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Mine tailings are the discarded materials resulting from mining processes after minerals have been extracted. They consist of leftover mineral fragments, excavated land masses, and disrupted ecosystems. The uncontrolled handling or discharge of tailings from abandoned mine lands (AMLs) poses a threat to the surrounding environment. Numerous untreated mine tailings have been abandoned globally, necessitating immediate reclamation and restoration efforts. The limited feasibility of conventional reclamation methods, such as cost and acceptability, presents challenges in reclaiming tailings around AMLs. This study focuses on phytorestoration as a sustainable method for treating mine tailings. Phytorestoration utilizes existing native plants on the mine sites while applying advanced principles of environmental biotechnology. These approaches can remediate toxic elements and simultaneously improve soil quality. The current study provides a global overview of phytorestoration methods, emphasizing the specifics of mine tailings and the research on native plant species to enhance restoration ecosystem services. [ABSTRACT FROM AUTHOR]

The rupture of the Fundão dam in Brazil released tons of mining tailings into the Doce River Basin (DRB). This investigation aimed to determine the bioaccumulation of metals in soft tissues of the bivalve Corbicula fluminea exposed to sediments collected in the DRB in four periods (just after, 1, 3, and 3.5 years after the dam rupture). In the exposure bioassays, the concentrations of Al, As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn in sediments and bivalve soft tissues were quantified. The concentration of some elements (As, Cd, Mn, and Al) in sediments exceeded the federal limits or regional backgrounds at some sampling sites, but their concentrations tended to decrease over time. However, higher concentrations of many elements were detected in the winter of 2019. Several elements were detected in C. fluminea soft tissues, but the bioaccumulation factors were generally low or not related to those elements associated with the ore tailings, evidencing that the bioavailability of metals to bivalves, in laboratory conditions, was limited. Integr Environ Assess Manag 2024;20:87–98. © 2023 SETAC Key Points: The bivalve Corbicula fluminea exposed to sediments collected in the Rio Doce after the Fundão dam failure generally showed low bioaccumulation of metals, as evidenced by the low bioaccumulation factors; some bioaccumulated elements, such as Cu, were not related to the ore tailings.The concentrations of metals and As were high after the dam rupture, and the levels of As, Cd, Mn, and Al in sediments exceeded the federal limits or regional backgrounds at some sampling sites, but their levels tended to decrease over time.The concentrations of metals and As in soft tissues of C. fluminea did not correlate with the respective levels in the sediments, suggesting limited bioavailability of metals or the organisms' ability to cope with metals and metalloids. [ABSTRACT FROM AUTHOR]

Background: In 2015, the Fundão dam in Mariana, Brazil, collapsed, leading to the discharge of iron mining tailings (MT) that caused significant damage to the environment and human health. This study aimed to evaluate the potential effects of MT on four terrestrial species, including the soil invertebrates Folsomia candida (Collembola), Enchytraeus crypticus (Oligochaeta), and the plants Avena strigosa and Brassica rapa, after the Fundão dam collapse. Methods: MT samples were collected from the topsoil of a contaminated site, and the total concentrations of potentially toxic elements (PTE) were determined. Soil organisms were exposed to different proportions of MT (0 % as the control, 25 %, 50 %, 75 %, and 100 %) in two soil types, including a background soil (BS) from a non-contaminated site in the area of study, and a natural soil (NS) from a well-documented place where there is no evidence of contamination. Results: The study found that the addition of MT increased soil pH and influenced the toxicity of MT to invertebrates, with F. candida reproduction being more impacted in background soil (BS) and E. crypticus being more affected in natural soil (NS). Reproduction of F. candida and E. crypticus significantly decreased at 100 % of MT exposure. Furthermore, exposure to MT caused phytotoxicity in plants, and B. rapa was found to be more sensitive than A. strigosa, suggesting it is a suitable bioindicator. B. rapa showed significant reductions in most measured endpoints at 100 % of MT, while A. strigosa had declines in shoot length and dry biomass at 75 % of MT. Chromium was a PTE of environmental concern since its concentration in MT surpassed its prevention limit (75 mg kg−1) and exceeded even its thresholds for industrial areas (400 mg kg−1). Conclusion: The findings can contribute to future strategies for the management of MT and underscore the importance of considering sublethal effects (e.g., reproduction) in environmental risk assessments. However, further research is needed to develop effective strategies for mitigating the negative impacts of MT on soil ecosystems.

In the context of the challenges imposed by climate change, which exerts constant pressure on water security in Morocco, the Moulouya River, one of the main sources of surface water, frequently undergoes spatiotemporal variations in its quality. This situation is particularly worrying in the upstream part of the river, where the old Zaida mine is located, which is now inactive and leaves significant residues in the form of slag heaps in direct contact with the waters of the Moulouya River. To assess the impact of this abandoned mining waste, eight (08) water sampling stations (S1 to S8) were chosen to analyse the concentrations of two (02) essential metals, namely, lead and zinc. The results revealed lead concentrations of approximately 0.13 mg/L on average during the dry period and 0.09 mg/L during the humid period. The average zinc concentration was 0.29 mg/L during the dry season and 0.32 mg/L during the humid season. The maximum concentrations were recorded at the stations closest to the aforementioned mine, in particular, S1, S2 and S3. Other maximum concentrations were observed at station S6. These results highlighted the significant impact of mining slag heaps exposed to the open sky on the physico-chemical and metallic quality of Moulouya waters. This finding highlights the urgency of continued monitoring of this vital water resource to protect it against potential risks of contamination.

Canada’s mineral reserves can play a very important role in curbing climate change if natural alkaline minerals are used for the process of mineral carbonation. In this work, the potential of using two Canadian natural silicates for accelerated carbonation is experimentally assessed: kimberlite mine tailing (Mg0.846Al0.165Fe0.147Ca0.067SiO3.381) from the Northwest Territories, and mined wollastonite ore (Ca0.609Mg0.132Al0.091Fe0.024SiO2.914) from Ontario. The aim of this work was to evaluate the weathering reactivity and CO2 uptake capacity via carbonation of these two comminuted rocks, both of which are made up of a mixture of alkaline minerals, under process conditions that spanned from milder to intensified. Research questions addressed include: does kimberlite contain a sufficient amount of reactive minerals to act as an effective carbon sink; is dehydroxylation necessary to activate kimberlite, and to what extent does it do this; do secondary phases of wollastonite hinder its reactivity; and can either of these minerals be carbonated without pH buffering, or only weathered? Incubator, slurry, and pressurized slurry methods of accelerated weathering and carbonation were used, and the effect of the process parameters (temperature, solid-to-liquid ration, reaction time, CO2 level, pH buffer) on the CO2 uptake and crystalline carbonates formation is tested. The reacted samples were analyzed by pH test, loss-on-ignition test, calcimeter test, and X-ray diffraction analysis. Results showed that wollastonite ore (rich in fast-weathering CaSiO3) is more suitable for accelerated carbonation than kimberlite tailing (containing slow-weathering hydrated magnesium silicates and aluminosilicates) when only its capability to rapidly form solid carbonates is considered. Incubator and pressurized buffered slurry methods proved to be most effective as under these conditions the precipitation of carbonates was more favorable, while the unbuffered slurry reaction conditions were more akin to accelerated weathering rather than accelerated carbonation.

Iron mining residue was evaluated as a potential catalyst for heterogeneous Fenton/photo-Fenton degradation of sulfonamide antibiotics. The residue contained 25% Fe2O3 and 8% CeO2, as determined by X-ray fluorescence spectroscopy, as well as other minor phases such as P2O5, SiO2, and TiO2. X-ray photoelectron spectroscopy analysis revealed a lower content of iron oxides on the surface, which restricted interaction of the residue with H2O2. Despite this limitation and the relatively low specific surface area (26 m2 g-1) of the crude iron mining residue (without any pretreatment), the material presented high catalytic activity for Fenton degradation of sulfonamide antibiotics. The degradation was strongly dependent on the initial pH, showing the highest efficiency at pH 2.5. For this condition, a concentration of sulfathiazole below the detection limit was obtained within 30 min, under black light irradiation and using 0.3 g L-1 residue, with low H2O2 consumption (0.2 mmol L-1). The residue also provided highly efficient sulfathiazole degradation in the dark, with the concentration of the antibiotic decreasing to an undetectable level after 45 min. Simultaneous degradation of two sulfonamide antibiotics revealed higher recalcitrance of sulfamethazine, compared to sulfathiazole, but the levels of both antibiotics decreased to below the detection limit after 45 min. The residue was very stable, since no significant concentration of soluble iron was detected after the degradation process. Furthermore, high catalytic activity was maintained during up to five cycles, showing the potential of this material for use as a low-cost and environmentally compliant catalyst in Fenton processes. [ABSTRACT FROM AUTHOR]

• Resources from mining residues as option for diversifying critical mineral supply. • Valorization of these materials is a prerequisite for becoming secondary resources. • The understanding of mining residues as resource has to be culturally resonant. • Expertise of scientists, everyday experience, mining history are important factors. Recycling and extracting secondary resources from dumped materials has been considered as an option for generating a supply of critical minerals. Materials that are understood as secondary resources were already in use in society, but became devaluated and have been discarded as useless and worthless. In this article, we argue that the process of valorization that shifts material from the category of 'worthless' to the category of 'valuable' is a prerequisite for the making of secondary resources. We conceptualize valorization as a social process of framing in which the collective understanding of waste materials changes. Taking a frame theoretical approach, we aim to reveal how the understanding of waste materials as resources resonates culturally in two German case study regions. We will demonstrate that there are three features that influence the cultural resonance of this understanding quite differently in the two regions: the credibility of frame articulators, narrative fidelity and experiential commensurability. In one of the regions the resource frame is made culturally resonant through the acknowledged expertise of scientists and industries that tie in with the region's history and daily experiences, while in the other region, the resource frame is weakened due to bitter memories of historical developments and contested knowledge claims. By linking ideas from valorization studies with concepts from strategic framing, we are contributing to the scientific discourse regarding the production of secondary resources. [ABSTRACT FROM AUTHOR]

Abstract Waste from gold mining (Au) is a threat to the ecosystem and human health because it contains high levels of potentially toxic elements (PTEs). Organic waste and biochar can be used to recover contaminated soils from mining areas because they have the potential to immobilize PTEs and improve soil fertility, enabling revegetation. The objective of this study was to investigate the efficiency with which organic residues and biochar immobilize PTEs in a multicontaminated soil of a small-scale Au mine in the state of Pará. The soil from a gold mining area was mixed with different proportions (v/v) of coffee ground residues (B coffee), Brazil nut tegument residues (BN), açai palm stone residues (A), and Brazil nuts biochar residues to determine which treatment is best for immobilizing PTEs. The treatments with the addition of BN and A resulted in low pH and high contents of organic matter (OM) and phosphor (P) The BN increased the available levels of Ba and reduced the available levels of Ni. The addition of coffee ground residues and biochar increased the uptake of Ba, Pb, and Ni in lettuce plants compared to treatments with BN and A. Plants grown with A showed higher dry matter yield and lower absorption and translocation of PTEs. Thus, the addition of BN and A residues in PTE phytostabilization programs in PTE-multicontaminated soils is a potential possibility. Highlights • Brazil nut residues decreased Ba and Pb contents in lettuce plants and increased P, K and MO levels in the soil. • Lettuce plants cultivated in contaminated soils and açaí residues presented lower absorption and translocation of PTEs. • Biochar and coffee grounds increased the available concentration of Ba in soil. • Waste Brazil nut and açaí have potential for use in phytostabilization programs PTEs in soils. [ABSTRACT FROM AUTHOR]

Highlights • The modified BCR®SEP does not ensure selective mineral dissolution of mine residues. • Its application to mine residues systematically induces underestimated results. • Protocol´s optimization would differ too much from the standardized original. • Toxic metals mobility from mine residues can not be assess by the modified BCR®SEP. Abstract Mining residues management is one of the greatest challenges for mining companies around the world. The increasing consciousness of the general public and governments about the potential threat that those residues can pose to the environment is demanding consistent and precise methodologies for assessing the potential release of toxic metals. On this regard, the modified BCR® sequential extraction procedure (SEP) is frequently the chosen assessing protocol. However, this protocol was designed to study soils and sediments with low to moderate metal pollution, and validation of its applicability to mining residues is missing. The present research covers this gap of knowledge by subjecting selected highly polluted mining residues to the modified BCR®SEP. On the light of these results, it was confirmed that most of the metal bearing minerals in the mining residues were not completely dissolved in the corresponding SEP and, therefore, the application of BCR®SEP to mining residues systematically leads to an underestimation of metals mobility. The necessary changes to optimize the BCR®SEP to study mining residues would set a extraction procedure distinctively different from the original; thus it is strongly recommended to use alternative approaches to assess toxic metals mobility in highly polluted mining residues. [ABSTRACT FROM AUTHOR]

Theisen sludge is a complexly contaminated scrubber dust, which arised during the production of copper stone. Besides high contents of heavy metals, it also contains approximately 10% of a tar like organic fraction. Inorganic and organic components both represent an environmental risk and the assessment of potential remediation activities requires a detailed analysis of the contaminants. In this study, the organic part of the scrubber dust was analyzed by highly resolving gas chromatographic and mass spectrometric methods. Lower molecular weight compounds were analyzed by comprehensive gas chromatography (GC × GC-MS). A complex mixture of aliphatic and aromatic hydrocarbons was observed, which was predominantly composed of aromatic hydrocarbons with one to 4 rings with different number and length of alkylsubstituents. The most abundant heteroatomic compounds observed are benzo- and dibenzothiophenes and their alkylated homologues, but also phenols, carbazoles and acridines could be observed. Higher molecular weight compounds were analyzed by fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Two different ionization methods, electrospray ionization (ESI) and graphite assisted laser desorption ionization (LDI), were used in positive and negative ionization mode. Compounds with masses up to 1450 u are observed. The results were evaluated based on the number of formulas in the molecular formula classes and their distribution in double bond equivalents versus carbon number plots ( DBE - n C plots). The results from both ionization polarities show significant differences regarding the quality of observed molecular formulas and both ionization methods. [ABSTRACT FROM AUTHOR]

Mining and metallurgy generate residues that may contain thallium (Tl), a highly toxic metal, for which it is currently not feasible to determine its geochemical speciation through X-ray absorption spectroscopy due to a combination of very low contents and the interference of accompanying high arsenic contents. Therefore, fractionation studies in residues and soils are required to analyze the mobility and bioavailability of this metal, which in turn provide information to infer its speciation. For this purpose, in this work a modification of the BCR procedure was applied to residues and contaminated soils from three mining zones of Mexico and two mining zones of Spain, spanning samples with acidic to alkaline pH values. The Tl extraction procedure consisted of the following fractions: (1) water-extractable, (2) easily exchangeable and associated to carbonates, associated to (3) poorly-crystalline and (4) crystalline Fe and Mn oxyhydroxides, and (5) associated to organic matter and sulfides; and finally a residual fraction as associated to refractory primary and other secondary minerals. The extracted contents were analyzed by Inductively-Coupled Plasma with Mass Spectrometry. Surprisingly, water-soluble, in Tl(I) oxidation state, was detected in most areas, regardless of the pH, a fact that has not been reported before in these environments, and alerts to potential health risks not previously identified. Most of the samples from a metallurgy area showed high levels of Tl in non-residual fractions and a strong correlation was obtained between extracted Mn and Tl in the third fraction, suggesting its association to poorly crystalline manganese oxides. In the majority of samples from purely mining environments, most of the Tl was found in the residual fraction, most probably bound to alumino-silicate minerals. The remaining Tl fractions were extracted mainly associated to the reducible mineral fractions, and in one case also in the oxidizable fraction (presumably associated to sulfides). Capsule: Soluble Tl(I) was found in all soil samples contaminated with either mining or metallurgical wastes. Additionally, in those affected by metallurgical wastes a very strong Tl-Mn correlation was found. [ABSTRACT FROM AUTHOR]

Strategic elements are essential for industrialized countries and both, demand and prices are constantly increasing. The exploitation of so far unutilized polymetallic mining waste could ensure a reliable supply. Mining residues, like the investigated German flue dust deposit from copper ore smelting, represent a promising approach for metal extraction. By bioleaching, the sulfide bonded metals can be dissolved from the mineral phase. Downstream processes are required to separate the target elements from the obtained multicomponent leaching solution. One promising technology is nanofiltration (NF). Three polymeric NF membranes (NF99HF, UTC-60, NP010) were screened to investigate the separation performance of Co, Cu, Ge, Mo, Re, and Zn in a dead-end set-up, in particular the pH-dependent retention. The study shows that pH and thus, the formed ionic species have a major influence on retention and separation performance. Mainly based on size exclusion, a selective separation of Re seems feasible with the NF99HF and UTC-60 at pH 7. Under acidic conditions, a separation during concentrating cannot be realized in dead-end by NF because shearing forces and the build-up concentration as well as the electric field gradient forces the permeation of the solutes. However, if the recovery and ionic strength of the solution is set low, the selectivity can be increased even at pH 2. [ABSTRACT FROM AUTHOR]

Natural weathering of ultramafic rocks in mine tailings captures atmospheric CO 2 through the formation of magnesium carbonates. The Dumont Nickel Project (DNP) is of particular interest as it will generate 1.7 Gt of ultramafic residues. A field experiment has been conducted at the DNP site in order to understand the process of natural CO 2 sequestration. Two experimental cells were built using waste rock and mineral processing tailings and were instrumented with gas sampling ports and probes to monitor water saturation and suction. A decrease of the interstitial gas-phase CO 2 concentration in both cells, from atmospheric values (∼390 ppmv) near the surface to ∼100 ppmv near the bottom, reflects active CO 2 consumption by the residues. The total carbon content of the weathered DNP mine waste ranges from 0.2 wt% to 6.5 wt% C. Hydrotalcites supergroup minerals (pyroaurite-3R, brugnatellite, pyroaurite 2-H), aragonite, nesquehonite, dypingite and hydromagnesite were absent from the unweathered residues and precipitated in the cells during passive mineral carbonation. In situ measurements using Wavelength-Scanned Cavity Ring Down Spectroscopy reveal an increase of δ 13 C (air) from −8‰ near the surface of the cells to ∼2‰ near the bottom that is correlated with the decrease in CO 2 concentration. This trend is explained by kinetic carbon isotope fractionation during dissolution of atmospheric CO 2 in interstitial water (Δ DIC-CO2 = −11.2‰). Secondary carbonates, precipitated from the interstitial water, are characterized by a moderately high δ 18 O and low δ 13 C. These isotopic compositions of the carbonates are consistent with precipitation in an evaporative environment where the kinetic carbon fractionation during atmospheric CO 2 dissolution produces interstitial water depleted in 13 C. Moreover, isotopic compositions of hydrotalcite supergroup minerals and other carbonate minerals are consistent with modern precipitation from the weathering of mining residue. These observations demonstrate the atmospheric source for the sequestered CO 2 and help constrain a conceptual model of the carbonation reaction in the residues. [ABSTRACT FROM AUTHOR]

La adición de diferentes materiales con vistas a mejorar el proceso anaerobio ha venido incrementándose en los últimos tiempos existiendo bases teóricas bien fundamentadas para la realización de esta práctica. Este proceso biológico, requiere no sólo de macronutrientes (N, P, K, S), elementos vitales para el desarrollo de los microorganismos y que deben estar presentes en grandes cantidades, sino también de los denominados micronutrientes y factores estimulantes al proceso, los cuales en cantidades muy pequeñas (trazas), son esenciales para el óptimo desarrollo de los microorganismos, como es el caso de algunos metales obligatorios (Fe, Ni y Co). En este trabajo se presenta un estudio preliminar del efecto de la adición de residuales mineros cubanos como catalizadores del proceso anaerobio. Se realizó la caracterización de dicho residual minero (Cola), empleado en los ensayos experimentales. Se demostró que la Cola SI aporta nutrientes esenciales al proceso de depuración anaerobia de aguas residuales. Hubo mayor efectividad en condiciones extremas: poco sustrato y concentraciones tóxicas de Nitrógeno y Azufre, y en cualquiera de las variantes analizadas, la mejor respuesta se obtuvo con una concentración de Cola igual a 3 mg/L, con una eliminación de materia orgánica de más del 80%.The addition of several compounds in order to improve anaerobic process has been increased during last decades, being well-sustained by theoretical bases. This biological process requires not only macronutrients (N, P, K, S), essential elements in large quantities for microorganisms well developments, but also those known as micronutrients and stimulating elements which in a very small concentrations are of vital importance for the optimum microorganism development, as the case of obligatory metals like Fe, Ni and Co. A preliminary study of mining residues effect on anaerobic process is presented in this paper. Mining residues can be a perfect metal supplier, and indeed act as a biocatalyst. A characterization of the used mining residue (Cola) was made. It was demonstrated that Cola did contribute essential nutrients to wastewater anaerobic process. There was better effectiveness under extreme conditions: less substrate and toxic concentrations in Nitrogen and Sulphur. In all cases, the best answer was obtained when Cola concentration was around 3mg/l, with an organic matter removing of more than 80%.

Specialized acidophilic bacteria and archaea are able to extract valuable metals such as copper, gold, cobalt, nickel, zinc, and uranium from sulfide ores. This process is known as bioleaching and its application in the mining industry as biomining. Laboratory studies also demonstrated bioleaching of oxide ores such as laterites and of mining residues such as mine tailings as well as metal recycling from waste (secondary mining). Metals being leached have to be recovered from acidic polymetallic solutions (mine and process waters) which is possible via biosorption or biomineralisation. [ABSTRACT FROM AUTHOR]

This study poses a methodology in order to simultaneously quantify ACC deaminase and IAA levels in the same culture medium. Ten bacterial strains isolated from plant rhizosphere naturally settled in mining residues were chosen. These bacterial strains were characterized as PGPB, and all of them showed at least three characteristics (indole-3 acetic acid and siderophore production, ACC deaminase enzyme activity, and inorganic phosphate solubilization). Taxonomic identification showed that the strains belong to Enterobacter, Serratia, Klebsiella, and Escherichia genera. Similarly, both the ACC deaminase enzyme activity and the IAA synthesis in the presence of Cu, As, Pb, Ni, Cd, and Mn were measured. The results showed that both the ACC deaminase enzyme activity and the IAA synthesis were higher with the Pb, As, and Cu treatments than with the Escherichia N16, Enterobacter K131, Enterobacter N9, and Serratia K120 control treatments. On the other hand, Ni, Cd, and Mn negatively affected both the ACC deaminase enzyme activity and the IAA production on every bacterium except on the Klebsiella Mc173 strain. Serratia K120 bacterium got a positive correlation between ACC deaminase and IAA in the presence of every heavy metal, and it also promoted Helianthus annuus plant growth, showing a potential use in phytoremediation systems. [ABSTRACT FROM AUTHOR]

One of the largest accidents with mine tailings happened in Brazil in 2015, with the rupture of the Fundão dam, and the physical characteristics of these tailings make it difficult to recover degraded areas. Hymenaea courbaril is a tree species native to Brazil that has low nutritional and water requirements, besides its capacity for survival in contaminated environments. In this study we hypothesized that inoculation with diazotrophs would improve the growth and physiology of H. courbaril in tailings, favoring the reforestation process aiming the recovery of the accident site. Every 20 days for 60 days, we investigated the morphophysiology of H. courbaril grown in iron mine tailings or soil, with the addition of nitrate (N-positive control), non-inoculation (negative control) or inoculation with native diazotrophic bacteria previously isolated from the tailings (UNIFENAS100-569; UNIFENAS100-654 and UNIFENAS100-638). We found that H. courbaril has survival capacity under mine tailings, with no growth alteration in the tailings, although there were signs of reduced ability for photoprotective responses. Inoculation with diazotrophic bacteria improved physiological aspects of H. courbaril and strain UNIFENAS100-638 was the most effective in favoring total growth of plants, net photosynthetic rate and root morphology under mine tailings. The survival capacity and growth of H. courbaril indicates the possibility of its use for reforestation in areas degraded by mine tailings. Further studies are necessary in field conditions and with a larger experimental period to more thoroughly understand H. courbaril tolerance. [Display omitted] • Hymenaea courbaril shows survival capacity under iron mine tailings.. • Diazotrophic bacteria inoculation enhances physiological aspects of H. courbaril. • Our pseudomonas UNIFENAS100-638 is effective in favoring H. courbaril 's growth under mine tailings. • Seedlings of H. courbaril show some capacity of reforestation in areas degraded by mine tailings. • Hymenaea courbaril could be used in the afforestation of contaminated areas. [ABSTRACT FROM AUTHOR]

The carbonation of chrysotile and nickel mining residues was studied under ambient laboratory conditions to assess their response under various potential field conditions (pore saturation, watering episodes, temperature, CO2 diffusion, and dissolved oxygen) and to a variety of natural and chemical enhancers (sulfide minerals, brucite, chelate ligands, ionic liquids, and carbonic anhydrase enzyme). Watering of the residues to achieve partial pore saturation was critical for optimal ambient CO2 sequestration by mediating magnesium leaching and CO2 absorption, and by favouring diffusion of gaseous CO2 in pores deep inside the residues. Increasing temperature stimulated CO2 uptake whereas dissolved oxygen triggered undesirable oxidative precipitation and passivation by iron (III) hydroxides. The latter effect was attenuated through addition of depassivation chelates, which impeded iron precipitation and enhanced carbonation under ambient conditions. Pyrite and pyrrhotite, as natural acid generators, failed to improve ambient carbonation by fostering iron passivation to the detriment of mining residue dissolution whereas the use of carbonic anhydrase inhibited formation of magnesium carbonates. Ionic liquids were found suitable for magnesium extraction under alkaline conditions but inefficient for inducing carbonate precipitation. The lower rate of carbonation with hydrophobic ionic liquid-water mixtures was ascribed to a slower gas-liquid mass transfer of CO2 to the liquid, which primarily prompted a loss of gas-liquid interfacial area due to viscous effects and bubble coalescence. [ABSTRACT FROM AUTHOR]

The most typical enhancement for electrokinetic remediation (EKR) involves the neutralization of the alkaline front generated at the cathode by the addition of an acid to the catholyte. Although the use of strong and weak acids can be found in the literature, there is still a clear lack of reliable comparisons between them. This paper presents a comparison of the results obtained for a real lead contaminated soil treated by EKR enhanced with nitric or with acetic acid. The divergences that are usually observed in those experimental results obtained when using constant voltage drop are avoided here by the use of EKR with constant current intensity and the disposition in series of the soil lab columns. Important differences are observed in the behavior of the system when the acid was changed. The time needed to achieve the same metal recovery is more than 3 times longer for the nitric acid. A standard sequential extraction procedure was used to fractionate the lead concentration in the soil according to its mobility in a before- and after-treatment way. Regardless of these important differences observed in the remediation time, the fractionation results after the experiments were almost the same for the two acid enhanced EKRs. [ABSTRACT FROM AUTHOR]

Highlights: [•] Experimental monitoring of carbon dioxide diffusion and sequestration. [•] Carbon dioxide breakthrough time across nickel mine residue is estimated. [•] Pores liquid saturation was a major factor influencing CO2 diffusion. [•] Partially saturated pores combined fast CO2 dissolution and sequestration. [ABSTRACT FROM AUTHOR]

Highlights: [•] CO2 produced during dry and ionic liquid assisted birch torrefaction is monitored. [•] Torrefaction was combined with ultramafic mining residues to capture emitted CO2. [•] Presence of CH4 and CO in the torrefaction gas did not affect the carbonation rate. [•] Native brucite content of mining residues broadly dictated the carbonation rate. [•] Effect of temperature and residue pore water on the carbonation rate was studied. [ABSTRACT FROM AUTHOR]

Mining to obtain ferronickel by the pyrometallurgical process involves a calcination stage that generates a highly metallic solid dust. This study evaluated the bioavailability of metals from calcination dust after being ingested by Oreochromis niloticus. Chemical analysis was performed on the whole body and histological analysis was performed on the gills and gastrointestinal tract of fish to evaluate potential bioaccumulation. After 96 h of exposure to the dust, gill tissue contained a small amount of particulate matter, while the gastrointestinal tract was filled with the material, generating high values of metals in the fish whole body chemical analysis. However, after 15 and 30 days in clean water, both the gills and gastrointestinal tract were nearly devoid of particles and metal concentrations in the fish whole body had largely returned to baseline levels. [ABSTRACT FROM AUTHOR]

The addition of several compounds in order to improve anaerobic process has been increased during last decades, being well-sustained by theoretical bases. This biological process requires not only macronutrients (N, P, K, S), essential elements in large quantities for microorganisms well developments, but also those known as micronutrients and stimulating elements which in a very small concentrations are of vital importance for the optimum microorganism development, as the case of obligatory metals like Fe, Ni and Co. A preliminary study of mining residues effect on anaerobic process is presented in this paper. Mining residues can be a perfect metal supplier, and indeed act as a biocatalyst. A characterization of the used mining residue (Cola) was made. It was demonstrated that Cola did contribute essential nutrients to wastewater anaerobic process. There was better effectiveness under extreme conditions: less substrate and toxic concentrations in Nitrogen and Sulphur. In all cases, the best answer was obtained when Cola concentration was around 3mg/l, with an organic matter removing of more than 80%. [ABSTRACT FROM AUTHOR]

The use of solid mining residues (Cola) which contain a certain amount of Hi, Fe and Co, to stimulate anaerobic processes was evaluated. The effect over methane production and chemical oxygen demand (COD) removal efficiency was analysed. The studies were carried out in discontinuous reactors at lab scale under mesophitic conditions until exhausted, 0, 3, 5 and 7 mgCola l-1 doses were applied to synthetic wastewater. Volatile fatty acids (VFA) and sucrose were used as substrate, sulphur and nitrogen concentration, being the noise variable. Cola addition at dose around 5 mg l-1, turned out to be stimulating for the anaerobic process. It was the factor that most influenced on methane production rate together with VFA and high content of volatile suspended solids. In the case of methane yield, pH was the control factor of strongest influence. Higher values of COD removal efficiency were obtained when the reactors were operated with sucrose at relatively low pH and at the smallest concentration of nitrogen and sulphur. Solid residues dose and the type of substrate were the factors that had most influence on COD removal efficiency. [ABSTRACT FROM AUTHOR]

The aim of the present study is the evaluation of the effects of the acid drainage of three abandoned mining sites: SBOthmane, Kettara and Dra-sfar, on water and sediment quality of the Tensift River and its two temporary tributaries, the Kettara and El-Coudia Oueds. These mining sites located near Marrakesh contain mining residues abandoned for ten to twenty years. They are presently in an agricultural region of the Haouz district. In each site, these uncontrolled mining residues present a high level of metallic sulphide and generate, during rainy periods, leaching products which have physical and chemical characteristics of acid mine drainage (AMD). These percolates display an acidic pH ranging from 2.5 to 5.2, a high electric conductivity, large amounts of sulphate and heavy metals, especially under dissolved form (e.g.Cd: 17.34 mg l -1 ; Fe: 1734 mg l -1 ; Zn: 3935 mg l -1). Except for Pb, the free ionic form is the most abundant metallic form, as showed by calculations using the speciation GEOCHEM program. The analysis of water and sediments of the surrounding superficial aquatic ecosystems shows a modification of water chemical facies and an enrichment in heavy metals, mainly under the solid phase for Fe, Pb, Cu, Co, Cr and Ni, and under dissolved fraction for Cd and Zn. The dissolved fraction of these metals is dominated by the free ionic form, considered as available for organisms. Furthermore, sediments contain important quantities of heavy metals (Pb: 1450 μg g-1, Zn: 1562 μg g-1) with an available fraction which is higher than 40% for the Cd and Zn. The abundance of trace elements (free ionic and available forms) in water and sediment presents a durable risk of their transfer to food chains. [ABSTRACT FROM AUTHOR]

The big flood in the upper Elbe River catchment area has revealed a wide spectrum of problems with contaminated sediments. So far, an effective strategy for managing contaminated sediments on a river basin scale is still missing and it seems that not much has been learned from the lessons received during the last decade. In the following overview, special emphasis is given to the utilization of geochemically-based techniques for sediment remediation, which can be applied in different parts of a river basin. The examples presented here are mostly from the Elbe River catchment area. In general, new technical problem solutions need a set of practical process knowledge that uses a wide range of simulation techniques, as well as models in different spatial and temporal scales. The evaluation of recent flood events clearly demonstrates the importance of chemical expertise in the decision-making process for the sustainable development in river basins. [ABSTRACT FROM AUTHOR]

Canada's mineral reserves can play a very important role in curbing climate change if natural alkaline minerals are used for the process of mineral carbonation. In this work, the potential of using two Canadian natural silicates for accelerated carbonation is experimentally assessed: kimberlite mine tailing (Mg0.846Al0.165Fe0.147Ca0.067SiO3.381) from the Northwest Territories, and mined wollastonite ore (Ca0.609Mg0.132Al0.091Fe0.024SiO2.914) from Ontario. The aim of this work was to evaluate the weathering reactivity and CO2 uptake capacity via carbonation of these two comminuted rocks, both of which are made up of a mixture of alkaline minerals, under process conditions that spanned from milder to intensified. Research questions addressed include: does kimberlite contain a sufficient amount of reactive minerals to act as an effective carbon sink; is dehydroxylation necessary to activate kimberlite, and to what extent does it do this; do secondary phases of wollastonite hinder its reactivity; and can either of these minerals be carbonated without pH buffering, or only weathered? Incubator, slurry, and pressurized slurry methods of accelerated weathering and carbonation were used, and the effect of the process parameters (temperature, solid-to-liquid ration, reaction time, CO2 level, pH buffer) on the CO2 uptake and crystalline carbonates formation is tested. The reacted samples were analyzed by pH test, loss-on-ignition test, calcimeter test, and X-ray diffraction analysis. Results showed that wollastonite ore (rich in fast-weathering CaSiO3) is more suitable for accelerated carbonation than kimberlite tailing (containing slow-weathering hydrated magnesium silicates and aluminosilicates) when only its capability to rapidly form solid carbonates is considered. Incubator and pressurized buffered slurry methods proved to be most effective as under these conditions the precipitation of carbonates was more favorable, while the unbuffered slurry reaction conditions were more akin to accelerated weathering rather than accelerated carbonation. [ABSTRACT FROM AUTHOR]

Mining residues are usually stockpiled because of their understudied physico-chemical properties and of their abundance, which make their valorization challenging. In this work, a cold-bonding granulation apparatus was built in order to transform a mining residue sludge from an apatite ore, into artificial aggregates suitable for use in civil engineering. A 25 rpm rotation speed, 15° angle relative to horizontal, and an ideal feeding amount of the granulation drum, as such as the liquid (supernatant) distribution method, were preliminary determined. Effects of rotation speed, liquid content, and granulation time were then studied to evaluate the best combination for appropriate aggregate size distribution. Box-Behnken experimental designs were used to investigate the evolution of compressive strength of the individual aggregates when Portland cement is added to the mix, and when granulation time varies, around the critical liquid content of 14% of total weight. Thus, the possible parameters combinations which allow a maximization of compressive strength without exclusively increasing cement content, were determined and used to confirm the Box-Behnken predictions. Spherical aggregates were thus manufactured, with diameters mainly comprised between 5 and 40 mm, and compressive strength comparable to those of commercialized aggregates, up to 7 MPa and to 3 MPa for aggregates with diameters respectively below and above 10 mm. Paths for greater consolidation as prior homogenization, use of humid cure conditions, and use of other additives emerge from literature and from the results presented. [Display omitted] [ABSTRACT FROM AUTHOR]