Treatment of bauxite residues acidic leaching (first part) Текст научной статьи по специальности «Химические технологии»

Treatment of bauxite residues - acidic leaching (first part)

Srecko R. Stopica, Vladimir Damjanovicb, Radislav Filipovicc,

Mary D. Kamarad, Bernd G. Friedriche

a RWTH Aachen University, IME Process Metallurgy and Metal Recycling, Aachen, Federal Republic of Germany, e-mail: [email protected], corresponding author, ORCID iD: ©https://orcid.org/0000-0002-1752-5378

b Alumina Ltd, Zvornik, Republic of Srpska, Bosnia and Herzegovina, e-mail: [email protected], ORCID iD: ©https://orcid.org/0000-0002-5375-440X

c Alumina Ltd, Zvornik, Republic of Srpska, Bosnia and Herzegovina, e-mail: radislav. [email protected], ORCID iD: ©https://orcid.org/0009-0000-9938-2499

d RWTH Aachen University, IME Process Metallurgy and Metal Recycling, Aachen, Federal Republic of Germany, e-mail: [email protected], ORCID iD: ©https://orcid.org/0009-0005-1923-3570

e RWTH Aachen University, IME Process Metallurgy and Metal Recycling, Aachen, Federal Republic of Germany, e-mail: [email protected], ORCID iD: ©https://orcid.org/0000-0002-2934-2034

DOI: 10.5937/vojtehg71-46212; https://doi.org/10.5937/vojtehg71-46212

FIELD: chemical technology ARTICLE TYPE: original scientific paper

Abstract:

Introduction/purpose: Bauxite residue as a waste product from the aluminium industry produced through the Bayer process is mainly composed of iron oxide, titanium oxide, silicon oxide and undissolved alumina together with a wide range of other oxides and a minor content of rare earth elements, gallium, vanadium and scandium, which vary according to the country of origin of the bauxite. The extraction of valuable elements from bauxite residues and the minimisation of bauxite residues during different treatments are an open research field.

ACKNOWLEDGMENT: This research was funded by the Federal Ministry for Education and Research Grant Number 03SF0626C "Verbundvorhaben GSP Green H2: WASCAL Internationales Masterprogramm für Energie und Grünen Wasserstoff (IMP-EGH)".

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Methods: Different hydrometallurgical and pyrometallurgical methods were used for the treatment of bauxite residues. In this study, the results of the hydrometallurgical treatment of bauxite residue from Alumina Zvornik using sulfuric acid and hydrochloric acid will be shown in order to study the change of the mineralogical composition. Leaching efficiency will be calculated using the ICP OES analysis. The XRD-Analysis was used for the characterization of the initial material and solid residues studying the change of the mineralogical phases.

Results: Leaching of bauxite residues with sulphuric and hydrochloric acid leads partially to the change of mineralogical structure and the transfer of elements into a liquid phase. Natural precipitation of iron is observed over time. Silica gel formation is confirmed during leaching of bauxite residues with hydrochloric acid.

Conclusion: A new research strategy for treating bauxite residue is needed in order to ensure a complete change of the initial minearlogical structure and the most efficient transfer of metals into a liquid phase.

Key words: bauxite residues, aluminium, hydrometallurgy, acid, recycling, rare earth elements.

Introduction

The Bayer process is a traditional industrial method for the production of alumina from bauxite ore. The chemical quality of precipitated aluminum hydroxide, and consequently the final alumina product in the Bayer process directly depends on the level of impurities in a refinery's Bayer liquor. Under optimal reaction parameters (temperature and time), it is possible to remove iron, zinc and copper from the Bayer liquor using a precipitation agent such as calcium hydroxide with an efficiency of more than 90%, in such a way that the treated solution is still economically usable in the following stages of processing while obtaining different types of aluminum trihydrate. (Damjanovic et al, 2020)

In Europe, alumina refineries operate in Bosnia and Herzegovina (Alumina, Zvornik), France, Hungary, Germany, Greece, Ireland (AAL), Romania (ALUM), Spain and Ukraine, while significant BR deposits from refineries that have stopped their operations (legacy sites) exist in former Yugoslavia (Podgorica, Kidricevo, Mostar, Obrovac), Italy, France (RT), Germany, Hungary and other countries. The current BR production level in the EU is 6.8 million tonnes per year while the cumulative stockpiled level is a staggering >250 million tonnes (dry matter).

The mineralogical structure of bauxite residue, where nearly 80 % consists of three of these phases: cancrinite, sodalite and hematite, is shown in Table 1. (Castaldi et al, 2008)

Table 1 - Typical mineralogical structure of bauxite residue (in wt. -%) g

Таблица 1 - Типичный минералогический состав бокситового шлама (в

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структура бок процентима)

Табела 1 - Типична минералска структура бокситних остатака (у тежинским о

Cancrinite [Na6Ca1.5Al6Si6O24(CO3)1.6]: 29.0-33.0

Sodalite [Na8(Cl,OH)2Al6Si6O24]: 16.0-24.0

Hematite [Fe2O3]: 27.0-29.0

Boehmite [AlO(OH)]: 5.0-6.0

Gibbsite [Al(OH)3]: 4.0-5.0

Anatase [TiO2]: 5.0

Andradite [Ca-Fe-Al-Si oxides]: 4.0

Quartz [SiO2]: 2.0

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Bauxite residues contain scandium and gallium (Approx. 50-150 ppm) and up to an order of magnitude higher for elements such as: vanadium and rare earths elements (0.05-0.5 %). Since 1991, MYTILINEOS, Greece, has been doing pioneering research on BR handling and reuse, | focusing initially on massive low value applications such as use as a raw material for geopolymer bricks, cement clinker production, iron production, bricks and tile production, soil remediation (vegetation), extraction of rare J earth elements, and road substrate.

Due to the generation of large amounts of bauxite residue (red mud), an alternative method, called the Pedersen Process was considered in order to prevent bauxite residue generation (Lazou et al, 2020). In the conventional Pedersen Process, iron in bauxite is separated in the form of ><s pig iron through a carbothermic smelting-reduction step which has a & carbon dioxide emission similar to that during conventional iron production. In order to eliminate the carbon dioxide emission of this step, the focus of their work was to reduce the iron oxides of bauxite ore by hydrogen gas prior to smelting and minimizing the use of solid carbon materials for the reduction. Calcination and reduction of bauxite ore by hydrogen was studied by the thermogravimetry method supported by the microstructural and phase analysis confirming that the reduction of hematite to magnetite and magnetite to iron starts at temperatures below 560 °C with a slow rate and is faster at higher temperatures. At higher temperatures, i.e., 860, 960, and 1060 °C, the formation of hercynite (FeAhO4) retards the complete reduction to metallic iron.

The possibilities to recover rare earths from bauxite residues, which commonly contain only low concentrations of rare-earth elements, but are available in very large volumes and could provide significant amounts of

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rare earths to European countries are the main research subject of the European funded projects (EURARE; REMOVAL, SCALE, REDMUD) in the last ten years. The extraction rate of the rare earth recovery from these industrial waste streams is a part of a comprehensive, zero-waste, "product-centric" valorisation scheme, in which applications are found for the residual fractions that are obtained after removal of not only the rare earths but also other critical metals such as scandium, vanadium and gallium and especially the base elements: aluminium, titanium and iron (Binnemans et al, 2015).

Unfortunately, the extraction of aluminium, iron and titanium from bauxite residue under acid leaching is limited due to an insufficient amount of acidic solution from leaching caused by the polymerization of silica (Rivera et al, 2017). Kinetic studies have demonstrated that, at constant temperatures, silica dissolution increases with increasing acid concentrations, but it decreases when the temperature is increased and the acid concentration is reduced. This is due to the enhancement in the solubility of monomeric silicic acid formed during acidic leaching. The control mechanisms of silica dissolution have been described according to the shrinking core model by a chemical reaction stage, i.e., silica polymerization, followed by a diffusion stage, because of the silica gel adsorbed on the surface of the particles that limits the metal extraction. The recovery of iron, titanium, aluminium, and rare earth elements from bauxite residues preventing silica gel formation was performed using the dry digestion process with sulphuric acid and hydrogen peroxide (Alkan et al, 2018). The operational parameters were investigated and the addition of 2.5M hydrogen peroxide into 2.5M sulfuric acid was decided to be the best leaching condition to have favored quartz formation with a suppressed rhomboclase precipitation. Since the leaching reactions are mainly controlled by diffusion, no significant increase in the efficiencies was observed after 30 minutes of leaching. While Si gel was not formed in the oxidative environment, high titanium extraction from bauxite residue was only achieved when hydrogen peroxide was introduced into the acidic solution.

The combined pyrometallurgical and hydrometallurgical treatment of bauxite residue for the recovery of valuable metals included firstly carbothermic reduction (Xakalashe & Friedrich, 2018). The reductive smelting of bauxite residue uses coke as the reductant between 1500 and 1550°C and acidic to basic fluxes to low temperature smelting and the production of conditioned slag. Additional conditioning of bauxite residue with basic oxygen furnace slag and bottom ash as fluxing agents in the smelting process was performed in order to recover the valuable metals

with the exclusive use of the secondary resources as slag formers (Lucas et al, 2018). The final products based on aluminium, titanium, rare earth elements and scandium were obtained after a hydrometallurgical treatment using leaching, filtration, and precipitation (Yagmurlu et al, 2019).

The aim of this work is to offer the first information about the characterisation of bauxite residue from Alumina, Zvornik, and study its behaviour after a hydrometallurgical treatment using hydrochloric and sulphuric acid under the atmospheric pressure in the absence of hydrogen peroxide!

Methods

The mineralogical characterization of the samples was carried out using the X-ray diffraction technique - XRD. After the measurement, we processed the spectral images of the sample with the help of Difrac software, EVA v 4.2.2. The obtained values d (26), which are characteristic for each mineralogical phase, were compared with the literature data in the existing database, and thus we identified the present crystal phases.

The sample preparation was performed in single steps. The samples needed to be prepared so that their granulation was about 50^m, so that a flat-surface pallet could be made in polyethylene molds. In most samples, it was difficult to fulfill this condition due to the hardness of the samples that could not be prepared in the crucible. Regardless of the difficulties, making a pallet that did not have a flat surface was successful. The operational conditions are present in Table 2:

Table 2 - Operational data for the XRD-measurement

Таблица 2 - Оперативные данные для рентгеноструктурного анализа Табела 2 - Операциони подаци коришПени за рендгеноструктурну анализу

Device Model Producer Current Voltage Time per step Range 26 step

XRD Endeavor D8 Bruker 40mA 35KV 40mA 10-90 0.5

In order to determine the elements in the ppm range, the samples are measured on the ICP-OES device, using an optical emission technique that uses inductive-coupled plasma as a source. This technique is intended for analysing trace elements and requires translating the sample into an acidic solution. The sample preparation was performed using iSo

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6607-1985 method. The method involves the destruction of the sample with three concentrated acids (sulfuric, nitric and hydrochloric) at the beginning, and the treatment of the precipitate with hydrofluoric acid to translate residual elements (except SiO2) into a solution. After this preparation, a complete dissolution was expected. Total dissolution was confirmed during the treatment of solid residue obtained in the leaching experiments at 90°C.

Material

Due to its properties such as high alkalinity, bauxite residue can be used as an input material in various neutralization processes. Three different types of bauxite residue were compared, as shown in Table 3.

Table 3 - Chemical Composition of BR (Lucas et al, 2021)

Таблица 3 - Химический состав бокситового шлама (Lucas et al, 2021) Табела 3 - Хемц'ски састав бокситних остатака (Lucas et al, 2021)

Percent (%) Fe2O3 Al2O3 CaO SiO2 TiO2 Na2O C2O3 Sc (ppm)

Germany 35.3 15.7 6.7 14.0 11.4 8.9 0.2 86

Greece 44.0 23.0 10.2 5.5 5.6 1.8 0.3 122

Zvornik 49.3 12.0 8.2 10.5 4.6 2.5 0.13 76

This table shows that the bauxite residue from Zvornik, Bosnia and Herzegovina contains mostly iron oxide. The Greek bauxite residue contains more scandium, aluminium oxide, and chromium oxide but smaller content of sodium oxide than the German and Zvornik ones. The bauxite residue from Germany is highly alkaline due to the presence of sodium hydroxide from the Bayer process. Bauxite residue was provided from Alumina Ltd, Zvornik, Bosnia and Herzegovina, as the starting raw material. The Alumina factory has been in the continuous production mode since October 6, 1978, and continuously processes bauxite and produces alumina, hydrates, zeolites, and other related aluminosilicate products. The Alumina company currently has about 1500 employees, which is about 25 % of all employees in Zvornik. Alumina owns a red mud disposal site located about 5 km from the factory. The transportation of the red mud suspension from the factory to the landfill is carried out by suitable pumps. The area of the red sludge landfill is about 1 km2, as shown in Figure 1.

Figure 1 - Area of the accumulated bauxite residue in Zvornik, Bosnia and Herzegovina Рис. 1 - Площадь скопления бокситового шлама в г.Зворник, Босния и

Герцеговина

Слика 1 - Површина акумулисаног бокситног остатка у Зворнику, Босна и

Херцеговина

During the operation of the Alumina Ltd. company, about 19.4 x 106 m3 of red mud suspension was disposed of. Depending on the quality of bauxite, the amount of completely dry red mud typically ranges from 0.8 to 2 tons of tailings per ton of alumina produced. The Alumina Ltd. company from Zvornik uses bauxite with a silicon dioxide modulus between 8.5 and 12. Accordingly, the amount of red mud that is separated and disposed of at the landfill is about 1.0 - 1.2 tons per ton of AhO3 produced, or approximately 400,000 t / per year. The installed technical-technological equipment at the clearing plant is of a continuous (uninterrupted) nature, where there are five installed autoclave batteries of 11-12 interconnected autoclaves in series (each autoclave has 50 m3).

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The bauxite residue from alumina was filtrated, washed and dried at 105 °C for 24 h.The chemical composition of bauxite residue is shown in Table 4.

Table 4 - Chemical composition of BR, Zvornik Таблица 4 - Химический состав бокситового шлама в г.Зворник Табела 4 - Хемц'ски састав бокситних остатака у Зворнику

Compounds % Compounds %

Ignition loss at 1000°C 8,32 Ga2Ü3 0,225

SiO2 10,52 CuO 0,007

Fe2O3 49,29 K2O 0,159

Na2O 2,45 TI2O3 0,088

TiO2 4,59 MnO 0,145

CaO 8,23 MgO 0,627

Al2O3 12,03 NiO 0,034

Ag2O 0,001 PbO 0,019

BaO 0,014 P2O5 0,930

Cr2O3 0,133 ZnO 0,016

SC2O3 0,011 V2O5 0,135

Co2O3 0,012 SrO 0,075

One additional elemental ICP -OES analysis was performed in order to establish the content of rare earth elements (REE) presented in Table 5:

Table 5 - Content of rare earth elements in BR, Zvornik Таблица 5 - Содержание редкоземельных элементов бокситового шлама

в г. Зворник

Табела 5 - Садржаj елемената ретких земаъа у бокситним остацима у Зворнику

Content Pr Sc Y La Ce Nd Sm Tb total

ppm 12 76 133 114 250 96 11 8 700

As shown in Figure 2, the XRD-analysis found the following phases: hematite, perovskite, cancrinite, cancrinite, ilmenite, calcite, diaspore, gibbsite, and hydrogarnet. Iron is available in the hematite and ilmenite structures. Titanium is present in perovskite and ilmenite structures, while aluminum is available in the structures of cancrinite, diaspore, boehmite, gibbsite, and hydrogarnet.

Figure 2 - XRD-analysis of BR from Zvornik Рис. 2 - Рентгеноструктурный анализ бокситового шлама в г. Зворник Слика 2 - Рендгеноструктурна анализа бокситног остатка из Зворника

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Figure 3 - XRD-analysis of solid residue after leaching with 1mol/L hydrochloric acid at

90 °C for 2 hours

Рис. 3 - Рентгеноструктурный анализ твердого шлама после выщелачивания 1 моль/л соляной кислоты при 90°C в течение 2 часов Слика 3 - Рендгеноструктурна анализа чврстог остатка после лужена 1 Mol/L хлороводоничном киселином на 90°C, у тра]ашу од два сата

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Experimental

The first experiments were performed in order to study the change of the mineralogical structure during leaching experiments. The leaching was performed using 1mol/l hydrochloric acid and 1mol/L sulfuric acid at 90 °C with a solid/liquid ratio 1:10 and a mixing rate of 200 rpm for 2 hours. The obtained XRD-analysis results are shown in Figures 3 and 4.

Figure 4 - XRD-analysis of solid residue after leaching with 1mol/L sulphuric acid at

90 °C for 2 hours

Рис. 4 - Рентгеноструктурный анализ твердого шлама после выщелачивания 1 моль/л серной кислоты при 90°C в течение 2 часов Слика 4 - Рендгеноструктурна анализа чврстог остатка после лужена 1 Mol/L сумпорном киселином на 90°C, у тра]ашу од два сата

The comparative analysis of the obtained XRD-analysis results is presented in Table 6.

The analysis of the initial bauxite residue in Figure 2 has shown that Fe is present in the hematite and ilmenite structure, Ti in perovskite and ilmenite and Al in cancrinite, diaspore, boehmite, gibbsite and hydrogarnet. Direct leaching of BR (as shown in Figs. 3 and 4) confirms that the mineral structure is not only changed, but also some new compounds are found such as vuagnitit, brownmillerite, anhydrite (CaSO4), as shown int Figure 3. The addition of sulphuric acid leads to the formation of unsoluble calcium sulphate.

Table 6 - Comparative analysis of the mineralogical phases Таблица 6 - Сравнительный анализ минералогических фаз Табела 6 - Упоредна анализа минералошких фаза

Material

Red mud

(Bauxite

residue)

Solid residue after a leaching of BR with hydrochloric acid

Solid residue after a leaching of BR with sulfuric acid

Process

Bayer (autoclave) T=150°C t=2 hours addition of NaOH

Leaching of BR using

1 mol/L HCl, 90 °C, 120 min

Leaching of BR using

1 mol/L H2SO4, 90 °C, 120 min

Mineral

Hematite

Perovskite

Cancrinite

Ilmenite

Calcite

Diaspore

Gibbsite

Hydrogarnet

Hematite

Perovskite

Hydrogarnet

Diaspore

Gibbsite

Goethite

Zoisite

Hematite

Perovskite

Ilmenite

Calcite

Diaspore

Boehmite

Goethite

Gibsite

Vuagnatit

Brownmillerite

Quartz

Anhydrite

Phase composition

Fe2Oз CaTiOз

AlзSiзNa4O14.з5

FeTiOз

CaCOз

AlOOH

Al(OH^

Alз.бCaзH9.87бO12

Fe2Oз CaTiOз

Alз.бCaзH9.87бO12 AlOOH Al(OH)з FeOOH

Ca2Ab(SiO4)(Si2O7)O(OH)

Fe2Oз

CaTiOз

FeTiOз

CaCOз

a-AlOOH

Y-AlOOH

FeOOH

Al(OH)з

CaAlSiO4(OH)

Ca2(Al,Fe)2O5

SiO2

CaSO4

6 8 0

-9 6 0

The analysis of the obtained solution with the calculated leaching efficiencies is shown in Table 7:

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Table 7 - Chemical composition of the obtained solution and the calculated leaching

efficiency

Таблица 7 - Химический состав полученного раствора и рассчитанная эффективность выщелачивания Табела 7 - Хемц'ски састав доби^еног раствора и израчуната ефикасност

лужена

Elements from solutions are presented as compounds Leaching with 1M HCI (90°C, 2hours, s/L: 1/10) Leaching with 1M H2SO4 (90°C, 2hours, s/L: 1/10)

Content (mg/L) Leaching Efficiency (%) Content (mg/L) Leaching Efficiency (%)

AI2O3 7190 59.76 7292 60.61

SiO2 2351 22.34 1369 13.01

P2O5 84.7 9.10 128.1 13.76

V2O5 8.8 6.51 41.4 30.66

SrO 12.6 16.8 7.9 10.53

Ga2O3 10,9 4.84 22.4 9.95

K2O 46.2 29.05 56.4 35.47

Y2O3 16.3 9.65 13.6 8.05

NiO 4.44 13.08 9.1 26.76

Cr2O3 15.3 11.50 19.1 14.36

MnO 11.2 7.7 15.2 10.45

Ce2O3 13.3 4.54 4.0 1.37

SC2O3 4.98 45.27 5.82 52.90

PbO 5.27 27.73 4.4 23.16

Fe2O3 718 1.46 1096 2.23

TiO2 233 5.07 441 9.60

For aluminum, the maximum leaching efficiency was about 60 % for both used acids. The small leaching efficiency has confirmed that the leaching time of 2 hours was not enough to ensure complete leaching efficiency. Leaching efficiency from scandium is maximal for critical metals (52.90 %), but not sufficient.

Therefore, the increased concentration of solution, reaction temperature, and duration of process in the presence of hydrogen peroxide will be considered in order to increase leaching efficiency. The formation of silica gel is confirmed in a study of the leaching process with sulfuric acid under the atmospheric pressure, as shown in Figure 5:

Figure 5 - Formation of silica gel after sulfuric acid leaching at 90°C Рис. 5 - Образование силикагеля после сернокислотного выщелачивания при

90°C

Слика 5 - Формираше силика гела након раствараша сумпорном киселином на

90°C

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Natural precipitation of iron from the obtained solution has been confirmed after leaching with hydrochloric acid, as shown in Figure 6!

Figure 6 - Natural precipitation of iron after hydrochloric acid leaching at 90°C Рис. 6 - Естественное осаждение железа после солянокислотного выщелачивания при 90°C Слика 6 - Природно таложеше железа након раствараша хлороводоничном

киселином на 90°C

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The formation of silica gel and the natural precipitation of iron can be prevented through the dry digestion process in the presence of hydrogen

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peroxide, as mentioned in the literature review. The performed experiments of acidic leaching confirmed some difficulties related to a direct leaching process. Therefore, highly efficient technology is proposed to improve leaching efficiency of valuable metals. The pyrometallurgical method can ensure destroying the mineralogical structure of bauxite residue forming a more suitable slag structure for better leaching using different acids. A combined pyrometallurgical and hydrometallurgical method for the treatment of bauxite residue will be reported in the future in order to improve a direct leaching process.

Conclusion

The hydrometallurgical treatment of bauxite residue with 1mol/l hydrochloric acid and 1mol/L sulphuric acid at 90°C for 2 hours leads to a maximum leaching efficiency of aluminium about 60 %, 53 % of scandium and a minimum efficiency of other valuble elements, respectively. The analysis of the changes in the mineralogial structure has revaled that small changes are possible during the hydrometallurgical treatment. A new research strategy for the treatment of bauxite residue is needed in order to ensure a full change of the initial mineralogical structure and the most efficient transfer of metals from bauxite residues to a liquid phase. The formation of unsoluble calcium sulphate is found during leaching with sulphuric acid. The silica gel formation and the natural precipitation of iron from the solution are some difficulties that can be prevented using dry digestion. The following step is an improvement of a direct leaching process using a pyrometallurgical method such as hydrogen plasma reduction.

References

Alkan, G., Yagmurlu, B., Cakmakoglu, S., Hertel, T., Kaya, S., Gronen, L., Stopic, S. & Friedrich, B. 2018. Novel Approach for Enhanced Scandium and Titanium Leaching Efficiency from Bauxite Residue with Suppressed Silica Gel Formation. Scientific Reports, 8, art.number:5676. Available at: https://doi.org/10.1038/s41598-018-24077-9.

Binnemans, K., Jones, P.T., Blanpain, B., van Garven, T. & Pontikes, Y. 2015. Towards zero-waste valorisation of rare-earth-containing industrial process residues: a critical review. Journal of Cleaner Production, 99, pp.17-38. Available at: https://doi.org/10.1016/jjclepro.2015.02.089.

Castaldi, P., Silvetti; M., Santona, L., Enzo, S. & Melis, P. 2008. XRD, FTIR, and thermal analysis of bauxite ore-processing waste (red mud) exchanged with heavy metals. Clays and Clay Minerals, 56, pp.461-469. Available at: https://doi.org/10.1346/CCMN.2008.0560407.

Damjanovic, V., Kostic, D., Ostojic, Z., Perusic, M., Filipovic, R., Oljaca, Dj., Obrenovic, Z. & Micic, V. 2020. The Influence of Process Parameters on Removing Iron, Zinc and Copper Impurities from Synthetic Bayer Liquor. In: TRAVAUX 49, Proceedings of the 38th International ICSOBA Conference, virtual, pp.325-334, November 16-18 [online]. Available at:

https://icsoba.org/assets/files/publications/2020/AA21S.pdf [Accessed: 1 June 2023].

Lazou, A., van der Eijk, C., Balomenos, E., Kolbeinsen, L. & Sfarian, J. 2020. On the Direct Reduction Phenomena of Bauxite Ore Using H2 Gas in a Fixed Bed Reactor. Journal of Sustainable Metallurgy, 6, pp.227-238. Available at: https://doi.org/10.1007/s40831 -020-00268-5.

Lucas, H., Alkan, G., Xakalashe, B. & Friedrich, B. 2018. Conditioning of bauxite residue with bottom ash in view of recovery of valuable metals: A sustainable approach. In: 2nd international Bauxite Residue Valorisation and Best Practices Conference (BR2018), Athens, Greece, pp.263-270, May 7-10.

Lucas, H., Stopic, S., Xakalashe, B., Ndlovu, S. & Friedrich, B. 2021. Synergism Red Mud-Acid Mine Drainage as a Sustainable Solution for Neutralizing and Immobilizing Hazardous Elements. Metals, 11(4), art.number:620. Available at: https://doi.org/10.3390/met11040620.

Rivera, R.M., Ulenaers, B., Ounoughene, G, Binnemans, K. & van Gerven, T. 2017. Behaviour of Silica during Metal Recovery from Bauxite Residue by Acidic Leaching. In: Travaux 46, Proceedings of 35th International ICSOBA Conference, Hamburg, Germany, pp.547-556, October 2-5 [online]. Available at: https://icsoba.org/assets/files/publications/2017/BR13S%20-%20Behavior%20of %20Silica%20during%20Metal%20Recovery%20from%20Bauxite%20Residue %20by%20Acidic%20Leaching.pdf [Accessed: 1 June 2023].

Xakalashe, B. & Friedrich, B. 2018. Combined carbothermic reduction of bauxite residue and basic oxygen furnace slag for enhanced recovery of Fe and slag conditioning. In: 2nd international Bauxite Residue Valorisation and Best Practices Conference (BR2018), Athens, Greece, pp.233-240, May 7-10.

Yagmurlu, B., Alkan, G., Xakalashe, B., Schier, C., Gronen, L., Koiwa,I., Dittrich, C. & Friedrich, B. 2019. Synthesis of Scandium Phosphate after Peroxide Assisted Leaching of Iron Depleted Bauxite Residue (Red Mud) Slags. Scientific Reports, 9, art.number:11803. Available at: https://doi.org/10.1038/s41598-019-48390-z.

Обработка бокситового шлама - кислотное выщелачивание (первая часть)

Сречко Р. Стопич, корреспондент, Владимир Дамяновичб, Радислав Филипович6, Мери Д. Камарада, Бернд Г. Фридриха

а Технический университет города Ахен, Институт металлургических процессов и рециклирования металлов, г. Ахен, Федеративная Республика Германия

б ООО „Алумина", г. Зворник, Республика Сербская, Босния и Герцеговина

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РУБРИКА ГРНТИ: 61.13.21 Химические процессы ВИД СТАТЬИ: обзорная статья

Резюме:

Введение/цель: Бокситовый шлам, являющийся побочным продуктом алюминиевой промышленности, получаемый по способу Байера, в основном состоит из оксида железа, оксида титана, оксида кремния и нерастворимого оксида алюминия, а также широкого спектра других оксидов и незначительного содержания редкоземельных элементов, галлия, ванадия и скандия. Извлечение ценных элементов из бокситового шлама и минимизация его образования в ходе обработки являются недостаточно исследованной областью.

Методы: В обработке бокситового шлама использовались различные гидрометаллургические и пирометаллургические методы. В данном исследовании представлены результаты гидрометаллургической обработки бокситового шлама из глинозема Зворник с использованием серной и соляной кислот с целью изучения изменения минералогического состава. Эффективность выщелачивания рассчитана на основании анализа ICP OES. Рентгеноструктурный анализ был использован в изучении свойств исходного материала и твердого шлама и в изучении изменений минералогических фаз.

Результаты: Выщелачивание бокситового шлама серной и соляной кислотой частично приводит к изменению минералогической структуры и преобразованию элементов в жидкую фазу. С течением времени наблюдается естественное осаждение железа в состоянии покоя. Подтверждено образование силикагеля в процессе выщелачивания бокситового шлама соляной кислотой.

Выводы: В области обработки бокситового шлама необходимо разработать новую исследовательскую стратегию с целью обеспечения полного изменения исходной минералогической структуры и наиболее эффективного преобразования металлов в жидкую фазу.

Ключевые слова: бокситовый шлам, алюминий, гидрометаллургия, кислота, рециклирование, редкоземельные элементы.

Третира^е бокситних остатака - луже^е (први део)

СреПко Р. Стопив, аутор за преписку, Владимир Дам]анови^, Радислав Филиповийб, Мери Д. Камарада, Бернд Г. Фридриха

а Технички универзитет у Ахену, Институт за процесну металурги]у и рециклира^е метала, Ахен, Савезна Република Немачка

б Алумина доо, Зворник, Република Српска, Босна и Херцеговина

ОБЛАСТ: хеми]ске технологи]е

КАТЕГОРИJА (ТИП) ЧЛАНКА: оригинални научни рад

Сажетак:

Увод/цил: Остатак од лужена боксита jе отпадни продукат из индустр^е алумин^ума настао у Баjеровом процесу саставлен од оксида железа, титана, силиц^ума и нераствореног алумин^ум-оксида са широким спектром других оксида и минималним садржа]'ем елемената ретких земала, гал^ума, ванад^ума и сканд^ума, ко\и се меша сагласно земли из ще потиче. Екстракц^а вредних елемената из бокситног остатка и минимизац^а бокситног остатка кроз различите третмане су отворено истраживачко поле.

Методе: Различите хидрометалуршке и пирометалуршке методе коришЯене су за третираше бокситних остатака. У раду су приказани резултати хидрометалуршког третмана коришЯешем сумпорне и хлороводоничне киселине како би се проучиле промене минералског састава. Ефикасност лужена биЬе израчуната коришЯешем ИЦП ОЕС анализе. Рендгеноструктурна анализа коришЯена jе за карактеризац^у почетног материала и чврстог остатка проучаваjуfiи промене минералошких фаза.

Резултати: Раствараше бокситног остатка сумпорном и хлороводоничном киселином води делимично до промене минералске структуре и трансфера елемената у течну фазу. Природна преципитац^а железа присутна jе током стаjаша. Формираше силика гела потвр^ено jе током раствараша бокситних остатака хлороводничном киселином.

Заклучак: Нова истраживачка стратег^а неопходна jе за третираше бокситног остатка како би се обезбедила потпуна промена минералошке структуре и много ефикасн^и пренос метала у течну фазу.

Клучне речи: бокситни остатак, алумин^ум, хидрометалург^а, киселина, рециклираше, елементи ретких земала.

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Paper received on / Дата получения работы / Датум приема чланка: 28.06.2023. Manuscript corrections submitted on / Дата получения исправленной версии работы / Датум достав^а^а исправки рукописа: 01.12.2023.

Paper accepted for publishing on / Дата окончательного согласования работы / Датум коначног прихвата^а чланка за об]ав^ива^е: 02.12.2023.

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© 2023 Авторы. Опубликовано в «Военно-технический вестник / Vojnotehnicki glasnik / Military Technical Courier» (www.vtg.mod.gov.rs, втг.мо.упр.срб). Данная статья в открытом доступе и распространяется в соответствии с лицензией «Creative Commons» (http://creativecommons.org/licenses/by/3.0/rs/).

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