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AZERBAIJAN CHEMICAL JOURNAL № 1 2022 ISSN 2522-1841 (Online)
ISSN 0005-2531 (Print)
UDC 661.8, 669.094, 536.66
SLUDGE-FREE PRODUCTION OF PURE ALUMINA FROM ROCKS CONTAINING
IRON OXIDES AND SILICA LA.TalibH1, G.M.Samedzade\ J.M.Alieva2, A.N.Mammadov1,3, R.G.Gamidov\
A.M.Gasimova\ G.V.Shadlinskaya4
M.Nagiyev Institute of Catalysis and Inorganic Chemistry, NAS of Azerbaijan Azerbaijan Technological University 3Azerbaijan Technical University 4Azerbaijan State Pedagogical University
ira_talibli@mail. ru
Received 22.10.2021 Accepted 12.11.2021
It has been established that the extraction of aluminum from the rocks containing large amounts of alkali-soluble silicates and iron oxides can be processed by the acid-alkali method, except for the formation of wasted sludge. The carried out thermodynamic analysis showed the possibility of carrying out the process of reduction of a mixture of aluminum and iron sulphate salts with hydrogen. The optimal conditions for the reduction of aluminum and iron sulphates with hydrogen have been found with the production of S2 and SO2 and stub in the gas phase. Pure aluminum is obtained from stubby the Bayer method.
Keywords: Acid-alkali method, thermodynamic analysis, derivatogram, sulphate salts, hydrogen, stub, degree of reduction and extraction.
doi.org/10.32737/0005-2531-2022-1-68-72
Introduction
The use of pure alumina in various industries is growing every year. The purest alumina is obtained after the processing of aluminum-containing raw materials according to the alkaline Bayer scheme. With desiliconization, |si= Al2O3/SiO2 350-600 is achieved, depending on the requirements of the consumer. For example, alumina of the GOO brand should contain no more than 0.02% SiO2, 0.03% Fe2O3, 0.4% Na2O, etc. Considering that during desiliconiza-tion in the alkaline method, per 1 kg of SiO2, Na2O and Al2O3 lose up to 0,6 kg and 1 kg, respectively, as well as up to 1 kg of wasted red mud is formed, then the high requirements for bauxite, from which alumina is obtained, are understandable [1-7]. However, the world reserves of high-quality bauxites with a low content of SiO2 (|i(SiO2) >8) are limited. In this regard, studies are being carried out on the processing of low-quality raw materials with a high content of iron and silicon oxides, which is more than enough: these are low-grade bauxites, niphelines, kaolinites, alunite and other aluminosilicates [6-15].
One of the methods for processing high-silica raw materials is sintering. However, during processing, 1 ton of alumina produces 10 tons of cement, the implementation of which is problematic [6-8]. And also, in the process of sintering for 1 ton of alumina during the firing of fuel, 14 tons of carbon dioxide are formed. And under the Kyoto agreement for the emission of 1 t of carbon dioxide into the atmosphere, a fine of 5 to 20 euros is imposed [8-10].
Therefore, rocks containing an increased amount of silicates, including bauxites, are proposed to be processed by acid methods. In the presence of iron oxides in the rock, in the process of cleaning the litter, during acid processing, alumina losses also occur and mountains of wasted unclaimed silicate - iron oxide sludge are formed [6-11].
The analysed method of acid-base processing allows at the first stage to purify the product extracted from silicon oxide, and the latter (purified silica) can be used for the production of glass, porcelain, or construction purpose [6].
At the second stage, from acidic salts, according to the alkaline Bayer scheme, pure alumina and sludge are obtained in the form of
iron compounds. The use of sulfuric acid at the first stage leads to the loss of alkali in the second stage, to the formation of a large amount of sodium sulfate, which is of little use in industry. To reduce alkali losses, preliminary reduction of sulfate salts of aluminum and iron with the use of gaseous reducing agents was proposed to obtain SO2, S, H2O in the gas phase and the stub composed of Al2O3, Fe2O3 and FS in the gas phase [6].
Thermodynamic analysis
This article discusses the possibility of reducing a mixture of Al2(SO4)3 and Fe2(SO4)3 sulfate salts by hydrogen in a flow reactor according to reaction 1.
In literature alumina sulphate is known to be reduced with the solid, vaporous and gaseous reducing agents [1, 2]. The reduction of ferrous sulfate by gaseous reducing agents is less known, apparently in connection with reaction 6, in which the reverse process is more likely. Preliminary thermodynamic analysis of possible reactions (1-6)
2(Al2(SO4)3 ■ Fe2(SO4)3)+27H2^2Al2O3+Fe2O3+ +2FeS+6SO2+2S2+27H2O (1)
3Fe2(SO4)3+16H2^2Fe2O3+2FeS+7SO2+16H2O (2) Fe2(SO4)3+3H2^Fe2O3+3SO2+3H2O (3)
Fe2(SO4)3+12H2^2FeS+12H2O+S (4)
Fe2(SO4)3+UH2^FeO+FeS+S2+UH2O (5)
FeS+SO2+H2^FeO+S2+H2O (6)
was carried out using the Gibbs energy values calculated according to the Temkin-Shvartsman formulas:
AGT = AH098 - T • AS098 - T • (M0Aa + M1Ab + M-2AC)
The data of thermodynamic values are taken from tables [17-19]. The Gibbs energy values obtained for reactions (1 -6) depending on the temperature change are presented in the form of curves in Figure 1.
As can be seen from the curves of the Gibbs energy variations versus temperature, the processes proceeding according to reactions 1 and 4 with the production of SO2, S, S2, H2O gaseous products and stub in the form of Al2O3,
Fe2O3, FeS have the greatest negative potential. Pure alumina and sludge in the form of iron oxides and sulphides are obtained from the stubby Bayer method. They can be used in the production of cast iron. At the same time AG in reaction 6, depending on the temperature is positive. Therefore, we can say that this direction of the reaction (6) is unlikely.
Fig. 1. AG variations in reactions 1-6 versus, to.
Experiments and discussion of their results
For a practical study of recovering the sulphate salts of aluminum and iron, a salt obtained from a model solution of sulphate salts containing Al2O3 and Fe2O3, respectively, 20.5 and 9%, based on their natural content in rocks with kaolinite, was used. Figure 2 shows a deri-vatographic analysis of the sulphate salts obtained in a nitrogen environment.
As can be seen on the DTA curve of the derivatogram, 4 endothermic effects, accompanied by weight loss on the TG curve are observed. The first endothermic effect at 1210C refers to the loss of hygroscopic water in the range of 108-1700C and amounts to 12% of the fraction mass. The second endothermic effect at 2630C is in the 230-2850C temperature range. The presence of the endothermic effect can most likely be attributed to the release of an excess of sulfuric acid adsorbed during the precipitation of aluminum and iron sulphate salts, which is 3% of the mass fraction of the sample.
Fig. 2. Derivatogram of a mixture of sulfate salts of aluminum and iron in a nitrogen environment.
In the 515-720 C temperature range at a temperature of 5950C, a third endothermic effect is observed, which, not quite ending, turns into the fourth one at 6550C. The third endo-thermic effect corresponds to the decomposition of aluminum sulphate, and the fourth one to the decomposition of iron sulphate [20].
For the study, from the obtained mixture of sulphate salts, which was dehydrated at 350-4000C, a sample of 0.3 g was reduced with hydrogen in an alundum boat in a flow-through quartz reactor in the form of a tube. The temperature was measured over the sample in the boat with a thermocouple. The experiments were carried out within 520-5800C with an interval of 200C. When the required temperature was reached, the boat was moved into the reaction zone and hydrogen was started up.
The process was carried out for 60 minutes, then the boat with the reduced product, stub moved into the cold zone of the tube, the hydrogen was shut off and the reactor was purged with nitrogen, and the heating was turned off. The stub was transferred into a beaker with a 10% alkali solution, and at a tem-
perature of 900C with stirring on a magnetic stirrer, leaching was carried out for 50 min. The degree of reduction was determined by the residual content of SO3 in the stub, which transformed into the alkaline solution, and by the amount of aluminum oxide, the degree of its extraction and passivation during the reduction of sulphate salts was determined [1- 4,20].
The degrees of sulphate salts recovered and of the alumina extracted versus the temperature of the reduction process are shown in the form of curves in Figure 3. From curve 1 in Figure 3 you can see that the degree of recovery of sulphate salts with the temperature rise increases from 66 to 80% at 500-5200C, reaching 92-98 and up to100% at 540-5600C, remaining at the level of 98-100% at 560-5800C for a recovery time of 60 min. However, if the recovery degree increases with increasing temperature, then the degree of alumina extraction in Figure 3, curve 2 decreases to 98-100% at 5600C, and at 5800C it drops to 88-92%, which is undesirable.
Thus, with a recovery time of 60 min the optimal recovery temperature should be conside-
red in the range of 550-5650C, in which there is a complete recovery of sulfate salts and the extraction of aluminum. An increase in temperature over 5600C is not desirable, as this leads to the passivation of aluminum and a decrease in its solubility in alkalis.
Fig.3. Dependence of the degree of recovery of sulphate salts and the extraction of aluminum from the stub on the process temperature with a recovery time of 60 min.
Conclusions
Thermodynamic analysis showed the possibility of reactions 1 -5 and their intensification with increasing temperature since the negative value of AG in reactions increases at the same time. From the AG value, it can be assumed that the reduction process proceeds in accordance with reactions 1 and 4.
Derivatographic analysis in a nitrogen environment showed that the applied sulphate salts contain 12% of hygroscopic water, released up to 1700C with an endo effect on the DTA curve at 1200C. The second endothermic effect at 2630C is in the temperature range of 230-2850C. The presence of the endothermic effect, most likely, can be attributed to the release of the residual hydroscopic water and an excess of sulfuric acid, adsorbed during the precipitation of aluminum and iron sulphate salts, constituting 3% of the mass fraction of the sample. The next two endothermic effects at 5950C and 6550C relate to the decomposition of aluminum and iron sulphates.
Practical reduction of a mixture of the aluminium and iron sulphate salts with hyd-
rogen showed that carrying out the process with an increase in temperature in the range of 500-5800C for one hour leads to the decomposition of the sulphate salts and at 550-5650C a 99100% degree of reduction and extraction of aluminum from the stub is achieved. A further increase in temperature does not affect the degree of recovery, however, it leads to passivation of aluminum, the yield of which decreases to 88-92% at 5800C.
It is shown that the extraction of aluminum from rocks containing large amounts of alkali-soluble silicates and iron oxides (5-14%) is possible by the acid-alkali method excluding the accumulation of waste sludge. At the same time, after acid leaching, the remainder of quartz and silicate sand is a necessary raw material in the glass, porcelain and construction industries. Sulphate salts of aluminum and iron are easily separated by an alkaline method. To save alkali, sulphate salts can be pre-reduced as shown to produce SO2 and S for the production of sulfuric acid and stub. The stub undergoes alkaline processing according to Bayer to obtain pure aluminum and sludge in the form of an oxide and sulphide mixture of iron, which can be used to produce cast iron.
References
1. Layner A.I. Proizvodstvo glinozema. Uchebnoye posobiye. M.: Gosudarstvennoye nauchno-tekhni-cheskoye izdatel'stvo literatury po chornoy i tsvet-noy metallurgii, 1961. 620 s.
2. Labutin G.V. Alunity. M.: Metallurgiya, 1965.100 s.
3. Layner Yu.A. Kompleksnaya pererabotka alyu-miniy soderzhashchego syr'ya kislotnymi sposo-bami. M.: Nauka, 1982. 208 s.
4. Shakhtakhtinskiy G.B., Khalilov A.N., Aslanov G.A. Polucheniye alyuminiyevykh soley iz bed-noalutinizirovannykh porod Zaglikskogo mes-torozhdeniya. Baku: Elm, 1972. 128 s.
5. Abbasova S.I. Izvlecheniye alyuminiya v vide razlichnykh soyedineniy iz mestnykh glinistykh porod. Avtoreferat na soiskaniye uchenoy stepeni kandidata khimicheskikh nauk. Baku: Institut khimicheskikh problem NANA, 2003. 25 s.
6. Az. Pat. i 2019 0055 "Tamiz aluminium oksidin alinmasi usulu". Samad-zada Q.M, Osgarov Q.R. §adlinskaya G.V., Xalilova H.X., Cahandarov §.C, Talibli i.Q. 2019.
7. Vaytner V.V. Issledovaniye azotnokislotnoy pere-rabotki alyumosilikatov dlya polucheniya oksida
alyuminiya. Diss. kan. tekh. nauk. Yekaterinburg RGB OD 2004.145 s.
8. Vaytner V.V., Kalinichenko I.I. Proizvodstvo gli-nozema iz otkhodov ugledobychi. Ural'skiy gosu-darstvennyy tekhnicheskiy universitet - UPI. 2002. P. 88-92.
9. Eldib Amr Bas'yuni Saad (Arabskaya Respublika Yegipet) Kompleksnaya pererabotka nizkosort-nogo alyuminiysoderzhashchego syr'ya Yegipta s polucheniyem metallurgicheskogo glinozoma i poputnoy produktsii Sankt-Peterburg, 23.06.2021.
10. Matveyev V.A. Fiziko-khimicheskiye i technolo-gicheskiye osnovy povysheniya effektivnosti kompleksnoy pererabotki nefelinsoderzhashchego syr'ya kislotnymi metodami Diss. dok. tekh. nauk. 2009.
11. Dubovikov O.A. Termokhimicheskoye konditsio-nirovaniye sostava nizkokachestvennykh boksitov i ikh pererabotka shchelochnymi sposobami. Diss. dok. tekh. nauk. 2012. 319 s.
12. Loginova I.V. Kyrchikov A.V., Penyugalova N.P. Tekhnologiya proizvodstva glinozema. Uchebno-ye posobiye. Yekaterinburg: Izd-vo Ural'skogo universiteta, 2015. 336 s.
13. Pat i 2020 0087 BN 1029102021 "Alunit filizinin emali usulu" Hamidov R.H., ibrahimov O.A., Teymurova E.A, Agayev A.i. 2020.
14. Pat i 2020 0072 "Alunit filizindan aluminium oksidin alinmasinin elektrokimyavi usulu". Hami-dov R.H, Tahirli H.M, Tagiyev D.B. 2020.
15. Pat i 2021 0032 "Alunit filizinin damirsizlaçmasi usulu". Hamidov R.H. 2021.
16. Loginova I.V., Shoppert A.A., Rogozhnikov D.A., Kyrchikov A.V. Proizvodstvo glinozema i ekono-micheskiye raschety v tsvetnoy metallurgii Ucheb-noye posobiye. Yekaterinburg: Izdatel'stvo UMTS UPI, 2016. 253 s.
17. Ryabin V.A., Ostroumov M.A.,Svit T.F. Termo-dinamicheskiye svoystva veshchestv. Spravoch-nik. L.: Khimiya, 1977, 392 s.
18. Kratkiy spravochnik fiziko-khimicheskikh velichin. Pod red. Ravdelya A.A. i Ponomarevoy A.M. L.: Khimiya,1983. 232 s.
19. Termicheskiye konstanty veshchestv. vyp. V111. Tablitsy prinyatykh znacheniy. Pod red. Glushko V.P. M.: 1978. 560 s.
20. Kelbaliyev G.I., Sadykhov F.M., Samedzade G.M., Tagiyev D.B. Teoriya i praktika granuliro-vaniya poroshkoobraznykh materialov. Baku: "Lyaman nashriyat poligrafiya" MMS.2016. 328s.
torkíbíndo domír oksídlorí va sílíkatlar olan fílízlordon tomíz alümíníum
oksídín tullantisiz alinmasi
I.A.Talibli, Q.M.Samadzada, C.M. Oliyeva, A.N.Mammadov, R.H. Hamidov, A.M. Qasimova, G.V.§adlinskaya
Müayyan edilmi§dir ki, tarkibinda böyük miqdarda qalavida hall olan silikatlar va damir oksidlari olan filizlardan gilin (glinozem) Qixarilmasi, talab olunmayan tullantilarin amala galmasi istisna olmaqla, tur§u-qalavi üsulu ila emal edilmakla mümkündür. Aparilan termodinamiki analiz alüminium va damir sulfat duzlari qari§iginin hidrogenla reduksiyasinin mümkünlüyünü göstarmi§dir. Alüminium va damir sulfatlarin, qaz fazasinda S2 , SO2 va kek alinmaqla, reduksiyasinin optimal §araiti tapilmüjdir. Tamiz gil kekdan Bayer üsulu ila alinir.
Afar sözlar: Tur§u-q3Í3vi üsulu, termodinamiki analiz, derivatoqramma, sulfat duzlari, hidrogen, kek, reduksiya v3 gixim dsrscssi.
БЕЗШЛАМОВОЕ ПОЛУЧЕНИЕ ЧИСТОГО ГЛИНОЗЕМА ИЗ ПОРОД, СОДЕРЖАЩИХ ОКСИДЫ
ЖЕЛЕЗА И КРЕМНЕЗЕМА
И.А.Талыблы, Г.М Самедзаде, Дж.М. Алиева, А.Н.Мамедов, Р.Г. Гамидов, А.М.Гасымова,
Г.В.Шадлинская
Определено, что извлечение глинозема из пород, содержащих большие количества щелочерастворимых силикатов и оксидов железа возможно кислотно-щелочным методом, с исключением образования невостребованных шламов. Проведенный термодинамический анализ показал возможность осуществления процесса восстановления смеси сульфатных солей алюминия и железа водородом. Найдены оптимальные условия восстановления сульфатов алюминия и железа водородом с получением в газовой фазе S2 и SO2 и кека. Чистый глинозем получают из кека по методу Байера.
Ключевые слова: Кислотно-щелочной метод, термодинамический анализ, дериватограмма, сульфатные соли, водород, кек, степень восстановления и извлечения.
