Regionalized Life Cycle Inventories of Global Sulfidic Copper Tailings

The effect of biopolymer stabilisation on biostimulated or bioaugmented mine residue for potential technosol production

Mine waste can be transformed into technosol as an ecological strategy. Despite its importance to soil functions, biological activity is often overlooked. Biopolymers can serve as innovative tools for bioremediation, facilitating chemical reactions and creating networks to encapsulate contaminants. This work aims to assess the use of bioleached and stabilised residues from a tungsten mine for technosol production. The first objective was to evaluate mine tailings for their bioleaching potential by biostimulation or bioaugmentation with strain Diaphorobacter polyhydroxybutyrativorans B2A2W2. The second was to evaluate the effect of Portland cement or biopolymers such as Carboxymethyl Cellulose (CMC) or Xanthan Gum (XG) on the stabilisation of bioleached residues. The impact of biopolymers on residues' characteristics, such as metal leaching, number of cultivable microorganisms, compression strength and ecotoxicity was evaluated using flow systems. Over time, bioleached metallic elements decreased, except for iron (Fe). Biostimulated and stabilised residues exhibited similar trends; both CMC and cement showed low leaching rates and viable microorganisms in the same order (106 CFU × ml-1). However, bioaugmented residue stabilised with XG showed 106 CFU × ml-1 viable microorganisms and increased 2.2-fold Fe leaching than BA_Control. CMC addition to bioaugmented residue reduced 5.9-fold Fe leaching and increased 100-fold viable microorganisms. By utilising both biological and engineering approaches to characterise the technosol, this study contributes to advancing knowledge of technosol production. The residues biostimulated and stabilised with CMC produced a material useful for bio-applications, with low toxicity and metal leaching, useful for bio-applications. XG was the best stabiliser for geotechnical engineering applications, with improved compression strength. In conclusion, the study demonstrates the usefulness of biopolymer treatment for residues and emphasises the importance of selecting the appropriate biopolymer for the intended function of technosols.

Sulfate-reducing consortium HQ23 stabilizes metal(loid)s and activates biological N-fixation in mixed heavy metal-contaminated soil

Sulfate-reducing bacteria (SRB) are used in the remediation of mine pollution; however, the mechanism of stabilizing multiple heavy metal(loid)s by the SRB consortium under low oxygen conditions needs further study. Indigenous microflora were extracted from non-ferrous metal-contaminated soil co-inoculated with enriched SRB consortium and assembled as the HQ23 consortium. The presence of Desulfovibrio (SRB) in HQ23 was confirmed by 16S rRNA sequencing and qPCR. The effects of culture media, dissolved oxygen (DO), SO42¯, and pH on the HQ23 growth rate, and the SO42¯-reducing activity were examined. Data indicates that the HQ23 sustained SRB function under low DO conditions (3.67 ± 0.1 mg/L), but the SRB activity was inhibited at high DO content (5.75 ± 0.39 mg/L). The HQ23 can grow from pH 5 to pH 9 and can decrease mobile or bioavailable Cr, Cu, and Zn concentrations in contaminated soil samples. FTIR revealed that Cu and Cr adsorbed to similar binding sites on bacteria, likely decreasing bacterial Cu toxicity. Increased abundances of DSV (marker for Desulfovibrio) and nifH (N-fixation) genes were observed, as well as an accumulation of nitrate-N content in soils suggesting that HQ23 stimulates the biological N-fixation in soils. This study strongly supports the future application of SRB for the bioremediation of heavy metal-polluted sites.

Efficient carbamazepine degradation by modified copper tailings and PMS system: Performance evaluation and mechanism

It is a green and sustainable path to establish cheap solid waste-based catalyst to establish peroxymonosulfate (PMS) catalytic system for the degradation of carbamazepine (CBZ) in water. In this study, durable copper tailing waste residue-based catalyst (CSWR) was prepared, and efficient CSWR/PMS system was constructed for catalytic degradation of CBZ for first time. The morphology and structure of CSWR changed from clumps to porous and loose amorphous by alkali leaching and medium temperature calcination. The reconstructed surface of the CSWR exposes more active sites promotes the catalytic reaction and increases the degradation rate of CBZ by more than 39.8 times. And the CSWR/PMS achieved a CBZ removal of nearly 99.99 % in 20 min. In particular, perovskite-type iron-calcium compounds were formed, which stimulated the production of more HO• and SO4•- in the system. DFT calculation shows that CSWR has stronger adsorption energy and electron transfer ability to PMS molecules, which improved the degradation efficiency of the system. In general, this study proposed a means of high-value waste utilization, which provided a new idea for the preparation of solid waste based environmental functional materials and is expected to be widely used in practical wastewater treatment.

Revealing the release and migration mechanism of heavy metals in typical carbonate tailings, East China

Refining the occurrence characteristics of tailings hazardous materials at source is of great importance for pollution management and ecological reclamation. However, the release and transport of heavy metals (HMs) from tailings under rainfall drenching in simulated real-world environments is less well portrayed, particularly highlighting the inherent neutralisation in tailings wastes under superimposed dynamic conditions. In this study, dynamic leaching columns simulating actual conditions were used to observe the release and transport of HMs from tailings under acid rainfall infiltration at spatial and temporal scales. The release rate of trace elements (e.g., As, Cr, Ni, Pb, Cd) is high. Neutralisation in the presence of carbonate rocks in the gangue reduces HMs release intensity from tailings with high heavy metal content, along with the precipitation of iron oxides and chromium-bearing minerals, etc. In addition, the vertical differentiation of HMs is more relevant to physical processes. In the absence of carbonate rocks in gangue, the lowest pH value is reached within 1.2 h after acid rain infiltrates the tailings. At the same time, Cu, Zn and Cd are released significantly from the minerals at the superficial level. The release of As(III) is mainly concentrated in the early and late stages of water-rock contact.

Remarkable Spatial Disparity of Life Cycle Inventory for Coal Production in China

Coal is the primary energy source in China, and its life cycle inventory (LCI) is widely used as background data for life cycle assessment studies. Previous research indicates that the inventory of coal production varies regionally. However, the development of complete regionalized LCIs for coal production is quite limited. Here, we establish the first provincial-level LCIs of local coal production and market for coal in China, based on a database of 6,122 coal mines and developed models. In the inventory results of local coal production, the coefficients of variation (CVs) of nine indicators exceed 0.5, especially SO2 and particulate matter emission factors (CVs > 1). Compared with that, the interprovincial coal trade homogenizes the provincial production inventory of market for coal relatively, despite four indicators with CVs exceeding 0.5. Therefore, the regionalized inventory with remarkable spatial differentiation can provide more accurate fundamental data for future research such as electricity production. Furthermore, CH4 emissions from coal production account for 24% of China's total methane emissions, highlighting its significance in mitigating global warming. Moreover, through the increasing coal trade, the significant and implicit plunder of water resources from the three coal net-exporting provinces, located in water-scarce areas, should be noted.

Toward sustainable reprocessing and valorization of sulfidic copper tailings: Scenarios and prospective LCA

There has been increasing attention recently to reprocessing of mining waste, which aims to recover potentially valuable materials such as metals and other byproducts from untapped resources. Mining waste valorization may offer environmental advantages over traditional make-waste-dispose approaches. However, a quantitative environmental assessment for large-scale reprocessing, accounting for future trends and a broad set of environmental indicators, is still lacking. This article assesses the life cycle impacts and resource recovery potential associated with alternative waste management through mine tailings reprocessing at a regional scale. Sulfidic copper tailings in the EU were selected as a case study. We perform prospective life cycle assessments of future reprocessing scenarios by considering emerging resource recovery technologies, market supply & demand forecasts, and energy system changes. We find that some reprocessing and valorization technologies in future scenarios may have reduction potentials for multiple impact indicators. However, results for indicators such as climate change and energy-related impacts suggest that specific scenarios perform sub-optimally due to energy/resource-intensive processes. The environmental performance of reprocessing of tailings is influenced by technology routes, secondary material market penetration, and choices of displaced products. The trade-off between climate change and energy related impacts, on the one hand, and toxicity impacts, on the other hand, requires critical appraisal by decision makers when promoting alternative tailings reprocessing. Implementing value recovery strategies for building material production, can save up to 3 Mt. CO₂-eq in 2050 compared to business as usual, helping the copper sector mitigate climate impacts. Additional climate mitigation efforts in demand-side management are needed though to achieve the 1.5 °C climate target. This work provides a scientific basis for decision-making toward more sustainable reprocessing and valorization of sulfidic tailings.

An Integrated Model to Conduct Multi-Criteria Technology Assessments: The Case of Electric Vehicle Batteries

The large-scale adoption of low-carbon technologies can result in trade-offs between technical, socio-economic, and environmental aspects. To assess such trade-offs, discipline-specific models typically used in isolation need to be integrated to support decisions. Integrated modeling approaches, however, usually remain at the conceptual level, and operationalization efforts are lacking. Here, we propose an integrated model and framework to guide the assessment and engineering of technical, socio-economic, and environmental aspects of low-carbon technologies. The framework was tested with a case study of design strategies aimed to improve the material sustainability of electric vehicle batteries. The integrated model assesses the trade-offs between the costs, emissions, material criticality, and energy density of 20,736 unique material design options. The results show clear conflicts between energy density and the other indicators: i.e., energy density is reduced by more than 20% when the costs, emissions, or material criticality objectives are optimized. Finding optimal battery designs that balance between these objectives remains difficult but is essential to establishing a sustainable battery system. The results exemplify how the integrated model can be used as a decision support tool for researchers, companies, and policy makers to optimize low-carbon technology designs from various perspectives.

Synergistic mechanism and application of microbially induced carbonate precipitation (MICP) and inorganic additives for passivation of heavy metals in copper-nickel tailings

Tailings are one of the largest quantities of hazardous waste in the world, and their treatment is difficult and expensive. In this work, a new, low-cost technique coupling microbially induced carbonate precipitation (MICP) and inorganic additives was proposed, optimized, and applied. The results showed that CaO was the best additive among the six tested, with an optimum dosage of 5%. A 90-day experiment indicated that the MICP-CaO coupled technique was highly effective for all the concerned heavy metals (Cu, Ni, Pb, and Cr) in the Cu-Ni tailings. During the stabilization period (20-90 days), the passivation rates were stable at 78.8 ± 2.9% (Cu), 78.1 ± 1.0% (Ni), 89.2 ± 1.0% (Pb), and 97.8 ± 0.5% (Cr), 2%-866% higher than the single technique of either MICP or CaO. Multiple analyses demonstrated that the synergistic effect of MICP and CaO produced a large amount of calcite (1.5% of the tailings). This calcite cemented the tailings particles, sequestrated heavy metal ions into the lattices, and played a key role in heavy metal passivation. Moreover, CaO and MICP improved the strength and compactness of solidified body, respectively. This work demonstrates the feasibility of the MICP-CaO coupled technique in tailings solidification, which can be applied in practical projects.

Life Cycle Energy Consumption and GHG Emissions of the Copper Production in China and the Influence of Main Factors on the above Performance

The copper demand and production in China are the largest in the world. In order to obtain the trends of the energy consumption and GHG emissions of copper production in China over a number of years, this paper uses a life cycle analysis method to calculate the above two indexes, in the years between 2004 and 2017. The life cycle energy consumption ranged between 101.78 and 31.72 GJ/t copper and the GHG emissions varied between 9.96 and 3.09 t CO2 eq/t copper due to the improvements in mining and smelting technologies. This study also analyses the influence of electricity sources, auxiliary materials consumption, and copper ore grade on the life cycle performance. Using wind or nuclear electricity instead of mixed electricity can reduce energy consumption by 63.67–76.27% or 64.23–76.94%, and GHG emissions by 64.42–77.84% or 65.08–78.63%, respectively. The GHG emissions and energy consumption of underground mining are approximately 2.97–7.03 times that of strip mining, while the influence of auxiliary materials on the above two indexes is less than 3.88%.

Environmental impact of mining and beneficiation of copper sulphate mine based on life cycle assessment

China is a major producer of copper concentrate as its smelting capacity continues to expand dramatically. The present study analyzes the life cycle environmental impact of copper concentrate production, along with selection of a typical copper sulphate mine in China. Life cycle assessment (LCA) was conducted using SimaPro with ReCiPe 2016 method. The midpoint and endpoint results were performed with uncertainty information based on Monte Carlo calculation. Normalization of midpoint results revealed that impact from the marine ecotoxicity category was the largest contributor to the total environmental impact, followed by freshwater ecotoxicity, human carcinogenic toxicity, human non-carcinogenic toxicity, and terrestrial ecotoxicity. The mining activity, backfilling activity, and electricity generation were proved to be the dominant factors. In addition, main processes and substances to the identified key categories were also classified. Specifically, the cement production in the backfilling process, blasting activity, on-site emission, and electricity generation was regarded as the critical processes. Copper to air and zinc emission to water were considered the critical substances. The sensitivity analysis revealed the most effective measure to solve the environmental problems caused by the concentrate production process, which is controlling on-site emissions and reducing pollution from cement production. Finally, the corresponding technical and management measures were proposed to facilitate the development of cleaner metal industry.