Advancing phytomining: Harnessing plant potential for sustainable rare earth element extraction.

Rare earth elements (REEs) are pivotal for advanced technologies, driving a surge in global demand. Import dependency on clean energy minerals raises concerns about supply chain vulnerabilities and geopolitical risks. Conventional REEs productionis resource-intensive and environmentally harmful, necessitating a sustainable supply approach. Phytomining (agromining) utilizes plants for eco-friendly REE extraction, contributing to the circular economy and exploiting untapped metal resources in enriched soils. Critical parameters like soil pH, Casparian strip, and REE valence influence soil and plant uptake bioavailability. Hyperaccumulator species efficiently accumulate REEs, serving as energy resources. Despite a lack of a comprehensive database, phytomining exhibits lower environmental impacts due to minimal chemical usage and CO2 absorption. This review proposes phytomining as a system for REEs extraction, remediating contaminated areas, and rehabilitating abandoned mines. The phytomining of REEs offers a promising avenue for sustainable REEs extraction but requires technological advancements to realize its full potential.

Fly ash treatment via conventional and microwave-assisted organic acid leaching: kinetics and life cycle assessment.

Heedless disposal of oil-based fly ash contributes to the contamination of the air, water, and soil. Acid leaching of industrial solid wastes is recognized as a versatile, cost-effective, and environmentally friendly solid waste treatment approach. The present study investigated the viability of conventional leaching (CL) and microwave-assisted leaching (MAL) of predominant heavy metals from Mazut-burnt fly ash. For this purpose, the practicality of four organic acids with various specifications (ascorbic, gluconic, citric, and oxalic acids) on the dissolution efficiency of fly ash components was examined. Utilization of oxalic acid led to achieving full V recovery, complete Fe removal, and Ni enrichment in the residue in both CL and MAL setups. The Ni content of the sample was enriched from 6% in the calcinated sample to 23.7% in the oxalic acid leaching residue. Using citric acid resulted in the co-extraction of V, Ni, and Fe with nearly 70% V, 50% Ni, and 89% Fe dissolved in CL. The dissolution efficiencies were slightly lower in MAL. Oxalic acid was selected as the most promising organic acid reagent for fly ash treatment, so its CL kinetics was studied and defined by the shrinking particle model. The model showed that the controlling steps in the leaching of V differ over time, changing from a chemical reaction before 60 min to fluid film diffusion or mixing afterward. The kinetic study proved MAL as an effective technique in overcoming the leaching kinetic barriers. A life cycle assessment study was conducted to determine the environmental impacts of the proposed process. Accordingly, the MAL using oxalic acid was the most environmentally friendly process among the studied ones, and the utilization of microwaves leads to the reduction of the leaching processes' environmental impacts by decreasing the processing time.

Upcycling spent graphite in LIBs into battery-grade graphene: Managing the produced waste and environmental impacts analysis.

This study focuses on connecting graphite demand to battery materials demand, providing a solution to the identified shortage of battery materials and promoting sustainable development. This research used modified Hummer's method to synthesize graphene from the recycled graphite and compared it with graphene synthesized from purified recycled graphite. The purification of recycled graphite was implemented by acid curing-leaching and calcination. The analysis showed that the reduction reaction effectively removed oxygen-containing functional groups from the graphene, resulting in enhanced quality of the produced graphene. Hummer's waste acid was used as a leaching reagent for different LIBs' cathode types in waste management. The waste acid was found to be a strong reagent for transition metals leaching and obtained almost full recoveries of Li, Co, Mn, and Ni from spent LIB cathodes. The synthesized graphene exhibited higher specific surface areas and conductivity values compared to battery-grade graphite. The electrochemical performance of the graphene sheets in lithium half-cells was evaluated, and it was found that the graphene synthesized from recycled graphite enabled increased lithium insertion at active sites, suggesting its potential for enhanced lithium retention. Furthermore, a life cycle assessment study was conducted to evaluate the environmental impacts of the recycling and synthesis processes. This study demonstrates the potential of recycling graphite from spent battery anodes to produce high-quality graphene with improved electrochemical properties.

Environmental impact assessment of a novel third-generation biorefinery approach for astaxanthin and biofuel production.

A novel third-generation biorefinery approach, including two paths of Ethanol/methane production pathway (EMP) and the direct methane production pathway (DMP), for astaxanthin and ethanol and biogas production from the freshwater microalgae Haematococcus pluvialis was developed previously. To ensure its environmental sustainability, a comprehensive life cycle assessment (LCA) study was conducted based on 1-GJ energy generation from biomethane as the functional unit. Results indicate that the EMP pathway had higher environmental impacts on all categories due to more stages and chemicals/energy consumption (at least five times greater effect). Results showed that while the enzymatic hydrolysis step followed by the fermentation stage was the main contributor to all environmental categories in the EMP route, astaxanthin induction dominated all environmental categories in the DMP route. The results showed that sodium nitrate, phosphate salts, inoculum sludge, acetone, and electricity had considerable environmental impacts. Moreover, despite low enzyme usage in enzymatic hydrolysis, these proteins significantly impacted all environmental categories in this stage. The baseline analysis concluded that to produce 1 GJ energy from methane, about 88 kg and 13 kg CO2 were generated from the EMP and DMP pathways, respectively. A sensitivity analysis was also conducted to compare various ratios of chemicals, such as phosphate salts, with high contributions to enzymatic hydrolysis and astaxanthin induction stages in the EMP and DMP routes, respectively. Finally, the LCA results revealed that the DMP pathway is more environmentally friendly with the same economic value of biomethane and astaxanthin production. This LCA study updated the data related to the environmental assessment of processes to utilize H. pluvialis to produce biofuels and astaxanthin simultaneously.

Assessing the environmental impact of gold production from double refractory ore in a large-scale facility.

Despite the strict environmental management regulations, there is still a considerable adverse impact on the ecosystem and human health when it comes to large-scale gold mining operations. Gold mining is an energy-intensive process that can discharge substantial quantities of chemicals combined with gaseous emissions into the environment. Considering gold mining's significant role in Nevada's economy and the growing concern about climate change, it's necessary to investigate the environmental burdens of this sector. To provide a comprehensive environmental perspective on the large-scale gold mining operations in Nevada, this study used a life cycle assessment (LCA) approach to evaluate the environmental burdens of gold production from double refractory ores in the roasting process. The Tool for Reduction and Assessment of Chemical and Other Environmental Impacts (TRACI) method was used to evaluate the categories of acidification, ozone depletion, global warming, smog, carcinogenics, non-carcinogenics, respiratory effects, and fossil fuel depletion. Results showed that major contributors to greenhouse gas (GHG) emissions were grinding and off-gas treatment stages being responsible for 34.80 % and 56.10 % of the total global warming, respectively. The carbon footprint for producing one kg of gold was 12,200 kg CO2-eq. Sensitivity analysis was also employed on electricity to observe the influence of electricity on key contributor stages. A 10 % change in electricity reduced the GHG emissions in crushing and grinding by 12.2 % and 7.10 %, respectively, while delivering an insignificant effect on the off-gas treatment. Significantly, this study stands as the first initiative to apply LCA in the North American mining industry, with a unique focus on the off-gas treatment post-roasting and its associated emissions. Our findings can serve as a foundational database, aiding stakeholders in making informed decisions and enhancing sustainable practices in the gold mining industry.

Valorization of fly ash by nickel ferrite and vanadium oxide recovery through pyro-hydrometallurgical processes: Technical and environmental assessment.

The fly ash (FA) from the combustion of heavy oil in power stations is characterized by fine particles containing toxic metals. The sample utilized in this study was gathered from the dust precipitators of seven heavy-oil-consuming Iranian power plants. Substantial quantities of heavy metals, particularly vanadium, iron, and nickel, have been detected in the sample, indicating both its potential utility and hazard to the soil and groundwater. The harmful consequences of FA disposal on the environment have led to the adoption of recycling as a treatment approach in this study. The valorization of FA was investigated by producing nickel ferrite (NiFe2O4) and vanadium pentoxide (V2O5) through a novel approach using a combination of pyro-hydrometallurgical processes, which resulted in proposing a recycling closed-loop flowsheet. Roasting was first practiced to form NiFe2O4 by reacting the nickel and iron content of the FA. The NiFe2O4 showed a low dissolution against inorganic acids (H2SO4, HCl, and HNO3). The vanadium content of the FA showed a remarkable recovery in H2SO4 (91%) and HCl (95.6%), while the dissolution of Ni was limited to 16.85% and 17.5%, respectively. The produced NiFe2O4 acted well in response to the magnetic field, and its purity was further increased to 95-96% through a two-stage process consisting of grinding and magnetic separation. The nano-sized spherical NiFe2O4 with saturation magnetization of 34.66 and 30.82 emu. g-1 was obtained from H2SO4 and HCl residues, respectively. The dissolved vanadium was recovered as V2O5 via oxidation-precipitation in sulfate media and oxidation-ammonium precipitation in chloride solution. The purity of V2O5 in sulfate and chloride media was 93% and 98.5%, respectively. Finally, a life cycle assessment (LCA) study was performed on the suggested methods to track the ecological effects of extracting V and Ni from oil combustion FA. According to the performed LCA, H2SO4 was determined as the proper leaching reagent considering the environmental and technical aspects.

Comparative life cycle analysis of critical materials recovery from spent Li-ion batteries.

The development of new generations of electric vehicles is expected to drive the growth of lithium-ion batteries in the global market. Life Cycle Assessment (LCA) method was utilized in this study to evaluate the environmental impacts of various hydrometallurgical processes in critical materials recovery from lithium-ion battery (LIB) cathode powder. The main objective of this work was to fill the knowledge gap regarding the environmental sustainability of various processes in LIB recycling and to generate a comprehensive comparison of the environmental burdens caused by numerous hydrometallurgical methods. According to this investigation, leaching with acetic acid, formic acid, maleic acid, and DL-malic acid demonstrates lower environmental impacts compared to lactic acid, ascorbic acid, succinic acid, citric acid, trichloroacetic acid, and tartaric acid. Among inorganic acids, nitric acid and hydrochloric acid show higher environmental impacts compared to sulfuric acid. Furthermore, the results of this study indicate that leaching with some organic acids such as citric, succinic, ascorbic, trichloroacetic, and tartaric acids leads to higher negative environmental impacts in most environmental categories compared to inorganic acids like sulfuric and hydrochloric acid. Therefore, not all organic acids utilized in the leaching of critical and strategic materials from cathode powder can enhance environmental sustainability in the recycling process. The results of the solvent extraction study as a downstream process of leaching show that sodium hydroxide, organic reagents, and kerosene have the highest environmental impact among all inputs in this process. Generally, solvent extraction has a greater environmental impact compared to the leaching process.

Characterization of contaminant leaching from asphalt pavements: A critical review of measurement methods, reclaimed asphalt pavement, porous asphalt, and waste-modified asphalt mixtures.

In recent years, the pavement industry has been seeking sustainable development through recycling reclaimed asphalt pavement and reusing other waste materials as replacements for asphalt mixture constituents. Incorporating waste material into asphalt mixture and the presence of pollutants such as exhaust fumes and gasoline due to vehicle traffic may lead to contaminants leaching from asphalt pavements to underlying soil layers and groundwater aquifers, posing serious risks to ecosystems and the environment. To cast light on contaminant leaching from asphalt pavements, this article presents a comprehensive review of the literature that is divided into four research areas: evaluation of leaching measurement methods, leaching from recycled asphalt materials, leaching characteristics of porous asphalt pavements, and waste-modified asphalt mixtures. Moreover, a critical discussion of bibliometric data, literature content and knowledge gaps in this domain is provided to help highway agencies and environmental scientists address contaminant leaching from asphalt pavements. Finally, some potential research directions are suggested for future research works.

The role of concrete in life cycle greenhouse gas emissions of US buildings and pavements.

Concrete is a critical component of deep decarbonization efforts because of both the scale of the industry and because of how its use impacts the building, transportation, and industrial sectors. We use a bottom-up model of current and future building and pavement stocks and construction in the United States to contextualize the role of concrete in greenhouse gas (GHG) reductions strategies under projected and ambitious scenarios, including embodied and use phases of the structures' life cycle. We show that projected improvements in the building sector result in a reduction of 49% of GHG emissions in 2050 relative to 2016 levels, whereas ambitious improvements result in a 57% reduction in 2050, which is 22.5 Gt cumulative saving. The pavements sector shows a larger difference between the two scenarios with a 14% reduction of GHG emissions for projected improvements and a 65% reduction under the ambitious scenario, which is ∼1.35 Gt. This reduction occurs despite the fact that concrete usage in 2050 in the ambitious scenario is over three times that of the projected scenario because of the ways in which concrete lowers use phase emissions. Over 70% of future emissions from new construction are from the use phase.

Environmental life cycle assessment on the separation of rare earth oxides through solvent extraction.

Over the past decade, Rare Earth Elements (REEs) have gained special interests due to their significance in many industrial applications, especially those related to clean energy. While REEs production is known to cause damage to the ecosystem, only a handful of Life Cycle Assessment (LCA) investigations have been conducted in recent years, mainly due to lack of data and information. This is especially true for the solvent extraction separation of REEs from aqueous solution which is a challenging step in the REEs production route. In the current investigation, an LCA is carried out on a typical REE solvent extraction process using P204/kerosene and the energy/material flows and emissions data were collected from two different solvent extraction facilities in Inner Mongolia and Fujian provinces in China. In order to develop life cycle inventories, Ecoinvent 3 and SimaPro 8 software together with energy/mass stoichiometry and balance were utilized. TRACI and ILCD were applied as impact assessment tools and LCA outcomes were employed to examine and determine ecological burdens of the REEs solvent extraction operation. Based on the results, in comparison with the production of generic organic solvent in the Ecoinvent dataset, P204 production has greater burdens on all TRACI impact categories. However, due to the small amount of consumption, the contribution of P204 remains minimal. Additionally, sodium hydroxide and hydrochloric acid are the two impactful chemicals on most environmental categories used in the solvent extraction operation. On average, the solvent extraction step accounts for 30% of the total environmental impacts associated with individual REOs. Finally, opportunities and challenges for an enhanced environmental performance of the REEs solvent extraction operation were investigated.

Recovery of lithium and cobalt from spent lithium-ion batteries using organic acids: Process optimization and kinetic aspects.

An environmentally-friendly route based on hydrometallurgy was investigated for the recovery of cobalt and lithium from spent lithium ion batteries (LIBs) using different organic acids (citric acid, Dl-malic acid, oxalic acid and acetic acid). In this investigation, response surface methodology (RSM) was utilized to optimize leaching parameters including solid to liquid ratio (S/L), temperature, acid concentration, type of organic acid and hydrogen peroxide concentration. Based on the results obtained from optimizing procedure, temperature was recognized as the most influential parameter. In addition, while 81% of cobalt was recovered, the maximum lithium recovery of 92% was achieved at the optimum leaching condition of 60°C, S/L: 30gL-1, citric acid concentration: 2M, hydrogen peroxide concentration: 1.25Vol.% and leaching time: 2h. Furthermore, results displayed that ultrasonic agitation will enhance the recovery of lithium and cobalt. It was found that the kinetics of cobalt leaching is controlled by surface chemical reaction at temperatures lower than 45°C. However, diffusion through the product layer at temperatures higher than 45°C controls the rate of cobalt leaching. Rate of lithium reaction is controlled by diffusion through the product layer at all the temperatures studied.

Recovery of zinc from leach residues with minimum iron dissolution using oxidative leaching.

Leaching was performed to recover zinc from a zinc leach residue which contained 9.87% Zn and 4.93% Fe. During sulfuric acid leaching, Fe was dissolved as well as Zn which can reduce the Zn extraction efficiency. Leaching the residue in the presence of an oxidizing reagent such as hydrogen peroxide or manganese dioxide significantly reduced the iron content of the leach liquor. Effect of pH, temperature, solid/liquid ratio, reaction time and hydrogen peroxide or manganese dioxide concentration on the recovery of zinc and iron in non-oxidative and oxidative leaching conditions were investigated. By using the optimum oxidative leaching conditions, iron recovery reduced from 70% in non-oxidative leaching to 0.4 and 5% in the presence of MnO(2) and H(2)O(2), respectively, with acceptable Zn recovery. This reduction in the iron content was due to the different iron compounds formed at different conditions.