US1617887A - Manufacture of lead compounds - Google Patents

Description

R. WILHELM Feb. 15, w27.

MANUFAGTURE 0F LEAD coxvrPouNDsl 3 sheetsnsneei 1 Filed Sept. 24. 1925 `.20.55750 .P DmODDm@ mm W@ LUMJJOU .Cm/3o v MN O R. WILHELM MANUFACTURE OF LEAD COMPOUNDS Feb. 1,5, 1927.

Filed sept. 24. 1925 5 sheets-Sheet 2 w WRX OTrWQJD.

VPatented Feb. 1927.

" UNITED STATES PATENT OFFICE. ,V

REINHOLD WILHELM, OF SOUTH MELBOURNE, VICTORIA, AUSTRALIA, ASSIGNOB T0 THE COMMONWEALTH WHITE LEAD &; IPAIISPIISr PROPRIETARY LIMITED, OF MEL- BOURNE, ,AUSTRALIA, A COMPANY REGISTERED UNDER THE LAWS OF THE STATE or VICTORIA.

MANUFACTURE or LEAD COMPOUNDS.

I Application led September 24, 1925. Serial No. 58,357, and in Australia March 30, 1925.

This invention relates to the manufacture of lead compounds and -more particularly to the manufacture of lead oxides (massicot and read lead), carbonates of lead and sulphates of lead. y

The primary object of the invention is to obtain, with econom and safety, an intermediate compound o lead in such form that it can be readily converted into the final lead compounds of high puritysuitable for the manufacture of pigments of great covering capacity, the manufacture of flint glass and, in general, for commercial purposes Where a high grade product is required.

In the production of lead monoxidel (PbO)` preparatory to its conversion into lead compounds it is known to subject metallic leadI to the action of heat in' the presence of'a blast or current`of air, the lead being converted to a finely divided powder and carried away in the air current from which itis separated, mainly aslead monoxide, and collected for subsequent treatment by selected re-agents to form the required lead compounds'. 4

Owing to the injurious effect of lead or its compounds upon the'health of the operatives if the dust isinhaled or absorbed into the system and also on account of economy,l

of thepowder of lead or its compounds. It is also advantageous, in converting thev leadA into the desired compounds, that a relatively large area of the lead should be exposed to the` re-agents in order that the latter may react thoroughly with the lead.

The present invention provides a process which fulfills these conditions and enables a high grade product to be obtained with expediency. The invention in its broad aspect, comprises the production of a brlquettc from dust-sized particles of partly-oxidized lead (which may be wholly or partially converted thereafter into partly-oxidized and hydrated lead) and which will be referred to hereinafter as partly-oxidized lead dust, or simply as dust, these particles being separated from each other in the briquette by minute spaces which maybe occupied by air, water, re-agents or reaction products, and the subsequent treatment of the b`riquettes by selected re-agents` according to the nature of the product required. The br1quettes are of such formation as to allow thorough and effective penetration by the desired re-agent without the need for agitating machinery or devices, which, when employed in such operations 4have been 1iable to cause escape of dust and consequent contamination of the atmosphere and also absorb a considerable amount of power.

The temperature to which the metallic lead is heated to effect pulverization is, in accordance with this invention, so low and the rateof conversion of the lead into dust is so rapid that contamination of the lead by the material constituting the apparatus is negligible.

The mode of dividing or reducing the metallic lead into dust, according to this invention, is such that the possibility of the dust. escaping tothe atmosphere is eliminated owing to the fact that the vessel or dust producer in which pulverization takes .place is under a slightly negative pressure relative to the atmosphercrpressure. That is to say the air current is induced into and through the dust producer in such a manner as to positively prevent the loss of an dust. This fine dust is preferably mixe with water to form a coherent mass which may be moulded or pressed into briquettes, which, for the production of certain compounds, may or may not be aged as hereinafter described, and suitably treated for the production of the specified lead compounds.

From the period at which the dust is formed to the stage whereat it is moulded into the briquettes, the dust is contained within a leak proof system or within a systern wherein all leaks are inward; and as the dust is in the form of a moist coherent mass when it arrives at the moulding station, there is not any free dust liable to escape and contaminate the atmosphere. The briquettes so produced rapidly harden or set and may be easily -handled with the least possible danger to the operatives, lwhilst they have been found to be readily permeably to re-acting mediums.

In order to ensure thepbest results it is desirable that the briquettes are so shaped that any-particle thereof is within about half an inch of a free or exposed surface so as to allow effective and thorough penctration ofthe re-agents.

The utilization of the partly-oxidized lead dust in the .form of the said briquettes is an important feature of the lnvention. For instance if, in the manufacture of red lead, (Pb3O4) the lead dust was placed in a roasting furnace, only a comparatively thin layer of the dust could be used to secure proper conversion unless agitators or stirrers were employed. If the dust was introduced in thicker'layers, stirring or agitat` ing devices would be necessary to enable effective penetration of the re-agents, and there would always be a possibility of the dust being scattered so that collecting devices would be required for its recovery.

In the transformation of metallic lead to lead monoxide (massicot PbO) and red lead (13h30,) there should be a gain in weight of approximately 7% and 10% respectively; therefore, with proper supervision and elflcient dust collecting devices the cost of conversion according to this invention should be largely, if not wholly, compensated for by this increase.

1t is well known that the highest grade of red lead is a material known as orange mineral or orange lead and this is usually obtained by roasting white lead (normally 2PbCO3.Pb(OH) 2) at .a temperature below.

dull redl heat (not higher than 550o C.) and such a result is achieved by the present in vention by roasting the briquettes at a temperature below dull red heat (not higher than 550o C.) after they have been aged.

But in order that this invention may be better understood reference will now be made to the accompanying drawings which are to be taken as part of this specification and read herewith, and whichl illustrate, somewhat diagrammatically, a preferred form o f apparatus for use in this invention Figure l is ay part sectional elevation of a suitable apparatus for reducing or dividing lead into dust, collecting the dust and mixing. water' therewith to form a plastic mass sui able for moulding into briquettes in accordance with the present invention.

Figure 2 1s a cross sectional View of a rotary drum or container in which the lead is reduced to dust form as an initial step in the production of lead compounds.

Figure 3 indicates a suitable type of press for. moulding the hydrated lead dust into britluettes.

,Figure 4 s a perspective view of a briquette of a preferred formation -in accordance with the invention.

Figure 5 is a vertical sectional view of the briquette.

Figure 6 is a part sectional elevation showing a suit-able muie furnace wherein the briquettes may be converted into desired compounds such as litharge and red lead.

quettes do not require to be aged Figure 7 is a chart in which the process for producing briquettes, formed from partly-oxidized lead dust, for conversion into specific lead compounds is indicated step by ste I llii carrying out the invention metallic lead (see Figure '1) is pulverized at A by the action of heat in the presence of a current of air, which latter carries the particles of lead dust away in suspension. 'lhe dustvis precipitated from the air current at B and is mixed with water at C to form a plastic, coherent mass. The coherent mass is then moulded at D into briquettes of a suitable shape which are allowed to set or harden at E. For conversion into certain lead compounds the briquettes are first aged at F before treatment by the appropriate re-action agents, whilst for other compounds the briprior to treatment by re-action agents.

For example, aged briquettes may be subjected to heat treatment in the presence of air as indicated at Gr and H for conversion, respectively, into lead monoxide PbO (massicot) and red lead Pb304). To produce lead sulphates the briquettes are aged and may then be subjected to acid treatment as indicated at J For carbonates of lead and certain other lead compounds, however, un-

, is introduced into the interior of a rotatable drum or cylinder 2 which may be sup'- ported by rollers 3 and provided with a toothed or sprocket wheel 4 whereby it may be rotated. The drum is suitably housed within a furnace 6 which 'may be oil fired as indicated at 7. The lead is preferably introduced into the drum 2 by way of a feed opening 8`at one end, and if desired the lead may be fed into the drum in a molten condition from a melting bath or receptacle 9 suitably disposed as to be heated by the furnace gases or products of combustion. A feed pipe" 11 leads from the bath t) to conduct the molten lead by way of the feed opening into the drum. A manually operable Valve 12 may be interposed in the feed pipe 11 in order to enable the rate of feed to be controlled and adjusted as desired.

|The rotatable drum, which vmay be constructed of cast iron or other suitable material, is preferably provided with a series of longitudinal partitions or ribs 13 which are spaced at circumferential intervals around the inner wall of the drum and form troughs 14. The ribs 13 project inwardly from the inner wall ina direction that is between a radial and a tangential direction. The rotary drum is heatedby the furnace to a temperature above the melting point of lili ' in quantity as drum and the dust collectors.

lead (but not so highly as to form massicot this quantity-formation would tend to choke up the drum and thus would interfere with the proper working of the process) and the rotation of the drum causes the lead mass to be carried around. 1n the troughs 14 and raised to such' a positlon that the lead mass overiows or runs out of the troughs and falls by gravity to the bottom Iof the drum. Air is induced through thefeed opening 8 of the drum 2 and caused tov pass longitudinally through the drum 2 and out of an outlet opening 16 at the other end to one or a series of dust separators or collectors as will be more fully referred to hereafter. Thus the streams of lead mass which fall from the troughs as aforesaid are in the direct passage of the induced air :current, whereby minute particles thereof are carried in suspension by theair current from which they are precipitated in the dust collec-tors to a ne dust or impalpable powder. The directon of the air current through the drum 2 and the dust collectors is indicated byarrovvs in Figure 1.

To provide for the separation and collection of the minute dust particles a stationary conduit or fitting 17 may be suitably supported in order to register with the outlet opening 16 of the drum and this conduitV may have a branch' leading to a first or primary dust collector 18 into Which the heavier particles of lead in the air current may fall by gravity. This lirst dust collector is preferably provided with an air inlet aperture 19 through which atmospheric air is induced into the conduit, the provision of this air inlet minimizing the liability ofvany of the lighter particles of lead dust falling into they first collector. It will be evident that the air entering this inlet aperture 19 will prevent the dust escaping from the first collectorinto the atmosphere so that perfect safety is ensured. The relatively heavy particles of dust collected in the first collector may be returned to the rotary drum 2 for further treatment at' desired intervals.

Another branch of the conduit 17 may be suitably connected as at 20 to a second dust collector 21,which may also be connected by a conduit 22 to a third dust collector 23,\

a suitable suction fan 24 being arranged to ensure a current of air passing through the It is to be understood that I do not Wish to limit myself to the precise arrangement of dust col-4 lectors herein described and illustrated and that a greater or'lesser number .thereof may be employedI as desired.

The dust precipitated by the collectors is preferably delivered into a casing 26, the interior of vvhich forms a combined conveying and mixing chamber 27 wherein the dust is mixed with Water and coniieyed to a briguette forming station. Accordingly the dust collectors 21 and 23 mayA have delivery openings 28 Which register with aperthereby form a coherent mass of a- .consis-y tency suitable for pressing or moulding into briquettes.

The pump 32 may be suitably driven from thescrew conveyor spindle 34 and means may be provided to regulate the rate of feed of the Water in accordance with the amount of dust entering the mixing chamber.

F rom the mixing chamber 27 the moistened dust is delivered to a press or a mould* ing apparatus 35 indicated diagrammatically yin Figure 3 Which is adapted to mould it into briquettes of the desired formation. The briquettes 36 may be made in the form of dat blocks or they may be of cylindrical form or again they may be made in the nature of rods of a limited diameter, but it is advisable that., Whatever shape is imparted to the briquettes, any particle thereof should be Within `about one half an inch from a free or exposed surface to allow thorough penetration of the re-acting agents. The briquettes are preferably moulded into the form of rectangular yblocks (Figures 4 and 5) and are perforated by a series of through passages 37, Whilst the exposed surfaces may, if desired, be provided with channels 38 as shown.

In instances Where it is necessary for the briquettes to be subjected to heat in order to bring about their conversion into the required product (for example in the production of redlead, Pb304) it is advisable that the dimensions of the passages 37 and the body of the briquette should be so proportioned as to permit proper radiation of the heat from the briquette, as otherwise local high temperature may prevail, causing fusion of a part of the briquette and thus preventing eifective penetration of the re-acting agents. A briquette 5" by 4 by 21/2 with evenly spaced perforations 37 and channels 38, has been found very suitable for carrying out the invention and is offfconvenient size and Weight for handling.

The dust, when moistened with water and moulded into briquettes as' aforesaid, tends lli to become heated and the briquettes speedily set or harden. f Upon exposure to moisture, they are inclined to turn greyish in colour owing to the formation of hydrate .and carbonate lof lead. In other Words they turn partially into a lrind of White lead, and

- uct desired; thus, in the production of white y lead, ageing is not essential, but if an unaged briquette be used in the production of red lead or litharge, the resultlng action may be so rapid as to render heat control difficult, and result in an unsatisfactory product.

If desired the briquette may be aged by exposure to air with or without the addition of moisture, or if desired the ageing may be conducted by exposing the briquettes to Warm moist air exhausted from drying chambers. It has been found, however, that the ageing is generally more thorough and complete when the briquettes are exposed to ordinary atmospheric air.

lVhen the briquettes are to be used for the production of red lead, Pb304, they vmay ybe first aged and then treated preferably in a cast iron mule furnace 41, (Figure 6) .at

a temperature-of not higher than 550 C.' Air is admitted through an inlet 42 at o'ne end of the Inutile furnace and an air exhaust flue 43 is provided-at the other end. The briquettes may be arranged in end to end formation (with slight spaces between ad] acent briquettes) upon suitable trays 44 adapted for insertion into the furnace in such manner that the perforations 37 of the series of.briquettes undergoing treatment are aligned, thereby providing longitudinal passageways for the air which is thus allowed to penetrate thoroughly into the briquettes. The inlet 42 of the furnace may be fitted with a door or closure 46 having apertures 47, and a suitable regulator 48 may be associated herewith to control the admission of air according to requirements. A damper 49 may Aalsobe interposed in the air exhaust flue 43 for a like purpose. The furnace may if desired be oil fired as indicated at 51 and the products of combustion may `be caused to follow a tortuous path as indicated by the arrows for the purpose of ensuring even leat distribution relative to the furnace 41.

, The numeral 52 indicates a discharge vent can be readily ground into line powder for commercial use. v

I have found that aged briquettes produced as aforesaid after only four hours roasting at a temperature not higher .than 550 C. (for example, about 490 C.) contain red lead, and that, by roasting the Vaged briquettes at a higher temperature,

complete conversion to yellow lead monoxide (massicot) is effected in less than two hours.

Where it is desired to produce white lead (white carbonate of lead) the briquettes,

with or without initial ageing, may be converted by the Dutch or stack method. thev briquettes being preferably stacked so that the perforations thereof provide a series of substantially vertical passageways for the circulation and penetration of the reaction gases.

To produce lead sulphates from the briquettes, by the inter-action of sulp'huric acid, itis esential that the briquette should be completely aged prior toy such treatment.

It will, however, be understood that the treatment to which the briquettes, whether aged or unaged, may be subjected for conversion into the various lead compounds or salts will vary according to the particular product desired, but these conversion processes will generally conform to known methods foi` converting metallic lead or lead oxides into the various salts, and, as such, need not be further described except to state that the briquettes may or may not be aged prior to conversion. v

Having now described my invention what I claim as new and desire to secure by Letters Patent is:- l

1'. A process for manufacturing lead compounds which consists in mixing dust-sized particles of partly-oxidized lead with water toproduce a plastic mass; forming `a briquette therefrom; and thereafter converting such briquette intothe required final lead compound by subjecting it to reactionary treatment.

2. In a process for manufacturing -lead compounds, the steps of pulverizing metallic lead to a fine dust by the action of heat in the presence of a current of air, precipitating the particles of dust from the air current, mixing the precipitated dust with water to form a coherent mass, and shaping said mass into briquettes for conversion into the required inel lead compounds by reactionary treatment.

3. A process for manufacturingl lead conipounds. which consists in pulverizing metallic'lead to a fine dust by the action of heat in the presence of a current of air, precipitating the particles of dust from the air current, mixing the precipitated dust with water to form a coherent mass, shaping said mass into briquettes, ageing the briquettes lln by exposure to air` and subjecting the aged briquettes to reactionary treatment for conversion into the required nal lead compounds.

4. A briquette for use in the manufacture of lead compounds, composed of dust-sized particles of hydrated. partly-oxidized lead separated from each other by minute spaces, the briquette being of such formation that any one of said dust-sized particles therein plastic mass, and shaping such mass into\ 1 briquettes for subsequent reactlonary treatment.

6. In the vmanufacture of lead compounds,

4the step of shaping a coherent mass of dust` sized particles of partly-05ndizedy metallic lead into briquettes 4for subsequent reactionary treatment.

7. In the manufacture of lead rompounds, the step of shaping a coherent mass of dustsized yparticles of partly-oxidized pig or metallic lead into briquettes for subsequent reactionary treatment, such briquettes having passages through them so that any particle in a briquette is within about half an inch of a free or exposed surface of the briquette. Y y

8. In the manufacture of lead compounds, the steps of mixing dust-sized particles of partly-oxidized lead with Water to form a plastic mass, and shaping such mass into briquettes for subsequent reactionary treatment, such briquettes having passages through them so that any partir-1e in a briquette'is Within about half an inch of a free or expoed surface of the briquette.

In testimony whereof I aflix my signature.

REINHOLD IVILHELM.

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