A Critical Review of the Enhanced Recovery of Rare Earth Elements from Phosphogypsum.

The increasing demand for rare earth elements (REEs), especially from new and innovative technology, has strained their supply, which makes the exploration of new REE sources necessary, for example, the recovery of REEs from phsophogypsum (PG). PG is a byproduct during the wet production of phosphoric acid, which is an attractive secondary resource for REEs due to a large amount of REEs locked in them. In most cases, REEs contained in PG are mainly encapsulated in the gypsum crystal, leading to a low leaching efficiency. Therefore, it is particularly important to use various methods to enhance the leaching of REEs from PG. In this review, we summarized and classified various enhanced leaching methods for the recovery of REEs from PG, and the advantages and disadvantages of different methods were compared. A joint method of recrystallization and RIL may be a promising enhanced leaching approach for the recovery of REEs from PG. Recrystallization could achieve both the complete REE release and simultaneous preparation of industrial materials with high value added, such as high-strength α-hemihydrate gypsum by phase transformation of PG, and the RIL technology could adsorb the releasing REEs and realize their efficient extraction. Such a combination appears to show significant advantages because of high REE recovery, as well as high value-added product preparation at low cost.

A novel circular approach to analyze the challenges associated with micro-nano plastics and their sustainable remediation techniques.

The mismanagement of consumer-discarded plastic waste (CDPW) has raised global environmental concerns about climate change. The COVID-19 outbreak has generated ∼1.6 million tons of plastic waste per day in the form of personal protective equipment (masks, gloves, face shields, and sanitizer bottles). These plastic wastes are either combustible or openly dumped in aquatic and terrestrial environments. Open dumping upsurges emerging contaminants like micro-nano plastics (MNPs) that directly enter the ecosystem and cause severe impacts on flora and fauna. Therefore, it has become an utmost priority to determine sustainable technologies that can degrade or treat MNPs from the environment. The present review assesses the sources and impacts of MNPs, various challenges, and issues associated with their remediation techniques. Accordingly, a novel sustainable circular model is recommended to increase the degradation efficiency of MNPs using biochemical and biological methods. It is also concluded that the proposed model does not only overcome environmental issues but also provides a sustainable secondary resource to meet the sustainable development goals (SDGs).

Summary of research progress on separation and extraction of valuable metals from Bayer red mud.

Bayer red mud is a strong alkaline solid waste discharged during alumina production. Due to large emissions and strong alkalinity, red mud is now mostly dammed or buried, which not only occupies huge land but also contaminates the surrounding ecosystem, causing the risk of collapse and landslide. In addition to its overall utilization in building materials, agriculture, the environment, and the chemical industry, red mud also contains valuable metals such as sodium, aluminum, iron, titanium, and scandium and is considered to be an important secondary resource. In this paper, the physicochemical properties and hazards of red mud are first introduced, and then, the overall utilization of red mud is summarized. Then, the latest research progress on the separation and extraction of valuable metals from red mud is reviewed in detail and a new comprehensive utilization method is recommended and evaluated. This paper also provides suggestions for the future development direction of the comprehensive utilization technology of red mud.

A comprehensive review on integrative approach for sustainable management of plastic waste and its associated externalities.

The management of post-consumer discarded plastic wastes (PCPW) creates new challenges in developing countries due to the lack of amenities, technological interventions, and associated negative environmental externalities. The fate of untreated recyclable and non-recyclable plastic wastes lies in open dumping along with other solid waste, and improper management leads to environmental externalities such as pollution, global climate change, and health issues. Additionally, open dumping upsurges the emerging microplastics and nano plastics (MNPs) contaminants. The externalities depend on the waste generating sources (household, industries, commercial), waste composition, and its characteristics. However, urban mining can minimize environmental externalities where waste plastics can convert into potential anthropogenic resources and also helps in achieving the target of sustainable development goals (SDGs 11 & 12). Moreover, various treatment technologies that help in the sustainable utilization of plastic wastes are extensively reviewed in this study and evaluate the costs benefits arising during various stages of treating plastic waste through recycling (R), incineration (I), and landfilling (L). The recycling of plastic waste has demonstrated the lowest impact on global warming potential (GWP) and total energy use (TEU), followed by landfilling and incineration (R < L < I). Nevertheless, when energy is recovered from inert (non-recyclable) plastic waste in the form of fuel or by its utilization in construction purposes, the environmental impacts are more negligible (Incineration < Landfilling). Therefore, this study determines the significance of circular economy with legislative approach and standards on plastic waste management, which help in reducing environmental externalities besides yielding a secondary resource as energy and materials through urban mining. A sustainable plastic waste management (SPWM) model is proposed for developing countries to convert plastic waste into resources and use it as a sustainable tool in urban mining.

Overview of recent developments of resource recovery from wastewater via electrochemistry-based technologies.

As the rapid increase of the worldwide population, recovering valuable resources from wastewater have attracted more and more attention by governments and academia. Electrochemical technologies have been extensively investigated over the past three decades to purify wastewater. However, the application of these technologies for resource recovery from wastewater has just attracted limited attention. In this review, the recent (2010-2020) electrochemical technologies for resource recovery from wastewater are summarized and discussed for the first time. Fundamentals of typical electrochemical technologies are firstly summarized and analyzed, followed by the specific examples of electrochemical resource recovery technologies for different purposes. Based on the fundamentals of electrochemical reactions and without the addition of chemical agents, metallic ions, nutrients, sulfur, hydrogen and chemical compounds can be effectively recovered by means of electrochemical reduction, electrochemical induced precipitation, electrochemical stripping, electrochemical oxidation and membrane-based electrochemical processes, etc. Pros and cons of each electrochemical technology in practical applications are discussed and analyzed. Single-step electrochemical process seems ineffectively to recover valuable resources from the wastewater with complicated constituents. Multiple-step processes or integrated with biological and membrane-based technologies are essential to improve the performance and purity of products. Consequently, this review attempts to offer in-depth insights into the developments of next-generation of electrochemical technologies to minimize energy consumption, boost recovery efficiency and realize the commercial application.

Physicochemical and FTIR spectroscopic analysis of fine fraction from a municipal solid waste dumpsite for potential reclamation of materials.

Improper municipal solid waste management in the past has landed most of this waste in open dumps of India. This dumped waste has a negative effect on the environment and human health and needs to be reclaimed either for material/energy recovery or to create space for future waste management. Since nearly half of the waste in dumpsites can be classified as fine fraction, in-depth knowledge of its characteristics is required to reclaim these dumpsites successfully. In this study, we characterize fine fraction, <4 mm, aged 1-10 years old, obtained from Mulund dumpsite in Mumbai, using physicochemical and spectroscopic analysis. The study also highlights different valorization routes to reclaim the fine fraction. The fine fraction was ~45% in the dumpsite and increased with the age of the waste. Visual inspection revealed that fine fraction older than five years was relatively homogeneous compared with younger fine fraction. Furthermore, pH (7.4-7.8) and electrical conductivity (0.70-1.92 mS cm-1) of the fine fraction met the Indian MSW compost standards; however, heavy metal levels were higher than the proposed standards. The fine fraction also had a high concentration of metals like aluminium (11 g kg-1) and iron (78 g kg-1), indicating metal recovery potential. Furthermore, Fourier Transform Infrared Spectroscopy results show that the fine fraction had dominant inorganic peaks and became relatively homogeneous with age. The study proposes fine fraction use as a secondary resource; however, some prior treatment would be required based on the application.

Magnetic separation of ferrous fractions linked to improved bioleaching of metals from waste-to-energy incinerator bottom ash (IBA): a green approach.

Ferrous fractions in incinerated bottom ash (IBA) are linked to lower metal dissolution. In the present study, a novel eco-friendly biotechnological approach has been tested for multi-metal leaching using meso-acidophilic Fe2+/S° oxidizing bacterial consortium from magnetically separated IBA, owing to the inherent property of IBA to release Fe2+. Comprehensive lab-scale studies, first-of-its-kind, considered all the potential elements to understand targeted metal dissolutions from the sample under differential conditions. Concentrations of metals, Al > Ti > Ni > Zn > Cu, as analyzed by ICP-OES, were targeted to be bioleached. XRD analysis indicated the sample to be amorphous with magnetite (Fe3O4) and iron (Fe) forming major phases in the magnetic part (IBAM) and titano-magnetite (Fe3-x. TixO4) and iron (Fe) for the nonmagnetic part (IBAN). The study indicated that 73.98% Cu, 98.68% Ni, 59.09% Zn, 58.84% Al, and 92.85% Ti could be leached from IBAM when the bioleaching system operates at pH 1.5, 5% pulp density for 8 days. Under similar conditions, within 6 days, 37.55% Cu, 87.99% Ni, 45.03% Zn, 40.72% Al, and 63.97% Ti could be leached from IBAN. Two routes were identified and the mechanism of action has been proposed for the leaching of metals.

Electrodialytic removal of tungsten and arsenic from secondary mine resources - Deep eutectic solvents enhancement.

Tungsten is a critical raw material for European and U.S. economies. Tungsten mine residues, usually considered an environmental burden due to e.g. arsenic content, are also secondary tungsten resources. The electrodialytic (ED) process and deep eutectic solvents (DES) have been successfully and independently applied for the extraction of metals from different complex environmental matrices. In this study a proof of concept demonstrates that coupling DES in a two-compartment ED set-up enhances the removal and separation of arsenic and tungsten from Panasqueira mine secondary resources. Choline chloride with malonic acid (1:2), and choline chloride with oxalic acid (1:1) were the DES that in batch extracted the average maximum contents of arsenic (16%) and tungsten (9%) from the residues. However, when ED was operated at a current intensity of 100 mA for 4 days, the extraction yields increased 22% for arsenic and 11% for tungsten, comparing to the tests with no current. From the total arsenic and tungsten extracted, 82% and 77% respectively were successfully removed from the matrix compartment, as they electromigrated to the anolyte compartment, from where these elements can be further separated. This achievement potentiates circular economy, as the final treated residue could be incorporated in construction materials production, mitigating current environmental problems in both mining and construction sectors.

Two-step bioleaching of copper and gold from discarded printed circuit boards (PCB).

An effective strategy for environmentally sound biological recovery of copper and gold from discarded printed circuit boards (PCB) in a two-step bioleaching process was experimented. In the first step, chemolithotrophic acidophilic Acidithiobacillus ferrivorans and Acidithiobacillus thiooxidans were used. In the second step, cyanide-producing heterotrophic Pseudomonas fluorescens and Pseudomonas putida were used. Results showed that at a 1% pulp density (10g/L PCB concentration), 98.4% of the copper was bioleached by a mixture of A. ferrivorans and A. thiooxidans at pH 1.0-1.6 and ambient temperature (23±2°C) in 7days. A pure culture of P. putida (strain WCS361) produced 21.5 (±1.5)mg/L cyanide with 10g/L glycine as the substrate. This gold complexing agent was used in the subsequent bioleaching step using the Cu-leached (by A. ferrivorans and A. thiooxidans) PCB material, 44.0% of the gold was mobilized in alkaline conditions at pH 7.3-8.6, and 30°C in 2days. This study provided a proof-of-concept of a two-step approach in metal bioleaching from PCB, by bacterially produced lixiviants.

Plantas silvestres con órganos subterráneos comestibles: transmisión cultural sobre recursos subutilizados en la Patagonia (Argentina) / Wild plants with edible underground storage organs: cultural transmission about neglected resourcesin Patagonia (Argentina)

En este trabajo documentamos el conocimiento y uso de plantas con órganos de almacenamiento subterráneos comestibles (POAS). Evaluamos los mecanismos de transmisión cultural por los que se difunde dicho conocimiento en 2 poblaciones rurales del Noroeste de la Patagonia argentina. Realizamos entrevistas (N = 34), observación participante y recolección de plantas. Los datos fueron analizados de forma cualitativa y cuantitativa. Un total de 6 especies son conocidas y actualmente 3 son utilizadas. La recolección ocurre mientras se realizan otras actividades como la cría del ganado o la búsqueda de plantas combustibles o medicinales. Los órganos subterráneos, en general, se consumen crudos in situ. El aprendizaje sobre las POAS ocurrió en la infancia por observación e instrucción por parte de adultos, principalmente las madres y las abuelas. La transmisión horizontal en contextos lúdicos también posee un papel importante. La singularidad de los contextos de uso y de aprendizaje confiere fragilidad a la continuidad de estos saberes y el mantenimiento de las prácticas de uso de las POAS.

In this study we documented the knowledge and use of wild plants with edible underground organs (PEUO). We have also evaluated the cultural transmission mechanisms in two rural populations of NW Argentinean Patagonia. Thirty-four informants were interviewed about this topic and they became part of participant observation and gathering join actions. Data were analyzed by quali and quantitative approaches. In total, 6 species are known by people, but only 3 species are used at present. Gathering occurs meanwhile other rural activities, such as cattle raising, medicinal plant collection or fuelwood gathering. Edible underground organs are generally consumed raw in situ. Cultural learning about plants with edible underground organs occurs in the childhood including observation and instruction activities from adults, mainly mothers and grandmothers. Horizontal transmission in ludic contexts has also an important role. The singularity about the learning and use contexts, give a certain fragility in the continuity in the practice of use of PEUO.

Diffuse competition for heterogeneous substrate in soil among six species of wood-decomposing basidiomycetes.

Competition among six wood decay fungi was studied using 15×15 mm wood blocks placed in 250×250 mm plastic trays filled with unsterilized sand or clay. The wood blocks were preinoculated with Heterobasidion annosum (Fr.) Bref., Resinicium bicolor (Alb. & Schw. ex Fr.) Parm., Phanerochaete sanguinea (Fr.) Hjortstam, Coniophora sp. DC. ex Me"rat, Armillaria borealis Marxmuller and Korhonen and Hypholoma capnoides (Fr.) Kummer before they were combined in all possible combinations in the trays. Two methods were used, one with all wood blocks inoculated, and one with sterilized non-inoculated wood blocks distributed between the inoculated ones. Wood blocks preinoculated with the six species were also used in a pairwise competition test. Following incubation for 9 months in darkness at 21°C, mycelia were reisolated and identified. R. bicolor was most successful at invading through the soil and replacing other species in the wood blocks. P. sanguinea, Coniophora sp. and H. capnoides also had some success.