Bayer Liquor Research Articles

Focused beam reflectance measurement for monitoring the extent and efficiency of flocculation in mineral systems

Focused beam reflectance measurement (FBRM), where a scanning laser focused through a sapphire window measures real‐time reflected chord distributions without solids dilution, is attractive for characterizing flocculation performance. An enhanced measurement principle in new FBRM instruments has implications for flocculation studies, demonstrated using hematite in synthetic Bayer liquor. Comparisons of previous (M500) and new (G400) instruments were complicated by the impact of their different physical dimensions upon flocculation hydrodynamics, but the G400 clearly measured larger chords. The original measurement principle based on a reflected intensity threshold counts large low‐density aggregates as multiple chords; in contrast, the change to “edge detection” (very low threshold) is more likely to see a single chord, an advantage for studying mineral systems (aggregates often >500 µm). The G400 also captures bimodal character in unweighted chord distributions, producing distinct peaks for aggregates and fines after suboptimal flocculation; such peaks are rarely well resolved in older FBRM. © 2013 American Institute of Chemical EngineersAIChE J, 60: 251–265, 2014

Characterisation of a Novel Genus of Oxalate-Degrading Beta-<i>Proteobacteria</i> Isolated from a Full-Scale Bioreactor Treating Bayer Liquor Organic Wastes

A novel industrial-scale bioreactor was implemented by Alcoa of Australia (Alcoa) at its Kwinana alumina refinery (Western Australia) for the degradation of oxalate, an organic byproduct of the Bayer alumina refining process. At the Kwinana refinery oxalate is removed from the Bayer Liquor via a separate side-stream as it increases the operating costs associated with the process and, at sufficiently high levels, may adversely affect the quality and yield of the final alumina product. The bioreactor process provides a more economic and environmentally friendly method for the treatment of removed oxalate compared with chemical conversion or storage of the solid by-product. In previous studies, the microbial community composition of the bioreactor was investigated and was found to be largely dominated by microorganisms of the α-, β- and γ-Proteobacteriasubgroups. During the present study, two bacteria that had the ability to use oxalate as a sole source of carbon and energy were isolated from samples obtained from the bioreactor. Phylogenetic and physiological analyses indicated that the two isolates were probably strains of a novel species of a novel genus within the β-Proteobacteriasubgroup. Isolation and characterisation of the microbial communities within the bioreactor system has the potential to improve process operation, which may have a positive impact on the biological oxalate destruction process and the footprint of alumina production.

Identifying possible associations of minor and trace elements with major elements in Jamaican hillside and catchment bauxites using multivariate analysis tools

Over the past 50years the quality of Jamaica’s mined bauxites has gradually changed from gibbsite/hematite dominated ores to ones that contain more boehmite and goethite and have higher concentrations of many minor and trace components. This presents evolving challenges to the Bayer process industry which must still meet the aluminum smelting industry’s alumina quality requirements. The extraction of unwanted elements from bauxite into the caustic liquors depends on their host minerals but routine X-ray diffraction methods used by the industry are often unable to identify minerals for minor and trace elements and therefore do not give indications of potential Bayer liquor contamination by such elements. We sought to combine elemental concentrations and qualitative X-ray diffraction information with factor and cluster analyses to identify the probable associations of minor and trace elements with major elements and so predict their likely dissolution properties. Bauxites (178) were selected from catchment (32; gibbsite/hematite) and hillside (146; gibbsite/boehmite/goethite) deposits based on exploration data and reanalyzed using a variety of analytical techniques. The quality of the data was assessed and then the data were transformed to centered lognormal ratios to allow for their compositional nature. The elemental data used in the factor analyses were limited to Al, Fe, Ti, Si, Ca, P, V, Cr, Mn and Zn (plus Mg and Zr for the catchment bauxite set) because of missing data for some bauxites. For both bauxite types 80% of the variability was accounted for within three factors. The hillside bauxites’ factors associated Al with Fe, Ti, V and possibly Cr, Mn with Zn and Ca with P while Si showed no associations. The catchment bauxites’ factors were similar except for the Ca–P link being weak and Ca possibly having a linkage with Si; Zr joined the Al–Fe–V–Ti–Cr group and Mg linked weakly with Ca. The cluster analyses included the above elements plus Sr, Ga, Pb, As, Sc, Co, Cu, Cd, Hf, La, Ce, Nd, Sm, Yb, Th and U and used Pearson correlation coefficients as distance measures to allow for the missing values. The identified clusters separated Al from Fe, particularly for the hillside bauxites, confirmed the isolation of Si, suggested minimal associations for Cr, confirmed the Mn–Zn associations, particularly within the catchment bauxites, and indicated that P was not associated with Ca in the catchment bauxites and only weakly associated in the hillside ores. These identified associations allow for predictions about the dissolution processes and potential Bayer liquor contamination. Our future work will seek to confirm these predictions and refine the models.

Crystallization of sodalite particles under Bayer-type conditions

The formation of desilication products (DSPs) is an important process in the pre-desilication step of the Bayer process, helping to limit the potential for unwanted scale on the heat exchangers by limiting the amount of silicate in the Bayer liquor. These solids generally have a crystalline sodalite structure, however, the fundamentals of crystallization are still to be fully understood. We show in this work that the DSP formed is initially amorphous when solution silicate is used. When kaolinite solids are present DSP is initially heterogeneously nucleated on the kaolinite but there is also a secondary nucleation event that occurs.

Relationship between Al(OH)3 solubility and particle size in synthetic Bayer liquors

Surface tension of sodium aluminate solution and the contact angle between Al(OH)3 particles and aluminate solution were measured, then the dependence of Al(OH)3 solubility on its particle size was calculated and thus the variation of the critical nucleus sizes was determined based on the Ostwald ripening formula. The results show that the Al(OH)3 solubility in sodium aluminate solution decreases with the increment of particle size, and the critical nucleus sizes increase with the rise of alkali concentration, caustic ratio and precipitation temperature. The results also imply that the presence of small particles in seeded precipitation system is an important factor to limit the depth of precipitation.

Volatile Products from the Degradation of Organics in a Synthetic Bayer Liquor

The formation of volatile substances such as hydrogen, methane, ketones, and aldehydes during alumina production using the Bayer process is of interest because of their process and occupational safety and health implications. To better understand how these substances are generated in the Bayer process, the decomposition of a selection of low- and high-molecular-weight organic materials has been studied at 180 °C in a synthetic Bayer liquor consisting of 6 m NaOH. The main vapor-phase products were identified using gas chromatography with thermal conductivity or mass spectrometry detection. The results showed that caustic degradation of organic compounds commonly occurring in Bayer process liquors produces a range of substances known to be present in alumina refinery emissions. The main volatile products were H2, CH4, and certain carbonyl compounds with low odor thresholds, such as 2-butanone and propanone. There was also some evidence for the production of volatile pentacyclic compounds.

Bauxite residue neutralisation precipitate stability in acidic environments

Environmental context Although land remediation programs for bauxite residues aim at vegetation coverage, the stability of compounds in the residues with acids produced by the vegetation has not been investigated. We show that, despite the instability of caustic components in the residues (negative effects on plant development), this instability actually assists in neutralising acidic soils. These results further affirm the suitability and sustainability of current land remediation programs for bauxite residues in terms of minimising acidic soil formation. Abstract This investigation used a combination of techniques, such as X-ray diffraction, inductively coupled plasma optical emission spectroscopy and infrared spectroscopy, to determine the dissolution mechanisms of the Bayer precipitate and the associated rate of dissolution in acetic, citric and oxalic acid environments. The Bayer precipitate is a mixture of hydrotalcite, calcium carbonate and sodium chloride that forms during the seawater neutralisation of Bayer liquors (waste residue of the alumina industry). The dissolution rate of a Bayer precipitate is found to be dependent on (1) the strength of the organic acid and (2) the number of donating H+ ions. The dissolution mechanism for a Bayer precipitate consists of several steps involving: (1) the dissolution of CaCO3, (2) formation of whewellite (calcium oxalate) when oxalic acid is used and (3) multiple dissolution steps for hydrotalcite that are highly dependent on the pH of solution. The decomposition of the Al–OH hydrotalcite layers resulted in the immediate formation of Al(OH)3, which is stable until the pH decreases below 5.5. This investigation has found that the Bayer precipitate is stable across a wide pH range in the presence of common organic acids found in the rhizosphere, and that initial decomposition steps are likely to be beneficial in supporting plant growth through the release of nutrients such as Ca2+ and Mg2+.

Recovery of gallium from Bayer liquor: A review

Bayer liquor is the biggest raw material resource for gallium production. Four kinds of methods have been developed to recover gallium from Bayer solutions, including fractional precipitation, electrochemical deposition, solvent extraction, and ion exchange. The fractional precipitation method is based on Al–Ga precipitation with CO2 and subsequent separation of Al and Ga with lime milk or sodium aluminate solutions. This approach is more environmentally friendly and with low cost, but the process is complicated. The electrochemical method includes both mercury cathode electrolysis and cementation. The electrolysis with mercury cathode has been prohibited in most countries because of high toxicity of mercury. Cementation is an electrochemical process realized by a displacement reaction between gallium and reductants, such as sodium amalgam, aluminum and aluminum–gallium alloy. Solvent extraction is an efficient method and by using Kelex 100 system about 80% of the gallium in Bayer liquor can be extracted. However, the kinetics of the extraction process has been proved to be very slow, which generally requires several hours. Ion exchange is the main method applied in industry for gallium recovery from Bayer liquor. Duolite ES-346 and DHG586 exhibit good extracting properties for gallium, and are used as industrial resins. Unfortunately, the co-extraction of vanadium and the degradation of the amidoxime groups still remain as the main problems during industrial application. In order to recover gallium from Bayer liquor efficiently, further research and development are necessary.

Growth Mechanisms and Kinetics of Gibbsite Crystallization: Experimental and Quantum Chemical Study

We present experimental and molecular modeling studies, which examine the influence of crystal growth modifiers (CGMs) on the crystallization mechanism and kinetics of gibbsite crystallization in supersaturated sodium aluminate solutions. Seeded, pure caustic sodium aluminate synthetic liquors and real industrial Bayer liquor containing significant amounts of organic and inorganic impurities, in the absence and presence of a CGM containing oleate ions, were investigated. Our results show massive growth of colloidal sized protrusions on the seed particle surfaces on addition of the CGM in the pure synthetic caustic aluminate liquors. Although the activation energies for both secondary nucleation and growth were found to be increased, the overall crystallization rate was surprisingly also increased by addition of CGM. This behavior is attributed to the increased pre-exponential factor possibly arising from higher probability of effective collisions due to more effective species orientation facilitating the crystallization process. The crystallization rate was significantly slower in the industrial Bayer liquor, most likely due to the presence of impurities; nevertheless, a greater degree of surface protrusions on crystal growth was noted on addition of the CGM. In conjunction with the experimental results, we use semiempirical quantum-chemical calculations to examine the underlying processes that result in the enhanced growth due to the presence of the CGM. Our quantum-chemical modeling results suggest that the increased crystallization rate may be due to a mechanism by which Al(III)-containing dimers are produced due to intervention by the oleate ion.

Precipitation of vanadium from Bayer liquor with lime

Based on the thermodynamic calculation for the precipitation of vanadium from Bayer liquor by lime, experiments were carried out to investigate the influence of temperature and CaO dosage on the vanadium precipitation rate when lime was added into Bayer liquor to precipitate vanadium directly. The results indicate that more than 80% of the vanadium can be precipitated directly from Bayer liquor by lime. Unfortunately, the obtained precipitation residues mainly consist of 3CaO•Al2O3•6H2O with very little vanadium content (V2O5, about 0.45%). An improved process, during which precipitation residues were used cyclically as precipitants for vanadium at high temperature (>150°C), was proposed after careful analysis on thermodynamic calculation and former experimental results. The improved process was proven completely feasible by experiments for the precipitation of vanadium from Bayer liquor to prepare vanadium-bearing residues with high vanadium content. With precipitation residues recycled, the V2O5 content increased to almost 3%. The appropriate conditions for the cyclical precipitation of vanadium include the C/A rate 0.4 for the first vanadium precipitation, cycle numbers 4–5, temperature 180°C–220°C, reaction time 1h and stirring speed 200rpm.

An investigation of the mechanisms of goethite, hematite and magnetite-seeded Al(OH) 3 precipitation from synthetic Bayer liquor

The precipitation of Al(OH) 3 from synthetic Bayer liquor at 70 °C seeded with goethite, hematite and magnetite particles was investigated in order to gain insight into the nucleation and growth mechanisms in the presence of these materials. A combination of characterisation techniques was employed including conductivity analysis, particle size analysis, electron microscopy and in situ synchrotron X-ray diffraction. The magnetite seed was less active for promoting Al(OH) 3 precipitation than the goethite and hematite, based on a comparison of the induction time before the onset of measurable precipitation. For each seed material, the early stages of precipitation were characterised by relatively slow deposition of gibbsite on the seed particles. Precipitation then proceeded via a two-stage mechanism, where gibbsite and small amounts of bayerite and nordstrandite precipitated concurrently. The outcomes of this investigation have implications for the nucleation and growth of scale on mild steel process equipment, and are also relevant for alumina reversion which causes significant process losses through uncontrolled precipitation.

The effect of glucose on the formation of the nanocrystalline transition alumina phases

Series of alumina powders were synthesized starting from sodium aluminate solution prepared from Bayer liquor. The neutralisation of sodium aluminate solution was performed with the use of sulphuric acid. The influence of glucose as a non-surfactant additive on the structure of alumina powders at moderate pH was investigated. The results show that the properties of the powders are influenced by the initial pH value of the solution, as well as the duration of the neutralisation step. High pHs lead to the formation of powders with heterogeneous structure with bayerite as a dominant phase, which during calcinations converts to η-alumina with high surface area. Addition of glucose to the starting aluminate solution leads to the formation of nanocrystalline boehmite with estimated average crystallite size less than 3 nm and high surface area (above 300 m 2/g). After calcinations, boehmite transforms to γ-alumina. The results have shown that during the heat treatment, structural transformations proceeded simultaneously with the significant changes in the textural properties of the obtained mesoporous γ- and η-alumina powders.

Organic compounds in the processing of lateritic bauxites to alumina: Addendum to Part 1: Origins and chemistry of organics in the Bayer process

This addendum to the review “Organic compounds in the processing of lateritic bauxites to alumina Part 1: Origins and chemistry of organics in the Bayer process” (Power and Loh, 2010) has been prepared in response to new information which has since been brought to the attention of the authors. This included a number of additional references which are not readily accessible through the usual search techniques. In particular, the prediction made in the review that Bayer liquors should contain a significant number of hydroxycarboxylates and polyhydroxycarboxylates is confirmed. Evidence for the existence of a particular suberin degradation product which is of interest to Bayer technologists is also presented, and a number of additional points of technical and historical interest are included.

Thermodynamics of impurities in hydrometallurgical processes

Impurities in hydrometallurgical process liquors frequently impact on product quality and yield, change physicochemical properties of the liquor, and form hard scale on heat exchangers and condensers. Organic compounds are of particular concern especially in the Bayer process, where impurities build up in the recycled liquor if not controlled. Depending on the redox state of the liquor, such compounds can undergo a variety of complex chemical reactions, including the formation of volatiles that can potentially cause environmental, health, and safety concerns. To aid in the development of appropriate control strategies, robust thermodynamic models for multicomponent aqueous systems containing large numbers of electrolytes and nonelectrolytes are required. Applications of thermodynamic models are discussed that range from the partitioning of volatile compounds in flash trains to the prediction of mixing properties of organic impurities with major Bayer liquor components.

Effect of mineral acids on the production of alumina nanopowder from raw bauxite

In this study a novel synthetic method for the large-scale production of spherical, high surface area and ultra-fine alumina (Al 2O 3) powder has been described. Synthetic Bayer liquor was extracted by alkali fusion of raw bauxite with sodium hydoxide. Alumina nanopowders were synthesised through a ball mill-aided precipitation method using the synthetic Bayer liquor and mineral acid precipitants. The powders produced were characterised by X-ray diffraction (XRD), particle size distribution (PSD), Fourier transform infrared spectroscopy (FTIR), Brunauer–Emmett–Teller surface area and pore size analysis, energy-dispersive spectroscopy (EDS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In this article, the effects of precipitants such as H 2SO 4, HCl and HNO 3 on crystallite and particle size, surface area, pore volume, and pore size and shape are reported. The experimental results prove that precipitation leads to an aggregated particle that is disaggregated by the ball-milling method. The ball milling process strongly influences the formation of uniform-sized spherical particles with a high surface area. It was revealed that nitric acid is an effective precipitant for controlling particle size and textural properties of Al 2O 3 powder. A nanopowder of γ-Al 2O 3 with an average crystallite size of 3 nm and an average particle size of 58 nm with a specific surface area (SSA) of 190 m 2 g − 1 is produced. This article elucidates a new method with a simple reaction scheme for the mass production of Al 2O 3 nanoparticles from raw bauxite for various commercial applications.

Characterization of Bayer Hydrotalcites Formed from Bauxite Refinery Residue Liquor

The precipitate formed during the seawater neutralization (SWN) of Bayer liquors has been characterized by a variety of techniques, including X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), inductively coupled plasma−optical emission spectroscopy (ICP-OES), infrared and Raman spectroscopy, and thermal analysis. Three mineralogical phases are detected: (1) hydrotalcite, (2) calcite (CaCO3), and (3) aragonite (CaCO3). It is proposed that two hydrotalcite structures form and have the formulas Mg8Al2(OH)12(CO32−,SO42−)·xH2O and Mg6Al2(OH)16(CO32−,SO42−)·xH2O. The Mg, Al molar ratio of the Bayer hydrotalcite is dependent on both the pH and the composition of the initial Bayer liquor. It is proposed that carbonate and sulfate ions are intercalated predominantly into the hydrotalcite interlayer; however, small amounts of arsenate, vanadate, and molybdate have been shown to be removed from solution. The formation of Bayer hydrotalcite assists in the removal of oxy-anions of transition metals ...

Modelling the solubility in Bayer liquors: A critical review and new models

An accurate and tractable model of solubility is a pre-requisite for any careful study of precipitation. Reviewing the abundant literature on the sodium aluminate solutions and Bayer Liquor, the authors point out the need for a new model for the apparent solubility of aluminium in actual Bayer Liquors and propose such a model, based on the well established Wesolowski's expression for the infinite dilution solubility and extended Debye–Hückel expression including a large empirical b I term for the “activity coefficient effect”. They suggest a chemical interpretation for this feature.

Molecular characterisation of the microbial community of a full-scale bioreactor treating Bayer liquor organic waste

Sodium oxalate is an organic impurity produced during the Bayer refining of bauxite as a result of the degradation of humic materials associated with the ore. Physico-chemical oxalate destruction techniques, such as combustion, are often expensive and often pose greater environmental risk than the storage of solid oxalate waste. Biodegradation is a more economical and environmentally friendly way to degrade oxalate, but the microbial communities responsible for oxalate degradation have remained largely uncharacterised. In the present work, the microbial community of a full-scale bioreactor achieving complete degradation of oxalate was characterised using 16S rRNA gene clone libraries followed by phylogenetic analysis of the cloned near full-length 16S rRNA sequences. The community was dominated by species belonging to the α-, β- and γ- Proteobacteria groups. Novel oxalate-degrading bacteria belonging to the genus Halomonas and the β- Proteobacteria group were isolated from the microbial community and are currently being characterised.

A review of the determination of organic compounds in Bayer process liquors

Bayer process liquors present a difficult and complex matrix to the analytical chemist, and the history of the application of modern analytical techniques to this problem is a case study in innovation. All Bayer process liquors contain organic compounds, in amounts varying from traces to several grams per litre. The total organic carbon content of Bayer liquors may be less than 5 g/L up to as much as 40 g/L. The presence of these organic impurities is of concern to Bayer technologists because they can have significant impacts on the economics of the process and the quality of the product. This review examines the history and current state-of-the-art of the analysis of organics in Bayer process liquors, and provides guidance on the applicable techniques matched to a comprehensive list of the compounds most likely to be present.

Desilication of synthetic Bayer liquor with calcium sulfate dihydrate: Kinetics and modelling

The desilication kinetics of synthetic Bayer liquor by use of calcium sulfate dihydrate (CaSO 4·2H 2O) was studied experimentally and modelled mathematically. Temperature, initial silica concentration, and the dosage of CaSO 4·2H 2O were found to be the main factors affecting desilication reaction. CaSO 4·2H 2O was proved to remove up to 95% silica from sodium aluminate solution under the optimum operation conditions. A surface integration kinetic model, assuming that the desilication process follows a pseudo-second-order kinetics, was developed and successfully model the experiment data of desilication process via CaSO 4·2H 2O at the range of operating conditions investigated. An activation energy of 52 kJ/mol was estimated for the desilication process with CaSO 4·2H 2O over the temperature of 80-100 °C. The desilication reaction products (DSP) were analyzed by XRD and SEM, and found to be mainly Hauyne (3Na 2O·2CaSO 4·3Al 2O 3·6SiO 2) and Lazurite (3Na 2O·CaSO 4·0.5Na 2SO 4·3Al 2O 3·6SiO 2). The final sulfate concentration in the liquor after desilication with CaSO 4·2H 2O was ~ 0.021 g/L.