Treatment Of Acid Mine Drainage Water Research Articles

Before-After Control-Impact field surveys and novel experimental approaches provide valuable insights for characterizing stream recovery from acid mine drainage

Mineral extraction has resulted in widespread stream impairment due to habitat degradation and water quality impacts from acid mine drainage (AMD). The North Fork of Clear Creek (NFCC), Colorado, USA was historically impaired by AMD from two major point-source inputs, with some stream segments devoid of aquatic life prior to remediation. In the summer of 2017, the North Clear Creek Water Treatment Plant (NCCWTP) began AMD water treatment. To predict and characterize the biological recovery of NFCC to improvements in water quality, we conducted stream mesocosm and field experiments, as well as biomonitoring of benthic communities using a Before-After Control-Impact (BACI) study design. The NFCC stream community responded rapidly to improved water quality. Benthic algal biomass increased at impacted sites and macroinvertebrate surveys showed significant increases in abundance, taxa richness, and emerging adult aquatic insects. However, the dominant taxa colonizing downstream segments of NFCC differed considerably from those predicted based on previous field and experimental results. We hypothesize that this discrepancy is the result of differences in metal exposure regimes observed between our field and mesocosm approaches (i.e., fluctuating vs stable), colonization attributes (i.e., open vs closed system), and spatiotemporal differences in metal sensitivity due to macroinvertebrate phenology. We expect continued biological recovery in NFCC, but habitat impairment and residual sources of metals will continue to impair aquatic life until those stressors abate. Applying a combination of controlled experimental and BACI field approaches to predict and evaluate AMD-remediation projects in the future will improve the ability to understand the physical, chemical, and biological mechanisms influencing stream recovery.

Acid Mine Drainage Treatment Using Bayer Precipitates Obtained from Seawater Neutralization of Bayer Liquor.

Bayer precipitates from the seawater neutralization of Bayer liquor waste from the alumina industry are shown to be a prospective solution for the remediation of acid mine drainage (AMD) water. Precipitates are varied in composition, albeit they are generally comprised of hydrotalcite (Mg6Al2(OH)16CO3∙xH2O), calcite (CaCO3), aragonite (CaCO3), mixed metal hydroxides (Mg2Al(OH)7), and halite (NaCl). Brucite (Mg(OH)2) is detected for lower Bayer liquor concentrations (1–3 g L−1 Al2O3) when the concentrations of aluminum and hydroxyl species are insufficient to promote hydrotalcite formation. The neutralizing capacity of the precipitates also varies with Bayer liquor composition. Treatment of AMD water with Bayer precipitates met discharge pH guidelines. The dissolution of hydrotalcite and brucite (1–3 g L−1 Bayer precipitates only) is responsible for the Bayer precipitate's neutralizing capacity, while calcium carbonate has a buffering affect at around pH 7. Manganese ions are the most challenging species to remove because high pH values are required (pH > 9), which is not possible with all precipitates tested. One caveat is that increasing the degree of manganese removal generates issues with excessive dissolved aluminum which exceeds discharge limits. Future research should address this latter problem and facilitate implementation of this approach to AMD remediation.

Alternative neutralisation materials for acid mine drainage treatment

This study reports the novel use of alkaline waste material from the alumina refining industry (Bayer liquor and precipitates formed by the seawater neutralisation of Bayer liquor), for the neutralisation of acid mine drainage (AMD) water. The hypothesis was that utilization of waste to treat waste can potentially result in environmental and economic benefits. The performance of Bayer liquor and Bayer precipitate was compared with conventional alkalis used for AMD neutralisation such as lime (Ca(OH)2), sodium hydroxide (NaOH), and sodium carbonate (Na2CO3). Target ions to remove from the AMD solution included Al (1233 mg/L), Cu (77.26 mg/L), Fe (16.7 mg/L), Ni (1.54 mg/L), Mn (161.5 mg/L) and Zn (48.89 mg/L)). Both alumina industry wastes were shown to produce treated water with acceptable discharge limits for all metals except Mn. Nevertheless, Bayer precipitate was shown to have an enhanced ability to remove manganese at lower pH (6.5–7.5) relative to lime, with residual Mn concentrations of 32.30 and 85.40 mg/L, respectively. Manganese discharge limits were challenging to meet due to pH values >9 being required wherein not only aluminium species redissolved but also the pH was not compatible with discharge regulations. Mechanistically, larger precipitates were found to positively influence the removal of heavy metals, with lime and Bayer precipitates forming the largest precipitates. Overall, Bayer precipitate was found to be a potential alternative for the treatment of AMD water.

Generation of reactive oxygen species in relevant cell lines as a bio-indicator of oxidative effects caused by acid mine water

Reactive oxygen species (ROS) production and resultant oxidative stress (OS) has been implicated as a pathway of toxicity in animal species exposed to pollutants. The gills of aquatic animals and the liver and kidneys of mammalian species are specific cellular sites of toxicity. Oxidative effects of acid mine drainage effluent (following passive and active treatment) impacting a natural stream were assessed using selected cell lines. Levels of pollutants such as heavy metals in acid mine drainage (AMD) effluent can be quantified following treatment, but it is unknown whether this is associated with equivalent reduction in toxicity. ROS production by AMD untreated (U) and after treatment (T) was quantified in a fish gill cell line (RTgill-W1) and in two mammalian cell lines (C3A human liver and Vero monkey kidney). ROS production was determined using the oxidant sensitive fluorogenic probe, 2′, 7′-dichlorofluorescein diacetate (DCFH-DA) following exposure to U and T, AMD water. Treatment of AMD water caused reduction in levels of Al, Zn, Fe, Si and Mn while levels of Cr, Cu, Ar and Hg remained unchanged. A dose-dependent increase in ROS production was observed for U and T. ROS formation decreased from 14% to 4.5%, 16.4% to 7.2% and 25.3% to 17.7% in the RTgill-W1, C3A, and Vero cell lines exposed to 100% AMD water, U and T. The presence of Mn and/or other ions in treated water and subsequent ROS formation indicates that water could still be toxic to cells and requires further processing. The DCFH-DA assay in several cell lines can be used to rapidly bio-monitor quality of AMD water related to formation of ROS and subsequent cellular effects. However, cut-off levels for cellular toxicity must be established to ensure safety of this water for aquatic animals and for animal and human consumption.

The study of leachability and toxicity of sludge after neutralization of Saraka and Robule AMD wastewaters

Acid mine drainage (AMD) waters are one of the most important ecological risks at the global level because of its high heavy metals content and strong acidity. Treatment of AMD water is a complex and expensive. One of the most widely used treatment process is the neutralization process of AMD. The result of neutralization is the production of sludge which may contain various other (heavy) metals, depending on the chemical characteristics of the mine water treated. In this paper, leachability and toxicity of the sludges obtained during the neutralization process of wastewater from Saraka and Robule acid mine drainage and the sludges after the stabilization process at different temperatures is tested. Sludge produced in the neutralization process of Robule AMD R4 (40) and stabilized on 105°C and 200°C shows a H8-corrosiveness characteristic. Stabilized sludge show tendency to lower leachability of zinc and copper, but without influence on sulphate leachability. Sludges that show a H8-corrosiveness needs additional stabilization/neutralization pretreatment prior temperature treatment.

Valorization of Phosphate Waste Rocks and Sludge from the Moroccan Phosphate Mines: Challenges and Perspectives

Sedimentary phosphate mines produce millions of tons of waste rocks during their open-pit mining. In addition, during ore phosphate beneficiation, fluorapatite is separated from associated gangue minerals by a combination of successive mineral processing steps that involve crushing / screening, washing, and flotation. These operations generate large volume of tailings (called phosphate sludge) that are deposited in large surface ponds and waste rocks stockpiled within the mining site. The potential reuse of these phosphate mine by-products (waste rocks and sludge) has been investigated in the last 10 years.The first investigated option consisted in using the alkaline waste rocks (APW) to control the acid mine drainage (AMD). Indeed, these alkaline mine wastes contain significant quantities of calcite (46 wt%) and dolomite (16 wt%) that help in neutralizing the acidity generated by the wastes from the closed Kettara mine, located near Marrakech, Morocco. The addition of 15 wt% APW to the coarse Kettara tailings produced leachates with significantly lower acidity and metal loads in comparison to the un-amended control sample. Secondly, the efficiency of APW was assessed in the laboratory as an alternative alkaline material for passive AMD water treatment. In semi-arid climate, the oxic passive treatment has been proven to be the most suitable. The pH of the water and its quality were significantly improved. As a third option, the hydrogeotechnical characterization of original and screened phosphate limestone waste rocks as well as the phosphate sludge showed their suitability for use as a component of store-and-release (SR) covers for industrial mine site reclamation. Lab tests (columns) and field tests (instrumented columns and experimental cells) showed that water infiltration can be controlled, even for extreme rainfall events (150mm/day), by 1 m thick of a SR cover made with APW. Further research is currently being investigated around the recycling and valorization of phosphate sludge from phosphate mines as ceramics. Furthermore, the overburden of the phosphates sedimentary basins are mainly composed of marls; limestones blocks; silex bed; silex nodule; marls and clays; silicified limestone; which have a significant reuse potential as marble-mosaic floor, mortars and concrete, and natural stone products slabs for floors and stairs.

The development of bio-carbon adsorbents from Lodgepole Pine to remediate acid mine drainage in the Rocky Mountains

Abstract Activated carbon adsorbents were produced from biomass locally available in the Rocky Mountain West, e.g. Lodgepole Pine ( Pinus contorta ), by vacuum pyrolysis at moderate temperatures followed by steam activation, for use as metal adsorbents for acid mine drainage (AMD). Wood cubes from fresh cut Lodgepole Pine ( P. contorta ) with different sizes, 3 and 12 mm, were made. Sawdust was also used to study the effect of sample size as well as sample material. We applied chemical pretreatment with potassium hydroxide before charring to improve the quality of the activated carbons. We compared the characteristics of the activated carbons, which were chemically pretreated, before and after washing with water. After washing, the BET surface area was found to increase and diffuse reflectance infrared spectroscopy showed changes in the carbon matrix. We then tested the samples for metal adsorption from AMD sampled from AMD sites in Colorado, Clear Creek County and the Leadville mine drainage tunnel, along with a commercial activated carbon for comparison. We used a batch method to measure maximum metal adsorption of the activated carbons. The metals chosen to be monitored were copper, cadmium, manganese, nickel, lead, and zinc, because they are the principal metals of interest for the test areas, and metal concentrations were determined by ion coupled plasma–atomic emission spectroscopy. The samples produced in this work outperformed the commercial activated carbon in two AMD water treatment tests and for the six metals monitored. This metal adsorption data indicate that locally produced inexpensive activated carbons can be used as adsorbents for AMD successfully.

An ecological risk assessment for a South African acid mine drainage

Biotic integrity assessment of a stream subject to acid mine drainage (AMD) indicated that a number of the expected taxa were absent. Acute and chronic toxicity assessment of water sampled in a stream subject to AMD impact indicate that even at near neutral pH the metal concentration in the water dominates the toxicity toward Daphnia pulex. Extending the observation period to the death of test cohort in an otherwise standard sub-chronic toxicity test, allowed for generating a life table for the D. pulex. The probability of population extinction was estimated from the statistical characteristics of a bootstrap estimation of the dominant eigenvalue of a Leslie matrix based on the life table. At the current concentration levels of metals, notably manganese and zinc, in the water, a high risk to aquatic life exists. It is suggested that the metal content of the stream water also be addressed in an AMD water treatment plan.

An ecological risk assessment for a South African acid mine drainage

Biotic integrity assessment of a stream subject to acid mine drainage (AMD) indicated that a number of the expected taxa were absent. Acute and chronic toxicity assessment of water sampled in a stream subject to AMD impact indicate that even at near neutral pH the metal concentration in the water dominates the toxicity toward Daphma pulex. Extending the observation period to the death of test cohort in an otherwise standard sub-chrome toxicity test, allowed for generating a life table for the D. pulex. The probability of population extinction was estimated from the statistical characteristics of a bootstrap estimation of the dominant eigenvalue of a Leslie matrix based on the life table. At the current concentration levels of metals, notably manganese and zinc, in the water, a high risk to aquatic life exists. It is suggested that the metal content of the stream water also be addressed in an AMD water treatment plan.