Method and apparatus for the smelting of material such as ore concentrates

A method and apparatus for smelting an ore concentrate or the like wherein the concentrate is first melted in an oxidizing atmosphere and the smelt is aftertreated with reducing gases to recover the metal values. The improvement consists in positioning a plurality of rows of lances in a smelting reactor in the direction of molten metal flow, the spacing between the rows of lances being substantially greater than the spacing between individual lances in each row. The reducing gas is blown with a high kinetic energy through each lance to cause an area of toroidal bath movement to occur where the gases from each lance impinge against the moving smelt. The spacing between the rows of lances is sufficiently large so that a relatively quiescent zone exists between the areas of toroidal bath movement between each of the rows. The molten metal and a relatively metal-free slag are withdrawn separately from the furnace enclosure.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention is in the field of smelting ore concentrates, particularly 
sulfide type materials wherein the ore concentrate is smelted with 
relatively pure oxygen in a cyclone smelter, followed by an aftertreatment 
in which the smelt is reduced to produce the metal as a molten layer with 
an overlying slag layer, the conditions of aftertreatment being carefully 
controlled to improve the efficiency of the overall process, and to reduce 
the amount of metal that is left in the slag. 
2. Description of the Prior Art 
In German OS No. 2,348,105 there is described a method in which 
fine-grained sulfur-containing ore concentrates are introduced into a 
cyclone reactor into which an oxygen-rich gas is blown through a 
tangentially discharging supply line. The ore concentrate is continuously 
calcined and melted in the cyclone reactor in the turbulent conditions 
existing in the reactor. The smelt is collected below the cyclone reactor 
and consists of a lighter slag phase and a heavier metal phase such as 
copper matte. The smelt is then metallurgically aftertreated by means of 
reducing gases which are blown onto the smelt through a lance so that 
metal oxides which are contained in the slag phase are converted into 
droplets of metal matte. With such an aftertreatment with reducing gases 
under these conditions, the lighter slag phase still contains relatively 
large amounts of metal in admixture with the smelt, so that the two mixed 
phases are withdrawn to another location where they are subsequently 
separated from each other by means of a separate centrifuge. Beyond the 
reduction of the oxides, no other aftertreatment of the melt is carried 
out. 
SUMMARY OF THE INVENTION 
The present invention provides a method and apparatus for smelting of ore 
concentrates, particularly sulfidic ore concentrates, including a melting 
zone and a reactor for aftertreatment of the smelt. In the reactor, there 
are a plurality of rows of lances operating under conditions such that 
slag conditioning is carried out under optimum conditions and material 
transfer as well as heat transfer are carried out quickly. The process of 
the present invention is characterized by a high space-time yield and the 
lighter slag phase and the heavier metal-containing phase no longer need 
be separated by means of a separate centrifuge. 
In accordance with the method of the present invention, the aftertreatment 
of the smelt is carried out by blowing reducing gases through a plurality 
of rows of spaced lances under conditions sufficient to form relatively 
fluid slag and heavier metal-containing phases which can be conveniently 
withdrawn from separate discharge areas in the furnace housing. 
In accordance with the present method, the gases are continuously blown 
onto the smelt through a plurality of top blowing lances in the form of 
concentrated streams of high kinetic energy. These high energy streams are 
continuously introduced to the phase boundary layer between the slag and 
the smelt and thoroughly mix the two so that heat transfer and material 
transfer proceed in the reactor at high velocities with the result that 
the lighter slag phase and the heavier metal containing phase can be 
separately withdrawn from the reactor quickly without the necessity of 
providing a separate centrifuge. 
In a preferred form of the present invention, the reduction gases which are 
blown onto the smelt consist of a hydrocarbon fuel gas such as methane, 
ethane or preferably propane in admixture with oxygen in less than 
stoichiometric amounts necessary for complete combustion so that the 
reduction reaction can be precisely controlled in terms of reduction 
potential to achieve a specific, selective degree of refining. For 
example, the conditions can be selected so that there is little or no 
reduction of any iron oxides present. Furthermore, the conditions can also 
be adjusted to volatilize off rare metal oxides such as germanium oxides 
and other rare metal oxides. 
The spacing between the rows of lances is correlated with the spacing 
between the individual lances in a row so as to produce highly turbulent, 
toroidal reaction zones immediately beneath each lance, which zones are 
separated from similar reaction zones in the next row of lances by a 
relatively quiescent liquid zone which prevents reverse mixing of slag 
constituents into the metal being refined in a previous row of lances. 
Furthermore, the kinetic energy of the reducing gases is adjusted so that 
the toroidal-shaped reaction areas beneath the lances are contiguous with 
each other or actually overlap slightly with each other. Each row of 
lances thus provides a separate reaction system, and the smelt slowly 
flowing under the lances is continuously reduced in a step-by-step 
reaction when the lances are fed with reduction gases having reduction 
potentials which increase from one row of lances to the next. In other 
words, the oxidation potential of the fuel gas-oxygen mixture fed to the 
lances decreases from one row of lances to the next so that the last row 
of lances involves the highest reduction potential and, of course, the 
lowest oxidation potential. 
The apparatus of the present invention includes a common furnace housing 
for smelting and reaction zones. A smelting cyclone is located within the 
smelting zone and is provided with means for introducing an ore 
concentrate therein. Means are also provided for introducing oxygen gas 
into the smelting cyclone. The furnace housing has a floor on which metal 
melted in the smelting cyclone collects, the floor being shaped to permit 
flow of molten metal and slag to occur from below the smelting cyclone 
into a reaction zone located in the furnace housing. In the smelting zone, 
a plurality of rows of lances are positioned with the spacing between 
individual lances in a row being substantially smaller than the spacings 
between rows. Means are provided for introducing reducing gases at high 
kinetic energy into each of the lances for impingement against the melt 
flowing therebeneath. Means are provided for withdrawing molten slag from 
the furnace housing and for separately withdrawing molten metal therefrom. 
In a peferred embodiment of the invention, the spacings between rows of 
lances are at least twice the spacing between individual lances in a row.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The invention, together with additional advantages and features are 
explained in greater detail in the embodiments of the invention 
schematically illustrated in the drawings. 
FIG. 1 illustrates a pyrometallurgical furnace installation for smelting 
fine-grained sulfidic copper ore concentrate which is supplied together 
with other reactants by means of an inlet 10 to a screw conveyor 11. The 
conveyor 11 supplies the materials through an inlet line 12 into the top 
of a melting cyclone 13. A stream of technically pure oxygen is admitted 
tangentially of the cyclone reactor 13 through a line 14. The finely 
divided feed material is calcined and melted in the smelting cyclone 13, 
whereupon the molten material drops into a furnace defined by a furnace 
housing 15. The melting cyclone 13 can be cooled by means of connecting 
the same to a water inlet line 16, and the cooling water is withdrawn by 
means of a return line 17. 
The temperatures in the smelting cyclone 13 may vary from about 
1500.degree. to 2400.degree. C., utilizing technically pure oxygen as the 
oxidizing gas. 
The raw material is heated very rapidly to these high temperatures in a 
fraction of a second while it is still in suspension or in a highly 
turbulent state. The combustion of the sulfur and other oxidizable 
components in the oxygen atmosphere usually supplies sufficient heat in 
order to permit the calcining and melting processes to proceed 
autogenously. 
A smelt 18 collects below the smelting cyclone 13 along the floor of the 
furnace housing 15, the smelt flowing in the direction of the arrow 19 by 
virtue of a sloping floor in the furnace enclosure. The smelt thus passes 
from the smelting zone to the reaction zone, and may pass underneath a 
partition 20 which is immersed into the smelt 18 to separate the oxidizing 
atmosphere in the smelting zone from the reducing atmosphere prevailing in 
the aftertreating, reaction zone. To this end, the smelting zone can be 
provided with its own waste gas exhaust line (not shown). 
The furnace may also be provided with an additional burner 21 in one wall 
of the furnace housing 15 to supply hot gases for compensating for heat 
losses. 
In the reaction zone, there is a plurality of rows of lances, the first row 
of which contains lances 22A, 22B and 22C, the second row containing 
lances 23A, 23B and 23C, and the third row in the direction of metal 
movement consisting of lances 24A, 24B and 24C. It is important to space 
the lances with respect to each row, and the spacing between rows, in 
order to secure the best results. The lances are fed with reducing gases 
through inlets 25, 26 and 27, respectively. These inlets deliver a mixture 
of a hydrocarbon fuel gas such as propane in admixture with small amounts 
of oxygen, the amount of oxygen being insufficient to provide for complete 
combustion of the hydrocarbon fuel gas. The amount of oxygen progressively 
decreases from inlet 25 through inlet 26 through inlet 27. In other words, 
the reducing potential increases in the direction of metal movement, and 
the oxidation potential, of course, decreases in that direction. The 
oxygen partial pressure in the gas can be as low as 10.sup.-12 atmospheres 
in the final lance, and is typically less than 10.sup.-5 atmosphere in all 
the lances. The high kinetic energy in the confined streams causes the 
surface of the melt to be indented somewhat as indicated in FIG. 1 by 
depressions 28, 29 and 30, respectively. As best seen in FIG. 2, these 
depressions take the form of a toroidal-shaped bath movement indicated in 
dotted lines, and this movement penetrates the molten bath to a specific 
bath depth. This assures a thorough agitation at least in the slag phase 
so that the processes of heat and material transmission take place with 
high velocities. As seen in FIG. 2, the pressure of the fuel gases being 
fed through the lances can be adjusted so that the toroidal depressions 28 
are just in contact with each other, or they can actually overlap. 
One of the important elements of the present invention is the proper 
spacing to be achieved between the rows of lances. We have found, for 
example, that it is important that the lances in a given row be spaced by 
a distance at least twice that by which the individual lances are 
separated in a given row. For example, the lances 23A, 23B, and 23C are 
spaced by a distance from the lances 22A, 22B, and 22C which is at least 
twice the spacing between the individual lances 22A, 22B, and 22C. This 
spacing provides a relatively quiescent zone between the rows of lances 
which avoids reverse mixing or backward mixing between the toroidal 
depressions 28, 29, and 30, respectively. Consequently, slag bath 
particles which have been removed in the first row of lances are not 
returned back to the vicinity of the reaction zone in that first row. 
Consequently, it is possible to substantially reduce the amount of copper 
in the slag phase, with a copper content of 0.5% or less in the slag phase 
being readily achievable. 
As a specific example, we can use a lance spacing of about 0.5 meters 
between the lances in a given row, and a spacing between rows of about 
1.15 meters. 
The heavier, metal-containing phase 31 is withdrawn through an outlet 32 on 
one side of the furance assembly, the outlet 32 being lower than an outlet 
33 on the opposite side of the furnace which is used to discharge slag off 
the floor of the furnace beyond the reaction zone. 
The method and apparatus of the present invention provide a very high 
reduction efficiency for treating sulfidic type ore concentrates, 
particularly in the production of copper. The reaction conditions can be 
very carefully controlled by controlling the gas pressure in the reaction 
zone, as well as the gas composition. Consequently, it is possible with 
the process and apparatus of the present invention to achieve selective 
reducing of the various metal oxides in the ore concentrate, with 
volatilization of rare metal oxides. The careful reaction conditions 
achieved in the process of the present invention makes it unnecessary to 
aftertreat the slag for the recovery of metal. 
It should be evident that various modifications can be made to the 
described embodiments without departing from the scope of the present 
invention.