Primary beneficiation of tantalite using magnetic separation and acid leaching

Primary beneficiation was successfully performed prior to dissolution of manganotantalite (sample A) and ferrotantalite (sample C) samples obtained from two different mines in the Naquissupa area, Mozambique. Magnetic separation removed the majority of iron and titanium, whereas H₂SO₄ leaching removed a large portion of thorium and uranium in these samples. Analytical results indicated that 64.14wt% and 72.04wt% of the total Fe and Ti, respectively, and ~2wt% each of Nb₂O₅ and Ta₂O₅ were removed from sample C (ferrotantalite) using the magnetic separation method, whereas only 9.64wt% and 8.66wt% of total Fe₂O₃ and TiO₂, respectively, and ~2wt% each of Nb₂O₅ and Ta₂O₅ were removed from sample A (manganotantalite). A temperature of 50°C and a leaching time of 3 h in the presence of concentrated H₂SO₄ were observed to be the most appropriate leaching conditions for removal of radioactive elements from the tantalite ores. The results obtained for sample A under these conditions indicated that 64.14wt% U₃O₈ and 60.77wt% ThO₂ were leached into the acidic solution, along with 4.45wt% and 0.99wt% of Nb₂O₅ and Ta₂O₅, respectively.     

Quantitative mineralogical characterization of chrome ore beneficiation plant tailing and its beneficiated products

Mineralogical characterization and liberation of valuable minerals are primary concerns in mineral processing industries. The present investigation focuses on quantitative mineralogy, elemental deportment, and locking-liberation characteristics of the beneficiation of tailings from a chrome ore beneficiation plant in the Sukinda region, Odisha; methods used for the study of the beneficiated tailings are QEMSCAN®, X-ray diffraction (XRD), and mineral chemistry by a scanning electron microscope equipped with an energy-dispersive spectrometer (SEM-EDS). The tailing sample was fine grained (69.48wt% below 45 μm size), containing 20.25wt% Cr₂O₃ and 39.19wt% Fe₂O₃, with a Cr:Fe mass ratio of 0.51. Mineralogical investigations using QEMSCAN studies revealed that chromite, goethite, and gibbsite are the dominant mineral phases with minor amounts of hematite, kaolinite, and quartz. The sample contained 34.22wt% chromite, and chromite liberation is more than 80% for grains smaller than 250 μm in size. Based on these results, it was predicted that liberated chromite and high-grade middling chromite particles could be separated from the gangue by various concentration techniques. The tailing sample was beneficiated by hydrocyclone, tabling, wet high-intensity magnetic separation (WHIMS), and flotation in order to recover the chromite. A chromite concentrate with 45.29wt% Cr₂O₃ and a Cr:Fe mass ratio of 1.85 can be produced from these low-grade chromite ore beneficiation plant rejects.     

Effectiveness of sodium silicate as gangue depressants in iron ore slimes flotation

The recovery of iron from the screw classifier overflow slimes by direct flotation was studied. The relative effectiveness of sodium silicates with different silica-to-soda mole ratios as depressants for silica and silicate bearing minerals was investigated. Silica-to-soda mole ratio and silicate dosage were found to have significant effect on the separation efficiency. The results show that an increase of Fe content in the concentrate is observed with concomitant reduction in SiO₂ and Al₂O₃ levels when a particular type of sodium silicate at a proper dosage is used. The concentrate of 58.89wt% Fe, 4.68wt% SiO₂, and 5.28wt% Al₂O₃ with the weight recovery of 38.74% and the metal recovery of 41.13% can be obtained from the iron ore slimes with 54.44wt% Fe, 6.72wt% SiO₂, and 6.80wt% Al₂O₃, when Na₂SiO₃ with a silica-to-soda mole ratio of 2.19 is used as a depressant at a feed rate of 0.2 kg/t.     

Occurrence mechanism of silicate and aluminosilicate minerals in Sarcheshmeh copper flotation concentrate

The Sarcheshmeh copper flotation circuit is producing 5×104 t copper concentrate per month with an averaging grade of 28% Cu in rougher, cleaner and recleaner stages. In recent years, with the increase in the open pit depth, the content of aluminosilicate minerals increased in plant feed and subsequently in flotation concentrate. It can motivate some problems, such as unwanted consumption of reagents, decreasing of the copper concentrate grade, increasing of Al₂O₃ and SiO₂ in the copper concentrate, and needing a higher temperature in the smelting process. The evaluation of the composite samples related to the most critical working period of the plant shows that quartz, illite, biotite, chlorite, orthoclase, albeit, muscovite, and kaolinite are the major Al₂O₃ and SiO₂ beating minerals that accompany chalcopyrite, chalcocite, and covellite minerals in the plant feed. The severe alteration to clay minerals was a general rule in all thin sections that were prepared from the plant feed. Sieve analysis of the flotation concentrate shows that Al₂O₃ and SiO₂ bearing minerals in the flotation concentrate can be decreased by promoting the size reduction from 53 to 38 μm. Interlocking of the Al₂O₃ and SiO₂ bearing minerals with chalcopyrite and chalcocite is the occurrence mechanism of silicate and aluminosilicate minerals in the flotation concentrate. The dispersed form of interlocking is predominant.     

Mechanism research on arsenic removal from arsenopyrite ore during a sintering process

The mechanism of arsenic removal during a sintering process was investigated through experiments with a sintering pot and arsenic-bearing iron ore containing arsenopyrite; the corresponding chemical properties of the sinter were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES), X-ray diffraction (XRD), and scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS). The experimental results revealed that the reaction of arsenic removal is mainly related to the oxygen atmosphere and temperature. During the sintering process, arsenic could be removed in the ignition layer, the sinter layer, and the combustion zone. A portion of FeAsS reacted with excess oxygen to generate FeAsO₄, and the rest of the FeAsS reacted with oxygen to generate As₂O₃(g) and SO₂(g). A portion of As₂O₃(g) mixed with Al₂O₃ or CaO, which resulted in the formation of arsenates such as AlAsO₄ and Ca₃(AsO₄)₂, leading to arsenic residues in sintering products. The FeAsS component in the blending ore was difficult to decompose in the preliminary heating zone, the dry zone, or the bottom layer because of the relatively low temperatures; however, As₂O₃(g) that originated from the high-temperature zone could react with metal oxides, resulting in the formation of arsenate residues.     

Thermodynamic analysis and preparation of β-SiC/ZrO2 composites

A predominance area diagram for the Zr-Si-C-O system at 1773 K was plotted according to correlative thermodynamic data. β-SiC/ZrO₂ composites were prepared based on the phase diagram by carbothermal reduction of zircon (ZrSiO₄) in argon atmosphere. Zircon and carbon black were mixed according to the C/ZrSiO₄ mass ratio of 0.2, and with 0, 1wt% and 2wt% extra addition of La₂O₃. Phase evolution of the mixture was investigated at 1723-1803 K by X-ray powder diffraction, and the microstructure of the product prepared at 1803 K for 4 h was examined by scanning electronic microscope. The results show that the decomposition of ZrSiO₄ and the formation of β-SIC can be promoted by increasing the heating temperature and adding La₂O₃. The β-SiC/ZrO₂ composites can be prepared at 1803 K for 4 h in a mixture of zircon, carbon black and La₂O₃, and the contents of β-SIC and m-ZrO₂ in the product sample with 2wt% La₂O₃ reach the highest values of 10.8wt% and 89.2wt%, respectively. The crystal size of the products is about 200 nm.     

Effect of interaction of refractories with Ni-based superalloy on inclusions during vacuum induction melting

This study documents laboratory-scale observation of the interactions between the Ni-based superalloy FGH4096 and refractories. Three different crucibles were tested—MgO, Al₂O₃, and MgO–spinel. We studied the variations in the compositions of the inclusions and the alloy–crucible interface with the reaction time using scanning electron microscopy equipped with energy dispersive X-ray spectroscopy and X-ray diffraction. The results showed that the MgO and MgO–spinel crucibles form MgO-containing inclusions (Al–Mg oxides and Al–Mg–Ti oxides), whereas the inclusions formed when using the Al₂O₃ crucible are Al₂O₃ and Al–Ti oxides. We observed a new MgAl₂O₄ phase at the inner wall of the MgO crucible, with the alloy melted in the MgO crucible exhibiting fewer inclusions. No new phase occurred at the inner wall of the Al₂O₃ crucible. We discuss the mechanism of interaction between the refractories and the Ni-based superalloy. Physical erosion was found to predominate in the Al₂O₃ crucible, whereas dissolution and chemical reactions dominated in the MgO crucible. No reaction was observed between three crucibles and the Ti of the melt although the Ti content (3.8wt%) was higher than that of Al (2.1wt%).     

Feasibility of co-reduction roasting of a saprolitic laterite ore and waste red mud

Large scale utilization is still an urgent problem for waste red mud with a high content of alkaline metal component in the future. Laterite ores especially the saprolitic laterite ore are one refractory nickel resource, the nickel and iron of which can be effectively recovered by direct reduction and magnetic separation. Alkaline metal salts were usually added to enhance reduction of laterite ores. The feasibility of co-reduction roasting of a saprolitic laterite ore and red mud was investigated. Results show that the red mud addition promoted the reduction of the saprolitic laterite ore and the iron ores in the red mud were co-reduced and recovered. By adding 35wt% red mud, the nickel grade and recovery were 4.90wt% and 95.25wt%, and the corresponding iron grade and total recovery were 71.00wt% and 93.77wt%, respectively. The X-ray diffraction (XRD), scanning electron microscopy, and energy dispersive spectroscopy (SEM-EDS) analysis results revealed that red mud addition was helpful to increase the liquid phase and ferronickel grain growth. The chemical compositions “CaO and Na₂O” in the red mud replaced FeO to react with SiO₂ and MgSiO₃ to form augite.     

Effect of diboron trioxide on the crushing strength and smelting mechanism of high-chromium vanadium-titanium magnetite pellets

The effect of diboron trioxide (B₂O₃) on the crushing strength and smelting mechanism of high-chromium vanadium-titanium magnetite pellets was investigated in this work. The main characterization methods were X-ray fluorescence, inductively coupled plasma-atomic emission spectroscopy, mercury injection porosimetry, X-ray diffraction, metallographic microscopy, and scanning electron microscopy-energy-dispersive X-ray spectroscopy. The results showed that the crushing strength increased greatly with increasing B₂O₃ content and that the increase in crushing strength was strongly correlated with a decrease in porosity, the formation of liquid phases, and the growth and recrystallization consolidation of hematite crystalline grains. The smelting properties were measured under simulated blast furnace conditions; the results showed that the smelting properties within a certain B₂O₃ content range were improved and optimized except in the softening stage. The valuable element B was easily transformed to the slag, and this phenomenon became increasingly evident with increasing B₂O₃ content. The formation of Ti(C,N) was mostly avoided, and the slag and melted iron were separated well during smelting with the addition of B₂O₃. The size increase of the melted iron was consistent with the gradual optimization of the dripping characteristics with increasing B₂O₃ content.     

Microstructure and electrolysis behavior of self-healing Cu-Ni-Fe composite inert anodes for aluminum electrowinning

The microstructure evolution and electrolysis behavior of (Cu₅₂Ni₃₀Fe₁₈)-xNiFe₂O₄ (x=40wt%, 50wt%, 60wt%, and 70wt%) composite inert anodes for aluminum electrowinning were studied. NiFe₂O₄ was synthesized by solid-state reaction at 950℃. The dense anode blocks were prepared by ball-milling followed by sintering under a N₂ atmosphere. The phase evolution of the anodes after sintering was determined by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The results indicate that a substitution reaction between Fe in the alloy phase and Ni in the oxide phase occurs during the sintering process. The samples were also examined as inert anodes for aluminum electrowinning in the low-temperature KF-NaF-AlF₃ molten electrolyte for 24 h. The cell voltage during electrolysis and the corrosion scale on the anodes were analyzed. The results confirm that the scale has a self-repairing function because of the synergistic reaction between the alloy phase with Fe added and the oxide phase. The estimated wear rate of the (Cu₅₂Ni₃₀Fe₁₈)-50NiFe₂O₄ composite anode is 2.02 cm·a-1.     

Mineralogy and carbothermal reduction behaviour of vanadium-bearing titaniferous magnetite ore in Eastern India

Vanadium-bearing titaniferous magnetite bands hosted by Precambrian gabbro-norite-anorthositic rocks or their metamorphic equivalents were discovered in some parts of Eastern Indian Shield, containing 48%–49% Fe (total), 10%–25% TiO₂, and 0.3%–2.20% V₂O₅ by mass. Mineralogical and petrological study, composition, and characterization of the vanadium-bearing titaniferous magnetite ore were carried out by scanning electron microscopy-energy dispersive X-ray (SEM-EDX), wave length X-ray florescence (WDXRF), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), X-ray diffraction (XRD), etc. Chemical beneficiation for valuable metals, such as Fe, Ti, and V, was performed by reduction roasting. The direct and indirect reduction were investigated by mixing the lump ore with solid activated charcoal in a closed reactor and purging the reducing gas mixture in standard reducibility index apparatus at different temperatures and time intervals. The reduction roasting parameters were optimized. Finally, the reduced samples were crushed and upgraded by magnetic separation. The results show that, the maximum mass fractions of magnetic and nonmagnetic parts achieved are 69.36% and 30.64%, respectively, which contain 10.6% TiO₂ and 0.84% V₂O₅ in the magnetic part and 36.5% TiO₂ and 0.22% V₂O₅ in the nonmagnetic part.     

Preparation of CaO-Al2O3-SiO2 system glass from molten blast furnace slag

To use the potential heat of molten blast furnace slag completely, a CaO-Al₂O₃-SiO₂ system glass (MSG) was prepared from the molten industrial slag. The corresponding method proposed in this study utilized both slag and its potential heat, improving the production rate and avoiding the environmental pollution. Using appropriate techniques, an MSG with uniform color and superior performances was produced. Based on the experimental results and phase diagram, the chemical composition of MSG by mass is obtained as follows: CaO 27%–33%, SiO₂ 42%–51%, Al₂O₃ 11%–14%, MgO 6%–8%, and Na₂O+K₂O 1%–4%. Thermodynamic processes of MSG preparation were analyzed, and the phases and microstructures of MSG were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that alkali metal oxides serve as the fluxes, calcium oxide serves as the stabilizer, and alumina reinforces the Si-O network. XRD and SEM analyses show that, the prepared MSG displays the glass-feature patterns, the melting process is more complete, and the melt viscosity is lowered with an increase in calcium oxide content; however, a continuous increase in slag content induces the crystallization of glass, leading to the formation of glass subphase. The optimum content of molten slag in MSG is 67.37wt%. With respect to bending strength and acid/alkali resistance, the performance of MSG is better than that of ordinary marble.     

Effect of modifying agents on the hydrophobicity and yield of zinc borate synthesized by zinc oxide

The aim of this study was to synthesize zinc borate using zinc oxide, reference boric acid, and reference zinc borate (reference ZB) as the seed, and to investigate the effects of modifying agents and reaction parameters on the hydrophobicity and yield, respectively. The reaction parameters include reaction time (1–5 h), reactant ratio (H₃BO₃/ZnO by mass: 2–5), seed ratio (seed crystal/(H₃BO₃+ZnO) by mass: 0–2wt%), reaction temperature (50–120℃), cooling temperature (10–80℃), and stirring rate (400–700 r/min); the modifying agents involve propylene glycol (PG, 0–6wt%), kerosene (1wt%–6wt%), and oleic acid (OA, 1wt%–6wt%) with solvents (isopropyl alcohol (IPA), ethanol, and methanol). The results of reaction yield obtained from either magnetically or mechanically stirred systems were compared. Zinc borate produced was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and contact angle tests to identify the hydrophobicity. In conclusion, zinc borate is synthesized successfully under the optimized reaction conditions, and the different modifying agents with various solvents affect the hydrophobicity of zinc borate.     

镍基合金CMSX-4在3.5wt.% NaCl溶液中的腐蚀行为

研究二代镍基合金CMSX-4在质量分数为3.5% NaCl溶液中的腐蚀行为,对该类合金在海洋性环境条件下的应用具有深远意义。通过动电位极化方法研究室温条件下镍基合金CMSX-4在3.5 wt.% NaCl溶液中的电化学行为,利用扫描电子显微镜（SEM）、能谱分析仪（EDS）和X射线光电子能谱仪（XPS）对合金表面阳极腐蚀产物进行微观形貌观察及成分分析。研究表明,CMSX-4合金具有一定的钝化能力,钝化区间比较宽广;在镍基合金CMSX-4表面上形成的腐蚀产物可大致分为两层,表层主要由Ni （OH）₂、Cr （OH）₃、Co （OH）₂和Al （OH）₃等氢氧化物组成,内层主要分布着NiO、Al₂O₃、CoO、Cr₂O₃和CrO₃等氧化物及组成合金基体的各种金属;由Ni （OH）₂和Cr （OH）₃等氢氧化物组成的腐蚀产物膜外层能够在腐蚀介质和金属之间产生较好的屏蔽效果;构成腐蚀产物膜内层的NiO、Al₂O₃、Cr₂O₃和CrO₃等氧化物有利于产物膜内层与外层之间建立一定的空间电荷区,对稳定腐蚀产物内层有很大帮助。研究表明CMSX-4合金在海洋性环境中具有一定的耐蚀性能。     

络合试剂对溶胶凝胶燃烧法合成LaCoO3的物化性能及对VOCs催化净化效果的影响

分别以甘氨酸、柠檬酸和丙烯酰胺辅助柠檬酸为络合试剂,采用溶胶凝胶燃烧法合成LaCoO_3复合氧化物,并对它们进行XRD、BET、SEM及O_2-TPD分析.实验结果表明,三种络合剂制备得到的产物均为纯钙钛矿LaCoO_3相;丙烯酰胺辅助柠檬酸溶胶凝胶燃烧法制得的LaCoO_3颗粒均匀且较小,比表面积最大,其O_2-TPD曲线中的峰面积最大,对苯完全催化氧化效果最好.     

In situ reaction mechanism of MgAlON in Al-Al2O3-MgO composites at 1700℃ under flowing N2

The Al-Al₂O₃-MgO composites with added aluminum contents of approximately 0wt%, 5wt%, and 10wt%, named as M₁, M₂, and M₃, respectively, were prepared at 1700℃ for 5 h under a flowing N₂ atmosphere using the reaction sintering method. After sintering, the Al-Al₂O₃-MgO composites were characterized and analyzed by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The results show that specimen M₁ was composed of MgO and MgAl₂O₄. Compared with specimen M₁, specimens M₂ and M₃ possessed MgAlON, and its production increased with increasing aluminum addition. Under an N₂ atmosphere, MgO, Al₂O₃, and Al in the matrix of specimens M₂ and M₃ reacted to form MgAlON and AlN-polytypoids, which combined the particles and the matrix together and imparted the Al-Al₂O₃-MgO composites with a dense structure. The mechanism of MgAlON synthesis is described as follows. Under an N₂ atmosphere, the partial pressure of oxygen is quite low; thus, when the Al-Al₂O₃-MgO composites were soaked at 580℃ for an extended period, aluminum metal was transformed into AlN. With increasing temperature, Al₂O₃ diffused into AlN crystal lattices and formed AlN-polytypoids; however, MgO reacted with Al₂O₃ to form MgAl₂O₄. When the temperature was greater than (1640 ±10)℃, AlN diffused into Al₂O₃ and formed spinel-structured AlON. In situ MgAlON was acquired through a solid-solution reaction between AlON and MgAl₂O₄ at high temperatures because of their similar spinel structures.     

Phase transformation behavior of titanium during carbothermic reduction of titanomagnetite ironsand

The reduction of titanomagnetite (TTM) ironsand, which contains 11.41wt% TiO₂ and 55.63wt% total Fe, by graphite was performed using a thermogravimetric analysis system under an argon gas atmosphere at 1423–1623 K. The behavior and effects of titanium in TTM ironsand during the reduction process were investigated by means of thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. During the reduction procedure, the titanium concentrated in the slag phase, where the phase transformation followed this sequence: FeO + FeTiO₃ → Fe₂TiO₄ → FeTiO₃ → FeTi₂O₅ → TiO₂. The calculated results for the reduction kinetics showed that the carbothermic reduction was controlled by the diffusion of ions through the product layer. Furthermore, the apparent activation energy was 170.35 kJ·mol-1.     

Magnetic and flotation studies of banded hematite quartzite (BHQ) ore for the production of pellet grade concentrate

To identify and establish beneficiation techniques for banded hematite quartzite (BHQ) iron ore, a comprehensive research on BHQ ore treatment was carried out. The BHQ ore was assayed as 38.9wt% Fe, 42.5wt% SiO₂, and 1.0wt% Al₂O₃. In this ore, hematite and quartz are present as the major mineral phases where goethite, martite, and magnetite are present in small amounts. The liberation of hematite particles can be enhanced to about 82% by reducing the particle size to below 63 μm. The rejection of silica particles can be obtained by magnetic and flotation separation techniques. Overall, the BHQ ore can be enriched to 65.3wt% Fe at 61.9% iron recovery. A flowsheet has been suggested for the commercial exploitation of the BHQ ore.