Impurities Accumulation on the Surface of Alumina Hydrate Particles in Bayer Technology

Dobra, Gheorghe; Iliev, S.; Anghelovici, Nicolae; Cotet, Lucian; Filipescu, Laurentiu

doi:10.37358/rc.19.2.6916

Cited by 4 publications

(4 citation statements)

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“…Furthermore, the method allows identification of the source and procedures to avoid contamination by controlling the technology in the right stage where the source is providing materials for contamination aluminum hydroxide particles. This ultimate advantage has led to the application of SEM microscopy coupled with EDX spectroscopy to the analysis of non milled and milled aluminum hydroxide samples [6]. The mechanism of contamination aluminum hydroxide with occluded impurities is simple and is taking place in correlation with three conditions coming from understanding the course of any crystallization process a) the presence of micron size particles in the supersaturated Bayer liquors due to the poor working of red filtration, and especially due to the poor quality of the filtering material -the freshly precipitated tricalcium aluminate; b) the fluctuation of supersaturation (control by the temperature-concentration relationship) in all stages of nucleation, agglomeration and growth of the particles in decomposition line of sodium aluminate, but especially, in the agglomeration stage; c) the crystallinity of the mineralogical phases and the share of amorphous particles fraction in the small size bauxite residue particles, conveyed by super-concentrated liquors in the crystallizing vessels [7][8][9][10][11][12][13].…”

Section: Resultsmentioning

confidence: 99%

Aluminum Hydroxide Impurities Occlusions and Contamination Sources

Dobra¹,

Garcia-Granda²,

Iliev³

et al. 2020

Rev. Chim.

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This paper is reporting the data concerning impurities occlusion in the dried, milled and classified aluminum hydroxide, the sources of contamination and the ways to control the purity of classified aluminum hydroxide as raw material for special aluminas. Mainly, all the micronic size particles, floating in the super-saturated Bayer liquors, are potential sources of occluded impurities in the aluminum hydroxide particles. There are several mechanisms for embedding the impurities in crystalline substances. Of these, most probable ones in the Bayer alumina process are: a) occlusion of the spent liquor drops containing impurities inside the polycrystalline aluminum hydroxide congregates; b) hetero-nucleation of aluminum hydroxide on the surface of particles or colloids containing one or more impurities (the foreign particles are seized inside a crystals or inside of a crystalline multi-particulate association); c) incorporation of available ions or molecule reactive fragments in the poor crystalline structures of aluminum hydroxide after nucleation, during different growth stages of all already aggregated particles, under certain super-saturations. d) building up bridges between the scanty aggregated particles or filling the inside hollows of these aggregates with new quickly crystallized material, including the particulate impurities, mainly, during large fluctuations of the super-saturation. Using scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy EDS (Apollo SSD detector, EDAX), the contributions of each of these mechanisms can be investigated simply and assumed from the collected data. It was shown that well crystallized phases originating directly from bauxite (like the aluminum substituted goethite and substituted hematite, rutile or quartz), as well as the well as the crystallized new born phases during specific Bayer reactions (like cancrinite, are not promoting directly the impurities occlusion. Poor crystalline phases (like sodalite and katoite or other secondary phases and their micronic size fragments are really sustaining impurities occlusion through all the acknowledged mechanisms.

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Section: Resultsmentioning

confidence: 99%

Aluminum Hydroxide Impurities Occlusions and Contamination Sources

Dobra¹,

Garcia-Granda²,

Iliev³

et al. 2020

Rev. Chim.

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“…In addition, due to the low concentrations of heavy metals there is practically not a concentration process of these elements in Bayer liquors, but only an accumulation in the bauxite residue. At most, tiny amounts appear as a surface contamination of the aluminum hydroxide [10].…”

Section: Heavy Metalsmentioning

confidence: 99%

“…It is possible that, at high concentrations of organic acids in the spent liquor, some organic acid salts to precipitate in the form of distinct crystals together with aluminium hydroxide. In this case, the advanced washing of the aluminium hydroxide particles may lead to the partial or total elimination of this form in impurity of the aluminium hydroxide [10].…”

Section: Aluminium Hydroxide Contamination By Occlusionmentioning

confidence: 99%

Heavy Metals as Impurities in the Bayer Production Cycle of the Aluminum Hydroxide from Sierra Leone Bauxite. Preliminary Study

Dobra¹,

Iliev²,

Cotet³

et al. 2021

Journal of Siberian Federal University. Engineering &Amp; Technologies

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This paper is reporting the data of a preliminary study on heavy metals distribution in the fluid and solid phases involved in dry and classified aluminium hydroxide production through Bayer process. For heavy metals released in the fluid phases, the main source of contamination is the bauxite through its mineralogical phases soluble or insoluble in alkaline solution. It was shown that predominant way to transfer contaminating elements in aluminium hydroxide particles is the occlusion of very fine particles coming from mineralogical phases of bauxite residue. New born mineralogical phases from bauxite residue, like poor crystallized sodalite and cancrinite, are the most active occlusion contaminants

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“…Aluminum hydroxide, as an intermediary wet product (gibbsite, Al2O3•3H2O), is industrially produced by Bayer process from different kinds of bauxites. The gibbsite quality, particle size, crystallinity and crystals morphology are strongly influenced by the Bayer process parameters [1][2][3][4][5][6].…”

Section: Introductionmentioning

confidence: 99%

Short review on mechanical activation in non-metallurgical alumina production

Kim¹,

Dobra²,

Isopescu³

et al. 2022

RJEEC

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The terms mechano-chemistry and mechanical activation of solid materials were introduced in chemical literature by Ostwald at the beginning of the XX century. Both terms cover a whole range of interconnected phenomena taking place during the mechanical action on solids or their separate parts participating in chemical reactions, phase transitions, mixing and creating composite materials, alloying and crystal growth in the solid state, deformation and changing physical and thermal properties, all of them at low temperature. The common effects of the mechanical activation on solid material are fracturing and reduction of particle sizes, generation of new reactive surfaces, diffusion of atoms of the reactant phase through the product phase, and quite significantly, accumulating energy in crystalline or amorphous structure (enough twists in atomic and molecular networks, tensions in atomic bond and active sites to trigger the nucleation of new phases). Mechanical activation is very used to produce all clean alumina mineralogical phases with uniform particle size dimensions from nano to macro size. Also, mechanical activation may extend the specific surface of some minerals, enhancing the yields in the solid-liquid extraction process. With adequate precursors, all phase transitions from amorphous to alfa α-Al2O3 can be carried out on the same route as in thermally activated alumina, but some other routes, impossible by thermal activation, might be followed. The difference between the two activation ways is that mechanical activation is made at room temperature.

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Impurities Accumulation on the Surface of Alumina Hydrate Particles in Bayer Technology

Cited by 4 publications

References 1 publication

Aluminum Hydroxide Impurities Occlusions and Contamination Sources

Aluminum Hydroxide Impurities Occlusions and Contamination Sources

Heavy Metals as Impurities in the Bayer Production Cycle of the Aluminum Hydroxide from Sierra Leone Bauxite. Preliminary Study

Short review on mechanical activation in non-metallurgical alumina production

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