CA1130573A

CA1130573A - Method and apparatus for refining molten raw metals, more particularly lead or zinc

Info

Publication number: CA1130573A
Application number: CA320,451A
Authority: CA
Inventors: Peter Paschen
Original assignee: Kloeckner Humboldt Deutz AG
Current assignee: Kloeckner Humboldt Deutz AG
Priority date: 1978-01-30
Filing date: 1979-01-29
Publication date: 1982-08-31
Also published as: GB2013248B; FR2415665A1; GB2013248A; DE2803858A1; BE873776A; AU4356779A; DE2803858C2

Abstract

ABSTRACT OF THE DISCLOSURE

A method for refining molten raw metal, more parti-cularly lead or tin, whereby the raw material is freed con-secutively of metallic impurities, characterized in that the saw metal flows continuously through directly consecutive re-action zones in which selective refining conditions are main-tained and into which solid and/or liquid and/or gaseous reagents are introduced and in that the reaction products floating upon the flowing metal and containing the impurities, are removed between the individual reaction zones.

Description

~L3~3 ~ he invention relates to a method and an apparatus for refininy molten raw me-tals, more particularly lead or zinc, whereby the raw metal is reed consecutively of its metallic impurities.
. Conventional metal re~ining, i.e. the refining of ~ lead or tin, is an intermittent process~ ~he raw metal arri~ing - from a shaft or reverberatory furnace, or some other mel.ting ~ unit, and containing irnpurities such as tin, lead, arsenic, "~ antimony, copper, nickel, cobalt, iron, silver, bismuth, e~c., and the raw metal arising during secondary metallurgy, is passed consecutively, in so-called "kettle" refining to the following stages:
i a) in the case of lead:
preliminary decopperizing, decopperizing, (including t`~ the removal of nickel and cobalt), removal of tin, removal of ~ arsenic and antimony, removal of silver (including gc,ld), re-.
moval of zinc, removal of bismuth, secondary refining~

b) in the case of tin:
~,r~
deferrization, decopperization, removal of arsenic, removal of antimony, removal of bismuth, if necessary removal of magnesium, sodium and zinc, removal of lead, secondary re- ~ -fining.
Siince each of these stages requires different reagents and, furthermore, since the partly refined raw metal would keep on picking up again impurities from preceding refining stages, due to incrustation on the edges of the kettle and sediment on the kettle bottom, each of the above-mentioned stages requires at least one kettle. Since spare kettles must be available because of the limited life of the kettles, and since interme-diate-heating kettles and casting Xettles are also required, lead works usually have between 10 and 15, and tin worXs between 4 and 10 or more, refining kettles (a total capacity of between ~L~L.36~73 30 and 200 t of molten metal).
The refininy reactions in each refining stage are different, and this means a variety of optimal temperatures:
a) in the case of lead:
preliminary decopperization: 1200 to 450C
decopperization 350 - 400 removal of tin, arsenic, antimony:
according to HARRIS 450 500 . hearth-furnace refining 300 removal of silver:
. .first stage 430 . second stage ends at 350 - :
removal of zinc (vacuum) 650 removal of bismuth:
. first stage 410 . second stage ends at 350 secondary refining 420.
b) in the case of tin:
removal of iron: 300 - 270 (possible in two stages) removal of copper 240 - 280 removal of arsenic:
. heating to 600 - 650 dross removal 360 removal of antimony 250 removal of bismuth:
. heating to 450 . allowing to cool to 250 ~:
removal of Mg/Na, ~ :
. heating to 425 . allowing to cool to 330 removal of lead 260 secondary refining 320,

-2-~3~ii7~

It will be gathered from -this that, in the course of kettle-refining, the raw metal is cooled down at least three times and is reheated at least -three times. This involves re-moving from the surface of the molten lead or tin at least ~
to 10 different reaction products (dross, foam and skimmin~s), which still requires more or less manual labour.
Heating the kettle, which may be heated wikh oil or gas, is an operation wi-th a heat-utilization efficiency of only 10 to 20%, with a heating velocity of 30~hour. The cooling velocity is of the same order of magnitude. Total temperature differences are at least 1500C, which means 50 hours (i.e. more than two days~ during which no reactions take place, but only heating or cooling is carried out. All of this means that the raw metal generally takes between 4 and 6 days to travel from the shaft or reverberatory furnace to the mould.
The space-time yield of classical lead and tin re-fining is thexefore extraordinarily poor (order of magnitude:
1 t/m .h), leading to high investment costs and loss of inter-est. Maintenance and labour costs are also high.
The disadvantages of conventional, intermittent ket-tle refining have resulted in efforts to operate some of the stages of lead refining continuously. - `~
- Thus in the past, and even quite recently, there have been proposals for continuous decopperization, even for continuous preliminary decopperization and also sulphur-de- `
copperization. In decopperizatio~ a temperature gradient is ~ -maintained in the hearth furnace, so that slag, mortar and/or ;
brick can be removed from the hotter upper zone, while the ~ ~-preliminarily decopperized lead can be removed from the cooler -lower zone. For sulphur-decopperizing, a series of 9 agitator- ~ ;
furnace reactors is proposed. Common to all of these processes A

is the fact that -~he space-time yield is still only between 1 and 3 t/m .h.
Investment costs for hitllerto-known partly~continu-ous method for lead refining are h:igher than for the inter-mittent method. Another disadvantage of the known processes is the poor environmental conditions uncler which they operate.
It is the purpose of the present invention to provide a method for refining metal, especially ~or refining lead and tin, which is noted for the high purity of the refined metal, a high space-time yield, comparatively low inves~ment, maintenance, labour ancl power costs, and little pollution. I-t is also the purpose of the invention to provide a simple appa~
ratus for -the execution of the said method.
According to the invention, in the case of a pro-cess of the kind mentioned at the beginning hereof, this pur-pose is achieved in that the raw metal flows continuously through directly consecutive reaction zones in which selective refining conditions are maintained and into which solid and/or liquid and/or gaseous reagents are introduced; and in that the reaction products floating upon the flowing metal, and contain-ing the impurities, are removed between the individual reaction zones. In this connection, the ~low of metal is adjusted so that the depth thereof is of the order to lcm.
In the case of lead refining, for example, the method according to the invention removes from the raw metal, in the consecutive reaction zones, first of all copper, then tin, arsenic, antimony, silver, zinc and possibly bismuth, the said raw metal entering the first reaction zone at about 1000C and leaving the last reaction zone at about ~00 to 500C. Since the method according to the invention uses no kettles, with incrustation on the walls and sediment on the bottoms, and since, on the other hand, the reaction products are rernoved ~13~5~

between the individual reaction zones, it is impossible for impurities already removed from the raw metal to be returned thereto. This continuous refining method dispenses with in-termediate heating and/or intermediate cooling of the flow of metal, and no power is therefore required for those purposes. -Investment, maintenance and labour costs are therefore very low, as are power costs, if any. Slow segregation processes, non-reacting gases (atmospheric nitrogen), kettle destruction by simultaneous chemico-corrosion attack, for example by lead and reaction products, and thermal kettle destruction by con-stant heating up and cooling down of the flow of metal being refined, are all eliminatedO The method according to the in-vention may be expected to produce a space-time yield of 40 t/m .h.
The installation for the execution of the refining method is characterized, according to the invention, in that the reactors are in the form of flat channels connected direct-ly together by intervening settling receptacles: in that under~
passes for the flow of metal are arranged between the individual reaction zones: and in that the flow of metal is continuous from the first to the last reaction zone. In its simplest ` -form, the;refinlng installation according to the inventlon consists of a single section, or a single pipe, with as many sections for reaction zones as there are impurities to be re-, .. .
moved from the raw metal. ~
: . : ~ ."
In one aspect of the present invention, there is provided a method of refining raw molten lead or tin by re-moving metallic impuritles therefrom in succession wherein the raw metal flows continuously through successive reaction 30 paths connected together in which the metal flow is set so that only a relatlvely amall depth of liquid is present ln the reaction paths, in which selectlve refining conditions 1 ~;.3~573 are maintained and into which solid and/or liquid a~d/or gaseous reagents are introduced; wherein the reaction products floating on the liquid metal and containing these impurities ::
are drawn off between the individual reaction paths.
The invention will now be described with reference to the accompanying drawings which show a preferred form thereof and wherein: :~
Figure 1 is a partial longitudinal section through a metal-refining installation according to the invention; ;
Figure 2 is a cross section along the line II-II
in Figure l; : :
"~' ' ' ~,.
,"~-, ,~ ~., :f.. ~:~
,, . .
~ , '" ","
: ~.
' '' -5a~

~3~573 Figure 3 shows anokher design of the refining in-stallation, in this case with a vextical reaction column, Figure 4 shows still another clesign of the refining installation.
According to Figure 1, molten lead 10, for example, at a temperature of about 1000C, passes from a shaft furnace, a holding furnace, or a storage kettle into the refining in-stallation according to the invention. The flow of lead may be comparatively small, for example 0,3 l/sec.; however, since it is continuous, the yearly output is 100~000 tons. The said installation consists of flat channels 11, 12, 13, 1~ connected directly together by intervening settling receptacles 15, 16, 17 underpasses 1~, 19, 20 for the flow of metal heing arranged in the said receptacles. The number of channels or reaction zones corresponds to the number of different impurities to be removed from the raw metal. Channels 11 to 14, which according to Fic3ure 2 are of U-shaped cross section, are made of iron. ~ ` -In the example of embodiment illustrated, the said channels are 150 cm in length, 15 cm in width, and the depth of the lead in the channel is 1 cm. A channel therefore contains 2,25 1 of lead. With the lead flowing at a rate of 0,3 l/sec., the per iod of residence of the lead in the channel, i.e. the reaction time, i3 7,5 sec. The length of the channels or reaction zones is determined by the length of the channel in which the reaction is the slowest. -Channels 11, 12, 13, 14 etc. all lie in a plane which slopes downwardly at a small angle to the horizontal, in the direction of the flow of metal. This slight slope allows the lead to flow continuously from the first to the last reaction zone. The slope of the channel may be adjustable. However, pumps may also be provided to carry the leacl along. Both the said channels and settling receptacles 15 to 17 may be adapted . . . , . . . , . , . . ~ . . , . . . . . . . . . . , . . . , . : - - , - , - . .. .

5q~

to be heated and/or cooled. The settling conditlons for the reaction product.s may therefore be improved hy cooling the said receptacles. Channels 11 to 14 are covered by hoods 21 to 24, all of which are connected to an exhaust-gas line 25 running to an exhaust fan 26~ Selective gas atmosphere and positive or negative pressures may be established in the closed reaction zones. Solid and/or liquid and/or gaseous reagents are supplied through pipelines 27, 28, 29, 30 and nozzles 31, passing through hoods 21 to 24 over the channels. Ten nozzles, for example, may be distributed over the length of each channel or reaction zone, the angles of the nozzles, and their distance from the lead being such that the entire surface of the lead is treated.
The nozzles may be made of steel, ceramic or synthetic material. The reagents, which are accurately metered, may con-sist of the following: oxygen, nitrogen, sulphur, phosphorus, sodium, zinc, chlorine and other halides, calcium magnesium, carbon dioxide, etc. Each reaction zone contains a means for ~;
measuring and controlling the temperature.
Each reaction zone terminates in an underpass 18-20 comprising a partition 32-34 which dips into the flow of lead -~
for the purpose of separating the reaction products containing ~
the impurities which float upon the surface of the lead. The ;
increase in the flow-cross-section in receptacles 15-17 reduces the flow velocity of the lead. This allows time for the reactior ~-products, all of which are specifically lighter than lead, to float to the surface thereof. Reaction products 35 are removed semi-continuously by means of a dross or slag skirnmer, for ex-ample. It is desirable to provide the underpasses also with exhaust hoods.
The individual metalllc impurities in the flow of ~--lead are removed as follows:
1. Removal of copper.
. ~ . .
-7- ;

The removal of copper, which is ef~ected in the first channel 11, is carried out from a copper content of about 2%
to 0,001%. The reagent is sulphur in liquid or vapour form or, according to a special characteristic of the invention, phos-phorus in liquid or vapour form. It is unnecessary to provide a carrier gas to blow the sulphur or phosphorus onto the flow of lead. The boiling temperatures of S and P are ~5 and 280C.
The amount of sulphur introduced, which is controllable, may be between S0 and 10 g. The reaction products formed are copper sulphide or copper phosphide. Other elernents may also be used as reagents, as long as they have a higher affini-ty for copper than for lead, as long as they do not remain in the lead them-selves, or remain only in small amounts, or can at least be easily removed from the lead, and as long as they form, with the copper, a reaction product which can be removed from the lead.
2. Removal of tin.
In the next reaction zone or channel, the amount of tin in the lead is reduced from 0,5 to 0,001%. The only reagent required is air, but oxygen may also be used, and this may be blown onto the flow of lead in amounts varying between 25 and 5 g/sec~

3. Removal o~ arsenic.
The amount of arsenic in the lead is reduced from 0,5 to 0,001%. The reagent used is industrially-pure oxygen at atmospheric pressure. Instead of oxygen, liquid sodium hydroxide may be used in controllable amounts of between about 20 and 5 g/sec.

4. Removal of antimony.
The antimony content of -the lead is reduced from about 2,5 to 0,OO:L%. The reagent used is oxygen at an increased pressure. Tin, arsenic and antimony may also be removed jointly 1~3~35~3 in a single reaction zone, using pres.surized oxygen as the reagent, but separate removal with different partial-pressures of oxygen is preferred.

5. Removal of silver.
The amount of silver in the lead is reduced from about 0,1 to 0,001%. The reagents used are liquid zinc, liquid sodium, or gaseous halides, for example bromine. ~or example, between 5 and 1 g/sec. are metered in drops, using nitrogen as the carrier gas. The reaction product formed is an inter-metallic compound of silver and zinc.

6. Removal of zinc.
The zinc content in the lead i5 reduced from abou-t 1 to 0,001%. Zinc removal is effected by means of oxygen, air, or liquid caustic soda in the presence of air, or by chlorina-tion (the reaction product is zinc chloride), or by vacuum di-stillation of the zinc at 600C, the zinc evaporating. The zinc may be returned to the silver-removing stage as a vapour or, after cooling, as a solid. If the reagent used is liquid NaO~, the amount thereof added controllably may be between 30 and 5 g/sec. ;
., . . :

7. Removal of bismuth.
The amount of bismuth in the lead is reduced from -~
O,05 to 0,005%. The reagent is liquid calcium and/or magnesium~
The amount of liquid magnesium added is merely a few g/sec.
The corresponding stages in the continuous refining of tin are:
1. Removal of iron: by injecting compressed air and, if necessary, pumping the molten metal through asbestos-cloth filters.
2, Removal of copper: by stirring-in sulphur and removal of the Cu-Sn-S reaction product.
3. Removal of arsenic: by stirring-in liquid alumi- -num, forming an intermetallic Al-As phase, and removing this _g_ ~`

s73 phase in the form of dry "dross".
4. Removal of antimony: as with AS, phase Al-Sb.
5. Removal of bismuth: by stirring-in Zn, possihly plus Mg, possibly plus Na, forming and removing mixed crystals containing bismuth.
6~ Removal of Mg/Na/Zn: by adding consecutively NaOH, S and an SnC12 solution. Sulphides, caustic soda, and chloride slags are formed into which the impurities are trans-ferred.
7. Removal of lead: this may be done either with chlorine gas or with SnC12. Lead-zinc-chloride is produced.
Upon leaving the last reaction zone, the finish-re-fined metal flows, at about 300 to 500C, into a conventional casting kettle, whence it may be pumped to a pig-casting machine The reagents may be introduced from above or below, onto or through the flow of molten metal, and at normal or in-creased pressure.
According to the example of embodiment in Figure 3, a vertical reaction zone or column 38 is arranged between two channels or reaction zones 3~,37, the said column replacing the settling receptacle and underpass shown in Figure 1. The re-agents, a reaction gas or inert gas, to assist in floating-up the reaction products, are introduced through nozzles 39.
Reaction products 40 are removed from the top of column 38.
The reaction zones may follow each other in any desired arrange-ment. This refining installation according to the invention is ~-easily adapted to an existing plant layout. ~ ~ -In the example of embodiment in Figure 4, molten metal 41 to be reEined flows through an elongated furnace or ~
pipe, the bottom of which slopes slightly downwardly in the ;
direction of the Elow. The said furnace or pipe is divided, by approximately vertical partitions 42, into chambers 43 in ~.

which different, selective-refining atmospheres can be main-tained, while the molten metal can flow communicatingly from one chamber to the next. The reagents are introduced into the chambers through lances 44, while solid reaction products 45, fl.oating upon the molten metal, and the gaseous reaction pro-ducts, are removed from the chambers~ The finish-refined metal leaves the installation at 46.

~. . , , -

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. A method of refining raw molten lead or tin by re-moving metallic impurities therefrom in succession wherein the raw metal flows continuously through successive reaction paths connected together in which the metal flow is set so that only a relatively small depth of liquid is present in the reaction paths, in which selective refining conditions are maintained and into which solid and/or liquid and/or gas-eous reagents are introduced; wherein the reaction products floating on the liquid metal and containing these impurities are drawn off between the individual reaction paths.

2. A method according to claim11 wherein the liquid is approximately 1 cm deep.

3. A method according to claim 1, wherein for refining lead in the successive reaction paths, first copper is re-moved from the raw metal and then tin, arsenic, antimony, silver, zinc and where applicable bismuth, this raw metal entering the first reaction path at approximately 1,000°C
and leaving the last reaction path at approximately 300 to 500°C.

4. A method according to claim 2, wherein for refining lead in the successive reaction paths, first copper is re-moved from the raw metal and then tin, arsenic, antimony, silver, zinc and where applicable bismuth, this raw metal entering the first reaction path at approximately l,000°C

and leaving the last reaction path at approximately 300 to 500°C

5. A method according to claim 1, or 2 or 3, wherein for tin refiners, iron, copper, arsenic, antimony, bismuth, Mg/Na/Zn and lead are successively removed continuously from the raw metal.

6. A method according to claim 4, wherein for tin refiners, iron, copper, arsenic, antimony, bismuth, Mg/Na/Zn and lead are successively removed continuously from the raw metal.

7. An apparatus for refining raw molten raw metal lead or tin comprising a series of reactors in which metallic im-purities are successively removed from the raw metal, wherein the reactors comprise flat channels which are connected to-gether for continuous metal flow, under-passages for the metal flow are arranged between the individual reactors comprising;
reaction-paths, and means for draining-off, between the respec-tive reactors, impurity-containing reaction products floating on the metal flow.

8. Apparatus according to claim 7, wherein settling tanks are interposed between adjacent channels.

9. Apparatus according to claim 7, wherein the channels of all of the reaction paths lie in a single plane downwardly inclined at a small angle with regard to the horizontal in the direction of the flow of metal.

10. Apparatus according to claim 7, wherein one or more of the reaction paths are arranged as reaction columns sub-stantially perpendicular to or at an angle to the horizontal.

11. Apparatus according to any one of claims 7 to 9, wherein each channel is covered by a hood connected to a waste gas line.

12. Apparatus according to any one of claims 7 to 9, wherein solid and/or liquid and/or gaseous reagents can be introduced into the reaction paths.

13. Apparatus according to any one of claims 7 to 9 wherein the under passages each have a separating wall arranged between the individual reaction stages, the separating wall extending into the metal flow to separate the reaction pro-ducts containing the impurities and floating on the flowing metal.

14. Apparatus according to claims 8 or 9, including heating and/or means whereby the reaction paths and associated settling tanks can be respectively heated and/or cooled.

15. Apparatus according to any one of claims 7 to 9, wherein the number of reaction paths corresponds to the num-ber of different impurities which are to be removed from the raw metal.