Note: Descriptions are shown in the official language in which they were submitted.
20 1 298 1
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REMOVAL OF ARSENIC, TIN ~ ANTIMONY
FROM CRUDF. T.F.~ CONT~TNING SITVF.R
R~cKGRouNn ~ND DFSCRIPTION OF T~F INVFNTION
This invention relates to a process for the
removal of arsenic, tin and antimony from crude lead
containing silver by means of industrial oxygen in a lead
smelting crucible, and a device for the execution of the
process.
The removal of tin, arsenic and antimony from
crude lead containing silver is presently carried out in
lead matallurgy in accordance with either the Harris process
or the reverberatory process.
The Harris process (Ullmann, 3rd edition, volume
4, pages 498-501) is used, along with the separation of tin,
arsenic and antimony, for the processing of tin-rich and/or
tellurium-rich lead, whereby valuable final products
accumulate which are in part highly concentrated. The
separation of the above-stated impurities from the crude
lead takes place with sodium hydroxide and a strong
oxidizing agent, preferably saltpeter, forming Na3SbO4,
Na3AsO4 and Na2SnO3 which accumulate in the form of a fluid
salt slag. The impurities removed from the crude lead
subsequently must be separated from the salt slag into
concentrated and lead-free products by means of
hydrometallurgic processes. The processing of the salt
slags, which is the actual nucleus of
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the Harris process, requires extensive equipment and thus
correspondingly high installation costs. The process is
also expensive and requires careful monitoring. For these
reasons the Harris process has not yet become widely
prevalent in most lead smelting plants.
In the more widely used reverberatory furnace
process (Ullmann, 3rd edition, volume 4, pages 498-501), the
antimony along with the arsenic and tin, is oxidized at 700
- 750C by means of atmospheric oxygen. For this purpose,
rectangular reverberatory or refining furnaces are used and
the exhaust gasses, after the temperature has dropped, are
conveyed in a cooling unit to a filter for removing dust.
The air, which is blown in through lance units into the lead
bath, oxidizes the tin, arsenic and antimony in that
sequence forming double oxides which are removed from the
furnace as fluid dross. Depending on whether a continuous
or discontinuous operation is used, drosses of 8-25% Sb, 1-
5% As and 30-50 ppm Ag are produced. In a continuous
reverberatory furnace process which is characterized by its
high conversion rate, drosses with only 8-13% Sb result. The
low antimony content leads to correspondingly high dross
quantities resulting in increased processing costs. The
drosses are additionally processed by means of reduction
melting into an alloy containing antimony and lead which is
termed "crude hard lead", and from which hard lead qualities
of commercially conventional quality are produced by means
of subsequent refining.
The above-stated processes are characterized by
high equipment expenses, such as for example, the processing
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of salt slags in the Harris process, and the cooling unit,
dust removal filter, reserve furnaces and so on like in the
reverberatory furnace process. They are also characterized
by a high energy consumption for the processing of large
S quantities of intermediate products, such as salt slags and
drosses, as well as by high operating costs.
Modern processes in both primary as well as
secondary lead smelting works for the separation of tin,
arsenic and antimony from crude lead use oxygen/air mixtures
in a conventional lead smelting crucible. In secondary lead
smelting plants the drosses can be processed without problem
because the crude lead of the secondary lead smelting plants
has only a very low silver content (<30 g Ag/t). In a
primary lead smelting plant in which a crude lead containing
a silver content of up to several thousand g Ag/t is
similarly processed, a dross is produced with 3.85% arsenic,
3.25% antimony and 1098 g/t of silver. See Proceedings of
the CIM Symposium on "Quality in Non-Ferrous
Pyrometalllurgical Processes", Vancouver [1985], pages 137-
140. During the subsequent reduction of the dross, thesilver contained therein moves into the hard lead from which
it can not be removed, resulting in a corresponding loss of
valuable metal. Furthermore, the hard lead which contains
silver can not be marketed as commercial hard lead because
the silver exceeds the permitted limits. Thus, this method
can only be carried out in primary lead smelters which
process crude lead containing silver if, before the
reduction to crude hard lead, the dross is separated in a
separate process step by liquation into an Ag-poor dross and
Ag-rich
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201 ~981
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crude lead. The liquation process is carried out for
example in a short-drum rotary furnace or in a liquation
hearth furnace. Because of the additional expense of
liquation, the advantage of the crucible refining is
considerably reduced.
Thus, it is clear that crucible refining by means
of air enriched with oxygen can only be carried out
economically, if the silver contents in the crude le~d are
very low, such as for example during the refining of scrap
lead in accordance with DE- PS 3 332 796 which must be
operated at temperatures of at least 630C.
The task of the present invention is to describe
a device and a process which avoid the above-stated
disadvantages, such as for example drosses containing
silver, additional consumption of reagents, higher operating
temperature, etc., during refining in the lead smelting
crucible, and in which the removal of tin, arsenic and
antimony is carried out through the use of industrial oxygen
in a conventional lead smelting crucible.
This task is solved in the process of the type
described above, by introducing oxygen into a turbulent
stream of fluid lead which is constricted to a proportionate
volume relative to the smelting crucible. With such.
introduction the lead, thoroughly mixed with oxygen, enters
into a larger volume for the purpose of calming, and the
elements which are to be separated off float on the surface
in the form of oxides and are skimmed off.
The process is carried out in a device which
comprises two cylinders of different volumes. The cylinders
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are positioned perpendicularly to one another, can be
adjusted relative to one another, and they project out above
the surface of the molten mass. The cylinders are suspended
on a traverse unit and the entire smelting crucible is
covered by a protective hood. The turbulent stream of the
lead is produced by means of lead pump, the discharge
opening of the pressure side of which lies above the level
of the lead. The turbulence in the small cylinder can also
be produced below the level of the lead by means of a nozzle
shaped discharge from the pump.
A device constructed in accordance with the
invention and for performing the process of the invention is
shown in schematic cross-section in the drawing.
The device employed for execution of the process
in accordance with the invention is of cylindrical shape and
connected with a lead pump 2. It essentially comprises a
sheet steel cylinder 1 the lower portion of which is
immersed in a lead bath 12 of the lead smelting crucible.
The cylinder 1 and the lead pump 2 form a portable unit
which, together with a traverse unit, is placed on the edge
of the crucible. In use the lead moves out of the crucible
through an opening 3 in the lower portion of the cylinder 1
and fills the crucible. By means of the lead pump 2, the
lead is pumped out of the crucible into a reaction tube 4 in
the form of a small cylinder which is located within the
cylinder 1. The reaction tube is attached vertically and
adjustably to the wall of the cylinder 1 and is immersed for
approximately two thirds of its overall length into the lead
bath located in the
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cylinder 1. The lead moving into the reaction tube
vertically from the top subsequently flows at reduced speed
through the cylinder 1 and flows back through the opening 3
located at the base of the cylinder into the lead smelting
crucible.
Industrial oxygen is blown into the reaction tube
through a lance unit 5. The oxygen and the lead are
thoroughly mixed by means of the strongly turbulent current.
The oxygen is entrained in the lead bath of the cylinder 1
and due to the good dispersion a rapid oxidation primarily
of secondary metals takes place. In the cylinder 1, the
current is slowed down enough so that the fluid dross 15
separates from the lead on the basis of the differences in
density, collects on the surface 16 of the bath of the
cylinder, and is able to flow off through the tap hole 6 in
the cylinder wall, through a channel 7, and into the
crucible bowl 8. The crucible remains continuously covered
by means of a protective hood 9 which is connected by means
of suction piping 10 with a dust-removal device. The
process can be carried out discontinuously, semi-
continuously or continuously.
The invention will now be illustrated in greater
detail to follow by means of two examples of execution.
F.XZ~MPT.F.
150,000 kg of decoppered crude lead containing
0.8% Sb, 0.05% As and 1,500 g/t Ag were refined by means of
industrial oxygen in a crucible at an initial temperature of
580C, in accordance with the invention described. After
one hour, the dross began to run off into a crucible bowl.
After
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300 minutes, a sample showed that the antimony and arsenic
had been removed. The final temperature was 610C and the
oxygen consumption was 210 Nm3. 3,400 kg of dross, with
30.2% Sb, 2.0% As and 9 g/t Ag, were produced.
F~XZ~MPT.F. 2
In a smelting works, the Sn-As-Sb removal is
controlled in accordance with the reverberatory furnace
process and replaced by means of the proposed process and
apparatus, by means of which the entirety of the first
runnings of the crude lead is now refined in a problem-free
manner. The smelting crucibles provided for furnace
refining were sufficient for the purpose of crucible
refining so that, apart from the simple refining apparatus
in accordance with the invention, no additional equipment
expense was necessary.
The following characteristic process data were
determined by the process in accordance with the invention:
1. The heating energy consumption, with
refining output remaining the same, dropped by 58 kWh/t.
2. Because of the qualities of cooling water
and compressed air not required in contrast with the
reverberatory furnace process, as well as the elimination of
the cooling of the exhaust gas, and the reduction of the
exhaust gas volume, it was possible to reduce the
consumption of power (including that for the oxygen
production) by 2.3 kWh/t of crude lead. Starting from a
crude lead with an average of 0.8~ antimony and 0.05%
arsenic, the dross accumulation is reduced relative to the
reverberatory furnace
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process, from 45 kg dross per ton of crude lead to 26 kg
dross/t of crude lead, so that during the further processing
of the dross with hard lead, 15 kWh/t of crude lead in
reduction energy, 6 kWh/t of crude lead in reduction energy
and 6 kWh/t of crude lead in heating energy were saved.
3. With first runnings of crude lead, for
example of 120,000 t/year, an energy savings of
approximately 9,760,000 kWh/year resulted. By means of this
method the disadvantages of refining furnaces, including the
removal of exhaust gas dust, is eliminated resulting in
operating costs which are markedly reduced together with a
considerable reduction of harmful effects on the atmasphere.
4. Since the dross arising in this method has a
low melting point because of the absence of portions of
additives, such as for example lime or sodium hydroxide, and
because smaller quantities of slag accumulate, the further
processing is more cost-effective.
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