Arsenic entrapment by nanocrystals of Al-magnetite: The role of Al in crystal growth and As retention.
The nature of As-Al-Fe co-precipitates aged for 120 days are investigated in detail by High Resolution Transmission Electron Microscopy (HRTEM), Scanning TEM (STEM), electron diffraction, Energy Dispersive X-Ray Spectroscopy (EDS), Electron Energy-Loss Spectroscopy (EELS), and Energy Filtered Transmission Electron Microscopy (EFTEM). The Al present in magnetite is shown to favour As incorporation (up to 1.10 wt%) relative to Al-free magnetite and Al-goethite, but As uptake by Al-magnetite decreases with increasing Al substitution (3.53-11.37 mol% Al). Arsenic-bearing magnetite and goethite mesocrystals (MCs) are formed by oriented aggregation (OA) of primary nanoparticles (NPs). Well-crystalline magnetite likely formed by Otswald ripening was predominant in the Al-free system. The As content in Al-goethite MCs (having approximately 13% substituted Al) was close to the EDS detection limit (0.1 wt% As), but was below detection in Al-goethites with 23.00-32.19 mol% Al. Our results show for the first time the capacity of Al-magnetite to incorporate more As than Al-free magnetite, and the role of Al in favouring OA-based crystal growth under the experimental conditions, and therefore As retention in the formed MCs. The proposed mechanism of As incorporation involves adsorption of As onto the newly formed NPs. Arsenic is then trapped in the MCs as they grow by self-assembly OA upon attachment of the NPs. We conclude that Al may diffuse to the crystal faces with high surface energy to reduce the total energy of the system during the attachment events, thus favouring the oriented aggregation.
Universidade Federal de Minas Gerais, Center of Microscopy, Belo Horizonte 31270901, Brazil; The University of Queensland, School of Earth Sciences, St Lucia 4072, Australia; National Institute of Science and Technology on Minerals Resources, Water and Biodiversity, INCT-Acqua, Brazil. Electronic address: ericotadeu@ufmg.br.
Erico T F
ET
Freitas
International Iberian Nanotechnology Laboratory, Braga 4715330, Portugal. Electronic address: daniel.stroppa@inl.int.
Daniel G
DG
Stroppa
Universidade Federal de Minas Gerais, Department of Chemistry, Belo Horizonte 31270901, Brazil; National Institute of Science and Technology on Minerals Resources, Water and Biodiversity, INCT-Acqua, Brazil. Electronic address: luciano.montoro@qui.ufmg.br.
Luciano A
LA
Montoro
Universidade Federal de Viçosa, Department of Soils, Viçosa 36570900, Brazil; National Institute of Science and Technology on Minerals Resources, Water and Biodiversity, INCT-Acqua, Brazil. Electronic address: jwvmello@ufv.br.
Jaime W V
JW
de Mello
The University of Queensland, School of Earth Sciences, St Lucia 4072, Australia; National Institute of Science and Technology on Minerals Resources, Water and Biodiversity, INCT-Acqua, Brazil. Electronic address: m.gasparon@uq.edu.au.
Massimo
M
Gasparon
Universidade Federal de Minas Gerais, Department of Metallurgical Engineering, Belo Horizonte 31270901, Brazil; National Institute of Science and Technology on Minerals Resources, Water and Biodiversity, INCT-Acqua, Brazil. Electronic address: ciminelli@demet.ufmg.br.
Virginia S T
VS
Ciminelli
D000327:Adsorption; D000535:Aluminum / Q000737:chemistry*; D001151:Arsenic / Q000737:chemistry / Q000302:isolation & purification*; D003460:Crystallization; D052918:Environmental Restoration and Remediation; D052203:Ferrosoferric Oxide / Q000737:chemistry; D058085:Iron Compounds / Q000737:chemistry; D058185:Magnetite Nanoparticles / Q000737:chemistry*; D053768:Metal Nanoparticles / Q000737:chemistry; D017348:Microscopy, Electron, Scanning Transmission; D046529:Microscopy, Electron, Transmission; D008903:Minerals / Q000737:chemistry; D053758:Nanoparticles / Q000737:chemistry*; D036103:Nanotechnology / Q000379:methods*; D046590:Spectroscopy, Electron Energy-Loss
D058085:Iron Compounds; D058185:Magnetite Nanoparticles; D008903:Minerals; C094886:goethite; D000535:Aluminum; D001151:Arsenic; D052203:Ferrosoferric Oxide
Al magnetite; Arsenic immobilization; As partitioning; As speciation