Acid mine drainage (AMD) treatment by neutralization: Evaluation of physical-chemical performance and ecotoxicological effects on zebrafish (Danio rerio) development

Efficiency of sodium phytate in the remediation of As, Mn, and Cu contamination in acid mine drainage using water hyacinth

The accumulation and uptake efficiency of heavy metals, including As, Mn, and Cu, in water hyacinth (Eichhornia crassipes (Mart.) Solms) grown in synthetic acidic wastewater supplemented with sodium phytate (SP) was examined. Three treatments were studied using synthetic acidic wastewater containing 0.25, 5.0, and 1.0 mg/L of As, Mn, and Cu, respectively, (SM + heavy metals) and having pH in the range of 4-6, which comprised of (1) control treatments using SM + heavy metals at pH 4, 5, 6 without SP, and treatments using SM + heavy metals at pH 4, 5, 6 with SP: Cu (2) in a 1:3 M ratio and (3) a 1:6 M ratio. The translocation factor (TF < 1) indicated that plants had a lower capacity to transport heavy metals from the roots to the stems. The shoots of water hyacinth exhibited the highest capacity to absorb and store As in the pH 4-treatment with SP (SP:Cu1:3 mol), whereas the roots showed the greatest capacity at pH 4 without SP. The roots and shoots of the water hyacinth showed the greatest capacity to take up and store Mn in the pH 5-treatment with a 1:3 M ratio of SP:Cu. The roots showed the greatest capacity to take up and store Cu in the pH 6-treatment, and the shoots showed the highest capability in the pH 5-treatment with 1:3 M ratio of SP:Cu. Moreover, analysis of the chemical forms revealed that As accumulated in the arsenate form, whereas Mn accumulated in the divalent form.

Effect of environmental level of methomyl on hatching, morphology, immunity and development related genes expression in zebrafish (Danio rerio) embryo

The extensive use of carbamate pesticides has led to a range of environmental and health problems, such as surface and groundwater contamination, and endocrine disorders in organisms. In this study, we focused on examining the effects of toxic exposure to the carbamate pesticide methomyl on the hatching, morphology, immunity and developmental gene expression levels in zebrafish embryos. Four concentrations of methomyl (0, 2, 20, and 200 μg/L) were administered to zebrafish embryos for a period of 96 h. The study found that exposure to methomyl accelerated the hatching process of zebrafish embryos, with the strongest effect recorded at the concentration of 2 μg/L. Methomyl exposure also trigged significantly reductions in heart rate and caused abnormalities in larvae morphology, and it also stimulated the synthesis and release of several inflammatory factors such as IL-1β, IL-6, TNF-α and INF-α, lowered the IgM contents, ultimately enhancing inflammatory response and interfering with immune function. All of these showed the significant effects on exposure time, concentration and their interaction (Time × Concentration). Furthermore, the body length of zebrafish exposed to methomyl for 96 h was significantly shorter, particularly at higher concentrations (200 μg/L). Methomyl also affected the expression levels of genes associated with development (down-regulated igf1, bmp2b, vasa, dazl and piwi genes), demonstrating strong developmental toxicity and disruption of the endocrine system, with the most observed at the concentration of 200 μg/L and 96 h exposure to methomyl. The results of this study provide valuable reference information on the potential damage of methomyl concentrations in the environment on fish embryo development, while also supplementing present research on the immunotoxicity of methomyl.

Acid mine drainage (AMD) treatment using galvanic electrochemical system Al-Cu

Acid mine drainage was evaluated using a galvanic (GV) electrochemical system, Al-Cu (anode/cathode), based on a 32 factorial design. The factors analyzed were anodic area/volume ratios (A/V) of 0.037, 0.072, and 0.112 cm2/cm3, and treatment time from 0.25-8 h, and analyses were performed in duplicate with 11 degrees of freedom. The response variables were the total dissolved solids and concentrations of As, Cu, Co, Cr, Pb, Fe, Ni, and S O 4 2 - . The pH, electrical conductivity, and temperature were monitored during the process. Significant differences between treatments were determined by analysis of variance with Tukey's test (p < 0.05) using Statgraphics Centurion XVI.I software. The results showed that a greater electrode surface, A/V ratio, and treatment time improved pollutant removal. The spontaneous reactions generated by the galvanic cell, through the current that flows owing to the potential difference between the Al and Cu electrodes, allows the removal of heavy metals, arsenic, and S O 4 2 - by coagulation and precipitation mechanisms. The removal efficiencies achieved were Cu (99.1%), As (76.6%), Ni (80.2%), Pb (83.6%), Cr (100%), Fe (93.71%), and 92.9% for sulfates. The X-ray diffraction and Raman analyses of the solid fraction indicated that cuprite was formed with a purity of 96%, and the recovery of Cu by the GV system may be a viable option for mining companies.

The interplay between microalgae and toxic metal(loid)s: mechanisms and implications in AMD phycoremediation coupled with Fe/Mn mineralization

Acid mine drainage (AMD) is low-pH with high concentration of sulfates and toxic metal(loid)s (e.g. As, Cd, Pb, Cu, Zn), thereby posing a global environmental problem. For decades, microalgae have been used to remediate metal(loid)s in AMD, as they have various adaptive mechanisms for tolerating extreme environmental stress. Their main phycoremediation mechanisms are biosorption, bioaccumulation, coupling with sulfate-reducing bacteria, alkalization, biotransformation, and Fe/Mn mineral formation. This review summarizes how microalgae cope with metal(loid) stress and their specific mechanisms of phycoremediation in AMD. Based on the universal physiological characteristics of microalgae and the properties of their secretions, several Fe/Mn mineralization mechanisms induced by photosynthesis, free radicals, microalgal-bacterial reciprocity, and algal organic matter are proposed. Notably, microalgae can also reduce Fe(III) and inhibit mineralization, which is environmentally unfavorable. Therefore, the comprehensive environmental effects of microalgal co-occurring and cyclical opposing processes must be carefully considered. Using chemical and biological perspectives, this review innovatively proposes several specific processes and mechanisms of Fe/Mn mineralization that are mediated by microalgae, providing a theoretical basis for the geochemistry of metal(loid)s and natural attenuation of pollutants in AMD.

Separation of Hydrochloric Acid and Oxalic Acid from Rare Earth Oxalic Acid Precipitation Mother Liquor by Electrodialysis

In this study, the hydrochloric acid from rare earth oxalic acid precipitation mother liquor was separated by electrodialysis (ED) with different anion exchange membranes, including selective anion exchange membrane (SAEM), polymer alloy anion exchange membrane (PAAEM), and homogenous anion exchange membrane (HAEM). In addition to actual wastewater, nine types of simulated solutions with different concentrations of hydrochloric acid and oxalic acid were used in the experiments. The results indicated that the hydrochloric acid could be separated effectively by electrodialysis with SAEM from simulated and real rare earth oxalic acid precipitation mother liquor under the operating voltage 15 V and ampere 2.2 A, in which the hydrochloric acid obtained in the concentrate chamber of ED is of higher purity (>91.5%) generally. It was found that the separation effect of the two acids was related to the concentrations and molar ratios of hydrochloric acid and oxalic acid contained in their mixtures. The SEM images and ESD-mapping analyses indicated that membrane fouling appeared on the surface of ACS and CSE at the diluted side of the ED membrane stack when electrodialysis was used to treat the real rare earth oxalic acid precipitation mother liquor. Fe, Yb, Al, and Dy were found in the CSE membrane section, and organic compounds containing carbon and sulfur were attached to the surface of the ACS. The results also indicated that the real rare earth precipitation mother liquor needed to be pretreated before the separation of hydrochloric acid and oxalic acid by electrodialysis.

Simultaneous removal of arsenite and arsenate from mining wastewater using ZIF-8 embedded with iron nanoparticles

Arsenic contamination is an increasing global environmental problem, especially in mining industry wastewater where both arsenite (As(III)) and arsenate (As(V)) have been routinely detected. In this paper, a novel porous metal-organic framework material (ZIF-8) was composited with iron nanoparticles (FeNPs) to form a functional material (ZIF-8@FeNPs) for the simultaneous removal of As(III)/(V) from wastewater. The material effectively removed both As(III) and As(V) with removal efficiencies of 99.9 and 71.2%, respectively. Advanced characterization techniques including X-ray photoelectron spectroscopy (XPS) and Fourier infrared (FTIR) indicated that removal of As(III) and As(V) involved complex formation. Adsorption kinetics followed a pseudo-second order kinetics indicating adsorption involved chemisorption. After four cycles of reuse the he removal rate of As species was still relatively high at > 60% When ZIF-8@FeNPs were used to remove As from real wastewater from acid mines the removal efficiency was 94.27%. Finally, a As(III) and As(V) removal mechanism was proposed.

Resource Utilization of Acid Mine Drainage (AMD): A Review

Acid mine drainage (AMD) is a typical type of pollution originating from complex oxidation interactions that occur under ambient conditions in abandoned and active mines. AMD has high acidity and contains a high concentration of heavy metals and metalloids, posing a serious threat to ecological systems and human health. Over the years, great progress has been made in the prevention and treatment of AMD. Remediation approaches like chemical neutralization precipitation, ion exchange, membrane separation processes, and bioremediation have been extensively reported. Nevertheless, some limitations, such as low efficacy, excessive consumption of chemical reagents, and secondary contamination restrict the application of these technologies. The aim of this review was to provide updated information on the sustainable treatments that have been engaged in the published literature on the resource utilization of AMD. The recovery and reuse of valuable resources (e.g., clean water, sulfuric acid, and metal ions) from AMD can offset the cost of AMD remediation. Iron oxide particles recovered from AMD can be applied as adsorbents for the removal of pollutants from wastewater and for the fabrication of effective catalysts for heterogeneous Fenton reactions. The application of AMD in beneficiation fields, such as activating pyrite and chalcopyrite flotation, regulating pulp pH, and leaching copper-bearing waste rock, provides easy access to the innovative utilization of AMD. A review such as this will help researchers understand the progress in research, and identify the strengths and weaknesses of each treatment technology, which can help shape the direction of future research in this area.

Passive multi-unit field-pilot for acid mine drainage remediation: Performance and environmental assessment of post-treatment solid waste

This study evaluated the performance of a passive multi-unit field-pilot operating for 16 months to treat acid mine drainage (AMD) from a coal mine in Colombia Andean Paramo. The multi-unit field-pilot involved a combination of a pre-treatment unit (550 L) filled with dispersed alkaline substrate (DAS), and six passive biochemical reactors (PBRs; 220 L) under two configurations: open (PBRs-A) and closed (PBRs-B) to the atmosphere. The AMD quality was 1200 ± 91 mg L^-1 Fe, 38.0 ± 1.3 mg L^-1 Mn, 8.5 ± 1.6 mg L^-1 Zn, and 3200 ± 183.8 mg L^-1 SO₄^2-, at pH 2.8. The input and output effluents were monitored to establish AMD remediation. Physicochemical stability of the post-treatment solids, including metals (Fe²⁺, Zn²⁺, and Mn²⁺) and sulfates for environmental contamination from reactive mixture post-treatment, was also assessed. The passive multi-unit field-pilot achieved a total removal of 74% SO₄^2-, 63% Fe²⁺, and 48% Mn²⁺ with the line of PBRs-A, and 91% SO₄^2-, 80% Fe²⁺, and 66% Mn²⁺ with the line of PBRs-B, as well as 99% removal for Zn²⁺ without significant differences (p < 0.05) between the two lines. The study of the physicochemical stability of the post-treatment solids showed they can produce acidic leachates that could release large quantities of Fe and Mn, if they are disposed in oxidizing conditions; contact with water or any other leaching solutions must be avoided. Therefore, these post-treatment solids cannot be disposed of in a municipal landfill. The differences in configuration between PBRs, open or closed to the atmosphere, induced changes in the performance of the passive multi-unit field-pilot during AMD remediation.

Inhibition of organosilane/ATP@HQ self-healing passivator for pyrite oxidation

Organosilane, with functional organic groups attached to inorganic silicon atoms, exhibits excellent passivation performance for pyrite. However, a considerable number of micro-cracks will gradually appear on the surface of passivation film under long-term corrosion of oxidizing medium, resulting in a significant decrease of passivation effect. To improve the stability and long-term performance of organosilane coating, a novel passivator (PT-ATP@HQ) with self-healing function was prepared to inhibit the oxidation of pyrite. We chose 3-mercaptopropyltrimethoxysilane (Prop-SH) and tetraethoxysilane (TEOS) as the host coating (PT), and attapulgite clay (ATP) loaded with 8-hydroxyquinoline (8-HQ) was used to endow the coating with better passivation and self-healing performance. The electrochemical and chemical leaching results showed that the addition of ATP@HQ greatly improved the passivation performance of PT coating. The passivation efficiencies of total Fe and SO₄^2- reached to 88.1% and 79.2%, respectively. We also found that the protective capability of the scratched PT-ATP@HQ coating can be recovered automatically through 8-HQ release from ATP. The passivation and self-healing mechanisms were investigated by FT-IR, XPS, ²⁹Si NMR, and other characterization methods, which were as follows: firstly, the organosilanes hydrolyzed to form highly active silanol groups, then dehydration condensation reaction occurred between silanol molecules and ATP@HQ to obtain cross-linked network structure connected by Si-O-Si bonds. After that, Si-OH groups reacted with the hydroxyl groups of pyrite to form Fe-O-Si bonds, thereby an inert and dense passivation film attached to the surface of pyrite. Once the passivation film is locally damaged, 8-HQ will automatically release to repair the cracks.

Ecotoxicity assessment of a molybdenum mining effluent using acute lethal, oxidative stress, and osmoregulatory endpoints in zebrafish (Danio rerio)

The present study investigated the ecotoxicity of raw mining effluent from the largest molybdenum (Mo) open-pit mine in the Qinling mountains, China, and the treated effluent with neutralization and coagulation/adsorption processes, using zebrafish (Danio rerio). The results showed the following: (1) the mining effluent is acid mine drainage (AMD) and is highly toxic to zebrafish with a 96-h median lethal concentration (LC₅₀) of 3.80% (volume percentage) of the raw effluent; (2) sublethal concentrations of the raw effluent (1/50, 1/10, and 1/2 96-h LC₅₀) induced oxidative stress and osmoregulatory impairment, as reflected by the alterations in activities of superoxide dismutase and catalase and contents of malondialdehyde, and inhibition of Na⁺, K⁺-ATPase activity in gills and muscle after 28 days of sub-chronic exposure when compared with the unexposed group; and (3) the treatment of the raw effluent with neutralizer (NaOH) and adsorbent activated carbon reduced the acute lethal effect of raw effluent. The used endpoints including acute lethal and biochemical parameters related to oxidative stress and osmoregulatory impairment in zebrafish are cost-effective for toxicity assessment of AMD like the studied Mo mining effluent. Mining effluent management strategies extended by these results, i.e., the restriction of discharging raw and diluted effluent to adjacent waterways and the introduction of bio-monitoring system across all mining drainages in this area, were also proposed and discussed.

Effect of neutralizing agents on the type of As co-precipitates formed by in situ Fe oxides synthesis and its impact on the bioaccessibility of As in soil

The bioaccessibility of heavy metals in soil is closely related to their potential risk. Therefore, developing techniques for reducing it needs considerable attention. In this study, we aimed to co-precipitate soil As(V) through an in situ formation of Fe oxides, thereby reducing its bioaccessibility. Soil As(V) was co-precipitated by introducing 2% Fe-nitrate (w/w) and 30% water (v/w) into soil at pH ~7. Two different neutralizing agents (NaOH and CaO) were used to induce the precipitation of Fe oxides, and their effects on the speciation of As were investigated. In all the stabilized soils, the exchangeable As fraction decreased, and the fraction of As bound to amorphous Fe oxides increased by a factor of more than 1.4. In contrast, a marked decrease in bioaccessibility of As was achieved using NaOH (40% to 7%). X-ray absorption spectroscopy analysis demonstrated that highly bioaccessible forms of calcium iron arsenate (yukonite and arseniosiderite) could be generated in CaO-stabilized soil. Our study found that neutralizing agents may play an important role in stabilizing As(V) and lowering its bioaccessibility through determining the type of formed Fe oxides in soil.

Removal of Pollutants from an AMD from a Coal Mine by Neutralization/Precipitation Followed by “In Vivo” Biosorption Step with the Microalgae Scenedesmus sp

This work evaluates the benefits of a complementary treatment step of acid mine drainage (AMD) using the algae Scenedesmus sp. in terms of algae biomass production, residual metal removal, and the toxicity of the discharged water. Conventional treatment by neutralization/precipitation of an AMD from a coal mine in Brazil was conducted with Ca(OH)2 at pH 8.7. Algal growth studies were performed in the treated AMD, with and without a nutrient supply. The raw effluent and treatments were compared in terms of residual concentration of metals and sulfate, conductivity, and toxicity with the Allium cepa and Daphnia magna test organisms. The results show that the conventional treatment allowed a major metal removal, reduction in the conductivity, and good indices in the toxicological parameters evaluated. The biosorption with in vivo microalgae improved the quality of the effluent for residual metals. No significant toxicity was observed to Allium cepa in all treatments performed, while the Daphnia magna test indicated a reduction in toxicity after the biosorption step. It was concluded that algae growth can be carried out in treated mine waters, providing algae biomass and helping to achieve the standards for water discharge.