US1957930A - Refining white metal scrap - Google Patents

Description

Patented May 8, 1934 UNITED STATES- PATENT OFFICE 1,951,930 REFINING wnrre METAL sonar No Drawing. Application July 19, 1930,

Serial No. 469,255 r 7 Claims. (01. 75-17) The invention relates to processes for refining so-called white metal 01' tinor lead-base alloys in which the impurities such as antimony, arsenic, copper or iron, are converted into mush com- 5 pounds for removal, and its object is to simplify the removal and the apparatus required, and more particularly to simplify such processes when aluminum is used as the mush producing agent.

According to this invention the alloy to be refined is melted and the appropriate quantity of aluminum is added thereto in the form of flat or substantially flat pieces, such as the cuttings from aluminum sheets, which are spread over the molten metal, floating thereon, and form a protective blanket on the metal more or less excluding air and thus preventing burning whilev the temperature of the metal, is being raised to the point where the aluminum will be dissolved thereby. The aluminum is actively stirred into the metal when the latter has reached say 600 C. or preferably 620 for a few minutes. For

this purpose a power-driven stirrer is used and which, to be suitable, must be capable of creating a, downward circulation carrying the alumi-' straight aluminum or alloy, depends ,on-the amount of impurities to be removed and for a substantially complete removal should be from two to three ninths of 'the amount of such impurities by weight more or less. If the proportion of impurity metal .or metals is merely to be reduced, as distinguished from complete removal, the amount of aluminum addition is regulated accordingly.

After the stirring in of the aluminum the metal is allowed to cool to a point belowsthat at .which the aluminum compounds referred are soluble therein, or within about 100 C. of the freezing temperature of the liquid metal, and'which is generally about 300 'C., tin being presentfor even less if the metal is high in tin. Cooling to this point causes all of the products of the reaction between the aluminum and the impurity metal or ,metals to collect and float high upon the molten mass in the form of a thick mush. The mush contains not only the aluminum compounds referred to but also holds a considerable portion of the mother liquor metal adhering to and Wetting its crystals or particles and the separation of the mush from such liquid metal constitutes the next step of the process.

This is done directly, and without any preliminary separation'or filtering, by stirring preferably wood sawdust into the mush while the latter is riding on the metal in which it was made and while it is still at a low temperature, desirably about 300 C. in an-average case, adding the sawdust at the rate of about three-quarters pound per minute more or less and continuing the addition and stirring until the metallic-looking mush turns into a dark gray powder riding on the molten metal. The amount of sawdust thus used will ordinarily be from onetenth to one-quarter of the weight of the aluminum by which the mush was produced, but more can be used. A power stirrer is advisable in order to mix the mush and sawdust quickly and thoroughly. The effect is to cause the mush to drop out about 90% of the molten metal which is wetting it, so that the proportion (by weight) of this metal in the heavy mush is reduced from something over to something less than 35% in the light powder and conversely the proportion of impurity metal carried by the mush is increased from 12 or 15% to over 50% in the dry powder. Other materials than sawdust are known to produce the same effect on the mush. by an'apparent change in the surface tension of the wetting metal, and all such materials, vegetable or otherwise, which have the capacity of drying the mush when stirred into the mixture are to be understood as comprehended by the term drying agent as used herein. The composition of the resulting fine'powder varies according to the impurity metals in the original metal. A typical composition when produced by sawdust as the drying agent may -be given as Per cent Sb and/or Cu and/or As and/or Fe 50: Aluminum -s 13:

Mother liquor metal, mainly lead or tin 35: Charcoal (from sawdust) 2:

Being very fine it takes fire with great ease and burns at times with violence. Wet with water it generates hydrogen and sufficient heat to make it catch fire in the air. For this reason, it is wise to cover it on the metal with a sheet iron cover, preventing access of air. After being covered an hour or so, it will besufliciently cool to permit it to be skimmed off without burning, or the kettle can be allowed to cool over night and the powder shovelled or swept off the solid metal as convenience may decide. With good operation, the powder may weigh between seven and eight times the weight "of aluminum added.

The metal separated from the mush contains some of the introduced aluminum. The amount will not be large if the original proportions were properly determined, say not' over .02%. This residual aluminum is now to be removed and that is doneby again heating the metal to a temperature, say between 560 C. and 600 C. A power stirrer is then put in and wood sawdust or like woody or vegetable material dumped on the .metal at the rate of say about 1 pound per minute for a five-ton kettle. The sawdust catches flre and covers most of the metal with flame or=glowing charcoal. A hood is attached to the frame of the stirrer and connected to a good draft, so regulated as to carry off the smoke and yet keep the metal substantially covered with. a reducing atmosphere. This is carried on until the metal (ata temperature of say 580 C.) ceases to have a silvery white appearance and when exposed to the air acquires a brown skin of oxide. This change is' marked and indicates the practically complete removal, usually. to less than $0570.10; the aluminum.

When the dross has been removed, the remaining metal represents the primary product of the process being pure lead or tin or alloy thereof;

generally lead-tin alloy, containing a reduced amount or none of the original constituent metals, which have been referred to as impurities, according to the amount of aluminum that was used in the treatment; or according as the original metal contained other constituents not removable by the aluminum treatment. The bycompounds of aluminum with the impurity metal or metals cooling the mixture to the point at which such compound orcompounds are insoluble in the liquid metal and separating the latter from the mush produced. I

2. A step in the process of purifying metals which consists in removing the wetting metal from a mush compound insoluble in such metal by stirring a drying agent into such mush while it is floating on the metal in which made, thereby causing the adhering metal to drop away from the mush crystals and become added to the main body of metal.

3. The process of eliminating antimony, arse: nic, copper, and iron present as impurity in the class of alloys having a predominating portion of tin or'lead, which consists in stirring aluminum into a molten body of such alloy, cooling the mixture to produce an aluminum compound mush, stirring woody material into said metal and mush until the mush assumes the condition of dry powder and then separating such powder and the released metal.

4. The process of eliminating antimony, arsenic, copper or iron present as impurity in the class of alloys having a predominating portion of tin or lead, which consists in stirring aluminum into a molten body of such alloy to produce an aluminum compound mush and performing the separation of such compound and the liquid metal only after treating said mush with a material adapted to cause the liquid to be released and drop away from the solid particles of the mush into the main body of liquid metal, thereby converting said mush into the condition of powder.

5. The process of eliminating antimony, arsenic, copper or iron present as impurity in lead or tin base alloys which comprises reacting with aluminum ona moltenbath of such an alloy to produce therein a mush compound floating on the bath, such compound comprising crystals of aluminum combined with the impurity metal or metals, releasing the wetting metal from the mush crystals, allowing such released metal to drop back into the supporting bath, and treating such bath to dross off any remaining aluminum therein.

.6. The process of eliminating antimony, arsenic, copper or iron present as impurity in lead or tin base alloys which comprises reacting with aluminum on a molten bath of suchalloy to produce a mu'sh of aluminum compound, releasing the liquid wetting metal from the solid particles of such mushwhile the mush is supported on the bath, allowing the bath to solidify and removing the dried mush from the surface of the solidified metal.

7. The process of eliminating antimony, arsenic, copper or iron present as impurity in lead or tin base alloys which comprises reacting with aluminum on a bath of such alloy to produce an aluminum mush compound, releasing the wetting metal from the solid particles of such mush while the latter is floating on the bath, removing the dried particles and thereafter stirring a vegetable material into said bath until any residual aluminum therein is substantially drossed ofi.

GUSTAVE E. BEHR, J3.