US1731365A - Method of refining lead - Google Patents

Description

r more expedient treatment for removal of imiojreceptacle in which the metal is Patented Get. 15, 1929 PATENT foF cs JOHN P. WALKER, OF HAMMOND, INDIANA METHOD OF REFINING LEAD No Drawing.

The invention relates to the refining of lead, and particularly to the removal of impurities from lead bullion.

An object of the invention is to provide a purities from unrefined lead than that afforded by the standard pyrometallurgical softening practice. i v

The treatment may be given in the same melted, and- ,completed in less time than is required by standard practice. This treatment in the same receptacle, for instance the kettle,permits saving of initial installation, or additional installation in case of desired increased tion comprises softening capacity. Other objects and advantages of the invention will appear from the body of tliespecification.

Briefly, the method of the present invencontacting the lead while in molten state with a hydrated compound which is infusible, or substantiall so, at the temperature of the bath. The hy rated compound employed is preferably hydrated lime and preferably also the molten body of metal skilled in the art of softening or improvfn is strongly agitated during the treatment.

The method may effectively be carried out by covering the surface of molten lead' in a suitable kettle of a type well known to those g lead, with the hydrated lime or other by drated compound, and forcing a stream of air or steam through the body of molten metal. The air or steam may conveniently be introduced through pipes submerged in the molten lead, or mechanical agitation may be employed, being preferably effected by means of the well known Howard mixer, or an equivalent agitator.

. It has also been found that the, improvement hereinafter described will reduce, for example, 32% arsenic and 1.1% antimony, contained in 100 tons of lead bullion, to 019% arsenic and .07 5% antimony in a period of thirteen hours.

It has also been found that this preliminary refining has a distinct advantage in reducing the time required in the refining operation,- as performed with softener furnaces, particularly in accelerating the removal of arsenic Application filed August 25, 1928, Serial No. 302,153.

or antimony when present in large amounts. For example, it has been found that when the impure lead bullion contains more than 2% arsenic and 1.3% antimony, 7 2 hours or more are required to remove these impurities from 200 tons by the standard softening practice. lVhen, however, bullion containing such excessive amounts of impurities is subjected to the method of the present invention, which may require from 512 hours, the sub sequent softening operation can be accomplished in 18 hours or even less time.

The efficiency of the process is by no means confined to the removal of arsenic and antimony. In actual plant application, the addition of hydrated lime at'the stage of removal of zinc from metal which has been previously desilverized with zinc, gives an intense reaction, and upon brisk stirring of the reagentinto the metal the surface of the bath breaks spontaneously into flame. This application speedily removes the absorbed zinc from the metal.

I will now describe 'an embodiment of the invention Which has proved to be efiective and practical, but it is to course that I do not thereby intend to limit myself to the particular materials, proportions, etc.; the same being given merely by way of example and for purposes of illustra tion only.

Lead bullion containing arsenic or antibe understood of mony is charged into a melting kettle of, say,

100 tons capacity and is melted by heat applied to the under surface of the kettle. The molten lead is heated to approximately 117 5 F. and maintained at this temperature during the treatment.

When the lead has become molten it is covered with a layerof 300-500 pounds of hydrated lime. The body of molten metal is stirred with a Howard mixer or equivalent device, or a stream of air or steam is passed,

or a number of streams of air or steam are passed, through the bath, for example by means of submerged, pipes. The pipes are conveniently secured to the 1111181 s1de of the kettle and extend down into the molten lead two-thirds of its depth or farther.

The treatment is continued generally for six hours or more, depending on, the impurity content. The powdered lime becomes lumpy or is agglomerated by the cementing action of uncombined oxides. These lumps are colored a light brown to yellow.

During the period of removal of arsenic and antimony a certain amount of lead is continuously oxidized to litharge and enters gold, etc., by methods well knownto those skilled in the art. When the lead is desilverized by the Parkes process using metallic zinc, the residual zinc absorbed by the lead may be speedily removed by the addition of lime followed by agitation with air or steam or with a mixer alone. This operation may be carried out preferably in another kettle than the one used for desilverizing. ,In case of unusual quantities of impurities the treatinent may of course be repeated, using fresh ime. 1

The method is also efliciently applicable in case the arsenic is present in the unrefined bullion in excess of 2% and the major softening is carried out with furnaces. In this case thetreatment is preferably continued only until the arsenic content is reduced to 2%, since the antimony is not removed until the greater part of the arsenic has been "eliminated. However, all of the arsenic, and antimony can be removed by the method if desired, viz, by prolonging the time of treatment and if necessary increasing the number of fresh additions of hydrated lime. Arsenic and antimony can be removed by treatment with lime in a'shorter period than is required for the same operation when carried out in the usual way in a standard softening furnace. The Weight of skim produced per unit of antimony removed is less in the treatment 'by the present method than in the usual furnace softening.

As indicated above, the operating factorsare somewhat variable. Temperatures as low as 800 F or perhaps a little lower, may be employed for zinc removal, but it has been found that the best elimination of arsenic and antimony is obtained when the method is carried out at a temperature of 1100 F. or higher.

The purpose of stirring the molten bullion is to bring all of the lead into contact with the lime .and to turn the metalover rapidly so that it will come in contact with the lime a number of times during the course of the tact. Other methods of stirring, such for example as by over-pumping, may of course be employed.

Hydrated compounds other than hydratedlime may be employed. Magnesium compounds may be substituted for the lime compounds. Hydrated lime, however; possesses the advantage of being finely divided and requires no preliminary treatment. also inexpensive, costing at the present time less than five cents per ton of lead treated. Experience provides, of course, the best indication of the percentage. of hydrated material to be employed, but tests so far made indicate that from about 0.2 to' 0.6% by A weight is suitable, and highly satisfactory elimination is obtained when an amount of hydrated lime equal to about 0.4% of the weight of the lead is employed, with bullion of average impurity.

As examples of the efliciency of the invention, plant experience has shown that the removal of arsenic from bullion when using hydrated lime, according to the process as described, is accomplished in less than half the time required for removal when using air alone. Also that a bullion which requires 36 hours forsatisfactory removal of antimony in a 2'00-ton softener, requires only 12 t6 18 hours when treated with hydrated lime in two kettles of 100 tons capacity each.

In the removal of zinc fromidesilverized lead, the reaction of the zinc with the hydrate is so intense that the hydrogen liberated bursts into flame spontaneously;

The active radical, or portion of the hydrate, is the combined water, which is liberated in the nascent state. Steam, the use of Which for removing zinc from desilverized lead is well known to the art, does not act so intensely because it is added as such, and is not a product of-the reaction.

- The chemical reactions when rising hydrated lime, as described in the process, I

belie; to be essentially as follows:

1. emoving zinc from desilverized lead:

Further oxidation of arsenic and antimony and combination with lime produces arseniates and flIltHDOIllfitCS.

The hydrogen, which would be expected.

to. reverse the reactions, is liberated at the free surface of the metal and is immediately removed from the zone of reaction, by virtue of its extremely low density, and the porous solid nature of the hydrated lime covering.

This solid nature of the reagent permittingthe free passage of hydrogen from the zone of reaction is an advantage of the process over the use of basic alkalles, such as caustic soda. Other advantages of the solid skims produced by hydrated lime over those resulting from use of caustic alkalies are as follows 1. They can be treated by common furnace practice, Without any additional chemical plant as required for regenerating or restoring expensive alkalies.

2. The separation of the skims from the remaining metal is more convenient.

3. The skims are far safer to handle. Any

moist tools applied to molten caustic alkali used for refining by means of air'or steamv alone.

Relative to the character of the lime dross, ordinary softener furnace skims high in arsenic are commonly supposed to carry the arsenic as lead arsenate. Experience has shown that an excessive amount of coal is required to reduce this lead arsenate in the residue furnace and leave a slag of required lead content. When the treatment according to the present invention is employed in kettles, the coal required for reduction in the residue furnacewhen treating the lime dross is normal. This would indicate that the arsenic in the lime dross is combined with the lime,- allowing the lead oxide as such to be easily reduced by coal. Herein therefore lies another articular advantage of the method of re ing in accordance with the present invention.

The lime due furnace with the other refinery by-prod ucts normally treated in this furnace, or it may be treated in a, blast furnace. If treated dross may be treated in the resicontacting lead in the molten state with a basic hydrated compound which is infusible at the temperature of the lead bath.

3. Method of refining lead which'comprises contacting lead in the molten state with hydrated limel 4. Method of refining lead which comprises contacting lead in the molten state with a hydrated compound which is infusible at the temperature of the lead bath and agitating the body of the metal.

5. Method of refining lead which comprises contacting lead in the molten state with hy: drated lime and agitating the body of the metal.

6. Method of refining lead which comprises contacting lead'in the molten state with hydrated lime' and agitating the body of the metal with a stream of gaseous fluid.

7. Method of refining lead which comprises contacting lead in. the molten state with hydrated lime and agitating the body of the metal with a stream of air.

8. Method of refining lead bullion which comprises heating the same to a temperature of from about 800 F. to about 1200 F mixing hydrated lime with the same and agitating the body of metal during the treatment.

9. Method of refining lead bullion which com rises heating the same to a temperature of trom' about 800 F. to about 1200 F., mixing hydrated lime with the same and agitating the body of metal during the treatment with a stream of air.

10. Method of refining lead bullion which comprises heating the same to about 117 5 F., mixing therewith from two tenths to sixtenths percent by weight of hydrated lime and agitating the body of metal during thetreatment. i Y

11. Method of refining lead buliion which comprises heating the same to about 117 5 F., mixing therewith from two-tenths to sixtenthspercent by weight of hydrated lime and agitating the body of metal during the treatment with a stream of air.

In testimony-whereof, I aflix my signature.

- q JOHN P. WALKER.

in the latter, the charge carries only'the amount of coke required to maintain the tem perature necessary for. a liquid slag. This 1. Method of refining lead which comprises I contacting lead in the molten statewitha hydrated compound which is infusible at the temperature of the lead bath.

2. Method of refining lead which comprises