US3031296A

US3031296A - Separation of lead and zinc

Info

Publication number: US3031296A
Application number: US766785A
Authority: US
Inventors: Davey Thomas Ronald Albert
Original assignee: Metallurgical Processes Ltd; National Smelting Co Ltd
Current assignee: Metallurgical Processes Ltd; National Smelting Co Ltd
Priority date: 1957-10-18
Filing date: 1958-10-13
Publication date: 1962-04-24
Anticipated expiration: 1979-04-24

Description

April 1962 T. R. A. DAVEY SEPARATION OF LEAD AND ZINC Filed 001;. 13,. 1958 3,03l,2% EPARATION OF LEAD AND ZINC Thomas Ronald Albert Davey, Avonmouth, England, as-

signor to Metallurgical Processes Limited, Nassau, Bahamas, and The National. Smelling Company Limited, London, England, carrying on business together in the Bahamas under the name and style of Metallurgical Development Company Filed Oct. 13, 1953, Ser. No. 766,785 Claims priority, application Great Britain Get. 18, 1957 4 Claims. (Cl. 75-88) This invention relates to the separation of lead and zinc from mixtures thereof.

A continuous process is known for removing zinc from lead by vacuum distillation, which produces metallic zinc containing a little lead from lead which has been desilverized by treatment with zinc. The zinc produced by this distillation is designed for re-use in the desilverizing of further lead bullion. In this process, zincife'rous lead is distilled in a vacuum chamber to produce zinc vapour which condenses on a core of solid zinc and runs down into a collecting pool. The lead content of this metallic zinc is sutiiciently high to restrict the number of commercial purposes to which it can be put.

It is known that zinc of low lead content can be produced from lead-containing zinc by a process of distillation with refluxing at atmospheric pressure. In a known process, the impure zinc is volatilized and the vapour is passed through a refluxing column containing a large number (generally greater than twenty) of trays for condensation and re-evaporation, and zinc that is substantially free from lead is condensed-from the vapour leaving the top of the refluxing column.

The present invention consists of a method of separating pure zinc from zinc of low lead content in which the lead-containing zinc is distilled under vacuum at temperatures of about 45 to 500 C., whereby the vapour obtained is practically free from lead. Under vacuum therefore the zinc (containing about 1% lead) can be distilled, and without the use of any refluxing column, zinc that is substantially free from lead can be obtained by condensing the zinc vapour so produced.

The present invention further consists of a process in which zinc-containing lead is distilled under vacuum and the lead contaminated zinc vapour is condensed in a circulated stream of molten zinc, which is at a lower temperature than the zinc-containing lead, zinc vapour being simultaneously evaporated from the circulated stream of molten zinc and condensed in a zone that is at a lower temperature than the circulated stream of molten zinc.

In one form of the present invention, zinc-containing lead, at a temperature above the melting point of zinc, flows through an outer annular evaporation zone of an evacuated vessel, a stream of molten lead-containing zinc at a lower temperature and still above the melting point of zinc, is circulated through an intermediate annular zinc-vapor refining zone of the evacuated vessel, and centrally disposed cooling means are provided in an innermost annular condensation zone of the evacuated vessel. By this means some of the zinc is evaporated from the zinc-containing lead, and is condensed in the stream of molten zinc and condensed in a zone that is at a lower zone. Zinc vapour is simultaneously evaporated from the stream of molten lead-containing zinc on the inner sides of the intermediate annular zone and solid zinc condenses and accumulates on the cooling zone to a point at which its temperature rises to the melting point of zinc and thereafter the zinc condensed here runs oii as molten zinc, the amount of molten zinc thus condensed being approximately equal to the amount of zinc evaporated from the zinc-containing lead. The circulated stream of molten lead-containing zinc is maintained at a temperature higher 2 than the melting point of zinc but lower than that of the zinc-containing lead, and lead accumulates in this leadcontaining zinc until it becomes saturated with lead, and zinc-saturated lead separates from a zone of the circulatory system outside the evacuated vessel.

The invention will be further described with reference to the accompanying drawing.

FIGURE 1 is a sectional elevation of one form of distillation apparatus incorporating the improvement.

FIGURE 2 is a section on the line IIII of FIGURE 1 and,

FIGURE 3 is an enlarged detail of FIGURE 1.

Lead containing about 1% zinc is supplied to the chamber l through a pipe 2 situated just below the surface of the molten lead in the annular well 3 at a temperature of about 560 C. The lead in this well builds up behind a rectangular flange 4 welded to the top of an outer annular spreading wall 5. This flange has holes 6 through which lead seeps evenly around the perimeter of the spreading wall 5. This Wall has an outwardly divergent lip 7 over which the lead flows in a thin stream coating the inside of the wall 5 with a layer of lead. The evaporating conditions in the chamber, with a pressure of less than 10 mm..mercury, cause the zinc in this lead to progressively evaporate out into the outer zone 8 of the chamber, as the lead flows down the wall 5 into a trough 9, at the bottom of which a pipe 10 leads to a bath of lead in the pct 11 from which it runs continuously or can be tapped from time to time; the length of the pipe 10 above the lead in pct 11 is greater than the height of a barometric column of lead. The zinc vapour passes inwards towards an intermediate annular system of inclined shelves one above the other, which face alternately outwards 12 and inwards 13 with connecting rods 12a and 13a (FIGURE 3). These shelves maybe constructed of refractory material or enamelled steel resistant to corrosion by zinc. These shelves are supplied with a continuous stream of molten zinc at a temperature of about 450 to 500 C. After circulating over the shelves the molten zinc falls into an annular trough 14a connected by a pipe 14b to a bath 14, from which a pump 15 sends it up the pipe 16 and into an annular trough 17, from which it overflows to cascade over the shelves again. The lead which is collected by the zinc separates out of the zinc in the bath l4 and can be taken off at 18.

The surfaces of the outwardly facing shelves 12, over which the zinc is flowing, are exposed to the incoming zinc vapor, containing less than 1% lead, coming from the relatively hot zinc vapor in zone 8, so that the zinc vapor condenses on shelves 12, and the latent heat of condensation of this zinc causes the temperature of the liquid zinc to rise by between 5 C. and C. From each of the shelves 12, the liquid zinc then flows on to one of the inwardly facing shelves 13, and, owing to the lower pressure of zinc vapor prevailing in the inner zone 19, the zinc re-evaporates from shelves 13, the latent heat of evaporation thus abstracted causing the temperature of the liquid zinc flowing over these shelves 13 to fall by approximately the same amount as it rose over shelves 12. This re-evaporated zinc vapor contains only 0.01% or less lead. The lower zinc pressure in zone 19 prevails because the zinc vapor condenses on the zinc collar 24). This vapour condenses on the innermost zinc collar 26* which builds up during the course of the process as a solid deposit on the condenser 21 with cooling pipe 2142 until the temperature on the outside is sufficient to cause the zinc to remain liquid and drip down off the collar. The molten condensed zinc flows down pipe 25, the lower end of which is submerged in molten zinc contained in pot 26, the length of pipe 25 being greater than the height of a barometric column of zinc. Any zinc vapour which enters the condenser 21 is prevented from forming a solid deposit by the installation of a radiant heater 22. The cold trap 23 is removable in order to clean out any deposit which may form on its water cooled walls. No zinc must be allowed to build up in the vacuum pipe 24.

Various modifications may be made within the scope of the invention.

I claim:

1. In the process for separating and recovering zinc from lead of low zinc content in which molten zinc-containing lead at a temperature above the melting point of zinc is introduced under vacuum into an evaporation zone to evaporate therefrom zinc vapors containing a small quantity of lead, and in which these lead-contaminated zinc vapors are condensed to liquid metal on a body of solidified zinc in a condensation zone maintained at a lower temperaturethan that of the evaporation zone, the liquid metal condensate being collected and recovered, the improvement which comprises the provision of an intermediate zinc-vapor refining zone disposed between said evaporation and condensation zones, said zinc-vapor refining zone having a circulating stream of molten zinc flowing therethrough at a temperature between that of the evaporation zone and that of the condensation zone, the lead-contaminated zinc vapors from the evaporation zone condensing in the circulating stream of molten zinc and zinc vapor contaminated with a lesser amount of lead simultaneously evaporating from said circulating stream of molten zinc without supplying additional heat to the intermediate zinc-vapor refining zone, the zinc vapor evaporated from the refining zone being condensed to relatively pure liquid zinc metal on the body of solidified zinc in the condensation zone.

2. In apparatus for separating zinc from lead of low zinc content comprising an evacuated vessel within which is provided an outermost annular spreading tube over which the molten zinc-containing lead flows in an even layer at a temperature above the melting point of zinc, and an innermost centrally disposed cooling means on which zinc vapors evaporated at the spreading tube are condensed, the improvement which comprises the provision of an intermediate annular zinc-vapor refining means disposed between said outermost spreading tube and said centrally disposed cooling means, said zinc-vapor refining means comprising a system of inclined trays disposed one above the other and facing alternately outwards and inwards, and means for maintaining a flow of molten zinc over said trays at a temperature above the melting point of zinc but below the temperature of the molten zinccontaining lead flowing over the spreading tube.

3. Apparatus according to claim 2 having collecting means for collecting molten zinc running off from the surface of solidified zinc condensed on the centrally disposed cooling means.

4. Apparatus according to claim 2 having collecting means for collecting lead-containing molten zinc that runs off the lower end of the annular zinc-vapor refining means, and means outside the evacuated vessel for recovering zinc-saturated lead which separates from said lead-containing zinc.

References Gated in the file of this patent UNITED STATES PATENTS 2,312,811 Gentil Mar. 2, 1943 2,349,409 Davis May 23, 1944 2,478,594 Queneau Aug. 9, 1949 2,720,456 Davey Oct. 11, 1955 2,823,111 Davey et a1. Feb. 11, 1958 2,939,783 Lundevall June 7, 1960 FOREIGN PATENTS 711,954 Great Britain July 14, 1954 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N0. 3,031,296 April 24, 1962 Thomas Ronald Albert Davey It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, lines 62 and 63, for molten zinc and condensed in a zone that is at a lower zone" read molten lead-containing zinc in the intermediate annular zone Signed and sealed this 14th day of August 1962.

(SEAL) Attest:

DAVID L. LADD ERNEST W. SWIDER I Commissioner of Patents Attesting Officer

Claims

1. IN THE PROCESS FOR SEPARATING AND RECOVERING ZINC FROM LEAD OF LOW ZINC CONTENT IN WHICH MOLTEN ZINC-CONTAINING LEAD AT A TEMPERATURE ABOVE THE MELTING POINT OF ZINC IS INTRODUCED UNDER VACUUM INTO AN EVAPORATION ZONE TO EVAPORATE THEREFROM ZINC VPORS CONTAINING A SMALL QUANTITY OF LEAD, AND IN WHICH THESE LEAD-CONTAMINATED ZINC VAPORS ARE CONDENSED TO LIQUID METAL ON A BODY OF SOLIDIFIED ZINC IN A CONDENSATION ZONE MAINTAINED AT A LOWER TEMPERATURE THAN THAT OF THE EVAPORATION ZONE, THE LIQUID METAL CONDENSATE BEING COLECTED AND RECOVERED, THE IMPROVEMENT WHICH COMPRISES THE PROVISION OF AN INTERMEDIATE ZINE-VAPOR REFINING ZOEN DISPOSED BETWEEN SAID EVAPORATION AND CONDENSATION ZONES, SAID ZINC-VAPOR REFINING ZONE HAVING A CIRCULATING STREAM OF MOLTEN ZINC FLOWING THERETHROUGH AT A TEMPERATURE BETWEEN THAT OF THE EVAPORATION ZONE AND THAT OF THE CONDENSATION ZONE, THE LEAD-CONTAMINATED ZINC VAPORS FROM THE EVAPORATION ZONE CONDENSING IN THE CIRCULATNG STREAM OF MOLTEN ZINC AND ZINC VAPOR CONTAMINATED FROM SAID CIRCULATING STREAM SIMULTANEOUSLY EVAPORATING FROM SAID CIRCULATING STREAM OF MOLTEN ZINC WITHOUT SUPPLYING ADDITIONAL HEAT TO THE INTERMEDIATE ZINC-VAPOR REFINING ZONE, THE ZINC VAPOR EVAPORATED FROM THE REFINING ZONE BEING CONDENSED TO RELATIVELY PURE LIQUID ZINC METAL ON THE BODY OF SOLIDIFIED ZINC IN THE CONDENSATION ZONE.