查看更多>>摘要：? 2021 Elsevier LtdThe study of the kinetics of REEs from secondary resources and the understanding of the mechanisms governing the leaching reactions are fundamental aspects for the design and the optimization of industrial processes. Despite their interest, the kinetic aspect of these valuable elements from secondary resources has not been reviewed yet. Therefore, a deep understanding of the major phenomena involved in the elementary stages of REEs leaching is extremely crucial and would allow setting up a comprehensive methodology for kinetics investigation. This review provides a state of the art on various kinetics approaches describing the leaching kinetics and mechanisms of REEs from secondary resources notably low-grade minerals, industrial residues as well as end-of-life products. Different existing kinetics models applied for the leaching were reviewed and deeply discussed. Meanwhile, comparative study of different leaching mechanisms was also realized for a better understanding of the REEs leaching reactions. More importantly, the effect of different leaching parameters on the kinetics was discussed for further optimization and development of REEs extraction processes from secondary resources. In addition, the comparison of different REEs secondary resources was provided in terms of content, availability and economic opportunities to target the most potentially and economically viable resources.
查看更多>>摘要：? 2022 Elsevier LtdSurface roughness plays a vital role in flotation, because it has a pronounced impact on colloidal interactions, i.e., solid-liquid adhesion. In the previous studies, the natural mineral surfaces with various roughness were mainly taken as research object and the adhesion force of liquid on mineral surfaces with various roughness after conditioning with surfactants remains unknown. To fulfil this gap, in this study, the role of surface roughness in the snap-in force (An attractive force when the water droplet sharply and instantaneously spreads on the mineral surface in less than 0.1 s) of water droplets on hematite and quartz surfaces after conditioning with soluble starch and dodecylamine (DDA) was investigated using a high-sensitivity microelectronic mechanical balance. Results revealed that the effect of surface roughness on the snap-in force of water droplets on hematite surfaces was distinctly affected by the concentrations of both DDA and soluble starch, while the effect of surface roughness on the snap-in force of water droplets on quartz surfaces was only significantly affected by DDA concentration. After conditioning with 2 × 10?4 mol/L soluble starch and 4 × 10?4 mol/L DDA under pH value of 8.75, increasing surface roughness increased the snap-in force of water droplets on hematite surfaces and decreased the snap-in force of water droplets on quartz surfaces, suggesting that increasing surface roughness could enlarge the difference in the snap-in force of water droplets on the surfaces of the two minerals. In addition, the snap-in force was found to be a linear correlation with the advancing contact angle, providing evidence that surface roughness could affect the wettability and thereby the snap-in force.
查看更多>>摘要：? 2021 Elsevier LtdThe uptake of bulk ore sorting technology is hindered by little knowledge in assessing its applicability for certain mine operation. The applicability of the bulk ore sorting technology, referred to as ‘sortability’, is a multi-folded concept and is influenced by many factors. Researchers have investigated the influence of some of the various factors, but few have done this in a holistic perspective and in a quantitative manner. In this research, nine influential factors of ore sortaibility were integrated in a mathematical framework based on fractal modelling approach. Box-Behnken design was applied and 130 block cave mine operations were hypothesized under different values of the factors. The influence of the factors on the ore sortability were investigated and factors of significant influence were identified. Results showed that ore property, sorting efficiency, metal price, processing cost and operation scale were the most significant factors in affecting the sortability for a mine operation. The research is intended to improve the understanding on the bulk ore sortability for mine productions under different conditions, and to provide a holistic perspective for applying the bulk ore sorting technology.
查看更多>>摘要：? 2021Ilmenite (TiO2 > 52%) can be upgraded to synthetic rutile (TiO2 > 88%) using a reduction and leaching process. Australian ilmenites (FeTiO3) contain variable amounts of titanium dioxide, iron oxide and other impurities. Ilmenites from different deposits can have different physical and chemical properties that affect ilmenite reduction and the final TiO2 content in synthetic rutile (SR). The main aim of this study was to characterise feed ilmenites using a wide range of traditional and advanced analytical techniques and to determine the effects of feed properties on the quality of the SR. Three different ilmenite samples were upgraded to SR using a comparable ilmenite to coal ratio, heating rate, reduction temperature, holding time, cooling temperature and acid leaching parameters. Differential scanning calorimetry, thermogravimetric analysis, Brunauer–Emmett–Teller (BET) surface analysis and sizing analysis data indicated a difference in physical and surface properties among the samples. Head samples had a TiO2 content between 60% and 65% and Fe2O3 content between 25% and 34%. XRF assay by size data confirmed a variation in the content of TiO2, Fe2O3 and impurities among different size fractions. XRD phase analysis indicated the samples were composed of ilmenite, pseudorutile and rutile. SEM morphology studies revealed that ilmenite particle shapes were sub-angular, sub-rounded or rounded. The study found a linear relationship between the metallisation as a result of processing and feed BET surface area. Feed ilmenites with higher BET surface area and fewer impurities resulted in higher SR quality.
查看更多>>摘要：? 2021 Elsevier LtdMineral processing tailings have increased dramatically, owing to the growing demands for minerals and metals over the past decades. These tailings pose significant hazards to local environments and human health. In this paper, the mechanical activation method was applied for improving the pozzolanic activity of siliceous tailings, and the activated siliceous tailings were used as admixtures in cement production. The geometrical characteristics, surface morphology, crystal structure, and pozzolanic activity of activated siliceous tailings were investigated systematically. Mechanical activation can reduce the particle size of tailings and increase the BET specific surface area up to 11.67 m2/g. The pozzolanic activity of activated tailings was enhanced to 81.15%. It is demonstrated that calcium silicate hydrate gels, ettringite (AFt), and hydrotalcite were the main hydrated products of activated tailings. The activated tailings were mixed in proportion with P?O 52.5 Portland cement to produce new cement. The new cement produced using 8% activated tailings can meet the requirement of P?O 52.5 Portland cement, exhibiting superior profits. This is a green method for bulk handling siliceous tailings and substituting Ordinary Portland Cement.
查看更多>>摘要：? 2021 Elsevier LtdIn this work, we investigated the flotation performance and selective adsorption mechanism of a chitosan derivative NMPC (N-methylene phosphonic chitosan) as an novel talc depressant in the flotation separation of chalcopyrite from talc. The single mineral flotation experiments demonstrated that without the talc depressant, both chalcopyrite and talc showed excellent floatability, thus the separation was difficult in the pH range of 3–11. When NMPC was added, the recovery of talc was reduced drastically but the recovery of chalcopyrite decreased slightly in the pH range of 3–9 at a concentration of 10 mg/L in pulp. Artificial mixed mineral flotation experiments also demonstrated that the effective separation of talc and chalcopyrite could be achieved when NMPC was employed as the depressant. The results showed that better grade and recovery were obtained in different proportions of chalcopyrite and talc, which meant the NMPC is better than CMC, Arabic gum in flotation separation of talc and chalcopyrite. Analysis of adsorption tests, FT-IR measurements, and XPS measurements suggested that NMPC was selectively adsorbed on the talc surface by physical adsorption which might result from the hydrogen bonding and hydrophobic interaction between NMPC and talc. Moreover, the sedimentation experiments disclosed that NMPC plays an important role in the flocculation and settling of fine talc.
查看更多>>摘要：? 2021 Elsevier LtdIn this paper, the role of ammonium sulfate ((NH4)2SO4) in the sulfurization flotation of azurite was investigated. The micro-flotation tests showed that (NH4)2SO4 improved the flotation recovery of azurite by 5.87 ～ 21.12 percentage points. FESEM, XPS and Contact angle analyses indicated that (NH4)2SO4 as a sulfurization regulator promoted the formation of copper sulfide products, and not involved in the formation of sulfurized products. The nucleation rate of the copper sulfide product was reduced in the initial stages of sulfurization after (NH4)2SO4 was added. Thus, covellite (syn, CuS) with larger crystal grains was formed on the azurite surface, as confirmed by X-ray diffraction. Ultimately, more copper sulfide products were formed on the azurite surface, enhancing the surface hydrophobicity of azurite.
Kallio R.Luukkanen S.Tanskanen P.Heikkinen E.-P....
12页
查看更多>>摘要：? 2021 The AuthorsScandium provides technological advantages particularly in solid oxide fuel cells and aluminum alloys. Potential new sources are investigated to respond to the expected increasing demand of this rare earth metal, which is currently classified as a critical raw material for the European Union. The recently discovered Kiviniemi mafic intrusion in Finland has been estimated to contain a total resource of 13.4 Mt of Sc with an average grade of 163 g/t. At Kiviniemi, Sc is incorporated within the lattices of ferrous silicates. Magnetic separation has been proposed as the first processing step to lower the amount of alkali-bearing diamagnetic minerals in Kiviniemi concentrates. Pyrometallurgical processing is suggested as the second step to decrease the amount of the ferrous oxide component from the concentrate prior hydrometallurgical processing. This study presents the first results of thermogravimetric experiments on pyrometallurgical reduction of the Kiviniemi concentrate up to temperatures of 1350–1500 °C. The aim of the study was to investigate the progression and extent of ferrous oxide reduction in the concentrate and to characterize the properties of resulting Sc-enriched slag and metal. The main reduction stage is initiated at ～ 950 °C with a sharp increase in the derivative conversion rates between 1050 and 1170 °C and high rates until ～ 1250 °C. Although complete reduction of FeO is achieved, the segregation of metal from the highly viscous slag will need to be promoted by adjusting the viscosity of the slag prior hydrometallurgical experiments.
查看更多>>摘要：? 2021 Elsevier LtdThe removal of sulfate derived from mine impacted waters is a major objective when treatment is focused on removing potentially toxic metals and metalloids, and neutralizing the acidity of these polluting waters. Here we report on the use of a mixed culture fixed-film column bioreactor including one acidophilic sulfidogen operated for 270 days to primarily remove sulfate from an acidic synthetic water that contained a low level of zinc (0.15 mM). Changing the hydraulic retention time (HRT) from 100 to 30 h caused minor perturbations in the removal of sulfate (～40%) using 6 mM of glycerol as carbon and electron source; however, lowering the HRT to 25 h did not sustain biosulfidogenesis. By increasing the concentration of glycerol as electron donor to catalyze the dissimilatory reduction of sulfate, it was possible to reduce the concentration of sulfate from 14 mM to ～3 mM. This corresponded to an ～80% removal efficiency from the acidic water feedstock, which is well below the lowest attainable concentration using conventional technologies such as gypsum precipitation. Molecular analyses of the column effluent demonstrated that the mixed culture population changed with varying concentrations of glycerol, highlighting a role for Clostridium sp. in the degradation (removal) of acetate produced in the bioreactor by Desulfosporosinus acididurans.
查看更多>>摘要：? 2021The South Namxe deposit in Vietnam contains unusually high quantities of parisite, in addition to minor quantities of other fluorocarbonates, such as synchysite and bastnaesite. Together these minerals constitute the main REE-bearing minerals. This carbonatite-related deposit presents tabular (dykes) or lens-form ore bodies, up to several tens of meters wide and tens to hundreds of meters in length, that are hosted in Permian limestone and Triassic basalts. The main gangue minerals in the ore bodies are from the barite-celestine solid solution series, ankerite and calcite. It was considered necessary to assess the different grain characteristics presented by the presence of parisite intergrowths and its association with minerals of the barite-celestine solid solution series to structure a probable initial beneficiation strategy. Mineral liberation analysis revealed that an optimal liberation particle size between 45 μm and 90 μm could be achieved without overgrinding the material. Additionally, it showed a strong mineral association between fluorocarbonates, baryto-celestine, and calcite. Grinding below 100 μm is necessary. One substantial energy saving potential is removing the host rock prior to grinding. The potential for pre-concentration with sensor-based sorting and selective comminution is investigated in a pre-study. Sensor-based sorting using X-ray transmission resulted in an enrichment of REE by a factor of 4, a reduction of the mass stream down to approximately 30%, and a loss of rare earths below 2%. Selective comminution using a pin mill, at a circumferential speed of 20 m/s, yielded a recovery of 96.5% of REE minerals and allowed rejection of 27% of barren material. This shows that both selective comminution and sensor-based sorting can be considered as complementary beneficiation steps when processing these REE ores.
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