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A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Molecular Structure".

Deadline for manuscript submissions: 30 November 2024 | Viewed by 13919

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Dr. Dun Wu

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Guest Editor

School of Earth and Space Sciences (Anhui Green Mine Engineering Research Center), University of Science and Technology of China, Hefei, China
Interests: geochemistry; structural characterization; mineralization; mineral crystal; metamorphism

Dr. Yuhang Gao

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Guest Editor

Anhui Green Mine Engineering Research Center, Hefei, China
Interests: mineralogy; geochemistry

Dr. Guangqing Hu

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Guest Editor

School of Earth and Space Sciences, University of Science and Technology of China, Hefei, China
Interests: environmental geochemistry of coal and mineralogical analysis of coal

Special Issue Information

Dear Colleagues,

The molecular structure of minerals is the basic feature of each mineral, the fundamental factor determining the mineral morphology, physical properties, and genesis, and an important symbol for the generation and evolution history of minerals. At present, the characterization techniques studying the molecular structure characteristics of minerals include XRD, thermal analysis, FTIR, Raman spectroscopy, and morphology observation techniques such as SEM and AFM. The characterization of mineral molecular structures can provide a scientific basis for the study of mineral genesis and evolution as well as the interpretation of various geological phenomena.

In recent years, research on the surface–interface interaction mechanism and environmental effect between minerals and environmental substances is very active. By combining with the latest means of mineralogical research, such as synchrotron radiation, in situ spectroscopy, adsorption models, computational simulation, etc., the surface–interface process and mechanism of minerals are revealed at the atomic and molecular levels, and the restriction mechanism of surface-derived minerals on the geochemical behavior of environmental substances is clarified.

The thermal and kinetic study of mineral molecular structures has also attracted much attention from the scientific community. There are corresponding change rules and internal relations in mineral chemical composition, internal structure, and physicochemical properties under high pressure (high temperature). Research on high-pressure new minerals and mineral phase transformation mechanisms is of great significance for the development of mineral resource utilization.

For this special issue on “Molecular Structure of Minerals”, we welcome the submission of original research articles, introducing the latest frontiers and developments in the characterization of mineral molecular structures, mineral evolution laws, mineral surface–interface interactions, high-pressure new minerals, and research on the mechanism of mineral phase transformation.

Dr. Dun Wu
Dr. Yuhang Gao
Dr. Guangqing Hu
Guest Editors

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Keywords

mineral element composition
mineral spectroscopy
genetic mechanism of minerals
high-pressure minerals
mineral surface–interface interaction
utilization of mineral resources

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Published Papers (10 papers)

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Editorial

Jump to: Research

4 pages, 177 KiB

Open AccessEditorial

Editorial for the Special Issue: “Spatial Structure of Minerals”

by Dun Wu, Guangqing Hu and Yuhang Gao

Molecules 2023, 28(20), 7226; https://doi.org/10.3390/molecules28207226 - 23 Oct 2023

Viewed by 793

Abstract

The spatial structure of minerals is a fundamental factor in determining the morphology, physical properties, and genesis of minerals [...] Full article

(This article belongs to the Special Issue Molecular Structure of Minerals)

Research

Jump to: Editorial

16 pages, 9957 KiB

Open AccessArticle

Effect of Pre-Sulfidization on the Octadecyl Amine Adsorption on the Smithsonite Surface and Its Flotation

by Mengtao Wang, Haobin Wei, Saizhen Jin and Guofan Zhang

Molecules 2024, 29(16), 3921; https://doi.org/10.3390/molecules29163921 - 20 Aug 2024

Viewed by 481

Abstract

The low-grade zinc oxide ore was sulfidized to increase the efficiency of flotation, but the effect of pre-sulfidization on the adsorption mechanism of octadecyl amine (ODA) on the smithsonite surface is currently unclear. In this study, the effect of pre-sulfidization on the adsorption mechanism of ODA and the flotation behavior was studied using smithsonite and pre-sulfidized smithsonite as the samples by zeta potential, contact angle measurement, total organic carbon analyzer (TOC), quartz microcrystalline balance (QCM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and micro-flotation tests. Micro-flotation tests showed that the pretreatment of sulfidization could improve the floatability of smithsonite. Zeta potential and contact angle measurements demonstrated that pre-sulfidization could favor the adsorption of ODA, which is further confirmed by the adsorption tests of ODA using TOC and QCM. Furthermore, FTIR and XPS analysis showed that pre-sulfidization changes the adsorption mode of ODA, changing it from physical adsorption to chemical adsorption. These results suggested that the favorable effect of pre-sulfidization on the adsorption of ODA and the flotation of smithsonite might provide important guidance for industrial application. Full article

(This article belongs to the Special Issue Molecular Structure of Minerals)

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15 pages, 3274 KiB

Open AccessArticle

Synthesis of High-Purity Hydroxyapatite and Phosphoric Acid Derived from Moroccan Natural Phosphate Rocks by Minimizing Cation Content Using Dissolution–Precipitation Technique

by Karim Benataya, Mohammed Lakrat, Othmane Hammani, Mohamed Aaddouz, Youssef Ait Yassine, Hatem A. Abuelizz, Abdelkader Zarrouk, Khalid Karrouchi and Elmiloud Mejdoubi

Molecules 2024, 29(16), 3854; https://doi.org/10.3390/molecules29163854 - 14 Aug 2024

Viewed by 553

Abstract

This study investigates, in the first part, the synthesis and purification of a poorly crystalline hydroxyapatite (HAp) using natural Moroccan phosphate (Boucraa region) as a raw material. Despite its successful preparation, the obtained HAp was contaminated by several metallic cations (mostly Cd, Pb, Sn, Ti, Mn, Mg, Fe, and Al) migrated from the natural rocks during the digestion process, inhibiting HAp application in several sectors. To minimize the existence of these elements, the dissolution–precipitation technique (DP) was investigated as a non-selective purification process. Following the initial DP cycle conducted on the precipitated HAp, the removal efficiency was approximately 60% for Al, Fe, Mg, Mn, and Ti and 90% for Cd and Pb. After three consecutive DP cycles, notable improvement in the removal efficiency was observed, reaching 66% for Fe, 69% for Mg, 73% for Mn, and 74% for Al, while Cd, Pb, and Ti were totally removed. In the second part of this study, the purified HAp was digested using sulfuric acid to produce high-quality phosphoric acid (PA) and gypsum (GP). The elemental analysis of the PA indicates a removal efficiency of approximately 89% for Fe and over 94% for all the examined cations. In addition, the generated GP was dominated by SO₃ and CaO accompanied with minor impurities. Overall, this simple process proves to be practically useful, to reduce a broad spectrum of cationic impurities, and to be flexible to prepare valuable products such hydroxyapatite, phosphoric acid, and gypsum. Full article

(This article belongs to the Special Issue Molecular Structure of Minerals)

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15 pages, 11176 KiB

Open AccessArticle

Study on Calcination Characteristics of Diaspore-Kaolin Bauxite Based on Machine Vision

by Longjiang Li and Jun Liu

Molecules 2024, 29(16), 3813; https://doi.org/10.3390/molecules29163813 - 11 Aug 2024

Viewed by 605

Abstract

D-K-type bauxite from Guizhou can be used as an unburned ceramic, adsorbent, and geopolymer after low-temperature calcination. It aims to solve the problem where the color of the D–K-type bauxite changes after calcination at different temperatures. Digital image processing technology was used to extract the color characteristics of bauxite images after 10 min of calcination at various temperatures. Then, we analyzed changes in the chemical composition and micromorphology of bauxite before and after calcination and investigated the correlation between the color characteristics of images and composition changes after bauxite calcination. The test results indicated that after calcining bauxite at 500 °C to 1000 °C for 10 min, more obvious dehydration and decarburization reactions occurred. The main component gradually changed from diaspore to Al₂O₃, the chromaticity value of the image decreased from 0.0980 to 0.0515, the saturation value increased from 0.0161 to 0.2433, and the brightness value increased from 0.5890 to 0.7177. Studies have shown that changes in bauxite color characteristics are strongly correlated with changes in composition. This is important for directing bauxite calcination based on digital image processing from engineering viewpoints. Full article

(This article belongs to the Special Issue Molecular Structure of Minerals)

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13 pages, 4199 KiB

Open AccessArticle

Utilization of Lead Nitrate to Enhance the Impact of Hydroxamic Acids on the Hydrophobic Aggregation and Flotation Behavior of Cassiterite

by Saizhen Jin, Xiaobo Liu, Yun Feng, Yanfei Chen, Mengtao Wang and Qingfei Xiao

Molecules 2024, 29(15), 3692; https://doi.org/10.3390/molecules29153692 - 4 Aug 2024

Viewed by 661

Abstract

Lead nitrate (LN) is frequently employed as an activator in the flotation of cassiterite using hydroxamic acids as the collectors. This study investigated the effect of LN on the hydrophobic aggregation of cassiterite when benzohydroxamic acid (BHA), hexyl hydroxamate (HHA), and octyl hydroxamate (OHA) were used as the collectors through micro-flotation, focused beam reflectance measurement (FBRM) and a particle video microscope (PVM), zeta potential, and the extended DLVO theory. Micro-flotation tests confirmed that LN activated the flotation of cassiterite using the hydroxamic acids as collectors. Focused beam reflectance measurement (FBRM) and a particle video microscope (PVM) were used to capture in situ data on the changes in size distribution and morphology of cassiterite aggregates during stirring. The FBRM and PVM image results indicated that the addition of LN could promote the formation of hydrophobic aggregates of fine cassiterite, when BHA or HHA was used as the collector, and reduce the dosage of OHA needed to induce the formation of hydrophobic aggregates of cassiterite. The extended DLVO theory interaction energies indicated that the presence of LN could decrease the electrostatic interaction energies (V_edl) and increase the hydrophobic interaction energies (V_hy) between cassiterite particles, resulting in the disappearance of the high energy barriers that existed between the particles in the absence of LN. Thus, cassiterite particles could aggregate in the presence of LN when BHA, HHA, or a low concentration of OHA was used as the collector. Full article

(This article belongs to the Special Issue Molecular Structure of Minerals)

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15 pages, 3848 KiB

Open AccessArticle

Terahertz Time-Domain Spectroscopic Characteristics of Typical Metallic Minerals

by Jingjing Zhang, Haochong Huang, Pengbo Zhao, Luyong Xu, Zhenbo Tan, Jinyuan Zhao, Enhui Yuan, Zhiyuan Zheng, Shanshan Li, Xinyu Li and Kunfeng Qiu

Molecules 2024, 29(3), 648; https://doi.org/10.3390/molecules29030648 - 30 Jan 2024

Cited by 2 | Viewed by 1291

Abstract

Accurate identification and understanding of various metallic minerals are crucial for deciphering geological formations, structures, and ages. Giving their pivotal role as essential natural resources, a microscopic exploration of metallic minerals becomes imperative. Traditional analytical methods, while helpful, exhibit certain limitations. However, terahertz time-domain spectroscopy, distinguished by its high signal-to-noise ratio, expansive frequency band, and low incident wave energy, is a promising complement to conventional techniques in characterizing metallic minerals. This study employs terahertz time-domain spectroscopy to examine samples of Stibnite, Sphalerite, Galena, and Pyrite originating from diverse geological conditions. The vibrations of molecules within these metallic minerals induce discernible changes in the terahertz spectra. Our findings untiate the extensive potential of terahertz time-domain spectroscopy in the characterization of metallic minerals, affirming its considerable practical value in mineral resource exploration. Full article

(This article belongs to the Special Issue Molecular Structure of Minerals)

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16 pages, 5831 KiB

Open AccessArticle

Effect of Wet-Dry Cycles on the Mechanical Performances and Microstructure of Pisha Sandstone

by Yanbing Zhao, Caiqian Yang, Feng Qu, Zhiren Wu, Kejie Ding and Zhishui Liang

Molecules 2023, 28(6), 2533; https://doi.org/10.3390/molecules28062533 - 10 Mar 2023

Cited by 2 | Viewed by 1596

Abstract

The effects of the wet–dry cycles on the chemical compositions, microstructure, and mechanical properties of Pisha sandstone were experimentally investigated in the current study. A series of uniaxial compression tests were conducted to validate the deterioration of the mechanical property of specimens after wet–dry cycles. In addition, the evolutions of the mineral compositions and microstructure characteristics were confirmed by X-ray diffraction (XRD) and scanning electron microscope (SEM). Experimental results indicated that with the increase of wet–dry cycles, the mechanical properties of Pisha sandstone gradually decrease. After five wet–dry cycles, the uniaxial compressive strength, elastic modulus, and fracture energy of specimens were reduced by 41.06%, 62.39%, and 31.92%, respectively. The failure mode of the specimen changes from inclined shear failure to peel failure. Compared to the initial specimens, the relative content of primary minerals after five wet–dry cycles declined by 5.94%, and the relative content of clay minerals after five wet–dry cycles increased by 54.33%. Additionally, the porosity of samples exhibits a positive correlation with wet–dry cycles. Compared to the initial specimens, the porosity of specimens after five wet–dry cycles increased by 176.32%. Finally, a prediction model of the correlation between uniaxial compressive strength and porosity is proposed and verified. Full article

(This article belongs to the Special Issue Molecular Structure of Minerals)

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14 pages, 4993 KiB

Open AccessArticle

Remediation of Soil Mercury by Modified Vermiculite-Montmorillonite and Its Effect on the Growth of Brassica chinensis L.

by Chang Li, Yuchen Li, Hua Cheng, Chunlu Jiang and Liugen Zheng

Molecules 2022, 27(16), 5340; https://doi.org/10.3390/molecules27165340 - 22 Aug 2022

Cited by 6 | Viewed by 1786

Abstract

In this study, the surface of vermiculite-montmorillonite was modified by MnO₂ loading. The modified vermiculite-montmorillonite was added to remediate the potentially toxic trace element (PTE) Hg present in soil containing coal gangue. Pot experiments were conducted to analyze and compare the pH values, Hg contents and Hg species present in coal gangue-containing soil, with and without the modified materials added, to determine whether the addition of modified materials had an effect on the growth of Brassica chinensis L. Results showed that with the addition of 35 g·kg⁻¹ modified vermiculite-montmorillonite, the pH of soil increased by a value of 0.79, compared with that in the control group. When 15 g·kg⁻¹ was added, the concentration of Hg in soil decreased by 98.2%. The addition of modified materials promoted the transformation of Hg in soil from a bioavailable form to an unavailable form; that is, the content of the residual form increased. The plant height and biomass of Brassica chinensis L. also increased, which indicated that the addition of modifiers can increase soil productivity, reduce the effects of PTEs on organisms in soil, and promote plant growth. Therefore, the addition of modified vermiculite-montmorillonite can achieve remediation of coal gangue-containing soil. Full article

(This article belongs to the Special Issue Molecular Structure of Minerals)

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12 pages, 3903 KiB

Open AccessArticle

Experimental Study on the Mechanical Properties and Microstructure of Metakaolin-Based Geopolymer Modified Clay

by Xianzeng Shi, Qingkun Zha, Shuqing Li, Guojun Cai, Dun Wu and Chaojiao Zhai

Molecules 2022, 27(15), 4805; https://doi.org/10.3390/molecules27154805 - 27 Jul 2022

Cited by 13 | Viewed by 2122

Abstract

Clay is found in some countries all over the world. It usually has low compressive strength and cannot be used as a bearing material for subgrade soil. In this paper, the influence of basicity on a metakaolin-based polymer binder to improve clay was studied. The effects of the molar concentration of the alkali activator, different concentration of the metakaolin-based geopolymer and curing time on unconfined compressive strength were studied. The alkali activator-to-ash ratio was maintained at 0.7. The percentage of metakaolin added to the soil relative to metakaolin and soil mixture was 6%, 8%, 10% and 12%. The sodium hydroxide concentrations are 2M, 4M, 6M and 8M. Unconfined compressive strength (UCS) was tested on days 3, 7, 14 and 28, respectively. Compared with original clay, the results show that the unconfined compressive strength increases with the increase in metakaolin content and molar concentration of NaOH. The maximum compressive strength of the sample with NaOH concentration of 8M and percentage of 12% was 4109 kN on the 28th day, which is about 112% higher than that of the original clay. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) results showed that the cementing compound covered the clay particles due to the reaction of the geopolymer with the clay, resulting in the formation of adhesive particles. The main purpose of this study is to verify the effectiveness and stability of metakaolin-based geopolymer binder polymerization under normal temperature and a strong alkali environment. The results can provide parameters for the application and promotion of metakaolin-based geopolymers in soil improvement engineering. Full article

(This article belongs to the Special Issue Molecular Structure of Minerals)

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17 pages, 5798 KiB

Open AccessArticle

Biocementation of Pyrite Tailings Using Microbially Induced Calcite Carbonate Precipitation

by Bo Kang, Fusheng Zha, Weihao Deng, Runkai Wang, Xianguo Sun and Zhitang Lu

Molecules 2022, 27(11), 3608; https://doi.org/10.3390/molecules27113608 - 4 Jun 2022

Cited by 23 | Viewed by 2530

Abstract

Tailing sand contains a large number of heavy metals and sulfides that are prone to forming acid mine drainage (AMD), which pollutes the surrounding surface environment and groundwater resources and damages the ecological environment. Microbially induced calcium carbonate precipitation (MICP) technology can biocement heavy metals and sulfides in tailing sand and prevent pollution via source control. In this study, through an unconfined compressive strength test, permeability test, and toxic leaching test (TCLP), the curing effect of MICP was investigated in the laboratory and the effect of grouting rounds on curing was also analyzed. In addition, the curing mechanism of MICP was studied by means of Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), X-ray diffraction spectroscopy (XRD), and scanning electron microscopy (SEM). The experimental results showed that MICP could induce calcium carbonate precipitation through relatively complex biochemical and physicochemical reactions to achieve the immobilization of heavy metals and sulfides and significantly reduce the impact of tailing sand on the surrounding environment. Full article

(This article belongs to the Special Issue Molecular Structure of Minerals)

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