US2125329A - Refining metal - Google Patents

Description

G. E. BEHR REFINING METAL Aug. 2, 1938.

Filed NOV. 8, 1,935

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REFINNG METAL Gustave E. Behr, Sewaren, N. d., assigner to National Lead Company, New York, N, Y., a corporation of New Jersey application November s, 1935, serian No. 48,854

(i Claims. (Ci. 'i5-7S) The invention relates to processes for the treatment of metals with water soluble reagents, for instance, caustic alkali, and in which steam is employed in reactive relation, or in which its presence is permissible. More particularly it relates to and is a development of the process disclosed in Dittmer Patent 1,976,333 forthe selective removal from lead, or from lead-antimony alloys, of tin, arsenic, etc. The object is the simplication of processes of this general character and of the Dittmer process in particular, and the invention is described below in connection with the latter, though without limitation thereto. 1

In the Dittmer process, the lead alloy from which the selective removal is to be made, is melted and then treated conjointly with molten sodium hydroxide and steam, resulting in the production of oxysalts of the tin and of the arsenic if present, which are taken up in the molten caustic mass while the lead, or lead and antimony as the case may be, are relatively unaffected and remain in the metal bath. `The steam promotes the reaction and, under proper temperature control, lends a high degree of selectivity to the process as between tin and arsenic on the one hand and the lead and antimony on the other, as pointed out in the Dittmer patent.

The Dittmer and other caustic treatment processes are not commercially practical unless the soda and the values in the oxysalts can be easily recovered. 'I'he usual procedure is to remove the salt-laden caustic mass from the kettle and treat it or mix it with water which dissolves the soda and any other solubles, such as sodium nitrate if that has been used, lwith the soda. vAfter metallic particles carried in the mass have been separated, the mixture is then concentrated to a certain gravity, and cooled to a certain .temperture, whereupon any insolubles and crystallized sodium or other salts are precipitated and removed, after which the remaining solution is evaporated to dryness and the soda stored to be used over again in the kettle. The separated metal is returned to the kettle.

By this invention the reclamation part of processes of this kind is substantially simplified and its cost reduced, including cost for equipment as well as operating cost, and in addition certain practical advantages are obtained as will presently become apparent.

In the accompanying drawing the invention is illustrated in diagram, Fig. 1 being a general plan and Fig. 2 an elevation of suitable equipment.

alloy of lead, antimony and tin with perhaps some arsenic and from which the tin and arsenic are to be removed, as contemplated by the Dittmer process, it is melted in a suitable kettle such -as indicated at I and therein treated simultaneously with steam and caustic alkali, preferably sodium hydroxide, under vigorous vortical stirring, as by means of a power stirrer, indicated generally by 2, mounted on or over the kettle. Such vortical stirrers are well known in the art and do not need illustration. Under the proper conditions practically all of the tin and arsenic are presently oxidized and Vtaken up by the caustic mass which in consequence gradually becomes thicker.

When such 'mass has accumulated a quantity of sodium salts but not so much as to make it Anon-fluid, the stirring is stopped and some of it is drawn off, or allowed to flow off from the surface of the metal on which it is iioating, through a cock or valve 3 and a conduit 4 to a launder 5 and thence to a receptacle 6. The outlet through the cock 3 will be understood to be located at an appropriate level for this purpose, above the metal level and below the caustic level and more than one can be provided, at different levels, if desired though only one is indicated. In any case the cock or cocks are desirably located inside of the kettle and the conduit 4 passes through the kettle wall, so that those parts are subject to the kettle heat and thereby kept from becoming plugged with congealed caustic. Obviously the caustic could be removed by ladle but the outflow system just described provides convenience and speed. Preferably, not enough of A encounters aqueous liquor or Water entering from a pipe I3 by which it is instantly disintegrated and the salts brought into solution or suspension. Depending on the metals constituting the alloy under treatment and the particular reagents used there may be more or less insoluble salts in the caustic mass, for instance, sodium stannate. Numeral 8 represents motor-driven stirring mechanism in receptacle 6 to maintain the suspension and 9 represents a motor-driven transfer pump, which is indicated as submerged in the liquid but which can be arranged elsewhere in the systemif desired.

By the operation of this pump, the solution or suspension is discharged, through a pipe l0 toV the upper part of one or the other of two settling tanks II and I2, which may be duplicates of each other and which are connected in the system by appropriate valve connections as indicated so that they can be used alternately. In the tank which is connected in service, opportunity is provided for the launder liquid to drop its solid matter.. such solids including the salts which have crystallized as well as the insolubles, all of which accumulate as sludge in the bottom of the tank. The relatively clear liquid above the sludge is taken off, by gravity flow or otherwise, by the pipe I3 above referred to and returned to the launder and receptacle 6, there to take up further soda and salts, in a circulatory manner. The pipe I3 is Vshown as having several connections I3a to each settling tank at graded levels in order to facilitate removal of clear liquid above the rising sludge level as the tank fills. A perfect separation of the solids is not necessary since the action is cumulative. v

The circulation between the launder 5 and the settling tank is more or less continuous, and the accumulation of solids in the connected tank can be allowed to continue until the liquid from the upper part is so thick with salts dissolved or suspended that it will just flow in the pipes. At such time and without reference to the attainment of any particular gravity or temperature, the tank is shut off from the circulation and its contents evacuated through the bottom cock I4 anddelivered bya pump I5 to a filter press indicated generally by I6. In this press the solids are collected in the form of a lter cake and the clear liquor, which is essentially a solution of caustic soda, is discharged by pipe I1 4to the storage tank I8.

From this tank it is withdrawn continuously or as needed by pipe I9 and delivered by the hose or pipe 20 at the end of the latter into the treating kettle I to which it thus returns the soda previously removed, while the steam resulting from the evaporation of the water of the solution on contact with the contents of the kettle, eitherescapes inactlvely to the ventilation system (not indicated) or serves asthe companion, reagent with the soda as in the Dittmer process. Except for the soda chemically combined and that entrained in the filter cake it is all returned to the kettle in the form of solution and more is of course added from time to time to make up for losses. To the extent that the soda mass may gradually accumulate salts or compounds which do not readily precipitate in the settling tanks, it can of course be treated for,` their removal from time to time but no such accumulation occurs in working on the ordinary run of secondary metals.

As a particular advantage of the process it may be noted that the removal of the molten caustic from the kettle While still fluid, is not only rapidly accomplished but automatically prevents the transfer to the launder of any kettle metal in the form of prill and thereby entirely eliminates the metal separation step necessary in the caustic alkali process as heretofore practiced, as well as the special apparatus required for it. When as heretofore customary, the soda is used in the kettle until it is so stiff it cannot longer bev stirred into the metal, it carries with it a con-' siderable quantity of prill which has to be separated, whereas by removing the mass while still too thin to suspend the prill, that is to say, while so thin that metal particles in it drop instantly back into the metal bath underneath, separation occurs in the kettle itself and substantiallyvno metal is carried off, which fact represents a material saving.

The filter cake derived from the press contains the oxysalts of the metals removed from the kettle and, depending upon what they are, maybe recovered in various ways. In the case of the removal of tin only from the kettle metal, the filter cake is largely sodium stannate, which can be sold as such, or electrolyzed to metallic -tin or smelted with lead dross to make solder stock.

vIt will,be apparent from the foregoing ,disclosure that by avoiding the costly step of reclaiming the soda in solid or dry form, as heretofore customary, the alkali treatment of metals is materially simplified and cheapened and further, that it is immaterial to the substantive invention what the nature or composition may be of the metals under treatment or the purposes of the treatment or the precise sequence of the steps. or the design of the apparatus, various modiflcations'and adaptations of the process being obviously capable of employment without departing from the scope and spirit of the invention.

The invention includes further, as a particular improvement on the Dittmer process, the delivery of the water or the return of the soda liquor directly into the throat of the deep vortex created by the stirrer in the treating kettle. Whereas it might be assumed and has heretofore been taken for granted that water introduced in liquid phase into the kettle of molten metal must be carefully directed onto the surface only of the melt in order to be there converted into steam and avoid explosions from confined evaporation below'the surface, I have found that this is not necessary and that by pointing the stream from the hose 20 directly into the center of thevortex the resulting steam, though produced under thel surface, ls utilized without explosive effect and further that by so doing the production rate of the process is materially increased. This central or sub-surface introduction of the returned soda liquor therefore characterizes. the preferred form of the new process. Y

I claim: v

1. In theA process of treating molten alloys of the kind in which an alloy-component isv reacted upon by a molten, water soluble reagent for the removal of such alloy-component, the improvement which consists in maintaining a circulation of an aqeous solution in a closed circuit, transferring the molten reagent from the kettle and depositing it in said circulation, separating accumulated solids from such solution and drawing of! some of such solution and returning it to the-kettle for further treatment of alloy.

2. In the process of treating molten alloys of the kind in which an alloy-component is 'reacted upon by a molten, water soluble reagent for the removal of such alloy-component, the improve-v ment which consists in maintaining a circulation of an aqueous solution in a closed circuit, transferring the molten reagent from the kettle while it is still thin enough not to hold metallic prill in suspension in it and depositing such molten reagent in said circulation,I allowing the solids in such solution to accumulate in a suitable chamber, removing and filtering such accumulated solids and delivering the lter liquor containing dissolved reagentA to the treatment kettle.

3. Apparatus for the caustic alkali treatment nieuwe of metals comprising e treating ltettle, e conduit thereon constituting e molten caustic overnow therefrom, and e, leunder receiving caustic from such overflow, in combination, with ineens cluding a settling tenir for circulating vwriter through seid launrier emi tenu und e, pipe conducting liquid from seid circulating ineens to said kettle.

i. Apparatus of the irind described, comprising e treating kettle, e. conduit thereon constituting a molten caustic overflow therefrom, und 1 e, launder receiving oeustie from such overnet?, in combination with e circulating pine system. inB cluding lseid leunder und including also e settling tenir, means for separating the liquor from the settlings in said tank end e pipe for conducting such liquor to seid kettle. Y

5. The process of treating molten lend elloys with caustic sode which consists in transferring the molten sode, Wliiie carrying the products et its reection with alloy ingredients, from the treatment kettle and inimneI it with water, sepuruting solids from such water und feeding such Witter' und the serleJ in solution therein into the treatment kettle tor continuing the caustic treatment of the alloy.

il. The process oi treating molten lee/1i alloys with caustic solle which consists in transferring molten soda from tl'le treatment kettle willie it is stili thin enough to flow freely enti let any metallic prill therein drop out oi it, milling Water with such transferred molten socle in e. suitable receptacle, circulating tile 'wett-:resorte mixture from seid receptacle through one or .mere sedi mentation tenias and been to seid receptacle, filtering out the accumulated solids in seid tenir end delivering the sepereted filter liquor into tile treatment kettle to serve es caustic sunnly.

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