Sept. '24, î[946. ' ' |_. c'. sTu'RBELLE ' 2 4, 0 82’ 4 l PRODUCTION 0F ALUMINUM File@ Jan. fle, 1945 v2 Sheets-,sheet 2 V SV i@NlY «müßen» â” ` - - -INVENTOR Luc/AN. c. „S'TUR-BH LE @à ' BY Qßf ATTORNEYS 2,408,241 Patented Sept. 24, 1946 UNITED ¿STATES >PA'rErVl‘ ` OFFICE g _Y Lucien C. Sturbelle, New York, N. Y. Application January 1s, 1943, serial No. 472,586 5 Claims. (Cl. 23--141) 1. Y This invention relates to the production of me tallic aluminum and particularly tothe produc material, such as fbauxites, clays, and coalv ashes. Metallic aluminum heretofore has been common ly obtained from sources of material which vare . tively. The lime is .used in an amount' calcu-- lated to give a slag containing a substantial amount of calcium ‘aluminate and preferably'acomposition falling within the area shownby the dot and dashlines in the phase equilibrium dia not plentiful in this country, but Which are rela ’ , to at least reduce the SiOz, FezOa and TiOz _to the elements silicon, iron, andtitanium respec-j " tion of the same from lowv grade sources of» raw tively rich in alumina. 2 erous material is used in an amount calculated ’ An object of this invention is to provide an improved, simple and inexpensive method of -pre paring metallic aluminum from low grade sources - gram of Fig. 2.- When the lime is calculated _to produce a slag that will fall Within this selected area of the phase diagram, the slag so produced of raw material, which will require a minimum of outside energy and of additional reagents; with will disintegrate into a fine powder when the slag has been cooled, such as to about 96 degrees C. which the by-productswill also be useful mate and is mainly a cli-silicate of calcium> and alu_-` rials of commercial value, and which will require 15 minum and a calcium aluminate. The propor only relatively simple and inexpensive apparatus. tion of lime» can be easily precalculatedby ref Another object of the invention is to provide erence to said phase diagram, so as to producea an improved, simple and inexpensive process of slag which will have these characteristics.r obtaining aluminum oxide and aluminum hydrox This mixture of the aluminum-containing ma-ide of relatively pure grades, which may be em 20 terial, the carboniferous material, and the lime ployed .by any of the Well-known processes for is smelted, either continuously or in batches >as the production of metallic aluminum. , desired, in a suitable furnace, and an electric Other objects and advantages Will be apparent furnace is very suitable for this purpose. When from the following description of an example of the mixture has been smelted, the result is a the invention, and the novel features will be par-v metal alloy and a slag, which are tapped from ticularly pointed out hereinafter in connection time to time from- the bottom of the furnace into with the appended claims. f \ _» ï ' a tapping mold which -is preferably conical in shape, the temperature of the smeltedmass be Fig. 1V is a flow sheet illustratingr the successive ing approximately 1600 to 1800 degrees C. The steps in one example of the process according Inthe drawings: to this invention; and _ f . " ' ._ ‘ A ' mold with the tapped mixture of' metal and slag , . therein is allowed to cool by itself, during which Fig. 2 is a diagram of a'portio-n of a phase equilibrium diagram of refractory oxides, which is advantageously .employedin connection With this invention. . , ' The diagram of Fig. 2 is knownas a compost-` tion~temperature phase equilibrium> diagram of the refractory oxides, which is published by the United States Steel Corporation, Research Lab oratory, and identified as Plate 2. Similar dia grams have been published by other concerns covering approximately the same subject matter, and this diagram illustrates the characteristics and properties of'compositions of the oxides of calcium, aluminum andsilicon, and changes in such characteristics and properties which occur as relative proportions of the -different compo nents vary. Only that portion of the chart to Which this invention relates has been illustrated. Low grade bauxites are characterized by their 10W content of alumina, which is usually between 30% and 55% aluminum oxide, A1203, with a high content of silica or iron oxide, or both. 35 the slag stratii’ies separately from vthe metal al -lo'y,~and when the ’temperature reaches about 96 degrees C. this slag swells and disintegrates into . a powder which is easily separated from the metal. The metal is largely a ferro-silicon alloy, plus impurities such as titanium, and the slag has an appearance very much like a basalt rock. The metal’alloy is marketable because it has usefulness in various industries and is not an economic loss. The slag is disintegrated into ñnely divided particles which are then leached with a sodium carbonate (NazCOs) solution, which gives a solution of sodium aluminate and a pre cipitate of calcium carbonate. After the leaching has been completed, the solid residue is sepa rated from the liquid in any suitable manner, such as by filtration. Preferably, the residue after separation of the liquid is Washed in order to recover as much as possible of the excess of the sodium carbonate and of solutions of sodium aluminateV which may adhere to the residue. Clays and ashes have a content of approximately While any suitable leaching, filtering and Washing 30% to 50% of SiO2, 30% to 50% of A1203, the 55 aparatus may, of course, be employed, one suit-y remaining content including _Fe-203, TiOz, etc. able for this purpose ,is disclosed in my copending This raw material (loW grade bauxite, clay or application Ser. No. 331,265, ñled April 23, 1940.l ashes), according to Athis invention is mixed with The composition _ofthe desired slag, as explained, a carboniferousv material, rsuch as co_al„` carbon, is largelya ldil-silicate of calcium and aluminum cokeor charcoal, and with lime.“ The Ycarbonit 60 and. a Calcium aluminate, and when such apoW 2,408,241 3 der is leached by the sodium carbonate, the re~ one which disintegrates upon cooling to facilitate its separation from the metal alloy, and be in easily leachable condition, a slag of modified com actions are as follows: 3CaO.Al2O3-1-Na2CO3-i-2H2O= 20a (OH) 2+Na2O~Al2Os-l-CaCO3 and 4 While the composition of the slag is preferably position, but contatining calcium aluminate, may be reduced to powder form in any suitable man ' ner, such as by atomizing it while fluid, or cru-she ing it, but this entails additional operations and expense that can be avoided by selecting the pro~ The residue from the leaching operation after 10 portion of lime-to produce a slag that yswells and it has been washed, as explained, is calcined, disintegrates upon cooling. The lime should, which converts it into carbon dioxide gas andV a therefore, preferably be calculated to give a slag residue containing lime. The lime so formed is that melts at a temperature not materially above used in place of fresh lime for mixing with fresh approximately 1600 degrees C., contains not in aluminum bearing materials and carbon to pI'o excess of approximately 52% or less than ap vide fresh charges to. be smelted, as above ex proximately 30% of alumina, a silica content‘less plained. The carbon dioxide gas> is used in a later than approximately 20% and a lime content. of step of the. process., which will be explained 47% to 70%. Such a slag on coolingv should cause shortly. , The solution from the filtration operation may contain s-ome silicious material which preferably crystallization of lone or more of tricalcium lsili 20 cate, tricalcium aluminate, 5:3' calciumalunii~ should be removed. Therefore, this solution from the filtration operation is preferably heated to a temperature approximately from 100 to 125 de grecsl C. and with 29 to 34 pounds per square inch pressure, with the -result that the silicious con tent is coagulated and settles. The mixture is then allowed to settle, and by adding to this set tung mixture 9» Small partv 0f the cake remaining upon the filter in the preceding operation, the set tling out is aided. It is difficult to ñlter out a 30 gelatinous silica, and for that reason, the gelati nous material is settled out andv with some of the solution is cycled or sent backwardsl to and mixed with the source of the sodium carbonate solution for the leaching operation. The clear liquid from .the settling operation is then reacted upon with the carbon dioxide obtained' from the calcination of the filtration residue. lows: This reaction isA as Yfol' This precipitates aluminum hydroxide inr rela nate, calcium aluminate, and' alpha and beta di calcium silicate, which are crystals appearing within the area deñned by the dot and dash line in the phase diagram of Fig. 2. A slag of this composition will disintegrate automatically as it cools, such as around 96 to 100 degrees C. As an example of the use of such a phase dia gram, let it be supposed that there is a slag of the following composition: . Per cent SlOz ____________________________________ _- 20 A1203 ___________________________________ __ 30 CaO ____________________________________ __ 50 This would locate the» slag on the. phase diagram (Fig. 2) at approximately the point “0.” From the diagram and by reference, it- will` be observed that such a slag lies betweenl the isotherms 1600 and 1500, so that the melting point. will be about 1530 degrees C. If such a, slag is tapped olf at 40 1600 degrees C., it will be liquid and the elements are mixed together as a homogeneous solution, but when it cools, as soon as a temperature of about 15.30 degrees C. is reached. some of the elements will` begin to crystallize in accordance This mixture, after this reaction, is then filtered 45 with well established laws shown by the diagrams, to remove the sodium carbonate solution which .and the ñrst. crystals formed will be 2CaO.SiO2, is returned to the source of sodium- carbonate because this compound has a melting point of used for the leaching operation, and since sub 2130 degrees C. andr this slag isv located in the stantially all ofthe sodium carbonate is recov~ di-silicate zone. The equilibrium of the slag is de ered and re-usedv for this purpose, it is only neces tively pure form in a solution of sodium carbonate. sary to add a small amount of fresh sodium car 50 stroyed, more crystals are formed, and aY liquidus of a lower melting point is separated, the compo bonate as a make-up solvent» Similarly the lime sition of the liquid part following the arrows on recovered by the calcination of the solids residue linesl shownA in the drawings.l The. separated crys following the leaching is nearly suñicient to pro tals being mostly 2CaO.SiOz with little A1203, the vide the li-me required for treating afresh (111211 tity of rawv material containing aluminum,- and 55 quantity of the latter in the liquidus increases. The. eutectic of this zone has a melting pointv of only a small amount of make-up lime need be aboutI 1336 degrees C. and will freeze last, but be cause many crystals of di-silicate have been formed and the quantity of silica present is lowy minum hydroxide is then calcined so as to con- 60 a large part of the alumina will crystallize as alu minate of calcium. When all of the slag is crys vert it into a relatively pure aluminum oxide, tallized, one obtains a mixture of t A1203, which is then converted into. metallic alu minum in any suitable manner, such as by an elec 1. Crystals of ZCaQSiOz trolytic aluminum cell, and the metallic alu 2. Eutectic containing CaO.A12O3.SiO2 65 minum4 may then be formed into suitable insots 3. Aluminate of’calcium. for marketing. added and that lime can> be added as limestone to solids residue from the leaching step and calcined therewith. This separated precipitate of alu During this calcination of the aluminum hy The first of these components of this crystal lized mass h'as the property of swelling at about droxide, hot gases are driven off, and these gases 96 degrees C., the second is insoluble in soda ash, may be used in the purification of the solution received from the leaching operation. Such gases 70 or sodium carbonate, and the third is soluble in soda ash, giving a solution of sodium aluminate do not enter into the chemical reaction, but are land a precipitate of carbonate of lime. used to heat the leached liquid and coagulate the Ifv now, for example, the lime is calculated to , impurities therein, such as the silicious material. give a slag of nearly the same composition but '_I'hus very little, if any, heat is lost by such cal» 75 situated at' “0'” at the other side- of the bound cination of the aluminum hydroxide. 2,408,241 .5 6 Y >bon dioxide resulting from such calcination as the source of carbon dioxide employed to pre cipitate the alumina, and returning the calcined solid residue to new batches of charging stock increase in lime and the eutectic will melt at 1265 degrees C. with a composition of: 5 together with sufficient fresh lime and carbon to maintain the proportionsr stated for the forma Percent tion of ferrosilicon and said slag. A1203 _____ __ 20 3. In the process set forth in claim 1, the fur SiOz 40 ary line, the first crystals formed would be Gehlenite >at 1596 degrees C., which is richer in A1203 than the slag. Th'eremaining liquidus will CaO __ __ _. ther steps of purifying the sodium aluminate solution obtained by leaching the slag by heat 38 This will give a separation of some lime and the whole product will be insoluble in sodium carbonate.` Therefore, to get a leachable prod ing said solution to a temperature of from 120° to 125° C., and under a pressure of from 29 to 34 pounds per square inch, thereby to coagulate the uct, it is important to have the composition of the slag fall approximately within the area en closed by the dot and dash lines, which is the boundary of th'e ternary crystallization ñeld joinf 15 ing the point 2CaO.SiOz to 5CaO.3Al2Oa and toV Y CaO.Al2O3. For practical reasons, it is better to avoid going over the 1600 degrees C. isotherm be cause that would give too vhigh a melting point with too low a content of A1203 and too low a v fluidity. In other words, the compositionshould silica therein, and separating the silica by set tling. 4. In the process set forth in claim 1, the fur ther-steps of purifying the sodium aluminate solution obtained by leaching the slag which comprise heating said solution under pressure, adding to the solution a small part of the leached slag, and settling the separated silica and said leach'ed slag. 5. In a process of producing metallic aluminum preferably remain in the zone alpha 2CaO.SlO2 from low ,grade sources of alumina containing and within the limited area defined by the dot substantial amounts of silica, such as low grade and dash lines. bauxites, clays, and coal ashes, the steps of mix To express the matter in a slightly different ing the alumina bearing material from said manner, the lime sh'ould be calculated to give a sources with carboniferous material and lime, slag which has a composition varying from with the carboniferous material present in an 3CaO.Al2Oa to 5CaO.AlzO3 with a silica compo amount approximately suilicient to reduce the nent not greatly exceeding more than one mole. 30 silica, iron oxide and titanium oxide to silicon, It will be understood that various changes in iron and titanium and the'formation of silicon the details and materials, as well as proportions, alloys, and with the lime present in an amount which have been herein described and illustrated sufñcient to give, upon smelting of the mixture, in order to explain the nature of the invention, a slag which contains calcium aluminate and di may be made by those skilled in the art within calcium silicate’and wherein the calcium alumi the principle and scope of th'e invention as ex nate is present as tricalcium aluminate and 5:3 pressed in the appended claims. l ' calcium aluminate and mixtures thereof, said ' I claim as my invention: slag further'being such as to disintegrate auto y 1. In a process of producing alumina by fusion matically upon cooling, smelting th'e mixture, of low grade and silicious alumina-bearing mate 40 cooling the same to effect a separation of the rial with carbon and lime and subsequent extrac alloyed metals from the slag and the solidiñca tion of the alumina from the resulting slag by tion of the yslag with disintegration at low tem leaching with sodium carbonate, the steps com peratures, leaching the disintegrated slag with prising adding to the low grade alumina-bearing - a sodium carbonate solution to form a solution material enough carbon to convert iron and sili con contained therein to the metallic state with of sodium aluminate and a residue of dicalcium the formation of a ferrosilicon, and enough lime / to form a, slag separating on cooling from said ferrosilicon composed essentially of dicalcium silicate and calcium aluminate in which the ra- ’ tio of lime to alumina is between three parts of lime to‘one of alumina and five parts of lime to th'ree of alumina, heating the mixture to fusion and for a time sufficient to form said ferrosilicon and slag, cooling the mass to effect separation of the ferrosilicon from the slag,'leaching the slag with a solution of sodium carbonate, thereby to extract substantially all of the alumina there in as sodium aluminate in solution and leave a residue composed essentially of dicalcium sili cate and calcium carbonate, purifying the solu tion from colloidal silica contained therein, pre cipitating the alumina from the purified solution by adding thereto carbon dioxide and thereby regenerating sodium carbonate, returning the regeneratedsodium carbonate solution to leach further quantities of slag, vand recovering the precipitated alumina. ,_ 2. In th'e process set forth in claim 1, the fur ther steps of calcining the residue of dicalcium silicate and calcium carbonate, utilizing the car-_ silicate and precipitated calcium carbonate, heating the liquid from the leaching step to coag ulate the silicious content thereof, separating the coagulated silica by settling, treating the so pur ified liquid with carbon dioxide to precipitate aluminum hydroxide and form a solution of so dium carbonate, separating th'e aluminum hy droxide from said solution to form aluminum hy droxide with the liberation of hot gases, using the heat of said gases to heat the liquid from the leaching operation to effect the coagulation of -the silicious content, calcining the residue of dicalcium silicate and calcium carbonate to re lease carbon dioxide and recover'a lime-silica mixture, using the released carbon dioxide as lthe precipítant for the aluminum hydroxide, return ing. the lime-silica mixture to fresh charges of alumina bearing material together with such quantities of lime and carbon as are required to “ form the said auoys and slag, returning the solu tion of sodium carbonate` regenerated by the pre cipitation of the aluminum hydroxide to the f leaching step, and treating the precipitated alu minum hydroxide to recover aluminum there from. LUCIEN C. STURBELLE.