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Kotte-Hewa DJ, Durce D, Salah S, Vantelon D, Smolders E. Association of rare earth elements with secondary mineral phases formed during alkalinization of acid mine drainage. THE SCIENCE OF THE TOTAL ENVIRONMENT 2024; 948:174895. [PMID: 39032740 DOI: 10.1016/j.scitotenv.2024.174895] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/07/2024] [Revised: 06/17/2024] [Accepted: 07/17/2024] [Indexed: 07/23/2024]
Abstract
Rare Earth Elements (REE) are present in acid mine drainage (AMD) in micromolar concentrations and AMD discharge may lead to an environmental risk. Alkaline Passive Treatment Systems (PTS) are often used to treat AMD and trap toxic trace elements. This study was set up to identify mechanisms by which REE are trapped in or on secondary phases formed in a PTS. Batch alkalinization experiments were performed to simulate PTS by sequentially increasing the pH of AMD collected from the Tharsis mining area inside the Iberian Pyrite Belt and synthetic AMD water samples via CaCO3 addition. The solids that precipitated up to pH ~4 and between pH 4-6 were collected and characterized by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) in combination with Scanning Electron Microscope/Energy Dispersive X-ray spectroscopy (SEM/EDX) and synchrotron-based X-ray Absorption Spectroscopy (XAS) and synchrotron-based Micro-X-ray Fluorescence (μ-XRF). Results reveal that REE are mostly scavenged between pH 4-6 in association with Al and Fe phases, whereas a smaller fraction is scavenged at pH ~4 by association with gypsum. Synchrotron-based analysis evidences the incorporation of La3+ into the gypsum structure by substituting Ca2+, indicating a co-precipitation mechanism with gypsum occurring mainly at low pH. Results from parallel adsorption and co-precipitation tests suggest that the REE scavenging between pH 4-6 could be due to a combination of adsorption and co-precipitation on Al(OH)3 and ferrihydrite. This implies that in PTS, REE would be mainly found in Al- (and Fe-) oxyhydroxides occurring in deeper layers of the PTS, i.e., where higher pH-values occur, though a small fraction, especially the light REE, could also be found incorporated into gypsum in the upper layers.
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Affiliation(s)
- Dileesha Jayahansani Kotte-Hewa
- Belgian Nuclear Research Centre, SCK CEN, Boeretang 200, Mol 2400, Belgium; KU Leuven, Department of Soil and Water Management, Kasteelpark Arenberg 20, 3001 Heverlee, Belgium.
| | - Delphine Durce
- Belgian Nuclear Research Centre, SCK CEN, Boeretang 200, Mol 2400, Belgium
| | - Sonia Salah
- Belgian Nuclear Research Centre, SCK CEN, Boeretang 200, Mol 2400, Belgium
| | - Delphine Vantelon
- LUCIA Beamline, SOLEIL Synchrotron, L'Orme des Merisiers, Départementale 128, 91190 Saint-Aubin, France
| | - Erik Smolders
- KU Leuven, Department of Soil and Water Management, Kasteelpark Arenberg 20, 3001 Heverlee, Belgium
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2
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Millán-Becerro R, León R, Romero-Matos J, Moreno-González R, Pérez-López R. Towards circular and sustainable restoration of a deeply polluted river basin: The Odiel River catchment (SW Spain). THE SCIENCE OF THE TOTAL ENVIRONMENT 2024; 907:168078. [PMID: 37898213 DOI: 10.1016/j.scitotenv.2023.168078] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/07/2023] [Revised: 10/20/2023] [Accepted: 10/21/2023] [Indexed: 10/30/2023]
Affiliation(s)
- Ricardo Millán-Becerro
- Department of Earth Sciences & Research Center on Natural Resources, Health and the Environment (RENSMA), University of Huelva, Campus 'El Carmen', s/n, 21071 Huelva, Spain; Department of Mineralogy and Petrology, University of Granada, Fuentenueva s/n, Granada 18071, Spain.
| | - Rafael León
- Department of Earth Sciences & Research Center on Natural Resources, Health and the Environment (RENSMA), University of Huelva, Campus 'El Carmen', s/n, 21071 Huelva, Spain
| | - Jonatan Romero-Matos
- Department of Earth Sciences & Research Center on Natural Resources, Health and the Environment (RENSMA), University of Huelva, Campus 'El Carmen', s/n, 21071 Huelva, Spain
| | - Raul Moreno-González
- Department of Earth Sciences, Drone Service, Institute for Marine Research (INMAR), University of Cadiz, Campus Rio San Pedro, s/n, 11510 Puerto Real, Spain
| | - Rafael Pérez-López
- Department of Earth Sciences & Research Center on Natural Resources, Health and the Environment (RENSMA), University of Huelva, Campus 'El Carmen', s/n, 21071 Huelva, Spain
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Tu Z, Wu Q, He H, Zhou S, Liu J, He H, Liu C, Dang Z, Reinfelder JR. Reduction of acid mine drainage by passivation of pyrite surfaces: A review. THE SCIENCE OF THE TOTAL ENVIRONMENT 2022; 832:155116. [PMID: 35398133 DOI: 10.1016/j.scitotenv.2022.155116] [Citation(s) in RCA: 18] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/24/2022] [Revised: 04/02/2022] [Accepted: 04/04/2022] [Indexed: 06/14/2023]
Abstract
Acid mine drainage (AMD), a source of considerable environmental pollution worldwide, has prompted the development of many strategies to alleviate its effects. Unfortunately, the methods available for remedial treatment of AMD and the damage it cause are generally costly, labor-intensive, and time-consuming. Furthermore, such treatments may result in secondary pollution. Alternatively, treating the AMD problem at its source through pyrite surface passivation has become an important topic for research because it has the potential to reduce or prevent the generation of AMD and associated pollution. This review summarizes various pyrite anti-corrosion technologies, including the formation of various passivating coatings (inorganic, organic and organosilane) and carrier-microencapsulation. Several effective long-term passivators are identified, although many of them currently have important deficiencies that limit their practical application. Combining the mechanisms of existing passivation agents or new artificial materials, while considering environmental conditions, costs, and long-term passivation performance, is a feasible direction for future research.
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Affiliation(s)
- Zhihong Tu
- College of Environmental Science and Engineering, Guilin University of Technology, Guilin 541004, China.
| | - Qi Wu
- College of Environmental Science and Engineering, Guilin University of Technology, Guilin 541004, China
| | - Hongping He
- CAS Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
| | - Shu Zhou
- College of Environmental Science and Engineering, Guilin University of Technology, Guilin 541004, China
| | - Jie Liu
- College of Environmental Science and Engineering, Guilin University of Technology, Guilin 541004, China; Collaborative Innovation Center for Water Pollution Control and Water Safety in Karst Area, Guilin University of Technology, Guilin 541004, China
| | - Huijun He
- College of Environmental Science and Engineering, Guilin University of Technology, Guilin 541004, China; Guangxi Key Laboratory of Environmental Pollution Control Theory and Technology for Science and Education Combined with Science and Technology Innovation Base, Guilin University of Technology, Guilin, Guangxi 541004, China
| | - Chongmin Liu
- College of Environmental Science and Engineering, Guilin University of Technology, Guilin 541004, China; Guangxi Key Laboratory of Environmental Pollution Control Theory and Technology for Science and Education Combined with Science and Technology Innovation Base, Guilin University of Technology, Guilin, Guangxi 541004, China
| | - Zhi Dang
- The Key Lab of Pollution Control and Ecosystem Restoration in Industry Clusters, Ministry of Education, South China University of Technology, Guangzhou 510006, China
| | - John R Reinfelder
- Department of Environmental Sciences, Rutgers University, New Brunswick, NJ 08901, USA
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Nooraiepour M, Masoudi M, Hellevang H. Probabilistic nucleation governs time, amount, and location of mineral precipitation and geometry evolution in the porous medium. Sci Rep 2021; 11:16397. [PMID: 34385483 PMCID: PMC8361100 DOI: 10.1038/s41598-021-95237-7] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2021] [Accepted: 07/22/2021] [Indexed: 11/09/2022] Open
Abstract
One important unresolved question in reactive transport is how pore-scale processes can be upscaled and how predictions can be made on the mutual effect of chemical processes and fluid flow in the porous medium. It is paramount to predict the location of mineral precipitation besides their amount for understanding the fate of transport properties. However, current models and simulation approaches fail to predict precisely where crystals will nucleate and grow in the spatiotemporal domain. We present a new mathematical model for probabilistic mineral nucleation and precipitation. A Lattice Boltzmann implementation of the two-dimensional mineral surface was developed to evaluate geometry evolution when probabilistic nucleation criterion is incorporated. To provide high-resolution surface information on mineral precipitation, growth, and distribution, we conducted a total of 27 calcium carbonate synthesis experiments in the laboratory. The results indicate that nucleation events as precursors determine the location and timing of crystal precipitation. It is shown that reaction rate has primary control over covering the substrate with nuclei and, subsequently, solid-phase accumulation. The work provides insight into the spatiotemporal evolution of porous media by suggesting probabilistic and deterministic domains for studying reactive transport processes. We indicate in which length- and time-scales it is essential to incorporate probabilistic nucleation for valid predictions.
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Affiliation(s)
- Mohammad Nooraiepour
- CO2 Storage Research Group, Department of Geosciences, University of Oslo, Blindern, P.O. Box 1047, 0316, Oslo, Norway.
| | - Mohammad Masoudi
- CO2 Storage Research Group, Department of Geosciences, University of Oslo, Blindern, P.O. Box 1047, 0316, Oslo, Norway
| | - Helge Hellevang
- CO2 Storage Research Group, Department of Geosciences, University of Oslo, Blindern, P.O. Box 1047, 0316, Oslo, Norway
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Turingan COA, Fabella DJA, Sadol KAN, Beltran AB, Alorro RD, Orbecido AH. Comparing the performance of low‐grade nickel ore and limestone for treatment of synthetic acid mine drainage. ASIA-PAC J CHEM ENG 2020. [DOI: 10.1002/apj.2457] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Casey Oliver A. Turingan
- Department of Chemical Engineering, Gokongwei College of EngineeringDe La Salle University 1004 Manila Philippines
| | - Divina Joyce A. Fabella
- Department of Chemical Engineering, Gokongwei College of EngineeringDe La Salle University 1004 Manila Philippines
| | - Kim Ahmed N. Sadol
- Department of Chemical Engineering, Gokongwei College of EngineeringDe La Salle University 1004 Manila Philippines
| | - Arnel B. Beltran
- Department of Chemical Engineering, Gokongwei College of EngineeringDe La Salle University 1004 Manila Philippines
| | - Richard D. Alorro
- Department of Mining Engineering and Metallurgical Engineering, Western Australian School of Mines: Minerals, Energy and Chemical EngineeringCurtin University Kalgoorlie Western Australia 6430 Australia
| | - Aileen H. Orbecido
- Department of Chemical Engineering, Gokongwei College of EngineeringDe La Salle University 1004 Manila Philippines
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6
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Evaluation of Dispersed Alkaline Substrate and Diffusive Exchange System Technologies for the Passive Treatment of Copper Mining Acid Drainage. WATER 2020. [DOI: 10.3390/w12030854] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The study evaluates the performance of the novel ADES (alkaline diffusive exchange System), SDES (sulfidogenic diffusive exchange system) and DAS (Dispersed Alkaline Substrate) technologies for the passive treatment of high-strength acid mine drainage (AMD) from copper mining (pH~3, 633 mg Cu L−1). The chemical DAS and ADES prototypes showed the best performance in the removal of Cu, Al, and Zn (98–100%), while the biochemical SDES reactors achieved a high sulfate removal rate (average of 0.28 mol m−3 day-1). Notably, the DES technology was effective in protecting the sulfate-reducing communities from the high toxicity of the AMD, and also in maintaining bed permeability, an aspect that was key in the ADES reactor. The DAS reactor showed the highest reactivity, accumulating the metallic precipitates in a lower reactor volume, allowing to conclude that it requires the lowest hydraulic residence time among all the reactors. However, the concentration of precipitates resulted in the formation of a hardpan, which may trigger the need of removing it to avoid compromising the continuity of the treatment process. This study suggests the development of new treatment alternatives by combining the strengths of each technology in combined or serial treatments.
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Delgado J, Barba-Brioso C, Ayala D, Boski T, Torres S, Calderón E, López F. Remediation experiment of Ecuadorian acid mine drainage: geochemical models of dissolved species and secondary minerals saturation. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2019; 26:34854-34872. [PMID: 31655982 DOI: 10.1007/s11356-019-06539-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/12/2019] [Accepted: 09/12/2019] [Indexed: 06/10/2023]
Abstract
Acid mine drainage is one of the main environmental hazards to ecosystems worldwide and it is directly related to mining activities. In Ecuador, such acidic-metallic waters are drained to rivers without treatment. In this research, we tested a laboratory combined (Ca-Mg) Dispersed Alkaline Substrate (DAS) system as an alternative to remediate acid drainage from the Zaruma-Portovelo gold mining site, at El Oro, Ecuador. The system worked at low and high flow hydraulic rates during a period of 8 months, without signs of saturation.. Analysis of physico-chemical parameters and water composition (ICP-OES, ICP-MS) demonstrated that treatment effectively increased water pH and promoted the retention of about 80% of Fe, Al, Mn and Cu. Under acid conditions As, Cr and Pb concentrations decreased with Fe and possible precipitation of jarosite and schwertmannite. However, the homogeneous depletion of Cr at pH above 6 could be related to ferrihydrite or directly with Cr (OH)3 precipitation. After DAS-Ca, sulphate, phosphate and rare earth elements (REE) concentrations decreased to 1912, 0.85 and 0.07 mg/L respectively, while DAS-Mg contributed to form a complex model of minor carbonate and phosphate phases as main sink of REE. DAS-Mg also promoted the retention of most divalent metals at pH values over seven. Thus, this low cost treatment could avoid environmental pollution and international conflicts. Anyway, further investigations are needed to obtain higher Zn retention values. Graphical abstract.
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Affiliation(s)
- Joaquín Delgado
- Department of Physical, Chemical and Natural Environments, Faculty of Experimental Sciences, Pablo de Olavide University, 41013, Seville, Spain
- Centre for Marine and Environmental Research, Faculty of Science and Technology, Algarve University, 8005-139, Faro, Portugal
| | - Cinta Barba-Brioso
- Department of Crystallography, Mineralogy and Agricultural Chemistry. Faculty of Chemistry, Seville University, 41012, Seville, Spain.
| | - Diana Ayala
- Department of Civil and Environmental Engineering, Biogeochemistry Dual Major Program, The Pennsylvania State University, State College, PA, 16802, USA
| | - Tomasz Boski
- Centre for Marine and Environmental Research, Faculty of Science and Technology, Algarve University, 8005-139, Faro, Portugal
| | - Sandra Torres
- National Research Institute of Geology, Mining and Metallurgy, 170124, Quito, Ecuador
| | - Edmundo Calderón
- National Research Institute of Geology, Mining and Metallurgy, 170124, Quito, Ecuador
| | - Flavio López
- National Research Institute of Geology, Mining and Metallurgy, 170124, Quito, Ecuador
- Central University of Ecuador, 170129, Quito, Ecuador
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8
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Labastida I, Armienta MA, Lara RH, Briones R, González I, Romero F. Kinetic approach for the appropriate selection of indigenous limestones for acid mine drainage treatment with passive systems. THE SCIENCE OF THE TOTAL ENVIRONMENT 2019; 677:404-417. [PMID: 31059883 DOI: 10.1016/j.scitotenv.2019.04.373] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/15/2019] [Revised: 04/24/2019] [Accepted: 04/25/2019] [Indexed: 06/09/2023]
Abstract
Acid mine drainage treatments using limestones have been widely reported in the literature; however, additional studies are needed to select the most effective limestone type based on an adequate characterization and in consideration of the kinetics of the rock's reaction upon exposure to high iron concentrations. In this study, with the aim to select the most appropriate limestone to use in a passive treatment system, the regular characterization (calcium carbonate analysis, determination of specific superficial area, and porosity) was complemented with a heterogeneous kinetic analysis of limestone dissolution. The physico-chemical conditions of high acidity and a high Fe concentration were similar to those measured in leachates from the "Compañía Minera Zimapán" (CMZ) tailings impoundment located in a historical Mexican mining zone. Column experiments were carried out with the selected limestone to treat leachates from two tailing deposits; one highly weathered and un-active (CMZ) and the other still active (San Miguel Nuevo). Removal efficiencies close to 100% were reached for arsenic, iron, cadmium, and aluminum. There was also a partial removal of zinc and silica, and the pH increased close to neutrality. Electrical conductivity, sulfate levels, and oxidation reduction potential were also measured during the experiments. Concentration profiles for some elements were established. Chemical results, stoichiometric relationships between elements obtained by scanning electron microscopy-energy dispersive spectroscopy, and scanning electron microscopy-wavelength dispersive spectroscopy allowed for determining the chemical associations of the elements at the surface. The results indicated that the methodology for limestone selection to treat AMD from San Miguel Nuevo tailings was adequate; however, additional studies are required to improve the permeability and the lifetime of the system used to treat CMZ leachates.
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Affiliation(s)
- Israel Labastida
- Universidad Autónoma Metropolitana, Unidad Azcapotzalco, Departamento de Energía, Av. San Pablo 180, 02200 Ciudad de Mexico, Mexico; Universidad Nacional Autónoma de México, Posgrado en Ciencias de la Tierra, UNAM, 04510 Ciudad de México, Mexico
| | - M Aurora Armienta
- Universidad Nacional Autónoma de México, Instituto de Geofísica, UNAM, 04510 Ciudad de Mexico, Mexico.
| | - René H Lara
- Departamento de Ciencia de Materiales, Facultad de Ciencias Químicas, Universidad Juárez del Estado de Durango, Av. Veterinaria S/N, Circuito Universitario, 34120 Durango, Dgo, Mexico
| | - Roberto Briones
- Facultad de Ingeniería, Instituto de Metalurgia, Universidad Autónoma de San Luis Potosí, Sierra Leona 550, Lomas 2ª sección, C.P. 78210, San Luis Potosí, S.L.P., Mexico
| | - Ignacio González
- Universidad Autónoma Metropolitana, Unidad Iztapalapa, Departamento de Química, Av. San Rafael Atlixco No. 186, Col. Vicentina C.P., 09340, Iztapalapa, Ciudad de Mexico, Mexico
| | - Francisco Romero
- Universidad Nacional Autónoma de México, Instituto de Geología, UNAM, 04510 Ciudad de Mexico, Mexico
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Rakotonimaro TV, Neculita CM, Bussière B, Genty T, Zagury GJ. Performance assessment of laboratory and field-scale multi-step passive treatment of iron-rich acid mine drainage for design improvement. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2018; 25:17575-17589. [PMID: 29667051 DOI: 10.1007/s11356-018-1820-x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/08/2017] [Accepted: 03/19/2018] [Indexed: 06/08/2023]
Abstract
Multi-step passive systems for the treatment of iron-rich acid mine drainage (Fe-rich AMD) perform satisfactorily at the laboratory scale. However, their field-scale application has revealed dissimilarities in performance, particularly with respect to hydraulic parameters. In this study, the assessment of factors potentially responsible for the variations in performance of laboratory and field-scale multi-step systems was undertaken. Three laboratory multi-step treatment scenarios, involving a combination of dispersed alkaline substrate (DAS) units, anoxic dolomitic drains, and passive biochemical reactors (PBRs), were set up in 10.7-L columns. The field-scale treatment consisted of two PBRs separated by a wood ash (WA) reactor. The parameters identified as possibly influencing the performances of the laboratory and field-scale experiments were the following: AMD chemistry (electrical conductivity and Fe and SO42- concentrations), flow rate (Q), and saturated hydraulic conductivity (ksat). Based on these findings, the design of an efficient passive multi-step treatment system is suggested to consider the following: (1) Fe pretreatment, using materials with high ksat and low HRT. If a PBR is to be used, the Fe load should be < 26 g/m3 substrate/day (Fe < 200 mg/L) and SO42- < 110 g/m3 substrate/day; (2) PBR/DAS filled with a mixture with at least 20% of neutralizing agent; (3) include Q and ksat (> 10-3 cm/s) in the long-term prediction. Finally, mesocosm testing is strongly recommended prior to construction of full-scale systems for the treatment of Fe-rich AMD.
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Affiliation(s)
- Tsiverihasina V Rakotonimaro
- Research Institute on Mines and Environment (RIME)-University of Québec in Abitibi-Témiscamingue (UQAT), 445, boul. de l'Université, Rouyn-Noranda, QC, J9X 5E4, Canada
| | - Carmen Mihaela Neculita
- Research Institute on Mines and Environment (RIME)-University of Québec in Abitibi-Témiscamingue (UQAT), 445, boul. de l'Université, Rouyn-Noranda, QC, J9X 5E4, Canada.
| | - Bruno Bussière
- Research Institute on Mines and Environment (RIME)-University of Québec in Abitibi-Témiscamingue (UQAT), 445, boul. de l'Université, Rouyn-Noranda, QC, J9X 5E4, Canada
| | - Thomas Genty
- Research Institute on Mines and Environment (RIME)-University of Québec in Abitibi-Témiscamingue (UQAT), 445, boul. de l'Université, Rouyn-Noranda, QC, J9X 5E4, Canada
| | - Gérald J Zagury
- RIME, Department of Civil, Geological, and Mining Engineering, Polytechnique Montréal , Montréal, QC, Canada
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Ayora C, Macías F, Torres E, Lozano A, Carrero S, Nieto JM, Pérez-López R, Fernández-Martínez A, Castillo-Michel H. Recovery of Rare Earth Elements and Yttrium from Passive-Remediation Systems of Acid Mine Drainage. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2016; 50:8255-8262. [PMID: 27351211 DOI: 10.1021/acs.est.6b02084] [Citation(s) in RCA: 87] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Rare earth elements and yttrium (REY) are raw materials of increasing importance for modern technologies, and finding new sources has become a pressing need. Acid mine drainage (AMD) is commonly considered an environmental pollution issue. However, REY concentrations in AMD can be several orders of magnitude higher than in naturally occurring water bodies. With respect to shale standards, the REY distribution pattern in AMD is enriched in intermediate and valuable REY, such as Tb and Dy. The objective of the present work is to study the behavior of REY in AMD passive-remediation systems. Traditional AMD passive remediation systems are based on the reaction of AMD with calcite-based permeable substrates followed by decantation ponds. Experiments with two columns simulating AMD treatment demonstrate that schwertmannite does not accumulate REY, which, instead, are retained in the basaluminite residue. The same observation is made in two field-scale treatments from the Iberian Pyrite Belt (IPB, southwest Spain). On the basis of the amplitude of this process and on the extent of the IPB, our findings suggest that the proposed AMD remediation process can represent a modest but suitable REY source. In this sense, the IPB could function as a giant heap-leaching process of regional scale in which rain and oxygen act as natural driving forces with no energy investment. In addition to having environmental benefits of its treatment, AMD is expected to last for hundreds of years, and therefore, the total reserves are practically unlimited.
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Affiliation(s)
- Carlos Ayora
- Institute of Environmental Assessment and Water Research, CSIC , Jordi Girona 18, 08034 Barcelona, Spain
| | - Francisco Macías
- Department of Geology, University of Huelva , Campus "El Carmen" s/n, 21071 Huelva, Spain
| | - Ester Torres
- Institute of Environmental Assessment and Water Research, CSIC , Jordi Girona 18, 08034 Barcelona, Spain
| | - Alba Lozano
- Institute of Environmental Assessment and Water Research, CSIC , Jordi Girona 18, 08034 Barcelona, Spain
| | - Sergio Carrero
- Department of Geology, University of Huelva , Campus "El Carmen" s/n, 21071 Huelva, Spain
| | - José-Miguel Nieto
- Department of Geology, University of Huelva , Campus "El Carmen" s/n, 21071 Huelva, Spain
| | - Rafael Pérez-López
- Department of Geology, University of Huelva , Campus "El Carmen" s/n, 21071 Huelva, Spain
| | - Alejandro Fernández-Martínez
- Institut des Sciences de la Terre, CNRS and Université Grenoble Alpes , 1381 Rue de la Piscine, 38041 Grenoble, France
| | - Hiram Castillo-Michel
- European Synchrotron Radiation Facility , 71 avenue des Martyrs, 38000 Grenoble, France
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11
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Liu J, He L, Dong F, Hudson-Edwards KA. The role of nano-sized manganese coatings on bone char in removing arsenic(V) from solution: Implications for permeable reactive barrier technologies. CHEMOSPHERE 2016; 153:146-154. [PMID: 27016809 DOI: 10.1016/j.chemosphere.2016.03.044] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/09/2015] [Revised: 03/03/2016] [Accepted: 03/10/2016] [Indexed: 06/05/2023]
Abstract
Although the removal of arsenic(V) (As(V)) from solution can be improved by forming metal-bearing coatings on solid media, there has been no research to date examining the relationship between the coating and As(V) sorption performance. Manganese-coated bone char samples with varying concentrations of Mn were created to investigate the adsorption and desorption of As(V) using batch and column experiments. Breakthrough curves were obtained by fitting the Convection-Diffusion Equation (CDE), and retardation factors were used to quantify the effects of the Mn coatings on the retention of As(V). Uncoated bone char has a higher retention factor (44.7) than bone char with 0.465 mg/g of Mn (22.0), but bone char samples with between 5.02 mg/g and 14.5 mg/g Mn have significantly higher retention factors (56.8-246). The relationship between retardation factor (Y) and Mn concentration (X) is Y = 15.1 X + 19.8. Between 0.2% and 0.6% of the sorbed As is desorbed from the Mn-coated bone char at an initial pH value of 4, compared to 30% from the uncoated bone char. The ability of the Mn-coated bone char to neutralize solutions increases with increased amounts of Mn on the char. The results suggest that using Mn-coated bone char in Permeable Reactive Barriers would be an effective method for remediating As(V)-bearing solutions such as acid mine drainage.
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Affiliation(s)
- Jing Liu
- The Key Laboratory of Solid Waste Treatment and Resource Recycle, Ministry of Education, Southwest University of Science and Technology, Mianyang, 621010, China; The State Key Laboratory of Coal Resources and Safe Mining, China University of Mining & Technology, Beijing, 100083, China
| | - Lile He
- The Key Laboratory of Solid Waste Treatment and Resource Recycle, Ministry of Education, Southwest University of Science and Technology, Mianyang, 621010, China
| | - Faqin Dong
- The Key Laboratory of Solid Waste Treatment and Resource Recycle, Ministry of Education, Southwest University of Science and Technology, Mianyang, 621010, China
| | - Karen A Hudson-Edwards
- Department of Earth and Planetary Sciences, Birkbeck, University of London, Malet St., London, WC1E 7HX, UK.
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12
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Rosa IC, Costa R, Gonçalves F, Pereira JL. Bioremediation of metal-rich effluents: could the invasive bivalve work as a biofilter? JOURNAL OF ENVIRONMENTAL QUALITY 2014; 43:1536-1545. [PMID: 25603239 DOI: 10.2134/jeq2014.02.0069] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Industrial effluents are important sources of contamination of water and sediments, frequently causing serious damage at different levels of biological organization. Management and treatment of harmful industrial wastes is thus a major concern. Metal-bearing effluents, such as acid mine drainage (AMD), are particularly problematic because metals can easily bioaccumulate in organisms and biomagnify across the trophic chain. Several solutions have been proposed to treat AMD, including active methods involving the addition of neutralizing agents and passive techniques that use natural energy sources for remediation. However, increasing environmental and economic requirements lead the constant search for more sustainable solutions. The present study explores the possibility of using , an invasive freshwater bivalve, as a bioremediation tool using AMD as a model, metal-bearing effluent. The study compares untreated and biotreated effluents at two dilution levels (4 and 10% v/v) following two distinct approaches: (i) chemical characterization of the metal concentrations in water complemented by determination of the accumulation in the clams' soft tissues and shells; and (ii) ecotoxicity assessment using standard organisms (the bacterium , the microalgae , and the cladoceran ). Significant removal of metals from water was recorded for both effluent dilutions, with higher purification levels found for the 4% effluent. The environmental toxicity of the effluents generally decreased after the treatment with the clams. Thus, this study provides evidence for the suitability of as a bioremediator for metal-bearing effluents, especially if the treatment can be materialized in a multistage configuration system.
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Labastida I, Armienta MA, Lara-Castro RH, Aguayo A, Cruz O, Ceniceros N. Treatment of mining acidic leachates with indigenous limestone, Zimapan Mexico. JOURNAL OF HAZARDOUS MATERIALS 2013; 262:1187-1195. [PMID: 22819958 DOI: 10.1016/j.jhazmat.2012.07.006] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2011] [Revised: 06/29/2012] [Accepted: 07/02/2012] [Indexed: 06/01/2023]
Abstract
An experimental study to evaluate the potential of using indigenous limestones in a passive system to treat acid mine drainage, at a mining zone of Mexico was carried out. Chemical and mineralogical characteristics of four types of native rocks (KIT1, KIT2, KSS, QZ) showed distinct CaCO3 contents. Synthetic aqueous leachates from an old tailings impoundment had a pH of 2.18, 34 mg/L As, 705 mg/L Fetotal, and 3975 mg/L SO4(2-). To evaluate dissolution behavior of rocks, kinetic batch experiments with an acid Fe-rich solution were performed. Decaying kinetic constants adjusting H(+) concentration to a first order exponential process were: KIT1 (k = 2.89), KIT2 (k = 0.89) and KSS (k = 0.47). Infrared spectrum and XRD of precipitates showed schwertmannite formation. To determine As and heavy metals (Fe, Cd, Zn, Al) removal from the synthetic leachates, batch experiments using KIT1 were developed. Arsenic decreased from 34.00 mg/L to 0.04 mg/L, Fe and Al were totally removed, and concentrations of Zn and Cd decreased 88% and 91% respectively. Analyses by IR and SEM-EDS indicate that co-precipitation with Fe-Hydroxides formed upon leachate interaction with limestone is the main As removal process. Chamosite, identified by XRD may participate in the removal of Al, SiO2 and a fraction of Fe.
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Affiliation(s)
- I Labastida
- Universidad Nacional Autónoma de México, Posgrado en Ciencias de la Tierra, UNAM, Mexico, DF., 04510, Mexico
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Hughes TA, Gray NF. Co-treatment of acid mine drainage with municipal wastewater: performance evaluation. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2013; 20:7863-7877. [PMID: 23161500 DOI: 10.1007/s11356-012-1303-4] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/04/2012] [Accepted: 11/05/2012] [Indexed: 06/01/2023]
Abstract
Co-treatment of acid mine drainage (AMD) with municipal wastewater (MWW) using the activated sludge process is a novel treatment technology offering potential savings over alternative systems in materials, proprietary chemicals and energy inputs. The impacts of AMD on laboratory-scale activated sludge units (plug-flow and sequencing batch reactors) treating synthetic MWW were investigated. Synthetic AMD containing Al, Cu, Fe, Mn, Pb, Zn and SO4 at a range of concentrations and pH values was formulated to simulate three possible co-treatment processes, i.e., (1) adding raw AMD to the activated sludge aeration tank, (2) pre-treating AMD prior to adding to the aeration tank by mixing with digested sludge and (3) pre-treating AMD by mixing with screened MWW. Continuous AMD loading to the activated sludge reactors during co-treatment did not cause a significant decrease in chemical oxygen demand (COD), 5-day biochemical oxygen demand, or total organic carbon removal; average COD removal rates ranged from 87-93%. Enhanced phosphate removal was observed in reactors loaded with Fe- and Al-rich AMD, with final effluent TP concentrations<2 mg/L. Removal rates for dissolved Al, Cu, Fe and Pb were 52-84%, 47-61%, 74-86% and 100%, respectively, in both systems. Manganese and Zn removal were strongly linked to acidity; removal from net-acidic AMD was <10% for both metals, whereas removal from circum-neutral AMD averaged 93-95% for Mn and 58-90% for Zn. Pre-mixing with screened MWW was the best process option in terms of AMD neutralization and metal removal. However, significant MWW alkalinity was consumed, suggesting an alkali supplement may be necessary.
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Affiliation(s)
- Theresa A Hughes
- Water Technology Research Group, Centre for the Environment, Trinity College Dublin, Dublin 2, Ireland,
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Ayora C, Caraballo MA, Macias F, Rötting TS, Carrera J, Nieto JM. Acid mine drainage in the Iberian Pyrite Belt: 2. Lessons learned from recent passive remediation experiences. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2013; 20:7837-7853. [PMID: 23508532 DOI: 10.1007/s11356-013-1479-2] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/15/2012] [Accepted: 01/07/2013] [Indexed: 06/01/2023]
Abstract
The Iberian Pyrite Belt (IPB), SW Spain and Portugal, contains about 100 abandoned mine wastes and galleries that release acid mine drainages (AMD) to the Tinto and Odiel rivers. In situ passive remediation technologies are especially suitable to remediate the drainages of these orphan sites. However, traditional remediation systems, designed for coal mines, have been demonstrated inefficient to treat the IPB mine waters. Due to their high acidity and metal loads, large amount of solids precipitate and fast clogging of porosity or passivation (coating) of the reactive grains occurs. To overcome these problems, the dispersed alkaline substrate (DAS) a mixture of fine-grained limestone sand and a coarse inert matrix (e.g., wood shavings) was developed. The small grains provide a large reactive surface and dissolve almost completely before the growing layer of precipitates passivates the substrate. The high porosity retards clogging. However, calcite dissolution only raises pH to values around 6.5, at which the hydroxides of trivalent metals (Al and Fe) precipitate, but it is not high enough to remove divalent metals. Caustic magnesia (MgO) buffers the solution pH between 8.5 and 10. A DAS system replacing limestone with caustic magnesia has been tested to be very efficient to remove divalent metals (Zn, Cd, Mn, Cu, Co, Ni, and Pb) from the water previously treated with calcite.
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Affiliation(s)
- Carlos Ayora
- Institute of Environmental Assessment and Water Research, CSIC, Barcelona, Spain,
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Klein R, Tischler JS, Mühling M, Schlömann M. Bioremediation of mine water. ADVANCES IN BIOCHEMICAL ENGINEERING/BIOTECHNOLOGY 2013; 141:109-72. [PMID: 24357145 DOI: 10.1007/10_2013_265] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Caused by the oxidative dissolution of sulfide minerals, mine waters are often acidic and contaminated with high concentrations of sulfates, metals, and metalloids. Because the so-called acid mine drainage (AMD) affects the environment or poses severe problems for later use, treatment of these waters is required. Therefore, various remediation strategies have been developed to remove soluble metals and sulfates through immobilization using physical, chemical, and biological approaches. Conventionally, iron and sulfate-the main pollutants in mine waters-are removed by addition of neutralization reagents and subsequent chemical iron oxidation and sulfate mineral precipitation. Biological treatment strategies take advantage of the ability of microorganisms that occur in mine waters to metabolize iron and sulfate. As a rule, these can be grouped into oxidative and reductive processes, reflecting the redox state of mobilized iron (reduced form) and sulfur (oxidized form) in AMD. Changing the redox states of iron and sulfur results in iron and sulfur compounds with low solubility, thus leading to their precipitation and removal. Various techniques have been developed to enhance the efficacy of these microbial processes, as outlined in this review.
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Affiliation(s)
- Robert Klein
- Institute of Biosciences, TU Bergakademie Freiberg, Leipziger Str. 29, 09599, Freiberg, Germany
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Macías F, Caraballo MA, Nieto JM. Environmental assessment and management of metal-rich wastes generated in acid mine drainage passive remediation systems. JOURNAL OF HAZARDOUS MATERIALS 2012; 229-230:107-114. [PMID: 22717063 DOI: 10.1016/j.jhazmat.2012.05.080] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/09/2012] [Revised: 05/21/2012] [Accepted: 05/22/2012] [Indexed: 06/01/2023]
Abstract
As acid mine drainage (AMD) remediation is increasingly faced by governments and mining industries worldwide, the generation of metal-rich solid residues from the treatments plants is concomitantly raising. A proper environmental management of these metal-rich wastes requires a detailed characterization of the metal mobility as well as an assessment of this new residues stability. The European standard leaching test EN 12457-2, the US EPA TCLP test and the BCR sequential extraction procedure were selected to address the environmental assessment of dispersed alkaline substrate (DAS) residues generated in AMD passive treatment systems. Significant discrepancies were observed in the hazardousness classification of the residues according to the TCLP or EN 12457-2 test. Furthermore, the absence of some important metals (like Fe or Al) in the regulatory limits employed in both leaching tests severely restricts their applicability for metal-rich wastes. The results obtained in the BCR sequential extraction suggest an important influence of the landfill environmental conditions on the metals released from the wastes. To ensure a complete stability of the pollutants in the studied DAS-wastes the contact with water or any other leaching solutions must be avoided and a dry environment needs to be provided in the landfill disposal selected.
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Affiliation(s)
- Francisco Macías
- Geology Department, University of Huelva, Campus El Carmen, E-21071 Huelva, Spain.
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Macías F, Caraballo MA, Nieto JM, Rötting TS, Ayora C. Natural pretreatment and passive remediation of highly polluted acid mine drainage. JOURNAL OF ENVIRONMENTAL MANAGEMENT 2012; 104:93-100. [PMID: 22484707 DOI: 10.1016/j.jenvman.2012.03.027] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/22/2011] [Revised: 02/28/2012] [Accepted: 03/08/2012] [Indexed: 05/21/2023]
Abstract
Acid mine drainage (AMD) from the Iberian Pyrite Belt has high acidity and metal concentrations. Earlier pilot experiments, based on limestone sand dispersed in wood shavings (dispersed alkaline substrate; DAS) have been shown to be an efficient treatment option. However, complete metal removal was not achieved, principally due to the high ferrous iron concentration in the inflow AMD. In order to oxidize and remove iron, a natural Fe-oxidizing lagoon (NFOL) was added prior to treatment with limestone-DAS. The NFOL comprises several pre-existing Fe-stromatolite terraces and cascades, and a lagoon with a volume of 100 m(3) built near the mine shaft. Downstream of the NFOL, the limestone-DAS treatment consists of two reactive tanks of 3 m(3) each filled with limestone-DAS reactive substrate, connected in series with two decantation ponds of 6 m(3) each and several oxidation cascades. The AMD emerging from the mine shaft displayed a pH near 3, a net acidity of 1800 mg/L as CaCO(3) equivalents, and mean concentrations of 440 mg/L Zn; 275 mg/L Fe (99% Fe(II)); 3600 mg/L SO(4); 250 mg/L Ca; 100 mg/L Al; 15 mg/L Mn; 5 mg/L Cu; and 0.1-1 mg/L As, Pb, Cr, Cd, Co, and Ni. The oxidation induced in the NFOL enhanced ferric iron concentration, showing an average of 65% oxidation and 38% retention during the monitoring period. The whole system removed a mean of 1350 mg/L net acidity as CaCO(3) equivalents (71% of inflow); corresponding to 100% of Fe, Al, Cu, Pb and As, and 6% of Zn.
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Affiliation(s)
- Francisco Macías
- Geology Department, University of Huelva, Campus El Carmen, E-21071 Huelva, Spain.
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Oliva J, Cama J, Cortina JL, Ayora C, De Pablo J. Biogenic hydroxyapatite (Apatite II™) dissolution kinetics and metal removal from acid mine drainage. JOURNAL OF HAZARDOUS MATERIALS 2012; 213-214:7-18. [PMID: 22341745 DOI: 10.1016/j.jhazmat.2012.01.027] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/13/2011] [Revised: 01/09/2012] [Accepted: 01/09/2012] [Indexed: 05/31/2023]
Abstract
Apatite II™ is a biogenic hydroxyapatite (expressed as Ca(5)(PO(4))OH) derived from fish bone. Using grains of Apatite II™ with a fraction size between 250 and 500 μm, batch and flow-through experiments were carried out to (1) determine the solubility constant for the dissolution reaction Ca(5)(PO(4))(3)(OH) ⇔ 5Ca(2+) + 3PO(4)(3-) + OH(-), (2) obtain steady-state dissolution rates over the pH range between 2.22 and 7.14, and (3) study the Apatite II™'s mechanisms to remove Pb(2+), Zn(2+), Mn(2+), and Cu(2+) from metal polluted water as it dissolves. The logK(S) value obtained was -50.8±0.82 at 25 °C. Far-from-equilibrium fish-bone hydroxyapatite dissolution rates decrease by increasing pH. Assuming that the dissolution reaction is controlled by fast adsorption of a proton on a specific surface site that dominates through the pH range studied, probably ≡PO(-), followed by a slow hydrolysis step, the dissolution rate dependence is expressed in mol m(-2) s(-1) as where Rate(25 °C) = -8.9 × 10(-10) × [9.96 × 10(5) × a(H+)]/[1 + 9.96 × 10(5) × a(H+)] where a(H+) is the proton activity in solution. Removal of Pb(2+), Zn(2+), Mn(2+) and Cu(2+) was by formation of phosphate-metal compounds on the Apatite II™ substrate, whereas removal of Cd(2+) was by surface adsorption. Increase in pH enhanced the removal of aqueous heavy metals. Using the kinetic parameters obtained (e.g., dissolution rate and pH-rate dependence law), reactive transport simulations reproduced the experimental variation of pH and concentrations of Ca, P and toxic divalent metal in a column experiment filled with Apatite II™ that was designed to simulate the Apatite II™-metal polluted water interaction.
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Affiliation(s)
- J Oliva
- Department of Mining Engineering and Natural Resources, Politechnical University of Catalunya, Bases de Manresa 61-73, Manresa 08242, Catalonia, Spain
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Caraballo MA, Macías F, Rötting TS, Nieto JM, Ayora C. Long term remediation of highly polluted acid mine drainage: a sustainable approach to restore the environmental quality of the Odiel river basin. ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2011; 159:3613-3619. [PMID: 21862191 DOI: 10.1016/j.envpol.2011.08.003] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2011] [Revised: 07/24/2011] [Accepted: 08/01/2011] [Indexed: 05/31/2023]
Abstract
During 20 months of proper operation the full scale passive treatment in Mina Esperanza (SW Spain) produced around 100 mg/L of ferric iron in the aeration cascades, removing an average net acidity up to 1500 mg/L as CaCO(3) and not having any significant clogging problem. Complete Al, As, Cd, Cr, Cu, Ti and V removal from the water was accomplished through almost the entire operation time while Fe removal ranged between 170 and 620 mg/L. The system operated at a mean inflow rate of 43 m(3)/day achieving an acid load reduction of 597 g·(m(2) day)(-1), more than 10 times higher than the generally accepted 40 g·(m(2) day)(-1) value commonly used as a passive treatment system designing criteria. The high performance achieved by the passive treatment system at Mina Esperanza demonstrates that this innovative treatment design is a simple, efficient and long lasting remediation option to treat highly polluted acid mine drainage.
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Affiliation(s)
- Manuel A Caraballo
- Geology Department, University of Huelva, Campus El Carmen, E-21071 Huelva, Spain.
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Caraballo MA, Rötting TS, Silva V. Implementation of an MgO-based metal removal step in the passive treatment system of Shilbottle, UK: column experiments. JOURNAL OF HAZARDOUS MATERIALS 2010; 181:923-930. [PMID: 20541861 DOI: 10.1016/j.jhazmat.2010.05.100] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/28/2009] [Revised: 05/21/2010] [Accepted: 05/22/2010] [Indexed: 05/29/2023]
Abstract
Three laboratory column experiments were performed to test the suitability of two different MgO-rich reagents for removal of Mn and Al from the out-flowing waters of Shilbottle passive treatment system (Northumberland, UK). The input water was doped with 100 mg/L Zn in order to extrapolate results to waters in sulphide mining districts. One column was filled with a Dispersed Alkaline Substrate (DAS) containing 12.5% (v/v) caustic magnesia precipitator dust (CMPD) from Spain mixed with wood shavings, two columns were filled with DAS containing wood shavings and 12.5% or 25% (v/v), respectively, of dolomitic lime precipitator dust (DLPD) from Thrislington, UK. The two columns containing 12.5% of CMPD or DLPD completely removed the contaminants from the inflow water during the first 6 weeks of the experiment (mean removal of 88 mg/L Al, 96 mg/L Zn and 37 mg/L Mn), operating at an acidity load of 140 g acidity/m(2)day. At this moment, a substantial increase of the Al and Mn water concentration in the out-flowing waters of Shilbottle occurred (430 g acidity/m(2)day), leading to passivation of the reactive material and to the development of preferential flow paths within less than another 6 weeks, probably mainly due to Al precipitates. Al should be removed prior to MgO treatment.
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