Search

Electroplating sludge is a typical heavy metal-containing hazardous waste with tens of millions of tons produced annually in China. Acid leaching is the most common method to extract valuable heavy metals for resource recycling and environmental protection. However, the coexisting elements, which are released from electroplating sludge to the leaching solution, will hinder the recycling of valuable heavy metals. In this work, dynamic acid-leaching experiments, X-ray diffraction analysis, and simulation calculations were conducted. It was found that coexisting elements (mainly Ca, Fe, and Al) account for a large proportion, and calcium salts as coexisting mineral phase (especially CaCO3) are ubiquitous in electroplating sludge. Moreover, the evolution of coexisting mineral phase plays an essential role in the acid-leaching process: (1) the dissolution of CaCO3 contributed a strong acid-neutralization capability and released Ca2+; (2) H2SO4 is the optimal extracting reagent, since it triggered the transformation of calcium salts to CaSO4·2H2O, reducing the Ca2+ concentration; (3) the coexisting elements Fe and Al would form ferrous and aluminum salt minerals with the acid-leaching process, which reduces the leaching of low-value elements. This work provides a new perspective on the acid-leaching mechanism of electroplating sludge, where the evolution of the mineral phase effect the release of valuable heavy metals and coexisting elements. This work also provides as comprehensive information as possible on electroplating sludge and inspires the improvement of the acid-leaching method. [ABSTRACT FROM AUTHOR]

In recent years, the rapid development of the domestic alumina industry has greatly accelerated the consumption of high-alumina–silica-ratio bauxite resources in China. The development of an efficient and clean utilization technology applicable to low-grade bauxite in China is not only a requirement for resource and environmental protection, but also a powerful guarantee to maintain the sustainable development of China's aluminum industry. Based on this, the authors' team proposed a new process for the treatment of low-grade bauxite ore via a calcification–carbonization method from the perspective of equilibrium solid-phase reconstruction and achieved the first industrial-scale trial run on the basis of existing laboratory research. The results show that the mass fraction of Na2O in bauxite residue can be reduced to 0.95% in the treatment of typical diaspore bauxite, the A/S in the bauxite residue can be reduced to 0.85 after two-time carbonization–alumina dissolution, and the actual alumina dissolution rate can reach 81.32%. The relevant results verified the feasibility and advantages of the calcification–carbonization method in industrial production. [ABSTRACT FROM AUTHOR]

Pyrite is common in coal gangue formed in a reduced environment and has a significant influence on the recycling utilization of coal gangue. Four types of pyrite with different structures and morphologies, namely octahedral pyrite framboid, pentagonal dodecahedral pyrite framboid, irregular grain pyrite, and euhedral octahedral crystalline pyrite, were selected from coal gangue to study their thermal behavior and phase transformation processes during heat treatments in different atmosphere via high-temperature XRD, TG-DSC, SEM-EDS, and XRF. The results show that pyrite in coal gangue can be decomposed into pyrrhotite when heated in an inert atmosphere. Pyrites with different morphologies and structures exhibit distinct thermal behavior. The higher S/Fe ratio promotes the better crystallinity of pyrite and thus lowers the phase transformation temperature from pyrite to pyrrhotite. The thermal decomposition temperature of the sulfur-rich and well crystalline pyrites was approximately 600 °C, and the transformation temperature of sulfur-deficit pyrites to pyrrhotite was approximately 640 °C. The S release rate from the former two pyrites was also slower than that from the latter two. The pyrites can be oxidized to nano-hematite when heated in an air atmosphere at above 400–500 °C, with the transformation proceeding in the sequence of pyrite–nano-microsphere magnetite–nano-microsphere hematite. The nano-hematite aggregates had a pseudomorph of the original pyrite crystals. This study has great significance for the high-level recycling utilization of coal gangue, such as iron removal and direct material. [ABSTRACT FROM AUTHOR]

The purpose of this study was to fully realize the clinical plausibility of a newly introduced yttria gradient monolithic multilayer dental zirconia and the current indication range for dental zirconia; hence, an investigation leading to a comprehensive understanding of the effect of yttria content on the properties of zirconia was undertaken. Each layer from a yttria gradient monolithic multilayer zirconia system with two types (esthetic and functional types, Meiying Zirconia, UPCERA, China) was selected for investigation of its chemical composition by X-ray fluorescence. Layers with yttria content interval of about 0.4 mol%-0.5 mol% were chosen for subsequent testing. Their phase fractions, grain sizes, low-temperature degradation (LTD) resistance, coefficient of thermal expansion (CTE), and mechanical properties were characterized. The yttria content from the occlusal to the gingival region was from 5 mol% to 4.1 mol% and 4.7 mol% to 3.2 mol% for esthetic type and functional type, respectively. Ultimately, we investigated the selected five yttria content layers, 5Y, 4.5Y, 4Y, 3.6Y, and 3.2Y. With increased yttria content, increasing cubic phase fractions (from 25.86 wt% to 58.53 wt%) and mean grain sizes (from 0.31 μm to 0.72 μm) were detected; monoclinic content after LTD decreased; and there was a decreasing tendency for CTE, although no statistically significant difference was found (F = 2.43, p = 0.117). In addition, yttria dopant showed no effect on elastic modulus (F = 2.43, p = 0.464) but slightly increased hardness (F = 4.10, p = 0.014). However, there were notable decreases in fracture toughness (F = 227.58, p < 0.001), biaxial flexural (F = 52.31, p < 0.001), and fatigue strength (F = 56.52, p < 0.001). The percentages of strength degradation from monotonic to fatigue tests were about 33%–40%, independent of yttria doping (F = 1.82, p = 0.136). [ABSTRACT FROM AUTHOR]

Monolayer transition metal dichalcogenides can normally exist in several structural polymorphs with distinct electrical, optical, and catalytic properties. Effective control of the relative stability and transformation of different phases in these materials is thus of critical importance for applications. Using density functional theory calculations, we investigate the effects of low-work-function metal substrates including Ti, Zr, and Hf on the structural, electronic, and catalytic properties of monolayer MoS2 and WS2. The results indicate that such substrates not only convert the energetically stable structure from the 1H phase to the 1T′/1T phase, but also significantly reduce the kinetic barriers of the phase transformation. Furthermore, our calculations also indicate that the 1T′ phase of MoS2 with Zr or Hf substrate is a potential catalyst for the hydrogen evolution reaction. [ABSTRACT FROM AUTHOR]

Vanadium (V), as a strategic metal, plays an important role in national security, economy, and infrastructure construction. The V-bearing shale ore should be vigorously developed in China because its' vanadium reserves of 87% of the total. To solve the problem of environmental issues and high production cost problems in the traditional V extraction method for shale ore, oxidation roasting pretreatment with efficient and clean properties was proposed in this work. A V 2 O 5 leaching efficiency of 94.33% was obtained under the pretreatment conditions of a roasting temperature of 700 °C, roasting time of 2 h, and particle size with −74 μm fraction of 80 wt%. The muscovite crystal was destroyed and the V was released from Al-O octahedral in the oxidation roasting process. Additionally, cracks and holes appeared on the surface of ore particles, which are conducive to the following acid leaching. The leaching residue was suitable for making silica fumes as a building material. Based on this study, a sustainable and high-efficient exploitation method was provided for the comprehensive utilization of V-bearing shale ore resources. [ABSTRACT FROM AUTHOR]

• Polyhalite ore started to decompose into anhydrite and langbeinite at 573 K. • The changes of internal models of vibration of SO 4 indicated a phase transformation. • The most probable mechanism function matched D3 Janders diffusion mechanism. • Calcination and hot-leaching could improve the extraction of potassium. In this paper, the thermal decomposition of polyhalite ore from Dayantan Playa in Qaidam Basin of China was investigated by X-ray powder diffractometry (XRD), Raman spectroscopy (Raman), and thermal analysis techniques (TG-DTG). The dehydration reaction of polyhalite ore takes place with the release of water and starts at about 510 K. The results of X-ray diffraction of roasting sample showed that polyhalite ore starts to decompose into anhydrite and langbeinite at 573 K. Raman spectroscopy, in conjunction with X-ray diffraction, was also used to follow the thermal decomposition of polyhalite ore. The changes of internal models of vibration of the SO 4 ions in sulfates indicated the phase transformation polyhalite, langbeinite, and anhydrite. The reaction kinetics of thermal decomposition of polyhalite ore were successfully modeled by a Coats-Redfern equation (ln g (α) T 2 = ln A R β E 1 − 2 R T E − E R T ) and the activation energy is found to be 208 kJ·mol−1. Additionally, the effect of roasting temperature on potassium extraction from polyhalite ore was studied. [ABSTRACT FROM AUTHOR]

• Using Modern technology to study the change of Vanadium-bearing shale after roasting. • Suspension oxidation roasting pretreatment as a novel technology was proposed. • The muscovite lattice expands under the influence of stress at high temperature. • Porous structure can improve oxidation rate of V(III). Vanadium is an important rare metal element. In China, a large amount of vanadium resources is stored in shale ore. Muscovite-type vanadium shale is a typical refractory vanadium ore. In production, roasting pretreatment is an effective method to enhance the vanadium extraction efficiency from muscovite-type vanadium shale. In this paper, the mechanism of enhanced vanadium extraction by suspension oxidation roasting pretreatment was investigated. A vanadium leaching rate of 75.24 % was obtained under the conditions: roasting temperature of 900 °C, roasting time of 3 h, the total gas flow of 600 mL/min, and air atmosphere, the roasted product was leached at leaching temperature of 65 °C, leaching time of 4 h, the acid dosage of 10 wt%, a liquid–solid ratio of 2:1. The results of phase transformation indicated that the lattice structure of muscovite was destroyed and released vanadium under the influence of high temperature. V(III) is oxidized to V(V) with acid solubility, during roasting process. The microstructure evolution and pore property analysis results show that the dense layered structure of main vanadium-bearing minerals transformed to loosen porous structure. The loose porous structure promotes the diffusion of gas or H atom into the lattice of muscovite in different processes. Therefore, the suspension oxidation roasting pretreatment could enhance the vanadium extraction from shale ore. [ABSTRACT FROM AUTHOR]

[Display omitted] • Modern technology was used to study mineralogical characteristics of V-bearing shale. • The key to vanadium extraction is to destroy the lattice of mica and oxidize V(III). • Oxidation roasting is an optimal process for V-bearing shale with complex structure. • After roasting, the holes and cracks will enlarge and improve vanadium leaching rate. Vanadium, as an important rare metal, was listed as national strategic metal in the 14th Five-Year Plan of China. Vanadium-bearing shale is a unique resource in China and the reserve of vanadium in its accounts for 87% of the total. However, the production processes for vanadium-bearing shale ores from various origins are different due to the difference in mineral composition, the occurrence of vanadium, and the embedded relationship of main minerals. Analyzing their process mineralogical characterization is key to selecting an efficient vanadium extraction process. Therefore, in this work, we systematically studied the mineralogical characteristics of vanadium-bearing shale from Shaanxi province. Analysis results of process mineralogical showed that vanadium was the most valuable element for recovery, with a grade of 1.67%. Mica was the main vanadium-bearing mineral and coexisted closely with limonite, kaolinite, quartz, and feldspar. In the mica, vanadium generally presented the trivalent state of form. According to the analysis of mineralogical characterization, the process of "oxidation roasting-acid leaching" was used to extract vanadium from the shale ore. Under the condition of roasting temperature 900 °C, roasting time 3 h, air flow 600 mL·min-1, leaching temperature 25 °C, leaching time 4 h, leaching acid dosage 10 wt% and the liquid–solid ratio of 2:1, vanadium leaching rate was 75.24%. After oxidation roasting, the lattice of mica was destroyed, and the distribution of V(Ⅴ) increased from 0 to 89.68%. Meanwhile, holes and cracks appeared on the surface of mica particles, which promoted the contact between vanadium and acid, and improved the leaching efficiency of vanadium. Therefore, a link between process mineralogical characterization and selection of vanadium extraction process could be developed, which would be helpful in the efficient utilization of vanadium-bearing shale resources. [ABSTRACT FROM AUTHOR]

Phosphogypsum (PG) is a common chemical by-product from wet process phosphoric acid production, accumulated stockpiles of 300 million tons in China. The challenge for the comprehensive utilization of PG is thorough removal of phosphorus and organic contaminants from PG, which inevitably entails the loss of overall whiteness and limits its utilization in building materials and other fields. This work investigated the speciation of phosphorus and organic contaminants in PG by FTIR spectroscopy, Raman spectroscopy, XRD, SEM-EDS and GC-MS. On this basis, by using K 2 S 2 O 8 as a mineralizer, PG was transformed into anhydrous calcium sulfate powder and the organic contaminants were fully decomposed (removal rate >80%, with residual TOC of 0.078%) under hydrothermal treatment. Under optimal hydrothermal conditions (0.3 M K 2 S 2 O 8 , heated at 120 °C for 12 h), the whiteness of product significantly improved from 40.9 to 97 and effective removal of phosphorus was achieved (more than 76%). The residual phosphorus in treated PG was 0.108%, which met the standard of PG as a building material in China GB/T-23456 2018 (P content < 0.2%). The mechanism study revealed that the phase transformation of calcium sulfate from dihydrate to anhydrous played a dominant role in the removal of phosphorus, H+ and SO 4 2- from K 2 S 2 O 8 decomposition facilitated the dissolution-recrystallization process of calcium sulfate, allowing the phosphorus in the lattice to escape. In addition, by thermal activation, K 2 S 2 O 8 generated free radicals of SO 4 •- and OH• dissipated the organic contaminants in PG. This work provides theoretical and practical bases for the harmless disposal and resource recycling of industrial by-product gypsum, and it is of great significance to build the "zero-waste city". • A feasible method was developed to efficiently remove phosphorus and organic contaminants from phosphogypsum. • The whiteness of product significantly improved from 40.9 to 97, with residual phosphorus of 0.108%. • The phase transformation of gypsum and oxidizing K 2 S 2 O 8 play an important role in the removal. [ABSTRACT FROM AUTHOR]

The city Khara Khoto is located in the Gobi desert in Inner Mongolia. This city was deserted in the late 14th century and rediscovered in the beginning of the 20th century. In the present study, ceramic sherds typical for the Khara Khoto area have been analysed using neutrons, laboratory X-ray diffraction, synchrotron radiation X-ray diffraction as well as optical microscopy as complementary probes in extracting information on the mineral phase compositions as well as on the firing conditions during the pottery production. The data evaluation was performed with the standard diffraction analysis package GSAS and the new developed program AmPhOrAe. The dominating phase is mullite (~60 %) compared to a variable mixture of SiO quartz and cristobalite phases (~35 %) and feldspar as a minority phase. Refiring experiments on one of the sherds allow estimating the firing temperatures of the ceramics within the region of 1,150 and 1,250 °C. [ABSTRACT FROM AUTHOR]

Abstract: The effect of pre-roasting on leaching of the gamierite laterite ore, obtained from Yunnan province, China, was investigated in this study. The phase transformation of laterite minerals roasted at different temperatures was investigated with X-ray powder diffraction (XRD). The roasting experiment results show that there are two phase transformation processes of dehydroxylation of goethite and lizardite at roasting temperatures of 277 °C and 610 °C, respectively, which accord with the result of DTA–TG analysis. Pre-roasting of the laterite not only alters its mineralogical composition but also increases its porosity and surface area, thus making it more amenable to leaching. Compared to the leaching result of raw ore and ores roasted at different temperatures, it indicates that increasing roasting temperature up to 300 °C appears to provide the optimum nickel recovery and further heating appears to be detrimental to the nickel recovery. [Copyright &y& Elsevier]

Limonite ore is a potentially important iron resource and widely distributed in the world. However, it is difficult to process by traditional methods due to the high water content and fine dissemination of aluminum and silica. In this paper, typical refractory limonite ore was studied by suspension magnetization roasting and magnetic separation technology. According to the pilot-scale study, optimum roasting conditions were determined as a capacity of 120 kg/h, CO dosage of 6.5 m3/h, N 2 dosage of 9.5 m3/h, roasting temperature of 460 °C, and gas flow of 16.0 m3/h. An iron concentrate with Fe grade of 64.97% and recovery of 94.53% was obtained using a suspension magnetization roasting – grinding – magnetic separation process. The material and roasted products were characterized by X-ray diffraction (XRD), mineral liberation analyzer (MLA), and backscattered electron (BSE) analyses. The results indicated that the iron oxide phase transformation was as follows goethite → hematite → magnetite → maghemite. The mineral dissemination analysis showed that fine grinding and magnetic separation was favorable to improve the quality of iron concentrates. However, some Al and Si were difficult to remove due to the isomorphism. The suspension magnetization roasting is feasible in economic terms, and the cost of magnetization roasting is $8 per ton. This technology will not only increase the available iron ore resource reserves but also alleviate the imbalance between supply and demand of iron ore in China. Image 1 • Suspension magnetization roasting technology is proposed to explore limonite ore. • An iron concentrate with Fe grade of 64.97% and recovery of 94.53% is obtained. • Goethite and hematite transform to magnetite and maghemite in this process. • Suspension magnetization roasting technology is feasible in economic terms. • It can alleviate the imbalance between supply and demand of the iron ore in China. [ABSTRACT FROM AUTHOR]

As a new "sink" of CO2 permanent storage, the depleted shale reservoir is very promising compared to the deep saline aquifer. To provide a greater understanding of the benefits of CO2 storage in a shale reservoir, a comparative study is conducted by establishing the full-mechanism model, including the hydrodynamic trapping, adsorption trapping, residual trapping, solubility trapping as well as the mineral trapping corresponding to the typical shale and deep saline aquifer parameters from the Ordos basin in China. The results show that CO2 storage in the depleted shale reservoir has merits in storage safety by trapping more CO2 in stable immobile phase due to adsorption and having gentler and ephemeral pressure perturbation responding to CO2 injection. The effect of various CO2 injection schemes, namely the high-speed continuous injection, low-speed continuous injection, huff-n-puff injection and water alternative injection, on the phase transformation of CO2 in a shale reservoir and CO2-injection-induced perturbations in formation pressure are also examined. With the aim of increasing the fraction of immobile CO2 while maintaining a safe pressure-perturbation, it is shown that an intermittent injection procedure with multiple slugs of hug-n-puff injection can be employed and within the allowable range of pressure increase, and the CO2 injection rate can be maximized to increase the CO2 storage capacity and security in shale reservoir. [ABSTRACT FROM AUTHOR]