Evaluation of red mud as surface treatment for carbon steel prior painting

doi:10.1016/j.porgcoat.2004.06.008

Progress in Organic Coatings

Volume 52, Issue 4, 1 April 2005, Pages 351-358

https://doi.org/10.1016/j.porgcoat.2004.06.008 Get rights and content

Abstract

Red mud (RM) is the waste product of the Bayer process for obtaining alumina from bauxite. The alkaline nature of RM suspensions together with the presence of Fe³⁺ species point towards the possibility of using RM as a good corrosion inhibitor for carbon steel. Based on this idea, the possible use of RM suspensions as pre-treatment for carbon steel was studied by recording the electrode potential and the electrochemical impedance spectroscopy (EIS) evolution with immersion time. Different parameters regarding the steel surface finishing (grinding, pickling or degreasing) and RM suspension condition (stirred or steady, decanted or filtered) have been considered in the study; the passivation was obtained when ground samples were immersed in decanted RM suspensions and subjected to continuous stirring. The influence of chlorides and pH were analysed by potentiometric titration. The obtained results indicate that treated samples depassivate at lower Cl⁻/OH⁻ ratio than untreated ones. Regarding the pH parameter, treated samples remain passive at lower pH values than the untreated ones. Finally, some treated and untreated samples were painted and subjected to cathodic polarisation experiments, including an artificial defect in the coating. The comparative study was done using EIS technique; the impedance diagrams would indicate an effective passivation of the steel surface for treated samples.

Introduction

Red mud (RM) is the insoluble residue remaining after the caustic digestion of bauxite, the ore used in the production of alumina through the Bayer process. This highly alkaline residue (pH = 10–12.5) is composed primarily of fine particles containing silica, aluminium, iron, calcium and titanium oxides and hidroxides (along with other minor components). The iron impurities are responsible for the brick red colour of the mud [1]. For every tonne of alumina produced, between 1 and 2 t (dry weight) of red mud residues are generated. This waste is a major environmental problem for areas where alumina industries are installed because of the alkaline nature and the chemical and mineralogical species present in RM [2].

Many attempts have been made over the years to find a use for this residue; some have been based on its possible usage as a partial substitute of clay in ceramic products (bricks, tiles, etc.) [3] or as an additive for mortar and concrete [4]. Attempts have also been made to use bauxite residue in agricultural applications, such as, in acidic soils or as a treatment for iron deficient soils [5]. Toxic heavy metals have been removed from aqueous solutions using red mud as an absorbent [6], [7]. Unfortunately, those applications have proven to be economically unsatisfactory and research should be continued.

The surface properties of red mud particles will strongly determine its behaviour, not only the composition but also the particle size that ranges between 50 Å and 1 μm. The caustic insoluble bauxite minerals are hematite (Fe₂O₃), aluminium goethite ((Fe, Al)OOH), and titanium oxides; occasionally, boehmite (AlOOH) may be present depending on the extraction conditions. The aluminium loss in the Bayer process is due to the formation of a insoluble by-product named “Bayer sodalite”, 3(Na₂O·Al₂O₃·2SiO₂·nH₂O)·Na₂X, where X may be CO₃⁻, SO₄⁻, 2OH⁻, 2Cl⁻ or a mixture of them, depending on the digesting liquor composition. The n value ranges from 0 to 2 [8]. Most of these minerals and oxides exhibit acid/base type behaviour [9], which is expected to occur on the surface of red mud particles. Surface charge properties of red mud have been studied by means of potentiometric titration, the RM particles in alkaline aqueous solutions carry ionised surface hydroxyl groups, S single bond O⁻ (S denotes red mud surface), these active sites can favour the adhesion between red mud particles and a metallic surface. On the other hand, when protons are added to RM aqueous solutions, the surface hydroxyl groups adsorb H⁺ ions, resulting in a nearly constant pH in the bulk solution, which indicates a certain buffering character [8], [10], [11]. Besides, Cl⁻ ions can replace the surface single bond OH groups, i.e., RM particles can capture aggressive ions, like Cl⁻, from the environment. In this field, previous studies have been carried out to evaluate the steel corrosion inhibition using RM aqueous solutions or red mud as an additive to cement paste (steel embedded in mortar) when Cl⁻ ions are present [12], [13], [14]. The obtained results indicate that red mud is good corrosion inhibitor against chloride attack in this alkaline media.

Finally, the presence of Fe³⁺ species indicates a certain redox activity; in this way, attempts to use RM as an anodic pigment in anticorrosive paints have been reported [15], [16].

Following those experiences, and based on the previous works by our group, the present paper deals with the possible use of RM as an alternative pre-treatment of carbon steel. The traditional treatments, based on chromate conversion layers, are hazardous and new environment-friendly alternatives are being investigated [17], [18]. Bearing this in mind, the first part of this study is focused on the assessment of the conditions which enable optimal surface passivation. Once those parameters were defined, the second part was devoted to the evaluation of such pre-treatment with a comparative study between painted samples previously treated, and grinded carbon steel without treatment.

Section snippets

Experimental

Carbon steel samples (S = 4 cm²) were prepared with different surface finishing: ground, pickled with HCl acid or degreased with trichloroethylene. The passivation procedure was direct immersion in a red mud suspension. The RM was supplied by ALCOA factory located in San Cibrao (Northwest of Spain) with a chemical composition (w/w, %): Fe₂O₃ (37%), TiO₂ (20%), Al₂O₃ (12%), SiO₂ (9%), CaO (6%), Na₂O (5%), H₂O (1000 °C) (11%). The RM suspensions were prepared by adding 20 g of solid to 1 l of distilled

Surface passivation conditions

Fig. 1 depicts the corrosion potential evolution with immersion time for carbon steel samples immersed in stirred and decanted RM suspensions, with different steel surface finishing. This parameter seems to be critical: the higher initial potentials correspond to the ground sample, where the pre-existing oxides are mechanically removed. In the case of degreased and pickled samples, cleaning is less effective and some oxides may remain on the steel surface. In alkaline media, those oxides,

Conclusions

The study of different parameters which can affect the steel surface passivation indicates that the better conditions correspond to ground surfaces immersed for about 24 h in stirred and decanted red mud suspensions. Based on the X-ray diffraction results, iron and aluminium oxo-hidroxides are the only RM components deposited on the metallic surface, not as a continuous layer but as discrete distribution of particles.

The presence of RM particles promote Cl⁻ ions adsorption on the steel surface

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Cited by (54)

Toward sustainable green alumina production: A critical review on process discharge reduction from gibbsitic bauxite and large-scale applications of red mud
2023, Journal of Environmental Chemical Engineering
In 2021, global alumina production reached over 135 million tons and discharged approximately 200 million tons of red mud, leading to severe environmental safety hazards. More than 70% of raw materials originated from gibbsitic bauxite. This work reviews existing and potential process from open literature to treat gibbsitic bauxite and reduce red mud discharge from the alumina production process, which are divided into two categories. The first strategy involves non-Bayer methods such as smelting reduction, reduction roasting, sub-molten salt, ammonium sulfate roasting, acid leaching, and calcification–carbonation. The current obstacle to implementing these methods is the lack of economics, making industrial application challenging. The second potential industrial application strategy is to modify the current Bayer process, with critical measures involving the enhancement digestion of inert aluminum-bearing minerals, dissociation and recovery of iron minerals, and separation of desilication products. Analyzing the reaction mechanism and process flow clarify that the modified Bayer method is more favorable to the cost-effectively and synergistic extraction of aluminum, iron, and other elements. The red mud obtained by the modified Bayer process can be efficiently utilized. Therefore, a mini-summary of the areas where red mud is expected to be substantially dissipated (e.g., the steel industry, cement building materials, and ecological restoration of red mud stockpiles) is provided. The review can advance the current technology on the comprehensive utilization of gibbsitic bauxite, especially process discharge reduction approaches and large-scale abatement ways for red mud. Our results can contribute to the future development of sustainable green alumina production.
A review of the sustainable utilisation of red mud and fly ash for the production of geopolymer composites
2022, Construction and Building Materials
This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/locate/withdrawalpolicy).
This article has been retracted at the request of the Editor-in-Chief.
Upon post-publication investigation, it was found that this paper and another published in Case Studies of Construction Materials (https://doi.org/10.1016/j.cscm.2022.e00994) contain mostly the same data. The papers contain 6 common tables and 15 common figures. The text in each paper appears to have been edited to avoid plagiarism checking software. Both papers were initially submitted on the same day. This constitutes an instance of duplicate submission and duplicate publication. Submission and publication of both papers represents a manipulation of the publication process and a violation of the journal policy on Publishing Ethics.
Sustainable utilization of red mud waste (bauxite residue) and slag for the production of geopolymer composites: A review
2022, Case Studies in Construction Materials
This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/locate/withdrawalpolicy).
This article has been retracted at the request of the Editor-in-Chief.
Upon post-publication investigation, it was found that this paper and another published in Construction and Building Materials (https://doi.org/10.1016/j.conbuildmat.2022.128892) contain mostly the same data. The papers contain six common tables and 15 common figures. The text in each paper appears to have been edited to avoid plagiarism detection software. Both papers were submitted on the same day. This constitutes duplication submission and duplicate publication. As such, this article represents a misuse of the scientific publishing system. The scientific community takes a very strong view on this matter and apologies are offered to readers of the journal that this was not detected during the submission process.
Co-Author Afonso Azevedo disagrees with the retraction and was not a co-author of the retracted CBM paper. Other co-authors have not responded.
Characteristic, hazard and iron recovery technology of red mud - A critical review
2021, Journal of Hazardous Materials
Red mud (RM) is the major waste material with strong alkaline discharged which is during the alumina extraction process. The global stock of RM has exceeded 4 billion tons and its disposal as a solid waste has always been a thorny environmental problem. However, RM is widely considered to be a potential resource due to its high content of valuable metal components such as iron. High-iron RM is rich in iron and can potentially become a valuable resource if the iron can be extracted effectively. It is of great research value and profound significance to recover iron from high-iron RM. This paper systematically reviews the iron recovery methods for resource utilization of high-iron RM, and divides the technology of iron recovery from high-iron RM into three aspects: physical separation method, pyrometallurgy method (reduction smelting and reduction roasting) and hydrometallurgy method (acid leaching). The basic principles and effect of iron extraction of the above technologies are summarized respectively, and the advantages and disadvantages of different technologies are compared. It is pointed out that the feasibility and economic cost are the main factor restricting the industrial application of these technologies. Therefore, it is of great significance to overcome various problems and difficulties, and develop innovative processes and technologies, which can realize the recycling and utilization of iron in high-iron RM and realize the reduction of RM emission at the same time.
Evaluation of red mud as filler in Brazilian dense graded asphalt mixtures
2020, Construction and Building Materials
Red mud is a waste resulting from the bauxite refining to produce aluminum. A large amount of red mud generated and inadequately disposed of in the environment, evidence the immediate necessity in developing methods to reuse this hazardous waste in the productive chain. In this scenario, a viable and environmental alternative is the red mud used as filler in asphalt mixtures production. This work aims to evaluate the potential application of red mud as filler in dense asphalt mixture. Three percentages of red mud as filler were tested (3, 5 and 7%). The methodology encompassed the red mud chemical analysis, the asphalt mixtures design and production, and then, mechanical tests, such as moisture-induced damage and, permanent deformation through French Rutting Tester (FRT) traffic simulator were performed. The red mud tests included X-ray diffraction, fluorescence, specific mass, laser granulometry, pH and scanning electron microscopy. As Brazilian dense-graded mixture allow the total filler content of 7%, in order to vary the red mud percentage, stone powder filler (size ≤0.075 mm) was also used. As a result, the granulometry test showed that red mud could be used as filler. The chemical analysis detected the presence of 0.20% of vanadium pentoxide (V₂O₅) indicating that red mud is a hazardous waste. Three asphalt mixtures were produced using different percentages of red mud, Mixture 2 (3% of red mud and 4% of stone powder); Mixture 3 (5% of red mud and 2% of stone powder); Mixture 4 (7% of red mud). The conventional mixture with 7% stone powder filler was the reference (Mixture 1). The moisture-induced damage showed that red mud mixtures presented greater tensile strength by diametral compression in comparison to the reference mixture. As for permanent deformation resistance, Mixture 3 (5% of red mud and 2% of stone powder) performed better than the others, with 3.50% of rutting depth at 30,000 cycles.c In general, concerning conventional mixture, red mud ones presented rutting reduction from 42.63% (reference) to 12.82 (mixture 3). This study showed the viability of reinserting the red mud in the production chain and the possible road construction use. The red mud as filler in asphalt mixtures production showed as an option to contribute and mitigate the disposal problems, as well, as an environmentally friendly alternative.
A review on advances in sustainable energy production through various catalytic processes by using catalysts derived from waste red mud
2019, Renewable Energy
Citation Excerpt :
Normally, different composition of RM includes Fe2O3, Al2O3, SiO2, Na2O, TiO2, CaO, MgO and other constituents such as K, V, Cr, Mn, P, Ga, Mg, Zn, Nb, Th, and Ni dispersed in smaller amounts in an alkaline medium [11,67,75–78]. The composition of RM originated from different plants across the world are shown in Table 2 [12,13,16,17,20,22–24,27,34,38,40,49,50,56,69,79–88]. The X-ray diffraction analysis (Fig. 2) confirmed different mineralogical phases of various elements in RM, such as hematite (α- Fe2O3), gibbsite (Al(OH3), quartz (SiO2), calcite (CaCO3), calcium silicate (Ca2(SiO4), sodium aluminate (NaAlO2) and sodalite (Na8Al6(SiO4)6Cl2) [89].
Conversion of wastes to energy and other value-added products is considered as a suitable method towards energy security. Wastes from various sources are becoming potential feedstocks for energy production through different techniques. The economy and sustainability of these processes demand the use of low-cost catalysts. Red mud (RM) is one of the most abundantly produced industrial wastes from aluminum industries. Such a huge production of RM, its alkaline nature and the presence of a small quantity of radioactive elements make it an environmental liability. Out of various utilization methods, RM as a catalyst for different chemical processes has been very successful. Presence of many valuable metals in RM, in particular, Fe makes it a suitable catalyst for energy production through processes such as pyrolysis, hydrotreating, transesterification and H₂ production from biomass and other sources. This article critically reviews the advances in sustainable energy production through different processes mentioned above by RM based catalysts. Different characterization, activation and stability study of RM along with outcomes and mechanism of these processes are discussed. Furthermore, drawbacks associated with the low catalytic activity of RM and works that need to be carried out in the future for the improvement of its catalytic activity are discussed in detail.

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Evaluation of red mud as surface treatment for carbon steel prior painting

Abstract

Introduction

Section snippets

Experimental

Surface passivation conditions

Conclusions

Colloids Surf. A

Cem. Conc. Res.

Water Res.

Colloids Surf. A

Electrochim. Acta

Prog. Org. Coat.

Corros. Sci.

Corros. Sci.

Electrochim. Acta

Light Met.

Res. Ind.