US3254988A - Thermal reduction - Google Patents

Description

`une 7, 1966 w. SCHMIDT ET Ax. 3,254,988

THERMAL REDUCTION Filed July 19, 1965 5 Sheets-Sheet 1 BGVaQLLNBD s33a93c1 Banlvasdwal INVENTOIB WALTHER SCHMIDT GEORGE PARKER KOCH BY 7 M Mw ATTORNEYS June 7, 1966 w. SCHMIDT ET AL I THERMAL REDUCTLON Filed July 19, 1963 3 Sheets-Sheet 2 INVENTOIS WALTHER SCHMIDT GEORGE PARKER KOCH ATTORNEYS `lune 7, 1966 w. SCHMIDT ET AL 3,254,988

THERMAL REDUCTION Filed July 19, 1963 5 Sheets-Sheet I5 CHARGE:

SILICO N H EAT RAW ALLOY M ERCURY EXTRACTION l l RAW ALLOY I ANO MERCURY l SEPARATION MERCURY INTERMETAUIC COMPLExEs l slLICON i OISTILILUON DlsTl LLATION MELTING CRINOAND slEvE I M CUR Y SILICONALLIC i MERCURY ER Y lNTERMET ALUMINUM COMPLEXES l l FLOTATION lNTERMErALLIC I SILI CON J COMPLEX FIGB INVENTORS WALTHER SCHMIDT GEORGE PARKER KOCH BY @www ATTORNEYS 3,254,988 THERMAL REDUCTIN Walther Schmidt and George Parker Koch, Henrico County, Va., assignors to Reynolds Metals Company, Richmond, Va., a corporation of Delaware Filed .luly 19, 1963, Ser. No. 296,283 16 Claims. (Cl. 75-68) This invention relates to the direct thermal reduction of alumina-bearing materials to form aluminum alloys and more particularly, to the thermal smelting of raw -aluminum-silicon alloys for the specic purpose of further purifying them so as to obtain either partially purified alloys or aluminum of commercial purity. This invention is particularly useful for the preparation of aluminumsilicon alloys having more than 50% of aluminum and containing minor amounts of contaminants such as iron, titanium, carbon, etc.

The thermal reduction of alumina-bearing materials to form aluminum alloys is well known in the art and usually involves treatment of oxidic ores such as alumina, bauxite, clay, kaolin, kyanite, etc. with suflicient carbon, at elevated temperatures, in order to reduce the charge to the metallic state. However, the many problems attending such a reduction reaction are also well known in the art and have, in fact, seriously hindered the heretofore practiced thermal reduction processes from becoming economically optimized. As is well known, it takes a certain amount of energy, usually in the form of electrical energy, to reduce alumina-bearing materials to the corresponding liquid metal. If, in fact, the liquid metal can- .not be fully recovered, a significant economic defect in the reduction process is developed in that expended energy, which has a direct relationship to cost, has served no useful purpose. In this regard, it is known, for example, that the aluminum metal resulting from the reduction of the alumina-bearing ores has a tendency to be vaporized out of the reaction zone and into the atmosphere, thereby detracting from the overall yield of aluminum. Additionally, and perhaps more significantly, the reduced aluminum metal easily back reacts with the carbon present as the reducing agent or the carbon monoxide inherently formed in the reaction system to yield aluminum carbide. The presence of aluminum carbide is exteremely undesirable, not only due to the fact that additional energy has to be expended in order to extract aluminum from aluminum carbide, but also due to the fact that aluminum carbide can form a fused ternary system with aluminum and aluminum oxide. The fused ternary system is extremely viscous and creates many practical operating problems since it accumulates at the cooler parts of the furnace building up gummy masses which ultimately must be removed by shutting down the furnace and clean-- ing it.

There have been many proposals made in the prior art in an attempt to solve the problems hereinabove referred to but, for the mostpart, the prior art solutions have not been completely satisfactory. The most com-mon proposal involved counteractin-g the formation of aluminum carbide by the simultaneous reduction of silica to form silicon. It has long kbeen recognized that 2 moles of aluminum carbide will react with 3 moles of silica to give 8 moles of aluminum plus 3 moles of silicon. The addition of silica to the feed Was for the purpose of destroying the aluminum carbide formed by the reaction of the aluminum and the carbon present in the system. However, a very practical problem encountered in the use of silica is the fact that severe losses of aluminum from vaporization will result unless an excess of silica is employed in order to lower the vapor pressure of the aluminum. Thus, for commercial operations the smelting of an alloy having a ratio of about 60% aluminum to about Patented .lune 7, 1966 lss 40% silicon is a Well established compromise both for counteracting they formation of aluminum carbide and preventing the loss of -aluminum through vaporization.

However, when a relatively large amount of silica is employed as a furnace feed, the feed tends to form fused masses before silica will be substantially reduced. `Reference to the phase diagram of alumina and silica which appears in FIGURE 1 will show that a ratio of 57% A1203 and 43% SiO-2 has a melting point of about 1810 C. It can be seen that operating with a relatively high portion of silica can lead to the formation of gummy viscous products containing oxides, carbides and reduced metals which tend to .accumulate at the cooler parts of the furnace, thereby ultimately causing complete shutdown of the smelting furnace. Moreover, it is conventional practice to charge the furnace -feed in the form of briquets in which the canbonaceous reducing agent is finely divided throughout the briquet, and if fusion of the oxides occurs, the carbonaceous material has a tendency to segregate from the liquid, thereby leaving the oxide unreduced. Another problem encountered with the use of high amounts of silica resides in the fact that the fused masses which can form, crust over `and hinder the escape of carbon monoxide, which is inherently formed in the reaction system. It is therefore essential to provide a briqueted furnace feed which does not readily yfuse but tends to keep in shape until it is reduced to metal. Therefore, again (with reference to FIGURE 1, it would be more preferred to operate to the right of the 1810 point, .but beyond this point in the diagram insufficient silica would be present to counteract the formation of aluminum carbide as well as to sufliciently lower the vapor pressure of aluminum to minimize losses due to vaporization from the hot zone.

In an attempt to arrive at an improved process, the prior art resorted'to replacing a portion of the silica with metallic silicon. The use of a furnace feed comprising alumina, silica, and metallic silicon did, in fact, accomplish the desired objectives of counteracting the formation of aluminum carbide as well as sufficiently lowering the vapor pressure of aluminum in order to minimize losses due to vaporization. However, the advantages gained in the heretofore proposed prior art processes by the cyclic use of silicon in the furnace feed -were to a large extent offset by the losses in both products and starting materials due to inefliciencies resulting from improper integration of the various steps of the process as a whole.

Therefore, it is the primary object of this invention to provide a novel process for the direct thermal reduction of alumina-bearing materials to form aluminum alloys and subsequently beneciating the raw alloys in such a manner that losses of desired products will be minimized.

It is still another object of this invention to provide a novel process for the production of aluminum-silicon alloys wherein elemental silicon is added to the furnace feed and the various process steps are integrated in such -a manner so as to mutually co-act to obtain an efficient and economical process.

Other advantages and objects Will become apparent from the ensuing description of the novel process.

It has now been found that the above objectives can be attained by carrying out the thermal reduction of aluminabearing ores, in the presence of elemental silicon, in such a manner involving multiple separation and recycle steps so as to fully integrate each and every operation resulting in a very compact and eicient continuous process.

The novel process of this invention is carried out by adding elemental silicon to the furnace feed in a conventional electrical submerged arc furnace and subsequently recovering the silicon and recycling it back to the furnace.

FIGURE 2 represents a typical ilow sheet of the novel process and the invention will become clearer with reference thereto. As can be seen, the furnace feed is composed of three components, one being a carbonaceous reductant, preferably in the form of coke or charcoal, the second being a mixture of alumina and silica or alumina and silica-bearing ores, such as bauxite, clay, kaolin, kyanite, or mixtures thereof, and the third component being elemental silicon. The furnace feed is heated at a ternperature of about 2000 C. until the oxides are reduced to the metallic state and the liquid alloys are tapped. The liquid alloys are then allowed to cool'and silicon begins to crystallize out of the charge at ,about 1000 C. thereby enriching the liquid in aluminum. When cooling approaches the eutectic point, which occurs at about 578 C., an aluminum-silicon alloy exists in the liquid phase and contains about 12% silicon whereas the solid phases consist of free silicon and various intermetallic compounds of aluminum and/or silicon with impurities such as iron, titanium, calcium, chromium or manganese. The solid and liquid phases are then separated by any number of conventional techniques including filtration, decantationv and centrifuging. Up to thisA stage the instant process follows generally the teachings of the prior art. However, at this point the vast majority of the prior art processes either discarded the solid phases or recycled them back to the furnace feed.

It can be seen that either of the two alternate prior art procedures resulted in serious economic deficiencies in the process when it is considered as an entity. It is pointed out that as -a practical matter the separation of the solid and liquid phases of the raw alloy cannot be accomplished at 100% efficiency. Assuming e.g. a raw alloy of which the eutectic constituent is 70% of the total weight, a good efficiency of 90% separaton would yield 63 parts liquid ph-ase and would leave 7 parts eutectic within 37 parts solid phase or 19.5% `of thelatter being eutectic.

Since the eiciency depends on very close controls of ternperature and its uniformity throughout the segregated matter, batches with less efficiency occur frequently. If the eiiiciency is only 80%, the amount of trapped eutectic within the solids would be 31.8% of the solids.A Fluctuations between these limits or even more are to be considered quite normal under the conditions of practical operations. If the solid phases were then discarded it can be seen that a twofold detriment occurred in the process. In the first place, some valuable aluminum-silicon alloy, as well as elemental silicon, was lost, and secondly, more elemental silicon had to be added to the next charge in the furnace feed lthus increasing the overall cost of operation.

However, if in fact the solid phases were not discarded but recycled back to the furnace, serious operational and economic problems arose. With from 20 to 30% of the eutectic aluminum alloy contained in the solid phases, the conductivity of the recycle briquets was very much enhanced. As can well be appreciated, the eutectic, which is molten at 578 C., can fuse together forming conductive bridges which tend to locally shorten out the current. Since with a-given ampere output of the transformer equipment the heat output depends on the resistance, it can seriously drop if the resistance is reduced. One extremely serious consequence of having a liuctuation of heat output resides in the f-act that the maximum temperature in the reduction furnace cannot be obtained in the shortest possible time. As is well known in the art, the formation of aluminum carbide from alumina is favored attemperature from `about 1700 -to l800 C. whereas the reduction of alumina to aluminumis favoredat about 2000" C. Therefore, if the heat output of the furnace is affected due to the aforementioned conductive bridges, the charge material dwells too long at the 1700 to 1800 temperature, thereby causing economic difficulties as regard to the eiiiciency of the process. Additionally, another disadvantage stemming from recycling back solid phases containing an unduly, high percentage of eutectic is the fact that under the driving force of a given voltage, higher conductivity often results in stray currents into the furnace space remote from the reduction zone, thereby creating a situation wherein current expended ldoes not function to reduce the charge but rather adds to the danger zone in which carbide formation is favored. l

Other disadvantages of the heretofore proposed processes stem from the very nature of the thermal reduction itself. It is pointed out that while the smelting of aluminum silicon alloys is a very delicate operation requiring extreme care and control, the treatment of segregating crystals out of the raw alloy and separating the resulting liquid and solid phases is a cruder metallurgical operation subject to many fluctuations from batch to batch. As a practical matter small changes of temperature may result in variations in the amount of eutectic retained within the mass of crystals. Thus, if a centrifugal separation is employed the eiiciency with one of the same alloy may vary as much as between 55-65% recovery of liquid phase due to the difficulties involved in controlling uniform distribution of temperature and also due to human factors entering into this type of'operation, such as occasional delays in timing. Therefore, the heretofore proposed processes attempted to perform a delicate smelting operation requiring an extremely high degree of uniformity and coupled it with a treatment of much cruder nature yielding a recycle metal of varying composition. The process of the instant invention solves this problem by conditioning the recycle solid phases so as to obtain a uniform and controlled composition while at the same time recovering valuable products from itl In direct opposition to the prior art teachings the process of the instant invention neither recycles the solid phases obtained from the initial separation of the liquid and solid phases by conventional techniques such as filtration, decantation and, more preferably, centrifuging, nor does it discard them. Instead the instant invention re- `sides in further treatment of the solid phasesvin order to remove a substantial portion of the eutectic aluminumsilicon alloy contained therein so as to minimize the heretofore enumerated disadvantages stemming from recycling back a lcomposition containing too high a percentage of eutectic alloy. The separation of the eutectic alloy from the solid phases'can be accomplished merely by comminuting the solid phases in a ball mill and then passing the reduced particles through'a screen ranging from 30-300 mesh, and more preferably 140-200 mesh. It has been found that the fraction which does not pass through the screen, i.e., the coarser fraction, Will contain an extremely high percentage of aluminum-silicon eutectic, whereas the portion-passing through the screen is silicon, virtually free of aluminum-silicon alloy. The aluminum-silicon alloy can either then be added to the aluminum-silicon alloy previously recovered in the liquid phase, or even more desirably, recycled back to the raw alloy and again reseparated in the manner above 'described. The silicon is of course recycled back to the furnace.

It can be seen that this separationdoes, in fact, increase the efiiciency and economy of the process in that it not only allows for more aluminum-silicon alloy to be recovered than has heretofore been possible, but it also minimizes the danger of forming conductive bridges due to recycling the eutectic alloy back into the furnace.

A further modification of the separation process is necessary when impure or naturally occurring ores are smelted since certain amounts of intermetallic complexes or compounds, mainly of iron and titanium, but occasionally with other metals such as calcium, manganese and chromium, are Ainherently formed due to the fact that these naturally occurring ores contain these metals as impurities and these metals can combine with either or both of the aluminum and silicon and form compounds or complexes which have only a very limited solubility in the liquid eutectic which is extracted, i.e., by centrifuging` Therefore, when impure or naturally occurring ores areused the solid phases would contain a substantial amount of these impure metallics. It is evident that cyclic use of these complex materials would lead to great operational difliculties, especially when it is considered that commercial smelting operations are continuous 24 hour operations. The problems arising are directly related to the fact that the recycled iron and/ or titanium contained in the solid phases would add to the iron and/ or titanium .being introduced by the impure ores and after several cycles these metals, or compounds thereof, would accumulate and become an unduly high percentage of the feed which would overburden the furnace. It can be seen that the production of an alloy with a high degree of purity would become considerably difficult since the composition of the raw alloy would change with every cycle.

Therefore, the instant process would make a further separation of the solid phases in order to remove the intermetallic complexes from the silicon thereby assuring uniformity of recycled material. The separation is carried out by treating the fraction which passes through the screen either as it is or after further comminution. For optimum results it is recommended to further comminute to -270 mesh since it lhas been observed that at or below that degree of fineness the silicon crystals are almost entirely liberated from the crystals of intermetallic compounds and/or complexes. The separation of silicon from the intermetallic complexes can be accomplished in any convenient manner but particular preference is given to flotation treatments.

The flotation separation can be carried out by subjecting `the mixture of silicon and intermetallic complexes to froth flotation utilizing a fluoride salt and a lluorine-containing acid as the flotation medium. The fluoride salts which are operable are not narrowly critical and include a wide variety of fluoride salts, the only limitation being that the particular fluoride salt be sufliciently Water soluble to provide a source of fluoride ions. However, preference is given to the alkali metal fluorides, including sodium, potassium and lithium fluoride, as well as mixtures thereof. Similarly, a wide variety of fluorine-containing acids can be employed provided they are sufficiently soluble in water to provide fluoride ions. Although hydrofluoric acid is the preferred fluorine-containing acid, other fluorine-containing acids can be employed such as fluoroboric, fluorosilicic, fluorochromic, fluorogermanic, fluoroplumic, fluorophosphoric, fluorosulfonic, etc.

The flotation process is carried `out simply by introducing the feed into a conventional flotation cell provided with means for supplying air to the lower portion thereof and containing an aqueous solution of the fluoride salt, adding an appropriate amount of ilumine-containing acid, conditioning for a period of time ranging from l to 60 minutes and then floating. In this manner relatively pure silicon metal will be recovered in the overflow from the cells whereas the remaining constituents will be depressed and will pass out in the underflow from the cells.

The amount of fiuorine-containing acid and fluoride salt which is employed in aqueous solution will obviously vary depending not only on the specific acid and salt used, but on the exact nature of the mixture desired to be treated, but also on the degree of efficiency desired. However, it has been found that for about an 80% efficiency in the recovery of free silicon about 30.0 milliliters of the fluorine-containing acid and about 40.0 grams of the fluorine salt in 2.5 liters of water should be employed for 500 grams of the material desired to be treated. It is to be understood, however, that the above limits are a minimum only and in actual practice the fluorine-containing acid can range from about 5.5 to 50 milliliters per 100 grams of feed, and the fluoride salt can range from 4 to 35 grams per 100 grams of feed. Additionally it is preferred that suflicient water be used so that the pH of the flotation system range from 3.4 to 5.5.

The silicon thus obtained by the separation is then recycled back to the furnace feed, thus assuring a uniformity of operation. The intermetallic complexes are substantially Within the tailings and can either be discarded or sold. y

It is to be understood, however, that the process of this invention is also applicable to the preparation of commercially pure aluminum rather than aluminum-silicon alloys. In this connection reference is made to FIGURE 3 where a typical flow sheet for a process for the production of aluminum is set forth. It can be seen that the basic steps of this invention do not change whether pure aluminum or an alloy is desired to be produced. If pure aluminum is the desired product, the procedure involved would reside in treating the raw alloy with a metallic solvent such as lead, zinc, mercury, etc., as is well known in the art, in order to leach out the aluminum followed by separating the liquid and solid'phases by centrifuging, filtering, etc. The aluminum is then recovered from the liquid metallic solvent by any number of conventional techniques, inclu-ding distillation and melting `in order to obtain commercially pure aluminum. As can be seen from FIGURE 3, the solid phases are processed in the identical same manner as described with reference to FIGURE 2 so that this invention is equally applicable for the production of either pure aluminum or partially purified aluminum-silicon alloys.

A further modification of the process of the instant invention for the production of commercially pure aluminum as outlined in FIGURE 3 would be to follow the process outlined in FIGURE 2 until the raw alloy is separated into the liquid phase and solid phases and then to continue to process the solid phase as set forth in FIGURE 2 while subjecting the partially purified liquid phase to mercury extraction as shown in FIGURE 3.

It is to be understood that although the invention has been described with reference to cooling the raw alloy to the eutectic temperature Vof about 578 C. prior to separating the liquid and solid phases, many variations of the temperature are possible. It is known that the composition of an aluminum-silicon alloy varies with the temperature at which the raw alloy is cooled and the specific compositions obtained at a particular temperature are a matter of preference depending on the intended use for the finished alloy. However, in the vast majority of commercial operations this temperature ranges from 578-680 C. with a temperature of about 610 C. being the most preferred.

The following examples will illustrate the best mode now contemplated for carrying out this invention.

Example l This example will illustrate the novel process of this invention for the preparation of an aluminum-silicon alloy. In this example, relatively pure feed materials are employed.

A conventional electrical submerged are furnace is charged with briquets containing a sufiicient amount of a carbonaceous reducing agent and the following constituents:

Kaolin Bayer Alumina Pick-up Silico Iron, kg kg. Oxides, Metal, Oxides, Metal, kg. kg. kg. kg.

Totals- 45. 56 23. 03 91. 30 48. 35 0. 12 28. 50

. ed by repeated centrifugal separation.

The charge is then reduced in a conventional manner and tapped to yield a raw alloy of the following composition:

Kg. Aluminum 61.00 Silicon 37.80

Titanium 0.10

Iron 1.10

The raW alloy is cooled to approximately 610 C. and subjected to separation by a centrifuge to yield a liquid phase and solid phases havingthe following compositions:

Liquid, kg. Solid; kg.

Al 53. 20 7. 80 Si- 8. 50 Fe 0. 65 Ti 0. 06

Total 62. 41

The solid phases are then comminuted in a ball mill From the above example it can be seen that the process of the instant' invention offers considerable advantages over the heretofore practiced processes. In the -rst place the ner portion (-100 mesh) yis predominantly silicon and can be recycled to the'furnace feed without danger of shorting out the current due to the formation of conductive bridges caused by too high va percentage of eutectic in the recycle. Also, the coarser fraction (+100 mesh) may be used to produce silicon containing aluminum alloys, c g. by dilution With cornmercial aluminum to obtain alloys like those commonly known as Nos. 13, 330 or 380 or can be remelted and united with the raw alloy in order to be cyclically puri- Additionally it is evident that the recovery of useful alloys is raised from 62.41 kg. to 71.50 kg. (62.41+9.09), an increase of approximately 14%.

Example Il This example will also illustrate the preparation of an -aluminum-silicon alloy but it differs from Example I in that impure feed materials are employed rather than the pure Bayer alumina.

A conventional electrical submerged arc furnace is charged with briquets containing a sufficient amount of a carbonaceous reducing agent and th'e lfollowing constituents:

'8 The charge is then reduced in a conventional manner and tapped to yield the raw alloy of the following composition:

Aluminum 455.1 Silicon 179.8 Titanium 28.6 Iron 12.8 Total 676.3

The raw alloy is cooled to approximately 610 C. and is then subjected to separation by centrifuging to yield -a liquid phase vand solid phases having the following composition:

Metal Liquid Phase Solid Phase (kgJ (kg.)

Totals 409. 5 266. 8

The solid phases are then comminuted in a ball mill and sieved through a 200 mesh screen with the following results:

Metal +200 mesh -200 mesh (kg.) (kg.)

From the above it can be seen that the +200 mesh fraction is of sufficient purity to be treated in identically the same manner as disclosed in Example I. Hoivever, the 200-mesh fraction contains a substantial amount of iron'and titanium, due to the use of impure feed materials and at this stage cannot be recycled back to the reduction furnace without experiencing many operational difficulties. Therefore, the -2010 mesh fraction is then subjected to froth otation which is carried out by dispersing the 147.6 kg. of lthe 200 mesh fraction into Water to which is added sufficient sodium fluoride and concentrated hydrofluoric acid so that the pH ranges from 3.4 to 5.5. The mixture is then conditioned and oated with the following results:

Metal Froth (Con- Tails, (kg.)

centrate), (kg.)

From the above example, it can be seen that in the concentrate substantially pure silicon was recovered which can be recycled back to the furnace feed. The tailings may either be discarded or can be sold for such purposes as steel deoxidation or related purposes in which the tailings can act as a reductant, e.g. in producing magnesium from dolomite. Additionally, since the tailings contain a fairly 'high concentration of titanium, the material can also be used to recover titanium compounds which can also be sold.

From this example it can be seen that the novel process of this linvention does in fact optimize production of aluminum-silicon alloys. It can be seen that by comminuting and sieving the solid phases a substantial amount of additional aluminum-silicon alloy is recovered and, by further treatment of the finer mesh fraction by flotation, that relatively pure silicon can be recovered which can be recycled back to the furnace thereby making the operation a completely integrated one.

It is to be understood that although the above two examples have shown the production of aluminum-silicon alloys the process of this invention is equally applicable to the production 4of commercially pure aluminum. Thus for example, the aluminum-silicon alloy, either in its raw state or in its partially purified state, can be subjected to conventional mercury extraction resulting in leaching out most of the aluminum by mercury and thereafter separating the aluminum amalgam from the insoluble silicon and various intermetallics, as is well known in the art. The aluminum can then be recovered from the amalgam by melting and distillation.

The screen sizes referred to in the specification and claims are United States Bureau of Standards, Standard Screen Series, 1919 as set forth at page 878 of Langes Handbook of Chemistry, 8th Edition (1952).

What is claimed is:

1. A process for the production of a partially purified aluminum-silicon alloy from oxidic ores which comprises:

(a) Charginga reduction furnace with a feed com? prising alumina, silica, elemental silicon and a carbonaceous reducing agent;

(b) Heating the feed until the oxides are reduced to the metallic state and a raw alloy is formed;

(c) Tapping the resulting raw liquid alloy;

(d) Cooling the raw alloy to a temperature ranging from -about 578-680 C. so as to form liquid and soli-d phases;

(e) Separating the resulting liquid phase consisting of substantially purified aluminum-silicon alloy from the solid phases comprising elemental silicon, intermetallic complexes and a portion of the eutectic aluminum-silicon alloy;

(f) Comminuting the solid phases and separating them into a coarse fraction capable of being retained on `a 30-300 mesh screen and into a fine fraction capable of passing through said 30-300 mesh screen;

(g) Recycling the coarse fraction consisting of substantially pure aluminum-silicon alloy, back to the raw alloy;

(h) Separating elemental silicon from the fine fraction consisting of a mixture of elemental silicon and intermetallic complexes; and

(i) Recycling the elemental silicon back to the furnace.

2. The process of claim 1 wherein the separa-tion of elemental silicon from a mixture of the same with the intermetallic complexes is accomplished by subjecting the mixture to froth flotation with a flotation medium comprising a fluoride salt and a fiuorine-containing acid.

3. The process of claim 2 wherein the uorine-containing acid is hydrofluoric acid and the fluoride salt is sodium fluoride.

4. A process for the production of aluminum from oxidic ores which comprises:

(a) Charging a reduction furnace with a feed comprising alumina, silica, elemental silicon and a carbonaceous reducing agent;

(b) Heating the feed until the oxides are reduced to the metallic state and a raw alloy is formed;

(c) Tapping the resulting raw liquid alloy;

(d) Cooling the raw alloy to a temperature ranging from about 578-680 C. `so as to form liquid and solid phases;

(e) Separating the resulting liquid phase consisting of substantially purified aluminum-silicon alloy from the solid phases comprising elemental silicon, intermetallic complexes and a portion of the eutectic aluminum-silicon alloy;

(f) Comminuting the solid phases and separating them -into a coarse fraction capable of being retained on a 30-300 mesh screen and into a fine fraction capable `of passing through said 30-300 mesh screen;

(g) Recycling the coarse fraction consisting of substantially pure aluminum-silicon alloy back to the raw alloy;

(h) Separating the elemental silicon from the fine fraction consisting of a mixture of elemental silicon and intermetallic complexes;

(i) Recycling the elemental silicon back to the furnace;

(j) Treating the aluminum-silicon alloy liquid phase with a metallic solvent for aluminum; and

(k) vRecovering substantially pure aluminum.

5. The process of claim 4 wherein the separation of silicon from a mixture of the same with the intermetallic complexes is -accomplished by subjecting the mixture to froth flotation with a flotation medium consisting of a fiuorine-containing acid and a fluoride salt.

6. The'process of claim 5 wherein the fluorine-containing acid is hydrofluoric acid and the fluoride salt is sodium fluoride.

7. The process of claim 4 wherein the metallic solvent for aluminum is selected from the group consisting of mercury, zinc and lead.

8. The process of claim 7 wherein the metallic solvent is mercury.

9. A process for the production of a partially purified aluminum-silicon alloy from oxidic ores which comprises:

(a) charging a reductionr furnace with a relatively pure feed comprising alumina, silica, elemental silicon and a carbonaceous reducing agent;

(b) heating the feed until the oxides are reduced to the metallic state and a raw alloy is formed;

(c) tapping the resulting raw liquid alloy;

(d) cooling the raw alloy to a` temperature ranging from about 578-680 C. so as to form liquid and solid phases;

(e) separating the resulting liquid-phase consisting of substantially purified aluminum-silicon alloy from the solid phases comprising elemental silicon, intermetallic complexes and a portion of the eutectic aluminum-silicon alloy;

(f) Comminuting the solid phases and separating them into a coarse fraction capable of being retained on a 30-300 mesh screen and into a fine fraction capable of passing through said 30-300 mesh screen;

(g) recycling the fine fraction `back to the smelting furnace.

10. A process for the production of a partially purified aluminum-Silicon alloy from oxidic ores which comprises:

(a) charging a reduction furnace with a relatively pure feed comprising alumina, silica, elemental silicon and a carbonaceous reducing agent;

(b) heating the feed until the oxides are reduced to the metallic state and a raw alloy is formed;

(c) tapping the resulting raw liquid alloy;

(d) cooling the raw alloy to a temperature ranging from about 578-680 C. .so as to form liquid and solid phases;

(e) separating the resulting liquid phase consisting of substantially puried aluminum-silicon alloy from the solid phases comprising elemental silicon, intermetallic complexes and a portion of the eutectic aluminum-silicon alloy;

(f) com minuting the solid phases and separating them int-o a coarse fraction capable of being retained on a 30-300 mesh screen and into a fine fraction` capable of passing through said 30-300 mesh screen;

(g) recycling the coarse fraction consisting of substantially purified aluminum-silicon alloy back to the raw alloy; and

(h) recycling the fine fraction back to the smelting furnace.

11. A process for the production of aluminum from oxidic ores which comprises:

(a) charging a reduction furnace with a feed comprising alumina, silica, elemental silicon and a carbonaceous reducing agent;

(b) heating the feed until the oxides are reduced to the metallic state and a raw alloy is formed;

(c) tapping the resulting raw liquid alloy;

(d) cooling the raw alloy to a temperature ranging from about 578-680 C. so as to form liquid and solid phases;

(e) separating the resulting liquid phases consisting of substantially purified aluminum-silicon alloy from the solid phases comprising elemental silicon, intermetallic complexes and a portion of the eutectic aluminum-silicon alloy;

(f) comminuting the solid phases and separating them into a coarse fraction capable of being retained on a 30-300 mesh screen and into a fine fraction capable of passing through said 30-300 mesh screen;

(g) recycling the fine fraction back to the smeltng furnace;

(h) treating the aluminum-silicon alloy, obtained as liquid phase in step (e), with a metallic solvent for aluminum; and

(i) recovering substantially purel aluminum.

12. A process for the production of aluminum from oxidi; ores Which comprises:

(a) charging a reduction furnace with a feed comprising alumina, silica, elemental silicon and a carbonaceous reducing agent;

(b) heating the feed until the oxides are reduced to the metallic state and a raw alloy is formed;

(c) tapping the resulting raw liquid alloy;

(d) cooling the raw alloy to a temperature ranging from about 578-680 C. so as to form liquidand solid phases;

(e) separating the resulting liquid phase consisting of substantially purified aluminum-silicon alloy from -the solid phases comprising elemental silicon, intermetallic complexes and a portion of the eutectic aluminumsilicon alloy;

(f) comminuting the solid phases and separating them into a coarse fraction capable of being retained on a 30-300 mesh screen and into a fine fraction capable of passing through said 30-300 mesh screen;

(g) recycling the coarse fraction consisting of substantially purified aluminum-silicon alloy back to theraw alloy;

(h) recycling the fine fraction back to the smelting furnace;

(i) treating the aluminum-silicon alloy, obtained as liquid phase in step (e), with a metallic solvent for aluminum; and

(j) recovering substantially pure aluminum.

13. A process for the production of aluminum from oxidic ores which comprises:

(a) charging a reducti-on furnace with a relatively pure feed comprising alumina, silica, elemental silicon and a carbonaceous reducing agent;

(b) lheating the feed until the oxides are reduced to the metallic state and a raw alloy is formed;

(c) tapping -the resulting raw liquid alloy;

(d) treating the aluminum-silicon alloy with a metallic solvent for aluminum;

(e) recovering substantially pure aluminum;

(f) comminuting the solid phases and separating them into a coarse fraction capableof being retained on a 30-300 mesh screen and into a fine fraction capable of passing through said 30-300 mesh screen; and

(g) recycling the fine lfraction back to the smelting furnace.

14. A process for the production of apartially `purified aluminum-silicon alloy from oxidic ores whichV comprises:

(a) charging a reduction furnace with a feed comprising alumina, silica, elemental silicon and a carbonaceous reducing agent;

(b) lheating the feed until the oxides are reduced to the metallic state and a raw alloy is formed;

(c) tapping the resulting raw liquid alloy;

(d) cooling the raw lalloy to a temperature ranging from about 578-680 C. so as to form liquid and solid phases;

(e) separating the resulting liquid phase consisting of substantially purified aluminum-silicon alloy from the solid phases comprising elemental silicon, intermetallic complexes and a portion of the `eutectit: aluminum-silicon alloy;

(f) comminuting the solid phases and separating them into a coarse fraction capable of being retained on a 30-300 mesh screen and into a fine fraction capable of passing through said 30-300 mesh screen;

(g) separating elemental silicon from the fine fraction consisting of a mixture of elemental silicon and intermetallic complexes; and

(h) recycling the elemental silicon back to the furnace.

15. A process for thev production of aluminum from oxidic ores which comprises;

(a) charging a reduction furnace with a feed comprising alumina, silica, elemental silicon and a carbonaceous reducing agent;

(b) heating the feed until the oxides are-reduced t0 the metallic state and a raw alloy is formed;

(c) tapping the resulting raw liquid alloy;

(d) cooling the raw alloy to a temperature ranging from about 578-680 C. so as to form liquid and solid phases;

(e) separating the resulting liquid phase consisting of substantially purified aluminum-silicon alloy from the solid phases comprising elemental silicon, intermetallic complexes and a portion of the eutectic aluminum-silicon alloy;

(f) comminuting the solid phases and separating them into a coarse fraction capable of being retained on a 30-300 mesh screen and into a fine fraction Capable of passing through said 30-30() mesh screen;

(g) separating the elemental silicon from the fine fraction consisting of a mixture of elemental silicon and intermetallic complexes;

(h) recycling the elemental silicon back to the furnace;

(i) treating the aluminum-silicon alloy liquid phase with a metallic solvent for aluminum; and

(j) recovering substantially pure aluminum.

16. A process for the production of aluminum from oxidic ores which comprises:

(a) charging a reduction furnace with a relatively purefeed comprising alumina, silica, elemental silicon an a carbonaceous reducing agent;

(b) heating the feed until the oxides are reduced to the metallic state and a raw alloy is formed;

(c) tapping the resulting raw liquid alloy;

(d) treating the aluminum-silicon alloy with a metallic solvent for aluminum;

(e) recovering substantially pure aluminum;

(f) comminuting the solid phases and separating them into a coarse fraction capable of being retained on a 30-300 mesh screen and into ya fine fraction capable lof passing through said 30-300 mesh screen;

(g) separating the elemental silicon from the fine fraction consisting of a mixture of elemental silicon and intermetallic complexes; and

(h) recycling the elemental silicon back to the furnace.

l (References on following page) References Cited by the Examiner UNITED STATES PATENTS Cowles 75-68 Hoopes 75-68 Lester 75--68 McLellan 75-68 Loomis 75-68 1 4 3,102,805 9/ 1963 Messner 75-68 3,116,997 1/ 1964 Kohlmeyer 75-68 FOREIGN PATENTS 156,854 6/ 1954 Australia. 672,216 5/ 1952 Great Britain.

DAVID L. RECK, Primary Examiner. H. W. CUMMINGS, Assistant Examiner.

Claims (1)

1. A PROCESS FOR THE PRODUCTION OF A PARTIALLY PURIFIED ALUMINUM-SILICON ALLOY FROM OXIDIC ORES WHICH COMPRISES: (A) CHARGING A REDUCTION FURNACE WITH A FEED COMPRISING ALUMINA, SILICA, ELEMENTAL SILICON AND A CARBONACEOUS REDUCING AGENT; (B) HEATING THE FEED UNTIL THE OXIDES ARE REDUCED TO THE METALLIC STATE AND A RAW ALLOY IS FORMED; (C) TAPPING THE RESULTING RAW LIQUID ALLOY; (D) COOLING THE RAW ALLOY TO A TEMPERATURE RANGING FROM ABOUT 578-680*C. SO AS TO FORM LIQUID AND SOLID PHASES; (E) SEPARATING THE RESULTING LIQUID PHASE CONTAINING OF SUBSTANTIALLY PURIFIED ALUMINUM-SILICON ALLOY FROM THE SOLID PHASES COMPRISING ELEMENTAL SILICON, INTERMETALLIC COMPLEXES AND A PORTION OF THE EUTECTIC ALUMINUM-SILICON ALLOY; (F) COMMINUTING THE SOLID PHASES AND SEPARATING THEM INTO A COARSE FRACTION CAPABLE OF BEING RETAINED ON A 30-300 MESH SCREEN AND INTO A FINE FRACTION CA-

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