Natural attenuation of arsenic in the environment by immobilization in nanostructured hematite
Graphical abstract
Introduction
The release of As into the environment from geogenic sources is ultimately controlled by the chemical stability of As-bearing mineral phases. Therefore, the thorough structural and chemical characterization of these phases is necessary to fully assess As mobility in different environmental matrices. The chemical stability of solid As-bearing phases in aqueous systems is conventionally established using extraction methods designed to measure the degree of mobilization under specified environmental conditions, such as the Toxicity Characteristic Leaching Procedure – TCLP (Ghosh et al., 2004, Jong and Parry, 2005), and sequential extraction methods and bioaccessibility tests (Cappuyns et al., 2002, Guo et al., 2007, Anawar et al., 2008, Karak et al., 2011, Larios et al., 2012a, Larios et al., 2012b). These procedures, however, provide only indirect evidence for As association with its host mineral phases while the actual nature of these phases remains unknown.
The structural characterization of As-bearing phases by traditional analytical techniques is not trivial, and in view of these difficulties, synchrotron-based analytical techniques combined with theoretical molecular modeling or with other spectroscopic techniques have been increasingly applied to investigate As distribution, speciation, and bonding characteristics, with advances in our understanding of As stability (Paktunc et al., 2008, Morin et al., 2009, Chakraborty et al., 2011, Duarte et al., 2012a). Transmission electron microscopy (TEM) techniques are especially useful for the characterization of solid phases at the nanoscale, with better spatial resolution than any other technique. However, few TEM investigations of As-bearing minerals have been described in the literature (Carlson et al., 2002, Ouvrard et al., 2005, Paktunc et al., 2008, Morin et al., 2009, Kendall et al., 2013). The difficulties in the accurate characterization of As compounds in environmental samples by conventional techniques lie in the markedly particles heterogeneity and small grain size. To overcome these difficulties we combined different TEM techniques such as Nano-Beam Electron Diffraction (NBD), Energy Dispersive X-ray Spectroscopy (EDS), Electron Energy-Loss Spectroscopy (EELS), and High Resolution Transmission Electron Microscopy (HRTEM), which give the highest spatial resolution needed in the analyses of phases at nanoscale.
In this work we used HRTEM, NBD, EDS and EELS to investigate the As-bearing phases and the distribution of As in Fe–Al-oxisols used as liners in sulfide tailings disposal facilities. A recent study from our group (Duarte et al., 2012b) investigated As speciation in the same oxisol liners as well as in the tailings after 10 years of disposal. The bulk analysis were done using a sequential extraction procedure (SEP), X-ray diffraction (XRD) and X-ray Absorption Spectroscopy Near Edge Structure (XANES) analyses. Arsenic was found mainly as As(V) in the oxisol samples and as arsenopyrite in the tailings. Up to 69% of the total As content in the oxisol was found associated with Fe and Al crystalline phases, which were not dissolved even under strongly acidic and reduction conditions. This crystalline fraction of the Fe–Al-oxisol liners is investigated in this present study, and it will be demonstrated that As is immobilized in the structure of secondary crystalline Al-hematite.
Section snippets
Sample description
Tailings of As-sulfide concentrates from the hydrometallurgical processing plant of a gold mine in Minas Gerais, Brazil were stored for more than 10 years in three disposal facilities sealed with an enriched Fe and Al oxisol. In 2011 and 2012 the tailings of two of these facilities (namely F2 and F3) were excavated and reprocessed, and samples of the oxisol liners (OL) were recovered for analysis. A sample from the local natural oxisol (LNO) was also investigated. This sample represents the
Natural oxisol
The chemical analysis showed that the As content in the natural oxisol was 12 + 7 mg kg−1. The main phases identified by XRD analysis (diffractogram not shown) were quartz, kaolinite, gibbsite, muscovite, hematite, goethite, and goethite. TEM analysis showed the presence of ferrihydrite, goethite and hematite (data shown in S1). Structural Al was identified in all these phases by the EDS analysis. Arsenic was not detected by EDS.
Oxisol liner
The As content in the oxisol liners ranged from 1950 mg kg−1 in sample
Environmental implications
The proposed mechanism for As fixation into the Al-hematite structure accounts for As immobilization in Fe–Al-(hydr)oxides present in the oxisols, and can be viewed as a natural remediation process. The high concentrations of Al in oxisols enhance As uptake by increasing the surface area of ferrihydrite, and may improve the long-term stability of As-bearing hematite under reducing conditions. An intermediate Al-goethite phase is likely to form at some stage of the process, but hematite is the
Conclusions
The mechanism of As immobilization in natural Fe–Al-oxisol was investigated. An oxisol liner was exposed to As-bearing sulfide tailings for over 10 years in a gold mine site. Although the role of Fe–Al-(hydr)oxides in As fixation is well established, our work showed for the first time significant amounts of As (1.6 ± 0.5 wt.%) distributed in crystalline Al-hematite with an As/Fe atomic ratio of 0.026 ± 0.006. The presence of As in the Al-hematite structure is consistent with a slight increase of the c
Acknowledgments
The authors are grateful to the Brazilian government agencies – CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico), Fapemig (Fundação de Amparo a Pesquisa do Estado de Minas Gerais) and CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior) for financial support. Kinross Brasil Mineração is gratefully acknowledged for supplying the samples used in this investigation. The authors also acknowledge the Science Without Borders program for the PVE fellowship to M.
References (41)
- et al.
Evaluation of various chemical extraction methods to estimate plant-available arsenic in mine soils
Chemosphere
(2008) - et al.
Arsenic pollution at the industrial site of Reppel-Bocholt (north Belgium)
Sci. Total Environ.
(2002) - et al.
Spectroscopic studies of arsenic retention onto biotite
Chem. Geol.
(2011) - et al.
As(III) immobilization on gibbsite: investigation of the complexation mechanism by combining EXAFS analyses and DFT calculations
Ceochim. Cosmochim. Acta
(2012) - et al.
Determination of the oxidation state for iron oxide minerals by energy-filtering TEM
Micron
(2006) - et al.
Adsorption of arsenic(III) and arsenic(V) from groundwater using natural siderite as the adsorbent
J. Colloid Interface Sci.
(2007) - et al.
Evaluation of the stability of arsenic immobilized by microbial sulfate reduction using TCLP extractions and long-term leaching techniques
Chemosphere
(2005) - et al.
Fractionation and speciation of arsenic in three tea gardens soil profiles and distribution of as in different parts of tea plant (Camellia Sinensis L.)
Chemosphere
(2011) - et al.
Effects of arsenic incorporation on jarosite dissolution rates and reaction products
Ceochim. Cosmochim. Acta
(2013) - et al.
Arsenic pollution and fractionation in sediments and mine waste samples from different mine sites
Sci. Total Environ.
(2012)
Natural manganese oxide: combined analytical approach for solid characterization and arsenic retention
Ceochim. Cosmochim. Acta
Synthesis and phase transformations involving scorodite, ferric arsenate and arsenical ferrihydrite: implications for arsenic mobility
Ceochim. Cosmochim. Acta
EMS - a software package for electron diffraction analysis and HREM image simulation in materials science
Ultramicroscopy
Coprecipitated arsenate inhibits the thermal transformation of 2-line-ferrihydrite: Implications for long-term stability of ferrihydrite
Chemosphere
Sample Preparation Handbook for Transmission Electron Microscopy
The Effect of antimonate, arsenate, and phosphate on the transformation of ferrihydrite to goethite, hematite, feroxyhyte, and tripuhyite
Clay. Clay Miner.
Structural incorporation of As5+ into hematite
Environ. Sci. Technol.
Organic additive-free synthesis of mesocrystalline hematite nanoplates via two-dimensional oriented attachment
Cryst. Eng. Comm.
Scavenging of As from acid mine drainage by schwertmannite and ferrihydrite: a comparison with synthetic analogues
Environ. Sci. Technol.
Electron-energy-loss-spectroscopy near-edge fine structures in the iron-oxygen system
Phys. Rev. B
Cited by (29)
Arsenic removal and fixation by iron (oxyhydr)oxides: What is new?
2023, Current Opinion in Environmental Science and HealthRecent advances toward structural incorporation for stabilizing heavy metal contaminants: A critical review
2023, Journal of Hazardous MaterialsDefects induced by Al substitution enhance As(V) adsorption on ferrihydrites
2021, Journal of Hazardous MaterialsCitation Excerpt :Aluminum has been shown not only to alter the physicochemical properties of ferrihydrite, such as solubility, bioavailability, and secondary mineralization to more thermodynamically stable Fe oxyhydroxides phases, like goethite and hematite, but also to affect the retention of aqueous contaminants, such as arsenic (Adra et al., 2016; Masue et al., 2007), chromium (Ni et al., 2016), phosphorus (Liu and Hesterberg, 2011), and uranium (Massey et al., 2014). Our previous works have demonstrated that Al favors As immobilization within the structure of oriented aggregates of Al-for-Fe oxyhydroxide-substituted nanoparticles, found both in natural and synthetic samples (Freitas et al., 2015, 2016; Ladeira and Ciminelli, 2004). Freitas et al. suggested that As first adsorbs onto AlFh nanoparticles and then is incorporated into the crystalline nanoparticles’ aggregates, hindering further release into the environment.
Facile preparation of iron oxyhydroxide–biopolymer (Chitosan/Alginate) beads and their comparative insights into arsenic removal
2021, Separation and Purification TechnologySeven potential sources of arsenic pollution in Latin America and their environmental and health impacts
2021, Science of the Total EnvironmentCitation Excerpt :The results of the studies carried by Ono et al. (2012) and Guilherme et al. (2014), who showed the presence of high concentrations of As (up to 2666 mg kg−1) and very low As bioaccessibility (<4.2%) in tailings in the gold mining area in Paracatu, corroborate this. Arsenic was predominantly present as [As(V)] and associated with poorly crystalline Fe arsenate, which explains the low bioaccessibility of As and highlights the importance of Fe oxides in immobilizing As in the environment (Freitas et al., 2015). Rezende et al. (2015) evaluated As mobility in the Paracatu River sediments.