AU480552B2 - A process for obtaining metals from oxidised ores or concentrates - Google Patents

Description

S9 04 6 73 or This invention relates to the treatment of ores iron concentrates containing a metal less oxidisable than form. and, in addition, iron at least partly in oxidised The combined heat and chemical treatment of oxidised than ores of copper, nickel and other metals less oxidisable The firs.t iron is normally carried out in several stages. the melting stage comprises reduction at a temperature below at a point of the metal, and the second stage a treatment is obtained. higher temperature during which the liquid metal 1,325,488 for Thus, in the process according to French Patent can be carried the treatment of nickeliferous ores, production the follow- out using coke dust as the reducing agent, whilst combustion of ing operation is carried out by blowing oxygen, the iron producing the required increase in temperature. It has also been proposed (French Patent 2,040,425) Agglomerates to treat nickel ores in the following manner. iron oxide containing the ore, which consists of nickel oxide, in a first and gangue, and a carbonaceous fuel, are prepared stage. These agglomerates are then heated to a temperature their of from 1000 to 1200 C, i.e. to a temperature below 0

nickel oxide melting point, which results in reduction of the metallic state. and, possibly, of part of the iron oxide to the The "calcined" agglomerates, which optionally have then intro- non-powdered carbonaceous fuel added to them, are and duced into a rotary melting furnace heated by burners, 0 results heated to a temperature of from 1450. to 1550 C. This a similarly in the formation of a liquid ferronickel alloy and liquid scoria which is separated by decantion. By selecting the quantities of carbonaceous reducing it is agent added to the ore or "calcined" agglomerates, 480552

59,046 73 possible to establish more or less reducing conditions. This process is complicated because it requires two different furnaces, one for "calcining" the agglomerates and the other for melting, the melting furnace being of the rotary type to facilitate rabbling. On the other hand, it is difficult to act on the composition of the metal obtained other than through the carbon content of the agglomerates, because a modification to the atmosphere prevailing in the rotary furnace has little or no effect due to the poor con- tact between this atmosphere and the bath. In another known process (French Patent 2,020,720), the ore is initially agglomerated with coal, after which the agglomerates are passed downwards first through a carbonisat- ion chamber, whose walls have openings through which the volatile materials produced escape, and then through the main chamber of a shaft furnace. This process obviously has the advantage of simplicity. However, in cases where it is desired to control the compositions of the metal and slag with a degree of precision, it is only possible to act by way of the atmosphere prevailing at the bottom of the furnace within narrow limits beyond which there is a danger of an excessive reduction in temperature. One disadvantage common to all these processes is that they lack flexibility and are difficult to carry out in such a way as to ensure optimum yield from the economic point of view. This optimum yield has to be obtained with allowance in particular for the fact that there is a relat- ionship between the composition of the metal bath and the composition of the slag, and for the fact that the purity

-3 480552

59,046 /73 of the metal can be improved by accepting higher losses in

the slag. In French Patents 353,029 and 586,539, it was pro- posed to act on the composition of the metal obtained by

introducing iron or iron ore into the melting bed, but

unfortunately these additions in no way lessened the lack of flexibility which is a criticism of conventional

processes. There are three separate operations which take place successively during reduction, namely reduction of all the oxide of the metal selected and of a little oxide of undesir- able, more oxidisable metals (for example iron), the generat- ion of heat to melt the reduced metal and the adjustment of the contents of the metal bath and of the scoria to the required levels through reoxidiation of the undesirable metal. It is clear that it is not easy to obtain a high degree of flexibility if these three operations interfere with one another or are governed by the same parameters. Conventional processes use carbon introduced into the charge as reducing agent for the first operation and as fuel for the second. On the other hand, an oxygen-containing gas is generally introduced at the bottom of the furnace,

participating in the second operation as a supporter of combustion, and in the third operation as oxidising agent. The quantities of carbon and oxygen introduced are essentially determined by the temperature to be reached, and the condit- ions are necessarily of a highly reducing nature in the first operation and of a highly oxidising nature in the last oper- ation, which explains the difficulties encountered in keeping

4- 480552

59,046 m3 possible to establish more or less reducing conditions. This process is complicated because it requires

two different furnaces, one for "calcining" the agglomerates

and the other for melting, the melting furnace being of the

rotary type to facilitate rabbling. On the other hand, it

is difficult to act on the composition of the metal obtained

other than through the carbon content of the agglomerates,

because a modification to the atmosphere prevailing in the

rotary furnace has little or no effect due to the poor con-

tact between this atmosphere and the bath.

In another known process (French Patent 2,020,720),

the ore is initially agglomerated with coal, after which the

agglomerates are passed downwards first through a carbonisat-

ion chamber, whose walls have openings through which the

volatile materials produced escape, and then through the

main chamber of a shaft furnace.

This process obviously has the advantage of

simplicity. However, in cases where it is desired to

control the compositions of the metal and slag with a degree

of precision, it is only possible to act by way of the

atmosphere prevailing at the bottom of the furnace within narrow limits beyond which there is a danger of an excessive

reduction in temperature.

One disadvantage common to all these processes is

that they lack flexibility and are difficult to carry out

in such a way as to ensure optimum yield from the economic

point of view. This optimum yield has to be obtained with

allowance in particular for the fact that there is a relat-

ionship between the composition of the metal bath and the

composition of the slag, and for the fact that the purity

3 480552

59,04 6 /73 losses in of the metal can be improved by accepting higher the slag. pro- In French Patents 353,029 and 586,539, it was obtained by posed to act on the composition of the metal bed, but introducing iron or iron ore into the melting lessened the lack unfortunately these additions in no way

of flexibility which is a criticism of conventional processes. take place There are three separate operations which of all the successively during reduction, namely reduction oxide of undesir- oxide of the metal selected and of a little iron), the generat- able, more oxidisable metals (for example the adjustment of ion of heat to melt the reduced metal and scoria to the the contents of the metal bath and of the the undesirable required levels through reoxidiation of metal. a high It is clear that it is not easy to obtain interfere degree of flexibility if these three operations parameters. with one another or are governed by the same into Conventional processes use carbon introduced operation and as the charge as reducing agent for the first

fuel for the second. On the other hand, an oxygen-containing of the furnace, gas is generally introduced at the bottom a supporter of participating in the second operation as agent. combustion, and in the third operation as oxidising are essentially The quantities of carbon and oxygen introduced and the condit- determined by the temperature to be reached, in the first ions are necessarily of a highly reducing nature the last oper- operation and of a highly oxidising nature in in keeping ation, which explains the difficulties encountered

59,046 n3 THE COMPOSITION OF THE METAL AND OF THE SLAG WITHIN THE

LIMITS SELECTED. THE PROCESS ACCORDING TO THE INVENTION USES DIFFERENT MEANS FOR EACH OF THE OPERATIONS. FOR THE FIRST REDUCING OPERATION. IT MAKES USE OF THE OBSERVATION THAT. IN AN AGGLOMERATE CONTAINING BOTH CARBON AND METAL OXIDES, THE METAL OXIDES ARE REDUCED BY THE CARBON IRRESPECTIVE OF THE TYPE OF ATMOSPHERE SURROUNDING THE AGGLOMERATES. FOR THE SECOND OPERATION, IT MAKES USE OF SUCH APPARATUS AS COMBUSTION CHAMBERS WHICH PRODUCE GASES OF HIGH TEMPERATURE OUTSIDE THE ZONE IN WHICH THE ORE IS SITUATED. THE COMPOSITION OF SAID GASES BEING ADJUSTED, BY THE USE OF OXYGEN. IN ACCORDANCE WITH THE IRON CONTENT OF THE METAL AND THE METAL CONTENT IN THE SLAG. FOR THE THIRD OPERATION, IT USES A CONTROLL- ABLE INJECTION OR OXYGEN-CONTAINING GAS. A PROCESS OF THIS KIND HAS A MUCH HIGHER DEGREE OF FLEXIBILITY THAN CONVENTIONAL PROCESSES BY VIRTUE OF THE FACT THAT THE QUANTITY OF CARBON INTRODUCED WITH THE ORE CAN BE FIXED ON THE SOLE BASIS OF THE COMPOSITION OF THIS ORE, AND CORRESPONDS TO THE QUANTITY REQUIRED FOR REDUCING THE REQUIRED METAL OXIDE WITH ONLY A SLIGHT EXCESS TO ENSURE THE REDUCTION IS COMPLETE AT ALL POINTS. FEEDING OF THE COMBUSTION CHAMBERS IS REGULATED TO OBTAIN THE MOST FAVOURABLE UTILISATION OF ENERGY IRRESPECTIVE OF THE COM- POSITION OF THE ATMOSPHERE PREVAILING IN THE FURNACE, AND THE QUANTITIES OF OXYGEN SUBSEQUENTLY INTRODUCED ARE CALCULATED SOLELY ON THE BASIS OF THE QUANTITY AND PURITY OF THE METAL IT IS REQUIRED TO OBTAIN. THE PROCESS ACCORDING TO THE INVENTION COMPRISES THE FOLLOWING STAGES:

59,04 6 n3 preparing agglomerates containing, in intimate ad-

mixture the ore or concentrate and a quantity of carbon

sufficient for reducing all the required metal and part of

59,04 6 R3 the iron into the metallic state,

treatment in a sha4 furnace in the presence of hot gases produced outside the furnace whose composition is adjusted on the principle that,if the metal produced

shows an excessive iron content, the proportion of oxygen

is increased, and that the proportion of oxygen is reduced

if the slag contains too much of the required metal, and

separating the liquid metal and liquid slag.

A binder whose composition is derived from that

of the required slag by subtracting the gangues present in

the ore or concentrate, is preferably used for preparing

the agglomerates.

A small quantity of gasifiable substances may

optionally be added to the charge of the furnace in large

portions so as to produce in the mass voids which promote

circulation of the gases. Non-powdered carbonaceous fuel

can be employed for this purpose, being used in a small

proportion in relation to the total charge.

The hot gases are with advantage produced in com-

bustion chambers equipped with burners and arranged outside

the furnace, the oxygen content being adjusted by means of

nozzles injecting compressed air or oxygen which open either

into the combustion chamber or into the duct connecting it

to the shaft of the furnace or directly into the furnace.

The agglomerates are heated in the upper part of

the furnace and, when the temperature is sufficient (around

8000C or higher or lower depending upon the metals), the re-

action between the carbon and the oxides commences. All the

metal and some of the iron are reduced to the metallic state

irrespective of the atmosphere prevailing in this part of

59,04 6 n3 the furnace. This is because, in each agglomerate, reaction

of the carbon with the oxides produces an evolution of

gaseous CO and CO 2 which, directed towards the outside,

isolates the interior from the surrounding atmosphere.

In the lowest zones where the temperature is higher,

melting begins and is accompanied in particular by the form-

ation of droplets of molten metal charged with iron. Depend- ing upon the type of atmosphere prevailing in this zone, the

iron then undergoes selective oxidation by which it is

restored to the oxide state in a more or less large quantity.

In view of the limited size of these droplets, the chemical

equilibrium is reached before the droplets fall to the bottom

of the furnace. In this way, it is possible very easily to

regulate the operation either to give a highly pure metal

or a minimal loss in the slag or an intermediate result

corresponding to an economic optimum.

One particularly favourable application of the

invention is where the reduced ore is a concentrate obtained

by the segregation process. This is because concentrates of this kind normally consist of a core containing the carbon

and iron oxide and of a peripheral layer of the required

metal oxidised to a greater or lesser extent. Preparation of the agglomerates merely involves agglomerating these concen-

trates, which are in the form of extremely fine particles

microns), with a binder. X, w' In the case of so-called TORCOI/cupriferous con- centrates, whose composition is as follows:

55 to 80% of copper, some of which is sometimes

oxidised, the rest being metallic,

2 to 15% of carbon,

59,04 6 n3 2 to 20% of iron oxide, above all Fe3 0 4

rest: various gangues,

the process can be carried out as follows:

1) Agglomerating the concentrates with a binder whose

composition and quantity are calculated in such a way that

melting of the agglomerates produces from 10 to 60 kg of

slag for 100 kg of copper, this slag containing: 15 to

of Si02, 10 to 35% of CaO MgO, 0 to 30% of A1 20 3 and

to 60% of FeO;

2) Treating the agglomerates in a vertical furnace

at a temperature above the melting point of copper in the

presence of hot gases whose rate of flow and composition

are calculated in such a way that, following combustion of

the carbon in the charge, the excess oxygen leaves 0.2 to

2% of the copper in oxidised form, and a quantity of iron

amounting to between 1 and 5% of the weight of the copper

in metallic form.

3) Separating the liquid metal and liquid scoria.

The limits to the quantity and quality of the slag

correspond on the one hand to the fact that the slag should

be sufficiently fusible to allow suitable separation by

decantation and, on the other hand, to the need to have the

smallest possible quantity of slag.

Calculation shows that, at equilibrium, the Cu and

Fe contents of the metal: (Cu)m and (Fe) and of the slag:

(Cu)s and (Fe)s are all connected by the following relation

for a temperature T:

(Cu) s (Fe) m K(T) (Cu) (Fe)s

59,04 6 /73 Where K is a constant governed solely by T, (Cu)m is

approximately 1, Fe/Cu (Fe)s L where Fe/Cu is the ratio of the contents in the concentrate and L the quantity of slag based on the weight of copper produced. The loss of copper in the slag PCu, based on the metal produced, is equal to (Cu) s L. It follows from this that PCu (Fe)m K Fe/Cu

Experience has in fact shown that, for a concen- trate with an Fe/Cu value of 0.17, the values are as follows:

(Fe)m (Cu)s PCu

0.5 0.16

0.7 0.23

3 0.8 0.27 1 2.5 0.8 5 1.6

Accordingly, for any given concentrate, there is

a range of conditions for operating the furnace under which

it is possible to obtain the desired results. Conditions

of an excessively oxidising or excessively reducing nature

result in departure from the favourable zone either through

an exaggerated loss of copper or through an excessive con-

centration of iron in the metal.

The width of the range and the value of the product

59,04 6 n3 (Fe)m PCu are governed by the coefficient K which varies

as a function of the temperature. It is of advantage to

maintain the lowest possible temperature, although the

viscosity of the slag does impose a limit in this respect

because it has to be low enough to ensure effective separat-

ion of the metal issuing from the furnace.

In practice, slags with the compositions specified

earlier enable favourable results to be obtained with the

usual "TORCO" concentrates. For example, a "TORCO" concentrate with the follow-

ing percentage coposition was subjected to treatment:

Cu Fe C 0 As Mn S302 CaO

69.8 12 4 6.5 1 0.2 4.5

A12 0 3 MgO S C1 0.8 0.1 0.5 0.1 These concentrates were agglomerated by the addition of bentonite containing 60% of SiO 2 and 18% of A12 0 3 and

hydraulic lime containing 23% of SiO 2 and 60% of CaO, in quantities of 2.5 kg and 5 kg, respectively, per 100 kg of concentrate. The agglomerates, 10 to 25 mm in diameter, were dried and then introduced at the top of a vertical furnace. This furnace (cf. drawing) comprises a charging hopper a rectangular shaft 3.75 m tall and 5m x im

in section, the walls of which are formed by water-circulation tanks a hearth which is supported by jacks and on which the tanks rest when the furnace is in operation (the hearth has a chrome-magnesia lining); ten fuel-burning

59,046 /73 combustion chambers opening into the furnace which, in addition to the burner are provided with a lateral inlet for additional air The copper and the slag are collected together in a covered heat-insulated forehearth where they decant. The slag is collected by continuously running off from an overflow, the metal is removed by running off every few hours. The furnace is fed with agglomerate at a rate of 8 t/hour with 70-80 mm. lumps of coke added at a rate of 0.4 t/hour. The combustion chambers each burn 50 kg of fuel per hour and each receive 800 m3/hour of air which corresponds to an excess of air of The metal run off essentially contains 96% of copper, 3% of iron and 1% of arsenic. It has the character- istics of a blister copper and is fed into an anode melting furnace. The slag, which is produced at a rate of 40 kg per 100 kg of metal, has the following composition: FeO 53.5%, SiO 2 27.5%, CaO 13.5%, A12 03 MgO Cu 0.7%.

Claims (1)

1. 59,046 n3

   THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS&-

   CONTAINING 1. A PROCESS FOR TREATING ORES OR CONCENTRATES

   A METAL LESS OXIDISABLE THAN IRON AT LEAST PARTLY IN IRON AND

   OXIDISED FORM IN WHICH AGGLOMERATES CONTAINING THE ORE OR CON-

   AGENT ARE PREPARED AND TREATED IN A VERTICAL CENTRATE AND A REDUCING

   FURNACE IN THE PRESENCE OF HOT GASES PRODUCED OUTSIDE THE FURNACE,

   A LITTLE IRON AND A LIQUID A BATH OF THE LIQUID METAL CONTAINING

   OF THE METAL ARE OBTAINED AT THE BOTTOM SLAG CONTAINING A LITTLE

   OF THE FURNACE, AND THE BATH IS SEPARATED FROM THE LIQUID SLAG

   AGGLOMERATES CONTAIN A QUANTItY OF CARBON SUFFICIENT WHEREIN THE

   REQUIRED METAL AND SOME OF THE IRON TO THE FOR REDUCING ALL THE

   OR CONCENTRATE ARE IN METALLIC STATE, WHEREIN THE CARBON AND THE ORE

   AND WHEREIN THE COMPOSITION INTIMATE ADMIXTURE IN EACH AGGLOMERATE,

   IN THE BOTTOM PART OF THE FURNACE IS OF THE ATMOSPHERE PREVAILING

   IF THE METAL PRODUCED SHOWS AN REGULATED ON THE PRINCIPLE THAT,

   THE PROPORTION OF OXYGEN IS INCREASED, EXCESSIVE IRON CONTENT,

   IS REDUCED IF THE SLAG CONTAINS AND THAT THE PROPORTION OF OXYGEN

   TOO MUCH OF THE REQUIRED METAL.

   AS CLAIMED IN CLAIM 1, WHEREIN THE ATMOSPHERE 2. A PROCESS

   IN THE BOTTOM PART OF THE FURNACE IS OBTAINED BY SIMULTANEOUSLY

   COMBUSTION CH- INTRODUCING INTO IT HOT CRUDE GASES EMANATING FROM

   BURNERS AND ARRANGED OUTSIDE THE FURNACE, AMBERS EQUIPPED WITH

   OF NOZZLES INJECTING THE OXYGEN CONTENT BEING ADJUSTED BY MEANS

   COMPRESSED AIR OR OXYGEN.

   PROCESS CLAIMED IN CLAIM 1 3. THE APPLICATION OFTHE

   BY THE SEGREGATION TO THE TREATMENT OF COPPER CONCENTRATES OBTAINED

   PROCESS, WHEREIN IT COMPRISES THE FOLLOWING stages: 5 9,04 6 73 a binder whos S Agglomerating the concentrates with such a way that composition and quantity are calculated in of slag melting of the agglomerates produces 10 to 60 kg 15 to 45% of per 100 kg of copper, this slag containing

   SiO 2 10 to 35% of CaO MgO, 0 to 30% of A1 2 0 3 and 20 to

   of FeO, r, s

   treating the agglomerates in a2shaft- furnace at e

   in the prese temperature above the melting point of copper are calcul of hot gases whose rate of flow and composition carbon in in such a way that, following combustion of the copper charge, the excess oxygen leaves from 0.2 to 2% of betweer oxidised form, and a quantity of iron amounting to

   1 and A0% of the weight of the copper in metallic form,

   separating the liquid metal and liquid scoria.

   4. A process for treating ores or concentrates con- lea taining iron and a metal less oxidisable than iron at

   partly in oxidised form substantially as hereinbefore describe.

   DATED this 8th day of AUGUST, 1973

   COMPAGNIE GENERALE D'ELECTROLYSE DU PALAIS

   EDWD. WATERS SONS, Patent Attorneys, Russell Street, MELBOURNE, ND/MF. AUSTRALIA.

   S that this and the preceding pages are a true A.tcopy -f pages of the -n originally lodged. 9 7 Allr 7~ or17 197

   inV

   59,04 6 n3 THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:-

   1. A PROCESS FOR TREATING ORES OR CONCENTRATES CONTAINING

   IRON AND A METAL LESS OXIDISABLE THAN IRON AT LEAST PARTLY IN OXIDISED FORM IN WHICH AGGLOMERATES CONTAINING THE ORE OR CON-

   CENTRATE AND A REDUCING AGENT ARE PREPARED AND TREATED IN A VERTICAL FURNACE IN THE PRESENCE OF HOT GASES PRODUCED OUTSIDE THE FURNACE, A BATH OF THE LIQUID METAL CONTAINING A LITTLE IRON AND A LIQUID

   SLAG CONTAINING A LITTLE OF THE METAL ARE OBTAINED AT THE BOTTOM

   OF THE FURNACE, AND THE BATH IS SEPARATED FROM THE LIQUID SLAG

   WHEREIN THE AGGLOMERATES CONTAIN A QUANTITY OF CARBON SUFFICIENT

   FOR REDUCING ALL THE REQUIRED METAL AND SOME OF THE IRON TO THE METALLIC STATE, WHEREIN THE CARBON AND THE ORE OR CONCENTRATE ARE IN INTIMATE ADMIXTURE IN EACH AGGLOMERATE, AND WHEREIN THE COMPOSITION

   OF THE ATMOSPHERE PREVAILING IN THE BOTTOM PART OF THE FURNACE IS REGULATED ON THE PRINCIPLE THAT, IF THE METAL PRODUCED SHOWS AN EXCESSIVE IRON CONTENT, THE PROPORTION OF OXYGEN IS INCREASED,

   AND THAT THE PROPORTION OF OXYGEN IS REDUCED IF THE SLAG CONTAINS

   TOO MUCH OF THE REQUIRED METAL.

   2. A PROCESS AS CLAIMED IN CLAIM 1. WHEREIN THE ATMOSPHERE

   IN THE BOTTOM PART OF THE FURNACE IS OBTAINED BY SIMULTANEOUSLY

   INTRODUCING INTO IT HOT CRUDE GASES EMANATING FROM COMBUSTION CH-

   AMBERS EQUIPPED WITH BURNERS AND ARRANGED OUTSIDE THE FURNACE.

   THE OXYGEN CONTENT BEING ADJUSTED BY MEANS OF NOZZLES INJECTING

   COMPRESSED AIR OR OXYGEN.

   3. THE APPLICATION OF THE PROCESS CLAIMED IN CLAIM 1

   TO THE TREATMENT OF COPPER CONCENTRATES OBTAINED BY THE SEGREGATION

   PROCESS. WHEREIN IT COMPRISES THE FOLLOWING stages: 59,046 /73 wh. Agglomerating the concentrates with a binder such a way th. composition and quantity are calculated in 60 kg of slag melting of the agglomerates produces 10 to 15 to 45% of per 100 kg of copper, this slag containing

   Si0 2 10 to 35% of CaO MgO, 0 to 30% of A1 2 0 3 and 20 t

   of FeO,

   -7 treating the agglomerates in a-saf-t- furnace at

   in the pre temperature above the melting point of copper are calc of hot gases whose rate of flow and composition carbon i in such a way that, following combustion of the 2% of coppe charge, the excess oxygen leaves from 0.2 to to betwe oxidised form, and a quantity of iron amounting tSZ 1 and/1OI of the weight of the copper in metallic form,

   separating the liquid metal and liquid scoria.

   4. 4 process for treating ores or concentrates cor at IE taining iron and a metal less oxidisable than iron

   partly in oxidised form substantially as hereinbefore

   describe.

   DATED this 8th day of AUGUST, 1973

   COMPAGNIE GENERALE D'ELECTROLYSE DU PALAIS

   EDWD. WATERS SON! Patent Attorneys, Russell Street, MELBOURNE, AUSTRALIA. ND/MF.

   ;hat this and the preceding pages re a true copy -ef pages of the n origina!ly lodged. 7 AHII, 1/97 L. I ri

   9,04 6 [73