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Barrier and Functional Materials from Waste Materials for Pollutants—Second Volume

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

Deadline for manuscript submissions: closed (30 June 2023) | Viewed by 13897

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Dr. Quanzhi Tian

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National Engineering Research Center of Coal Preparation and Purification, China University of Mining and Technology, Xuzhou 221116, China
Interests: solid waste treatment; stabilization/solidification; inorganic materials; heavy metal transformation; soil remediation
Special Issues, Collections and Topics in MDPI journals

Dr. Yanfei Chen

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School of Metallurgy and Environment, Central South University, Changsha, China
Interests: minerals processing; wastewater treatment; recycling of secondary resources
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Dr. Yangchao Xia

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National Engineering Research Center of Coal Preparation and Purification, China University of Mining and Technology, Xuzhou, China
Interests: coal/mineral/solid waste flotation separation; interfacial regulation with chemicals; micro-nano scale interface characterization

Dr. Peng Li

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School of Chemical Engineering, Zhengzhou University, Zhengzhou 450000, China
Interests: coal conversion and untilization; valuable untilization of preparation of coal-based composite carbon materials; separation of carbon resources and critical metals from coal and coal-based solid waste
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Pollutants, especially for radionuclides, are considered to have a high priority for immobilization because of their high toxicity and long half-lives. These pollutants can trigger environmental contamination, which can result from activities such as waste disposal and nuclear waste reprocessing. Thus, the retention of pollutants is an important issue for preventing environmental contamination and helping to maintain safe ecosystems. For the disposal and treatment of radioactive, chemotoxic, and mixed wastes, barrier materials and related materials are commonly applied worldwide in repository systems. In addition, during industrial activities, large amounts of industrial wastes/byproducts are produced and occupy large areas of land, waste materials that have limited applications. Therefore, the application of wastes for the treatment of pollutants remains a hot topic of current research. In order to solve the above-mentioned problems, it is urgent to develop the appropriate analytical and technical solutions for waste utilization and pollutant control. This Special Issue is focused on the development of new technology for the waste management and emerging pollutants control as well as the description of detailed retention mechanisms.

Dr. Quanzhi Tian
Dr. Yanfei Chen
Dr. Yangchao Xia
Dr. Peng Li
Guest Editors

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Keywords

hazardous wastes
solidification/stabilization
sorption
characterization
waste management

Published Papers (9 papers)

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Research

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11 pages, 5299 KiB

Open AccessArticle

Utilization of Phytic Acid as a Selective Depressant for Quartz Activated by Zinc Ions in Smithsonite Flotation

by Mengtao Wang and Saizhen Jin

Molecules 2023, 28(14), 5361; https://doi.org/10.3390/molecules28145361 - 12 Jul 2023

Viewed by 723

Abstract

It is difficult to separate smithsonite from quartz with metal ion activation through flotation using sodium oleate (NaOL) as the collector. The inevitable Zn²⁺ in the flotation process of zinc oxide ore makes the separation of smithsonite and quartz more difficult. Thus, this study investigated the use of phytic acid (PA) as a flotation depressant to separate smithsonite from Zn²⁺-activated quartz while utilizing sodium oleate as the collector. Microflotation tests indicated that phytic acid could selectively inhibit the flotation of Zn²⁺-activated quartz without affecting the flotation of smithsonite. The measured zeta potentials revealed that the existence of phytic acid hindered sodium oleate adsorption to the surface of Zn²⁺-activated quartz but had little influence on the adsorption of smithsonite. Zn²⁺ dissolution tests and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy analysis indicated that the phytic acid could dissolve the Zn²⁺ from the minerals’ surfaces into the solution. In conjunction with X-ray photoelectron spectroscopy results, the analysis indicated that phytic acid could adsorb onto the Zn²⁺-activated quartz surface and eliminate active sites for sodium oleate adsorption by dissolving the active Zn²⁺ from the quartz surface into the solution. Full article

(This article belongs to the Special Issue Barrier and Functional Materials from Waste Materials for Pollutants—Second Volume)

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16 pages, 5348 KiB

Open AccessArticle

Hydrophobic Flocculation of Fine Cassiterite Using Alkyl Hydroxamic Acids with Different Carbon Chain Lengths as Collectors

by Saizhen Jin, Qing Shi and Leming Ou

Molecules 2023, 28(9), 3911; https://doi.org/10.3390/molecules28093911 - 05 May 2023

Cited by 1 | Viewed by 1202

Abstract

This work investigated the hydrophobic flocculation of cassiterite using four alkyl hydroxamic acids with varying carbon chain lengths, i.e., hexyl hydroxamate (C₆), octyl hydroxamate (C₈), decyl hydroxamate (C₁₀) and dodecyl hydroxamate (C₁₂), as collectors. Microflotation tests were performed to investigate the flotation behaviour of cassiterite in the presence of the four alkyl hydroxamic acids. Focused beam reflectance measurement (FBRM) and a particle video microscope (PVM) were used to analyse and monitor the real-time evolution of the particle size distribution of cassiterite and the images of flocs during flocculation. The extended DLVO theory interaction energies between the cassiterite particles were calculated on the basis of the measured contact angle and the zeta potential of cassiterite to determine the aggregation and dispersion behaviour of the cassiterite particles. The microflotation test results suggested that the floatability of cassiterite improved with the increase in the carbon chain length of hydroxamates. FBRM, PVM images and extended DLVO theory calculation results indicated that when C₆ was used as the collector, the cassiterite particles could not form hydrophobic flocs because the total potential energy between them was repulsive. When C₈, C₁₀ and C₁₂ were used as collectors, the energy barrier amongst particles decreased with increasing hydroxamate concentration. The lowest concentrations of C₈, C₁₀ and C₁₂ that could cause the hydrophobic aggregation of cassiterite were approximately 1 × 10⁻³, 1 × 10⁻⁴ and 2 × 10⁻⁵ mol/L, respectively. The aggregation growth rate and apparent floc size increased with an increasing collector concentration. Hydroxamic acid with a longer carbon chain could induce the cassiterite particles to form larger flocs at a lower concentration in a shorter time. Full article

(This article belongs to the Special Issue Barrier and Functional Materials from Waste Materials for Pollutants—Second Volume)

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12 pages, 2675 KiB

Open AccessArticle

Effect of Unavoidable Ion (Ca²⁺) in Pulp on the Dispersion Behavior of Fine Smithsonite

by Zhongyi Liu, Jie Liu, Yinfei Liao, Chenxi Jin and Zilong Ma

Molecules 2022, 27(24), 9026; https://doi.org/10.3390/molecules27249026 - 18 Dec 2022

Viewed by 1327

Abstract

The efficient dispersion of particles is a prerequisite for the efficient flotation of fine smithsonite. However, unavoidable ions (Ca²⁺) in the pulp have become a challenge for the efficient separation of fine smithsonite, due to the high content of pulp and small radius of hydrated ions. Therefore, the dispersion behavior and mechanism of Ca²⁺ action on smithsonite are important for improving the efficiency of smithsonite flotation. In this study, the effects of Ca²⁺ on the dispersion behavior of fine smithsonite were studied using a turbidity test. The results showed that the dispersion behavior of smithsonite was good in the absence of Ca²⁺ at a range of pH = 4–12. However, the measured turbidity values of smithsonite decreased with the addition of calcium ions. In particular, the dispersion behavior of smithsonite became worse at pH > 10. Zeta potential test results showed that the smithsonite’s surface potential shifted positively, and the absolute value of potential decreased in the presence of Ca²⁺. The results of X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) analysis showed that calcium ions were adsorbed on the smithsonite surface, which may have caused ion exchange or the generation of calcium hydroxide precipitation leading to particle coalescence behavior. The calculations of solution chemistry and DLVO theory indicated that calcium ions adsorbed on the surface of smithsonite to form Ca(OH)⁺ or precipitation, which reduced the potential energy of interparticle interactions and led to the disruption of dispersion behavior of smithsonite. Full article

(This article belongs to the Special Issue Barrier and Functional Materials from Waste Materials for Pollutants—Second Volume)

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10 pages, 2484 KiB

Open AccessArticle

Study on the Influence of Metal Ions on the Dispersion of Fine Calcium Gangue Minerals

by Zhongyi Liu, Jie Liu, Yinfei Liao, Zilong Ma and Chenxi Jin

Molecules 2022, 27(24), 8963; https://doi.org/10.3390/molecules27248963 - 16 Dec 2022

Cited by 1 | Viewed by 1006

Abstract

In this study, the calcium gangue material calcite (−10 μm) was used to investigate the effects of different kinds of metal ions and dosages on the dispersion behavior of calcite. The test results showed that the dispersion behavior of calcite was poor under strongly alkaline conditions without the addition of metal ions, and the reason for that was calcite dissolved ions. The degree of influence of different metal ions on calcite dispersion behavior was Fe³⁺ > Mg²⁺ > Na⁺. The three metal ion dosage tests showed that the dispersion behavior of calcite became poorer with the increase of metal ion dosage. This mainly showed that with the increase of Na⁺ dosage, the trend of the dispersion behavior of calcite was not obvious, but with the increase of Fe³⁺ and Mg²⁺ dosage, the trend of calcite dispersion behavior changed more. The dispersion behavior of calcite was devastated by 5 × 10⁻⁴ mol/L Fe³⁺ at pH = 4–12. The different mechanisms of the three metal ions were identified by zeta potential, solution chemistry, and XPS analysis. Na⁺ only changed the zeta potential value of the calcite surface, which acted as a compressed electric double layer. However, the formation of metal hydroxide species or metal hydroxide surface precipitation due to the adsorption of Fe³⁺ and Mg²⁺ on the mineral surface resulted in the change of the dispersion behavior of calcite. Full article

(This article belongs to the Special Issue Barrier and Functional Materials from Waste Materials for Pollutants—Second Volume)

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12 pages, 1131 KiB

Open AccessArticle

Contact-Piezoelectric Bi-Catalysis of an Electrospun ZnO@PVDF Composite Membrane for Dye Decomposition

by Buwen Jiang, Xiaoxuan Xue, Zuxiang Mu, Haoyuan Zhang, Feng Li, Kai Liu, Wenqian Wang, Yongfei Zhang, Wenhui Li, Chao Yang and Kewei Zhang

Molecules 2022, 27(23), 8579; https://doi.org/10.3390/molecules27238579 - 05 Dec 2022

Cited by 5 | Viewed by 2006

Abstract

The treatment of organic pollutants in wastewater is becoming a great challenge for social development. Herein, a novel contact-piezoelectric bi-catalysis of a ZnO@ PVDF composite membrane was prepared by electrospinning technology. The obtained ZnO@PVDF composite membranes is superior to the pure PVDF membrane in decomposing methyl orange (MO) under ultrasonication at room temperature, which is mainly attributed to the synergy effect of the contact-electro-catalysis of dielectric PVDF, as well as the piezoelectric catalysis of tetrapodal ZnO and the β-phase of PVDF. The heterostructure of the piezoelectric-ZnO@dielectric-PVDF composite is beneficial in reducing the electron/hole pair recombination. As compared to the pure PVDF membrane, the catalytic degradation efficiency of the ZnO@PVDF composite membrane was improved by 444.23% under ultrasonication. Moreover, the reusability and stability of the composite membrane are comparable to those of the traditional powdered catalyst. This work offers a promising strategy for improving the pollutant degradation by combining contact-electro-catalysis with piezoelectric catalysis. Full article

(This article belongs to the Special Issue Barrier and Functional Materials from Waste Materials for Pollutants—Second Volume)

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13 pages, 2929 KiB

Open AccessArticle

Non-Destructive Detection of Moldy Walnuts Based on Hyperspectral Imaging Technology

by Junyan Xu, Daochun Xu, Xiaopeng Bai, Rongchao Yang and Jiale Cao

Molecules 2022, 27(20), 6776; https://doi.org/10.3390/molecules27206776 - 11 Oct 2022

Cited by 1 | Viewed by 1205

Abstract

Walnuts with their shells are a popular agricultural product in China. However, mildew from growth can sometimes be processed into foods. It is difficult to visually determine which walnuts have mildew without breaking the shells. A non-destructive method for detecting walnuts with mildew was studied by combining spectral data with image information. A total of 120 “Lüling” walnuts with shells were used for the mildew experiment. The characteristics of the spectral data from six surfaces of all samples were collected in the range of 370–1042 nm on days 0, 15, and 30. The spectrum was pretreated using SNV, and the feature bands were extracted using PCA and modeled using a support vector machine (SVM). The results show that the overall classification accuracy was 93%, with an of accuracy of 100% for INEN walnuts (normal internally and externally). The accuracy for IMEM walnuts (mildew internally and externally) reached 87.29%. There was an accuracy of 78.6% for IMEN walnuts (mildew internally and normal externally). The non-destructive detection of mildewed walnuts can be undertaken using hyperspectral imaging technology, which provides a new technique for exploring the mechanisms of walnuts with mildew. Full article

(This article belongs to the Special Issue Barrier and Functional Materials from Waste Materials for Pollutants—Second Volume)

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17 pages, 5523 KiB

Open AccessArticle

Effect of Ultrasonic Pretreatment on Flocculation Filtration of Low-Rank Coal Slurry

by Aosheng Yang, Yinfei Liao, Maoyan An, Yijun Cao, Zhe Yang, Hourui Ren, Hailong Su, Qiqi Zou and Luojian Chen

Molecules 2022, 27(19), 6460; https://doi.org/10.3390/molecules27196460 - 30 Sep 2022

Cited by 8 | Viewed by 1307

Abstract

The efficient filtration of low-rank coal (LRC) slurry was significantly beneficial to the production process of wet coal beneficiation. However, relatively few studies have been reported on novel pretreatment methods for the efficient filtration of LRC slurry. In this paper, the mechanism of ultrasonic pretreatment to promote flocculation and filtration of slurry was studied. The hydrophobic variation of the slurry surface was measured by contact angle and XPS. The flocculation properties of slurry were characterized using zeta potential and FBRM. The effects of filter cake porosity and ultrasonic pretreatment on slurry filtration resistance were calculated by L-F NMR and Darcy’s theory. The results showed that the ultrasonic pretreatment promoted the flocculation and filtration performance of LRC slurry, increased the filtration rate, and decreased the cake moisture content. Meanwhile, the contact angle of LRC increased significantly from 50.1° to 67.8° after ultrasonic pretreatment, and the surface tension of the filtrate decreased from 69.5 to 53.31 mN/m. Ultrasonic pretreatment reduced the absolute value of the zeta potential of coal slurry from 24.8 to 21.0 mV, and the average chord length of flocs increased from 5–10 μm to 25–30 μm, thus weakening the electrostatic repulsion between coals to promote floc formation. In addition, the pore tests and filtration theory calculations showed that the ultrasonic pretreatment significantly improved the permeability of the filter cake to water and reduced the resistance to slurry during filtration. In particular, the mesopore porosity increased by 9.18%, and the permeability increased by 2.937 × 10⁸ m². Therefore, this contributed to the reduction of slurry filtration resistance. This research provides an efficient method for promoting the efficient filtration of slurry. Full article

(This article belongs to the Special Issue Barrier and Functional Materials from Waste Materials for Pollutants—Second Volume)

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12 pages, 2536 KiB

Open AccessArticle

Synergistic Treatment of Congo Red Dye with Heat Treated Low Rank Coal and Micro-Nano Bubbles

by Ning Han, Rong Cui, Haisen Peng, Ruize Gao, Qiongqiong He and Zhenyong Miao

Molecules 2022, 27(13), 4121; https://doi.org/10.3390/molecules27134121 - 27 Jun 2022

Viewed by 1385

Abstract

In this study, the adsorption method and micro-nano bubble (MNB) technology were combined to improve the efficiency of organic pollutant removal from dye wastewater. The adsorption properties of Congo red (CR) on raw coal and semi-coke (SC) with and without MNBs were studied. The mesoporosity of the coal strongly increased after the heat treatment, which was conducive to the adsorption of macromolecular organics, such as CR, and the specific surface area increased greatly from 2.787 m²/g to 80.512 m²/g. MNBs could improve the adsorption of both raw coal and SC under different pH levels, temperatures and dosages. With the use of MNBs, the adsorption capacity of SC reached 169.49 mg/g, which was much larger than that of the raw coal at 15.75 mg/g. The MNBs effectively reduced the adsorption time from 240 to 20 min. In addition, the MNBs could ensure the adsorbent maintained a good adsorption effect across a wide pH range. The removal rate was above 90% in an acidic environment and above 70% in an alkaline environment. MBs can effectively improve the rate of adsorption of pollutants by adsorbents. SC was obtained from low-rank coal through a rapid one-step heating treatment and was used as a kind of cheap adsorbent. The method is thus simple and easy to implement in the industrial context and has the potential for industrial promotion. Full article

(This article belongs to the Special Issue Barrier and Functional Materials from Waste Materials for Pollutants—Second Volume)

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Review

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21 pages, 2397 KiB

Open AccessReview

Application of Geopolymer in Stabilization/Solidification of Hazardous Pollutants: A Review

by Quanzhi Tian, Yingchu Bai, Yinhai Pan, Changshuai Chen, Shuo Yao, Keiko Sasaki and Haijun Zhang

Molecules 2022, 27(14), 4570; https://doi.org/10.3390/molecules27144570 - 18 Jul 2022

Cited by 24 | Viewed by 3041

Abstract

Geopolymers, as a kind of inorganic polymer, possess excellent properties and have been broadly studied for the stabilization/solidification (S/S) of hazardous pollutants. Even though many reviews about geopolymers have been published, the summary of geopolymer-based S/S for various contaminants has not been well conducted. Therefore, the S/S of hazardous pollutants using geopolymers are comprehensively summarized in this review. Geopolymer-based S/S of typical cations, including Pb, Zn, Cd, Cs, Cu, Sr, Ni, etc., were involved and elucidated. The S/S mechanisms for cationic heavy metals were concluded, mainly including physical encapsulation, sorption, precipitation, and bonding with a silicate structure. In addition, compared to cationic ions, geopolymers have a poor immobilization ability on anions due to the repulsive effect between them, presenting a high leaching percentage. However, some anions, such as Se or As oxyanions, have been proved to exist in geopolymers through electrostatic interaction, which provides a direction to enhance the geopolymer-based S/S for anions. Besides, few reports about geopolymer-based S/S of organic pollutants have been published. Furthermore, the adsorbents of geopolymer-based composites designed and studied for the removal of hazardous pollutants from aqueous conditions are also briefly discussed. On the whole, this review will offer insights into geopolymer-based S/S technology. Furthermore, the challenges to geopolymer-based S/S technology outlined in this work are expected to be of direct relevance to the focus of future research. Full article

(This article belongs to the Special Issue Barrier and Functional Materials from Waste Materials for Pollutants—Second Volume)

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