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The flotation of diasporic bauxite is to separate diaspore (valuable mineral) from aluminosilicate minerals (gangue minerals, mainly including kaolinite, illite and pyrophyllite), and the microscopic interaction force between the two types of minerals and air bubbles determines the separation efficiency. In this paper, based on the extended Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, the van der Waals, electrostatic and hydrophobic interaction between particles of the four minerals mentioned above and air bubbles in collectorless solution were calculated first, and then diaspore and kaolinite were taken as examples to analyze the influence of various factors such as electrolyte concentration, mineral particle size, air bubble size, collector type (dodecylamine hydrochloride (DAH) and sodium oleate (NaOL)) and concentration, and pulp pH on the interactions between the particles of valuable mineral and gangue minerals and air bubbles. The results showed that the total extended DLVO interactions between the four minerals and air bubbles were repulsive in most cases in collectorless solution. The increase in electrolyte concentration reduced the interaction force or even changed the direction of the force under certain circumstances. The addition of DAH and NaOL can reduce the adhesion energy barrier of kaolinite-bubble and diaspore-bubble respectively. Each type of minerals exhibited a specific interface interaction response with air bubbles in each collector with different pH values. The research results have theoretical guiding significance for the optimization and directional control of diasporic bauxite flotation conditions.

Работа посвящена изучению высокотемпературного гидрохимического разложения минеральных комплексов диаспор-бемитовых бокситов методом Байера с извлечением макрокомпонентов - алюминия и железа в присутствии металлических восстановителей. Проведены рентгенофазовые исследования, направленные на определение состава и структуры новых соединений в магнетизированном красном шламе. По результатам физико-химических исследований продуктов выщелачивания рекомендованы оптимальные параметры восстановительного выщелачивания бокситов СУБРа, направленные на извлечение алюминия и синтез магнетита. Выявлены закономерности влияния вида металлического восстановителя на морфологию, фазовый состав, размер частиц в красном шламе (КШ). The work is devoted to study of the high-temperature hydrochemical decomposition of mineral complexes of diaspore-bemite bauxites by the Bayer method with the extraction of macro-components-aluminum and iron in the presence of metal reducing agents. X-ray phase studies were performed to determine the composition and structure of new compounds in magnetized spent red mud. Based on the results of physical and chemical studies of leaching products, optimal parameters for reducing leaching of bauxite are recommended, aimed at extracting aluminum and synthesizing magnetite. The regularities of the influence of the type of metal reducing agent on the morphology, phase composition, and particle size in the red mud are revealed.

High-iron bauxite, which is a typically unmanageable form of bauxite due to its high contents of iron and diaspore, has not been used by alumina producers. An advanced roasting technique for removing iron from high-iron bauxite, based on static pre-roasting in air and suspension roasting by hydrogen under fluidized conditions followed by magnetic separation was developed in this study. The influences of pre-roasting temperature, suspension roasting temperature, roasting time, and H2 concentration were investigated. The phase transformations of the samples were investigated using X-ray diffraction, vibrating sample magnetometry, field emission scanning electron microscopy, and Brunauer-Emmett-Teller method. After pre-roasting at a temperature of 750 °C for 30 min, diaspore (AlOOH) and goethite (FeOOH) in the raw high-iron bauxite ore were transformed into Al2O3 and Fe2O3, respectively. The optimal suspension roasting conditions were determined to be a roasting temperature of 600 °C with a H2 concentration of 25% for 4 min. The reduction sample was subjected to magnetic separation and a non-magnetic product (aluminum concentrate), with alumina recovery of 80.64% and iron removal of 85.32%, was obtained. Such a non-magnetic product could be used as a raw material for the Bayer process in the alumina production industry, while the magnetic product could be used as a supplementary material for iron ore resources.

In this study, a diaspore sample is evaluated as a dual source of alumina and potash. The thermal treatment of diaspore with sodium hydroxide yielded alumina and potash values. Microwave heating resulted in enhanced diffusion with improved precipitate purity and recovery with a significant reduction in reaction time. The thermal treatment precipitate comprises alumina purity of 48% with a recovery of 49%. The mechanical milling route yields optimal conditions of 8 h milling followed by acid leaching in 2 M HCl at 50°C for 1 h with ~ 70% and 45% potash and alumina extraction, respectively. The dissociation of the muscovite structure is crucial for high extraction values, and milling time was found to be the significant factor. The milling route at optimal conditions yielded an alumina precipitate with ~ 89% purity with a surface area of 104.6 m2/g and a sylvinite-rich solution, which can be used in fertilizer application.

Corundum primary deposits in Greece occur in four locations: Paranesti in Drama and Gorgona in Xanthi, both belonging to the wider Rhodope Massif, as well as, Ikaria island and Kinidaros in Naxos island, both belonging to Attic-Cycladic Massif. Eight samples were examined with spectroscopic methods (FTIR, UV-Vis, EDXRF) in order to better characterize these four primary deposits: two pink sapphires from Paranesti, a pink and a blue sapphire from Gorgona, two blue sapphires from Ikaria and three blue sapphires from Kinidaros. Under the microscope, all samples present characteristics linked to post-crystallization deformation, decreasing their gem quality. The FTIR absorption spectra of all samples present in different relative intensities, bands of boehmite, diaspore, goethite, mica and/or chlorite inclusions and CO2 in fluid inclusions. Boehmite and diaspore inclusions are most likely epigenetic. In the UV-Vis spectra, the pink color of the samples is linked with Cr3+ absorptions and the blue color with absorptions due to Fe2+-Ti4+ intervalence charge transfer. EDXRF analyses in the studied samples show relatively high titanium and iron concentrations that are related with mineral inclusions. Gallium is slightly variable in samples from different regions, also, different colored samples from Gorgona present diverse gallium content.

Milling corundum nanoparticles High-purity corundum (α-Al 2 O 3 ) nanoparticles could enable applications such as more stable catalyst supports or precursors for high-strength ceramics. Milling of corundum only produces micrometer-scale particles, and direct synthesis from other aluminum oxides that would be likely starting materials, such as γ-Al 2 O 3 , fails because of the high activation barrier for converting the lattice structure of these cubic close-packed oxides. Amrute et al. show that ball milling of boehmite, γ-AlOOH, created ∼13-nanometer-diameter corundum nanoparticles of high purity through a mechanically induced dehydration reaction and by the effect of milling impacts on the surface energy of the particles. Science , this issue p. 485

With the rapid development of China's aluminum industry and the depletion of high-quality bauxite resources, technology for the clean and efficient utilization of non-traditional bauxite resources has become the focus in related fields. The alumina-to-silica mass ratio of low-grade high-iron sedimentary bauxite from Yunnan, China is 2.65; diaspore and goethite coexist in this bauxite. To enhance the utilization efficiency of bauxite, the hydrometallurgy process of the “calcification-carbonation method” (CCM) had been proposed, and the research results indicated that the addition of lime promoted the transformation of the goethite phase significantly, and the replacement ratio of Al in goethite decreased from 16.02% to 12.15% for a calcification temperature of 200 °C. The Gibbs free energy for the generation of Ca3(Fe0.87Al0.13)2(SiO4)1.65(OH)5.4 decreases gradually with an increase in the reaction temperature, and an excessive decomposition temperature in the carbonization process is not conducive to the decomposition of the garnet phase. The calcification reaction is controlled by diffusion and chemical reaction, and the activation energy in the temperature range from 220 to 260 °C (determined using a high-pressure DSC) is 38.4 kJ/mol; it is 19.6 kJ/mol in the temperature range from 260,276.8 °C. Fe completely dissociates from hydrogarnet upon carbonization, and the main silica-containing phases in the digested slag are unreacted hydrogrossular and calcium silicate. The CCM enhanced the recovery ratios of Al2O3 and Fe from high-iron diasporic bauxite by ~20% and 10%, respectively, compared with those in the Bayer process, and the Na content decreased to lower than 0.1% in the CCM slag; this can be used as cement raw material directly. Thus, the clean and efficient utilization of low-grade high-iron sedimentary bauxite was achieved using the CCM.

Low-grade diasporic bauxite in central Guizhou Province, China, contains Li that can be exploited and utilized. In this paper, several methods were used to determine the main chemical components in low-grade diasporic bauxite, which were Al2O3, SiO2 and TiO2, and the main minerals were diaspore, boehmite, kaolinite, illite and anatase. Independent Li minerals were not found. According to chemical phase analysis, Al mainly exists in diaspore, boehmite, kaolinite, and illite, while Li mainly exists in clay minerals along with a small amount in diaspore and boehmite. Li is inferred to be mainly ionically connected to the external hydroxyl group of kaolinite and the interlayer of illite; and partially occupies the site of missing hydrion in the diaspore and boehmite crystals.

The Arbanos bauxite deposit is located in the Iran-Himalayan karst-type bauxite belt and about 25 km northeast of Bukan city, northwestern Iran. The bauxite ores occur as layers and lenses along the contact of the carbonate (limestone and dolomite with intercalations of shale) of the Ruteh Formation (Upper Permian) and dolomite of the Elika Formation (Triassic). Hematite, kaolinite, and diaspore are the major rock-forming minerals in the ores, accompanied by lesser amounts of chlorite, montmorillonite, chamosite, siderite, goethite, boehmite, calcite, rutile, anatase, zircon, and quartz. Mass balance calculations indicate that the distribution of Ni, V, and Cr is controlled by the iron oxyhydroxides, whereas the distribution of Ba and Sr is controlled by kaolinite. The bivariate diagrams of the Sm/Nd versus the conservative elemental indices such as TiO2/Al2O3, Al2O3/Hf, Al2O3/Nb, and Nb/Ta reveal that the shale of the Ruteh Formation is the most plausible parent rock for the bauxite ores. The factor analysis method indicates that the paleo-environmental changes, soil redox state, and water activity in the pedogenic environments played a fundamental role in distribution of the major, minor, and trace elements.

The Semirom karst type clayey bauxite is located in the Zagros zone, a part of the Irano-Himalayan belt, and occurs between the Sarvak and Ilam Formations. The Albian to Cenomanian limestone bedrock of the Sarvak Fm is a part of a platform ramp environment including clay bearing components. Diaspore, boehmite, kaolinite, and hematite are the major ore-forming minerals. Elemental mobility determinations reveal that Th and the critical metals Co, Ni, and Cr are enriched in the bauxitic horizons relatively to the Upper Continental Crust. Further, only one sample is outlier for more than one critical metal (Cr, Co, Ni, and Ga) likely recording a specific event during bauxitization. The outlier is enriched in Ni, Co, Ga, and Th, is depleted in Cr, and shows a large positive Ce anomaly (Ce/Ce∗ = 3.03). The outlier may record an event characterized by more acidic and oxidizing conditions and may have a regional relevance. R-mode factor analysis suggests that Cr and Co are likely adsorbed onto oxy-hydroxides probably in horizons also concentrating secondary phosphates hosting HREE and Th. Nickel is instead likely adsorbed onto titanium oxides which concentrate in the pool of highly insoluble detrital phases also including zircon whereas diaspore and boehmite are important in controlling both Ga and LREE. The low contents of Ni and Cr associated to the Semirom clayey bauxite exclude a provenance from a mafic protolith. Further, most of the samples have Eu/Eu∗ values close to those observed in the Sarvak Fm marly limestone, suggesting that the clayey component within the underlying limestone acted as protolith. The oxygen and hydrogen isotopic composition of the kaolinite-rich separates from the Semirom deposit indicates temperature never lower than 30 °C, supporting the idea of the Zagros basin close to the equator during the Cenomanian-Turonian under a warm and humid tropical climate with heavy rainfall.

The Poci bauxite deposits in western Henan, China, are hosted in the lower member of Upper Carboniferous Benxi Formation, unconformably overlying upon the paleokarst surface of the Ordovician Majiagou Formation. The orebodies comprise a high-grade bauxite horizon (characterized by the association of diaspore-illite-anatase) and a basal iron-rich horizon (diaspore-goethite-hematite-illite-anatase), sandwiched between the overlying clayey layer (illite-diaspore-goethite-anatase) and the underlying clayey layer (illite-diaspore-microcline-goethite). Geochemical investigations reveal that Rb, Cs, Ba, Cu, Zn are depleted, while B, Ga, Bi, V, Sc, Zr, Hf, Nb, Ta, W, U and Th are enriched in bauxite horizons. B is highly enriched in bauxite ores and clays (contents 176–1061 ppm) and positively associated with SiO2, indicating B is mainly hosted in clay components, e.g. dominantly illite, which are considered a mixture of authigenic minerals transformed from kaolinites during diagenesis and unaltered detrital minerals. Mass change calculations reveal that Hf, Zr, Nb, Ta, U, Th, Sc, Cr, and Ga are stable relative to TiO2 during the bauxitization process, indicating these elements are mainly associated with anatase and diaspore. The bauxite horizons and the underlying clays are more enriched in total REE contents (ΣREEs) and display more intense LREE/HREE fractionation than the overlying clays. Provenance analysis shows that parental materials of Poci bauxites were mainly derived from felsic-dominated igneous rocks along the southern margins of the North China Craton, with minor contribution from siliciclastic sedimentary rocks and argillaceous components of underlying carbonates. A conceptual model is proposed for the formation and evolution of Poci bauxites. Uplift caused by the North Qinling orogenesis along the southwestern margin of NCC led to the formation of karstic topography, allowing aluminum-rich source materials to be transported to the low karst plain and transformed into incipient bauxites under hot and humid tropical conditions. When the platform was submerged, Fe2+ ions were released from Fe/Al oxides/hydroxides under the reducing conditions associated with bacteria activity in an organic-rich environment, and redeposited as pyrites and siderites, generating a high-grade bauxite horizon and an iron-rich bauxite horizon. This marine modification resulted in further aluminum enrichment of bauxite ores.

Propyl gallate (propyl 3, 4, 5-trihydroxybenzoate; PG) was introduced as a new type of collector for diasporic bauxite flotation. The flotation performance of PG for diaspore and kaolinite was evaluated by comparing PG with sodium oleate (NaOl) as a typical collector through micro flotation tests. The results indicated that PG had higher collection ability for diaspore than for kaolinite at 15 mg/L and pH 7–9. Compared with NaOl, PG also exhibited higher selectivity for diaspore against kaolinite. Analyses of zeta potentials, adsorption amount, Fourier transform infrared spectra (FTIR) and X-ray photoelectron spectra (XPS) revealed that PG adsorbed onto diaspore surfaces through chemical adsorption and hydrogen bonding, whereas PG hardly adsorbed onto kaolinite surfaces. Specifically, PG chelated with Al atoms on the diaspore surfaces by forming five-member rings through its ortho oxygens. These findings indicated that PG could be adopted as a novel collector for diaspore flotation and the activated phenolic hydroxyl groups also offered new insights for the development of flotation collectors.

This lecture text presents features of the fascinating mineral corundum and its gem varieties, ruby and sapphire. The geologic occurrences of its varieties and the best-known world localities are presented in detail. The mineralogy and crystallography of corundum, as well as its occurrence forms, are discussed. The origin of their colour varieties and their usage are described, in addition to their important physical characteristics. Applications in the watch and laser industries and as an abrasive material, among others, are included. The ruby variety from dolomite marble in North Macedonia exhibits the unique optical phenomenon known as diasporescence–the inclusion of diaspore crystals in the corundum matrix. This phenomenon affects the parting of corundum crystals and influences their colour, density and hardness. Therefore, special attention is paid here to morphological and physical characteristics of the Macedonian gem corundum.

Silicate minerals (such as kaolinite) are common gangues in diaspore type bauxite, which are easy to be mudding and adhered to the diaspore surface in the flotation system, thus affecting the flotation recovery. Fluid flow enhancement with agitation is one of the more effective ways to improve the dispersion of aluminum–silicate minerals and reduce flotation entrainment. Whether high shear agitation could also change the surface properties of mineral particles was investigated through dispersion experiment of diaspore and kaolinite slurry in this paper. The results show that a high turbulence environment was beneficial to enhance the mass transfer of reagents and change the surface properties of mineral particles. With the increase of stirring strength, the contact angle and zeta potential of two minerals were increased at the same dispersant dosage, and the dispersion of two minerals was further improved.

International audience; The dissolution rates of Green Monster Mine epidote at temperatures of 25, 100 and 200 °C, and over the pH range 2–11, were determined from far-from equilibrium experiments performed in both batch and mixed-flow reactors. Epidote dissolution rates based on silicon release decrease with increasing pH to pH ∼ 8, then increase in response to further pH increases. The apparent relative metal release rates from epidote at chemical steady-state were found to vary with pH and temperature, in part due to secondary phase formation. At 100 and 200 °C, Al is preferentially released relative to Si at alkaline pH, but preferentially retained by the solid at 2

Using an effective collector is often the key to improving the flotation recovery of valuable mineral concentrates. China’s diaspore-type bauxite is a refractory ore, since silicate minerals, such as kaolinite, are often closely embedded with diaspore. Propyl gallate (PG) is an effective and novel collector of diaspore. Detailed flotation behaviors of diaspore and kaolinite with PG and traditional collector sodium oleate (NaOL) were investigated in this work. The effects of stirring speed, aeration volume, slurry pH, and collector dosage on the flotation recovery of the two minerals were discussed. The results show that, compared with the traditional collector NaOL, PG had better collection and selectivity for diaspore since the collector PG could increase the hydrophobic difference of diaspore and kaolinite than NaOL. Under the optimal flotation conditions: 1600 r/min of stirring speed, 60 mL/min of aeration volume, 60 mg/L of PG dosage, and slurry pH 9, the flotation recovery of diaspore and kaolinite are 88.5% and 23.4%, respectively.

Surface pretreatment on minerals prior to flotation was proved to increase the selectivity of separation process. Organic acid pretreatment of low-grade diasporic-bauxite was conducted, and the effects of oxalic acid on bauxite flotation were investigated in this work. The oxalic acid pretreatment mechanisms were studied by adsorption measurements, zeta potential testing, XPS analysis, and ICP analysis. The flotation results showed that the oxalic acid treatment could significantly improve Al2O3 recovery from 75.39% to 81.88% and decrease SiO2 recovery from 53.26% to 47.30%. The adsorption capacity of diaspore for sodium oleate (NaOL) increased by 8.50%, while that of kaolinite decreased by 11.72%. XPS analysis revealed that oxalic acid treatment improved the relative contents of unsaturated Al at diaspore surface beneficial to the adsorption of NaOL. While the relative contents of Al at kaolinite surface was decreased due to the Al dissolution revealed by ICP results. Zeta potential analysis indicated that oxalic acid changed the surface property of minerals favorable for the selective adsorption of NaOL on diaspore surface rather than kaolinite surface. These findings provided a promising direction for surface pretreatment of low-grade bauxite using oxalic acid for the improvement of the flotation desilication.

The pyrophyllite-rich ferruginous (PRF) bauxites in northwestern Iran from the Irano–Himalayan karst belt are deposited on the paleokarst of the middle Permian carbonate sequence of the Ruteh Formation. They were selected from the lowermost part of weathered profiles from 9 karst bauxite deposits, belonging to different stratigraphic positions. These bauxite deposits share similar mineralogical and geochemical features. Powder-XRD analyses show that the bauxites consist of diaspore, hematite, and pyrophyllite, with lesser amounts of goethite, rutile, anatase, illite, and clinochlore. Among minor constituents, single crystals, such as monazite, florencite, and zircon, were detected by SEM–EDS analyses. The positive Ce anomaly of the PRF bauxites (1.0–2.2), the relevant depletion of mobile elements, and values of the La/Y ratio (1.0–3.2) indicate that the PRF bauxites formed in a well-drained environment, characterized by a prevailing alkaline environment, promoting the stability of Fe (oxyhydr)oxides. The mineralogical composition of the PRF bauxites affects the distribution of trace elements: the redox-sensitive trace elements Ni, Cr, Co, Ce, U, and V are probably controlled by Fe (oxyhydr)oxides, whereas most of high field strength elements, such as critical metals Hf and Nb, are hosted in the pool of resistant minerals. Gallium co-varies with Al2O3, indicating this critical trace metal is distributed by diaspore. Phosphate-bearing minerals probably played an efficient role in concentrating light (LREE: La Sm) and heavy (HREE: Eu Lu plus Y) rare earth elements during the generation of the PRF bauxites. The mineralogical control on the distribution of LREE and HREE, coupled with the preferential complexation of HREE in an alkaline environment clearly affect the (La/Yb)ch and (LREE/HREE)ch fractionation ratios. Based on the Th Zr and TiO2–Zr binary diagrams, the concentration of trace elements Zr, Cr, and Ga, bivariate plots of Ta (ppm) versus Al2O3 (wt%) and TiO2 (wt%), and the discriminant function 3 against discriminant function 4 variation diagram, basalt rocks within carbonate bedrocks of the Ruteh Formation have considered to be a probable provenance for the PRF bauxites, similar to some bauxite deposits from the Mediterranean-type karst bauxite belt of different ages, especially northern and northwestern Iran and western India.

Aiming at the effective utilization of the abundant high-alumina iron ores with low iron grade, the influence of alumina concentration and type on high-temperature characteristics was clarified based on the analyses of eight typical iron ores. The results indicate that high-temperature characteristics of iron ores in various alumina types are different. Higher Al2O3 concentration is deleterious to assimilability and liquid phase fluidity, but the influence extent of each alumina type is substantially different. Kaolinite (Al2O3&middot, 2SiO2&middot, 2H2O) contributes to correspondingly better assimilability, followed by hercynite (Fe(Fe, Al)2O4), gibbsite (Al(OH)3), diaspore (AlO(OH)), and free state alumina (Al2O3) in turn. Diaspore promotes relatively higher liquid phase fluidity, followed by kaolinite, free state alumina, and hercynite, while gibbsite possesses the maximum adverse impact. Kaolinite and hercynite are more beneficial to form dendritic or acicular silico-ferrite of calcium and alumina (SFCA) with high strength due to the better reactivity, and gibbsite and diaspore lead to more formation of relatively lower strength lamellar or tabular SFCA, while free state alumina is preferable to form disseminated SCFA with rather poorer strength. Kaolinite and hercynite are the most desirable alumina types for sintering rather than free state alumina.

The major type of bauxite in China is low-grade diasporic bauxite, which is mainly composed of diaspore and kaolinite. Separation of silicate minerals by flotation technology can meet the requirements of Bayer process, but Na+, K+ and Cl− deriving from mineral dissolution and entrainment in flotation water will inevitably mix in the flotation slurry, which will affect the flotation of bauxite. The results of flotation show that NaCl and KCl have little effect on the flotation of diaspore, but NaCl has a beneficial effect on kaolinite flotation. It may be attributed to the ion size order Na+ < K+ < Cl−. Na+ has the ability to enter the layer spacing of kaolinite due to its smaller size, which increases the zeta potential and the dipole-dipole force between kaolinite and sodium oleate, therefore improving the flotation of kaolinite. In addition, Na+ has “salt effect” on the anionic collector, which also promotes the flotation of kaolinite. This study may have some reference significance to the industry flotation of diasporic bauxite.

In-situ single-crystal and powder X-ray diffraction (XRD) experiments were performed on diaspore at high temperatures. The powder XRD experiments showed that the dehydration reaction from diaspore to corundum occurs between 703 and 733 K. The in-situ single-crystal XRD measurements of diaspore could successfully determine the cell parameters, fractional atomic coordinates and anisotropic displacement parameters at high temperatures, i.e., from 295 to 698 K. Temperature variations in the cell parameters indicate that thermal expansion of the a-axis is a little higher than those of the b-axis and the c-axis. However, the axial thermal expansivity is not as anisotropic as was previously suggested. The results of structure refinements indicate that such lattice expansion behavior is the result of thermal expansion of the tunnels through O2–H···O1 hydrogen-bond separation in the diaspore structure. To the best of our knowledge, this is the first time that the thermal expansion of diaspore has been investigated at an atomic level by in-situ single-crystal XRD experiments at high temperatures.

The active sites of mineral surfaces play an important role in many industrial processes, such as mineral flotation and dewatering. This paper was aimed to investigate the effect of Al- and Si-active sites on the mineral crystal faces exposed to water on the electrokinetic properties, surfactant adsorption, and floatability of diaspore and kaolinite, which are, respectively, the valuable and gangue minerals in the processing of diasporic bauxite ores. Specifically, the acid treatment was used to change the physicochemical properties of diaspore and kaolinite minerals for their selective flotation. Microelectrophoresis method was used to determine the zeta (surface) potential of diaspore and kaolinite particles before and after the acid treatment as a function of pH. The change in the surface potential was analyzed applying the theory on the electrical double layers at the solid-solution interface. The proton donor–acceptor reactions occurring simultaneously on amphoteric alumina or/and silica sites of diaspore and kaolinite were considered. The mass balances were applied to link the surface active sites with the minerals charge and potential. Comparing the modeling with the experimental data revealed the significant decrease in the Al-active sites and increase in the Si-active sites by the acid treatment. Single mineral flotation and surfactant adsorption tests of diaspore and kaolinite before and after the acid treatment were carried out using sodium hexametaphosphate (HMP) and dodecylamine hydrochloride (DAH) as a depressant and a collector, respectively. After the acid treatment, the adsorption density of depressant on both diaspore and kaolinite decreased due to the reduced density of Al-active sites on the minerals surfaces. The changes of collector adsorption capacity and floatability of diaspore were very small while those of kaolinite were significantly increased. These changes were caused by decreasing the density of Al-active sites (covered by HMP and thereby preventing DAH adsorption) on both diaspore and kaolinite and increasing the density of Si-active sites of kaolinite (not covered by HMP and thereby facilitating DAH adsorption). The results clearly indicated that the acid treatment was shown to be conducive to changing the active Al- and Si-sites on diaspore and kaolinite and thereby improving their flotation separation.

Desulfurization is a critical problem in the efficient exploitation of high-sulfur bauxite resources. This study synthesized a novel thioether-containing hydroxamic acid (2-BTHA) by click-esterification-hydroxylamine oximation for flotation separation of pyrite from diaspore. DFT calculations indicated the functional groups of 2-BTHA were hydroxamate and thioether groups. Flotation results demonstrated 2-BTHA can effectively separate pyrite from diaspore under weak acidic conditions without adding vulcanizing agent. The UV-absorbance and surface energy tests explained introducing a thioether group improved the adsorption of Fe2+ on the collector, thus reducing its surface energy, hydrophilic index and free energy of bubble-mineral interaction, conducive to selective flotation. Zeta potential, infrared spectrum analyses and XPS further proved 2-BTHA could chemically adsorb on pyrite rather than on diaspore. It mainly reacted with pyrite surface Fe to form Fe-S bonds and five-membered hydroxamate-(O, O)-Fe rings. This research provides a potential multi-functional collector for green and efficient utilization of high-sulfur bauxite.

The Bayer process is a conventional method for refining bauxite in the production of alumina. The Al/Si ratio in bauxite before feeding to the process must be enriched to more than eight by reducing impurities (mainly aluminosilicates). Therefore, diasporic bauxite ores (Al/Si

Permian karstic bauxite and its Quaternary derivative, in western Guangxi, southwestern, South China Block, possess a total tonnage greater than 0.5 billion tons. The primary late Permian karstic bauxite formed in reduced environment in the background of Tethyan accretionary orogenesis. And as one consequence of Cenozoic convergence of the Indian and Eurasia continents, the primary orebody was uplifted, eroded and re-sedimented within Quaternary laterite. The geochemical variation and its controls during the ore transformation from Permian to Quaternary remain poorly understood. Quaternary ore blocks comprise an inner zone of fresh ore, and then it gradually transited through a middle zone to a margin with extensive weathering. One such bauxite block was selected and further subdivided into twenty-three samples for geochemical and mineralogical analysis. The inner and middle zones contain similar mineralogical compositions, dominated by diaspore and amesite, with minor illite, anatase, goethite, pyrite, zircon, and rutile. The margin is composed of diaspore, with small amounts of amesite, boehmite, illite, goethite, anatase, kaolinite, zircon, rutile, and barite. Bauxite in all three zones is composed of mainly Al, Si, Fe, and Ti, and high contents of Zr, Cr, Li, F, S, Zn, V, Sr, Nb, Ba, and REE. Variations in Fe2+ and Fe3+ between the three zones were observed. The elements Si, Al, Fe2+, Mg, Ba, Cr, F, Li, Ni, Zn, and REE decrease from the core of the ore block outwards, corresponding to an increase in S and Fe3+. Depletions in Si, Al, Fe2+, Mg, Ba, and Cr were caused by the dissolution of amesite. Most of the Al and Si in amesite were lost during the weathering, and minor retained to form kaolinite. Depletions in Li, Ni, and Zn resulted from changes in the depositional environment between the late Permian and Quaternary. Dissolution of REE-bearing fluorocarbonates resulted in depletions of REE and F. The enrichment of Fe3+ and S was related to the precipitation of goethite, hematite, and barite in an oxidizing environment, while local enrichment of Ce resulted from the redox change of Ce3+ → Ce4+ under the same condition. This shows that the chemical composition of laterite enwrapping the bauxite also took part in Quaternary bauxite transformation. This study shows that the elements migrations during bauxite transformation were influenced by multiple independent factors except for the elemental attributes.

A systematic study of diasporic bauxite flotation using commercial oleic acids with different iodine values as collector was conducted in this paper. Bench scale flotation tests for diasporic bauxite ore and micro-flotation tests for relevant pure minerals (including diaspore, pyrophyllite and kaolinite) were carried out at different conditions using commercial oleic acids with iodine values of 65, 121 and 131. The results suggest that an increase in the iodine value of oleic acid would lead to improved flotation separation of diaspore from aluminosilicates. Use of the commercial oleic acid with iodine value of 131 in closed-circuit flotation tests allowed us to obtain a concentrate with alumina-to-silica (A/S) ratio of 5.33 and alumina recovery of 85.56% from the feed ore (A/S ratio = 3.39). Chemical analyses of these commercial oleic acids found that an increase in the iodine value was associated with increased proportion of linoleic acid in the commercial oleic acids. To fundamentally understand the correlation between the iodine value of commercial oleic acids and the efficiency of flotation separation of diaspore from aluminosilicates, the computational studies of frontier molecular orbital energy of oleic and linoleic acid were done, and the results suggest that linoleic acid has higher chemical activity than oleic acid and its chemical adsorption on diaspore is more stable than that of oleic acid.

We studied the gallium (Ga) isotopic composition of the Xiaoshanba bauxite deposit in central Guizhou Province, southwest China. Claystone with kaolinite as the main mineral has δ71GaIPGP values of − 0.22‰ to + 0.19‰ (−0.04‰ on average), whereas bauxite with diaspore as the main mineral has δ71GaIPGP values of − 0.60‰ to − 0.15‰ (−0.35‰ on average). Other samples with diaspore and kaolinite as the main minerals have δ71GaIPGP values between those of the claystone and bauxite (−0.20‰ on average). Dolostone from the Loushanguan Group has δ71GaIPGP values of − 0.28‰ to − 0.18‰ (−0.24‰ on average). Samples with kaolinite as the main mineral have higher δ71GaIPGP values than samples with diaspore as the main mineral. However, δ71GaIPGP values in the dolostone are lower than those of the claystone. Based on vertical variations in δ71GaIPGP values and Ga/Al ratios, we speculate that weathered dolostone from the Loushanguan Group may have higher δ71GaIPGP values than unweathered dolostone. In addition, for both of the Jiujialu and Wulongsi ore bodies, samples from the upper part of the profile are relatively enriched in heavier Ga isotopes than samples in the lower part. During the process of bauxite ore formation, supergene weathering and Ga re-precipitation could have led to enrichment in lighter Ga isotopes. This mechanism of isotopic enrichment has the potential to record the material source of the bauxite. The results of leaching experiments show that, during supergene weathering, Ga is more available to the leaching liquid than Al under neutral to weakly alkaline conditions, whereas Al is more soluble than Ga under weakly acidic conditions. In natural deposits, samples with a high degree of weathering show an obvious decoupling between Ga and Al; consequently, in a given sedimentary environment, samples with kaolinite as the main mineral have higher Ga concentrations than samples with diaspore as the main mineral. Clay minerals such as kaolinite can be important resources of Ga.

The middle Triassic Kani Zarrineh bauxite deposit, in the Irano–Himalayan belt, located 20 km northwest of Saqqez city in northwestern Iran, occurs in depressions of the early Triassic bedrock carbonates of the Elika Formation. The ores formed during the Carnian Pluvial Event under high atmospheric pCO2 conditions and humid episodes. Powder-XRD analyses revealed that the Kani Zarrineh bauxite is mainly composed of diaspore, hematite, and kaolinite. There is a broad inverse relationship between hematite abundance and diaspore abundance in the profile with a downward increase of hematite and an upward increase of diaspore. Among minor constituents, single crystals rich in high field strength elements, such as florencite, monazite-(Ce), xenotime-(Y), and zircon were detected by SEM-EDS analyses. R-mode factor analysis indicates that most of the variance of the dataset is explained by a factor accounting for the competition between the Al2O3–TiO2–Ga–HFSE pool and the SiO2–Fe2O3–U–first row transition metals pool, and related to the coupled effect of a change of redox conditions and climatic regime. The other two factors are related to the importance of phosphate minerals (e.g., florencite and monazite) in hosting LREE, and to the influence that the chemistry of the soil solutions, especially pH, exerted in promoting the preferential mobility of HREE. Both these factors contribute to explaining LREE/HREE fractionation in the Kani Zarrineh bauxite ores. A negative correlation between the Ce/Ce* and the TOC (r = –0.91) corroborates the fact that bauxitization occurred in an environment characterized by a progressive increase in Eh upward. The coupled Ce/Ce* increase and TOC decrease upward are likely related to soil aeration, a progressive increase in soil temperature, and a reduction in soil moisture. An upward decrease of soil moisture is also consistent with an increase in the abundance of Al hydroxides that require drier conditions than those necessary for the formation of Fe oxyhydroxides. Finally, the evaluation of elemental mobility and results of the R-mode factor analysis indicate that, in addition to Al, high field strength elements Nb and Ta can be used confidently for assessing parental affinity of the Kani Zarrineh bauxite ores. The Al/Ta and Nb/Ta ratios and the Sm/Nd and Eu/Eu* provenance proxies reveal that mafic rocks interbedded in the early Triassic bedrock carbonates of the Elika Formation are likely protoliths of the Kani Zarrineh bauxite ores. This finding is consistent with what is observed for some bauxite deposits from the Mediterranean-type karst bauxite belt, especially from northwestern Iran of different ages that basalt rocks were the parent rock of these deposits.

More than 0.5 billion tons of late Permian bauxite overlies the karstic topography of the Maokou Formation of western Guangxi in China. Here, we provide new mineralogical, geochemical, Sr–Nd–Pb isotopic, and pyrite S isotope and trace element compositional data for the Pingguo bauxite deposit, aiming to further our understanding of the genesis of Permian bauxite. The Pingguo bauxite contains three distinct layers: a lower layer dominated by ferric clay or weathered iron ore, a middle layer of cryptocrystalline and oolitic bauxite ore, and an upper layer dominated by argillaceous bauxite. The bauxite ore is mainly diaspore, pyrite, chamosite, and anatase, whereas the argillaceous bauxite contains diaspore, kaolinite, pyrophyllite, pyrite, and anatase. Two types of pyrite have been identified within the bauxite: fine-grained and framboidal pyrite (Py1) occurring in aggregates and coarse-grained and euhedral pyrite (Py2). Py1 is enriched in trace elements and is thought to have a diagenetic origin, whereas Py2 is deficient in trace elements and is considered to have formed by later recrystallization. The S isotopic composition of pyrite (−34.11 to −18.91‰) and visible ovoid microorganisms within the bauxite provide evidences of microbial activity during bauxite formation. The Sr–Nd–Pb isotopic composition of the bauxite indicates that these ores were generated by the weathering of basalts belonging to the Emeishan Large Igneous Province (LIP) and limestones of the Maokou Formation. Microorganisms were likely to have enhanced the dissolution and weathering of the parent rock and facilitated the precipitation of diaspore under near-surface conditions.

In the present work, a combination of various techniques is utilized for the study of nano-mineralogy and -geochemistry of high-grade karst-type bauxite (Al-rich and Fe-depleted samples; Al2O3 ca. 80 wt.%) from the Parnassos-Ghiona mines located in Greece. Initial characterization using PXRD and electron microscopy in microscale and mesoscale (SEM-EDS including STEM mode), proved the presence of “Fe-Cr-Ti-containing diaspore”, anatase and minor rutile. The study by means of 57Fe Mössbauer spectroscopy, in correlation with magnetic susceptibility measurements and, complemented, with Synchrotron-based spectroscopies at the microscale (SR micro-XRF and micro-XANES/-EXAFS), indicated that Fe3+, in contrast to [6]Cr3+, is not exclusively a component of the diaspore structure. While Cr3 + substitutes Al3 + in octahedral sites of diaspore ([6]Cr3+ ↔ [6]Al3+), the electron microscopy in nanoscale (TEM-EDS & EELS) revealed that Fe exists in the form of peculiar Fe3+-bearing nanominerals (most likely maghemite-type phases) between 25 and 45 nm in size, in addition to the Fe3+ ions substituting Al3+ in the diaspore structure. Moreover, it was proven that TiO2 polymorph mineral nanoparticles, particularly rounded anatase mesocrystals and nanocrystals and individual needle-shaped rutiles, are dispersed into the diaspore matrix. Thus, diaspore in the studied bauxite concerns -in fact- a distinct Fe3+-Cr3+-AlOOH low-T authigenic phase, demonstrated for the first time in literature. On the other hand, the observed TiO2 mineral nanoparticles (formed, together with diaspore, during diagenesis) and Fe nanominerals (formed during epigenesis) were hitherto unknown not only for the allochthonous karst-type bauxite deposits of Greece, but also for the overall bauxite deposits, worldwide.

There are 6 semi-precious gemstones in Turkey that are the most significant in terms of abundance and authenticity. These include smoky quartz, blue chalcedony, chrysoprase (aka Senkaya emerald), diaspore (aka sultanite/zultanite), sepiolite (aka meerschaum/Eskisehirstone), and jet (aka Oltustone). The smoky quartz occurs in the south of Buyuk Menderes Basin within metamorphic rocks of the massif. Chalcedony occurrences are in Canakkale and Saricakaya (Eskisehir). Chrysoprase is acquired in Bursa, Alasehir (Manisa) as yellowish green in color, Biga (Canakkale), Sivrihisar (Eskisehir) and Senkaya (Erzurum) as dark green in color. Diaspore occurs in Milas (Mugla), Soke (Aydin), Tire (Izmir), Bolkardagi Gerdekkilise area and Saimbeyli (Adana). Sepiolite occurrences are limited to Kibriscik-Koroglu (Bolu), Eskisehir and Konya. Jet (aka Oltustone) occurs in Oltu area (Erzurum). These are the major varieties that has been used to produce both jewelry and ornamental objects among which the prayer beads are one of the most indispensable object of oriental cultures in particular. These are also considered to be the authentic gems of Turkey and exported as raw and processed in into many forms. As for the prayer beads, lightness, color, durability, hardness, and cost are the main criteria. Thus, the Oltustone has been the major source for decades. However, the Eskisehir stone and blue chalcedony are becoming popular as well.

This paper focuses on the scandium speciation in bauxite residues of different origin. Insights into mineral-chemical similarities and differences of these materials will be presented and links to their natural geological background discussed. The presented research should provide fundamental knowledge for the future development of efficient and viable technologies for Sc-recovery from bauxite residues derived from different bauxites and accumulating at different localities. In total, five bauxite residues were investigated which originated from Greece, Germany, Hungary and Russia (North Ural & North Timan) using a combination of different analytical tools. Those included: laser ablation inductively coupled plasma mass spectrometry, X-ray absorption near edge structure (XANES) spectroscopy, μ-Raman spectroscopy as well as scanning electron microscopy and electron microprobe analyses. X-ray fluorescence and inductively coupled plasma mass spectrometry were used to determine the overall chemical composition. The investigated samples were found to exhibit a relatively homogenous distribution of Sc between the larger mineral particles and the fine-grained matrix except for Al-phases like diaspore, boehmite and gibbsite. These phases were found to be particularly low in Sc. The only sample where Sc mass fractions in Al-phases exceeded 50 mg/kg was the Russian sample from North Ural. Fe-phases such as goethite, hematite and chamosite (for Russian samples) were more enriched in Sc than the Al-phases. In fact, in Greek samples goethite showed a higher capacity to incorporate or adsorb Sc than hematite. Accessory minerals like zircon, rutile/anatase and ilmenite were found to incorporate higher mass fractions of Sc (>150 mg/kg), however, those minerals are only present in small amounts and do not represent major host phases for Sc. In Russian samples from North Ural an additional Ca–Mg rich phase was found to contain significant mass fractions of Sc (>500 mg/kg). μ-XANES spectroscopy was able to show that Sc in bauxite residue occurs adsorbed onto mineral surfaces as well as incorporated into the crystal lattice of certain Fe-phases. According to our observations the bauxite type, i.e. karstic or lateritic, the atmospheric conditions during bauxitization, i.e. oxidizing or reducing, and consequently the dominant Sc-bearing species in the primary bauxite influence the occurrence of Sc in bauxite residues. In karstic bauxites, underlying carbonate rocks can work as a pH-barrier and stabilize Sc. This prevents the Sc from being mobilized and removed during bauxitization. Hence, karstic bauxites are more prone to show a Sc enrichment than lateritic bauxites. Reducing conditions during bauxitization support the incorporation of Sc into clay minerals such as chamosite, which can dissolve and reprecipitate during Bayer processing causing Sc to be redistributed and primarily adsorb onto mineral surfaces in the bauxite residue. Oxidizing conditions support the incorporation of Sc into the crystal lattice of Fe-oxides and hydroxides, which are not affected in the Bayer process. The genetic history of the bauxite is therefore the major influential factor for the Sc occurrence in bauxite residues.

Above two billion tons of bauxite were formed during the exposure of the North China Craton (NCC) in 445–300 Ma. Mineralogical, geochemical, and isotopic analyses of karstic bauxite deposits in the Sanmenxia area situated within southern NCC were conducted to explore the genetic processes of Carboniferous bauxite. The bauxite contains three layers: a lower Fe-bearing claystone layer, a middle bauxite ore layer, and an upper claystone layer. Fe-bearing claystone is dominated by illite and hematite in the uplift and illite, siderite, and pyrite in the depression. Bauxite ore is composed of diaspore, illite, pyrite, and anatase, and the upper claystone consists of illite, diaspore, and anatase. Distinct pyrite δ34S values (11.7–15.2 and −11.5 to 1.0), illite (87Sr/86Sr)i (0.711917–0.713588 and 0.708000–0.711057) and eNd(t) (−12.2 to −11.4 and −11.8 to −9.7) values, and the immobile elemental ratios were obtained between the lower Fe-bearing claystone and upper bauxite ore and claystone. Together with chemistry of detrital rutile, it is denoted the Fe-bearing claystone was formed from the underlying limestone, whereas the bauxite ore and claystone were derived from both igneous rocks along craton margin and regional Precambrian metamorphic rocks. The visible microorganisms and wide development of framboidal pyrite with negative δ34S within the bauxite ore provide evidences of microbial activity during bauxite formation. Bio-leaching process after the deposition of allochthonous source materials caused the downward migration of ions (Al3+, Fe2+, Ti4+, REE3+, etc.). These ions encountered an alkaline and reducing condition in the karstic depression, forming diaspore, pyrite, and anatase and REE enrichment at the bottom of bauxite ore. This large input of raw materials, warm and humid climate, and microorganisms led to large-scale bauxite formation in the NCC during late Carboniferous.

The Badamlu karst bauxite deposit, located 55 km southeast of Miandoab city in northwestern Iran occurs in karstic depressions of carbonates of the late Permian Nessen Formation. The studied bauxitic ores have a dominant pelitomorphic texture, and locally developed ooidic, pisoidic, and clastic textures in a pelitomorphic matrix. Mineralogically, the bauxite ores are composed mostly of diaspore, hematite, and kaolinite, as well as lesser amounts of rutile, chlorite, goethite, and illite. In addition, REE minerals, such as churchite and cerianite were detected. Cerianite occurs in the core of ooids, and churchite is surrounded by a kaolinite-rich matrix. Churchite and cerianite formed in acidic and oxidizing conditions in the uppermost part of the weathered profile, respectively. Total rare earth elements La-Lu contents in the bauxite ores range widely from 29.1 to 2138.2 ppm (average = 746.5 ppm, std = 722.3 ppm), with Ce being the dominant REE (1.3–1825.0 ppm, average = 606.7 ppm, std = 645.1 ppm). The ΣREE contents, (LREE/HREE)ch ratio, and Ce anomaly in the bauxite ores increase upward through the profile, in which LREE and HREE are La–Eu and Gd–Lu, respectively. The Ce anomaly in the bauxite ores has a bimodal distribution with higher Ce anomalies in the upper 7.5–m-thick succession (2.7–20.8, average 10.5), compared to the lower and middle 4.5–m-thick succession (0.1–0.3, average 0.1). The downward decrease in the Ce anomaly may be due to the lack of cerianite and a decrease in the oxidation state. The REE distribution patterns normalized to chondrite exhibit a variable depletion/enrichment of LREE and HREE, with a negative Eu anomaly (0.3–0.7).

In this paper, a novel surfactant, 2-amino-6-decanamidohexanoic acid (AHA-10) was synthesized and used as a collector for flotation separation of diaspore and aluminosilicate minerals. The adsorption mechanism of AHA-10 onto diaspore was also evaluated by FTIR spectra, zeta potential, XPS and solution chemistry. The flotation results demonstrated that AHA-10 exhibited superior collecting power to diaspore and good selectivity against kaolinite and illite, and could effectively recover diaspore from bauxite ores contained aluminosilicate minerals at pH around 10. The analyses of FTIR spectra, zeta potential and solution chemistry inferred that at pH around 10, AHA-10 might chemisorb on diaspore surfaces by formation of Al O and Al N bonds. AHA-10’s unique properties, such as characteristic bond model to Al atoms on diaspore surfaces, double hydrophobic groups and intermolecular hydrogen bonds between neighboring AHA-10 molecules coated on diaspore surfaces, rendering a weakening surface energy and enhancing hydrophobicity of diaspore particles.

Turkey hosts essential bauxite deposits, typically of the karstic-type. The most economically important bauxite deposits of Turkey form in the Seydisehir-Akseki region of the central Taurides Mountains. The Mortas and Dogankuzu deposits are the most important deposits in that region. The bauxite beds contain boehmite, hematite, rutile, smectite, quartz, diaspore, calcite, pyrite, marcasite and goethite. Brown to red-colored bauxite minerals are massive, oolitic – pisolitic textured. The Seydisehir schists could be possible parent rocks of bauxites, and have unearthed acidic source (mostly granite) with hornblende and plagioclase minerals. The schists were compositionally mature with minimal alkali feldspar sediments. The Mortas deposit is 400 m long and up to 40 m thick; it averages 10 m thick. It has about 5 million tons of ore reserves, with ~50 percent Al2O3. The Dogankuzu bauxite deposit is situated 2 km southwest of the Mortas deposit, with 14.9 million metric tons of ore at 61 percent Al2O3. The Dogankuzu ore was deposited on a fault-controlled karst surface of Cenomanian limestone succession, which was overlain by 5- to 10-cm-thick Santonian limestones. The bauxite has been mined by the Seydisehir aluminum factory, which was founded in 1973, and privatized in 2005. The plant is capable to produce 65.000 ton liquid aluminum per year, around 15% of Turkey’s Aluminum demand.

Contact resonance atomic force microscopy (CR-AFM) is a nondestructive technique based on atomic force microscopy (AFM) that allows one to perform single-point measurements as well as surface mapping of the indentation modulus of a material. In this work, we demonstrate the potential of CR-AFM in applied mineralogy research. As a case study, we report the characterization of natural and thermally treated diaspore. Natural diaspore samples from the Ilbirdagi diasporic metabauxite (diasporite) deposit in the Milas (Mugla) region in Turkey were heat treated in a muffle furnace causing them to transform from diaspore to corundum. After the treatment, the samples had a polycrystalline structure with ordered micrometer-size rectangular grains of uniform crystallographic orientation. Nanomechanical characterization by CR-AFM allowed us to visualize inclusions with different mechanical properties and to determine the average indentation modulus of the surface of the thermally treated diaspore. Quantitative maps of the indentation modulus reveal the variation of the indentation modulus on the surface of single micro-grains with nanometer spatial resolution.

The flotation of diaspore and three kinds of silicate minerals, including kaolinite, illite and pyrophyllite, using an organosilicon cationic surfactant (TAS101) as collector and starch as depressant was investigated. The results show that both diaspore and aluminosilicate minerals float readily with organosilicon cationic collector TAS101 at pH values of 4 to 10. Starch has a strong depression effect for diaspore in the alkaline pH region but has little influence on the flotation of aluminosilicate minerals. It is possible to separate diaspore from aluminosilicate minerals using the organosilicon cationic collector and starch depressant. Further studies of bauxite ore flotation were also conducted, and the reverse flotation separation process was adopted. The concentrates with the mass ratio of Al2O3 to SiO2 of 9.58 and Al2O3 recovery of 83.34% are obtained from natural bauxite ore with the mass ratio of Al2O3 to SiO2 of 6.1 at pH value of 11 using the organosilicon cationic collector and starch depressant.

The formation of Al (oxy)hydroxide on the basal surface of muscovite mica was investigated to understand how the structure of the substrate controls the nucleation and growth of secondary phases. Atomic force microscopy images showed that solid phases nucleated on the surface initially as two-dimensional islands that were ≤10 Å in height and ≤200 Å in diameter after 16-50 h of reaction in a 100 μM AlCl3 solution at pH 4.2 at room temperature. High-resolution X-ray reflectivity data indicated that these islands were gibbsite layers whose basic unit is composed of a plane of Al ions octahedrally coordinated to oxygen or hydroxyl groups. The formation of gibbsite layers is likely favored because of the structural similarity between its basal plane and the underlying mica surface. After 700-2000 h of reaction, a thicker and continuous film had formed on top of the initial gibbsite layers. X-ray diffraction data showed that this film was composed of diaspore that grew predominantly with its [040] and [140] crystallographic directions oriented along the muscovite [001] direction. These results show the structural characteristics of the muscovite (001) and Al (oxy)hydroxide film interface where presumed epitaxy had facilitated nucleation of metastable gibbsite layers which acted as a structural anchor for the subsequent growth of thermodynamically stable diaspore grown from a mildly acidic and Al-rich solution.

In search of new mineral raw materials with industrial potential, we identified a deposit located in the southwest of Oujda (in the Northeastern Morocco). The physicochemical analyses indicate that the ore consists mainly of diaspore, topaz and quartz, and also secondary minerals. The presence of topaz in the ore is explained by hydrothermal action on the structure of diaspore. The investigation of structural transformations reveals complex reaction mechanisms that result in a mixture of corundum-mullite at 1200℃, which is of great industrial interest. Thus, the peculiarity of this ore is the presence of fluorine and secondary minerals.

The flotation behaviors of diaspore and three kinds of silicate minerals — kaolinite, illite and pyrophyllite — using an organosilicon cationic surfactant as collector were investigated as functions of reagent concentration and pulp pH. The results show that the organosilicon cationic collector QAS122 is a suitable collector for the flotation of aluminosilicate minerals but has weak collecting ability with regard to diaspore, enabling the flotation separation of diaspore from silicate minerals using QAS122 as collector. The flotation of a bauxite ore was then studied in detail. Finally, a reverse flotation separation process was used to process a low-grade bauxite ore. It was concluded that use of the organosilicon cationic collector is effective. A concentrate with aluminum oxide (Al2O3) to silicon dioxide (SiO2) mass ratio, or A/S, of 9.67 was obtained from natural bauxite ore with A/S of 6.07 at pH of around 11. The Al2O3 recovery rate was 81.72 percent.

The Amir-Abad karst-type bauxite deposit is located in the Irano–Himalayan bauxite belt, 8 km of south of Maragheh city in northwestern Iran. The bauxite ores occur as layers and lens-shaped pockets in the contact of the Triassic dolomitic limestone of the Elika Formation and the Lower Jurassic sandstone, siltstone, shale, and coal of the Shemshak Formation. Based on the PXRD and SEM-EDS analyses, the bauxite ores mainly consist of diaspore, hematite, and kaolinite group minerals (e.g., kaolinite and montmorillonite), with lesser amounts of goethite, anatase/rutile, and zircon. Nickel, Cr, Co, and V show a pattern similar to Fe; they were leached from the uppermost parts of the profile by acidic percolating solutions, and concentrated toward the carbonate bedrock under alkaline conditions. Aluminum, Nb, Ga, Ta, Th, Hf, and Zr can be regarded as less mobile elements. Variations of the La/Y, (ΣLREE/ΣHREE)N, and (La/Yb)N ratios across the weathering profile, together with leaching of alkali and alkaline earth metals indicate an acidic environment in the uppermost parts, and a basic environment in the basal parts of the profile. Mineral control and physico-chemical conditions (e.g., Eh and pH) probably had effective roles in the behavior of elements during weathering. Based on the concentration of trace elements, such as Zr, Cr, and Ga, and the conservative elemental indices (e.g., Sm/Nd, Ti/Zr, and Nb/Ta), the basaltic rocks were a plausible source rock for the Amir-Abad karst-type bauxite deposit.

The Carboniferous karstic bauxite-bearing rock series in central Guizhou Province in southwest (SW) China is rich in trace elements, particularly Li, Ga, V, and rare earth elements (REEs), which have potential for comprehensive utilization as independent deposits or associated resources. However, the host minerals of Li, Ga, V, and REEs are not well-constrained because the sedimentary rocks are characteristics by complex mineral composition and fine mineral particles. This situation considerably hinders the compressive utilization of these trace elements in bauxite. Herein, laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) was successfully applied to element geochemistry analysis of hydrous minerals (diaspore/boehmite, kaolinite, and illite) in karstic bauxite samples, based on the principle that laser ablation data of all oxides were normalized to the sum of 100% minus the total volatile components of the mineral chemical formula. The analysis showed signal stabilization. Results indicated that the bivariate plots of selected elements had characteristics similar to statistical results of whole-rock samples from global bauxites, thereby indicating that the LA–ICP–MS analysis data were reliably but artificially herein. Combined with whole-rock geochemistry studies, the analysis results revealed that smectite may be the main host minerals of Li. Furthermore, Ga was enriched in diaspore/boehmite; V was mainly enriched in iron-bearing minerals, particularly chlorite; and REE-independent minerals, such as monazite, were the main host minerals of REEs in the Carboniferous karstic bauxite in SW China. This study contributed to the knowledge on the use of in-situ method for the element geochemistry investigation of hydrous minerals and sedimentary rocks.

In this study, the effects of four fine minerals, which were fine diaspore (FDIA), kaolinite, illite, and pyrophyllite (D50 is about 4.55 &mu, m, D80 is about 10.78 &mu, m), on the pulp rheology of the diaspore and pyrite mixed ores (D50 is about 120.53 &mu, m, D80 is about 187.36 &mu, m) and the recovery of pyrite were investigated through flotation tests, pulp rheology measurements, and sedimentation tests. It was found that fine minerals could change the pulp rheology and affect the pyrite recovery. The apparent viscosity of the mixed ores slurry increased with the addition of FDIA, kaolinite, and illite and the pyrite recovery decreased in varying degrees. When the addition was 15 wt.%, the recovery of pyrite decreased from 92.3% to 60.8%, 81.4%, and 84.7%, respectively. The addition of pyrophyllite had a significant deteriorating effect on flotation. When the addition of pyrophyllite was 5 wt.%, the pyrite recovery was reduced to 49.2%, and when the addition was further increased to 15 wt.%, the pyrite recovery reduced to 28.5%. However, the effect of pyrophyllite addition on the pulp rheology of the mixed ore was not remarkable. Pyrophyllite affected pyrite recovery not only by affecting the rheological behavior of the pulp, but also because pyrophyllite was adsorbed on the surface of pyrite and diaspore, producing hetero-aggregation, which made it difficult for the pyrite particles to collide with the bubbles effectively. This was the main reason for the reduction of pyrite recovery. Generally, the order in which the reduction of pyrite recovery was affected by the additions of fine minerals was pyrophyllite &gt, FDIA &gt, kaolinite &gt, illite.

Froth flotation has been proved to be the economic way to upgrade the low-grade diasporic bauxites by desilication of kaolinite. However, the recovery rate of diaspore varied significantly in industry due to water quality (cations) and the mechanism remains unknown. This report investigates the effect of common water hardness cations (Ca2+ and Mg2+) on the recovery of diaspore and kaolinite using micro-flotation at various pH values. The results show that adding Ca2+ significantly enhanced the diaspore recovery rate even under acidic conditions (pH = 4–7). In contrast, adding Mg2+ reduced the diaspore recovery rate to below 50% when the pH value was between 8 and 9 while adding Ca2+ increase the recovery rate to above 95%. In addition, adding either cation shows minimal change to the recovery of kaolinite. The mechanism has been revealed by thermodynamics speciation, zeta potential and synchrotron-based near edge X-ray adsorption fine structure (NEXAFS) spectroscopy. The change of both dipole-dipole interaction and hydrogen bonding plays a vital role on this cation effect.

High concentrations of rare earth elements (REE) are found in the bauxite deposits in the Songqi area of Henan Province, North China. However, no studies have been carried out on the occurrences of REE in these bauxite ores. In this study we explored the REE occurrence and their possible enrichment mechanism in the Songqi bauxite deposits using petrographic observation, X-ray diffraction (XRD), scanning electron microscope with energy dispersive spectroscopy (SEM-EDS), and LA-ICP-MS techniques. The major aluminum-rich ore mineral in the Songqi bauxite deposits is diaspore, and other coexisting minerals include clay mineral aggregates, with minor amounts of hematite, pyrite, anatase, and zircon. The bauxite ores are rich in REE and also some other critical metals (Li, Zr, Nb, and Ga). Most of the REE are adsorbed in the form of ions on the surface of clay minerals and diaspore, and some heavy rare earth elements (HREE) exist in the form of xenotime. The SEM-EDS and LA-ICP-MS analyses show that REE is closely related to the content of P and therefore it is possible that other dispersed and minor P-bearing rare earth minerals may occur in the bauxite deposits except for the possible co-adsorption of P and REE in the clays and diaspore.

Diasporic bauxite represents one of the major aluminum resources. Its upgrading for further processing involves a separation of diaspore (the valuable mineral) from aluminosilicates (the gangue minerals) such as kaolinite, illite, and pyrophyllite. Flotation is one of the most effective ways to realize the upgrading. Since flotation is a physicochemical process based on the difference in the surface hydrophobicity of different components, determining the adsorption characteristics of various flotation surfactants on the mineral surfaces is critical. The surfactant adsorption properties of the minerals, in turn, are controlled by the surface chemistry of the minerals, while the latter is related to the mineral crystal structures. In this paper, we first discuss the crystal structures of the four key minerals of diaspore, kaolinite, illite, and pyrophyllite as well as the broken bonds on their exposed surfaces after grinding. Next, we summarize the surface chemistry properties such as surface wettability and surface electrical properties of the four minerals, and the differences in these properties are explained from the perspective of mineral crystal structures. Then we review the adsorption mechanism and adsorption characteristics of surfactants such as collectors (cationic, anionic, and mixed surfactants), depressants (inorganic and organic), dispersants, and flocculants on these mineral surfaces. The separation of diaspore and aluminosilicates by direct flotation and reverse flotation are reviewed, and the collecting properties of different types of collectors are compared. Furthermore, the abnormal behavior of the cationic flotation of kaolinite is also explained in this section. This review provides a strong theoretical support for the optimization of the upgrading of diaspore bauxite ore by flotation and the early industrialization of the reverse flotation process.

The effect of iron ions in backwater on the flotation of diaspore bauxite was investigated by ICP measurement, micro-flotation tests, zeta potential measurements and solution chemistry analyses. The concentration of iron ions in backwater was 1 × 10−5 mol/L measured by ICP. The micro-flotation results indicated that iron ions activated the flotation of diaspore at pH 4 and depressed the flotation of diaspore at pH 7, while activated the flotation of kaolinite at pH 4–9. In particular, the flotation of kaolinite had a great increase in the presence of iron ions at pH 8–9, the pH value usually used in industry flotation. The iron ions were adsorbed on the mineral surface mainly in the formation of Fe(OH)3(s). It changed the zeta potential of minerals and modified the surface properties of minerals, then transformed the interaction between minerals and collectors, and finally affected the flotation of diaspore and kaolinite. The study might have some reference significance to the industry flotation.

The mineralogical and geochemical characteristics of the Yunfeng bauxite in Qingzhen were investigated through the handle specimen observation, thin section analysis, XRD、SEM and Element geochemistry. The mineral analyses reveal that diaspore, kaolinite and chlorite are the major minerals in the bauxite with small amounts of boehmite and pyrite. Geochemical investigations reveal that the main components in the bauxite are Al2O3, SiO2 and TFe2O3, the minorcomponents are TiO2, MgO and P2O5. In the process of weathering, some trace elements, such as Zr, Cr, Nb and Hf, are enriched. Zr vs Hf and Nb vs Ta display higher positive correlation. Trace elements show that Loushanguan Formation is the main source of material for the bauxite formation and there may be exist other precursor rock provide few material for the bauxite formation. Ore deposit formed in a O-poor,reducing Marine sedimentary environment.

In this paper, a novel surfactant, N-(6-(hydroxyamino)-6-oxohexyl)decanamide (NHOD) was synthesized and used as a collector for flotation separation of diaspore and aluminosilicate minerals. The adsorption mechanism of NHOD onto diaspore was also investigated by FTIR spectra, zeta potential measurement and XPS. The flotation results demonstrated that NHOD exhibited superior collecting power to diaspore and selectivity against kaolinite and illite and could effectively realize flotation recovery of diaspore from bauxite ores contained aluminosilicate minerals under neutral conditions. The results of XPS, FTIR spectra and zeta potential illustrated that at around pH 7.0, NHOD might chemisorb on diaspore surfaces through Al O coordination bonds formed by binding its C( O)NHOH or C( O)NH chelate groups with aluminum atoms on diaspore surfaces. NHOD's unique properties, such as characteristic bond patterns onto diaspore surfaces, two hydrophobic groups, and intermolecular hydrogen bonds between neighboring NHOD molecules coated on diaspore surfaces, rendered it to be a superior flotation collector for diaspore.