Mineral Phase Transformation Research Articles

Density functional theory study on vanadium selective leaching separation from iron in stone coal via Fe2O3 (001) surface passivation

When vanadium is extracted from stone coal, iron impurities readily precipitate and reduce the purity of the vanadium product. Thus, separating vanadium from iron impurities at source is essential. The mechanism of surface passivation of Fe2O3 (001) for the selective leaching separation of vanadium from iron in stone coal was established in the present work. Analysis of mineral phase transformation and microscopic morphology indicates that Fe2O3 in stone coal can undergo a reaction with HF and F-. Subsequently, the hematite surface was covered with FeF3 passivation layer, resulting in the inhibition of hematite dissolving reaction. The results of density functional theory (DFT) computations demonstrate that the HF and F- can reform the Fe2O3 (001) surface via sedimentary behavior at mineral interface, and the adsorption energy can be down to -99.93kJ/mol for the F- adsorption configuration. During sulfuric acid leaching with CaF2 as an aiding agent, the transfer of electrons from Fe atoms to F atoms can weaken the stable Fe-F bonds and decrease the reactive activation of Fe atoms in Fe2O3. This study demonstrates the separation of vanadium from iron by means of hematite passivation in the attendance of fluoride at the atomic level of analysis.

Adsorption characteristics of As(III) by schwertmannite: new findings in mineral-phase transformation and microbial effects

The amount of As(III) adsorbed and the interfacial process are closely associated with the phase transformation of Schwertmannite (SCH). At present, studies on the adsorption characteristics of As(III) on SCH and the accompanying phase transformation process, especially the related mechanisms under the mediation of iron-reducing bacteria (FeRB) and sulfate-reducing bacteria (SRB), are limited in existing literature. With the help of continuous characterization, the adsorption behavior of As(III) on SCH was explored, as well as the transformation processes of SCH during these processes. The findings revealed that the SCH, synthesized by the KMnO4 oxidation and ethanol modification methods, exhibited excellent physical adsorption capacity for As(III) due to their increasing specific surface area and porosity. At room temperature (20°C), the saturation adsorption capacities of As(III) by M-SCH and Y-SCH reached 62.69 and 58.62 mg/g, respectively. Moreover, the generation and phase transformation of As(III)-bearing ferrihydrite were observed within a 60-min timeframe. It is the first time this phenomenon has been observed in such a short time, which is presumed to be an intermediate stage in the transformation of SCH into goethite. Furthermore, both FeRB and SRB could enhance the adsorption capacity of SCH for As(III). Comparatively, SRB has a more substantial impact on SCH’s phase transformation. These insights are valuable for the practical application of SCH in treating As(III) pollution.

Exploring microwave activation as a novel method for activating coal gangue: Focus on microwave activation mechanisms and hydration characteristics of cementitious supplementary materials

To support the decarbonization of the cement industry, coal gangue (CG) has potential as a supplementary cementitious material. The calcination process significantly impacts the phase transformation of clay minerals and the pozzolanic activity of CG. This study involved calcination of CG at 600 ℃ and 800 ℃ using both microwave and thermal activation methods. Employ XRD, XPS, FTIR, TG, and SEM to examine the impact of calcination mechanism on the crystal structure, element binding energy, chemical bonds, microstructure, and mineral composition of CG. The results indicate that the transformation of kaolinite in CG to metakaolin is completed around 600 °C. Microwave activation increased the reactive aluminate content in CG, enhancing pozzolanic activity and promoting secondary hydration with cement. This process generated additional C-(A)-S-H gels and AFm phases, which filled matrix pores, increased system density, and improved mechanical properties. The optimal activation method for CG was identified as microwave activation at 600 °C.

Hydrogen-based mineral phase transformation mechanism investigation of pyrolusite ore

Hydrogen-based mineral phase transformation mechanism investigation of pyrolusite ore

Hydrogen-based mineral phase transformation of bastnaesite: Detailed assessment of physicochemical properties and flotation behavior

Iron-bearing rare earth ores are valuable mineral resources, and the hydrogen-based mineral phase transformation (HMPT) process has significant development potential. In this study, the changes in physicochemical properties and flotation behavior of bastnaesites subjected to HMPT were investigated. The results show that bastnaesite decomposed slowly below 600 °C, but increased roasting temperature and time enhanced the decomposition, resulting in a roasted product with over 85 % rare earth oxide (REO) grade. HMPT also increased the initial pH of the flotation pulp from about 7.5 to 11.0 and increased La and Ce ion concentrations. By increasing the dosage of SHA, flotation recoveries comparable to the raw ore can be achieved. The HMPT process converted bastnaesite to REOF, which formed complex phases such as Ce7O12 and REF3 when exposed to air. This process resulted in significant damage to the particle structure, increased porosity, reduced geometric particle size, and improved wettability. After HMPT, Ce on the particle surface existed predominantly as Ce4+, which formed Ce(OH)4 precipitation during flotation, inhibiting SHA adsorption. The increased particle porosity facilitated deeper SHA penetration and greater adsorption, resulting in higher SHA dosage compared to the raw ore.

A zero-carbon emission approach for the reduction of refractory iron ores: Mineral phase, magnetic property and surface transformation in hydrogen system

In this study, a feasible strategy, named hydrogen mineral phase transformation (HMPT) technology, is proposed and employed to achieve efficient and clean recovery of Hainan Shilu refractory iron ore (HSRIO). The influences of HMPT roasting temperature, roasting time, and H2 concentration on the separation index of HSRIO are investigated. Under the optimal experimental conditions, the iron concentrate grade increases from 62.5% to 67.9%, and the iron recovery increases from 65.0% to 94.7% compared with the original beneficiation process. In addition, the evolution of mineral phases, magnetic properties, and mineral microstructures is analyzed using XRD, VSM, SEM, and high-temperature hot-stage microscopy. It is revealed that the transformation of hematite to magnetite occurs during the HMPT process, with the newly formed magnetite exhibiting a loose and porous reticulation structure. This study is of guiding significance for the development of Hainan Shilu refractory iron ore with high efficiency and zero-carbon emission.

A Novel Biomineralized Collagen Liquid Crystal Hydrogel Possessing Bone-like Nanostructures by Complete In Vitro Fabrication.

The microstructure of bone consists of nano-hydroxyapatite (nano-HA) crystals aligned within the interspaces of collagen fibrils. To emulate this unique microstructure of bone, this work applied two biomimetic techniques to obtain bone-like microstructures in vitro, that is, combining the construction of collagen liquid crystal hydrogel (CLCH) with the application of a polymer-induced liquid precursor (PILP) mineralization process. Upon the elevation of pH, the collagen macromolecules within the collagen liquid crystal (CLC) were activated to self-assemble into CLCH, whose fibrils packed into a long and dense fiber bundle in high orientation, emulating the dense-packed matrix of bone. We demonstrated that the fibrillar mineralization of CLCH, leading to a bone-like nanostructured inorganic material part, can be achieved using the PILP crystallization process to pre-mineralize the dense collagen substrates of CLCH with CaCO3, immediately followed by the in situ mineral phase transformation of CaCO3 into weak-crystalline nano-HA. The combination of CLCH with the biomineralization process of PILP, together with the mineral phase transformation, achieved the in vitro simulation of the nanostructures of both the organic extracellular matrix (ECM) and inorganic ECM of bone. This design would constitute a novel idea for the design of three-dimension biomimetic bone-like material blocks for clinical needs.

Phase transformation of schwertmannite in paddy soil under different water management regimes and its impact on the migration of arsenic in soil

Schwertmannite (Sch) holds a great promise as an iron material for remediating Arsenic (As)-contaminated paddy soils, due to its extremely high immobilization capacities for both arsenate [As(V)] and arsenite [As(III)]. However, there is still limited knowledge on the mineral phase transformation of this metastable iron-oxyhydroxysulfate mineral in paddy soils, particularly under different water management regimes including aerobic, intermittent flooding, and continuous flooding, and how its phase transformation impacts the migration of As in paddy soils. In this study, a membrane coated with schwertmannite was first developed to directly reflect the phase transformation of bulk schwertmannite applied to paddy soils. A soil incubation experiment was then conducted to investigate the mineral phase transformation of schwertmannite in paddy soils under different water management regimes and its impact on the migration of As in paddy soil. Our findings revealed that schwertmannite can persist in the paddy soil for 90 days in the aerobic group, whereas in the continuous flooding and intermittent flooding groups, schwertmannite transformed into goethite, with the degree or rate of mineral phase transformation being 5% Sch >1% Sch > control. These results indicated that water management practices and the amount of schwertmannite applied were the primary factors determining the occurrence and degree of mineral transformation of schwertmannite in paddy soil. Moreover, despite undergoing phase transformation, schwertmannite still significantly reduced the porewater As (As(III) and As(V)), and facilitated the transfer of non-specifically adsorbed As (F1) and specifically adsorbed As (F2) to amorphous iron oxide-bound As (F3), effectively reducing the bioavailability of soil As. These findings contribute to a better understanding of the mineralogical transformation of schwertmannite in paddy soils and the impact of mineral phase transformation on the retention of As in soil, which carry important implications for the application of schwertmannite in remediating As-contaminated paddy soils.

Sulfidation of Cd-Sch during the microbial sulfate reduction: Nanoscale redistribution of Cd

Schwertmannite (Sch) is found in environments abundant in iron and sulfate. Microorganisms that utilize iron or sulfate can induce the phase transition of Schwertmannite, consequently leading to the redistribution of coexisting pollutants. However, the impact of the molar ratio of sulfate to iron (S/Fe) on the microbial-mediated transformation of Schwertmannite and its implications for the fate of cadmium (Cd) have not been elucidated. In this study, we examined how S/Fe influenced mineral transformation and the fate of Cd during microbial reduction of Cd-loaded Schwertmannite by Desulfovibrio vulgaris. Our findings revealed that an increase in the S/Fe ratio facilitated sulfate-reducing bacteria (SRB) in mitigating the toxicity of Cd, thereby expediting the generation of sulfide (S(-II)) and subsequently triggering mineral phase transformation. As the S/Fe ratio increased, the predominant minerals in the system transitioned from prismatic-cluster vivianite to rose-shaped mackinawite. The Cd phase and distribution underwent corresponding alterations. Cd primarily existed in its oxidizable state, with its distribution being directly linked not only to FeS content but also showing a robust correlation with phosphorus. The coexistence of vivianite and FeS minerals proved to be more favorable for Cd immobilization. These findings have significant implications for understanding the biogeochemistry of iron (oxyhydr)oxides and Cd fate in anaerobic environments.

An innovative process for recovery of ilmenite using mineral phase transformation followed by magnetic separation

Recovery of fine ilmenite is challenging, resulting in significant waste of titanium resources. In this paper, the mineral phase transformation technology was proposed to strengthen the surface magnetism of fine ilmenite. The results demonstrated that in the oxidation stage, the suitable oxidation temperature was 700 °C and the oxidation time was 30 min. In the reduction stage, the ideal reduction temperature was 575 °C, the CO concentration was 20 %, and the reduction time was 3 min. Under the optimized roasting conditions, the roasted sample was separated by staged low-intensity magnetic separation, and titanium concentrate with a TiO2 grade of 46.24 % and recovery of 67.62 % was obtained. The XRD, SEM and VSM analysis implied that the oxidation products of ilmenite were hematite and rutile, where hematite was enriched on the surface of the particles and formed a layer of 2–5 μm. After reduction roasting, the hematite layer was directionally transformed into magnetite, which significantly enhanced the magnetism of the particles and created conditions for the recovery of titanium by low-intensity magnetic separation.

Preparation of superior magnetite concentrate from waste tailings with clean energy: Semi-industrial utilization, economic profits, and environmental benefits

The effective utilization and clean recycling of tailings are important to solve land occupation and waste mine pollution problems. A semi-industry experiment of hydrogen-based mineral phase transformation for tailings is conducted with a roasting temperature of 500 °C, a reducing gas concentration of 20 %, a total gas volume of 12 m3/h, and a handing capacity of 100 kg/h. A concentrate product with an iron grade of 66.75 % and a recovery of 82.79 % was obtained. The detail roasted iron phases of 23.96 % Fe3O4 (A) and 47.93 % Fe3O4 (B) were obtained. The maximum saturation magnetization increased from 6.69 to 18.96 A·m2·kg−1 after roasting. The surface of Fe3O4 occurred on the iron mineral surface. The SEM-EDS results showed the order of reduce behavior. In addition, the pollutions of the roasting process were controlled strictly, and the final benefit was calculated to be $33.86 million.

Fluidization characteristics of ore particles for downstream hydrogen mineral phase transformation equipment

Fluidized roasting is an effective way to deal with refractory iron ores. Fluidization is a prerequisite for the effective occurrence of physical and chemical reactions. This article conducts cold state experiments on Single-layer Overflow type Reaction Chamber, using hematite ore and quartz as bulk particles，processing pressure drop signals to analyze and explain gas-solid motion. The results indicate that the gas flow average pressure drop being stable is the criterion for the fluidized bed, the bulk properties significantly affect the critical fluidization characteristics. Pressure drop pulsation is an important characteristic of fluidized bed, fluidized gas velocity, initial bed height, and bulk properties all affect the amplitude of bed pressure drop pulsation, and the spectrum analyses of bed pressure drop signals all exhibit “High-energy and Low-frequency”. This study has certain guiding significance for the structural design optimization and engineering scaling of Downstream Hydrogen Mineral Phase Transformation Equipment.

Green approach for separating iron and rare earths from complex polymetallic solid residues via hydrogen-based mineral phase transformation: A pilot-scale study

The Bayan Obo low-grade polymetallic ore (BOLPO) has been abandoned for many years owing to its difficult beneficiation and remains as a solid residue. This is causing significant ecological damage to the surrounding environment. In this pilot-scale study, hydrogen-based mineral phase transformation (HMPT) technology and associated equipment were used to successfully separate iron and rare earths from BOLPO, demonstrating stable operation for 48 h. Optimal HMPT conditions included a feed rate of 120 kg/h, HMPT temperature of 500 °C, gas flow rate of 3.5 m3/h and gas concentration of 22.5 vol%. After grinding and flotation defluorination, the obtained iron concentrate had a TFe grade of 65.26 wt%, a recovery of 85.29 wt%, and a low F grade of 0.28 wt%. Product analysis revealed phase transformations of iron and rare earths during the HMPT process, which increased the magnetic difference between the magnetic and non-magnetic products. The formation of pores and cracks during this process also facilitates the subsequent separation of iron and rare-earths. This study paves the way for clean and efficient iron and rare earth separation with regional mineral recovery potential.

Comprehensive recycling of slag from the smelting of spent automotive catalysts

Spent automotive catalyst is a valuable source of platinum group metals (PGMs), making them crucial secondary resources. Currently, the main process for recovering PGMs from these catalysts is metal capture method. The smelting process would produce a significant amount of residual slags containing various components like SiO2, Al2O3, CaO, Fe2O3, Na2O, as well as high levels of heavy metals including Cr, Pb, and Ni. These slags are considered either solid waste or hazardous waste and usually disposed of in landfills, which can have detrimental effects on the environment. Furthermore, the smelting slags also contain approximately 2–5 % rare earth elements and trace amounts of precious metal elements. In this study, vacuum carbothermal reduction is employed to pretreat the smelting slags. This method not only successfully removes the heavy metal element lead, but also efficiently achieves the recovery of rare earths, and the enrichment of platinum group metals by mineral phase transformation of cerium-zirconium solid solution and in-situ iron capture. The lead removal rate exceeded 99 %, and the grade of precious metals in the enrichment process was approximately 12 times higher than the original material, with a recovery rate more than 90 %. The leaching rate of rare earths also increased from less than 50 % to more than 95 % after vacuum carbothermal reduction. The effect of vacuum carbothermal reduction pretreatment on the smelting slag phase was systematically studied, and the mechanism behind the increasing rare earth leaching rate due to this pretreatment was further analyzed.

High efficiency separation of bastnaesite (REFCO3) and monazite (REPO4) in mixed rare earth concentrate by heating under N2 and leaching with HCl/AlCl3

Bayan Obo mixed rare earth (RE) concentrate is one of the most significant rare earth mineral resources worldwide. However, the concentrated sulfuric acid roasting method, which is commonly used to treat ores, generates pollutants such as waste gas, wastewater, and leach residue, resulting in the squandering of the associated resources. This paper introduces a green process involving selective mineral phase transformation (MPT) by heating, followed by leaching to separate bastnaesite and monazite in a mixed RE concentrate to facilitate their subsequent decomposition or extraction. The effects of the MPT conditions on rare earth extraction were investigated. During the MPT process, bastnasite decomposed into REOF, which is more easily leached, whereas monazite remained unchanged. Under suitable conditions, the leaching efficiency of REOF reached 93.7%, while that of monazite (REPO4) was only 3.2%. Furthermore, the content of monazite in the leach residue was 91.2%. Compared to the mixed RE concentrate, numerous cracks and pores were generated on the surface and inside the MPT products. Furthermore, the total pore volume and specific surface area significantly increased, which made the reaction between the MPT products and hydrochloric acid more efficient. Thus, the MPT process facilitated the leaching of bastnasite and its separation from monazite.

Isothermal and non-isothermal decomposition mechanisms of bastnaesite during the hydrogen-based mineral phase transformation

The hydrogen-based mineral phase transformation-flotation process can realize the efficient development of iron-bearing rare earth ores. The isothermal and non-isothermal decomposition mechanisms of bastnasite in the hydrogen atmosphere were studied to optimize the hydrogen-based mineral phase transformation process. The thermal decomposition of bastnasite first produced REOF, which would react with oxygen to produce rare earth oxides and fluorides during the analysis process. The thermal decomposition was an endothermic reaction, and the generated gas were mainly CO2 and trace CO, with a mass loss of about 20%. Increasing the temperature can greatly promote the thermal decomposition. After thermal decomposition, the particles showed a layered structure, and many parallel slits run through the particles. The porosity and specific surface area of the particles were significantly improved. The apparent activation energy of isothermal decomposition was 71.80 ± 5.40 kJ/mol, and the kinetic mechanism was random nucleation and growth model (n = 2). The apparent activation energy of non-isothermal decomposition was 201.96 kJ/mol, and the kinetic mechanism was phase-boundary controlled reaction mechanism (n ≈ 2).

Green iron recovery through hydrogen-based mineral phase transformation using ultrafast air-cooling for heat recycling: A pilot-scale investigation

The utilization of ultrafast air-cooling has been proposed to reduce energy consumption in hydrogen-based mineral phase transformation (HMPT) technology for more sustainable iron recovery. Optimal conditions, including a grinding fineness of −74 μm accounting for 90 wt%, a reducing gas concentration of 20 vol%, a roasting temperature of 540 °C, and an air-cooling temperature of 300 °C, yielded an iron concentrate with a TFe grade of 59.29 wt% and a recovery of 89.40 wt%. The beneficiation indexes obtained by ultrafast air-cooling were comparable to those of the N2-cooling method. The reaction mechanisms were comprehensively studied to optimize the process, which revealed controlled oxidation of artificial magnetite to maghemite and hematite under ultrafast air-cooling conditions. The heat released during oxidation was recycled, leading to reduced energy consumption. Furthermore, ultrafast air-cooling increased particle porosity and cracks, thereby reducing subsequent grinding energy requirements. This research advances carbon reduction efforts in the steel industry, facilitating the transition to carbon neutrality.

Hydration and properties of hydrogen-based mineral phase transformation iron ore tailings as supplementary cementitious material

Almost all iron ore tailings (IOTs) required activation prior to use as SCMs, which limited their application in building materials. This study investigated HMPT-IOTs and discovered that they possess latent hydraulic and pozzolanic properties. In order to better utilize as SCM, mechanical properties, hydration reactions, hydration products, microstructure, and pores were comprehensively studied through mechanical tests, hydration heat tests, XRD, SEM, TG, and MIP. The results show that when HMPT-IOTs replace cement at 10 wt%, 20 wt% and 30 wt%, the compressive strength at 28 days is 41.9 MPa, 47.9 MPa and 37.5 MPa, respectively. When the substitution amount reaches 30 wt%, it will reduce the cumulative heat of hydration and promote early hydration reactions. The main hydration products are ettringite and Ca(OH)2. As the nucleation site of C–S–H, hydration products are interconnected, making the microstructure denser. At this substitution level, Ca(OH)2 consumption was about 2% at 28 days of age. Simultaneously, the total pore volume was only 0.01 mL/g greater than that of the control group, and the number of micropores and transition pores decreased by approximately 3%.

Novel process for facile preparation of mesoporous silica-based materials with controllable pore structure from coal fly ash

Extraction of silica from fly ash to produce mesoporous silica materials is one of the most important utilization approaches. Mesoporous silica could not be synthesized on a large-scale by conventional sol-gel method. In this paper, facile preparation of mesoporous silica with controllable pore structure from fly ash by the template-free process via two steps of mineral phase transformation and selective acid etching was proposed. The influence of crystalline structure and acid etching degree on structure of as-synthesized mesoporous silica materials was revealed, as well as mechanism of crystalline structure transformation and pore structure formation. The results show that mullite and quartz could be transformed into acid-soluble kaliophilite when fly ash reacted with K2CO3 at temperature of 800–1100 °C. The hexagonal kaliophilite would be transformed into orthorhombic KAlSiO4–O1 phase when the temperature is controlled at 1100 °C. Mesoporous silica with specific surface area of 475.93 m2/g and 642.57 m2/g could be synthesized from activated fly ash with kaliophilite and KAlSiO4–O1 phase crystalline structure. By controlling the degree of acid etching, mesoporous silica materials with different pore structures can be obtained. This paper provides a cost-effective and large-scale process for the preparation of mesoporous silica materials with controllable pore structure from solid waste fly ash.

Magnetic separation for recovering iron resources from acid-leaching tailings of laterite nickel ore through mineral phase transformation

The acid-leaching tailings of laterite nickel ore is a typical hazardous waste in the laterite nickel ore industry. The current treatment involves stacking and landfills, which leads to considerable environmental pollution and resource wastage. The reduction of hazardous waste and the recovery of iron resources have environmental and economic value. In this study, a mineral phase transformation technology was proposed. The suitable transformation conditions were 700 ℃, 30 min, and 30 % CO, and optimal grinding and magnetic conditions were −37 μm content 92.42 % and 143.35 kA·m−1, respectively. Then the iron grade and recovery reached 52.00 % and 80.11 %, respectively. Meanwhile, hematite has converted into strongly magnetic magnetite with saturation magnetization increased from nearly 0 A·m2·kg−1 to 28.49 A·m2·kg−1. And particles transformed from dense to a porous honeycomb structure. Therefore, the mineral phase transformation achieves recovering iron resources during reducing hazardous waste. It proposed a new way of resource utilization of laterite nickel ore acid-leaching tailings which has positive environmental and resource benefits.