Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~z~z~
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
-- 2 --
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
-- 3 --
9Z
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
-- 4 --
2~;~
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.
-- 5 --
~ 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
-- 7
~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
-- 8 --
~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 %
- 10 -
~%~
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 %
- 11 -
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 %
- 12 -
~L2~
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.
- 13 -
