METALLURGICAL PROCESS FOR TREATING SILICON-ALUMINOUS-ALKALINE ORES, IN PARTICULAR LEUCITIC ORES

Abstract: A process for treating silicon-aluminous-alkaline ores, in particular leucitic ores, based on the reduction with carbon of said ores in an electric arc furnace for the discrete obtainment of rough aluminium-silicon alloys, on one side, and of potassic ashes on the other side, the former intended for the siderurgical-metallurgical production and the latter for the potassic fertilizer pro­ duction.

Description: "Ketallurgical process for treating silicon-aluminous alkaline ores, in particular leucitic ores, and aluminium-silicon alloys and potassic ashes so obtained" This invention relates to a metallurgical-type process applied to silicon-aluminous-alkaline ores, in particular to leucitic ores, for the discrete obtainment of rough aluminium-silicon alloys for siderurgy-metallurgy on one side, and of potassic ashes for fertilizers on the other side. Background of the invention Several processes have been proposed in the last sixty years for recovering aluminium oxide -Al203- and potassium oxide - K20 - from silicon-aluminious-alkaline ores, such as feldspars (orthoclase, leucite, sanidine and still others), notoriously widely available in nature and consequently potential important alternative raw materials for obtaining aluminium and potassium which, as is known, find broad utilizations in metallurgy (aluminium and alloys thereof) and in agriculture (potassic fertilizers). All the above said processes are based on an acid or alkaline attack of the alkaline silicon aluminate, usually involving a plurality of wet treatments, such as leachings, decantations, filtrations, etc. Among said processes, a few onesowJt of the oldest are cited hereinbelow (evidencing, for simplicity's sake, only the type of chemical attack characterizing them), from which the most recent processes are derived, name ly - the process according to Italian Patent No. 535793 (1925) based on the attack with nitric acid - HNO3 - and hydrochloric acid - HCl -; - the processes according to: French Patent No. 527066 (1920), British Patent No. 195084 (1923), French Patent No. 693074 (1930), and British Patent No. 342617 (1930), all based on the attack with lime - CaO - at 1000-1400 C; - the process based on the attack with sodium nitrate - NaN03 - under pressure, according to the documents cited by Rev. Prod. Chim. 28, 1925, 221; - the process according to French Patent No. 556994 (19?2) based on the attack with calcium hydrate - Ca(OH)2 - under pressure (for the only recovery 2 of potassium in the form of hydrate -KOHX Xore recently several other processes have been developed, out of which, for example, a process based on the attack with hydrochloric acid, another based on the dry attack by sintering with sodium carbonate - Na CO - and calcium carbonate - CaCO3 - and a further one based on the attack with sulphuric acid - H2S04 - : : this last process has been then developed distincted into derived processes substantially based (after the various acid attack operations leading to the forming of double sulphate of potassium and hydrated aluminium - E2S04. Al2(SO4)3.24 H2O -) on - separation of aluminium by precipitation -thereof with am monia - NH3 - in the form of hydrated aluminium - Al(OH)3 - and subsequent calcination of the latter to aluminium oxide - Al2O3 - (which is, therefore, one of the finished products); - utilization of the solution of ammonium sulphate - (NH4)2SO4 - and of potassium sulphate - K2SO4 - (co produced in the aforesaid precipitation with ammonia) according to one of the three alternatives sumzmarized hereinbelow - alternative a) : final production of potassium sulphate and of ammonium sulphate and mixtures thereof, through various fractionated separation operations (evaporations, coolings, centrifugations, dryings). Said sulphates are intended for fertilizers; - alternative b) : final production of K2SO4 (for fertil izers) and of clinker for cement, by means of the follon ing main operations : decomposition with lime - CaO - of said solution of aluminium sulphate and potassium sulphate for re-obtaining ammonia (which is recycled, for being reutilized, to the separation of aluminium by precipitation, as mentioned hereinbefore), and utilization of the residual mixture in water consisting of calcium sulphate - CARS, - (in suspension) and potassium sulphate (in solution) for the final production of K2SO4 (by filtration, orystallization, centrifugatin, drying), and of clinker for cement (filtration and decomposition of calcium sulphate, addition of additives and of coal); - alternative c) : it follows alternative b) with the only exception that calcium sulphate (filtered from said mixture in water of calcium sulphate and potassium sulphate), is utilized, for the anionic portion - SO4 for the production of ammonium sulphate (for fertilizers), and for the cationic portion - Ca - for the reuse of the latter in the form of CaO in said first decomposition step of the solution of ammonium sulphate and potassium sulphate. Ssid CaSO4 rertilization step is based on a leaching operation with arrjnonis and carbon dioxide - C 2 - where from said ammonium sulphate is obtained, on one side, and, on the other side, CaCO3 which, by decomposition, provides aforesaid CaO and CO2. The processes schematically-reported hereinbefore suffer from considerable drawbacks, in particular : - for the processes based on the acid attack, serious difficulties arise during the separation of the silica (which often is in the colloidal form) and during the decomposition of the alluminium salts, with remarable losses of process acid utilized for the attack. It is furthermore necessary to employ high amounts of said acid for fixing potassium in the form of salt, as well as the ammonium anion - in the form of salt too - when the process includes the use of ammonia; - for the processes based on the alkaline attack there is the necessity of employing high amounts of Ca0 and f co-prodicing great amounts of products intended for the cement industry, which have a low economic value. By consequence, the above-cited processes are - for the reasons described and specified hereinbefore - substantially complex and sntieconomic. In spite of this, in even more recent years - to stress the importance of the problem in question - further attempts have been made at succeeding in industrially utilizing the silicon-aluminous-alkaline ores by means of various processes, which however appear substantially as modified processes of the ones indicated and schematiaally described hereinabove. In partici,lar there are cited hereinbelow, with the relevant main featuring data, the following pm cesses: - the process according to b.S. Patent No. 3679361 (1972), which comprises an attack with sulph1tric acid (and the consequent known forming of double sulphate of aluminium and potassium), a calcination of said double sulphate with forming of sulphur dioxide - SO2 - (successively utilized for producing swllphuric acid, the latter being re- tilized in the same process) and of K2SO4 - Al2O3 wherefrom snccessively, by leaching, filtering and crystallizetion, K2SO4 (for fertilizers) and Al2O3 are obtained, the latter, after drying, being conveyed to its known utilizations: : - the process based on the attack with nitric acid and separation of the iron impurities -Fe3 - by extraction with acetylacetone and trichloroethylene (Paolini, Sebastiani and Variali - Chim.Ind. 62, 1980, 3); - the process based on the attack with HCl, after calcining at 120000 (Cocco, Colussi e Neriani - Chim.Applic. Ind., 1979, 77). The aforesaid three processes, as well as the preceding ones, do not depart however from the line of the classic predominantly chemical process. Beljajew - Rapoport and Firsanowa in the volume "Application of the Electrothermal Processes to the Aluminium Metallurgy" 2nd vol. (1957) diffusely treat the behaviour of alumina and silica in the electric furnace reduc- tion processes, in particular the behaviour of clays and kalins (aluminium silicates Al2O3. 2SiO2. 2H2O), which may be somethimes impure owing to the presence of alkalis (K20, Na2O). In snch work it is said that in the case of utilizetion of clays or gneiss granites impure due to alkalis, the reduction reaction trend is determinantly jeopardized by the presence of said alkalis in the reaction charge. As far as is known there are no processes based on the direct reduction of silicon-aluminous-alkaline ores which enable to substantially obtain, in a single basic metallurgical operation, the separation of aluminium and silicon, on one side, and of the alkali, on the other side (potassium, in this specific case). Also recent sti,dies carried out with a view to producing alu minium-silicon alloys in electric furnaces or by reduced tion in blast furnaces, consider the utilization of raw materials consisting of aluminium silicates, but not of alkaline silicon-aluminates. From the foregoing it is apparent that the problem of the recovery of aluminium and potassium from silicon-aluminous-alkaline ores has not yet found a satisfactory solution either by metallurgical processes or by typical ly chemical processes, especially wet-processes, the lat ter exhibiting serious drawbacks connected, on one side, with the large sizes of the plants in relation to the high masses of reagents and products involved (among which many inerts) and to the large number of process steps, and, on the other side ,with the low substance yields. Summary of the invention It is an object of the present invention to provide a process of the metallurgical type, which permits the re covery of aluminium and potassium from silicon-alumin- olas-alkaline ores, avoiding the above-mentioned drawbacks. It is another object of the present invention to accom plash said recovery of aluminium and potassium in chemically useful forms suited to their successive utilization in the metallurgical field and in the fertilizers field, respectively. These and still other objects, which will be more clearly apparent to those skilled in the art from the following description and examples, are achieved, according to the present invention, by a process based on the direct carbo-electro-thermal reduction of the above said ores (hereinafter referred to as Siliconaluminatepetassic ). Description of the invention More particularly said process consists, according to the present invention, in the following consecutive essential steps - preparation, by musing conventional methods and apparatuses, of the agglomerate (for example in the form of spherical granules or in other technically equivalent forms) of the silicon-aluminate-potassic ore with a reducing substance, sich as coke, lignite, anthracite, charcoal; - direct reduction of said agglomerate in an electric arc furnace, known in the art, by choosing and adjusting the r2n parameters of said furnace for its actual "arc" running, though in a highly ionised and therefore conduetive environment, d1çe to the presence of alkaline metals, perticulerly potassium, in the reaction medium; ; - casting of aluminium and silicon (with titanium, iron, calcium impurities) formed in said reduction and separation, by conventional techniques, of the ashes in powder containing potassium and optionally sodium (potassic ashes), entrained by the furnace gases. Said ashes may be tilized, also directly, by employing known processes, in the fertilizing formulations for agriculture. The aluminium-silicon alloy, formed in the solidification step of the abovesaid cast, can be directly utilized as deoxidising agent in siderurgy, or it may be conveyed to enrichment and plrification processes for the production of aluminium-silicon alloys having a high percentage of aluminium. The process in question, as is schematically described in the foregoing, is better illustrated by the following examples, which are given only for exemplifying purposes and are not intended to be a limitation of the present invention. In such examples, the compositions are expresses by symbols and known chemical formules, and as percentages by weight (unless otherwise specified). Example 1 A test was carried out using a lot of 1 ton of a silioon-aluminous-potassic ore having the following composition (referred to the not dried ore as such) - Al2O3 ....................... 24% - SiO2 ...................... 50% - Fe2O3 ...................... 1% - TiO2 ...................... 0.5 % - CaO ....................... 2.5 % - K2O ...................... 9.8 % - Na2O ..................... 1.0 % - MgO ...................... 0.5 % - Other impi,rities and "calcination losses" 10.7% A portion of said ore was mixed with coke and clay as a binder in order to get about 100 kg of a charge containing about 12% of coal, at the end of the pre paration of said charge, after drying of same, the fol lowing composition (calculated on the dry product) hav ing been obtained : : - Al2O3 ................... 23.87 % - SiO2 .................... 51.30 % - TiO2 .................... 0.52 % - Fe2O3 .................... 1.05 % - CaO ........................ 2.10 % - Na2O ....................... 0.84 % - K2O ........................ 7.46 % - KgO ......................... 0.42 % - C ..................... 11.78 % - Other impurities ..... 0.66 % 40 kg of charge having said composition were agglomerated, by means of a tray granulator in the form of pellets (spherical granules) having a diameter of 15-20 mm, and were charged (over an approximate 10-hour period during the reduction process) into a single-phase electric arc furnace (with a graphite electrode having a diameter of 85 mm), after a furnace preheating time of about 5 hours at approx. 150000 (arc zone). The furnace's running conditions were the following (expressed by known symbols) - Voltage between electrode and bottom of the furnace ............. 20 V - Current density ..................... 15 A/cmê -Effective power ....................... 15 kW - cos f 0.8 - Temperature of the charge ............ 2200-2250 C After a 3-hour dwell time of the charge in the furnace under the abovesaid running conditions, three successive castings of aluminium-silicon alloy were effected at three-hour intervals, and during the run the potassic ashes, entrained by the furnace gases, were. coileeted- by means of an air filter. Data and results relating to the above said test are reported hereinbelow : - Weight balance at the end of the test - Charge utilized for the forming of the autoerucible in the furnace ... approx. 1 kg - Charge resulting not reduced ...... approx. 2 kg - Casting product (Al-Si and impurities) .................. 13.75 kg - Potassic ashes .................... 4.5 kg - Gas losses ............... difference to balance. - Castings : - Product of the 1st casting ........ 3.5 kg - Product of the 2nd casting ........ 4.5 kg - Product of the 3rd casting ........ 5.75 kg - Average analysis of the cast product - Fe ......................... 2.15 % - Si ......................... 59.12 % - Al ......................... 33.16 % - K . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . absent - C . . . . . . . . . . . . . . . . . . . . . . . . . 0.08 f - Ca ........................... 4.37 % - Ti ... . . . . . . . . . . . . . . . . . . . . . 0 . 0.7 % - Na ......................... absent - Mg ......................... traces - Other substances to 100 ..... 0,42 % - Recovery yields (in the cast product in respect of the dry ore, net from the charge utilized for the auto crucible and from the not reduced one) - Aluminium ................ 90 ç - Silicon . . . . . . . . . . . . . . . . . 85 % - Composition of the potassic ashes : - Si (present in part as Si and in a small part reoxidized as SiO2) ............... 29 % - Na ................... 4.68 % - K ....................... 54 % - Al ...................... 9.31 % - C . . . . . . . . . . . . . . . . . . . . . . . . . traces - SO2 ..................... 1.2 % - Others ................. balance to 100. Example 2 A test was carried out by utilizing 500 kg of an ore of the same lot of Example 1, which was successively enriched with Al 203 to obtain - after such enrichment an "enriched ore" having the following composition (referred to the not dried. product) - Al2O3 ............................ 30.0% - SiO2 .............................. 48.0% - TiO2 ............................. 0.5% - Fe2O3 ............................ 0.8% - CaO ............................... 2.0% - Na2O .............................. 0.5% - K2O .............................. 9.0% - MgO .............................. 0.6% - Other impurities and "calcin ation losses" .............. balance to 100. A part of said enriched ore was mixed with coke and potas sic aluminate as binder, in order to obtain about 170 kg of a charge at about 12% of coal, this obtaining, at the end of the preparation of said charge, after drying of same, the following composition (on a dry basis) - Al2O3 . . . . . . . . . . . . . ... 31.0% 2 SiO .... . . . . . . . . . . . . . 41. 5% 2 - TiO2 ............................ 0.45% - Fe2O3 ........................... 0.7% - CaO ............................. 1.8% - Na2 0 . . . . . . . . . 0.7% - K2O .............................. 11.04% - MgO .............................. 0.5% - C ................................ 12.0% - Other imparities .............. balance to 100. 150 kg of a charge having said composition were agglomerated, by means of a tray-gramulator, in the form of spheric granules ("pellets") having a diameter of 15-20 mm, and were fed to the same singlephase electric furnace of Example 1 over a time-period of about 38 hovrs, after a preheating time of the furnace itself, as in Example 1. The furnace running conditions were the following: - Voltage between electrode and furnace bottom ............ 22 V -Current density ................. 17 A/cmê - Effective power .................. 17.4 kW - cos# .................... 0.81-0.83 - Temperature of the smokes ... 25-28 C. After a 3-hour r'in, 11 castings of aluminium-silicon alloy were carried out at intervals of about 3 hours, adding to the furnace feeding charge, after the first two castings, Wooden shavings for purposes of rendering the reaction mass more porous and of facilitating the release of the reaction gases. The potassic ashes were gathered as in Example 1. Data and results relating to the abovesaid tests are reported hereinbelow - Weight balance at the end of the test - Charge utilized for the forming of the autoorucible in the fur nace ............................... about 2.0 kg - Charge resulting not reduced ... about 1.8 kg - Total cast alloy (Al-Si and impurities) ................................ 48.26 kg - Potassic ashes ............................ 22.76 kg - Average analysis of the cast product - Al ............................ 43.68% - Si ............................ 49.20% - Fe ............................ 1.48$ - C .............................. 0.06% - Ca ............................... 3.89% - Ti ................................. 0.80% - Mg ................................. 0.85% - Others substances to 100 ....... 0.04% - Recovery yields (evalueted as in Example 1) -Aluminium (in the alloy) ...... 88 % - Silicon (in the alloy) ... 84 % - Potassium (in the ashes) substantially ................. 100% - Composition of the potassic ashes - Si ........................ 19.85% - Na ....................... 3.34% - K ........................ 60.19 % - Al ............................ 12.21% - SO2 ............................. 2.2 % - CO2 ............................. 1.0 % - Other substance ..... the balance to 100. Example 3 A portion of the same "enriched ore" of Example 2 was mixed with anthracite coal, lignite and potassium alumin ate as binder, in order to obtain about 160 kg of a charge at about 12.5% of coal (5% of which consisting of said lignite), thus obtaining at the conclusion of the preparation of said charge, after drying of same, the following composition (on a dry basis) - Al2O3 ....................... 30.6 % - SiO2 ........................ 41.9% - TiO .......................... 0.46% - Fe2O3 .......................... 0.80% - CaO ............................ 1.65% - Na2O ........................... 0.75% - K2O ............................ 9.85% - MgO ............................ 0.40% - C ................................ 12.50% - Other impurities ................ the balance to 100. 150 kg of a charge having said composition were agglomerated as in Example 2, dried at about 200 C and fed to the same single-phase electric furnace of Example 1 in about a 35-hour period (after preheating of said fur- nace as in the preceding Examples). The furnace running conditions were the following - Voltage between electrode and furnace bottom ............... 17 V - Current density ............... 16 A/cmê - Effective power ................. 12.8 kW - cos # ............................ 0.83 -Temperature of the smokes .... 25-28 C. After a 3-hour run, 12 castings of aluminium-silicon alloy were carried out at intervals of 2.5-3 hours, adding to the furnace feeding charge, after the first two castings, wooden shavings as in Example 2, and collecting the potassic ashes as in Example 1. Data and results relating to the abovesaid test are reported hereinbelow : - Charge utilized for the forming of the autoorucible in the furnace ........................ 2.1 kg - Charge resulting not reduced.. 1.2 kg - Total cast alloy .................. 50.15 kg - Potassic ashes ...................... 20.66 kg - Average analysis of the cast product - Al ................................... 43.13% - Si ................................... 50.19% - Fe ................................... 1.63% - Ca ........................... 3.41% - Ti ............................... 0.80% - Mg ............................... 0.69% - C ................................. 0.08% - Other substances to 100 ...... 0.07% - Recovery yields (evaluated as in Example 1) - Aluminium (in the alloy) ..... 9191 % - Silicon (in the alloy) ... 88 % - Potassium (in the ashes) .................... substantially ............. 100% - Composition of the potassic ashes - Si ............................ 16.65% - Na...................... - K 59.34 S - Al........................ 10.36% - CO ....................... 2.50% 2 2.50% - SO2 ...................... 2.84% - Other substances the balance to 100. No presence of aluminium carbide was observed in the Al-Si alloys obtained in abovesaid Examples 1, 2 and 3. This invention, as illustrated in the description and in the foregoing Examples, is susceptible of modificactions and variations all falling within the scope of the inventive concept of the invention itself, and the process details may be substituted by other technically equivalent elements. In partioular the electric furnace can be of the three -phase type and the relevant operative conditions can be adapted, according to what is known in the art, to such type of furnace.

Claims: Metallurgical process for treating silicon-alzlminons- -alkaline ores, in particular leucitic ores, and al uminium-silicon alloys and potassic ashes so obtained". Claims 1. A metallurgical process for extracting aluminium and potassium from sil icon-aluminous-alkaline ores, characterized in that a fractionated co-production of a raw aluminium-silicon alloy and of a potassic ash is accomplished by direct reduction of said ores with coal in an electric arc furnace 2. A process according to claim 1, characterized in that it comprises a first step in which said ore is ag glomerated with coal in the form of blocks, preferably ovules or balls of 1-5 cm diameter, a second step in which said ovules are subjected to a direct reduction in an electric arc furnace, and a third step in which said alloy is obtained by casting and said ash is obtained as residue, separated from said alloy. 3. A process according to claims 1 and 2, character ized in that the coal for said reduction is selected from coke, anthracite, lignite and charcoal, and the amount of same added to said ore ranges from 9% to 16% by weight, preferably from 11% to 13% by weight, expressed as "fixed carbon". 4. A process according to claims 1 and 2, characterized in that said direct reduction in the electric arc furnace is accomplished at a temperatire ranging from 2000 to 2400 C, with a voltage not lower than 15 V, and with a eurrent density of 8-18 A/cm2, preferably of 12-16 A/cm2. 5. A process according to the preceding claims, characterized in that said ores are of the leucitic type. 6. Aluminium-silicon alloys, characterized in that they are obtained according to the process claimed in the preceding claims a n d are substantially free from potassium and sodium. 7. Potassic ashes, characterized in that they are obtained according to the process claimed in the preceding claims and exhibit a minimum potassium content of 40 by weight.

Inventors: LANDI, MARIA FABRIZIA C/O ALLUMINIO ITALIA S.P.A.
Applicants: ALLUMINIO ITALIA S.P.A.
Application year: 1982
Main classification: C22C1
IPC codes: C22C1, C05D1, C22B21