Acid Mine Drainage Generation Research Articles

Modeling the influence of forest vegetation and climate change on the long-term performance of a cover with capillary barrier effects used to control acid mine drainage: the Lorraine case study

ABSTRACT The Lorraine mine site in Témiscamingue region (Québec, Canada) was reclaimed with a cover with capillary barrier effects (CCBE) to limit acid mine drainage generation. The main objective of this study is to predict the long-term hydrogeological behaviour of the CCBE at Lorraine site, including the influence of vegetation and climate change (CC). Numerical simulations showed that performance of the CCBE is: (1) not affected by forest vegetation and CC in the saturated zone in the north of the Lorraine site and (2) more sensitive to vegetation in the unsaturated zone in the south where the phreatic level is low.

Oxidative Dissolution Process of Sphalerite in Fe2(SO4)3-O3 System: Implications for Heavy Metals Removal and Recovery.

Metal sulfides in waste rocks and tailings are susceptible to serious soil and water contamination due to the generation of acid mine drainage (AMD) during stockpiling. The hydrometallurgical process is one of the most essential heavy metal remediation technologies through harmless disposal and resource utilization of the waste sulfides. However, atmospheric hydrometallurgy of sulfides still faces great challenges due to low leaching efficiency and high cost. In this work, we proposed a cooperative leaching system (Fe2(SO4)3-O3) and investigated the oxidative dissolution process of sphalerite (ZnS). Under the optimal conditions, the extracted zinc reached 97.8%. Reactive oxygen species (ROS) (·OH, 1O2 and ·O2-) were identified in the radical quenching experiments. The dissolution of sphalerite did not show passivation due to the ozone's capability to oxidize the sulfur in sphalerite to sulfate. In addition, stirring rate, O3 inlet concentration, and Fe2(SO4)3 concentration had a significant effect on the dissolution of sphalerite. Meanwhile, the apparent activation energy was 24.11 kJ/mol based on kinetic fitting, which indicated that the controlling step of the reaction was mainly a diffusion process. This work demonstrated the cooperative effect of sphalerite leaching in the O3-Fe2(SO4)3 system and provided a theoretical reference for efficient and atmospheric dissolution of sphalerite.

Inhibition of iron oxidation in Acidithiobacillus ferrooxidans by low-molecular-weight organic acids: Evaluation of performance and elucidation of mechanisms

The catalytic role of Acidithiobacillus ferrooxidans (A. ferrooxidans) in iron biooxidation is pivotal in the formation of Acid Mine Drainage (AMD), which poses a significant threat to the environment. To control AMD generation, treatments with low-molecular-weight organic acids are being studied, yet their exact mechanisms are unclear. In this study, AMD materials, organic acids, and molecular methods were employed to gain a deeper understanding of the inhibitory effects of low-molecular-weight organic acids on the biooxidation of iron by A. ferrooxidans. The inhibition experiments of A. ferrooxidans on the oxidation of Fe2+ showed that to attain a 90 % inhibition efficacy within 72 h, the minimum concentrations required for formic acid, acetic acid, propionic acid, and lactic acid are 0.5, 6, 4, and 10 mmol/L, respectively. Bacterial imaging illustrated the detrimental effects of these organic acids on the cell envelope structure. This includes severe damage to the outer membrane, particularly from formic and acetic acids, which also caused cell wall damage. Coupled with alterations in the types and quantities of protein, carbohydrate, and nucleic acid content in extracellular polymeric substances (EPS), indicate the mechanisms underlying these inhibitory treatments. Transcriptomic analysis revealed interference of these organic acids with crucial metabolic pathways, particularly those related to energy metabolism. These findings establish a comprehensive theoretical basis for understanding the inhibition of A. ferrooxidans' biooxidation by low-molecular-weight organic acids, offering a novel opportunity to effectively mitigate the generation of AMD at its source.

Prediction of Acid Mine Drainage Generation from Mine Waste at an Abandoned Mining Site in a Semi-arid Environment

Prediction of Acid Mine Drainage Generation from Mine Waste at an Abandoned Mining Site in a Semi-arid Environment

Complex electrical measurements of waste rock during acid mine drainage generation and release: Kinetic column tests

Acid mine drainage (AMD) emanating from waste rock piles (WRPs) at mining sites is a global concern. Successful rehabilitation of these sites requires effective characterization and monitoring of the waste rock during AMD generation/release. Traditional approaches involve ex-situ analysis of waste rock and porewater samples collected via corings and monitoring wells; however, this is highly disruptive, costly, and provides sparsely distributed point information across enormous volumes typical of WRPs. Geoelectrical techniques are a promising approach for non-invasive continuous imaging; however, their application has been limited to ‘one-off’ imaging with few studies on monitoring waste rock evolution. The objective of this study is to assess the geoelectrical signatures of changing waste rock during AMD generation/release. Field waste rock samples were extracted from three mine WRPs and first characterized for mineralogy and acid generation potential. Kinetic tests were then performed on each sample using leaching columns and humidity cells, with simultaneous measurements of effluent quality and complex electrical conductivity (real and imaginary components measure conduction and polarization, respectively). Results show that real conductivity was highly sensitive to changes associated with AMD leachate quality (e.g., 28,800 to 68 mg/L acidity) and surface of the waste material. Imaginary conductivity measurements identified changes in the waste mineralogy over time, though these signatures were not very distinct, which is likely due to low sulfide contents and limited oxidation (e.g., 0.59 wt% sulfide and 33% air saturation). This study improves our understanding of geoelectrical signatures associated with real waste rock, demonstrating the potential application of the electrical resistivity tomography and induced polarization techniques for mine waste investigations.

Implementation of swampy forest system for acid mine drainage treatment to meet threshold value

Coal mining with the area of the potential acid-forming category can generate acid mine drainage. Acid mine drainage (AMD) that has been formed must be appropriately managed. There are two techniques to treat AMD by the challenge specificity, including the prohibitive cost of the conventional active treatment with an uncertain process and the passive treatment, which faces time constraints and a wider area for preparation. A novel swampy forest system is a development to overcome the weaknesses of conventional processing by naturally responsive mitigation, reducing cost and speed, which results in greater capacity in AMD treatment. The swampy forest system implemented in coal mining relies on three main components: empty fruit bunches as organic matter, grass, and selected tree species planted in the treatment pond. The system effectively changes the non-compliance parameters of wastewater when entered at the system’s inlet to meet the threshold value after processing. It allows for flowing to the public bodies references with the applicable regulation.

Mineralogical Studies of the Tanjung Iron Mine in the Bone, South Sulawesi: Implication for AMD Generation

The iron ore of abandoned iron mine at the Tanjung Arae in Bone Regency has been investigated with the aim to analyze mineralogical characteristics and its potential for generating acid mine drainage (AMD). Mineralogical properties of the iron ore were analyzed using optical microscopy and X-ray diffraction (XRD) methods. Results of analysis reveal that the samples are dominated by iron oxide minerals such as magnetite, hematite and goethite. Other minerals are also present such as quartz, birnessite, pyrite and chalcopyrite. Mostly pyrite [FeS2] and chalcopyrite [CuFeS2] have been undergoing alteration which are characterized by weathering rims of those crystals and transformed into goethite and hematite. It is shown that the existence of pyrite [FeS2] and chalcopyrite [CuFeS2] may have significant roles in triggering the generation of AMD.

Metagenomic insight into the acidophilic functional communities driving elemental geochemical cycles in an acid mine drainage lake

Acidophiles play a key role in the generation, evolution and attenuation of acid mine drainage (AMD), which is characterized by strong acidity (pH<3.5) and high metal concentrations. In this study, the seasonal changes of acidophilic communities and their roles in elemental cycling in an AMD lake (pH∼3.0) in China were analyzed through metagenomics. The results showed eukaryotic algae thrived in the lake, and Coccomyxa was dominant in January (38.1%) and May (33.9%), while Chlorella in July (9.5%). The extensive growth of Chlamydomonas in December (22.7%) resulted in an ultrahigh chlorophyll a concentration (587 μg/L), providing abundant organic carbon for the ecosystem. In addition, the iron-oxidizing and nitrogen-fixing bacterium Ferrovum contributed to carbon fixation. Ammonia oxidation likely occurred in the acidic lake, as was revealed by archaea Ca. Nitrosotalea. To gain a competitive advantage in the nutrient-poor environment, some acidophiles exhibited facultative characteristics, e.g. the most abundant bacterium Acidiphilium utilized both organic and inorganic carbon, and obtained energy from organic matter, inorganic sulfur, and sunlight simultaneously. It was suggested that sunlight, rather than chemical energy of reduced iron-sulfur was the major driver of elemental cycling in the AMD lake. The results are beneficial to the development of bioremediation strategies for AMD.

Short-Term Predictions of Evaporation Using SoilCover at the Near-Surface of a Mine Waste Pile following Heavy Rainfall Events

Accurate measurements and predictions of near-surface soil drying and evaporation following heavy rainfall events are often needed for research in agriculture and hydrology. However, such measurements and predictions at mine waste pile and tailing settings are limited. The prediction of evaporation at mine waste piles is essential for many problems in geotechnical engineering, including the design of soil cover systems for the long-term closure of hazardous waste sites, and thus mitigates, for example, the generation of acid mine drainage (AMD) and metal leaching. AMD is one of mining’s most serious threats to the environment. This study investigated the short-term (8 days) and medium-term (27 days) drying rates and evaporative fluxes at the surface and near-surface of the Deilmann South waste-rock (DSWR) pile at the Key Lake uranium mine, northern Saskatchewan, using the gravimetric (GV) method and SoilCover (SC) model, respectively, during and following heavy rainfall events for the environment. The SC simulation results showed that during the weather-controlled stage (Stage I) of the first 5-day period of rainfall events, while the surface was wet, the potential evaporation (PE) was equal to the actual evaporation (AE) (i.e., AE/PE = 1). As the surface became drier on Day 6, the cumulative PE began to separate from the cumulative AE and the surface’s drying rate rapidly diverged from those at the deeper depths. This occurrence signaled the onset of the soil profile property-controlled stage (Stage II). As the drying continued, the surface became desiccated and the slow-rate drying stage (Stage III) was established from Day 7 onward. The SC-simulated AE results were compared to those measured using the eddy covariance (EC) method for the same test period at the DSWR pile in a different study. The comparison showed that the two methods yielded similar AE results, with 18% relative errors. The results of this study provided the opportunity to validate the SC model using actual data gathered under field conditions and to ascertain its ability to accurately predict the PE and AE at the surfaces of mine waste piles.

Geochemistry and mineralogy of legacy tailings under a composite cover

Remediation by a composite cover was implemented on partly oxidized sulfide-rich tailings in northern Ontario, Canada to reduce the production and release of acid mine drainage (AMD). The impact of the cover on sulfide oxidation rates and trace element mobility was initiated a decade after cover installation via multi-year measurements of pore-gas concentrations, pore-water and groundwater sampling and analysis, mineralogical studies of the tailings, selective chemical extractions, and synchrotron-based X-ray absorption experiments. Depleted pore-gas O2 concentrations, circumneutral pH, and improvement in water quality were observed at one detailed sampling location, suggesting that the cover decreased AMD generation and transport. Carbon and sulfur isotope ratios indicate sulfate reduction occurred at the base of the tailings. In contrast, near-atmospheric pore-gas O2 concentrations, low pH, and elevated aqueous concentrations of Fe, sulfate, Zn, Cu, As, and Pb were observed at another location, suggesting localized sulfide oxidation. Trace elements in the tailings are associated with secondary crystalline and amorphous Fe(III) oxyhydroxides, covellite, and Fe(III) hydroxysulfate phases, formed prior to cover installation. Substantial reductive dissolution of Fe(III) oxyhydroxides due to the isolation of the tailings from the atmosphere by the cover was not observed. Concentrations of Zn and Mn remained elevated due to limited sequestration under the current acidic to circumneutral pH. Although secondary Fe(III) oxyhydroxides contain As(V) and As(III), which were released by arsenopyrite oxidation, dissolved As persists. Due to localized sulfide oxidation, element remobilization, and limited capacity for sulfate reduction, diminished water quality, with elevated aqueous concentrations of sulfate, Zn, As, and Mn, may endure.

Rates of iron(III) reduction coupled to elemental sulfur or tetrathionate oxidation by acidophilic microorganisms and detection of sulfur intermediates

Bioleaching processes and acid mine drainage (AMD) generation are mainly driven by aerobic microbial iron(II) and inorganic sulfur/compound oxidation. Dissimilatory iron(III) reduction coupled to sulfur/compound oxidation (DIRSO) by acidophilic microorganisms has been described for anaerobic cultures, but iron reduction was observed under aerobic conditions as well. Aim of this study was to explore reaction rates and mechanisms of this process. Cell-specific iron(III) reduction rates for different Acidithiobacillus (At.) strains during batch culture growth or stationary phase with iron(III) (∼40 mM) as electron acceptor and elemental sulfur or tetrathionate as electron donor (1% or 5 mM, respectively) were determined. The rates were highest under anaerobic conditions for the At. ferrooxidans type strain with 6.8 × 106 and 1.1 × 107 reduced iron(III) ions per second per cell for growth on elemental sulfur and tetrathionate, respectively. The iron(III) reduction rates were somehow lower for the anaerobically sulfur grown archaeon Ferroplasma acidiphilum, and lowest for the sulfur grown At. caldus type strain under aerobic conditions (1.7 × 106 and 7.3 × 104 reduced iron(III) ions per second per cell, respectively). The rates for five strains of At. thiooxidans (aerobe) were in between those for At. ferrooxidans (anaerobe) and At. caldus (aerobe). There was no pronounced pH dependence of iron(III) reduction rates in the range of pH 1.0–1.9 for the type strains of all species but rates increased with increasing pH for four other At. thiooxidans strains. Thiosulfate as sulfur intermediate was found for At. ferrooxidans during anaerobic growths on tetrathionate and iron(III) but not during anaerobic growths on elemental sulfur and iron(III), and a small concentration was measured during aerobic growths on tetrathionate without iron(III). For the At. thiooxidans type strain thiosulfate was found with tetrathionate grown cells under aerobic conditions in presence and absence of iron(III), but not with sulfur grown cells. Evidence for hydrogen sulfide production at low pH was found for the At. ferrooxidans as well as the At. thiooxidans type strains during microaerophilic growth on elemental sulfur and for At. ferrooxidans during anaerobic growths on tetrathionate and iron(III). The occurrence of sulfur compound intermediates supports the hypothesis that chemical reduction of iron(III) ions takes place by sulfur compounds released by the microbial cells.

Investigating acid mine drainage potential and alteration properties of Zn-Pb wastes from Görgü (Malatya, Türkiye) region

Acid mine drainage (AMD) is one of the main causes of environmental threats resulting from mining activities, yet efficient characterization and prediction of AMD potential of wastes play an important role in preventing AMD. In this study, the chemical and mineralogical properties of fresh waste samples, collected from waste ponds of the Görgü (Malatya) zinc-lead ore processing plant, were determined and the results were used to explain its AMD potential. Alteration properties of the wastes in water was investigated by monitoring certain properties of the prepared suspension with respect time. Additionally, pyrite concentrate particles were added into the suspensions at certain proportions to evaluate its effect on the AMD generation and alteration. Analysis and test results showed that the raw waste was rich in carbonate and poor in pyritic sulfur, and hence did not have the AMD generation potential. The pH, electrical conductivity, and metal ions concentrations of the suspension medium were determined at regular intervals, and obtained data were found very beneficial to explain the time-dependent behavior of waste in water. After the depletion of liquid in the suspension, the remained solid residuals were chemically and mineralogically analyzed to compare with raw waste. It was concluded that sufficient aeration and stirring of suspension is required for noticeable alteration of the waste.

The geochemical processes affecting the mobility of Cu, Pb, Zn during phytostabilization on sulfidic mine tailings revealed by a greenhouse study

Sulfidic mine tailings have the potential to release toxic metals into the surrounding environment. Phytostabilization can stabilize these toxic metals in the rhizosphere, providing a sustainable method for mine reclamation. However, previous research has not examined the inorganic geochemical processes in the rhizosphere that are significant for controlling acid mine drainage. Therefore, a greenhouse study was conducted to explore the geochemical processes affecting the mobility of Cu, Pb, and Zn through the establishment of phytostabilization on sulfidic mine tailings. The mineralogy of substrates before and after experiments and the changes in metal concentrations and pH of the drainage were analyzed. The results showed that at the end of the experiments, pH of pot substrates with plants became acidic (pH ranging from 2.59 to 3.77), the concentrations of Cu, Pb, and Zn in the drainage increased (up to 20.14 mg/L of Cu, 2.28 mg/L of Pb, and 3199.87 mg/L of Zn), leading to the generation of acid mine drainage. It was concluded that, in addition to the sulfide oxidation, two other acidification processes played a role: the decomposition of organic matter and the release of roots exudates, in decreasing pH and increasing metal concentrations in the drainage from amended tailings. The acidity in the rhizosphere was neutralized sequentially through the following geochemical processes: (1) dissolution of carbonates, (2) dissolution of Al&Fe (oxy)hydroxide, and (3) silicates weathering. The long-term reliability of phytostabilization can be achieved by re-applying amendments to initiate these neutralization processes. This research has filled the research gap regarding the geochemical mechanisms controlling the migration of metals in the rhizosphere during phytostabilization with two grass species (Pascopyrum and Lolium multiflorum). It provides a valuable reference for designers and engineers when considering metal immobilization in sulfidic mine tailings through the technique of phytostabilization during mine reclamation and closure stage.

Experimental and numerical evaluation of the critical degree of saturation and critical exposure time of acid generating filtered tailings

Tailings filtration has many advantages (e.g., water recirculation, progressive reclamation, reduction of geotechnical risks and of environmental footprint) and is increasingly used by mining companies to improve the geotechnical stability of tailings storage facilities (TSF). However, low water content also exposes filtered tailings to oxidation thus increasing the risk for acid mine drainage (AMD) generation. Tailings management techniques must therefore be adapted to prevent contamination during operations. More specifically, tailings degree of saturation and exposure time should be controlled so they do not remain exposed too long to oxygen before reclamation work starts. The main objective of this research was therefore to evaluate the combined influence of the mineralogy and the degree of saturation on the time before filtered tailings start generating AMD. This work included (i) physical, chemical, hydrogeological and mineralogical characterization of different tailings, (ii) laboratory kinetic tests, (iii) calibration and validation of reactive transport numerical simulations, and (iv) numerical extrapolations and analysis. Results showed that AMD started when carbonates were depleted and that the critical time (i.e., the time tailings could be left exposed before AMD starts) strongly depended on the mineralogy. Maintaining the degree of saturation above 90% could contribute to delay the generation of AMD, and the greater the degree of saturation, the longer the critical time. However, the critical time became independent of the degree of saturation and depended only on the mineralogy when Sr< 90%. The results of this study tend to show that it should be possible to plan the deposition of reactive filtered tailings to limit the generation of AMD, for example by mixing reactive tailings with other tailings containing a greater neutralization potential and/or by regularly disposing of a new layer of tailings on the surface, with the maximum delay between two layers being shorter than the critical time.

Changes in microbial community structure during the biooxidation of iron and inorganic/organic sulfur provide prediction of acid mine drainage from coal spoil

To thoroughly investigate the formation mechanism of acid mine drainage (AMD) from coal mine spoil, this study conducted microbial shake flask experiments on gangue possessing inorganic and organic sulfur to predict the future generation of AMD. The results revealed that microbial-mediated sulfur oxidation effectively lowered the pH of leachate and increased metal ion and sulfate concentrations. The oxidation of pyrite sulfur and thiophene sulfur contributed to 70 % and 30 % of the total acid production, respectively, highlighting the importance of both processes in coal mine acidification. The abundance and diversity of the microbial community increased, with “new” iron and sulfur oxidizing bacterial species during acidification, with “new” iron and sulfur oxidizing bacterial species, such as Sulfobacillus sp. and Acidibacillus sp., emerging and constituting approximately one-third of the bacterial population. These bacteria survived desiccation and proliferated faster than A. ferrooxidans YQ-N3 when conditions favored growth.

Utilization of fly ash and bottom ash for tailings stabilization

To anticipate the problem of acid mine drainage generation from the tailings, the experiments on the use of fly ash (FA) and bottom ash (BA) were carried out by considering the neutralizing potential contained in these materials. The basic characteristics of the tailings, FA, and BA materials were tested through mineralogy and geochemical test. Geochemical static tests were carried out on various compositions and rates of FA and BA mixtures added to the tailings. Based on the results of these tests and the results of the Toxicity Characteristic Leaching Procedure (TCLP) test, a kinetic geochemical test was carried out using a column to determine the neutralization performance of FA and BA. The results of the quality test of leachate water coming out from the column for 6 weeks test period showed that a mixture of FA and BA with a ratio of 9:1, which was added to the tailings at the rate of 15 kg/ton of tailings was the optimum mixture that could neutralize the acidity formed, and also reduced the Pb and Cu content in the leachate.

Laboratory simulation of the swampy forest system for the passive treatment of acid mine drainage in coal mine reclamation areas

Coal mining that applies the open pit method has the potential to generate acid mine drainage. Acid mine drainage (AMD) treatments must include processes to mitigate significant challenges; these treatments include active treatment with high costs and process uncertainty and passive treatment with its limitations. The new concept of the swampy forest system involves the development of passive treatment for AMD, which lowers costs, increases capacity, and provides a natural process to mitigate the AMD that has been generated. A laboratory simulation experiment was carried out to obtain the basic data required for the swampy forest system treatment. The basic reference data determined in this study, including the total volume of water, the water debt flows into the swampy forest scale laboratory system and the retention time, were obtained to bring the parameter values that failed to meet the quality standards into compliance, according to the applicable regulations. The AMD swampy forest treatment design in the pilot project at the treatment field can apply a scaled-up version of the basic data from the simulation laboratory experiment results.

Phytoaccumulation of trace elements (As, Cd, Co, Cu, Pb, Zn) by Nicotiana glauca and Euphorbia segetalis growing in a Technosol developed on legacy mine wastes (Domingo Rubio wetland, SW Spain)

Sulfidic mine wastes have the potential to generate acid mine drainage (AMD) and release acid leachates containing high levels of iron, sulfate and potentially toxic elements (PTEs). Soils receiving AMD discharges are generally devoid of vegetation. Only a few metal-tolerant plant species can survive under such adverse soil conditions. This work investigates two plant species, Nicotiana glauca and Euphorbia segetalis, that have successfully colonized an AMD-impacted wetland area in south-western Spain. The uptake of PTEs from the soil by roots and their transfer and accumulation in the above-ground biomass were quantified. Results showed that these pioneer plants grew in patches of neutral soil within the wasteland despite the high concentrations of PTEs in the rhizosphere soil (up to: 613 mg kg−1 As, 18.7 mg kg−1 Cd, 6370 mg kg−1 Cu, 2210 mg kg−1 Pb and 5250 mg kg−1 Zn). The target organs of As, Cu and Pb accumulation were: root > leaf > stem in N. glauca, and root > stem > leaf in E. segetalis. Zinc and Cd showed a significant decrease in roots relative to aerial parts of N. glauca, and Co was preferentially partitioned in stems of N. glauca and leaves of E. segetalis. The soil–plant transfer coefficient values of PTEs in all parts of both plants were well below unity with the only exception of Cd in leaves of N. glauca (1.254), suggesting that roots acted as a barrier limiting the uptake of PTEs by plants. Interestingly, under the same soil conditions, N. glauca absorbed Cd in considerable proportions from soil and accumulated it in its leaves, while E. segetalis was not effective in transferring PTEs from roots shoots except for Co. In conclusion, soil pH and plant-related factors greatly influence the stabilization of PTE in the rhizospheric soil and produce inconsistencies in PTE phytoavailability. The findings of this study provide criteria to assist in natural remediation in other legacy contaminated sites worldwide.

Effect of mechanochemical activation on hydration properties of lead-zinc sulfide tailings for concrete construction

Proper management of mine tailings containing high amount of sulfide is a crucial issue in order to reduce their environmental hazards including generation of acid mine drainage and release of heavy metals. This study was conducted targeting to understand the effects of using lead-zinc sulfide tailings (LZSTs) as cement substitution on the hydration properties of concrete samples. Mechanochemical activation of the LZSTs containing 19.9% sulfide content in mixtures of 20%, 40%, 60%, 80% and 100% was performed to cement-replacement in concrete production. Analyzes were performed on the produced concrete samples. X-ray diffraction, compressive strength, toxicity characteristic leaching procedure (TCLP), mercury intrusion porosimetry, X-ray spectroscopy, scanning electron microscopy, energy-dispersive fourier-transform infrared spectroscopy, thermogravimetric analysis and differential thermal analysis were performed on the constructed concrete samples. The results of XRD analysis confirmed that introduction of activated tailings in the concrete construction led to form hatrurite (Ca3SiO5) phase. According to the TCLP, with increseasing curing days, leached amount of studied toxic metals decreased and was lower than the allowable limit. The results of the mercury intrusion porosimetry (MIP) indicated that as the curing time prolonged, the critical pore size was reduced from 150 to 50 nm in the constructed sample containing 20% activated tailings. Therefore, by activating the tailings, the specific surface area was enlarged and more cohesion took place in the concrete samples. The compressive strength results indicated that the compressive strength after 90 curing days in the constructed sample containing 20% activated tailings was 40.85 MPa, while it was 38.15 MPa in the control sample. In general, the results indicated that the mechanochemical activated of LZSTs with calcium carbonate can be a suitable alternative for cement (up to 40%) in the production of concrete samples.

Contamination assessment and availability of potential toxic elements from the Sidi Driss tailing pile (NW Tunisia) based on geochemical and geophysical methods

Mine wastes are of particular relevance, either because they represent a source of contamination by potential toxic elements (PTEs), or even because the high concentrations of some critical raw materials with economic interest can make their mining viable in the future.This work presents mineralogical, geochemical, and geophysical data aimed at a detailed characterization of an old tailing pile of the Sidi Driss mine (northern Tunisia) that exploited Pb and Zn concentrates. The results obtained from four drilling boreholes, reaching a maximum depth of 11 m, show high concentrations of metal(loid)s in the tailings, namely As, Ba, Cd, Mn, Pb and Zn. Apart from barium, the higher concentrations of these PTEs were found between 3 and 8 m depth. The availability of such metal(loid)s is higher in deeper sections of the tailing pond than on the surface, which is explained by the reduction and oxidation environments prevailing at these depths, respectively. Thus, at surface sulphides are oxidised and several metal(loid)s are released and leached. This oxidation process generates acid mine drainage (AMD), causing the dissolution of carbonates, such as cerussite, from which Pb is released and leached underground. In deeper sections of the tailing pond, reduction conditions prevent sulphide oxidation and the prevalence of circumneutral pH values. In such environments, carbonates are not dissolved and Pb leached from the surface precipitates (e.g., as anglesite, an insoluble sulphate), as demonstrated by sequential selective chemical extraction.Electrical resistivity tomography (ERT) showed low resistivity areas from surface to 8 m depth. This is a consequence of waterlogging on the surface (due to rainy events) and, on the subsurface, of high metal(loid) contents in tailings. High electrical resistivity was measured below this level (bedrock), but a connection between heavily contaminated horizons (tailings) and a subsequent layer of low resistivities (associated with groundwater) is observed, which is of particular concern.