other fuming agents. The sulphur combines with the residual tin, converting it to the volatile SnS which leaves the bath and is collected with other fumes in appropriate dust catchers or electrostatic precipitators.

As a further assistance to the reduction of the tin content of the slag in the slag well 37, a reducing flame or flames may be impinged onto the surface of the slag from burner(s) 40a. It is advantageous if these reducing flames, (supplemented by any reductants or fuming agents added at 40) cause the slag to circulate slowly as shown by the arrows 41.

In addition to the heating over the slag pool 37, it may be necessary to provide some additional heat at or near the point of injection of the oxygen-containing gas and tin oxide concentrates. This can conveniently be done by oil or gas burners 42 shown in FIG. 3. These flames are impinged at suitable angles so as to assist the incorporation of the concentrates into the tin-iron alloy bath.

The hot products of combustion from the burner(s) 42 leave the Iaunderlike furnace 24 via stack 30 which is conveniently located near to the point of entry of the liquids from the blast furnace 13.

Some of the heat value from the outgoing furnace gases may be recovered by means of a recuperator 43 or other suitable heat exchanger. The hot air so generated may then be used in the burner(s) 42 or in the blast for the low-shaft blast furnace 13 or in other applications about the smelter.

Dust and fume collectors (not shown) are advantageously employed to recover tin values in the gases leaving either the carbonizer 9, the low-shaft blast furnace 13 or the Iaunderlike furnace 24.

In the embodiment of the launderlike furnace depicted in FIG. 4 of the drawings the furnace is generally similar in structure to the embodiment shown in FIG. 2 but differs in that the bottom 25 of the launder reaction chamber 25b defined by the bottom 25, roof 28, and wall 27b and slag weir 39 is substantially flat throughout nearly all of its length.

As explained earlier, it is possible to smelt relatively low grade concentrates in the low-shaft blast furnace 13. It has been found, however, that it is desirable to use material richer in tin oxide, e.g., either concentrates or fume, in the secondstage operation. In the ore-dressing plant it is therefore good practice to produce a relatively small proportion of fairly high grade cassiterite concentrate for direct conversion to tin metal in the second stage Iaunderlike furnace 24 and to smelt the main bulk of the tin in the form of lower grade concentrates in the firstestage blast furnace 13. This procedure is illustrated diagrammatically in the flowsheet shown in FIG. 5, which is self-explanatory.

EXAMPLE 1 concentrates containing Sn 52.3% sio, 6.5% Fe 5.9% S 5.8% AI O, 3.5% CaO 0.3% Pb 0.3% Cu 0.16% Zn Nil As.Sb,Bi traces were blended with slaked lime and finely comminuted caking coal of the following proximate analysis Fixed c 55% Volatiles 35% Ash 7.5% (mostly sio,+Ai, 0,) Sulphur 0.8%

The blend, made up of 70% Concentrates 25-28% Coal 2-4% Slaked lime Sn 46.6% C 22.07: FeO 8.9% CaO 5.5% sio, 6.3% M 4.5% Others 6.2% by difference.

The diameter of the coked pellets ranged from about mm. to mm.

The temperature of the pellets at the top of the low shaft furnace ranged between 600 and 700 C. which ensured that considerable proportions of volatile oxides and sulphides (such as lead, antimony, arsenic) were eliminated in the furnace gases but only traces of tin were lost.

The smelting in the low-shaft furnace was extremely fast and approximately 200 lb. of 20% Fe tin-iron alloy was produced per hour along with slag, both at between l,200and l300 C. and were allowed to run out of a vertical slot type taphole via a covered launder 23 into the oil-fired launder furnace 24, lined with dense chrome-magnesia bricks.

Hot air entraining high-grade concentrates (68.5% Sn) was jetted into the metal in the bath via a dense A1 0 sheathed steel lance 30. The tin, tapped at 27 intermittently in these pilot plant trails, contained over 99.3% Sn The slags, also tapped semicontinuously in these pilot furnace runs, contained less than l.5% Sn. When some lime and pulverized coal was blown into slag well 34 and a little granulated pig iron shot was also added, the tin losses in slag were further reduced and analyses less than 1% Sn were obtained. Analyses for major constituents in the slags tapped in these trials were in the following ranges:

sio, 32-38% CaO |s 22% M20, 16-22% FeO 9-1 2% EXAMPLE 2 Concentrates of slightly higher iron content (the gangue mineral being chiefly magnetite) were smelted and refined in a larger furnace installation than that employed in example I.

Hardhead containing 30:1.5 Fe was tapped continuously from the blast furnace into the second furnace at a rate of 1,400 lb./hr. at a temperature between l,280 and 1,310 C.

High-grade concentrates containing 68.5% Sn were jetted into the metal, as in example 1, through two water-cooled lances, the tips of which were positioned at the slag line. Vigorous stirring and maintenance of temperature in the refining zone was achieved by the jetting action of oxidizing flames from three oil-air lances angled at approximately 70 to the vertical in the direction of slag flow.

The tin product was tapped continuously and contained 98.3% Sn; the slag was also tapped continuously and contained between 0.7-1 .0% Sn after being subjected to a fuming treatment in the slag well in which a finely pulverized blend consisting of 75 percent coal and 25 percent pyrites entrained in an oil-air medium was injected into the slag.

lclaim:

l. A method of smelting iron-containing tin ores and concentrates which comprises agglomerating particulate ironcontaining tin ore or concentrate with a particulate carbonaceous reducing agent to form pellets, carbonizing the pellets, feeding the hot carbonized pellets into a low shaft blast furnace continuously smelting the pellets in the blast furnace, to form a molten tin-iron alloy containing more than 10 percent iron and a liquid slag, continuously tapping the tin-iron alloy and liquid slag from the blast furnace into an elongated launderlike second furnace which is operatively connected to the blast furnace, refining the tin-iron alloy in the second furnace by injecting at least an oxidant thereinto, causing the tiniron to flow countercurrently to the slag along a substantial proportion of the length of the second furnace, forming in the second furnace a molten tin product and a liquid slag low in tin content, and tapping the molten tin product and the slag low in tin content from opposite ends of the second furnace.

2. A method of smelting iron-containing tin ores and concentrates which comprises agglomerating particulate ironcontaining tin ore or concentrate with a particulate carbonaceous reducing agent to form pellets, carbonizing the pellets, feeding the hot carbonized pellets into a low-shaft blast furnace, continuously smelting the pellets in the blast furnace to form a molten tin-iron alloy containing more than 10 percent iron and a liquid slag, continuously tapping the tin-iron alloy and liquid slag from the blast furnace into an elongated launderlike second furnace which is operatively connected to the blast furnace, refining the tin-iron alloy in the second furnace by injecting thereinto a stream of oxygen-containing oxidizing gas at a velocity or momentum sufficient to cause vigorous mixing and stirring of the tiniron alloy, causing the tin-iron to flow countercurrently to the slag along a substantial proportion of the length of the second furnace, forming in the second furnace a molten tin product and a liquid slag low in tin content, and tapping the molten tin product and the slag low in tin content from opposite ends of the second furnace.

3. A method according to claim 1, wherein the molten tiniron alloy product tapped from the blast furnace is reserved for subsequent refinement in a separate refining furnace.

4. A modification of the method according to claim 1 wherein liquid slag of very low tin content is tapped separately from the blast furnace and only molten tin-iron alloy is tapped from the blast furnace into the second furnace.

5. A method according to claim 1, wherein material of high SnO content is introduced into the molten tin-iron alloy in the second furnace simultaneously with a stream of oxygen-containing gas.

6. A method according to claim 1, wherein the pellets are rapidly carbonized with a final carbonizing temperature within the range of from about 500 to about 800 C.

7. A method according to claim 6, wherein the pellets are carbonized at a temperature within the range of 650 to 750 C.

8. A method according to claim 1, wherein the tin-iron alloy contains between about 20 and about 40 percent iron.

9. A method according to claim 1, wherein the liquid slag formed in the second furnace is flowed countercurrently to the tin-iron alloy along a substantial proportion of the length of the furnace.

10. A method according to claim 1, wherein the molten tiniron alloy and liquid slag are both tapped from the blast furnace into the second furnace at a point of entry along the length of the second furnace between about 10 and about 35 percent of the distance from the slag-tapping end.

11. A method according to claim 1, wherein a reductant is added to the relatively low tin content slag in the second furnace to still further decrease the tin content of the slag prior to tapping the slag from the second furnace.

12. A method according to claim 1, wherein at least one reducing flame is impinged onto the surface of the separated slag in the second furnace to assist reduction of the slag.

13. A method according to claim 1, wherein the tin content of the slag in the second furnace is decreased by a fuming treatment.

Claims

2. A method of smelting iron-containing tin ores and concentrates which comprises agglomerating particulate iron-containing tin ore or concentrate with a particulate carbonaceous reducing agent to form pellets, carbonizing the pellets, feeding the hot carbonized pellets into a low-shaft blast furnace, continuously smelting the pellets in the blast furnace to form a molten tin-iron alloy containing more than 10 percent iron and a liquid slag, continuously tapping the tin-iron alloy and liquid slag from the blast furnace into an elongated launderlike second furnace which is operatively connected to the blast furnace, refining the tin-iron alloy in the second furnace by injecting thereinto a stream of oxygen-containing oxidizing gas at a velocity or momentum sufficient to cause vigorous mixing and stirring of the tin-iron alloy, causing the tin-iron to flow countercurrently to the slag along a substantial proportion of the length of the second furnace, forming in the second furnace a molten tin product and a liquid slag low in tin content, and tapping the molten tin product and the slag low in tin content from opposite ends of the second furnace.
3. A method according to claim 1, wherein the molten tin-iron alloy product tapped from the blast furnace is reserved for subsequent refinement in a separate refining furnace.
4. A modification of the method according to claim 1 wherein liquid slag of very low tin content is tapped separately from the blast furnace and only molten tin-iron alloy is tapped from the blast furnace into the second furnace.
5. A method according to claim 1, wherein material of high SnO2 content is introduced into the molten tin-iron alloy in the second furnace simultaneously with a stream of oxygen-containing gas.
6. A method according to claim 1, wherein the pellets are rapidly carbonized with a final carbonizing temperature within the range of from about 500* to about 800* C.
7. A method according to claim 6, wherein the pellets are carbonized at a temperature within the range of 650* to 750* C.
8. A method according to claim 1, wherein the tin-iron alloy contains between about 20 and about 40 percent iron.
9. A method according to claim 1, wherein the liquid slag formed in the second furnace is flowed countercurrently to the tin-iron alloy along a substantial proportion of the length of the furnace.
10. A method according to claim 1, wherein the molten tin-iron alloy and liquid slag are both tapped from the blast furnace into the second furnace at a point of entry along the length of the second furnace between about 10 and about 35 percent of the distance from the slag-tapping end.
11. A method according to claim 1, wherein a reductant is added to the relatively low tin content slag in the second furnace to still further decrease the tin content of the slag prior to tapping the slag from the second furnace.
12. A method according to claim 1, wherein at least one reducing flame is impinged onto the surface of the separated slag in the second furnace to assist reduction of the slag.
13. A method according to claim 1, wherein the tin content of the slag in the second furnace is decreased by a fuming treatment.