CA1211292A

CA1211292A - Method for separating nonferrous metals from iron- oxide-containing residues

Info

Publication number: CA1211292A
Application number: CA000430649A
Authority: CA
Inventors: Wilhelm Kandler; Gerhard Mitter; Adolf Hoheneder
Original assignee: Voestalpine AG
Current assignee: Voestalpine AG
Priority date: 1982-06-18
Filing date: 1983-06-17
Publication date: 1986-09-16
Also published as: AT375405B; DE3366968D1; EP0097144A1; ZA834360B; JPS596337A; ATA236782A; EP0097144B1

Abstract

ABSTRACT OF THE DISCLOSURE:

There is described a method for separating nonferrous metals from iron-oxide-containing residues by thermal chlorination of the residues with elementary chlorine at an elevated temperature and cooling of the reaction gases with a sublimation of the sublimable chlorides formed. As starting material, converter dust from flue gases of the steel production or fine flue dust from blast furnaces is used. As reaction gas, technically pure chlorine gas in an excess of at least 2 : 1 relative to the stoichiometric amount necessary for the chlorination of the nonferrous metals to be separated, if desired mixed with inert gas, is used. The reaction temperature during the chlorination is maintained at between 600 and 800° C.

Description

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The invention relates to a method for separating nonferrous metals from iron-oxide~containing residues by thermal chlorination of the residues by means of element-ary chlorine at an elevated temperature and cooling of the reaction gases with a sublimation of the sublimable chlorides formed.
Methods of this kind are already known and described, for instance, in French patent No. 1,242,939 and in German patent No. 1,180,946. According to these methods, oxidic materials, such as metallurgical intermediate and waste products in lumpy form, i.e. in the form of pellets, briquets and the like, are reacted in a shaft furnace with chlorine-containing gases~ with a temperature of more than 800 C being applied. The reaction gas, which is drawn off on top of the shaft furnace according to German patent NoO
1,180,946 r is composed of the C0-, C02--and H20-containing ~ases coming from the heating zone of the shaft furnace, of the gases resulting from the chlorination and of the met21 chlorides. The hlorirlation gas is ntroduced into the lower part of the shaft furnace and conducted upwardly.
The amount of chlorine used corresponds to the stoichio-metric ratio based on the sublimable nonferrous metals.
This method is disadvantageous inasmuch as, at the high temperature applied, also a considerable amount of iron is chlorinated in addition to the nonferrous metals to be removed, and the volatile chlorides formed are com-monly precipitated during cooling of the reaction gas.

A neat separation of the nonferrous metals is not attaina~e.
Moreo~er, the plant materials and the tubings will be af-fected to quite a considerable extent at the high tempe-- 1 ' ~c~

~LZ~2~2 rature.
With the known technology, an excess of chlorine be-yond the stoichiometric ratio has to be prevented, because the recovery of the excessive chlorine is not possible for technical and economical reasons.
The invention aims at avoiding the disadvantages and difficulties pointed out and has as its object to ensure an exact separation of the nonferrous metals forming sub-limable chlorides, from the iron-oxide-containing residues, while avoiding chlorine losses, with the reaction speed being elevated as compared to the known mode of operation and the plant parts b~ing spared. Furtnermore, the method according to the invention is to provide, in a simple man-ner, the possibility of separating chlorinatable, but un-sublima~le nonferrous metals, such as magnesium and cal-cium, from the iron-oxide-containing residues.
This object is achieved according to the invention with a method of the initially defined kind by the com-bination of the following measures:
a~ that, as starting material, converter dust from flue gases of the steel production or fine flue dust from blast furnaces is used;
b) that, as reaction gas, technically pure chlorine gas in an excess of at least 2 1 relative to the stoichi-ometric amount necessary for the chlorination of the nonferrous metals to be separated, if desired mixed with inert gas, is used;
c) that the reaction temperature during the chlorination is maintained at between 600 and 800 C.
The first measure, i.eO to use the fine-particle LZ~2 starting material mentioned, with grain sizes of less than 100 ~m being preferred, but such up to about 3 mm grain size being processable alike, is one of the reasons for the high reaction speed, because charging substances having these particle sizes also have large surfaces. They are also particularly suitable to be processed by the fluidized bed method, since they can be kept floating by the usual flow speeds of the reaction gas.
The second measure, i.e. the utilization of a stoi-chiometric excess of chlorine gas, based on the nonferrous metals to be removed, also causes an acceleration of the reaction, wherein the chlorine gas, which may also cor.-tain a gas that is inert with regard to the reaction, such as nitrogen or a noble gas, serves as a -carrier gas in the chlorination phase and even in the sublimation phase.
After separation of the sublimable products, the chlorine gas that has not been used is recycled and, in the further course of the process, is guided in circulation ~ith a ccr.tinuous mode of operationO
Since, during the reaction of nonferrous metal com-pounds with chlorine, gaseous reaction products, such as oxygen, are formed, it is advantageous to remove the same from the reaction gas and to recycle the chlorine as well as, if necessary, the inert gas into ~he chlorination re-actor; this may, for instance, be effected in that the re-action gas, prior to being re-introduced into the chlori-nation reactor, is cooled to below the critical tempera-ture of chlorine, the chlorine gas is liquefied by apply-ing pressure and in this way is separated from the unde-0 sired gaseous components. Subsequently, the purified chlorine is returned to the reactor.
The temperature range to be observed as the third measure of the method according to the invention lies be-low the temperatures applied so far, which has the ad-vantage that the plant parts are spared, with the reaction speed yet being larger than with the known methods re-ferred to in the introductory part. At the same time, this involves advantages with regard to the energy expend-itures, and as a further outstanding advantage it is to be noted that, at this temperature, iron chloride will foxm only in negligibly small amounts. Finally, a further advantage of the low temperature adjusted according to the invention resides in the fact that it is operated in a range in which the melted ZnC12 exhibits a high vapor pressure, yet no complex cooling in front of the sublima-tion chamber is required, on the other hand. Zinc is that element which is in the way the most as the iron-oxide-containing residues are recycled into the iron or steel pro~uction process, si.nce it has dest-uct-ve effects, in particular on various furnace parts. If calcium and mag-nesium compounds are contained in the charging substances, the chlorides formed of these elements will not be heated up to the melting point with an appropriate temperature course. With melted components there is the danger that they form a coating on the particl.es of the charging sub-stances, which promotes the forma~ion of agglomeratesO The interior of such agglomerates is difficult to be reached by the reaction gas; the reaction course would be deceler-ated at least.
Heating of the chlorination reactor can be e-Efected

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by providing an indirect external heating of the chlori-nation reactor or by heating the reaction partners to be reacted to the reaction temperature prior to introducing the fine-particle charging substances and the reaction gas.
As already mentioned, the excess reaction gas pref-erably is guided in circulation, undesired gaseous reac-tion products, such as oxygen, each being removed from the reaction gas, partially or completely.
According to an advantageous embodiment, the chlori-nation o~ the fine-particle charging substances is carried out in a fluidized bed. In this manner, the separation is effected particularly qulckly and thoroughly.
Suitably, a mixture of chlorine gas and nitrogen is used as the reaetion gas in the initial state. Due to the higher overall flow rate of the reaction gas, the volatile nonferrous metal chlorides are led off more rapidly. Nitro-gen is readily available in large amounts and does not participate in any reactions in the range of chlorination ternperatures according to the invention.
In some cases, it is advantageous to carry out the ehlorination at an elevated pressure in order to obtain an even better separation effect my making use of the pressure dependency of the phase transition of the chlori-des. Moreover, the chloride formation rate is thus in-creased.
According to the invention, it is furthermore pro-vided to remove chlorinatable, but unsublimable nonferrous metals, such as calcium and magnesium, after the separa-tion of the sublimate by slurrying the starting material 0 residues in water and filtering.

~ 2 ~ Z

This mode of operation is recommended rather with relatively low contents of the charying substances of earth alkali metals, whereas, with higher portions of earth alkali carbonate, oxide or hydroxide, the fine-particle starting materials suitably are processed, prior to chlorination, for the separation of nonferrous metals that do not form sublimable chlorides, by treating them with acid, the obtained solution is separated and the residue is dried before being conveyed to the chlori-nation stage. To remove larger amounts of earth alkalimetals, it is more economical to dissolve them out by acid prior to the chlorination, since considerable amounts of chlorine gas are saved and, furthermore, a liberation of carbon dioxide during the chlorination is largely prevent-ed.
The invention will now be explained in more detail by way of two operational charts and examples.
According to Fig. 1, for instance sludge from wet dust-scrubbing of an ~D plan~ is supplied to a filter ag-gregate or a centrifugation means 2 via a conduit 1. Theiron-oxide-containing solid residue reaches a drier 3 and the waste water is conducted to a collection conduit 4.
The dry residue is taken to the chlorination reactor 5, into which also dry charging substances, for instance, metallurgical dusts, may be charged through conduit 6 without pretreatment. The reaction gas enters the reactor through conduit 7. In the reactor the chlorinatable non-ferrous metal compounds contained in the charging substan-ces, which are, in particular, compounds of zinc and of lead, but also - if present - Ca; Mg and alkali metal com-_ ~ _ ~z~L~z~

pounds, are converted into their chlorides. Sublimablechlorides, in particular ZnCl2 and, according to the pro-cess mechanism also lead chloride, possible NaCl and KCl as well as, perhaps, minimum amounts of FeCl3, are carried out with the excess reaction gas and get into a sublima-tion recipient 8, in which the gas phase cools off and the sublimable chlorides result in solid form. In most cases, the temperature losses on account of the plant design will suffice in order to bring about a sublimation in the re-cipient 8. The excess reaction gas is guided back into thereactor 5 through conduit 9. Undesired gaseous reaction products, such as oxygen, can partially or complete~y be removed in a separation plant (not illustrated). The chlorine losses resulting from the chloride formation are complemented through conduit 7 in a manner that the reac-tion gas or reaction gas mixture is kept substantially constant in its composition. Losses of inert gas possibly contained in the reaction gas occur in very slight amounts sc that a complementacion of the inerl gas yuided in circulation is necessary in great time intervals onlyO
The sublimated nonferrous metal chlorides are obtained in a very pure state, they are drawn off throu~h a dis-charge 10 and can be further used in subsequent method steps either separated from one another or directlyO
The charging substance residues treated with chlorine are slurried with water in a washing stage 11, the unsub-limable nonferrous metal chlorides thus being dissolved.
The solid slurry portions are separated in a separation stage 12 from the solution supplied to the collection conduit 4, and the purified iron-o~ide-containing residues ~2~g2 are drawn off through the outlet 13 and are reused for smelting.
The fine-particle charging substances, prior to the chlorination, can also be processed according to Fig. 2.
Fine-particle charging substances are supplied through conduit 1 in a manner analogous to the operational chart illustrated in Fig. 1, to a separation plant 2 at first.
The solid residue separated is treated with acid in a leaching stage 14, wherein, in particular, the Ca and Mg portions are dissolved out, which are largely present as hydroxides or carbonates. At this stage, strongly aqueous mineral acids are used, preferably hydr~chlori.c or sulphur-ic acid. In a further separation arrangement 2', the solids are separated from the acidic solution. The acidic solution is mixed in a neutralizing station 15, suitably with the basic solution from the first separation arrangement 2, and is neutralized, with a slurry precipitating that also contains portions of Zn and Pb. This slurry is guided back into the separation axrangement 2' through conduit 16 or is further processed separately. The aqueous supernatant is supplied from the station 15 to the waste water system through the outlet 17. The solids from the arrangement 2' are dried as much as possible in a drying plant 3, which is of a particular relevance with a view to preventing the formation of hydrogen chloride in the chlorination reactor.
The dried residue is introduced into the chlorination re-actor 5, to which also dry, untreated charging substances, such as metallurgical dusts, may be added through the con-duit 6.
In a -further sequence, the reaction gas is introduced ~2~ 9~

into the reactor through the conduit 7, the excess reaction gas streams through the sublimation recipient 8 and is guided bac]c into the reactor through the conduit 9, in a manner analogous to Fig. 1. As already explained, undesired gaseous reaction products can be removed from the reaction gas guided in circulation.
The sublimated chlorides are drawn off through the discharge 10.
With the method variant illustrated in Fig. 2 one can do without a further washing stage for the charging sub-stance residues treated with chlorine, the iron-oxide-con-taining residues directly can be drawn off from the reac-tor through the outlet 13 and supplied to smelting.
Example 1:
LD~sludge whose dry residue had the following compo-sition:
SiO2 1.5 % MnO 1.5 %
Fe23 64.9 % CaO 16.1 ~
FeO 3.0 % MgO 3.0 %
20 A12o3 0.3 % Na20 0.3 ~
ZnO 4.9 % K20 0.2 %
PbO 1.0 ~ C2 3.0 %
was filtered.
The filter cake was slurried in acid, wherein so muchacid was used that a pH of between 3 and 4 was reachedO
For this purpose, either 661 g of 36 % HCl/kg of filter residue or 342 g of 96 % H2S04/kg of filter residue were required. The solid residue obtained after filtration of the slurry in the dry state had the following composition:
30 SiO2 2.0 ~ MnO 1.7 %

g ~Z~ 3~2 Fe23 84.5 % CaO 2.6 %
FeO 1.0 % r~go o . 6 %
2 3 0.3 % Na20 0.3 %
ZnO 5.4 % K20 0.2 %
PbO 1.0 % C2 0.2 %
Cl~ 0.08 %
By acid treatment, the following oxide amounts are dissolved out of the LD-sludge on an average:
ZnO 10 to 18 % (depending on the ZnO-content) Fe203 about 1 %
CaO 74 to 80 % MgO 82 to 86 %
The residue obtained was dried and taken into a chlorination reactor. The flow rate of the chlorine gas was 144 1 (at normal conditions)/kg of charging substance h. At 700 C, 103.3 g of sublimate/kg of charging sub-stance were obtained ater 50 min, at 800 C 136.7 g of sublimate/kg of charging substance were obtained after the s~ne reaction time.
Comr~osition of the sublimate:
20 Reaction temperature 700 C 800 C
. _ . .
ZnCl2 78.0 % 58.9 %

FeCl3 19.6 % 29.9 ~

PbCl2 2.0 % 8.1 %

NaCl 0.1 % 1.5 %

KCl 0.1 ~ 1.6 %

Composition of the purified iron-oxide-containing resi-dues:

Reaction tem erature 700 C 800 C
P
SiO2 2~1 % n.d O

30 Fe203 8604 % 87.6 %

~%~

Reaction temperature 700C 800C
FeO 0.8 % 1.2 %
23 0.3 % n.d.
ZnO 0.49 % 0.38 %
PbO 0.47 % 0.04 %
MnO 1.80 % n.d.
CaO 2.40 % 2.10 %
MgO 0 50 % 0 40 %
Na20 0.40 % n.d~
10 K20 0.20 % n.d.
Cl~ 1) 3.40 % 3.40 %
1) Cl~ mostly is present in a state bonded to earth alkalis and alkalisO
The degree of dezincification thus amounts to 91.0 %
(700C~ and 92.6 % (800C), respectively, under the re-action conditions described.
ExamDle 2:
___ L
The solid portion of LD-sludge was separated by centri-fuaation. After drying, the residue ha'_ the ~ollowing com--20 positionO
SiO2 2.2 %
Fe23 72.6 % = 50.77 % Fe Al230.7 % = 0.37 % Al PbO0.6 % = 0.52 % Pb ZnO1.9 % = 1.52 % Zn TiO20.15 %
CaO13.07 %
MgO1.17 %
Na~O0 5 %
30 K200.4 %

C2 4.4 %
The flow rate of chlorine gas duri.ng the subsequent chlorination of the fine-particle charging substance ob-tained was 156.7 l (at normal conditions)/kg of dry resi-due h. The temperature during the chlorination reaction was maintained at between 680C and 710C.After 50 min 53.3 g of sublimate/kg o:E charging substance had co].lect-ed in the recipient, which was composed of 54.0 % ZnCl2, 42.75 % FeCl3~ 1.94 % PbCl2, 0.52 % NaCl and 0.69 -~ KCl.
10 The residue in the chlorination reactor had the fol-lowing composition:

SiO22.4 %

e2364.4 %

230.43 %
CaO13.30 %
MgO1.25 %
PbO0.14 %
ZnO0.17 %

cle16.2 %

20 The water-soluble portion of the residue was 24.8 %.

After slurrying in water and re-separation of the solids, the solid, dry residue was composed of SiO23.2 %

Fe2385.8 %

Al230.6 %

PbO0.18 %
ZnO0.21 %

TiO20.20 %
CaO2.0 %

MgO1.4 %

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Na20 O. 4 %
K20 0.3 In the aqueous phase the following co~pounds were contained in a dissolved state:
ZnC12 0.01 %
FeCl3 0.26 %
CaCl2 23.30 %
MgCl2 0.50 %
The attained degree of dezincification of 89 % is to be regarded as very satisfactory.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a method for separating nonferrous metals from iron-oxide-containing residues by thermal chlorination of a starting material comprised of said residues by a re-action gas comprised of chlorine at an elevated reac-tion temperature, and cooling of said reaction gas so as to cause a sublimation of the sublimable chlorides formed, the improvement wherein said starting material is selected from the group consisting of converter dust from flue gases of the steel production and fine flue dust from blast furnaces, said reaction gas is comprised of technically pure chlorine gas in an excess of at least 2 : 1 relative to the stoichiometric amount necessary for the chlori-nation of the nonferrous metals to be separated, and said reaction temperature is maintained at between 600 and 800° C during said chlorination.

2. A method as set forth in claim 1, wherein an inert gas is admixed to said reaction gas.

3. A method as set forth in claim 1, wherein said reaction gas in excess is guided in circulation and undesired gaseous reaction products, such as oxygen, are separated from said reaction gas.

4. A method as set forth in claim 3, wherein said un-desired gaseous reaction products are removed partially.

5. A method as set forth in claim 3, wherein said un-desired gaseous reaction products are removed com-pletely.

6. A method as set forth in claim 1, wherein said chlorination of said starting material is carried out in a fluidized bed.

7. A method as set forth in claim 1, wherein a mixture of chlorine gas and nitrogen is used as said reaction gas in the initial state.

8. A method as set forth in claim 1, wherein said chlori-nation is carried out at an elevated pressure.

9. A method as set forth in claim 1, further comprising the step of separating unsublimable, yet chlorinatable nonferrous metals, such as calcium and magnesium, after separation of the sublimate, by slurrying the starting material residues in water and filtering.

10. A method as set forth in claim 1, further comprising the steps of processing said starting material, prior to said chlorination, by treatment with acid so as to remove nonferrous metals that do not form sublimable chlorides, to obtain a solution and a residue, sepa-rating said solution, and drying said residue before supplying said residue to said chlorination stage.