Urban Mining Research Articles

Identification of Inefficient Urban Land for Urban Regeneration Considering Land Use Differentiation

Accurately identifying inefficient urban land is essential for urban regeneration and mining underutilized assets. Previous studies have primarily focused on examining the overall efficiency of land use without adequately considering the heterogeneity of urban land use types and comprehensive characteristics of urban quality. As a result, the spatial accuracy and precision of research findings have been relatively low. To address this gap, we developed a comprehensive method to identify inefficient urban lands for residential, commercial, and industrial use. The method integrated multi-source geographic data to quantitatively characterize the efficiency of different land use types considering six key dimensions, including building attribute, urban service, transportation condition, environmental quality, business performance, and production efficiency, utilized principal component analysis to reduce the multicollinearity and the dimensionality of the data, and identified land clusters with similar features that were inefficiently used by means of hierarchical clustering. By applying the method to Changsha, China, we validated its effectiveness. The results demonstrate that the method can accurately identify inefficient residential, commercial, and industrial land, with kappa coefficients of 0.71, 0.77, and 0.68, respectively. The identification results reveal the spatial distribution patterns of different types of inefficient land. Inefficient residential land is concentrated towards the city center, particularly in central areas. Inefficient commercial land is relatively evenly distributed, mainly outside the core commercial regions. Inefficient industrial land clusters towards the periphery, forming several agglomeration areas centered around industrial parks. By precisely identifying inefficient urban land and focusing on the key influencing factors, the proposed method enables the site selection of urban regeneration, site redevelopment evaluation, and optimization of urban resources.

Urban metabolic flow in China’s megacities doubled by material stock accumulation since the 21st century

Buildings, infrastructure, and durable goods play a critical role in urbanization, akin to bones and muscles that structure the human body. These stocks contribute to the exploitation of over half of the world’s resources and offer potential “urban mining” sources. However, the process of resource transformation regarding urban material stock growth and material flow alteration remains unclear. The metaphor of urban metabolism provides a new perspective to dissect this process, but current studies often spotlight only specific fragments, such as certain end-use types or materials. This study bridges this gap by establishing a comprehensive level-to-level analysis of urban “bone-muscle” metabolism in China’s megacities. This study presents a comprehensive analysis of urban metabolism in China’s megacities, tracking the lifecycle of material stock across over a hundred distinct end-use types and 12 categories of materials. Results indicate that annual metabolic flow in these cities has doubled since the early 21st century, reaching 264–737 Mt in 2018, with manufacturing, construction, and transportation as primary drivers. As accumulation intensifies, the material stock’s growth rate diminishes logarithmically, hinting at increased efficiency and a move towards a steady state. Concurrently, scrap flow is on the rise. Driven by population growth, per capita scrap is projected to reach 2.0–4.7 t/cap by 2035, and material stock is expected to rise 1.4–2 fold. Proactive population planning and coordinated development strategies can mitigate the risks associated with this growth and maintain urban system stability.

Az édesvízhiány története: Namíbia vízkészletei

This article introduces the various water resources available to Namibia, an arid country in southern Africa. With low and extremely variable annual rainfall and high evaporation rates, surface water is scarce. Permanent rivers are only found along the southern and northern borders. Ephemeral rivers flow for short periods after thundershowers and few reach the ocean. Many ephemeral rivers sink into the gravelly and sandy riverbeds, where they feed alluvial aquifers. Groundwater is the only water source for about 80% of the territory. Dams were built in ephemeral rivers to create artificial lakes that play an important role in water provision for urban areas, irrigation schemes and mines. Despite the extreme aridity, Namibia has a variety of wetland habitats, including five Ramsar sites.

Augmentation in bioleaching potential of indigenous Bacillus sp. ISO1 for metals recovery from waste computer-printed circuit boards.

The bio-cyanidation process of various cyanogenic microorganisms is found to be a sustainable and effective method for metals recovery from primary and secondary sources. This process has surpassed the limitations of the chemical cyanide treatment process; thus, prioritized as a promising approach for e-waste "urban mining" strategies. The main focus of the study was to enhance the bioleaching capacity of indigenous Bacillus sp. ISO1 and to implement optimized parameters in large-scale bioleaching operations. The assessment of various amino acids unveiled that like other cyanogenic microorganisms Bacillus sp. ISO1 also preferred glycine as a prime precursor for cyanide synthesis, as maximum metal solubilization was achieved with glycine amino acid. Other amino acids influenced the bacterial growth but not significantly affected the biocyanidation process. The evaluation and optimization of methionine as a lixiviant stimulator demonstrated that the addition of 1 mg/L methionine effectively enhance the production of glycine-utilizing cyanide lixiviant, that led to a significant solubilization of Cu (86%), Au (75%), and Ag (63%) metals. Furthermore, the kinetics of metal solubilization and operating conditions were explored at increased volume (i.e., 3 L working volume) of bioleaching medium to assess the industrial scale potential of this potent bacterial strain with optimized parameters such as temperature, pH, pulp density, and inoculum size. The significant recovery of Cu (˃ 60%) and other metals at this substantial volume suggested the implementation of a bioleaching process with this potent bacterial strain at industrial scale operations.

From waste to value: recovering critical raw materials from urban mines in the European Union and United States

From waste to value: recovering critical raw materials from urban mines in the European Union and United States

Chiropteran diversity and diet of fruit bats in a tropical dry forest of northern South America

Remnants of Tropical Dry Forest persist in urban and peri-urban areas and are essential for maintaining biodiversity and ecosystem services. However, the challenges facing the conservation of these respective forests have intensified with the encroachment of the urban frontier, mining activities, deforestation, and cattle ranching. In this context, our study aims to estimate the diversity of the order Chiroptera and characterize the diet of the family Phyllostomidae. This approach allows us to gain insights into the ecological dynamics and assess the status of Tropical Dry Forest fragments located within the urban and peri-urban areas of Cúcuta, Colombia. Field sampling was conducted from January to September 2018, with a total sampling effort of 2,160 hours/meter/net. Bats were sexed, morphometrically characterized, and had their feces collected for diet analysis before being tagged and released. We identified three families, nine genera, and 11 species. A total of 276 individuals were captured. Seven species were observed in the urban area and ten in the peri-urban zone; Artibeus lituratus and Carollia perspicillata were the most abundant species in both locations. The diet included seeds from the families Moraceae, Anacardiaceae, and Rosaceae. Our findings reveal that in areas with dense vegetation, such as peri-urban zones, frugivorous bats prefer to consume fruits of domesticated species, including economically significant fruits like guava and tomato. This dietary shift could alter seed dispersal patterns and the dynamics of the Tropical Dry Forest, highlighting the ecological importance of these flying mammals in ecosystem regeneration.

Energy-efficient electrochemical recovery of gold enabled by a thiourea-based electrolyte system

The application of non-cyanide baths in electroplating for gold recovery has drawn significant attention due to their clear benefits on the environment and human health. Among these alternatives, thiourea has emerged as a promising non-cyanide bath, and yet high energy and reagent consumption has impeded its widespread adoption. Herein, an energy-efficient gold recovery process via electroplating was developed to reduce bath depletion. The redox potentials of gold deposition using thiourea electrolyte were examined through linear sweep voltammetry, and the consumed energy during the electrochemical plating of gold was quantified. The gold deposition was achieved in the two-electrode system enabling a 97% recovery under 0.3 V of the cell voltage. The proposed system exhibited a significant reduction in energy consumption to 0.129 kWh∙kg−1, implying that the oxidation of free thiourea on the anode mainly contributed to the decrease in the applied voltage and energy. Furthermore, the suppression of the bath consumption was evaluated compared with electroless plating, another reliable deposition process, throughout monitoring gold desorption and deposition efficiencies during the cyclic use of thiourea. The retardation of the sorbent consumption was observed in the electroplating during the consecutive cycles, which inferred that the reduction of its oxidized form, formamidine disulfide, led to the regeneration of the agent on the cathode. Thus, the suggested electroplating process with a gold-thiourea bath shows great potential as a workable means of gold recovery from an economic standpoint with its low energy and sorbent consumption to realize the commercialization of urban mining in the electronic industry.

The complexity and interconnectedness of circular cities and the circular economy for sustainability

AbstractIn our study, we are evaluating the dynamic interplay between circular cities and the circular economy, revealing connections shaped by new research insights, using Web of Science database. We have in depth analysed 671 publications from 1990 to mid‐2023, employing Leximancer and VOSviewer tools. Our analysis uncovered key themes, including buildings, waste management, value chains, and sustainable development, linking the circular cities concept and circular economy framework. Emerging research trends, such as urban metabolism, urban mining, governance models, the built environment, sustainability benchmarks, and value chain management, signify deliberate shifts towards higher circular development and implementation. These trajectories harmonise with overarching sustainable development goals. Contemporary research emphasises urban mining, circular indicators, adaptive resource reuse, and urban structure regeneration. This focus facilitates transitioning from linear models to heightened circularity within urban contexts. Research inclination is shifting from traditional economic and environmental concerns towards holistic urban configurations that prioritise social integration, communal well‐being, and the dynamics of the social economy. Through this analytical expedition, we offer novel insights that enhance our understanding of the intricate symbiosis between circular cities and the circular economy. Our findings provide a scientific foundation for formulating targeted strategies by decision‐makers and guiding urban landscapes towards transformative trajectories aligned with sustainable development objectives and sustainable cities.

Techno-economic analysis of an integrated bio- and hydrometallurgical process for base and precious metal recovery from waste printed circuit boards

Electronic waste (e-waste) is one of the fastest-growing waste streams and is often referred to as an urban mine due to its high base and precious metal content. Printed circuit boards (PCBs) have been the focus of numerous studies investigating bio- and hydrometallurgical pathways to extract and recover metals of value. This study evaluated the economic feasibility of an integrated bio- and hydrometallurgical process for extracting and recovering base and precious metals from PCBs. The process consisted of collecting and processing PCBs, extracting and recovering base metals using biogenic sulfuric acid and ferric iron, and extracting and recovering precious metals using hydrometallurgical pathways. A preliminary techno-economic analysis (TEA) was conducted to examine the potential costs of a plant that can process 1,000 tons per year of PCBs in Australia. The key factors that influence the economic feasibility were identified, and the effects of various factors, such as process efficiencies and market conditions, on the plant's profitability were evaluated. This assessment provided insight into the economic aspects of the process and assisted in identifying critical research pathways. Based on this analysis, the proposed process is profitable under optimised conditions and can address many challenges associated with e-waste processing in Australia.

Copper recovery from waste printed circuit boards by NH3−(NH4)2S2O8–CuSO4 slurry electrolysis

The recovery of waste printed circuit boards (WPCBs) is always at the center of the issue of e-waste, and even “urban mining”. Slurry electrolysis has been certified as a new and efficient approach for directly recovering copper from WPCBs, although its current efficiency is not high. Therefore, an alkaline slurry electrolysis system with NH3−(NH4)2S2O8–CuSO4 was examined to improve the current efficiency because (NH4)2S2O8 produces SO4-· or ·OH in an alkaline environment. Factors such as the current density, concentration of NH3·H2O, (NH4)2S2O8, NaCl, and Cu2+, solid/liquid (S/L) ratio, and electrolysis time are discussed. The results showed that the NH3−(NH4)2S2O8–CuSO4 electrolyte could significantly impact the current efficiency and copper recovery rate. Under optimum conditions (4 mol/L ammonium hydroxide, 1 mol/L ammonium persulfate, 20 g/L copper ion(Ⅱ), 0.5 mol/L sodium chloride, S/L ratio of 30 g/L, 20 mA/cm2, and 3 h), the copper recovery rate was 90.10%, and the copper current density was significantly improved to 83.03%, which was considerably higher than that of the acidic slurry electrolysis system (approximately 70%). Because copper in the WPCBs and Cu2+ can form [Cu(NH3)2]+ with ammonia and ammonia persulfate, it is substantially easier to electrodeposit than [Cu(NH3)4]2+. Meanwhile, the purity of the obtained copper foil was > 99.986%, meeting the standard for commercial cathodic copper, and markedly higher than that of the acidic slurry electrolysis system. Thus, alkaline slurry electrolysis shows great potential for applications in the e-waste industry.

Marine materials as innovative metal sorbents suitable for applications in wastewater treatments

The growing interest for urban mining strategies has pushed the research towards innovative strategies for metal recovery from electronic waste. Nevertheless, the treatment of the resulting metal-rich wastewater is still an issue. In this context, the present paper shows a method to use the capacity of Ulva algae to adsorb metals for the treatment of a synthetic solutions which simulates that resulting from a printed circuit board recycling process. The experiments considered a copper‑zinc‑iron system, showing a copper adsorption capacity of biomaterial up to 65 mg/g, at pH 5, favoured by iron presence. The process needs a short time (around 15 min) and it is suitable to be performed in a fixed-bed column able to treat more than 30 L of copper-contaminated wastewater, decreasing the energetic costs for mixing (compared to the typical slurry-reactor configuration) with an almost completed metal removal. The sustainability of the process is further improved by the selection of a macroalga which often accumulates on beaches (becoming a waste to remove) complying with the circular economy pillars.

Making Post-Dystopian Future Possible: Alternative Policies for Bytom

This article follows the argument that urban dystopia is reserved not only for the sphere of the fictional but also as a state of reality that academic methods can capture and describe. Taking the example of the city of Bytom, a traditional centre of coal mining in Southern Poland, the article discusses four spheres where the dystopian present is clearly visible – namely, the four elements that led Bytom to a socio-economic and spatial collapse: depopulation, social polarisation and ghettoisation, degradation of the urban fabric and mining damage. Apart from showing empirical evidence, the article critically considers the possibilities of a post-dystopian urban future for the city. A discussion of possible policy answers to these dystopian trends is based on two possible visions of how the urban future could look. First, the semi-dystopian vision assumes that the expected direction and the results of current policies will lead to some improvement in the quality of the urban environment and the residents’ quality of life. Second, the post-dystopian future is based on an optimistic vision, which assumes that a post-dystopian future is possible. However, the desired salvation from the dystopian present will not come about through the search for new utopian visions. It will rely instead on the improvement and mitigation of some of the substantial social, economic and environmental problems that exist and continue to present an unbreakable social image.

Drivers and barriers to achieve a circular economy of small-IT: Case study from the city of Porto.

Advances in digital electronics delivered small and portable gadgets, changing human interface with technology. Demand for new small devices of Information and Telecommunication Technology (small-IT) that have a short lifespan, like smartphones and laptops, creates flows and accumulation of electronic resources. These include precious metals that show potential for Urban Mining and Circular Economy. To find out the extent of setting up an improved recycling, reuse and repair system, data collection was conducted through surveys, bin observations and social experiments. These methods enabled us to analyse stocks and flows, identify behavioural practices and map collection infrastructure. About 80% of domestic small-IT stocks are hibernated, meaning they could be directly reused or easily repaired. Results show four barriers that keep citizens from handing in their unused small-IT: Devices are kept as back-up, they contain sentimental value, citizens are suspicious of post-collection data confidentiality issues and there is a perceived high effort to recycle. Drivers to enhance circularity are: improving e-waste infrastructure, introducing economic incentives and raising awareness on environmental impacts of hibernated stocks. A more trustworthy and legitimate management system is expected to deliver safety and confidentiality of personal data and provide the quality that fits the expectations of citizens of a proper place to dispose of their valuable items.

Potentials of reusing steel skeleton structures from multistorey parking units for architectural applications

AbstractIn the context of urban mining, which aims to extend the value chain of building components to conserve resources, save energy, avoid waste, and reduce emissions, the reuse of structural steel has great potential, that has hardly been exploited to date.In Germany, a significant amount of steel is found within multistorey parking units. Due to the standardised and mass relevant steel used in these structures and considering their diminishing significance in the context of transportation transitions, these buildings offer specific opportunities for reuse.The research aims to investigate the reuse of structural steel from parking facilities in a new architectural design purpose with focus on multistorey residential buildings, as these will become increasingly important in the future construction due to the predicted growth of the world population and global cities.The research methodology begins by identifying the reuse potential of structural steel from parking units for future multi‐storey residential buildings. The study then delves into the exploration of hybrid construction methods, which involve incorporating standardized steel profiles with clay and reinterpreting historical cap ceilings. These approaches aim to foster the development of innovative architectural solutions.

Thorium Removal, Recovery and Recycling: A Membrane Challenge for Urban Mining.

Although only a slightly radioactive element, thorium is considered extremely toxic because its various species, which reach the environment, can constitute an important problem for the health of the population. The present paper aims to expand the possibilities of using membrane processes in the removal, recovery and recycling of thorium from industrial residues reaching municipal waste-processing platforms. The paper includes a short introduction on the interest shown in this element, a weak radioactive metal, followed by highlighting some common (domestic) uses. In a distinct but concise section, the bio-medical impact of thorium is presented. The classic technologies for obtaining thorium are concentrated in a single schema, and the speciation of thorium is presented with an emphasis on the formation of hydroxo-complexes and complexes with common organic reagents. The determination of thorium is highlighted on the basis of its radioactivity, but especially through methods that call for extraction followed by an established electrochemical, spectral or chromatographic method. Membrane processes are presented based on the electrochemical potential difference, including barro-membrane processes, electrodialysis, liquid membranes and hybrid processes. A separate sub-chapter is devoted to proposals and recommendations for the use of membranes in order to achieve some progress in urban mining for the valorization of thorium.

Techno-economic analysis of the sequential recovery of valuable metals from waste tantalum capacitors in Indian context

The necessity for urban mining of metals has arisen due to the growing demand for metals brought about by technological innovation, the depletion of natural resources, and the exponential growth in e-waste generation. However, to be industrially adaptable, any recycling process must be economically profitable. Therefore, in this article, an economic feasibility study was conducted to determine the profitability of the proposed recycling process for recovering valuable metals from waste tantalum capacitors. Firstly, an integrated process was developed for the recovery of almost all economically and strategically significant metals. A detailed elemental and metallurgical balance followed this to determine the mass flow of metals during various stages of treatment. Lastly, the economic feasibility analysis has been done by estimating various cost components from capital and operating costs (utilizing Indian cost as foundation for calculation) to evaluate the profit that might be made by operating the suggested recycling facility for a month. Sensitivity and scenario analysis further investigated the impact of the most significant cost component on the percentage profit. The findings of this study support the notion that the suggested recycling method has a great deal of potential value and is commercially feasible with an ample profit margin.

High-Resolution Mapping of Material Stocks in Belgian Road Infrastructure: Material Efficiency Patterns, Material Recycling Potentials, and Greenhouse Gas Emissions Reduction Opportunities.

Road infrastructure is an integral part of built environment stocks, as it delivers essential social and economic services. While previous work has assessed material stocks, flows, and embodied emissions, spatially refined mapping of materials accumulated in road infrastructure can highlight hitherto underappreciated synergies between improved spatial planning, material stock efficiency, and urban mining. In this study, we mapped the materials stocked in road infrastructure across Belgium, explored the patterns of material stock efficiency and the recyclability of end-of-life road materials, and examined the greenhouse gas (GHG) emissions reductions of improving stock efficiency and recycling. We assembled data scattered across various governmental sources and crowdsourced platforms and developed a comprehensive database to warehouse locational information on road typology, layer geometry and thickness, material characteristics, traffic volume, climatic conditions, and soil conditions. Our results reveal a strong but nonlinear correlation between material stock efficiency and population density, indicating that spatial planning can reduce the required road stocks and associated GHG emissions. Urban mining potentials in road infrastructure hinge on multiple factors, such as the proximity to recycling facilities and the degradation of pavements during use. Our counterfactual analysis shows that urban road planning and reusing recycled asphalt can cut GHG emissions by up to 53 and 70%, respectively. Therefore, material-efficient road planning and improved material recycling can help realize circular economy potentials and mitigate GHG emissions moving forward.

A mobile mapping solution for VRU Infrastructure monitoring via low-cost LiDAR-sensors

ABSTRACT LiDAR scanning is a widely-used method for accurately assessing roads and vehicular infrastructure. However, it can be costly and often overlooks infrastructure important for Vulnerable Road Users (VRU) like pedestrians and cyclists. Advances in electronics now permit high-performance LiDAR sensors made of standard semiconductor materials to be integrated into personal devices like smartphones and tablets. This study introduces a new classification category of handheld LiDAR systems for the purpose of VRU infrastructure mapping on a smaller scale. Qualitative experiments using a handheld LiDAR system were conducted to achieve low-cost mobile mapping of VRU infrastructure. The 3D Scanner App facilitated detailed and qualitative point cloud generation at low speeds. Moreover, it demonstrated precise detection of perpendicular potholes and bumps on roads. A quantitative analysis based on several infrastructure damages was performed, revealing mean average percentage errors of 3.53%, 4.43%, and 10.57% in the x-, y-, and z-directions, respectively. While the accuracy in the x- and y-directions is acceptable, the higher z-direction error indicates overestimation of infrastructural damage depth. In conclusion, the sensor's capabilities enable cost-effective mobile mapping solutions for VRU infrastructure monitoring, such as crowd-sourcing for urban data mining and urban digital twin interfaces, significantly reducing expenses compared to traditional sensors.

HUSH (Hiking in Urban Scientific Heritage): The Augmented Reality for Enhancing the Geological and Naturalistic Heritage in Urban Areas

Over the past two decades, significant efforts have been made to diversify the tourism industry and enhance its educational experience. One such endeavor is urban trekking and geotourism, which have emerged as important means of promoting geological knowledge. The recent advancements in augmented reality technologies as well as the increasing availability of ‘born digital’ data such as those gathered from social media create a basis for the development of immersive and customized touristic experiences. Urban scientific heritage, augmented reality, and data mining are the key elements of the HUSH project. Its first focus is the identification of the naturalistic components in a given urban area (flora, fauna, and geological features) through literature surveys and scientific research. These factors become points of interest (PoIs) along touristic paths, where they are connected to the historical and artistic components of the area. Augmented reality serves as the medium through which the user can access this content. The contents are delivered as videos, text, images, or interactive 3D models. The mobile application from this project is a useful tool for promoting geoheritage and naturalistic values in urban areas and for improving the awareness and the sustainability of our cities.

Design a reverse logistics network for end-of-life power batteries: A case study of Chengdu in China

China's policies contributed to the significantly growing sales of electric vehicles (EVs). Unproperly managing giant amounts of end-of-life (EOL) power batteries could result in resource waste and negative environmental impacts. Accelerating the construction of a reverse logistics network (RLN) for EOL power batteries in Chengdu plays an exemplary role in Western China. Using the mixed-integer linear programming (MILP) model with the aim of cost minimization, we design an RLN for EOL batteries in Chengdu based on the existing collection sites. Considering costs, sales of refurbished batteries and metals from EOL batteries, the network's profit in 2022 amounted to RMB 88.84 million. The RLN still faces challenges. 21,192 tons of EOL batteries that don't flow into the network prevent the recovery of many metal resources. In addition, wide variation in scrapping volumes by district, uneven distribution of nodes, and a few alternative sites put more load on nodes closer to the central district and aren't conducive to cost reduction and digestion of the urban mine. We agree that traceability management, the implementation of extended producer responsibility, increasing nodes in surrounding districts while rationalizing the layout, and government incentives and supervision contribute to the sustainability of the economy and resource supply.