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Innovative Strategies for Solid Waste Minimisation in the Mining and Minerals Industry

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A special issue of Minerals (ISSN 2075-163X). This special issue belongs to the section "Environmental Mineralogy and Biogeochemistry".

Deadline for manuscript submissions: closed (26 July 2021) | Viewed by 22625

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Special Issue Editors

Dr. Chongchong Qi

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School of Resources and Safety Engineering, Central South University, Changsha, China
Interests: solid waste minimisation; cemented paste backfill; pollution reduction; recycling; first-principles calculations; molecular dynamics; artificial intelligence
Special Issues, Collections and Topics in MDPI journals

Prof. Dr. Guichen Li

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Guest Editor

School of Mines, China University of Mining and Technology, Xuzhou, China
Interests: rock mechanics; reuse of solid waste materials; roadway surrounding rock control; grouting reinforcement; underground space development

Prof. Dr. Hakan Basarir

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Guest Editor

Department of Geoscience and Petroleum, Norwegian University of Science and Technology, Trondheim, Norway
Interests: rock mechanics; rock excavatability; numerical modelling; rock material and mass characterisation and classification; DAQ systems and modelling and optimisation in mining engineering structure design and other applications

Dr. Qiusong Chen

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Guest Editor

School of Resources and Safety Engineering, Central South University, Changsha 410083, China
Interests: groundwater friendly backfilling; comprehensive utilization of solid waste from mining, dressing and smelting
Special Issues, Collections and Topics in MDPI journals

Dr. Yuantian Sun

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Guest Editor

School of Mines, China University of Mining and Technology, Xuzhou 221116, China
Interests: data analysis using AI and ML; recycling; engineering materials; numerical modeling; simulation
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The evolution of the mining and minerals industry has been accompanied by a substantial increase in the amount of solid waste (i.e., mine tailings, coal gangue, coal fly ash, slag). The solid waste can come from numerous sources, from the exploration of prospective sites to the refining of minerals. Due to its high potential to cause widespread environmental damage, the treatment of solid waste has been one of the most daunting problems encountered by the mining and minerals industry.

Conventional methods of solid waste treatment, such as direct surface disposal, have many shortcomings that limit their wide application. These shortcomings include, but are not limited to, failure risk of the storage facility, occupation of land resources, potential heavy metal contamination, etc. Therefore, innovative strategies are needed for solid waste minimisation in the mining and minerals industry. Research has been carried out to improve the overall strategies of solid waste minimisation in different aspects. Some studies propose the minimisation method during the generation of solid waste, while others intend to design new means of solid waste recycling.

The purpose of this Special Issue is to bring together important works that have been carried out in the field of solid waste minimisation in the mining and minerals industry. The key areas that have been concentrated on include, but are not limited to, the following:

Fundamental studies on solid waste generation;
Advanced minimisation strategies during waste generation;
Innovative recovery and removal techniques for heavy metals in solid waste;
Fundamental studies on solid waste utilisation;
Co-recycling of solid waste from various sources;
Artificial intelligent-aided methods in solid waste minimisation;
Other improvements to conventional solid waste strategies.

Prof. Dr. Chongchong Qi
Prof. Dr. Guichen Li
Prof. Dr. Hakan Basarir
Prof. Dr. Qiusong Chen
Dr. Yuantian Sun
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Minerals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

sustainability
solid waste minimisation
waste generations
tailings management
waste disposal
heavy metals
utilisation
co-recycling
artificial intelligence

Published Papers (10 papers)

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Research

26 pages, 10107 KiB

Open AccessArticle

A Method of Backfill Mining Crossing the Interchange Bridge and Application of a Ground Subsidence Prediction Model

by Shuaigang Liu, Jianbiao Bai, Gongyuan Wang, Xiangyu Wang and Bowen Wu

Minerals 2021, 11(9), 945; https://doi.org/10.3390/min11090945 - 30 Aug 2021

Cited by 6 | Viewed by 1882

Abstract

The traditional backfill mining method is a technology developed by the general trend of green coal mining, but with a high cost and an impact on production efficiency. This paper proposes a structured backfill mining method with high-water materials and pillars. The evolution of roof pressure appearance is assessed through the sensor and monitoring system in the hydraulic support. The main roof fracture step distance is determined based on the roof structure characteristics of backfill mining, and the backfill step distance of underground structural backfill is 22.7 m considering the safety factor. Through the simulation results of Abaqus commercial simulation software, the roof subsidence evolution of different backfill schemes under temporary load and permanent load is compared, and the rationality of the backfill step distance is verified. Based on the probability integral method, the surface subsidence prediction model is proposed, then the final value and the maximum dynamic change value of the surface subsidence at the north and south ends of the interchange bridge by traditional mining and backfill mining are analyzed, which verifies the rationality of the structural backfill mining method. Full article

(This article belongs to the Special Issue Innovative Strategies for Solid Waste Minimisation in the Mining and Minerals Industry)

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16 pages, 4949 KiB

Open AccessArticle

Application of Lignite Combustion Waste Slag Generated in Heating Plants as a Partial Replacement for Cement. Part II: Physical–Mechanical and Physical–Chemical Characterization of Mortar and Concrete

by Milan Kragović, Nenad Ristić, Jelena Gulicovski, Andrijana Nedeljković, Snežana Pašalić, Ivica Ristović and Marija Stojmenović

Minerals 2021, 11(9), 925; https://doi.org/10.3390/min11090925 - 27 Aug 2021

Cited by 1 | Viewed by 1641

Abstract

The presented study is a continuation of the research with the aim of finding a useful value of hazardous waste slag generated by the combustion of lignite in heating plants and its application in the construction industry. The different amounts of cement (10%, 15%, 20% and 25%) were replaced with waste slag and silica fumes in mortars and concrete production. Detailed physical–mechanical characterization was performed on the mortar and concrete samples according to standard procedures. Test results indicated that the replacement of cement with slag and silica fumes reduces the physical and mechanical properties of mortar and concrete, but cement composites retained the required structural properties. If 15–20% is considered an acceptable level of compressive strength decrease, then it can be concluded that waste slag can be implemented in practice and be used as a construction material, with cement replacement in the maximal amount of 20% (17.8% of slag and 2.2% of silica fumes). On hardened mortar samples with maximal possible cement replacement (20%), physical–chemical characterizations were performed and included X-ray and infrared spectrophotometry, scanning electron microscopy, and thermal analysis. Results showed the absence of new phases and the presence of only those which were characteristic for starting samples, predominantly portlandite, quartz, calcite and calcium silicate-oxide. Full article

(This article belongs to the Special Issue Innovative Strategies for Solid Waste Minimisation in the Mining and Minerals Industry)

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14 pages, 2694 KiB

Open AccessArticle

Research on Strength Prediction Model and Microscopic Analysis of Mechanical Characteristics of Cemented Tailings Backfill under Fractal Theory

by Hongwei Deng, Tao Duan, Guanglin Tian, Yao Liu and Weiyou Zhang

Minerals 2021, 11(8), 886; https://doi.org/10.3390/min11080886 - 16 Aug 2021

Cited by 7 | Viewed by 1616

Abstract

In order to further study the internal relationship between the microscopic pore characteristics and macroscopic mechanical properties of cemented tailings backfill (CTB), in this study, mine tailings and ordinary Portland cement (PC32.5) were selected as aggregate and cementing materials, respectively, and different additives (anionic polyacrylamide (APAM), lime and fly ash) were added to backfill samples with mass concentration of 74% and cement–sand ratios of 1:4, 1:6 and 1:8. After 28 days of curing, based on the uniaxial compressive strength test, nuclear magnetic resonance (NMR) porosity test and the fractal characteristics of pore structure, the relationships of the compressive strength with the proportion and fractal dimension of pores with different radii were analyzed. The uniaxial compressive strength prediction model of the CTB with the proportion of harmless pores and the fractal dimension of harmful pores as independent variables was established. The results show that the internal pores of the material are mainly the harmless and less harmful pores, and the sum of the average proportions of the two reaches 73.45%. Some characterization parameters of pore structure have a high correlation with the compressive strength. Among them, the correlation coefficients of compressive strength with the proportion of harmless pores and fractal dimension of harmful pores are 0.9219 and 0.9049, respectively. The regression results of the strength prediction model are significant, and the correlation coefficient is 0.9524. The predicted strength value is close to the actual strength value, and the predicted results are accurate and reliable. Full article

(This article belongs to the Special Issue Innovative Strategies for Solid Waste Minimisation in the Mining and Minerals Industry)

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23 pages, 8890 KiB

Open AccessArticle

Experimental Study on Mechanical Properties of Paste Backfill with Flue-Gas Desulphurisation Gypsum under Combined Action of Dry–Wet Cycles and Chloride Erosion

by Sheng Wang, Feng Wang, Dawei Yin, Tianqi Jiang and Zhen Zhang

Minerals 2021, 11(8), 882; https://doi.org/10.3390/min11080882 - 15 Aug 2021

Cited by 5 | Viewed by 1803

Abstract

Flue-gas desulphurisation gypsum—a solid waste from power plants—can be used to prepare paste backfill for reducing costs. Most paste backfills are exposed to dry–wet cycles and chloride salt-rich water in mines. Therefore, the mechanical properties and damage mechanisms of paste backfill with desulphurised gypsum under the coupling action of erosion due to chloride with different concentrations and dry–wet cycles were investigated using methods such as visual observation, mass measurement, uniaxial compression, acoustic emission, Fourier-transform infrared spectroscopy, X-ray diffraction analysis, and field-emission scanning electron microscopy. With an increasing number of dry–wet cycles, the mass, elastic modulus, and strength of the paste backfill exhibited the trend of increasing first and then decreasing. The failure mechanism changed from mainly vertical fractures to the alternating development of vertical and horizontal fractures. The surface denudation effect of the specimens in a solution with a higher concentration was more severe under the same number of dry–wet cycles. In this study, the laws governing the mass change, strength change, degree of surface denudation, and failure pattern of desulphurised gypsum-filled specimens under different concentrations of chloride salt and different numbers of dry–wet cycles were derived. Full article

(This article belongs to the Special Issue Innovative Strategies for Solid Waste Minimisation in the Mining and Minerals Industry)

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16 pages, 3713 KiB

Open AccessArticle

Safety Analysis of Synergetic Operation of Backfilling the Open Pit Using Tailings and Excavating the Ore Deposit Underground

by Qinli Zhang, Bingyi Zhang, Qiusong Chen, Daolin Wang and Xiang Gao

Minerals 2021, 11(8), 818; https://doi.org/10.3390/min11080818 - 28 Jul 2021

Cited by 9 | Viewed by 2698

Abstract

The transition from open pit mining to underground mining is essential for mineral resources to achieve deep excavation. Recently, cemented paste backfill (CPB) has been proposed as a novel technology to achieve open pit backfill (OPB). The proposed method not only eliminates the danger of the open-pit slope but also reduces the disposal of waste tailings. In order to ensure safe mining during the synergetic operation of OPB and underground mining, it is of great significance to improve this technology. In the present study, an open-pit metal mine in Anhui Province was taken as the research object. Then, the safety of underground stope roofs, underground backfill pillars, and open-pit slopes was evaluated during OPB. To this end, numerical simulations were performed and experiments were conducted on a similar physical model. Accordingly, the backfill mechanical parameters were optimized. The obtained results show that backfill height exerts the most significant effect on the safety of roofs and underground backfill pillars, accompanied by small displacements along the vertical direction during the backfill process. Moreover, concentration was observed at the foot of the slope, while the overall structure remained stable with no considerable displacement. The overall safety factors met the safety requirements. Based on the obtained results, the optimal foundation strength, foundation height, backfill strength and backfill height were 4 MPa, 10 m, 1.5 MPa, and 120 m, respectively. Moreover, it was concluded that displacements in the abovementioned three regions tend to be stable when the backfill height exceeds 150 m without damage. The present article provides a certain theoretical and application guideline for OPB practices in similar metal mines and suggests possibilities for cleaner production. Full article

(This article belongs to the Special Issue Innovative Strategies for Solid Waste Minimisation in the Mining and Minerals Industry)

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16 pages, 11393 KiB

Open AccessArticle

Analysis of Strength and Microstructural Characteristics of Mine Backfills Containing Fly Ash and Desulfurized Gypsum

by Zhiqiang Huang, Erol Yilmaz and Shuai Cao

Minerals 2021, 11(4), 409; https://doi.org/10.3390/min11040409 - 13 Apr 2021

Cited by 57 | Viewed by 2950

Abstract

The utilization of solid wastes (SWs) as a potential resource for backfilling is not only conducive to environmental protection but also reduces the surface storage of waste. Two types of SWs, including fly ash (FA) and desulfurized gypsum (DG), were used to prepare cementitious backfilling materials for underground mined-out areas. Ordinary Portland cement (OPC) was used as cement in mine backfill. To better investigate the feasibility of preparing backfill materials, some laboratory tests, such as uniaxial compressive strength (UCS), scanning electron microscopy (SEM), and energy dissipation theory, were conducted to explore both strength and microstructural properties of backfilling. Results have demonstrated that the main components of FA and DG in this study are oxides, with few toxic and heavy metal components. The ideal ratio of OPC:FA:DG is 1:6:2 and the corresponding UCS values are 2.5 and 4.2 MPa when the curing time are 7 days and 14 days, respectively. Moreover, the average UCS value of backfilling samples gradually decreased when the proportion of DG in the mixture increased. The main failure modes of various backfilling materials are tensile and shearing cracks. In addition, the corresponding relations among total input energy, dissipated energy and strain energy, and stress–strain curve were investigated. The spatial distribution of oxygen, aluminum, silicon, calcium, iron and magnesium elements, and hydration product are explored from the microstructure’s perspective. The findings of this study provide both invaluable information and industrial applications for the efficient management of solid waste, based on sustainable development and circular economy. Full article

(This article belongs to the Special Issue Innovative Strategies for Solid Waste Minimisation in the Mining and Minerals Industry)

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15 pages, 2706 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Prediction of Postflotation Tailings Behavior in a Large Storage Facility

by Magdalena Wróżyńska

Minerals 2021, 11(4), 362; https://doi.org/10.3390/min11040362 - 30 Mar 2021

Cited by 2 | Viewed by 1862

Abstract

Extracting and copper production on a large scale generates large volumes of postflotation mine tailings. The scale of operation and development of tailings storage facilities (TSFs) forces the use of innovative solutions enabling safe storage now and in the future. Any changes to the operation require multi-directional monitoring of the impact of these changes on storage safety. The ongoing exploitation will be ensured by expansion of the TSF and a change in tailings storage technology. This approach will preclude the need for changes to the new location, such as changes of land use, and will minimise the volume of mine waste. The paper presents the results of pilot studies carried out to implement the change in postflotation tailings storage technology at Żelazny Most TSF (Poland) in the future. The aim of the paper was settlements prediction of tailings and comparison of deformations with observed settlements. Settlements prediction of tailings was made on the basis of the results of the DMT (Marchetti Dilatometer Test), recommended for the prediction of natural soil settlement. Depending on the analysed zone of the TSF, settlements ranged from a few centimetres to over 1.5 m. Despite the difference shown, the results of DMT and geodetic measurements indicate a convergent trend of settlement. Full article

(This article belongs to the Special Issue Innovative Strategies for Solid Waste Minimisation in the Mining and Minerals Industry)

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15 pages, 6336 KiB

Open AccessArticle

Stepwise Utilization Process to Recover Valuable Components from Copper Slag

by Siwei Li, Zhengqi Guo, Jian Pan, Deqing Zhu, Tao Dong and Shenghu Lu

Minerals 2021, 11(2), 211; https://doi.org/10.3390/min11020211 - 17 Feb 2021

Cited by 15 | Viewed by 2638

Abstract

Waste copper slag is a typical hazardous solid waste containing a variety of valuable elements and has not been effectively disposed of so far. In this paper, a stepwise extraction process was proposed to recover valuable elements (copper, iron, lead and zinc) from waste copper slag. The specific procedures are as follows: (1) A flotation process was adopted to enrich copper, and when the copper grade in the flotation concentrate was 21.50%, the copper recovery rate was 77.78%. (2) The flotation tailings were pelletized with limestone, then the green pellets were reduced, and the magnetic separation process was carried out. When the iron and copper grades in the magnetic concentrate were 90.21% Fe and 0.4% Cu, 91.34% iron and 83.41% copper were recovered, respectively. (3) Non-magnetic tailings were mixed with clinker and standard sand to produce common Portland cement. Several products were obtained from the waste copper slag through the proposed process: flotation concentrate, measured 21.50% Cu; magnetic concentrate, containing 90.21% TFe and 0.4% Cu; direct reduction dust, including 65.17% ZnO and 2.66% PbO; common Portland cement for building construction. The comprehensive utilization method for waste copper slag achieved zero tailing and has great potential for practical application. Full article

(This article belongs to the Special Issue Innovative Strategies for Solid Waste Minimisation in the Mining and Minerals Industry)

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10 pages, 3245 KiB

Open AccessArticle

Prediction Models for Evaluating the Strength of Cemented Paste Backfill: A Comparative Study

by Jiandong Liu, Guichen Li, Sen Yang and Jiandong Huang

Minerals 2020, 10(11), 1041; https://doi.org/10.3390/min10111041 - 21 Nov 2020

Cited by 12 | Viewed by 2066

Abstract

Cemented paste backfill (CPB) is widely used in underground mining, and attracts more attention these years as it can reduce mining waste and avoid environmental pollution. Normally, to evaluate the functionality of CPB, the compressive strength (UCS) is necessary work, which is also time and money consuming. To address this issue, seven machine learning models were applied and evaluated in this study, in order to predict the UCS of CPB. In the laboratory, a series of tests were performed, and the dataset was constructed considering five key influencing variables, such as the tailings to cement ratio, curing time, solids to cement ratio, fine sand percentage and cement types. The results show that different variables have various effects on the strength of CPB. The optimum models for predicting the UCS of CPB are a support vector machine (SVM), decision tree (DT), random forest (RF) and back-propagation neural network (BPNN), which means that these models can be directly applied for UCS prediction in future work. Furthermore, the intelligent model reveals that the tailings to cement ratio has the most important influence on the strength of CPB. This research can boost CPB application in the field, and guide the artificial intelligence application in future mining. Full article

(This article belongs to the Special Issue Innovative Strategies for Solid Waste Minimisation in the Mining and Minerals Industry)

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15 pages, 2138 KiB

Open AccessArticle

Waste Slag from Heating Plants as a Partial Replacement for Cement in Mortar and Concrete Production. Part I—Physical–Chemical and Physical–Mechanical Characterization of Slag

by Andrijana Nedeljković, Marija Stojmenović, Jelena Gulicovski, Nenad Ristić, Sonja Milićević, Jugoslav Krstić and Milan Kragović

Minerals 2020, 10(11), 992; https://doi.org/10.3390/min10110992 - 09 Nov 2020

Cited by 8 | Viewed by 1957

Abstract

Numerous factors influence the complexity of environmental and waste management problems, and the most significant goal is the reuse of materials that have completed their “life cycle” and the reduction in the use of new resources. In order to reduce impact of waste slag on the environment, in the present study, waste slag, generated in heating plants after lignite combustion, was characterized in detail and tested for application as a replacement for cement in mortar or concrete production. For physical–chemical characterization of slag, different experimental and instrumental techniques were used such as chemical composition and determination of the content of heavy metals, investigation of morphological and textural properties, thermal analysis, X-ray, and infrared spectroscopy. Physical–mechanical characterization of slag was also performed and included determination of activity index, water requirement, setting time and soundness. A leaching test was also performed. Presented results show that waste slag may be used in mortar and concrete production as a partial cement replacement, but after additional combustion at 650 °C and partial replacement of slag with silica fume in the minimal amount of 12%. The maximal obtained cement replacement was 20% (17.8% slag and 2.2% of silica fume). Full article

(This article belongs to the Special Issue Innovative Strategies for Solid Waste Minimisation in the Mining and Minerals Industry)

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