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Red mud is a red-coloured, mud-like solid waste discharged from the industrial aluminium production process, which has a high output and is a pollutant. It exhibits a small particle size and a large specific surface area and contains active oxides. In this study, "red mud" and "phosphate" were used as keywords to retrieve research hotspots and progress for the red mud as a phosphate adsorbent in the past 10 y. CiteSpace and VOSviewer visual literature analysis software were used to cluster countries, institutions, authors, and keywords. Related patents showed that research on the phosphate adsorption performance of red mud has considerably increased since 2013 and that China has made a significant contribution. This paper summarises the main chemical composition and modification methods of red mud and collects from literature the relevant mechanism research and data on phosphate adsorption/desorption using red mud as an adsorbent. Summarising data on the microstructure of red mud adsorbent, it is found that there are few reports on red mud as adsorbent based on density functional theory. This study suggests that the problem of the steric hindrance of the red mud adsorbent in the phosphate adsorption process needs further research. [ABSTRACT FROM AUTHOR]

Single-atom catalysis is a new field that has developed rapidly in recent years and has greatly helped the development of catalytic science. We have processed a large amount of literature data through the Web of Science database. The bibliometric method was used to analyze the development trend and research hotspots over the past 10 years since the concept of single-atom catalysis was proposed in 2011. Results show that the field of single-atom catalysis is currently at a high-speed development stage. China is in a leading position in terms of comprehensive strength, with the largest number of publications and great influence. Most productive journals and institutions are ACS Catalysis and Chinese Acad. Sci. Single-atom catalysis has the most research results in the field of chemistry. In addition, the most commonly used keywords are "density functional theory", "oxygen reduction reaction", "electrocatalysis", "co oxidation", "graphene", "heterogeneous catalysis", "platinum", "hydrogen evolution reaction", which reflect the research direction of the current field. This article reviews the main research content of single-atom catalysts in order to facilitate researchers understanding the current situation in the field, and to also provide some guidance for future research. [ABSTRACT FROM AUTHOR]

This paper aims to reveal the formation process of pitchblende by analyzing its microstructural features on the nanoscale and atomic scale. Herein, we selected pitchblende samples from drilling cores from the Miaoershan area, southern China, as the research objects. The microstructural features of pitchblende particle cores were analyzed using high-resolution transmission electron microscopy (HRTEM), electron diffraction, energy spectrum (EDS) and electron microprobe analysis (EMPA), combined with density functional theory calculations. The results of this study reveal that the pitchblende grain boundaries are not clear, as they exhibit a cloudy distribution and some preferred orientations under HRTEM. The selected area electron diffraction (SAED) analyses show discontinuous ring patterns that are coherent with the presence of a preferred orientation. The HRTEM results reveal that pitchblende is a complex aggregate composed of nanocrystals with a diameter of 3–7 nm and unit cell parameters of a0 = 0.556 nm. The elements in the pitchblende are characterized by an irregular and scattered distribution of Ca, As, S, Fe, Mn, and Si. We assume that the formation of pitchblende is related to hard-base fluid in a reduced environment containing As and S. We used density functional theory calculations to obtain the pitchblende crystal structure model and simulated the positions of the U and O atoms to provide a reference for further analysis of the pitchblende crystal structure. We conjecture that uranium ions of U4+, U5+ and U6+ may coexist in pitchblende (stoichiometry U3O7). [ABSTRACT FROM AUTHOR]

As an effective conservation material for wall paintings, ancient paper, and stone artifacts, nano Ca(OH)2 has been studied for more than two decades. However, the synthesis methods are expensive, complex, time‐consuming, or require considerable energy. To tackle the issue, we report, in this study, a facile, large‐scale, time saving, and economical method for synthesizing nano Ca(OH)2 (∼90 nm) at room temperature. This is achieved by controlling crystal growth of Ca(OH)2 at the (1‾010) facet (vertical direction) and (0001) facet (horizontal direction) with simultaneous addition of octyl phenyl polyoxyethylene ether (OPPE) and dimethylformamide (DMF) in the reaction. Density functional theory (DFT) calculations revealed that the crystal dimensionality tuning is caused by attaching OPPE to the (0001) facet and DMF to the (1‾010) facet of Ca(OH)2. Experimental results showed that the synthesized nano Ca(OH)2 has higher stability and carbonation degree than commercial Ca(OH)2 and was used for consolidating a 1300‐year‐old tomb painting, which is a very important, precious, and heavily damaged national treasure of China. The results demonstrate that the nano Ca(OH)2 shows excellent penetration into the painting, considerably improves the strength of the painting, and has no side effects on the color, pore distribution, and porosity of the painting. Our work will significantly facilitate the industrial production of nano Ca(OH)2 and its application in cultural heritage conservation. [ABSTRACT FROM AUTHOR]

In China, most of the high-sulfur iron ores have not been fully developed and utilized due to the lack of breakthrough progress in the research on the sulfur migration and the desulfurization mechanism during the roasting process. This study will focus on revealing the release and fixation mechanisms of sulfur during the roasting process to achieve the transformation of desulfurization from terminal treatment to process control. Experimental results show that as the roasting temperature increases, the release rate of SO2 also increases, reaching the maximum release rate at 900 °C. Simultaneously, it is found that at the same roasting temperature, the release rate and amount of SO2 under the O2/N2 atmosphere is significantly greater than that under the pure N2 and air atmospheres. Meanwhile, X-ray diffraction (XRD) is utilized to explore the phase composition of the roasted product and the sulfur release mechanism. In addition, the adsorption energy, stability and electron transfer of SO2 on the CaO surface are calculated through density functional theory (DFT), and the optimal adsorption active site perpendicular to the O atom (O-top) is also determined. Finally, the sulfur fixing agent CaO is used to study the SO2 fixation mechanism. When the concentration reaches 10%, the sulfur fixation efficiency reaches more than 80%. Therefore, this work will present basic knowledge and systematic guidance for the sulfur migration and release of high-sulfur iron ore under the oxidizing roasting process. [ABSTRACT FROM AUTHOR]

Collectors play a decisive role in froth flotation by selectively hydrophobizing mineral particles. The new understanding of the molecular design of collectors, their flotation mechanism and green manufacture is reviewed in this paper. The density functional theory (DFT) calculation opens a new avenue for understanding the reactivity of the groups and atoms in a collector molecule, and azolethione surfactants including oxadiazolethione, thiadiazolethione, triazolethione, amino-triazolethione and tetrazolethione, have been designed and developed as collectors. The combination application of the DFT calculation and in situ detection technologies establishes a new platform for flotation fundamental research, and the monomolecular layer of a sulfhydryl collector chemisorbed on chalcopyrite has been observed and measured, and the nature of froth flotation is further understood. The new synthetic technologies for collectors such as xanthates and hydroxamates have been developed to prepare them in near atom economy, which supported their green manufacture and industrial upgrading. The new understanding of flotation collectors will boost their future development. [ABSTRACT FROM AUTHOR]

Owing to containing high fraction of organic matter, the tannery sludge seemed to be fit for composting. Actually, it was intensively harmful to the environment, due to containing chromium (Cr). So it might undergo a long time of storage until finding a proper way to dispose it. In the storage period, it would expose the surrounding environment a risk via releasing Cr. In this study, an approach was proposed to minimize the amount of released Cr, and reveal the mechanism on immobilizing Cr. Collagen protein waste (CPW) was adopted to immobilize Cr, and it was evaluated via leaching experiment. The lowest leaching concentration of Cr was 12 mg/L, meeting the limits of related standard in China (GB 5085.3–2007, Tcr < 15 mg/L). Moreover, the compositions and functional groups of the optimum sample (12 mg/L) were also characterized, confirming that the dominant functional groups cross-linking with Cr were hydroxyl (-OH), carboxyl (-COOH), and epoxy (-COC). Importantly, density functional theory (DFT) calculation was also employed, suggesting that Cr was restrained by accepting electrons from O atoms donating by functional groups. [ABSTRACT FROM AUTHOR]