Mining Residues Research Articles

Selective leaching of copper and zinc from primary ores and secondary mineral residues using biogenic ammonia

With the number of easily accessible ores depleting, alternate primary and secondary sources are required to meet the increasing demand of economically important metals. Whilst highly abundant, these materials are of lower grade with respect to traditional ores, thus highly selective and sustainable metal extraction technologies are needed to reduce processing costs. Here, we investigated the metal leaching potential of biogenic ammonia produced by a ureolytic strain of Lysinibacillus sphaericus on eight primary and secondary materials, comprised of mining and metallurgical residues, sludges and automotive shredder residues (ASR). For the majority of materials, moderate to high yields (30–70%) and very high selectivity (>97% against iron) of copper and zinc were obtained with 1 mol L−1 total ammonia. Optimal leaching was achieved and further refined for the ASR in a two-step indirect leaching system with biogenic ammonia. Copper leaching was the result of local corrosion and differences in leaching against the synthetic (NH4)2CO3 control could be accounted for by pH shifts from microbial metabolism, subsequently altering free NH3 required for coordination. These results provide important findings for future sustainable metal recovery technologies from secondary materials.

Health workers’ health in face of disasters: what the experience in Brumadinho, Brazil, taught us

Abstract When the Dam I of Córrego do Feijão mine ruptured, in the municipality of Brumadinho, Minas Gerais, Brazil, on 25/01/2019, the released mudflow of iron mining residues caused environmental, human, social, cultural and economic damages in 18 municipalities. It also resulted in psychosocial suffering for all the populace and 272 immediate deaths, 259 of which were occupational accidents, thus being considered the largest expanded occupational accident in Latin America. In this context, the public health workers involved in the care of affected populations presented risks of developing mental illness. The team in the Workeŕs Health Reference Centre (Cerest) observed signs of mental suffering in multiple Primary Health Care workers of Brumadinho. Cerest professionals proposed the realization of therapeutic groups, which did not occur due to the high level of demand generated by the accident. As such, individual consultations were provided by 3 psychologists on duty, on the workplaces that had more complaints. 20 workers with symptoms like insomnia, fatigue and body aches were assisted.Among the 20 patients, 2 were referred to specialized treatment and 3 left the municipality. As such, despite having shown positive effects, the results from this therapeutic approach are not final. The consultations and formal identification of this demand based the creation of a care project centered in therapeutic groups for workers of the health system and other public sectors, like social assistance. This experience shows that the mental health of the response and repair workers was severely neglected. Said professionals, once inserted in a context of high demands and urgency, were not only subjected to more distress, but also had limited opportunities to seek or receive care. As an expanded occupational accident, the unique perspective from teams specialized in occupational health played a key role in this practice, which facilitated the proper assistance required for such a scenario. Key messages This experience reaffirms the need to include health care measures, including mental health, for workers responsible for assisting populations affected by disasters. Worker’s Health Reference Centres of the Brazilian public healthcare system have a prominent role in health vigilance and assistance for all workers affected by expanded occupational accidents.

Past and present anthropic environmental stress reflect high susceptibility of natural freshwater ecosystems in Romania

The concentrations of twelve heavy metals and trace elements (Cr, Mn, Co, Ni, Cu, As, Cd, Pb, Hg, Zn, Fe, and Al) in bed sediment and river freshwater that received sewage discharge, industrial wastewater inputs and mining residue were discussed. Spatial distribution, intra-annual trends and diffuse flux in 2019 in the middle and lower reaches of Olt River Basin (ORB) were investigated using inductively coupled mass spectrometry (ICP-MS) and atomic absorption spectroscopy (AAS). We applied correlation and principal component analysis (PCA) to quantify metal distribution relationship within environmental factors (pH, air temperature) and organic matter existing in the ORB. Moreover, the 87Sr/86Sr and 206Pb/207Pb isotope ratios analysis was employed to conclude the possible origin of the contamination. PCA analysis categorized metal presence in the four-component model, which explains 91% (May), 92% (July) and 93% (September) of the variance and indicates the potential origins of pollutants. The HCA and correlation analysis emphasized the relationship between trace elements, heavy metals in water and sediments and physicochemical characteristics of water. It was observed a high discrepancy in metal distribution between riverbed sediments and water body. In September, correlation indices highlighted sparse positive relationship with trace elements in water and mainly negative correlation values with trace elements from sediments. The origin of pollutants in sediments and water appear to be both natural and human-related activities. In all seasons increased the total exchangeable concentration of Ni, Cu and Zn in the sediments downstream sewage treatment plants and upstream of dams. The consideration of environmental factors and physicochemical characteristics of water is required to develop strategies for pollution management, assessment and mitigation in the actual condition of climate change.This study evaluated the heavy metals pollution in the Olt River Basin over three periods in 2019 under human-induced changes.

Toluene steam reforming using nickel based catalysts made from mining residues

Two nickel-based catalysts are used for toluene steam reforming: Ni-Olivine and Ni-UGSO (Nickel-UpGraded Slug Oxides). Both catalysts are made from mining residues and prepared by incipient wetness impregnation (IWI). The activity and stability of the two catalysts in toluene steam reforming are investigated and compared, at atmospheric pressure and 800 °C in a fixed bed reactor. Reaction temperature and Ni Loading effects are evaluated for the Ni-UGSO catalyst. The physicochemical properties of the catalysts were analyzed using the following characterization techniques: X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy dispersive X-ray (EDX), X-ray absorption near edge spectroscopy (XANES), Temperature Programmed Reduction (TPR) and Brunauer-Emmett-Teller (BET) specific surface area. Results showed that toluene conversion, mainly into CO and H2, reached up to (98 w%). The catalyst activity was tested in multiple 24 h time-on-stream continuous isothermal runs and no signs of deactivation were observed. Ni in Ni-UGSO has a strong metal-support interaction, which, according to characterization results, is due to the formation of a NiO/MgO solid solution. This catalyst exhibited an elevated catalytic activity along with a high resistance to carbon formation. Ni in Ni-Olivine has shown a weak metal-support interaction leading to the formation of filamentous carbon at the catalyst’s surface.

Electrodialytic treatment of secondary mining resources for raw materials extraction: Reactor design assessment

The sustainability of mining activities is compromised due to the high amounts of mining residues generated that have to be disposed of, often in open dams, that may cause environmental deterioration, e.g. release of toxic elements to water supplies. These residues are, however, secondary resources of raw materials. In the case of Panasqueira mine, they even are a source of tungsten, considered a critical raw material. The present work aims to assess the electrodialytic process efficiency for raw materials extraction from Panasqueira mine residues. Experiments were performed with 2 and 3-compartment electrodialytic reactors, applying current intensities between 50 and 100 mA, from 4 to 14 days, and sample suspensions enhanced with NaCl or effluent. Additionally, control experiments with no current application were carried out. The results showed that a 3-compartment reactor operating at 100 mA, with NaCl as supporting electrolyte, presented the highest extraction of copper (13%), tin (10%), tungsten (13%) and arsenic (63%).

Mine tailings as a raw material in alkali activation: A review

The mining industry produces billions of tons of mine tailings annually. However, because of their lack of economic value, most of the tailings are discarded near the mining sites, typically under water. The primary environmental concerns of mine tailings are related to their heavy metal and sulfidic mineral content. Oxidation of sulfidic minerals can produce acid mine drainage that leaches heavy metals into the surrounding water. The management of tailing dams requires expensive construction and careful control, and there is the need for stable, sustainable, and economically viable management technologies. Alkali activation as a solidification/stabilization technology offers an attractive way to deal with mine tailings. Alkali activated materials are hardened, concrete-like structures that can be formed from raw materials that are rich in aluminum and silicon, which fortunately, are the main elements in mining residues. Furthermore, alkali activation can immobilize harmful heavy metals within the structure. This review describes the research on alkali activated mine tailings. The reactivity and chemistry of different minerals are discussed. Since many mine tailings are poorly reactive under alkaline conditions, different pretreatment methods and their effects on the mineralogy are reviewed. Possible applications for these materials are also discussed.

ACID RESIDUES REMEDIATION FROM MINES USING BIOCHAR, MONOPOTASSIUM PHOSPHATE AND LIME

The Zimapan mining district in the state of Hidalgo (Mexico) generates residues with high content of Cu, Pb and Zn which have been disposed for decades on sites that could cause toxicity to the surrounding area. Simultaneously, district’s water dams have been affected by an invasive plant called water hyacinth ( Eichhornia crassipes ), both of problems require attention and remediation treatments. The objectives of this research were: a) to evaluate biochar derived from water hyacinth (H) in mining acid residues; and b) to compare its performance vs monopotassium phosphate (F), lime (L) and the phosphates mixtures with biochar (FH) or with lime (FL) by a bioassay of barley root growth, soluble metal and pH. In this investigation four substrates was used to emulate pollution gradients: 100 %-neutral pristine soil (M1); 100 %-acid mine residues (M4); and two mixtures soil: residues (w/w) of 65:35 (M2) and 35:65 (M3). The substrates were treated with the amendment (dose w/w): H (10 %-substrate), L (3.4 %-residues), F (0.06 %-soil + 0.6 %-residues), FH (0.06 %-soil + 0.6 %-residues + 10 %-substrate) y FL (0.06 %-soil + 0.6 %-residues + 3.4 %-residues) (22 total-treatments, blanks-included). This study shows that water hyacinth could be utilized as an acid mine residues treatment by converting it to biochar. It caused the increase of root length, pH and reduce the soluble Cu and Zn as with the others amendments when the residues were present. Although the reduction of soluble Pb with biochar was considerably lower than with lime in the residues-substrates.

Aerobic processes for bioleaching manganese and silver using microorganisms indigenous to mine tailings

Mining wastes containing appreciable concentrations of silver are considered alternative sources for metal extraction, although these wastes are often refractory due to the presence of manganese oxides. The high cost and/or environmental impact of the hydrometallurgical and pyrometallurgical extraction processes make it necessary to search for biotechnological processes for the solubilization of manganese compounds. This paper describes the characterization of chemoorganotrophic microorganisms indigenous to the tailings of a silver mine located in Coahuila, México, regarding their capability to remove manganese and silver present in these residues by lixiviation. The Bacterial and fungal strains isolated were identified by sequencing the rDNA 16S and ITS-1-ITS-2 genomic regions, respectively; the bacterial strains correspond to isolates of Roseospira sp. and Sphingomonas sp., whereas the fungal strains include isolates of Cladosporium sp. A, Cladosporium sp. B and Penicillium chrysogenum. These fungal strains show an effective capacity to lixiviate manganese and silver from solid mine residue when incubated in 9k medium; it was found that under these conditions, leaching of metals occurs due to a mixed biotic-abiotic process, which yields manganese and silver leaching efficiencies in the ranges of 58-74% and 40-67%, respectively. The fungal strains grown in the LMM medium and the bacterial strains incubated in the PDB medium caused leaching of manganese with a lower efficiency in the range of 0.17-0.24% and 1.42-1.73%, respectively; under these conditions, silver leaching by fungal and bacterial strains appeared to be reduced (< 0.1%).Through in vitro cultures, it was determined that P. chrysogenum and Sphingomonas sp. showed the highest levels of silver resistance.

Coating mortars based on mining and industrial residues

The present work assesses the feasibility of using mining and industrial residues as aggregates of coating mortars in terms of building thermal performance. For this purpose, we investigated four types of aggregates (river sand—REF, iron ore tailings—IOT, friable quartzite—QTZ, and steelmaking slag—SLG). Initially, the specific gravity (density) and thermal conductivity of the residue-based mortars were experimentally obtained. Subsequently, a sensitivity analysis was performed through energy simulations of two existing dwellings. Mortars with SLG and IOT presented the best performance due to their low thermal conductivity and, more importantly, their high density. Mortars with SLG presented 64% of thermal performance classifications as “superior” and “intermediate”, versus an average of 53% for the other aggregates. They were followed by those with IOT, REF and lastly those with QTZ. Therefore, these mortars are cost-effective and sustainable solutions to passively improve the thermal performance of buildings, as well as to mitigate the impacts of the disposal of these residues.

Biogeochemical assessment of the impact of Zn mining activity in the area of the Jebal Trozza mine, Central Tunisia.

Soil pollution associated with potentially toxic elements (PTEs) from mining residues is a significant problem worldwide. The decommissioned Jebal Trozza mine, located in central Tunisia, may pose a serious problem because of the possible high concentrations of PTEs present in its wastes. This mine is a potential source of contamination for agriculture in this area due to both direct causes (pollution of agricultural soils) and indirect causes (pollution of sediments that accumulate in a dam used for irrigation). The aim of the study reported here was to assess the effects of local mining activity in two respects: (1) in terms of soil quality, as determined by soil edaphological parameters and PTEs contents in the mining wastes and local soils; and (2) in terms of biological quality, as evaluated by quantification of enzymatic activity as an indicator of bacterial activity in soils and wastes. The mine tailings contained high levels of Pb (1.83-5.95%), Zn (7.59-12.48%) and Cd (85.95-123.25mgkg-1). The adjacent soils were also highly contaminated with these elements, with average concentrations of Pb, Zn and Cd that exceeded the European standard values for agricultural soils (3, 300 and 300mgkg-1 for Cd, Pb and Zn, respectively). Enzymatic dehydrogenase showed zero activity in waste piles and very low activity in PTE-contaminated soils, but this activity returned to normal values as the pollution decreased, thus demonstrating the effect that the contamination load had on the health of the studied soils. A Statistical Factor Analysis clearly distinguished three groups of samples, and these are related to the influence that mining on the soils and sediments had on the PTE concentrations and their effects on the biological quality of the soil. An environmental assessment based on the enrichment factor criteria indicated risk levels that varied from strongly to severely polluted. The risk appears to be greater close to the mine, where the highest PTE levels were determined.

Atmospheric carbon sequestration in ultramafic mining residues and impacts on leachate water chemistry at the Dumont Nickel Project, Quebec, Canada

Passive carbon mineralization in ultramafic mining residues, which allows the sequestration of CO2 through carbonate precipitation, is one of the options being considered to limit the accumulation of anthropogenic CO2 in the atmosphere. The Dumont Nickel Project (DNP) will generate approximately 1.7 Gt of utramafic mining residues over 33 years of production and the mine will release about 127,700 tonnes of CO2 each year. Using two experimental cells filled with ultramafic waste rock (EC-1) and milling residues (EC-2), the impacts of carbon mineralization on leachate water quality were studied and the quantity of sequestered carbon was estimated. Hydrotalcite supergroup minerals, aragonite, artinite, nesquehonite, dypingite and hydromagnesite precipitated through atmospheric weathering, while the inorganic carbon content of the weathered mining waste increased from 0.1 wt% to 4.0 wt%, which indicates active CO2 sequestration. The leachate water, sampled at the bottom of the experimental cells, is characterized by an alkaline pH (~9.5), a high alkalinity (~90 to ~750 mg/L) and a high concentration of magnesium (~50–~750 mg/L), which is typical from weathering of ultramafic rocks in a system open to CO2.Since 2012, the chemical composition of the leachate water has evolved seasonally. These seasonal variations are best explained by: (1) climatic variations over the year and, (2) increased carbonate precipitation between May and July. Increased carbonate precipitation decreased the alkalinity and magnesium concentrations in the leachate water and produced pore waters which were undersaturated with respect to carbonate minerals such as artinite and hydromagnesite. Carbonate precipitation thus self-limits carbon sequestration through a negative feed-back loop. The carbon sequestration potential of the DNP residues is also influenced by the hydrogeological properties of the residues. In cell EC-2, a high liquid/solid ratio, which limits carbonate precipitation, was maintained by the hydrogeological properties. Since 2011, an estimate of 13 kg of atmospheric CO2 has been sequestered in the milling residues (EC-2), which corresponds to a mean rate of 1.4 (±0.3) kgCO2/tonne/year. Using this mean rate, the 15 Mt of tailings produced each year, during the planned 33 years of mining operation, could potentially sequester 21,000 tonnes of CO2 per year by passive carbon mineralization, about 16% of the 127,700 tonnes of CO2 annually emitted by the planned mining operation.

Study on extraction and separation of Ni and Zn using [bmim][PF6] IL as selective extractant from nitric acid solution obtained from zinc plant residue leaching

For the ever-growing demand of nickel (Ni) resources in industry, the Ni recovery from the mining residues or waste has received considerable interest. Zinc plant residue contains valuable metals it may be recovered using conventional pyrometallurgical or hydrometallurgical processes. The present communication is focused on the selective recovery of Ni from the real nitric acid leach solution of zinc plant residue by solvent extraction (i.e. 1-Butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) as ionic liquid, Di-(2-ethylhexyl) phosphoric acid (D2EHPA) and diphenylthiocarbazone (dithizone)). At first step, leaching of filter cake with the nitric acid solution was examined experimentally and it was observed that nitric acid as a relatively strong oxidant, can adequately dissolve Ni and Zn. After that, Ni and Zn extraction behavior in the leach solution was studied and the influence of pH and extractant concentration were investigated on the extraction of the metals. The results indicated Ni can be effectively separated by controlling the pH values. Moreover, Ni can be selectively separated using dithizone combined with [bmim][PF6] at pH = 5.5 and the separation factor βNi/Zn can reach 2.27 × 105 in one extraction stage. The extraction mechanism of Ni was investigated using slope analysis and stripping efficiencies 100% have been achieved for Zn and Ni with 2.0 M HNO3. Thus, it can be concluded that the use of [bmim][PF6] as alternatives solvents which have a less significant environmental impact than the usual solvents in terms of emission of vapors is one of the promising approaches for nickel ion extraction from the real leaching solution of zinc plant residue.

Electrodialytic Hydrogen Production and Critical Raw Materials Recovery from Secondary Resources

Electrodialytic technologies are defined as treatment processes that promote the removal/recovery of substances in a matrix, based on the application of low-level current intensities. Additionally, along these processes hydrogen is self-generated, allowing them to operationally produce clean energy. This energy carrier is produced due to electrolysis reactions occurring at the cathode end of the electrodialytic reactor, when using inert electrodes. Herein, hydrogen production during the electrodialytic treatment of sewage sludge and mining residues suspensions (coupled with effluent or sewage sludge), at 50 and 100 mA, was assessed. During the electrodialytic treatment of sewage sludge, hydrogen purity production achieved 33%. When effluent or sewage sludge were used as enhancements in mining residues suspensions, hydrogen purity reached 71% and 34%, respectively. Furthermore, a proton-exchange membrane fuel cell was connected to the cathode compartment of the electrodialytic reactor. The electrical energy generated from self-hydrogen produced at 100 mA achieved ≈1 V in all performed experiments. Simultaneously, critical raw materials extraction, namely phosphorus and tungsten, was evaluated. When the process was applied to mining residue suspensions combined with sewage sludge, the highest extraction ratio of phosphorus (71%) and tungsten (62%) was observed.

Monitoramento reprodutivo de tartarugas marinhas na praia de Urussuquara/ES após o rompimento da barragem do Fundão em Mariana/MG

No dia 5 de novembro de 2015 ocorreu o rompimento da barragem de Fundão da mineradora Samarco, localizada no subdistrito de Bento Rodrigues-MG, a 35 km do centro do município brasileiro de Mariana-MG, aproximadamente 16.000 piscinas olímpicas de resíduos de mineração percolaram pelo distrito de Bento Rodrigues num período de apenas 11 minutos. A pluma deste impacto ambiental, se estendeu aproximadamente por 800 km na bacia do Rio Doce, entre Minas Gerais e Espírito Santo. O rio Ipiranga localizado entre os municípios capixabas de Linhares-ES e São Mateus-ES, foi um dos últimos locais atingidos pelos resíduos da bacia do rio Doce, tendo contato com o mar na restinga da praia de Urussuquara-ES, local que é berçário de tartarugas marinhas. O presente estudo realizado pelos cientistas e pesquisadores da Helium Corp Engenharia, teve como objetivo prospectar ninhos de tartarugas marinhas na praia de Urussuquara e realizar seu monitoramento sazonal, que teve início em setembro de 2017 e seu término em maio de 2018. Foram levantados um total de 23 ninhos com distribuição homogênea pela costa, a espécie com maior abundância de registros foi Chelonia mydas (Linnaeus, 1758) com 17 ninhos, seguido da espécie Caretta caretta (Linnaeus, 1758) com 5 ninhos, seguido da espécie Dermochelys coriacea (Linnaeus, 1766) com 1 ninho levantado. Por conseguinte a praia de Urussuquara deve ser conceituada como um lócus prioritário de importância mundial à proteção e conservação de tartarugas marinhas.

Applying Chemometrics to Evaluate Tungsten Mining Residues Potential As Partial Cement Replacement

Electroremediation and deep eutectic solvents are well-documented clean-up processes for metals extraction from solid matrices. Depending on the purpose, these treatments may generate a residue free of pollutants and critical raw materials. Several studies were conducted to re-insert treated secondary resources in building materials. However, there is a research gap in the improvement of reactive properties of these secondary resources. In addition, there is a lack of pozzolans that can optimize cementitious materials. This study investigates the pozzolanic reactivity of tungsten mining residues after receiving electrodialytic treatment in the presence of natural deep eutectic solvents. In all cases, thermal treatment after electroremediation potentiated the pozzolanic reactivity of tungsten mining residues, between 64% to 87%. The introduction of these pozzolanic resources in cementitious-based materials may increase their performance, enlarge the range of applications in the construction industry, reduce the environmental impact, and contribute to a circular economy.&#x0D; Keywords: electro-based technology, tungsten mining waste, construction material, pozzolanicity.

H2S adsorption on nanostructured iron oxide at room temperature for biogas purification: Application of renewable energy

The energetic use of biogas is limited by the presence of contaminants which hinder the process and generate excessive maintenance costs. This study aims to evaluate the H2S adsorption on nanostructured iron oxide (NIO), towards applications for landfill gas cleaning. The iron oxide utilized in this study is obtained from mining residues, which provides economic and environmental advantages compared to other recognized adsorbents. In order to determine the performance of NIO, adsorption tests were performed in a lab scale with the use of synthetic gas (H2S + N2) and a continuous up-flow reactor. Experiments produced data regarding the process efficiency as a function of different operating conditions including gas hourly space velocity, H2S inlet concentration and gas humidity. Fresh and sulfided samples were characterized by SEM, TEM, BET, EDX and XRD techniques. The characterization results suggest that under lower GHSV (1,250 h-1), lower H2S inlet concentrations (200 ppm) and dry gas, the highest breakthrough capacity was recorded at 2.5 mg H2S per gram of NIO. Due to the good efficiency in removing H2S under ambient conditions, NIO can be considered a cost-effective promising alternative for biogas desulfurization.

Structure of Rhodolith Beds and Surrounding Habitats at the Doce River Shelf (Brazil)

The world’s largest rhodolith beds have been reported from the Brazilian continental shelf. Highly biodiverse beds are located in Southeast Brazil, but ecological aspects of these beds remain unknown. Despite their ecological importance, rhodolith beds (RBs) have recently been subjected to a severe threat, when more than 35 million cubic meters of mining residues slid down a mountainside on 5 November 2015, after a collapse of a gigantic dam upstream (the Mariana disaster), causing a huge impact on the Doce River. Our aim is to assess rhodolith beds and adjacent coralline formations on the Doce River Shelf (DRS) after the dam collapse. This paper describes the distribution, abundance, vitality, size and shape, as well as unmapped bryozoan rich sediment formations in this area, serving as baseline knowledge for environmental monitoring. Four distinct biogenic sea bottom habitats (bryozoan bottoms, rhodolith beds, carbonate concretions, and reefs) were recognized at different depth ranges with distribution indicated to be mostly related to the local sedimentary regime. Mud sediments dominated the seafloor up to 35 m depth. On the mid shelf, bryozoan bottoms were recorded from 35 to 45 m depth. Crustose coralline algae (CCA) occurring as rhodoliths and carbonate concretions extend over 1953 km2 in the mid and outer shelf. Rhodolith beds predominate in these areas, totaling 1521 km2 of sea bottom and were more abundant at depths between 45 and 65 m, occupying an extensive area south of the Doce River mouth. Northward, rhodolith beds are less abundant or absent likely due to the long-term deposition of fine sediments in this region. Carbonate concretions and reefs covered by CCA occupy sparse areas on the outer shelf (65–105 m depth). Differences in rhodolith features recorded, including coverage, density and size, may be related to the Doce River sedimentation and related factors (e.g., hydrodynamics, depth, and light). However, since there are no previous detailed studies on RBs along the DRS, we could not assess the impact of sedimentation of dam wastes on RBs’ abundance and density. In any case, these are valuable results for the further monitoring of long-term effects. Considering that the growth of these rhodoliths is relatively slow, and that they are affected by the sedimentation from the Doce River, the implementation of a management and conservation plan for this area is necessary in order to preserve this ecosystem.

Contamination and toxicity in a subtropical Estuarine Protected Area influenced by former mining activities

Abstract The present paper reviews information about sources, fate, concentrations and toxicity of the metals found in the Cananeia-Iguape Estuarine Complex (CIEC), which is within a Ramsar site, the Cananeia-Iguape-Peruibe Environmental Protected Area (CIP-PA). The main sources of metals to CIEC are the former mining sites located upstream, on the Ribeira de Iguape River basin. Pb is reported as the element of primary concern, but Cu, Zn, Cr and As have been detected in sediments and biota. In general, higher levels of metals are associated with muddy sediments, in depositional portions of the estuary. Metals appear to be bioavailable, as sediment toxicity has been reported, together with bioaccumulation and sub-chronic effects in fish and invertebrates. Areas with higher concentrations of metals and more severe sediment toxicity are not necessarily the closest to the sources. The worse conditions occur in depositional sites, which depend on rainfall in catchment basin and hydrological processes in the estuary. In fact, during the flooding season the deposition of particles seems to move southward, carrying metals to the southern portion of the CIEC. The results suggest that the protection objectives are not being fully achieved, demanding actions to ensure control of both internal and external sources of contaminants for the CIEC. Additionally, new enforcements and actions are required to control the contamination sources of mining residues located upstream. The current review highlights that estuarine and marine protected areas may be impacted by contaminants released from distant sources, and this situation should be properly addressed in management plans.

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.

Catalytic Dry Reforming and Cracking of Ethylene for Carbon Nanofilaments and Hydrogen Production Using a Catalyst Derived from a Mining Residue

In this study, iron-rich mining residue (UGSO) was used as a support to prepare a new Ni-based catalyst via a solid-state reaction protocol. Ni-UGSO with different Ni weight percentages wt.% (5, 10, and 13) were tested for C2H4 dry reforming (DR) and catalytic cracking (CC) after activation with H2. The reactions were conducted in a differential fixed-bed reactor at 550–750 °C and standard atmospheric pressure, using 0.5 g of catalyst. Pure gases were fed at a molar ratio of C2H4/CO2 = 3 for the DR reaction and C2H4/Ar = 3 for the CC reaction. The flow rate is defined by a GHSV = 4800 mLSTP/h.gcat. The catalyst performance is evaluated by calculating the C2H4 conversion as well as carbon and H2 yields. All fresh, activated, and spent catalysts, as well as deposited carbon, were characterized by Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX), transmission electron microscopy (TEM), temperature programmed reduction (TPR), and thermogravimetric analysis (TGA). The results so far show that the highest carbon and H2 yields are obtained with Ni-UGSO 13% at 750 °C for the CC reaction and at 650 °C for the DR reaction. The deposited carbon was found to be filamentous and of various sizes (i.e., diameters and lengths). The analyses of the results show that iron is responsible for the growth of carbon nanofilaments (CNF) and nickel is responsible for the split of C–C bonds. In terms of conversion and yield efficiencies, the performance of the catalytic formulations tested is proven at least equivalent to other Ni-based catalyst performances described by the literature.