Bayer Plants Research Articles

Desilication of low alumina to caustic liquor seeded with sodalite or cancrinite

The aim of this study was to improve understanding of scale formation mechanisms and to provide theoretical support for development of scale inhibition strategies. Sodium aluminosilicate scaling on plant surfaces is a critical problem in Bayer refineries, particularly within digesters and heat exchangers. Although numerous studies have been carried out to understand the mechanisms of scale formation and to develop scale inhibition strategies in double-stream circuit Bayer plants, there is still insufficient relevant research on single-stream Bayer plants. We have studied the desilication behavior of a liquor of similar composition to spent cleaning caustic liquor, for which the aluminate concentration and A/C are both less than heat exchanger liquor. These concentration conditions were chosen in order to investigate the early stage of scale formation in single-stream Bayer plants by increasing the component of aluminosilicate bulk precipitate upon seeding and decreasing the relative degree of scaling.Solution desilication experiments were performed using spent cleaning caustic liquor at 140°C either without seeding or with sodalite (seed loading 1.125g L−1) or cancrinite seeding (seed loadings 1.125gL−1 and 2.850gL−1) in the presence of steel substrates. The solution desilication rate showed significant increase in the presence of seeds and was found to be greater in the presence of cancrinite seeds than sodalite of the same surface area. The desilication kinetics of the synthetic spent cleaning caustic liquor suggests predominant heterogeneous nucleation for unseeded desilication, a mixed secondary-nucleation and growth process for desilication on addition of sodalite seeding, and cancrinite seeding with both smaller and greater loading.A first layer, possibly amorphous, with high Al and low Si concentrations was observed by SEM and FIB/SEM on the coupon surface after desilication with or without seeds. We note that this layers forms despite the low A/C and high Si supersaturation suggesting that under single-stream heat exchanger conditions this may also be the first layer to form. XRD confirmed that sodalite formed on the coupons in unseeded and sodalite seeded desilication systems while cancrinite formed on the coupons upon cancrinite seeded desilication with both smaller and greater seed loading. The coupon from the cancrinite seeded liquor with high seed loading is least covered by scale amongst the coupons, suggesting that cancrinite seeding may be a potential strategy for reducing scale formation in single-stream Bayer circuits.

Solubility of Al2O3 in the Na2O−Al2O3−H2O−CH3OH System at (30 and 60) °C

To realize the objective of high alumina yield and a high molar Na2O/Al2O3 ratio in caustic solutions for Bayer plants, this paper presents the solubility of Al2O3 in methanol-water solvent mixtures with a fixed mass ratio of methanol to water 1:1 at (30 and 60)degrees C and containing various Na2O concentrations. The Al2O3 solubility in the Na2O-Al2O3-H2O-CH3OH quaternary system increases with an increase of Na2O concentration, reaching maximum values of 1.70% and 2.48% by weight at (30 and 60) degrees C, respectively. Then, the solubility decreases with a further increase in the Na2O concentration. The equilibrium solids are aluminum hydroxide Al(OH)(3) and mono-sodium aluminate hydrate Na2O center dot Al2O3 center dot 2.5H(2)O in the different alkali concentration regions. The data show that the solubility of Al2O3 in the Na2O-Al2O3-H2O-CH3OH quaternary system is much lower than that in the Na2O-Al2O3-H2O ternary system.

Determination of the gibbsite dehydration reaction pathway at conditions relevant to Bayer refineries

The calcination of gibbsite to alumina is the last major step in the Bayer process. Despite its commercial importance, little attention has been given to determining the gibbsite thermal dehydration reaction pathway under conditions of relevance to this commercial process. Results from this study show that, at the temperatures and high heating rates relevant to the Bayer plants, gibbsite dehydrates mainly via chi alumina, which then reacts to gamma alumina, theta alumina and alpha alumina. Dehydration via boehmite is a minor reaction pathway. Experimental results are also presented that indicate chi alumina can react to gamma alumina at low heating rates. It was shown that the phase compositions of different refinery smelter-grade aluminas, formed in fluid-bed calciners (FBCs), could be reproduced with laboratory-calcined aluminas by controlling the calcination time.

Corrosion behaviour and characterisation of iron in hot flowing Bayer liquors

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A study on the precipitation of radial alumina trihydrate

Alumina trihydrate is normally produced by precipitation from sodium aluminate liquors in Bayer plants. This study aims at investigating the various factors affecting the production of radial alumina trihydrate particles. Precise controlling of supersaturation and temperature as a function of time is important in producing the desirable shape and size of the particles. Morphological changes as a function of time were observed by scanning and transmission electron microscope study, and the results revealed the various particle growth mechanisms involved. In the presence of organic 3,4 dihydroxy benzoic acid (3,4 DHBA), radial seeds start to grow abnormally. Probably the organic contaminant is preferentially absorbed onto the lateral (1 0 0) + (1 1 0) faces, which promotes explosive formation of very small single-crystals or nuclei on the surfaces. The seed particle growth is simultaneously retarded. The basal (0 0 1) face of some crystals continues to grow and form long prism crystals.

The possibility of feedforward process control in bayer plants using precomputed setpoint values: Part II. Applications to the bayer alumina process

The Canadian Journal of Chemical EngineeringVolume 62, Issue 5 p. 672-683 Article The possibility of feedforward process control in bayer plants using precomputed setpoint values: Part II. Applications to the bayer alumina process L. Fáy, L. Fáy Computer Science Department, Eötvös Lóránd University, Budapest, HungarySearch for more papers by this author L. Fáy, L. Fáy Computer Science Department, Eötvös Lóránd University, Budapest, HungarySearch for more papers by this author First published: October 1984 https://doi.org/10.1002/cjce.5450620513Citations: 2AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume62, Issue5October 1984Pages 672-683 RelatedInformation

The possibility of feedforward process control in bayer plants using precomputed setpoint values: Part I — Fundamentals

La commande a boucle de reaction positive exige l'emploi de modeles mathematiques hautement fiables comme bases d'algorithmes de commande; toutefois ceux-ci excedent souvent la periode de marche desirable, ce qui conduit a des simplifications drastiques des modeles et a des compromis dans la plupart des cas pratiques. Ceci peut etre evite en emmagasinant dans une banque de donnees des valeurs pre-calculees de points de consigne correspondant aux valeurs discretes des parametres des modeles de simulation. Cet emmagasinage peut etre realise au moyen d'ordinateurs externes a grande vitesse et de microprocesseurs de faible cout

The coarsening of Bayer alumina trihydrate by means of crystallization modifiers

Modern aluminium smelting practice requires that Bayer plants produce coarse, sandy non-dusting alumina. However, the coarseness of Bayer products is normally achieved at the expense of lower liquor productivities. In the course of work carried out on the so-called ‘poisons” of alumina trihydrate seed, it was discovered that minute additions of fine calcium carbonate to Bayer seed slurries at the time of seeding can considerably decrease the fine fraction in the resulting final products without affecting the yield of alumina. The action of calcite in the precipitation is that of a crystal-growth modifier resulting in an improved particle agglomeration and making the agglomerated particles in the products more resistant to breakage in mixing and pumping operations.