RO125454A2

RO125454A2 - Process and electrolyte for producing aluminium

Info

Publication number: RO125454A2
Application number: ROA200800924A
Authority: RO
Inventors: Ioan Galasiu; Rodica Romola Galasiu; Sever Vasile Şerban; Emil Stepan
Original assignee: Institutul De Chimie Fizică "Ilie Murgulescu"; Institutul Naţional De Cercetare-Dezvoltare Pentru Chimie Şi Petrochimie - Icechim
Priority date: 2008-11-25
Filing date: 2008-11-25
Publication date: 2010-05-28

Abstract

The invention relates to a process and an electrolyte for producing aluminium by electrolysis in melted salts. According to the invention, the process uses an electrolytic cell having a pole gap of 1...4 cm, with carbon anodes and wettable cathodes made of composite materials containing TiBor ZrBas perforated plates placed under the anode and vertically movable to adjust the pole gap or remove damaged cathodes, the aluminium being deposited on the cathodes and running through the cathode perforations down to the aluminium layer on the cell bottom, the carbon block on the bottom of the electrolytic cell not being eroded by the mud layer deposited under the aluminium layer, as it is not alive, the working temperatures being in the range of 720...970°C. The electrolyte is a KF - AlFeutectic having a composition of 40...50 moles% of KF + 50...40 moles% AlF, at a melting temperature of 560...570°C, with admixtures of 1...3% NaF, LiF or CaFand, optionally, Mg F, BaF, NaCl, in a ratio of 1...7%, preferably 45 moles% of KF + 55 moles% of AlF, with admixtures of 2...3% NaF, LiF or CaF, and which do not form crusts on the cathode during low temperature electrolysis.

Description

PROCEDEU SI ELECTROLIT PENTRU FABRICAREA ALUMINIULUIPROCESS AND ELECTROLYTE FOR THE MANUFACTURE OF ALUMINUM

Invenția se refera la un procedeu si un electrolit pentru fabricarea aluminiului, prin electroliza in topitura, cu anozi de cărbune sau anozi inerti, cu dimensiuni stabile, obținuți din materiale non-carbon, si catozi de cărbune sau catozi umectabili, obținuți din materiale compozite care conțin TiB₂ sau ZrB₂.The invention relates to a process and an electrolyte for the manufacture of aluminum, by molten electrolysis, with coal anodes or inert anodes, with stable dimensions, obtained from non-carbon materials, and carbon cathodes or wettable cathodes, obtained from composite materials which contain TiB ₂ or ZrB ₂ .

Se cunosc numeroase procedee si compozitii de electrolit pentru fabricarea aluminiului, prin electroliza in topitura.Numerous electrolyte processes and compositions are known for the manufacture of aluminum by melt electrolysis.

In prezent, fabricarea aluminiului se face prin electroliza unor topituri criolit alumina, la temperaturi de 940 - 970°C. Din cauza temperaturii ridicate, consumul de energie electrica este mare. Astfel, consumul teoretic, calculat termodinamic este de 6,34 kWh/kg Al, in timp ce consumul practic este de aproximativ 14-15 kWh/kg Al. Datorita temperaturii ridicate de electroliza, toate materialele din care este construita celula de electroliza se degradează prin reacțiile la temperatiri ridicate cu criolit topit, iar durata de viata a celulelor este scurta, 2-3 ani. Prețul materialelor din care este construita celula de electroliza este ridicat. Pentru construcția ei se folosește un cheson din fier sub forma de cuva, in care se aseaza mai multe straturi de cărămizi refractare si izolante, iar peste acestea se aseaza catozii de cărbune. Repararea unei celule de electroliza implica un timp de staționare pentru racirea ei de la temperature de 970°C la temperature ambianta, demolarea si timpul necesar pentru reconstrucția ei. Toate acestea, împreuna cu prețul materialelor de construcție si prețul forței de munca măresc prețul de cost al aluminiului.Currently, the manufacture of aluminum is done by electrolysis of cryolite alumina melts, at temperatures of 940 - 970 ° C. Due to the high temperature, the electricity consumption is high. Thus, the theoretical consumption, calculated thermodynamically is 6.34 kWh / kg Al, while the practical consumption is about 14-15 kWh / kg Al. Due to the high electrolysis temperature, all the materials from which the electrolysis cell is built are degraded by reactions at high temperatures with molten cryolite, and the life of the cells is short, 2-3 years. The price of the materials from which the electrolysis cell is made is high. For its construction, an iron caisson is used in the form of a tub, in which several layers of refractory and insulating bricks are placed, and over them are placed coal cathodes. Repairing an electrolysis cell involves a downtime for its cooling from temperatures of 970 ° C to ambient temperatures, demolition and the time required for its reconstruction. All this, together with the price of building materials and the price of labor, increase the cost price of aluminum.

Electrolitul care se folosește in prezent la fabricarea aluminiului este criolit topit (Na₃AlF₆), cu adaosuri de A1F₃ in proporție de pana la 10 - 11%, CaF₂ in proporție de 4 - 6 %, A1₂O₃ in proporție de pana la 7 - 8%. Unele fabricatii mai adauga in electrolit LiF, MgF₂, NaCl in proporție de 1 - 5% si alte săruri. Temperatura de electroliza este in toate cazurile cuprinsa intre 940 - 970°C. Temperatura de topire a electrolitului poate fi coborâta prin adaosuri de A1F₃. Sistemul NaF - A1F₃ are un eutectic care topește la aproximativ 700°C, la un continui de A1F₃ de aproximativ 0,45 moli %. Aceste adaosuri, prezintă insa unele dezavantaje. In sărurile topite, conductia electrica este o conductie ionica. In cazul topiturilor criolit - alumina, curentul de electroliza este transportat spre catod de către ionii de sodiu care sunt ionii cei mai mici si mai mobili. Ceilalți ioni din topitura sunt ioni complecși, mari si cu o mobilitate mica. Din cauza aceasta, in vecinătatea catodului creste concentrația de NaF si in aceasta regiune din celula se solidifica electrolitul si se formează cruste solide pe suprafața catodului, deoarece electrolitii cu o concentrație mai mare de NaF au puncte de topire mai ridicate. Aceste cruste, daca ocupa parțial suprafața catodului măresc rezistenta electrica a ve'fThe electrolyte currently used in the manufacture of aluminum is molten cryolite (Na ₃ AlF ₆ ), with additions of A1F ₃ in proportion of up to 10 - 11%, CaF ₂ in proportion of 4 - 6%, A1 ₂ O ₃ in proportion up to 7 - 8%. Some manufactures add in the electrolyte LiF, MgF ₂ , NaCl in a proportion of 1 - 5% and other salts. The electrolysis temperature is in all cases between 940 - 970 ° C. The melting temperature of the electrolyte can be lowered by the addition of A1F ₃ . The NaF - A1F ₃ system has a eutectic that melts at about 700 ° C, at a continuum of A1F ₃ of about 0.45 mol%. However, these additions have some disadvantages. In molten salts, the electrical conduction is an ionic conduction. In the case of cryolite-alumina melts, the electrolysis current is transported to the cathode by sodium ions which are the smallest and most mobile ions. The other ions in the melt are complex ions, large and with low mobility. Due to this, the NaF concentration increases in the vicinity of the cathode and in this region of the cell the electrolyte solidifies and solid crusts form on the cathode surface, because the electrolytes with a higher NaF concentration have higher melting points. These crusts, if they partially occupy the surface of the cathode, increase the electrical resistance of the ve'f

-11- 2008 J-11- 2008 J

0-2008-00924-2 5 -11- 2008 electrolitului, sau întrerup curentul de electroliza in caz ca ocupa toata suprafața catodului. Pentru topirea crustelor este necesara ridicarea temperaturii electrolitului. In criolit pur, la temperatura de topire a acestuia de 1010°C, solubilitatea aluminei este 10 - 11%. In topituri cu exces mare de AIF3, in eutectic de exemplu, solubilitatea aluminei scade la 2 - 3%, ceea ce provoacă dificultăți in exploatarea celulelor de electroliza prin apariția efectelor anodice si a depunerilor de alumina pe vatra celulei.0-2008-00924-2 5 -11- 2008 electrolyte, or interrupt the electrolysis current in case it occupies the entire surface of the cathode. To melt the crusts it is necessary to raise the electrolyte temperature. In pure cryolite, at its melting point of 1010 ° C, the solubility of alumina is 10-11%. In melts with a large excess of AIF3, in eutectic for example, the solubility of alumina decreases to 2-3%, which causes difficulties in the operation of electrolysis cells by the appearance of anodic effects and alumina deposits on the hearth of the cell.

Procedeul pentru fabricarea aluminiului conform invenției, înlătură dezavantajele menționate anterior, prin aceea ca se folosește o celula de electroliza cu o distanta interpolara de 1-4 cm, cu anozi de cărbune si catozi umectabili preparati din materiale compozite care conțin TiB₂ sau ZrB₂ sub forma de placi perforate plasate sub anod, deplasabile pe verticala pentru reglarea distantei interpolare sau pentru schimbarea catozilor deteriorati, catozi pe care se depune aluminiul care se scurge prin perforațiile catodului in stratul de aluminiu de pe fundul celulei, strat care nu este sub tensiune si deci nu se mișca sub acțiunea câmpului electromagnetic, iar nămolul care se depune sub stratul de aluminiu nu mai erodează blocul de cărbune de pe fundul celulei, in felul acesta mărind durata de viata a celulei de electroliza, pentru electroliza folosindu-se un electrolit cu temperatura de topire joasa, in care electroliza se face la temperaturi de 720-970°C, sau folosește anozi inerti cu dimensiuni stabile, preparati din materiale non-carbonice, catozi din materiale compozite care conțin TiB₂ sau ZrB₂, electrozii sunt plasati in poziție orizontala, verticala sau oblica, cu o distanta interpolara de 0,5 - 1 cm si operează la temperaturi de 720 - 970 °C, procedeul de electroliza cu aceste topituri folosind in celula blocuri catodice de cărbune rezistente la atacul potasiului, iar electrolitul pentru fabricarea aluminiului, înlătură dezavantajele menționate anterior, prin aceea ca este preparat dintr-un eutectic KF - A1F₃ cu compoziția 40 - 50 moli % KF + 50 40 moli % AIF3, cu o temperatura de topire de 560 - 570 °C, cu adaosuri de 1 - 3 % NaF, LiF, sau CaF₂ si de asemenea, opțional MgF₂, BaF₂, NaCl in proporție de 1 - 7 %, de preferința 45 moli % KF + 55 moli % A1F₃, cu adaosuri de 2 - 3 % NaF, LiF sau CaF₂ si care nu formează cruste pe catod in timpul electrolizei la temperaturi joase, in acest electrolit solubilitatea aluminei fiind de 4-5%.The process for the manufacture of aluminum according to the invention removes the disadvantages mentioned above, in that an electrolysis cell with an interpolar distance of 1-4 cm is used, with carbon anodes and wettable cathodes prepared from composite materials containing TiB ₂ or ZrB ₂ sub in the form of perforated plates placed under the anode, movable vertically to adjust the interpolar distance or to change the damaged cathodes, cathodes on which aluminum is deposited which flows through the perforations of the cathode in the aluminum layer at the bottom of the cell, layer that is not live and therefore it does not move under the action of the electromagnetic field, and the sludge that deposits under the aluminum layer no longer erodes the coal block on the bottom of the cell, thus increasing the life of the electrolysis cell, for electrolysis using an electrolyte with a temperature of low melting, in which the electrolysis is done at temperatures of 720-970 ° C, or uses inert anodes with stable dimensions, prepared from non-carbon materials, cathodes from composite materials containing TiB ₂ or ZrB ₂ , the electrodes are placed in a horizontal, vertical or oblique position, with an interpolar distance of 0.5 - 1 cm and operate at temperatures of 720 - 970 ° C, the electrolysis process with these melts using in the cell cathode blocks of carbon resistant to potassium attack, and the electrolyte for the manufacture of aluminum, removes the disadvantages mentioned above, in that it is prepared from a eutectic KF - A1F ₃ with composition 40 - 50 mol% KF + 50 40 mol% AIF3, with a melting point of 560 - 570 ° C, with additions of 1 - 3% NaF, LiF, or CaF ₂ and also optionally MgF ₂ , BaF ₂ , NaCl in a proportion of 1 - 7%, preferably 45 mol% KF + 55 mol% A1F ₃ , with additions of 2 - 3% NaF, LiF or CaF ₂ and which do not form crusts on the cathode during electrolysis at low temperatures, in this electrolyte solubility of alumina being 4-5%.

Invenția prezintă următoarele avantaje:The invention has the following advantages:

- scăderea temperaturii de electroliza cu aproximativ 200 °C, ceeace duce la inseminate economii de energie electrica,- lowering of the electrolysis temperature by about 200 ° C, which leads to significant energy savings,

- creșterea duratei de viata a celulelor de electroliza, ceeace duce la economii privind investițiile, = 1 Ο Ο 8 - Ο Ο 9 2 4 - 2 5 -11- 2008- increase the life of electrolysis cells, which leads to savings on investment, = 1 Ο Ο 8 - Ο Ο 9 2 4 - 2 5 -11- 2008

- prin scăderea temperaturii de electroliza scade solubilitatea in electrolit a tuturor impurităților, ceeace permite obținerea unui aluminiu cu o puritate ridicata,- by decreasing the electrolysis temperature decreases the solubility in electrolyte of all impurities, which allows to obtain an aluminum with a high purity,

- celula de electroliza folosește o distanta interpolara mica, ceea ce duce de asemenea la economii de energie electrica.- the electrolysis cell uses a short interpolar distance, which also leads to energy savings.

se utilizează un electrolit cu un punct de topire scăzut si in care nu se formează cruste pe catod in timpul electrolizei.an electrolyte with a low melting point and in which no crusts form on the cathode during electrolysis is used.

Pentru micșorarea consumului de energie electrica, in cadrul invenției s-a realizat o celula de electroliza cu distanta interpolara micșorată, asa cum este prezentata in figura 1.In order to reduce the electricity consumption, an electrolysis cell with a reduced interpolar distance was made within the invention, as shown in figure 1.

In aceasta celula de electroliza, anozii sunt anozi de cărbune (1), catodul este un catod umectabil dintr-un material compozit care conține TiB₂ sau ZrB₂ sub forma de placa perforata, plasat sub anod, deplasabil pe verticala (2), electrolitul prin compoziția lui, permite coborârea temperaturii de electroliza pana la 720 °C. Pe fundul celulei de electroliza din figura 1, mai exista un strat de aluminiu topit (4), un strat de cărbune (5) si o captuseala din cărămidă refractara. Aluminiul se depune pe catodul umectabil, si fiind topit se scurge prin perforațiile catodului in stratul de aluminiu topit (4) de pe fundul celulei. Catodul este umectat de către aluminiul topit care formează o pelicula subțire pe suprafața catodului si se scurge in baia de aluminiu topit (4). Pelicula de aluminiu topit de pe catod nu mai este influențată de câmpul electromagnetic din celula deoarece este subțire, deci nu mai executa mișcări orizontale si verticale, permițând micșorarea distantei interpolare pana la 15 mm. Din baia de aluminiu, metalul se extrage periodic. Alt avantaj al acestui aranjament este ca baia de aluminiu topit nu este sub tensiune, deci nu mai executa mișcări circulare, iar nămolul (alumina + electrolit) care cade sub stratul de aluminiu nu erodează cărbunele de pe fundul celulei, ceeace duce la marirea duratei de viata a celulelor. Nămolul acumulat pe fundul celulei este extras, macinat si refolosit in celulele de electroliza. Catodul (2) este mobil si poate fi schimbat in caz ca se deteriorează.In this electrolysis cell, the anodes are coal anodes (1), the cathode is a wettable cathode of a composite material containing TiB ₂ or ZrB ₂ in the form of a perforated plate, placed under the anode, displaceable vertically (2), the electrolyte by its composition, it allows the lowering of the electrolysis temperature up to 720 ° C. At the bottom of the electrolysis cell of Figure 1, there is a layer of molten aluminum (4), a layer of coal (5) and a refractory brick lining. The aluminum is deposited on the wettable cathode, and being melted it drains through the perforations of the cathode in the molten aluminum layer (4) on the bottom of the cell. The cathode is moistened by molten aluminum which forms a thin film on the surface of the cathode and drains into the molten aluminum bath (4). The molten aluminum film on the cathode is no longer influenced by the electromagnetic field in the cell because it is thin, so it no longer performs horizontal and vertical movements, allowing the interpolar distance to be reduced to 15 mm. From the aluminum bath, the metal is periodically extracted. Another advantage of this arrangement is that the molten aluminum bath is not energized, so it no longer performs circular movements, and the sludge (alumina + electrolyte) that falls under the aluminum layer does not erode the coal on the bottom of the cell, which increases the life of the cell. cell life. The sludge accumulated on the bottom of the cell is extracted, ground and reused in the electrolysis cells. The cathode (2) is movable and can be replaced in case of damage.

Se dau in continuare cinci exemple de realizare a invenției:The following are five embodiments of the invention:

EXEMPLUL 1EXAMPLE 1

Intr-o celula de fabricare a aluminiului se folosesc anozi de cărbune, catodul este de asemenea de cărbune, peste care se gaseste un strat de aluminiu topit de aproximativ 20 cm. Prin influenta câmpului electromagnetic foarte intens (100.000 - 300.000 A), stratul de aluminiu topit executa mișcări orizontale (circulare) si verticale, astfel ca pentru a evita contactul intre gazele anodice (CO₂) si aluminiul topit, contact care micșorează randamentul de current din cauza reacției de reoxidare a aluminiului, este necesar ca distanta anod - catod (distanta interpolara) sa fie mare, 4-5 cm. In plus, din cauza mișcărilor circulare ale băii deCoal anodes are used in an aluminum fabrication cell, the cathode is also coal, over which there is a layer of molten aluminum of about 20 cm. Due to the influence of the very intense electromagnetic field (100,000 - 300,000 A), the molten aluminum layer performs horizontal (circular) and vertical movements, so as to avoid contact between anodic gases (CO ₂ ) and molten aluminum, contact that decreases the current efficiency of due to the reoxidation reaction of aluminum, it is necessary that the anode-cathode distance (interpolar distance) be large, 4-5 cm. In addition, due to the circular movements of the bathroom

- 2 Ο 0 8 - Ο Ο 9 2 4 - 2 5 -11- 2008 aluminiu topit, nămolul (alumina + electrolit) care cade de obicei sub stratul de aluminiu erodează blocul catodic de cărbune si micșorează durata de viata a celulelor de electroliza, Din cauza distantei interpolare mari, o parte din energia electrica folosita la electroliza (5860%) se transforma in căldură prin trecerea curentului prin acest strat de electrolit. Aceasta cantitate de căldură se pierde. Temperatura de electroliza este de 940 - 970 °C. Electrolitul topit este criolit, in care se adauga 7 - 8 % AIF3, 4 - 6 % CaF₂ si 1 - 6 % AI2O3.- 2 Ο 0 8 - Ο Ο 9 2 4 - 2 5 -11- 2008 molten aluminum, the sludge (alumina + electrolyte) that usually falls under the aluminum layer erodes the cathode block of coal and shortens the life of the electrolysis cells, Due to the large interpolation distance, some of the electrical energy used in electrolysis (5860%) is converted into heat by passing current through this electrolyte layer. This amount of heat is lost. The electrolysis temperature is 940 - 970 ° C. The molten electrolyte is cryolite, in which 7 - 8% AIF3, 4 - 6% CaF ₂ and 1 - 6% AI2O3 are added.

Consumul specific de current in aceste condiții de electroliza este de 14 - 15 MWh/t Al.The specific current consumption in these electrolysis conditions is 14-15 MWh / t Al.

EXEMPLUL 2EXAMPLE 2

Se folosește aceeași celula de electroliza ca cea din exemplul 1, care lucrează in aceleași condiții de intensitate de current, distanta interpolara, anozi de cărbune si baie de aluminiu topit pe fundul celulei.The same electrolysis cell is used as in Example 1, which works under the same conditions of current intensity, interpolar distance, coal anodes and molten aluminum bath on the bottom of the cell.

Se folosește un electrolit cu temperatura de topire joasa, cu compoziția : 50 moli % KF + 50 moli % AIF3 + 3 % LiF + 4 % CaF₂ + 3 % NaF + 4 % A1₂O₃, in care electroliza se face la o temperatura de 720 - 750 °C.An electrolyte with a low melting temperature is used, with the composition: 50 mol% KF + 50 mol% AIF3 + 3% LiF + 4% CaF ₂ + 3% NaF + 4% A1 ₂ O ₃ , in which the electrolysis is done at a temperature of 720 - 750 ° C.

In acest caz, consumul specific de current este de aproximativ 11,5 MWh/t Al.In this case, the specific current consumption is approximately 11.5 MWh / t Al.

EXEMPLUL 3EXAMPLE 3

Se folosește o celula de electroliza ca cea din figura 1. Anozii sunt anozi de cărbune, catodul este un catod umectabil dintr-un material compozit care conține TiB₂ sau ZrB₂ sub forma de placa perforata, iar electrolitul are compoziția data in exemplul nr, 1. Temperatura de electroliza este 940 - 970 °C. Distanta interpolara este de 2 cm sau mai mica. _An electrolysis cell such as the one in Figure ₁ is used. 1. The electrolysis temperature is 940 - 970 ° C. The interpolar distance is 2 cm or less.

In acest caz, consumul specific de current este de aproximativ 11,5 MWh/t Al, iar durata de viata a celulei de electroliza este mai lunga decât in exemplul nr. 1.In this case, the specific current consumption is approximately 11.5 MWh / t Al, and the life of the electrolysis cell is longer than in example no. 1.

EXEMPLUL 4EXAMPLE 4

Se folosește celula de electroliza fin figura 1, cu anozi de cărbune, catod umectabil fabricat din materiale compozite care conțin TiB₂ sau ZrB₂. Electrolitul este cel dat in exemplul nr. 2, cu temperatura de topire joasa.The fine electrolysis cell figure 1, with carbon anodes, wettable cathode made of composite materials containing TiB ₂ or ZrB ₂ is used. The electrolyte is the one given in example no. 2, with low melting temperature.

Distanta interpolara este de 2 cm sau mai mica, iar temperatura de electroliza este coborâta, pana la 720 - 750 °C.The interpolar distance is 2 cm or less, and the electrolysis temperature is lowered to 720 - 750 ° C.

In acest caz, exista toate avantajele aratate in exemplul nr. 3 si in plus, temperatura de electroliza scăzută.In this case, there are all the advantages shown in example no. 3 and in addition, the electrolysis temperature is low.

Consumul specific de current este in aceasta situație de 8,5 - 9 MWh/t Al, iar durata de viata a celulei de electroliza este de asemenea mai lunga decât in exemplul nr. 1The specific current consumption is in this situation of 8.5 - 9 MWh / t Al, and the lifetime of the electrolysis cell is also longer than in example no. 1

EXEMPLUL 5EXAMPLE 5

0- - 2 Ο Ο 8 ~ Ο Ο 9 2 4 Se folosește o celula de electroliza in care anozii sunt anozi inerti, cu dimensiuni stabile, fabricati din materiale care nu conțin carbon, cum sunt : materiale ceramice, cermeti sau metale si catozi umectabili din materiale compozite care conțin TiB₂ sau ZrB₂.0- - 2 Ο Ο 8 ~ Ο Ο 9 2 4 An electrolysis cell is used in which the anodes are inert anodes, with stable dimensions, made of non-carbon-containing materials, such as: ceramic materials, cermets or metals and wettable cathodes of composite materials containing TiB ₂ or ZrB ₂ .

Electrozii sunt plasati paralel, in poziție orizontala, verticala sau oblica, iar distanta interpolara este de 1 cm sau mai mica.The electrodes are placed parallel, in a horizontal, vertical or oblique position, and the interpolar distance is 1 cm or less.

Electrolitul topit este cel din exemplul nr. 2, cu temperatura de topire scăzută, iar temperatura de electroliza este coborâta pana la 720 - 750 °C.The molten electrolyte is the one from example no. 2, with low melting temperature, and the electrolysis temperature is lowered to 720 - 750 ° C.

Deoarece anozii nu conțin carbon, in timpul electrolizei nu se mai produce CO₂ sau alte gaze cu effect de sera, cum este CF₄, in schimb se produce oxigen prin electroliza aluminei, A1₂O3.Because anodes do not contain carbon, CO ₂ or other greenhouse gases, such as CF ₄ , are no longer produced during electrolysis, but oxygen is produced by electrolysis of alumina, A1 ₂ O3.

In acest caz, consumul specific de energie electrica este 10,5 - 11 MWh/t Al, alte avantaje fiind ca nu se mai folosesc anozi de cărbune, nu se mai degaja in atmosfera CO₂ si alte gaze cu efect de sera, in schimb se produce oxigen.In this case, the specific consumption of electricity is 10.5 - 11 MWh / t Al, other advantages being that no more coal anodes are used, no more CO ₂ and other greenhouse gases are released into the atmosphere, instead oxygen is produced.

BIBLIOGRAFIEBIBLIOGRAPHY

1. K. Grjotheim, C. Krohn, M. Malinovsky, K. Matiasovsky, J. Thonstad, “Aluminium Electrolysis. The Chemistry of the Hali - Heroult Process”, Aluminium - Verlag GmbH, Dusseldorf, Germany, l^st edition, 1977.1. K. Grjotheim, C. Krohn, M. Malinovsky, K. Matiasovsky, J. Thonstad, “Aluminum Electrolysis. The Chemistry of the Hali - Heroult Process ”, Aluminum - Verlag GmbH, Dusseldorf, Germany, l ^st edition, 1977.

2. K. Grjotheim, C. Krohn, M. Malinovsky, K. Matiasovsky, J. Thonstad, “Aluminium Electrolysis. Fundamentals of the Hali - Heroult Precess”, Aluminium - Verlag, Dusseldorf, Germany, 2^nd edition, 1982.2. K. Grjotheim, C. Krohn, M. Malinovsky, K. Matiasovsky, J. Thonstad, “Aluminum Electrolysis. Fundamentals of the Hali - Heroult Precess ”, Aluminum - Verlag, Dusseldorf, Germany, 2 ^nd edition, 1982.

3. J. Thonstad, P. Fellner, G.M. Haarberg, J. Hives, H. Kvande, A. Sterten, “Aluminium Electrolysis. Fundamentals of the Hali - Heroult Process”. Aluminium - Verlag, Dusseldorf, 3^rd edition, 2001.3. J. Thonstad, P. Fellner, GM Haarberg, J. Hives, H. Kvande, A. Sterten, “Aluminum Electrolysis. Fundamentals of the Hali - Heroult Process ”. Aluminum - Verlag, Dusseldorf, ^3rd edition, 2001.

Claims

2 5 -11- 2008

demand

1. Process for the manufacture of aluminum by melt electrolysis, characterized in that an electrolysis cell with an interpolar distance of 1-4 cm is used, with carbon anodes and wettable cathodes prepared from composite materials containing TiB ₂ or ZrB ₂ sub in the form of perforated plates placed under the anode, movable vertically to adjust the interpolar distance or to change the damaged cathodes, cathodes on which aluminum is deposited which flows through the perforations of the cathode in the aluminum layer at the bottom of the cell, layer that is not live and therefore it does not move under the action of the electromagnetic field, and the sludge that deposits under the aluminum layer no longer erodes the coal block on the bottom of the cell, thus increasing the life of the electrolysis cell, for electrolysis using an electrolyte with a temperature of low melting, in which the electrolysis is done at temperatures of 720-970 ° C.

Process according to Claim 1, characterized in that it uses inert anodes with stable dimensions, prepared from non-carbon materials, cathodes from composite materials containing TiB ₂ or ZrB ₂ , the electrodes being placed in a horizontal, vertical or oblique position with a interpolar distance of 0.5 - 1 cm and operates at temperatures of 720 - 970 ° C.

3. Electrolyte for the manufacture of aluminum by melt electrolysis, characterized in that it is prepared from a eutectic KF - AIF3 with a composition of 40 - 50 mol% KF + 50 - 40 mol% AIF3, with a melting temperature of 560 - 570 ° C, with additions of 1 - 3% NaF, LiF, or CaF ₂ and also optionally MgF ₂ , BaF ₂ , NaCl in a proportion of 1 - 7%, preferably 45 mol% KF + 55 mol% AIF3, with additives of 2 - 3% NaF, LiF or CaF ₂ and which do not form crusts on the cathode during electrolysis at low temperatures.