A review of the surface features and properties, surfactant adsorption and floatability of four key minerals of diasporic bauxite resources

Monitoring effects of hydrodynamic cavitation pretreatment of sodium oleate on the aggregation of fine diaspore particles through small-angle laser scattering

Hydrodynamic cavitation (HC) enhanced fine particle aggregation could be largely due to the generation of tiny bubbles and their role in bridging particles. However, the lack of adequate characterizations of aggregates severally limits our further understanding of the associated aggregation behaviors. In this study, the aggregation of fine diaspore particles was comparatively investigated in sodium oleate (NaOl) solutions with and without HC pretreatment through the small-angle laser scattering (SALS) technique in a shear-induced aggregation (SIA) system. Results showed that HC pretreatment caused the formation of bulk nanobubbles (BNBs), which significantly modified the particle interactions and thereby modified the size and mass fractal dimension (Df) of aggregates under different SIA conditions. Although HC pretreatment did not noticeably alter the gradual change trend of aggregate size and structure characteristics under specific variables, BNBs bridging facilitated the aggregation process towards the diffusion-limited cluster aggregation model, resulting in the formation of larger but looser aggregates. This effect was more pronounced under relatively high NaOl concentrations. Apart from BNBs, the aggregation was also affected by cavitation bubbles formed during shear cavitation, which was more significant under high stirring intensity conditions (i.e., 1800 rpm) than the low stirring intensity conditions (i.e., 600 rpm).

Extraction of alumina and silica from high-silica bauxite by sintering with sodium carbonate followed by two-step leaching with water and sulfuric acid

Efficient utilization of high-silica bauxite and minimization of bauxite residue are of great significance for the sustainable development of the alumina industry. In this paper, a novel process is proposed to extract Al2O3 and SiO2 from high-silica bauxite without residue discharge, that is, sintering bauxite with Na2CO3 followed by two-step leaching with water and sulfuric acid. The effects of the sintering parameters on the process were investigated, and the phase transformations during sintering and leaching were revealed by using phase diagram, thermogravimetric analysis (TGA) and differential scanning calorimetric (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS) methods. When the mixture of the high-silica bauxite and Na2CO3 with mole ratio of Na2O/(Al2O3 + SiO2) of 1 was sintered at 950 °C for 30 min, diaspore and kaolinite were primarily converted into Na1.95Al1.95Si0.05O4 and an amorphous phase, respectively. In the water leaching process, Na1.95Al1.95Si0.05O4 was dissolved while the amorphous phase underwent some transformations to form the water leaching residue, resulting in ∼84% of Al2O3 being extracted for alumina production. In the sulfuric acid leaching process, the amorphous phase in the water leaching residue dissolved, resulting in ∼13% of Al2O3 and ∼86% of SiO2 being extracted for the production of polyaluminium ferric sulfate (PAFS) and silica gel, respectively. The silica gel had a high purity, containing more than 88% of SiO2 after drying.

Is Micellar Catalysis Green Chemistry?

Many years ago, twelve principles were defined for carrying out chemical reactions and processes from a green chemistry perspective. It is everyone's endeavor to take these points into account as far as possible when developing new processes or improving existing ones. Especially in the field of organic synthesis, a new area of research has thus been established: micellar catalysis. This review article addresses the question of whether micellar catalysis is green chemistry by applying the twelve principles to micellar reaction media. The review shows that many reactions can be transferred from an organic solvent to a micellar medium, but that the surfactant also has a crucial role as a solubilizer. Thus, the reactions can be carried out in a much more environmentally friendly manner and with less risk. Moreover, surfactants are being reformulated in their design, synthesis, and degradation to add extra advantages to micellar catalysis to match all the twelve principles of green chemistry.

Surfactant Adsorption to Gypsum Surfaces and the Effects on Solubility in Aqueous Solutions

Vibrational sum frequency generation (VSFG) spectroscopy, conductometric titration measurements, and EDX elemental mapping were used to examine surfactant adsorption to the gypsum (010) surface and assess the effects of surfactant adsorption on gypsum solubility in aqueous solutions. Sodium dodecyl sulfate (SDS) and dodecyltrimethylammonium chloride (DTAC) were used as anionic and cationic surfactants, respectively. Gypsum/SDS interactions result in an ordered precipitate layer on the gypsum surface after water evaporation; gypsum/DTAC interaction did not show a similar effect, despite exposure of gypsum to equivalent amounts of surfactant. VSFG spectra showed that SDS molecules adsorb with their chains parallel to the gypsum surface; spectra from gypsum surfaces treated with DTAC, however, showed no measurable response, implying that these surfactants form disorganized aggregates with no polar ordering. Vibrational data were supported by independent EDX measurements that show a uniform distribution of SDS across the gypsum surface. In contrast, element-specific EDX images showed that DTAC clustered in tightly localized patches that left most of the gypsum surface exposed. The uniform adsorption of SDS on the gypsum surface suppresses long-term dissolution up to 40% when compared to samples exposed to DTAC. Gypsum samples in DTAC-containing solutions lose approximately the same amount of material to dissolution as samples immersed in pure water.

Synthesis of a Ternary Polysulfonate Dispersant and Its Suspension Performance

Allyl alcohol polyoxyethylene ether (APEG), hydroxyethyl methacrylate (HEMA) and styrene sodium sulfonate (SSS) were used as monomers to obtain a APEG-HEMA-SSS comb-like polymer, which was employed as the polysulfonate dispersant for pendimethalin suspensions in this paper. The comb-like polymer has an anionic polysulfonate backbone, hydrophilic APEG side chains and sulfonic acid groups, which makes the dispersant absorb easily on the surface of pendimethalin particles. The polysulfonate dispersant with good dispersion performance was screened out by orthogonal experiments. The surface tension, zeta potential, particle size and dynamic contact angle of the pendimethalin suspension with APEG-HEMA-SSS as dispersant were investigated. The dispersant improves the dispersibility and wettability of the pendimethalin suspension observably.

Extraction of lithium and aluminium from bauxite mine tailings by mixed acid treatment without roasting

Bauxite mine tailings can be used as the reserve resources of aluminium and lithium. In this study, a less energy consumption treatment method for extracting aluminium and lithium from bauxite mine tailings has been proposed, which used mixed acid to leach aluminium and lithium from tailings directly, avoided roasting for reducing energy consumption, and obtained effective results.The minerals in the tailings are kaolinite, diaspore, boehmite, anatase and illite, among others. The minerals have fine dissemination sizes and low liberation. Under the leaching conditions of Al and Li of an acid concentration of 60%, a liquid-solid ratio of 4 mL/g, a reaction temperature of 100 °C and a reaction time of 3 h, the highest leaching rates of Al and Li are 88.64% and 96.35%, respectively. In the leaching process, phosphoric acid reacts with Al and Li in the strong acidic environment provided by sulphuric acid to produce heteropoly acids or heteropoly acid salts that dissolve in the solution.

The role of bulk micro-nanobubbles in reagent desorption and potential implication in flotation separation of highly hydrophobized minerals

Micro-nanobubbles (MNBs) generated during hydrodynamic cavitation (HC) have been extensively studied in mineral processing field in the past two decades. Many researchers have claimed that MNBs can effectively promote the collection of fine particles in flotation, while studies on MNBs assisted mineral separation are rare. In this study, the role of bulk MNBs in desorbing flotation reagent was investigated, with the aim of illustrating the potential effects of MNBs on minerals separation. The results showed that bulk MNBs could efficiently remove the sodium oleate (NaOl) from diaspore surfaces, reducing the residual concentration of NaOl on solids, which was more significant when the amount of NaOl pre-adsorbed was relatively small. Furthermore, lower residual concentration of NaOl on solids caused by MNBs cleaning made the particles less hydrophobic and flocs more friable. Given that gangue entrapment in flocs was one of the main limits for high-selective flotation, the roles of MNBs in enhancing reagent desorption and associated flocs breakup and reorganization probably contribute to higher separation efficiency of different minerals, which was confirmed by the flotation results of diaspore/kaolinite mixture.

Effects of Fine Minerals on Pulp Rheology and the Flotation of Diaspore and Pyrite Mixed Ores

In this study, the effects of four fine minerals, which were fine diaspore (FDIA), kaolinite, illite, and pyrophyllite (D50 is about 4.55 μm, D80 is about 10.78 μm), on the pulp rheology of the diaspore and pyrite mixed ores (D50 is about 120.53 μm, D80 is about 187.36 μm) 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 > FDIA > kaolinite > illite.

Flotation Separation of Diaspore and Kaolinite by Using a Mixed Collector of Sodium Oleate-Tert Dodecyl Mercaptan

Sodium oleate (NaOl), a collector in diaspore flotation, has been widely used for more than 30 years, while its low selectivity becomes an issue under today's process requirement. This study introduced tert dodecyl mercaptan (TDM) together with NaOl as a mixed collector to improve selectivity in diaspore flotation. We found that using the mixed collector of NaOl/TDM (total concentration 0.1 mM, the molar ratio 8:2 of NaOl: TDM) at pH = 9-10 significantly effectively separated diaspore and kaolinite. Comparing the recovery of Al₂O₃ and the ratio of Al₂O₃ to SiO₂ (A/S) treated by NaOl/TDM (pH = 9) and NaOl (pH = 10), the Al₂O₃ recovery and A/S in concentrate for NaOl/TDM are 7.5% and 2.2 higher than that for NaOl in mixed mineral flotation. Also, surface tension measurements, Zeta potential measurements and Fourier Transform Infrared (FTIR) spectra analysis were used to examine its selectivity from a flotation mechanical perspective. Surface tension measurements show that mixed collector NaOl/TDM has stronger surface activity and hydrophobic association than NaOl. The results of Zeta potential measurements and FTIR spectra analysis indicate that NaOl and TDM can selectively co-adsorb diaspore through physical adsorption. Moreover, the adsorption of TDM promotes the adsorption of NaOl on diaspore. However, when NaOl/TDM treats on kaolinite together, TDM can hardly adsorb on mineral surface, nor can it promote the adsorption of NaOl.

Comparative Studies of Quaternary Ammonium Salts on the Aggregation and Dispersion Behavior of Kaolinite and Quartz

Fine particles in the presence of flotation reagents exhibit different dispersion and aggregation behaviors in a mineral suspension, and affect the flotation separation processes. In this study, the effects of three quaternary ammonium salts (i.e., dodecyltrimethylammonium chloride (DTAC), tetradecyltrimethylammonium chloride (TTAC), and hexadecyltrimethylammonium chloride (CTAC)) on the dispersion and aggregation behaviors of kaolinite and quartz were studied. The mechanism was systematically investigated using sedimentation tests, reagent adsorption analysis, zeta potential measurements, and SEM analysis. In the absence of reagents, the kaolinite and quartz particles exhibited good aggregation behaviors at acid and neutral pHs compared with alkaline conditions. Except for CTAC, the presence of DTAC and TTAC improved the aggregation behavior of both minerals in neutral and alkaline conditions. More, the sedimentation yields of both minerals were increased significantly with increasing the concentration of DTAC and TTAC. However, the increasing concentration of CTAC resulted in an increase in the dispersion of kaolinite and quartz particles under the same conditions. At neutral and alkaline conditions, the zeta potentials and adsorbed amounts of all three salts on the mineral surfaces were increased significantly with increasing the concentrations of salts, and the adsorbed amount adopted the following sequence: CTAC > TTAC > DTAC. The zeta potential results showed that the stronger adsorption of quaternary ammonium salts on mineral surfaces at neutral and alkaline conditions was mainly because of electrostatic interactions.