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1

DFT study on the polyol sacrificial agents for improved clay tolerance of polycarboxylate superplasticizers

He Zhihao, Huang Teng, Gao Meiben, Wang Enwen, Kong Desong, Li Meng

Physicochemical Problems of Mineral Processing

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2024

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Vol. 60, iss. 1

art. no. 184130

EN

With the gradual scarcity of high-quality sand and gravel resources, the increasing mud content in concrete aggregates could strongly adsorb on polycarboxylate superplasticizers (PCE), greatly reducing their working performance. Modifying the molecular structure of PCE or compounding sacrificial agents can effectively improve the tolerance to clay minerals. In this article, using different small molecule polyols and polypropylene glycol (PPG) as examples, density functional theory (DFT) was employed to simulate the adsorption between clay minerals and hydration products. This exploration aims to further understand the anti-clay performance of various sacrificial agents from the perspective of adsorption energy. Ca-montmorillonite (CaMMT) exhibits the lowest adsorption energy among different clay minerals, making it the preferred site for sacrificial agent adsorption. With an increase in hydroxyl number, the adsorption energy between polyol sacrificial agents and montmorillonite decreases. Among polymeric polyols, the adsorption energy between PPG 600 and montmorillonite is the lowest (-10.86 eV), indicating superior anti-clay performance by preferentially occupying active sites on montmorillonite. As the interlayer spacing of montmorillonite increases, the adsorption energy between PPG 600 and montmorillonite initially decreases and then increases, reaching the lowest value at c=15.5 Å. There are more electron transfers (0.858) compared to the electron gain and loss, confirming more interaction between the sacrificial agents and montmorillonite at 15.5Å. This article also provides a crucial theoretical basis for the structural design of anti-clay sacrificial agents, offering insights into addressing compatibility issues between PCEs and clay minerals.

2

Molecular simulation study on hydration of low-rank coal particles and formation of hydration film

Xia Yangchao, Yang Zili, Xing Yaowen, Gui Xiahui

Physicochemical Problems of Mineral Processing

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2019

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Vol. 55, iss. 2

586--596

EN

Water molecules in low-rank coal (LRC) significantly influence its upgrading and utilization. To investigate the hydration of LRC particles and the formation of a hydration film, molecular simulation techniques were innovatively used, including molecular dynamics (MD) simulations and density functional theory (DFT) calculations. The adsorption of water molecules on LRC and various oxygen-containing groups was analyzed. The results show that water molecules adsorb close to the LRC surface and form a large overlapping layer at the LRC/water interface. The radial distribution functions (RDFs) show that the adsorption affinity of water molecules on oxygen-containing sites is stronger than that on carbon-containing sites, and the RDF peaks indicate the existence of a hydration film. Moreover, the differences in adsorption between various oxygen-containing groups depend on both the number of hydrogen bonds and the adsorption distances. The calculated binding energies indicate that the adsorption capacity follows the order carboxyl > phenolic hydroxyl > alcoholic hydroxyl > ether linkage > carbonyl. Experimental results show that a high sorption rate exists between water vapor and LRC samples at the beginning of sorption, which verified the simulation results.

3

Application of sodium dodecyl glycinate to the flotation of deslimed molybdenum tailings

Bai Yang, Li Caixia, Song Wangfang, An Hongyun, Zhao Jingyu

Physicochemical Problems of Mineral Processing

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2019

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Vol. 55, iss. 5

1120--1131

EN

By researching the nonmetallic minerals in molybdenum tailings, this paper investigated the possible application of sodium dodecyl glycinate (SD) to deslimed tailings as an alternative to the large dosage and complex flotation reagent systems of conventional combination collectors (dodecylamine and sodium oleate). The floatability differences of nonmetallic minerals under different SD dosages were analyzed via pure mineral flotation experiments, and the adsorption behavior of SD onto different mineral surfaces was analyzed by quantum chemical calculations. The results of the calculated adsorption structures and energies of the different mineral surfaces show that SD was chemically adsorbed onto the albite (001), phlogopite (010), diopside (110), dolomite (101), calcite (104) and calcite (101) surfaces and that physical adsorption occurred at the phlogopite (001) surface. The corresponding adsorption trend was dolomite > calcite > diopside > albite > phlogopite. These results theoretically verify the feasibility of applying SD to the flotation of nonmetallic minerals in tailings and provide a basis for the selection of inhibitors needed for separating phlogopite from other minerals. In the flotation of deslimed molybdenum tailings, the recoveries of the nonmetallic minerals achieved with SD were close to those in pure mineral flotation, which was greater than the recoveries achieved with dodecylamine and sodium oleate (NaOl), and the dosage was reduced by approximately 25%.

4

Selective flotation of siderite and quartz from a carbonate-containing refractory iron ore using a novel amino-acid-based collector

Gu X., Zhu Y., Li Y., Han Y.

Physicochemical Problems of Mineral Processing

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2018

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Vol. 54, iss. 3

803--813

EN

A novel and highly-efficient amino-acid-based collector, α-ethylenediamine lauric acid (α-EDA-LA), was studied to selectively beneficiate carbonate-containing refractory hematite ores. Single mineral and synthetic mixture flotation tests were carried out to investigate its floating performance. Zeta potential, fourier transform infrared spectroscopy (FTIR) and Density Functional Theory-based molecular simulation were used to identify the adsorption mechanism. The flotation results showed that quartz could be collected effectively at pH 11.0-12.0 in the reverse flotation. For siderite, the recovery peaked at 83.4% at pH 8.0, where siderite presented different floatability from magnetite and hematite. Exploiting such difference, the separation of siderite could be achieved. Zeta-potential measurements showed that α-EDA-LA adsorption on the surfaces of siderite and quartz decreased the corresponding zeta potentials at pH of 8.0-10.0 and 8.0-12.0, respectively. This means the adsorption overcome the electrostatic repulsion between α-EDA-LA and the mineral surfaces. The molecular simulation indicated that no chemisorption took place between α-EDA-LA and quartz. FTIR analysis suggested that α-EDA-LA was adsorbed on quartz via hydrogen bonding. The adsorption of α-EDA-LA on siderite surface was dominated by chemisorption, while further enhanced by hydrogen bonding. This study filled the gap in the research on siderite flotation reagents and its adsorption mechanism.

5

Quantifying the spreading factor to compare the wetting properties of minerals at molecular level – case study: sphalerite surface

Mohseni M., Abdollahy M., Poursalehi R., Khalesi M. R.

Physicochemical Problems of Mineral Processing

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2018

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Vol. 54, iss. 3

646--656

EN

Spreading of water droplet on sphalerite surface was quantified at molecular level and was utilized for comparison of the wetting properties of sphalerite protonated and hydroxylated surfaces. Molecular dynamic simulations were used to characterize the wetting of sphalerite (110) plane. Experimental contact angles of water droplet on sphalerite surfaces were measured and the results were compared with simulated contact angles to ensure that the simulations are accurate enough for calculation of spreading factors. Shape descriptors such as perimeter, area, Feret’s diameters and circularity were used to characterize the shape of droplet-sphalerite interface at molecular level. Using the shape descriptors, different spreading factors were defined and calculated spreading factors were correlated with simulated contact angle. It was shown that spreading factors which were defined as the volume of water droplet divided by the area and Feret’s diameters, with correlation coefficient of 0.98 and 0.97, can be used as accurate tools for wetting comparison of functionalized sphalerite surface at molecular scale. Proposed approach also can be used for investigations on the effect of surface chemical and physical anisotropies on preferred wetting in specific direction at molecular scales.

6

Statistical Fluctuations along the Lennard-Jones Melting Curve

Patra R., Heyes D. M.

Computational Methods in Science and Technology

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2016

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Vol. 22, No. 1

5--17

EN

Statistical fluctuations and correlations between thermodynamic properties along the fluid side of the melting line of the Lennard-Jones (LJ) are determined using Molecular Dynamics (MD) computer simulation. Linear regression, the Pearson coefficient and other statistical measures are calculated. The cross correlation between the configurational part of the pressure and potential energy, and the repulsive and attractive parts of the potential energy are focussed on. Regression plots show that at constant temperature and constant total energy the Weeks-Chandler-Andersen (WCA) decomposition of the Lennard-Jones repulsive and attractive potential energy components show a qualitative change along the melting line. At low temperature the two components are correlated, while they are anticorrelated in the high temperature limit. There is an intermediate temperature range in which the two potential energy components are effectively uncorrelated. The various fluctuation trends along the melting line were found to be weakly dependent on the force field used to generate the distribution of states, namely, the LJ potential, inverse power potential with exponent 12, and the repulsive term in the WCA decomposition of the LJ potential.