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Temperature effects on cobalt hydroxide–cobalt carbonate competitive growth on carbonate surfaces
Cobalt (Co), a critical metal essential for various environmental and industrial processes, undergoes speciation and immobilization in natural systems, primarily interacting with existing mineral surfaces. Understanding the underlying mechanisms of Co immobilization on abundant carbonate surfaces under different environmental conditions is critical for predicting Co mobility, availability, and recovery. In this study, we investigated the temperature-dependent competition between CoCO 3 and Co(OH) 2 formation on calcite (CaCO 3 ) and magnesite (MgCO 3 ) surfaces. Using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS), we analyzed carbonate substrates exposed to CoCl 2 solutions at varying concentrations (0–500 μM) and temperatures (22, 50, and 80 °C). Magnesite surfaces promoted CoCO 3 formation due to its low lattice mismatch with sphaerocobaltite (CoCO 3 ). However, this slow-growing CoCO 3 component was progressively outcompeted by Co(OH) 2 formation as the temperature and/or initial Co concentration increased. On calcite surfaces, the poor lattice mismatch between calcite and sphaerocobaltite led to Co(OH) 2 outcompeting CoCO 3 formation at all three temperatures. These findings provide critical insights into the roles of substrate composition, solution chemistry, and temperature in controlling Co speciation and mobility. They carry important implications for environmental transport, geochemical cycling, and industrial recovery of cobalt in carbonate-rich systems.
Potential applications of microbial genomics in nuclear non-proliferation
As nuclear technology evolves in response to increased demand for diversification and decarbonization of the energy sector, new and innovative approaches are needed to effectively identify and deter the proliferation of nuclear arms, while ensuring safe development of global nuclear energy resources. Preventing the use of nuclear material and technology for unsanctioned development of nuclear weapons has been a long-standing challenge for the International Atomic Energy Agency and signatories of the Treaty on the Non-Proliferation of Nuclear Weapons. Environmental swipe sampling has proven to be an effective technique for characterizing clandestine proliferation activities within and around known locations of nuclear facilities and sites. However, limited tools and techniques exist for detecting nuclear proliferation in unknown locations beyond the boundaries of declared nuclear fuel cycle facilities, representing a critical gap in non-proliferation safeguards. Microbiomes, defined as “characteristic communities of microorganisms” found in specific habitats with distinct physical and chemical properties, can provide valuable information about the conditions and activities occurring in the surrounding environment. Microorganisms are known to inhabit radionuclide-contaminated sites, spent nuclear fuel storage pools, and cooling systems of water-cooled nuclear reactors, where they can cause radionuclide migration and corrosion of critical structures. Microbial transformation of radionuclides is a well-established process that has been documented in numerous field and laboratory studies. These studies helped to identify key bacterial taxa and microbially-mediated processes that directly and indirectly control the transformation, mobility, and fate of radionuclides in the environment. Expanding on this work, other studies have used microbial genomics integrated with machine learning models to successfully monitor and predict the occurrence of heavy metals, radionuclides, and other process wastes in the environment, indicating the potential role of nuclear activities in shaping microbial community structure and function. Results of this previous body of work suggest fundamental geochemical-microbial interactions occurring at nuclear fuel cycle facilities could give rise to microbiomes that are characteristic of nuclear activities. These microbiomes could provide valuable information for monitoring nuclear fuel cycle facilities, planning environmental sampling campaigns, and developing biosensor technology for the detection of undisclosed fuel cycle activities and proliferation concerns.
Informed Critical Mineral Recovery from Fossil Energy Waste Feedstocks
Critical minerals (CM), such as rare earth elements (REE), cobalt, nickel, and lithium, have important uses in modern energy and technologies, yet are vulnerable to potential supply chain disruptions. One potential domestic CM source is fossil energy wastes, such as coal combustion ash, acid mine drainage (AMD) and treatment solids (AMD solids), and Oil and Gas (O&G) drilling wastes (drill cuttings and produced waters). CM recovery from these feedstocks is promising due to their abundant quantity and fast availability as waste products. To develop informed and effective CM recovery, DOE’s National Energy Technology Laboratory (NETL) have collected and analyzed CM data for aforementioned fossil energy wastes, and utilized advanced geochemical characterization (e.g., synchrotron microprobe, sequential extraction and geochemical modeling) to identify the CM speciation and binding environments. Novel methods that recover multiple CMs while co-producing other valuable byproducts from these feedstocks have been developed. Successful examples include: (1) the discovery of easily mobile REE phases in Ca-rich coal combustion ash resulted in a patented REE recovery process from the ash feedstock while producing zeolite sorbents from the extraction wastes; (2) the successful identification of REE/Co/Ni/Zn hosting phases in acid mine drainage treatment solids (AMD solids) has informed the sequential CM recovery from AMD solids and has inspired lithium sorbent development from the extraction wastes; (3) the recovery potential of Li and other CMs in O&G produced waters and drill cuttings has been explored while the extraction residuals have been demonstrated to support plant growth as soil supplements. The innovations driven by characterization information have the potential to maximize CM recovery revenue, offset the cost of waste management and wastewater treatments while reducing the cost and environmental footprint of CM extraction.
Characterization Inform Sustainable Recovery of Critical Minerals from Fossil Energy Waste Feedstocks
Rare earth elements (REE) and other critical minerals (CM, e.g., Co, Ni, Li) have important uses in green energy and modern technologies, yet are vulnerable to potential supply chain disruptions. One potential domestic CM source is fossil energy wastes, such as acid mine drainage (AMD) and treatment solids (AMD solids), coal combustion ash, and Oil and Gas (O&G) drilling wastes (drill cuttings and produced waters). While they can contain lower CM concentrations then traditional ore, the quantity and fast availability as waste feedstock makes them a promising CM resource. To explore their promise, researchers at DOE’s National Energy Technology Laboratory (NETL) have collected and analyzed CM data for aforementioned fossil energy wastes, and utilized advanced geochemical characterization (e.g., synchrotron microprobe and sequential extraction) to identify the CM speciation and binding environments, and developed sustainable and targeted CM recovery. Successful examples include: (1) the discovery of easily mobile REE phases in Ca-rich coal combustion ash and developing a patented REE recovery process from Ca-rich Powder River Basin coal ash; (2) the successful identification of REE/Co/Ni/Zn hosting phases in acid mine drainage treatment solids (AMD solids) with diverse chemical composition (Al, Mn, or Fe-rich) informing the sequential recovery of different REE/CMs from AMD solids; (3) the recovery potential of Li and other CMs in O&G produced waters and drill cuttings. The innovations driven by characterization have the potential to offset the cost of waste management and wastewater treatments while reducing the cost and environmental footprint of CM extraction.
Mobilization of mercury from contaminated creekbank soils
The industrial use of mercury (Hg) led to the contamination of numerous watersheds worldwide, including the East Fork Poplar Creek (EFPC) in Tennessee, USA. Mercury can accumulate in creek banks and floodplain soils and is mobilized into downstream environments due to erosion from precipitation and flooding. Here, this study aimed to evaluate the geochemical conditions contributing to the release of Hg from contaminated soils in this watershed. Bank soil samples from the EFPC watershed with total Hg concentrations ranging from 27.2 to 1,425 mg·kg −1 were used in a series of batch experiments with artificial creek water at a solid-to-solution ratio of 1:30 to assess Hg release. Additional experiments examined Hg release across different soil size fractions and solid-to-solution ratios, as well as the effect of dissolved organic matter and time on Hg mobilization. Mercury release ranged from 0.011 to 0.17% of the total soil Hg and is correlated with total Hg concentrations. Variations in release among size fractions suggested heterogeneous distribution of labile Hg species. Results indicated two distinct solubility regimes depending on solid-to-solution ratios. Dissolved organic matter enhanced Hg release, and time-dependent experiments showed that changes in mercury speciation could decrease dissolved Hg concentrations over time. Identifying conditions that promote Hg mobilization from contaminated soils improves our understanding of Hg fluxes into downstream environments. Key factors influencing mercury release include soil characteristics, water chemistry, and temporal changes in mercury speciation.