Passive Treatment Of Acid Mine Drainage Research Articles

Simple Prototype Design of Phytoremediation Installation in Small Pilot Scale of Acid Mine Drainage Passive Treatment

Phytoremediation is usually applied to passively treat Acid Mine Drainage (AMD) by constructing a wetland. To increase the success of the AMD treatment method, laboratory trials were carried out on a pilot scale, and the experimental results were applied on an actual scale. Therefore, a simple design will be prepared for this research that replicates the wetland work system. This research aimed to produce a prototype that could be used for initial testing of phytoremediation on a smaller scale before being applied to field conditions. The installation design was created using Adobe Illustrator software. The trial lasted two months, using modified acid water and flowing it periodically as controlled droplets via an infusion tap into the media that used Typha sp and Pistia stratiotes L as phytoremediator agents. This equipment was tested with three acidity levels, 4, 5, and 6, repeated twice for two months. Results showed that the prototype was built using three buckets arranged in layers, each with its function. The phytoremediation process had successfully occurred in this study, and installation was suitable to support the process. There was a change in AMD acidity around the plants for five weeks and an increase in acidity the fourth week after treatment at the outlet. It could be seen that AMD with lower acidity levels resulted in greater plant damage in the sixth week, but Typha sp still showed resistance to an acidic environment.

Geochemical Behaviour of Rare Earth Elements Throughout an Acid Mine Drainage Passive Treatment System in the Lousal Mine Area, Portugal

A passive remediation system was installed between 2010 and 2015 at the Lousal legacy mine site in southwestern Portugal to minimize the impact of AMD. This is the first study of the geochemical behaviour of rare earth elements (REE) in the area after implementation of the passive treatment system. The total and dissolved concentrations of REE is similar throughout the basins/wetlands and acidic ponds in both sampling campaigns, which is mainly attributed to the conservative behaviour of these elements in acidic water. In areas where mixing of acidic and circumneutral water occurs, the REE were partially removed from solution by adsorption onto newly formed Al and Fe precipitates. Sorption onto the precipitates varies between the rare earths, with a preferential fixation of heavy REE (HREE) compared to the light REE (LREE). The normalized distribution patterns exhibit the characteristic convex-up enrichment in middle rare earth elements for AMD and display an enrichment of LREE relative to HREE in areas where mixing of waters occurs, and the pH is close to circumneutral.

Metagenomic analysis characterizes resistomes of an acidic, multimetal(loid)-enriched coal source mine drainage treatment system

Heavy metal(loid) contaminations caused by mine activities are potential hot spots of antibiotic resistance genes (ARGs) because of heavy metal(loid)-induced co-selection of ARGs and heavy metal(loid) resistance genes (MRGs). This study used high-throughput metagenomic sequencing to analyze the resistome characteristics of a coal source acid mine drainage passive treatment system. The multidrug efflux mechanism dominated the antibiotic resistome, and a highly diverse heavy metal(loid) resistome was dominated by mercury-, iron-, and arsenic--associated resistance. Correlation analysis indicated that mobile gene elements had a greater influence on the dynamic of MRGs than ARGs. Among the metagenome-assembled genomes, six potential pathogens carrying multiple resistance genes resistant to several antibiotics and heavy metal(loid)s were recovered. Pseudomonas spp. contained the highest numbers of resistance genes, with resistance to two types of antibiotics and 12 types of heavy metal(loid)s. Thus, high contents of heavy metal(loid)s drove the co-selection of ARGs and MRGs. The occurrence of potential pathogens containing multiple resistance genes might increase the risk of ARG dissemination in the environment.

Retention potential of a drained wetland in the Lusatian lignite mining district, Briesener Niedermoor, Germany, Europe

Acid mine drainage (AMD) is one of the most important global causes for polluted water. It occurs in mining areas due to oxidation of sulfide minerals. Depending on hydrological conditions, wetlands are considered suitable for passive treatment of AMD. The aim of the study was to characterize the long-term retention performance of a drained wetland, Briesener Niedermoor, in an iron and sulfate contaminated catchment area. The site is located in the Lusatian lignite mining district, Germany. Hydrological and hydrochemical measurements as well as time series of groundwater and surface water were evaluated and saturation conditions of iron species were determined using Phreeqc Interactive and EH–pH diagrams for the Fe–S–K–O–H system. Progressing peat degradation due to drainage leads to a hydraulic behaviour of the wetland that is more comparable to a rain bog than a fen, and thus to more pronounced oxic conditions. Groundwater feeds the wetland with significant loads of iron and sulfate, which are temporally stored in the wetland. At low surface water discharge, iron is removed and weak acidic pH is buffered by the dominant phase of schwertmannite (Fe8O8(OH)6SO4), usually during summer months. In winter, greater water availability initializes a high source strength from the wetland, that cannot be retarded. Thus, only during summer, there is a retention potential; in winter, the retention potential is not strong enough to prevent an inflow of iron and sulfate. Only a significant rewetting of the wetland may result in a restoration of the retention potential of the wetland Briesener Niedermoor.

Removal of Heavy Metals from Acid Mine Drainage by Red Mud-Based Geopolymer Pervious Concrete: Batch and Long-Term Column Studies.

Various metal ions in acid mine drainage (AMD) cause environmental pollution. Due to the unique advantages of heavy metal treatment and gelling properties, previous concretes incorporating red mud have attracted extensive attention in AMD passive treatment, which utilises naturally occurring chemicals to cleanse contaminated mine waters with low operating costs. This study aims to develop red mud-based geopolymer pervious concrete as an eco-friendly method to remove heavy metals in AMD. Compared with raw pervious concrete, red mud-based geopolymer pervious concrete improves the purification efficiency of heavy metals. The high rate of acid reduction and metal removal by the geopolymer is attributed to the dissolution of portlandite in red mud. Precipitation of metal hydroxides seems to be the dominant metal removal mechanism. Under optimal conditions (influent pH = 4.0 and the hydraulic retention time = 24 h), red mud-based geopolymer pervious concrete could completely remove Cu(II), Mn(II), Cd(II) and Zn(II) by up to 10 mg/L, 10 mg/L, 1.6 mg/L and 16 mg/L, respectively. When the influent pH is 2.5, the hydrolysis of Fe(III) released from red mud increases the consumption of OH-. Moreover, when the influent pH is 4.0, the precipitation of CaSO4 promotes the dissolution of portlandite and metal removal. Therefore, red mud has demonstrated feasibility in the manufacturing of geopolymer-based pervious concrete for purification AMD.

Assessing Alternative Supporting Organic Materials for the Enhancement of Water Reuse in Subsurface Constructed Wetlands Receiving Acid Mine Drainage

Acid mine drainage (AMD) is a global problem with severe consequences for the environment. South Africa’s abandoned mines are a legacy from the country’s economic dependence on the mining sector, with consequent negative impacts on ecosystems. AMD remediation includes active and passive techniques. Constructed wetlands (a passive technique) have lower operational costs but require larger spaces and longer timeframes to achieve the remediation of AMD, and are supported by anaerobic sulphate-reducing bacteria (SRB), which capable of remediating high-sulphate-laden AMD while precipitating dissolved metals from the AMD. Organic substrates supporting these activities are often the limiting factor. When enhancing existing passive AMD remediation technologies, alternative waste material research that may support SRB activity is required to support the circular economy through the reduction in waste products. Chicken feathers show potential as a substrate enhancer, boosting organic carbon availability to SRB, which sustains passive AMD treatment processes by achieving pH elevation, sulphate and metal reductions in AMD water for reuse. Microbial biodiversity is essential to ensure the longevity of passive treatment systems, and chicken feathers are proven to have an association with SRB microbial taxa. However, the longer-term associations between the AMD water parameters, microbial diversity and the selected substrates remain to be further investigated.

Changes in the prokaryotic diversity in response to hydrochemical variations during an acid mine drainage passive treatment

Acid mine drainage (AMD) causes major environmental problems and consequently, several treatments are proposed, favoring the passive systems because of their many advantages. The main goal of these procedures is the neutralization and removal of potentially toxic elements (PTE), yet little is known about the changes in the microbial assemblages in response to the hydrochemical variations during the treatments. Therefore, the main objective of this research was to determine the changes in the diversity and structure of the prokaryotic assemblages in a hybrid abiotic and biological (wetland) passive treatment system. The 16S rRNA gene survey showed that the AMD coming from the mine (pH 2.6) was mainly composed of acidophilic genera such as Acidithiobacillus, Leptospirillum, Ferritrophicum, and Cuniculiplasma (up to 76 % relative abundance). In the abiotic treatment, Acidiphilium was dominant in the sections with limestone filters (pH 2.2–4.8), followed by Limnobacter in the subsequent dolomite/limestone and phosphoric rock filters (pH 5.2–5.8). In these abiotic passive treatment sections, the microbial assemblage showed a limited diversity and richness. However, when the treated AMD reached the two final wetlands (pH ~6.8), the microbial diversity and richness increased, suggesting that further bioattenuation mechanisms might be occurring. Limnobacter and Novosphingobium were the main bacterial genera in the water samples of the wetland sections (Arundo donax). These changes in the composition of the microbial assemblages were highly correlated with the pH and Eh values during the treatment (p-value <0.001); however, the concentration of metal(loid)s such as Al, Cd, Fe, Mn, Ni, and Zn were also significantly related (p-value <0.05). In conclusion, the studied passive AMD treatment system enhanced the chemical quality of the treated AMD, showing high removal efficiencies for Al and Fe (> 99 %), and increasing the microbial diversity and richness in the effluent.

Study on the precipitation of iron and the synchronous removal mechanisms of antimony and arsenic in the AMD under the induction of carbonate rocks.

The ecological environment can be severely polluted and destroyed by the acid mine drainage (AMD) generated during the exploration and utilization of minerals. However, neutralized by carbonate rocks (a natural material in Karst regions), the AMD secondary iron flocs containing a large number of iron oxides or hydroxide can be precipitated in AMD. The metal ions, such as antimony (Sb) and arsenic (As), can be effectively removed by these neutralizing products. In this paper, the neutralization reaction of different acid solutions in an iron-antimony-arsenic system was induced by carbonate rocks to explore the removal effect of metals during this neutralization process. Meanwhile, taking the release amounts of iron (Fe), Sb, and As as well as the phase transformation of minerals at different pH levels as stability indexes, we quantitatively analyzed the chemical stability of AMD neutralizing products (secondary iron flocs) containing Sb and As under the typical acid-base environment (pH = 3.0 ~ 9.0) of AMD and other waters. Results showed that the neutralization reaction with carbonate rocks induced the co-precipitation of Fe with Sb and As. When the concentration ratio of Fe, Sb, and As was 30:1:1, the pH of AMD raised from 3.0 to 7.28 within 72h, and the three elements were removed by 99%, 85%, and 90%, respectively. After soaking the AMD secondary iron flocs in an acid environment (pH = 3.0) for 30days, the release amount of Fe reached its peak of 0.070mg/g. Then, when the pH value increased to 4.0, the As and Sb showed their maximum release amounts of 14.90µg/g and 19.19µg/g, respectively. In addition, under acidic conditions, these AMD secondary iron flocs were easily transformed into the goethite with better crystallinity and higher structural stability. This study could help reveal the development of the secondary mineral during the treatment of AMD by carbonate rocks and understand the release characteristics of metals from AMD secondary products containing Sb and As, which sheds light on and provides theoretical foundations for the passive treatment of AMD containing these two elements in the future.

Role of the Tree Species Selected in Developing Swampy Forest System for Passive Treatment of Acid Mine Drainage

Coal mining is one of economic sector that requires forestry area in Indonesia. Most of coal mining concession are forestry area loan use from the government and during mining operation facing with acid mine drainage (AMD). AMD passive treatment can be integrated with revegetation process that related with better handling of overburden (OB) with potential acid forming (PAF) during reclamation processed. The most expensive methods and uncertainty process are the use of quick lime in treatment of AMD. During operation and preparing mine closure stage need to create the effective one to comply with the regulation. “Swampy Forest (SF) system” is an alternative method of sustainable and naturally process. Selecting the appropriate tree species as a preliminary process to develop a better SF system by batch experiment in the form of a forest constructed wetland. The tree species selected are Nauclea orientalis (lonkida tree) and Melaleuca cajuputi (kayuputih tree) as non-local species then Nauclea subdita (bangkal tree) and Melaleuca leucadendron (galam tree) as local species have been selected. Local species higher in Fe and Mn adsorption in pH of AMD &lt;4 then nonlocal species higher in Fe and Mn adsorption on pH of AMD &gt;4 condition.

Efficiency of thermally activated eggshells for acid mine drainage treatment in cold climate

The selection process for a technology to treat the mine drainage is influenced by its performance, technical feasibility and cost. For the last decades, the mine industry has been searching for green methods to treat the acid mine drainage (AMD). This study evaluated thermally activated eggshells as a potential alternative for AMD treatment in cold climate. It was found that metal removal efficiency depended on the eggshells’ calcination temperature and on the solid: liquid ratio. Eggshells calcined at 900 °C and employed in a solid: liquid ratio of 0.3% increased the pH of a mine effluent from 2.5 to 6.9 at 20 °C and to 9.2 at 4 °C, respectively. Heavy metal concentrations were reduced as follows: As <0.0005 mg/L, Cd 0.00022 and 0.00009 mg/L, Cu 0.0061 and 0.0091 mg/L, Co 0.0338 and 0.0016 mg/L, Cr 0.0015 and 0.0022 mg/L, Fe <0.01 mg/L, Ni 0.0291 and 0.0024 mg/L, Mo <0.0005 mg/L, Se 0.0033 and 0.0044 mg/L, and Zn 0.007 and 0.022 mg/L, at 20 °C and 4 °C, respectively. Consequently, the treated mine effluent satisfied both the Quebec and Canadian regulations. Based on these results, thermally activated eggshells could be efficiently employed for the active and passive treatment of AMD in a cold climate.

Passive Treatment for Acid Mine Drainage Partially Restores Microbial Community Structure in Different Stream Habitats

The assessment of the degree to which biological communities in streams impaired by acid mine drainage (AMD) are restored by passive treatment has focused primarily on eukaryotic-cell organisms and microbial processes. The responses of microbial community structure to passive treatment have received much less attention, even though functional processes such as nutrient cycling and organic matter decomposition depend on taxonomic composition. Our objective was to determine the degree to which passive treatment restored microbial communities in three types of habitats: aqueous, leaf, and sediment. To assess their recovery, we compared the community composition in these habitats based on 16S rRNA gene sequencing at three different stream sites: an untreated AMD site (U), a remediated site below AMD passive treatment (T), and an unimpaired reference site (R). The acidity, conductivity, and soluble metal concentrations at T were found to be elevated compared to R, but generally 1–2 orders of magnitude less than at U. Microbial community composition was found to be synergistically affected by habitat type and AMD impact, with the similarity among communities in the three habitats increasing with the severity of the AMD. Sediment- and leaf-associated microbial communities at U were characterized by taxa that are tolerant to severe AMD. The absence of the nitrogen oxidizing bacterium Nitrospira in sediment communities at T and U was found to correspond to higher NH4+ concentrations compared to R, possibly because of the presence of iron oxyhydroxide precipitate. In contrast, the microbial composition was found to be similar between the T and R sites for both aqueous and leaf communities, indicating that passive treatment was more able to restore these communities to the reference condition than sediment communities. The remediation of AMD streams should consider the habitat-specific responses of microbial community composition and be guided by future studies that empirically couple changes in taxonomic composition to measured functional processes.

Passive treatment of acid mine drainage from the Sidi-Kamber mine wastes (Mediterranean coastline, Algeria) using neighbouring phosphate material from the Djebel Onk mine

Passive abiotic treatment of acid mine drainage (AMD) was investigated using phosphate mining residuals (raw low-grade phosphate ore, phosphatic limestone wastes, and phosphate mine tailings) from the Djebel Onk mine, Algeria. Laboratory batch tests were performed using the main expected lithologies of phosphate materials in contact with synthetic AMD, which had a low pH (3.08) and contained high concentrations of Fe (600 mg/L), Mn (40 mg/L), Mg (10 mg/L), Zn (20 mg/L), Cu (25 mg/L), As (50 mg/L), and sulfate (3700 mg/L). Phosphate materials were used as an oxic limestone drain to evaluate the increase in the pH of the AMD and metal removal by sorption and precipitation mechanisms. The results showed that all phosphatic lithologies were efficient in the passive treatment of AMD. The pH rapidly increased from 3.08 to 8.47 during water-rock interactions. The neutralization potential comparisons also showed that the phosphatic limestone wastes neutralized more acid than other lithologies. In addition, metals were efficiently removed (95.5% to 99.9%) by all materials. The results of batch sorption tests showed that the concentrations of metals in residual leachates did not exceed the Algerian criteria for industrial liquid effluents. Overall, these findings indicate that passive systems using phosphatic materials from the Djebel Onk mine can be effective for AMD treatment. The use of these mine wastes for passive treatment of AMD would allow the development of integrated management strategies for these residual materials in the context of sustainable development of phosphate mining.

Integration of cascaded aeration and neutralization for the treatment of acid mine drainage: Insights into the formation of jarosite

Acid mine drainage (AMD) treatment has become a major environmental issue confronting the global mining industry. For treating AMD economically and efficiently, a novel AMD passive treatment system consisting of cascaded aeration based biomineralization process driven by Acidithiobacillus ferrooxidans (A. ferrooxidans) LX5 followed by lime neutralization was developed. Compositions and structures of precipitates were measured through a scanning electron microscope equipped with an energy-dispersive X-ray spectrometry (SEM-EDS) and X-ray powder diffraction (XRD). Results showed that the biogenic Fe-minerals, with 1–1.5 μm diameter and 17.5 m2/g specific surface area, belonged to jarosite expressed as KFe3(SO4)2(OH)6 with Fe/S molar ratios between 1.61 and 1.68. The density and Fe2+ bio-oxidation rate of A. ferrooxidans LX5 immobilized on the surface of jarosite (namely immobilized cells) were approximately 8.3 × 108 cells/g and 7.3 mmol L−1 h−1, which were approximately 10 and 2.2 times higher than those of cultivating A. ferrooxidans LX5 solution used as the control (namely suspension cells). The constructed water-dropping system could supply sufficient oxygen for the Fe2+ bio-oxidation. The initial Fe2+ in the AMD was completely oxidized into Fe3+ and 41.8% of total Fe was removed during biomineralization. In addition, it was found that 34% of Zn2+, 21% of Cd2+, 42.7% of Cr3+, and 23.8% of Cu2+ were removed by co-precipitation or adsorption to jarosite simultaneously. With this novel treatment system, the amounts of lime addition required for AMD neutralization and toxic solid waste production were drastically decreased by about 70 wt% and 81.3 wt%, respectively, in comparison to the control (without biomineralization). These results show water-dropping aeration and A. ferrooxidans LX5 play a significant role in the Fe2+ bio-oxidation and removal of metal ions, and the integration of cascaded aeration and neutralization is a possibility for cost-effective treatment of highly acid and toxic metal-loaded AMD.

The Treatment of Acid Mine Drainage Using Vertically Flowing Wetland: Insights into the Fate of Chemical Species

In this study, the treatment of acid mine drainage (AMD) using vertically flowing wetland was explored. The wetland was enriched with Vetiveria zizanioides as a decontaminating media and soil as the substrate. Water was percolated through the substrate and the throughput samples were collected and characterized every five days for a period of 30 days. The obtained results revealed a tolerant index of 1.03 for Vetiveria zizanioides, and a net reduction of metals and sulfate. The removal efficacy of chemical species was observed to obey the following order: Fe (71.25%) &gt; Zn (70.40%) &gt; Mn (62%) &gt; Al (56.68%)&gt; SO42− (55.18%) &gt; Ni (35%) &gt; Cu (18.83%). The removal of chemical species was further aided by the used substrate, and this could be attributed to the accumulation of chemical species on the soil through precipitation, adsorption, and phyto-retention. As such, it could be deduced that the substrate plays a significant role in the removal of metals, while the grass and external factors accounted for the rest of the chemical species attenuation. The translocation assessment revealed that the distribution of chemical species was observed to be predominant in the roots, except manganese, which was transferred in the shoot (67%). The XRF, XRD, FTIR, and SEM-EDS analysis revealed the presence of AMD chemical species in the substrate and the grass components, hence confirming that the plants are playing a huge role in the removal of contaminants from AMD. The PH REdox EQuilibrium (in C language) (PHREEQC) geochemical model confirm that metals existed as di-and-trivalent complexes in AMD. Lastly, available metals were precipitated as metals hydroxides and oxy-hydrosulfates by the substrate. In light of the obtained results, vertically flowing wetland could be used for the passive treatment of AMD, and it will play a huge role in active and abandoned mines. However, prolonged assessment should be undertaken to understand its performance over a notable period of time.

Role of the Selected Grass Species in Developing of Swampy Forest System for Passive Treatment of Acid Mine Drainage

Acid Mine Drainage (AMD) is one of the consequences of environmental impact due to surface coal mining and has big challenge how to treat the AMD both active and passive treatment efficient and effectively. The most expensive method to actively raise the pH and concentration heavy metal reduction of this wastewater is the use of chemical additives. We present the development of passive treatment with Swampy Forest (SF) system as a new natural and sustainable method with lower costs, and greater environmental sustainability. The SF system consists of selecting organic matter and combining it with the planting of selected grass and tree species in the form of a forest constructed wetland. As a preliminary to the construction of the SF, a batch reactor system was used to carry out experiments to find the best individual grass species for SF as the development of AMD passive treatment. The four grass species selected were shown to reduce the concentration of Fe and Mn, which generally has out of threshold value, thus achieving the threshold parameter to comply with applicable regulations for managing mine wastewater.

Evaluation of Efficiencies of Locally Available Neutralizing Agents for Passive Treatment of Acid Mine Drainage

Acid mine drainage (AMD) generated from the mining industry elevates environmental concerns due to the pollution and contamination it causes to bodies of water. Over the years, passive treatment of AMD using alkalinity-generating materials have been widely studied with pH neutralization as its commonly observed mechanism. During the treatment process, heavy metal removal is also promoted by precipitation due to pH change or through adsorption facilitated by the mineral component of the materials. In this study, four materials were used and investigated: (1) a low grade ore (LGO) made up of goethite, calcium oxide, and manganese aluminum oxide (2–3) limestone and concrete aggregates (CA) composed of calcite, and (4) fly ash consisting of quartz, hematite, and magnetite. The performance of each alkalinity-generating agent at varying AMD/media ratios was based on the change in pH, total dissolved solids (TDS), oxidation reduction potential (EH); and heavy metals (Fe, Ni, and Al) removal and sulfate concentration reduction. Concrete aggregate displayed the most significant effect in treating AMD after raising the pH to 12.42 and removing 99% Fe, 99% Ni, 96% Al, and 57% sulfates. Afterwards, the efficiency of CA at various particle sizes were evaluated over 1 h. The smallest range at 2.00–3.35mm was observed to be most effective after 60 min, raising the pH to 6.78 and reducing 94% Fe, 78% Ni, and 92% Al, but only 28% sulfates. Larger particles of CA were able to remove higher amounts of sulfate up to 57%, similar to the jar test. Overall, CA is an effective treatment media for neutralization; however, its performance can be complemented by a second media for heavy metal and sulfate removal.

Economic Performance of Active and Passive AMD Treatment Systems Under Uncertainty: Case Studies from the Brunner Coal Measures in New Zealand

Acid mine drainage (AMD) often requires management long after mining operations have ceased. Cost-effective long-term passive treatment systems (PTS) are required for closure of mine sites. However, PTS research seldom defines well-constrained operational and financial parameters to enable confident decision making by mining companies. PTS are generally assumed to be a lower-cost alternative to active systems when used in favorable circumstances, but there is little objective information to define when they are more suitable than active treatment. Instead, general ‘rules-of-thumb’ for flow rates or acid loads are used to determine when PTS are best used. We used well-characterized AMD from multiple historic and active coal mine sites in New Zealand to test these rules-of-thumb from a financial perspective by modelling capital and operational costs over a 100 year timeframe. We present static and uncertainty-based cost assessments of a mussel shell reactor PTS compared to typical active AMD treatment systems at six mine drainage sources from the Brunner Coal Measures. We show that for expected AMD characteristics and duration of treatment, savings on operational costs with PTS can exceed the higher initial capital costs. In addition, the financial advantage of PTS over time may be achieved at flow rates and acidity loads that exceed the industry rules-of-thumb PTS limits. However, in some circumstances, cost projections for high up-front capital costs of purchasing all treatment media for the life span of the PTS is less favorable than discounted treatment media in active treatment systems over time. Understanding financial models of AMD treatment options during mine site design can help reduce the costs of operating and closing mine sites.

Performances of stabilization/solidification process of acid mine drainage passive treatment residues: Assessment of the environmental and mechanical behaviors

Residues from passive treatment of acid mine drainage (AMD) have variable chemical stability and could regenerate contaminated drainage. Stabilization/solidification (S/S) can prevent contaminant leaching. Residues were collected from a tri-step AMD field passive treatment system, operated for 6 years at the reclaimed Lorraine mine site, Quebec, Canada. General Use Portland cement (GU), blended binders based on GU with pozzolanic additives (ground-granulated blast-furnace slag; GGBFS and fly ash type C; FAC) were used as hydraulic binders, in proportions (w/w %) of 100GU, 20GU/80GGBFS, and 50GU/50FAC, respectively. Residues were mixed with wood ash (35%) and sand (25%), while reference samples (100% sand) were also prepared. Prior to S/S, raw materials were characterized. The S/S effectiveness was assessed mineralogically and mechanically (unconfined compressive strength; UCS). Environmental behavior assessment (static vs semi-dynamic leaching tests) was also performed. UCS results showed that strength increase with age. At 56 days, GU- (1.3 MPa) and GU/GGBFS (0.7 MPa) satisfied Quebec's strength requirements for landfill disposal (0.7 MPa), but not GU/FAC (0.6 MPa), while all samples satisfied USEPA criteria (0.35 MPa). The semi-dynamic test showed that all elements can be immobilized successfully in GU- and GU/GGBFS. The GU binder had the best stabilizing performance. Based on USEPA requirements, S/S using GU, GGBFS, and FAC can be also considered for contaminant immobilization in AMD passive treatment residues. Finally, the comparison between replicates using Student's t-test indicated good reproducibility of S/S treatment.

Passive remediation of mine impacted water using selected treatment media containing-bioreactor

This study was carried out to develop a passive treatment method to treat contaminated water with heavy metals caused by mining activities using organic, industrial, quarry and mining waste itself. In particular, this study aims to evaluate the performance of selected treatment media in treating Acid Mine Drainage (AMD) (i.e. Spent mushroom compost (SMC), limestone (LS), steel slag (SS) and ochre). A series of tests were conducted to determine the effectiveness of the treatment media in single and mixed substrates treatment. For single substrate, both SMC and SS showed promising overall heavy metal removal efficiency of 94.6% and 96.7%, respectively. As for mixed substrates, R3 (composed of 40% SS, 30% SMC, 20% LS and 10% ochre) gave the best performance in overall heavy metal removal. This treatment ratio (4:3:2:1) was then used in column experiment where continuous flow of synthetic AMD water was supplied. After 30 days, results showed that heavy metals (i.e. Fe, Mn, Pb, Zn, and Al) were reduced significantly with 91–100% removal efficiencies except for Mn (61.15% efficiency). Therefore, this study has proven that the media chosen in passive treatment of AMD are efficient in the removal of selected heavy metals and in increasing the pH of AMD, which can be applied for real on-site treatment of such cases.

Freezing/thawing effects on geochemical behavior of residues from acid mine drainage passive treatment systems

Passive systems are promising for the treatment of acid mine drainage (AMD) but generate metal-rich solids or residues. In subarctic climate, freezing/thawing (F/T) cycles may influence the chemical stability of waste, including residues from AMD passive treatment. The objective of this study was to assess and better understand the effect of F/T cycles on contaminants (metal and sulfates) leaching from AMD post-treatment residues. To do so, samples of residues WA50 (50 % wood ash and 50 % wood chips), PBR (30 % inorganic materials and 70 % organic substrate) and C50 (50 % calcite and 50 % wood chips) were collected from a laboratory tri-unit passive treatment system for iron-rich AMD (Fe-AMD) operated for over 1-year. To better understand the effect of freezing upon contaminant leaching, kinetic tests in weathering cells under wetting/drying (W/D) and F/T cycles were performed. Results showed that F/T cycles are likely to enhance the potential of metal leaching from post-treatment residues. The Fe leaching was 1.6-(for WA50), 3.2-(for C50) and 5.2-(for PBR) times higher under F/T cycles relative to the W/D cycles. Similarly, Zn leaching was 2.4-(for WA50), 4.9-(for PBR) and 5-(for C50) times higher under F/T cycles compared to the W/D cycles. Finally, Mn leaching was 2.4-(for WA50) and 5.2-(for PBR) times higher under F/T cycles relative to the W/D cycles but no difference in Mn concentration was observed for C50 residues. These findings suggest that during snow melt or early spring significant metal concentrations could be released while disposing AMD passive treatment residues.