US3674463A - Continuous gas-atomized copper smelting and converting - Google Patents

Abstract

A PROCESS FOR SMELTING COPPER SULFIDE CONCENTRATES AND SIMULTANEOUSLY CONVERTING THE THUS-PRODUCED MATTE TO FORM BLISTER COPPER, SLAG AND AN EFFLUENT GAS UNUSUALLY RICH IN SULFUR DIOXIDE IS CHARACTERIZED BY CONTINUOUS OPERATION IN WHICH BOTH SMELTING AND CONVERTING ARE CARRIED OUT IN

SUSPENSION OVER A COMMON FURNACE HEARTH BODY OF MOLTEN BLISTER COPPER, MATTE AND SLAG FROM WHICH THE MATTE TO BE CONVERTED IS SUPPLIED.

Description

July 4, 1972 J. c. YANNOPOULOS 3,674,463

CONTINUQUS GAS-ATOMIZED COPPER SMELTING AND CONVERTING Filed Aug. 4, 1970 5 Sheets-Sheet l Fluxes CQppe SuIfide Concenrrqte v Air/O2 FIG. 1

Pyrite A Furnace Gases V Shaft ,r-"I. T--,-..

Matte B|i$1'e|' Rec c|ed Copper y FIG. 2

Cooling I Water In Ii 1=Y E v L 1 Co n ce ntrclre 8 Flux Charge Gus Jets INVENTOR fj. John C. Yonnopoulos ."LQ'M av 28 15:? Z111K ATTORNEYS July 4, 1972 CONTINUOUS GAS-ATOMIZED COPPER SMELTING AND CONVERTING Filed Aug. 4, 1970 FIG. 3

J. c. YANNIOPOULOS 3,674,463

5 Sheets-Sheet Z I k R i l 0) N co N an N

2 i i "J 2-1- ID 01.! N O.\ \\\\Y.\\\\\\\ 0 0| 9 INVENTOR John C. Yonnopoulos y 1972 J. c. YANNOPOULOS 3,

CONTINUOUS GAS-ATOMIZED COPPER SMELTING AND CONVERTING 5 Sheets-Sheet 5 Filed Aug. 4, 1970 Q h R INVENTOR John C. Yonnopoulos ATTORNEYS July 4, 1972 J. c. YANNOPOULOS 3,674,463

CONTINUGUS GASATOMIZED COPPER SMELTING AND CONVERTING INVENTOR John C. Yonnopoulos a MM, 044. 77 Av EYS United States Patent 3,674,463 CONTINUOUS GAS-ATOMIZED COPPER SMELTING AND CONVERTING John C. Yannopoulos, Danbury, Conn., assignor to Newmont Exploration Limited, Danbury, Conn. Filed Aug. 4, 1970, Ser. No. 60,793 Int. Cl. C22b 9/10, 15/06 U.S. CI. 75-72 4 Claims ABSTRACT OF THE DISCLOSURE A process for smelting copper sulfide concentrates and simultaneously converting the thus-produced matte to form blister copper, slag and an efiluent gas unusually rich in sulfur dioxide is characterized by continuous operation in which both smelting and converting are carried out in suspension over a common furnace hearth body of molten blister copper, matte and slag from which the matte to be converted is supplied.

This invention relates to the smelting and converting of copper sulfide concentrates and, more particularly, to a process for carrying out these two operations simultaneously and continuously primarily in a gas-atomized state.

Although the smelting and converting of copper sulfide concentrates have been satisfactorily performed for decades through the combination of the reverberatory furnace and PeirceSmith converter, the following characteristics of the process have been considered unsatisfactory:

(l) Substantial fuel energy has to be provided to the reverberatory furnace, whereas the converter generates a significant amount of heat which cannot effectively be transferred to the reverberatory furnace;

(2) The intermittent recycling of slag rich in copper and in magnetite from the converter to the reverberatory furnace is known to cause high copper loss in the slag and, hence, to decrease the overal copper recovery;

(3) The batchwise movement of hot masses between the two separate furnaces increases the process cost (large cranes, railway systems, ladies, ladle repair shops, heat losses, etc);

(4) The low rate of smelting per unit reverberatory furnace;

(5) The poor temperature control and heat distribution in the Peirce-Smith converter. Non-uniform heat distribution leads to destructive hot spots in the refractories near the tuyere line and to cold regions remote therefrom;

(6) The production of slag in the Peirce-Smith converter which is high in magnetite and copper content; and

(7) The dilute sulfur dioxide-containing reaction gas produced in the reverberatory and in the cyclic operation of the converter is too expensive to process for its sulfur content and thus creates a pollution problem in its disposal.

Smelting copper sulfide concentrates in suspension, a significant modification in copper pyrometallurgy, has been in commercial operation during the last two decades and has been characterized by high throughput and high utilization of the heat generated during oxidation of the sulfides. This flash smelting, as it is called, produces copper matte which has to be transported to a converter in order to be converted to metallic copper. Although the flash smelting furnace process requires less fuel than a reverberatory smelting process and permits the production of sulfur dioxide in a more concentrated form, the copper content of the slag produced is high. Moreover, although the process in the flash smelting furnace is continuous, the matte produced is converted batchwise in a Peirce- Smith converter and therefore the overall copper making operation cannot qualify as continuous. The flash smelting process as presently operated cannot be adjusted to volume of the client converting, and thus produce metallic copper, by increasing the amount of oxygen admitted with the concentrate because the resulting oxidized slag is extremely high in magnetite and tends to solidify. It appears, therefore, that during flash smelting a matte and/or white metal phase is necessary to avoid a slag extremely high in copper and magnetite and to accommodate the matte collected during any slag cleaning treatment.

I have now devised a method of controlling the suspension or flash smelting of copper sulfide concentrates so that it can be combined with suspension converting of the matte produced in a continuous operation whereby the combined smelting and converting yields, as molten end products, a slag and blister copper and a gaseous product sufiiciently high in sulfur dioxide to permit eflicient recovery of its sulfur content. The present invention is thus an improvement in a continuous process for smelting a copper sulfide concentrate wherein a stream of an intimate mixture of particulate copper sulfide concentrate and siliceous fluxing material is charged downwardly into a suspension smelting zone and an oxidizing gas is charged at high velocity in a direction converging downwardly and inwardly against the falling stream of concentrateflux mixture so as to disperse the stream into a particulate smelting-promoting phase suspended in and carried downwardly in the oxidizing gas and thus form at the bottom of the vessel a molten body of blister matte and a supernatant layer of molten slag. The improvement in such a process, pursuant to the invention, comprises (a) introducing into the lower portion of the falling particulate smeltingproducing phase a jet stream of reducing material at a rate sufficient to maintain the partial pressure of oxygen below about l0 mm. of mercury in the atmosphere adjacent the surface of the slag layer, (b) charging into the upper portion of a converting zone a downwardly directed stream of molten copper matte, (c) charging an oxidizing gas at high velocity into the downwardly moving stream of molten matte at a plurality of peripherally located positions so as to disperse said stream into a particulate converting-promoting phase, (d) directing the descending particulate converting-promoting phase through the aforesaid atmosphere adjacent the supernatant slag layer, (e) collecting below the falling streams of smelted and converted materials a common body of the molten resulting products of the aforementioned smelting and converting in the form of a bottom layer of blister copper, an intermediate layer of copper matte and a supernatant layer of slag, and (f) returning the thus-formed molten copper matte to the top of the converting zone as the source of matte charged thereto. In the presently preferred embodiment of the invention, the smelting and converting zones are combined in a single zone, but they can be carried out separately above and in direct communication with a common body of the molten products therebeneath.

These and other novel features of the process of the invention will be more readily understood from the following description taken in conjunction with the accompanying drawings in which FIG. 1 is a schematic drawing of the process in which both smelting and converting are carried out in a common zone;

FIG, 2 is a cross-sectional detail view of the upper charging end of the apparatus shown in FIG. 1;

FlG. 3 is a side elevation of the furnace used in the process shown schematically in FIG. I;

FIG. 4 is a plan view of the furnace hearth taken along line 44 in FIG. 3;

FIG. 5 is a crosssectional view of the furnace hearth taken in the direction of the arrows 5 along line AA in FIG. 4;

FIG. 6 is a cross-sectional view of the furnace hearth 3 taken in the direction of the arrows 6 along the line A-A in FIG. 4',

FIG. 7 is a detailed material flow balance imposed on the schematic drawing of FIG. 1 pursuant to a specific example of operation of the process;

FIG. 8 is a schematic drawing of a modification of the process of the invention in which the smelting and converting zones are separate; and

FIG. 9 is a schematic drawing of another modification of the process in which the smelting and converting zones are separate.

In the process represented in FIG. 1, incorporating atomized dispersed converting and suspension smelting in a common zone, the ratio of oxygen to copper sulfide concentrate is adjusted to transform from 35 to 75% of the copper into blister copper and the rest into high grade matte. All of the silica required for a good slag is added with the concentrate at the top of the furnace shaft. The proportion of the silica charged, and the operating temperature, can be higher than in the Peirce-Smith converter inasmuch as the reactions are taking place in suspension and not in contact with the refractory walls. A fraction of the copper sulfide concentrate is also added near the bottom of the shaft as a temperature control and safeguard against a high partial pressure of oxygen which would otherwise cause magnetite formation. Copper and high grade matte are continuously tapped at one end of the furnace hearth, and slag is skimmed at the other end. The matte is recycled into the process, at the rate that it is produced, and is sprayed pneumatically down wardly into the top of the shaft. This recycled matte is converted exothermically to blister copper by the appropriate air flow.

In order to effect mixing of the copper sulfide concentrate with the fluxes and with the matte for the forma tion of the workable slag, a thin column of the incoming matte is encircled, as shown in FIG. 2, with a cylindrical ring charge of well mixed fine concentrate and fine fluxes which, in turn, are splashed, atomized and dispersed by a number of powerful jets of air or oxygen-enriched air. The violent action of the atomizing nozzles at the top of the shaft produces an intimate mixture of the reactants in the form of a co-current gravitational flow of a gasliquid suspension of the concentrate fiux-matte mixture moving downwardly through the shaft. Inasmuch a the converting-and slag-forming reactions take place a distance inwardly from the refractory walls, the proportion of the flux charged per unit of concentrate and the operating temperature of the mixture can be higher than in the conventional Peirce-Smith converter.

As pointed out hereinbefore, an appropriate fraction of the fine dry concentrate is blown with Garr guns or the like through four auxiliary entrances near the bottom of the shaft and using recycled flue gas or any conventional reducing gas as the carrier (FIG. 1). The resulting dispersion of fine concentrate among the falling droplets serves as a reducing agent to control the oxygen partial pressure of the gases in this portion of the smclt ing and converting none to an extremely low level and at the same time controls the temperature and formation of magnetite. This low oxygen partial pressure at the bottom of the shaft in the atmosphere adjacent the surface of the supernatant slag layer. generally below 10 and preferably below 10- min. of mercury. is an indispensable condition in the practice of the invention and can be achieved by one or more of the following expendients:

(a) Blow-in copper sulfide concentrates with hot inert stack gas:

(b) Mix coal fines with the concentrate or introduce reducing flames with the concentrates: or

(c) Move upwardly the auxiliary concentrate flash entrances (in other words, decrease the ratio of the respective heights h':h" in FlG. 1).

Control of the temperature and magnetite formation in the lower portion of the furnace shaft is effected by the secondary smelting of the concentrate charged at this point which consumes part of the heat produced in the shaft by the converting reaction and thus cools the liquidgas interface at the furnace hearth to the appropriate temperature. This cooling can be regulated by preheating (or not) the concentrate and by controlling the temperature of the carrier gas of the secondary smelting operation so that the temperature of the supernatant slag immediately below the shaft will permit the dissolving of any magnetite formed and not previously reduced as the reactants move downwardly through the low-oxygen atmosphere immediately above the surface of the slag layer. In this way, there is always an excess of non-reacted sulfur and iron (the iron being an indigenous constituent of the copper sulfide concentrate) at the bottom of the smelting shaft. The iron sulfide reduces any mag netite according to the reaction:

Thus, the partial pressure of oxygen at the bottom of the shaft can be always controlled to an extremely low level in spite of inadvertent random feed variations.

A cleaning treatment of the slag is advantageously provided through smelting of pyrite or pyrrhotite introduced by Garr gun blowers, or the like, into the low-oxygen containing atmosphere immediately above the surface of the slag layer in the furnace hearth. This, along with the countercurrent flow of slag versus matte in the settler as the result of separate withdrawal of the slag and matte from opposite ends of the furnace hearth, reduces copper losses and magnetite content in the slag. A copper concentrator middling product, low in copper and high in sulfur and iron, can be used in lieu of the pyrite or pyrrhotite for the overall economy of the copper extraction process.

The general configuration of the furnace for carrying out the foregoing procedure is shown in FIG. 3 with its accompanying liquid. The primary smelting zone 10 and the converting zone 11 are located within the furnace shaft 12, and the concentrate-flux mixture is supplied through a solid feeder 13 which air is supplied through nozzle 14 at the top wall of the shaft 12 in an arrangement such as that shown in FIG. 2. At the bottom of the shaft 12 there are openings 15 provided for supplying the auxiliary concentrate for smelting in the secondary smelting none 10a. A conventional tap 16 for blister copper 17 is provided at the bottom of the furnace hearth l8, and another conventional matte tap 19 is provided at the deep end of the hearth for drawing off the matte 20. The matte is collected in a recycling ladle 21 which is capable of being raised by a cable 22 to its upper dotted position where the ladle is tilted to pour its contents into a tundish 23 at the top of the furnace shaft 12. Pyrite, or pyrrhotite, for cleaning the slag is introduced through obliquely arranged openings 24 in the roof 25 of the furnace hearth. The supernatant slag layer 26 is drawn off through a conventional slag tap hole 27 located at the end of the furnacc hearth opposite the matte tap 19. The process gas ellluent is collected in an uptake section 28 and is removed through a flue 29.

As shown in FIGS. 4, 5 and 6, the furnace hearth is provided with different cross-sectional shapes under the smelting-converting zone and under the settling zone represented, respectively, by the arrows 55 and 66 at the transverse hearth line AA in FIG. 4. The hearth shape under the smelting-converting zone is shown in FIG. 5 and is substantially trough-shaped so that the interfaces between the hearth atmosphere and slag, the slag and the matte, and the matte and the blister copper progressively decrease in area. The hearth shape in the settler zone, shown in FIG. 6, is substantially rectangular.

Blister copper, matte of different grades up to white metal, slag, unreacted solids, and a gas phase with extremely low oxygen concentration, enter the settler system defined by the furnace hearth 18 at the bottom of the shaft. As these products, falling through the shaft and still continuously reacting, hit the surface of the liquid slag 26 in the molten bath, a sharp deceleration occurs which causes coagulation of similar phases and sinking of the heavier liquids. Three liquid phases (blister copper 17, matte 20 and slag 26) thus form and settle as three distinct layers. The concentrations of copper, sulfur, iron and oxygen in the matte are far from being uniform throughout the matte layer due to their dilferent origins in the shaft reaction zone and in the different reaction times of the individual droplets. Diffusion phenomena continue into the phases and among them. Due to specific gravity differences and to the continuing actions at the lower and upper interfaces of the intermediate matte layer, high grade matte (white metal) accumulates in contact with the bottom blister copper layer and matte poorer in copper sulfides accumulates immediately below the supernatant slag layer. The trough shape of the furnace hearth below the smelting-converting shaft makes the interphase surfaces area diminishing in the order of gas-slag, slag-matte and white metal-blister copper and thus slow down the tendency for reversal of the converting reaction to take place in the furnace hearth.

Matte is continuously tapped into the ladle which is vertically moved into the heated tundish whereby the matte is continuously recycled to the top of the shaft at the rate that it is produced. The main control on the matte production is the rate of secondary smelting of concentrate introduced through the auxiliary supply openings near the lower portion of the shaft. The optimum depth of the matte layer is advantageously controlled by continuously monitoring the density of the molten phases in the furnace with conventional gamma-ray density gages.

The following specific example of a material and heat balance is illustrative but not limitative of the continuous production of blister copper from chalcopyrite concentrate pursuant to the invention. Chalcopyrite concentrate of the following composition is the charged copper sulfide concentrate:

Percent:

C'uFeS z 83. 76 FeS: 7. 54

NoTu.Molstn1-e: 1% (dry basis).

The flux materials admixed with the copper concentrate are made up of quartzite of the following composition:

Percent SiO 98.8 Fe 0.2 MgO 0.2 A1 0 0.4

Moisture: 1% (dry basis).

and pulverized limestone with the following composition:

Percent Si0 4.0 A1 0 3.3 MgO 2.7 CaCO 89.0

The pyrite concentrate for the auxiliary flash operation to control copper losses in the slag has the following composition:

Percent:

NOTE.Molsture: 1% (dry basis).

With a furnace shaft inner diameter of 18 feet, copper concentrate charged at the rate of 1,080 tons per day, and air charged at the rate of 34,000 standard cubic feet per minute, the average linear velocity of the gas downwardly through the shaft is about 11 feet per minute at an average temperature of 1200 C.

The matte which is formed and recycled to the top of the furnace shaft contains 75% Cu, 20.9% S, 3.8% Fe and 0.25% 0 and 70% of the copper in the concentrate charged is converted to blister in the first pass.

The complete material balance per ton of concentrate fed is given in FIG. 7. Overall copper recovery is 98.9% and the slag and eflluent gas compositions are:

Slag: Percent Cu 0.29

FeO 43.8

Ffiao 8.0 S 1.1 FeS 0.2 SiO, 35.0 CaO 4.6 A1 0 2.5 MgO 1.0

Gas:

-, 16.9 N; 81.1 52 2 Had I::IIIIIIII::::::::: 1I1

The process is autogenous except for a minor quantity of fuel (12.7 standard cubic feet of natural gas/ton of copper concentrate) which is burned for the auxiliary pyrite smelting.

The process of the invention thus consists in effect of two systems represented by the numerals I and II in FIG. I:

System I, where smelting and partial converting is taking place: This is a system in suspension with extremely fast process rates. Strongly oxidizing conditions prevail at the top of this system and are attenuated towards its bottom. Excess silica and high temperature exist along this system, and the reacting species stay for an extremely short time (0.054. sec.) in it.

System II, where smelting and dc-converting" (the opposite to converting reactions) are taking place: With the intimate mixing of some concentrate flashed towards the falling products of System I, the oxygen activity drops to an extremely low level (P l0- mm. of mercury) and any magnetite formed is reduced according to the reaction:

In comparison with System I, the lower phases in System II (blister copper and matte) are quiescent and almost stagnant with an interface of restricted area. With the proper atomization in System I, the interphase area among the reacting phases is much larger than in System II. Therefore the rate q" (lb. cu/min.) at which blister copper is "de-converted" in System II is substantially smaller than the rate q (lb. cu/rnin.) at which blister copper is produced in System I. The difference between q and q" constitutes the production capacity of the process, and its magnitude depends on the degree of atomization in the shaft furnace, the oxygen content of the atomizing gas and the furnace size. Although all of the oxidizing gas is added through the top of the shaft, System I opcrates with a substantially stoichiometric oxygen deficiency due to the continuous recycling of the matte. This oxygen deficiency, along with the excess of silica flux, the high converting temperature and the very short residence time in the shaft, prevent the undesirable oxidation of iron to magnetite. In the furnace hearth, on the other hand, the extremely low oxygen partial pressure, the horizontal counter-current flow of slag and matte, the long residence time and the pyritic cleaning, produce a slag very low in copper.

Two modifications of the process of the invention are shown in FIGS. 8 and 9. In FIG. 8, an auxiliary furnace shaft is provided for gas-atomized converting of the recycled matte to blister copper. The smelting of the copper sulfide concentrate in suspension takes place in the main shaft in which no matte is recycled, and a minor fraction of the concentrate is blown through Garr guns at the bottom of this shaft as in the operation shown in FIG. 1. The recycled matte is suspension-converted in an adjacent shaft, and both shafts are in direct communication at their lower ends directly above the furnace hearth. In FIG. 9, the suspension-smelting of the copper sulfide concentrate is effected obliquely in a direction such that, as in FIG. 8, the discharge ends of the converting and smelting suspension zones are in direct communication above the furnace hearth. In both these alternative modifications, a distinct step of matte-converting in suspension is combined with a suspension-smelting step in a manner such that a very low partial pressure of oxygen prevails at the point where the products of the two-steps emerge and fall into the common molten phases in the single furnace hearth.

It will be seen, accordingly, that the process of the present invention is characterized by the following advantages:

(1) Process continuity in a single furnace and thus lower labor and maintenance cost;

(2) Excellent utilization of the converting reaction heat with the result that the process is substantially autogenous;

(3) Extremely short residence time in the oxidation zone controls magnetite formation and minifies copper losses;

(4) The process operates with an artificial oxygen deficiency imposed and controlled primarily by matte recycling. This oxygen deficiency and the control nonoxidizing gas phase immediately above the settler also discourage magnetite formation and decrease copper losses;

(5) Both smelting and converting take place primarily in suspension out of contact with the walls of the reaction, and thus refractory wear is less than in other processes;

(6) Excess silica can be used during the converting step with resulting improvement in overall copper recovery;

(7) The process does not use tuyeres and/or lances which, in prior are processes, have been extremely sensitive to high temperature wear and corrosion;

(8) The countercurrent movement of matte and slag in the molten body in the furnace hearth, along with the cleaning treatment of the highly fluid siliceous slag, reduces the copper loss to a lower level than during conventional smelting;

(9) The systems in suspension have high mass and heat transfer coefficients due to their inherently high interphase areas. A high rate of smelting per unit volume of furnace is thus obtained;

(10) The continuous nature of the process makes it adaptable to automated process control; and

(11) The process efiluent gas is produced continuously and with a high sulfur dioxide content readily amenable to efiicient recovery of its sulfur content.

I claim:

1. In a continuous process for smelting a copper sulfide concentrate to produce matte and slag in the form of superimposed molten phases wherein a stream of an intimate mixture of particulate copper sulfide concentrate and particulate siliceous fluxing material is charged downwardly into a suspension smelting zone and an oxidizing gas is charged at high velocity in a direction converging downwardly and inwardly against the falling stream of concentrate-flux mixture so as to disperse the stream into a particulate smelting-promoting phase suspended in and carried downwardly in the oxidizing gas and thus form at the bottom of the vessel a molten body of matte and a supernatant layer of molten slag, the improvement which comprises (at) introducing into the lower portion of the falling particulate smelting-promoting phase a jet stream of reducing material at a rate suflicient to maintain the partial pressure of oxygen below about 10- mm. of mercury in the atmosphere adjacent the surface of the slag layer, (b) charging into the upper portion of a converting zone a downwardly directed stream of molten copper matte, (c) charging an oxidizing gas at high velocity into the downwardly moving stream of molten matte at a plurality of peripherally located positions so as to disperse said stream into a particulate converting-promoting phase, (d) directing the descending particulate converting-promoting phase through the aforesaid atmosphere adjacent the supernatant slag layer, (e) collecting below the falling streams of smelted and converted materials a common body of the molten resulting products of the aforementioned smelting and converting in the form of a bottom layer of blister copper, an intermediate layer of copper matte and a supernatant layer of slag, and (f returning the thus-formed molten copper matte to the top of the converting zone as the source of matte charged thereto.

2. The process according to claim 1 in which the smelting and converting are carried out in a common zone by introducing the molten matte in a stream directed downwardly through the center of said common zone, charging the concentrate-flux mixture peripherally around and into the stream of molten matte, and directing the converging streams of oxidizing gas into the admixed streams of molten matte and concentrate-flux mixture to form therebelow said common molten body of blister copper, matte and slag.

3. The process according to claim 1 in which the suspension-smelting and suspension-converting are carried out in separate zones the lower ends of which both communicate with the low-oxygen atmosphere adjacent the surface of the supernatant slag layer in a furnace hearth common to the two suspension zones.

4. The process according to claim 1 in which the copper sulfide concentrate suspension is charged obliquely above the hearth of the furnace in a direction such that the discharge ends of the converting and smelting suspension zones are in direct communication in the low oxygen atmosphere adjacent the surface of the supernatant slag layer in the furnace hearth.

References Cited UNITED STATES PATENTS 3,459,415 8/1969 Holeczy 7572 X FOREIGN PATENTS 890,282 2/1962 Great Britain 7560 L. DEWAYNE RUTLEDGE, Primary Examiner J. E. LEGRU, Assistant Examiner US. Cl. X.R. 75-74

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