Acid Mine Drainage Samples Research Articles

Assessment of Characteristics of Acid Mine Drainage Treated with Fly Ash

Acid mine drainage (AMD) occurs naturally in abandoned coal mines, and it contains hazardous toxic elements in varying concentrations. In the present research, AMD samples collected from an abandoned mine were treated with fly ash samples from four thermal power plants in Singrauli Coalfield in the proximate area, at optimized concentrations. The AMD samples were analyzed for physicochemical parameters and metal content before and after fly ash treatment. Morphological, geochemical and mineralogical characterization of the fly ash was performed using SEM, XRF and XRD. This laboratory-scale investigation indicated that fly ash had appreciable neutralization potential, increasing AMD pH and decreasing elemental and sulfate concentrations. Therefore, fly ash may be effectively used for AMD neutralization, and its suitability for the management of coalfield AMD pits should be assessed further.

The removal of pollutants and natural organic compounds from acid mine drainage using a combination of bentonite clay and MgSO4

Abstract 200 mL of synthetic acid mine drainage (AMD) sample was poured into five 500 mL glass beakers and treated in a jar test and a shaker in sets of experiments, respectively. The samples were treated in small-scale laboratory experiments using synthetic AMD sample dosed with bentonite clay and MgSO4 respectively, and a flocculant consisting of the same reagents. The pH, EC, turbidity and oxidation reduction potential were measured. The removal of turbid materials in the samples dosed with a flocculant is higher compared to those of the samples dosed with each reagent alone. The samples with flocculant dosage show high removal efficiency of natural organic compounds and toxic metals, slightly higher compared to those with a dosage of a combination of bentonite clay and MgSO4. The removal efficiency of the samples treated in a shaker is better than those with rapid mixing. The SEM micrographs show sorption is a physico-chemical phenomenon.

Arsenic (V) Removal by an Adsorbent Material Derived from Acid Mine Drainage Sludge

Arsenic is a toxic element that is often found in drinking water in developing countries in Asia, while arsenic poisoning is a serious worldwide human health concern. The objective of this work is to remove arsenic (V) (As(V)) from water by using an adsorbent material prepared from mine waste, called MIRESORBTM, which contains Fe, Al. The performance of the MIRESORBTM adsorbent was compared with granular ferric hydroxide (GFH), which is a commercial adsorbent. Adsorbents were characterized by using scanning electron microscopy (SEM), X-ray fluorescence spectroscopy (XRF), X-ray diffractometry (XRD), and N2 sorption with Brunauer–Emmett–Teller (BET) analysis. The kinetics, isotherms, and pH-dependency of arsenic adsorption were interrogated to gain insights into arsenic adsorption processes. The maximum adsorption capacity of MIRESORBTM was 50.38 mg/g, which was higher than that of GFH (29.07 mg/g). Moreover, a continuous column test that used environmental samples of acid mine drainage was conducted to evaluate the MIRESORBTM material for practical applications. The column could be operated for more than 5840 bed volumes without a breakthrough. Successful operation of a pilot plant using MIRESORBTM adsorbent was also reported. Thus, these studies demonstrate MIRESORBTM as a highly efficient and economical adsorbent derived from recycled mine sludge waste.

Acid-adapted microalgae exhibit phenotypic changes for their survival in acid mine drainage samples.

Phenotypic plasticity or genetic adaptation in an organism provides phenotypic changes when exposed to the extreme environmental conditions. The resultant physiological and metabolic changes greatly enhance the organism's potential for its survival in such harsh environments. In the present novel approach, we tested the hypothesis whether acid-adapted microalgae, initially isolated from non-acidophilic environments, can survive and grow in acid-mine-drainage (AMD) samples. Two acid-adapted microalgal strains, Desmodesmus sp. MAS1 and Heterochlorella sp. MAS3, were tested individually or in combination (co-culture) for phenotypic changes during their growth in samples collected from AMD. The acid-adapted microalgae in AMD exhibited a two-fold increase in growth when compared with those grown at pH 3.5 in BBM up to 48h and then declined. Furthermore, oxidative stress triggered several alterations such as increased cell size, granularity, and enhanced lipid accumulation in AMD-grown microalgae. Especially, the apparent limitation of phosphate in AMD inhibited the uptake of copper and iron in the cultures. Interestingly, growth of the acid-adapted microalgae in AMD downregulated amino acid metabolic pathways as a survival mechanism. This study demonstrates for the first time that acid-adapted microalgae can survive under extreme environmental conditions as exist in AMD by effecting significant phenotypic changes.

The removal of turbid materials from AMD using bentonite clay, Fe or Al salt, MgCO3 and flocculent with varying agitations

Abstract A series of experiments was conducted using 200 mL of acid mine drainage (AMD) collected from Krugersdorp, South Africa, to determine turbid materials removal efficiency of a combination of bentonite clay, Fe or Al salt and MgCO3. The sample was poured into five 500 mL glass beakers using bentonite clay, FeCl3, AlCl3 and MgCO3 dosage respectively. The samples were treated in jar test at rapid and slow mixing, allowed to settle for 1 hour, then the pH, conductivity, total suspended solids (TSS), dissolved oxygen (DO) and oxidation reduction potential (ORP) were measured (exp A). A second and third similar sets of experiments were conducted with a combination of bentonite clay and MgCO3 (flocculent) dosage (exp B), and FeCl3 with slow mixing only (exp C). Experimental results revealed that the pH of treated effluent with bentonite clay does not exhibit significant increasing trend because of insignificant hydrolysis, whereas the pH of samples with FeCl3, AlCl3 and MgCO3 exhibit a slight decreasing trend, showing a low rate of hydrolysis. The DO and ORP of treated effluent does not show a significant changing trend compared to the untreated AMD sample. Residual TSS of the AMD samples treated with a flocculent is lower than the samples treated with bentonite clay, FeCl, AlCl3 and MgCO3. Residual turbidity of the samples with rapid mixing is identical to that of the corresponding samples with slow mixing. TSS removal efficiency of a flocculent is higher compared to other reagents. The results show that synthetic flocculent is an ideal replacement for inorganic coagulants. The scanning electron microscopy (SEM) micrographs exhibit slides with dense-sponge like flocs showing high adsorption capacity.

Solid-State pH Sensors for Mine Water Monitoring

Introduction The monitoring of water quality parameters such as pH, redox potential, and conductivity is essential in order to investigate the variety of hydrochemical processes occurring in aqueous environments. For a better understanding of these processes, measurements with high temporal resolution are needed, which cannot be achieved with manual sampling procedures. Hence, alternative technical analysis methods, such as sensors, are used to monitor relevant parameters in-situ. Unfortunately conventional probes often experience harsh or detrimental conditions during on-site deployment. All-solid-state potentiometric sensors have been proposed as robust alternatives for demanding environments that deliver results with sufficient accuracy, at relatively low-cost, with experimental and instrumental simplicity [1].This work focuses on the development of a solid-state pH sensor for the monitoring of mine water and acid mine drainage (AMD). AMD is the consequence of uncontrolled sulfidic mineral oxidation, typically as a result of ore or coal mining practices. The resulting outflow of acidic water, which can contain high concentrations of metal ions, is potentially disastrous to aquatic life and also poses a great threat to water supplies [2]. Our aim is to develop a robust and cost-effective sensor that enables in-situ AMD monitoring in mines and surrounding waterways, as well as pit lakes formed as the result of flooded open-pit mines. With increased spatial and temporal resolution in comparison to manual sampling, these sensors will help to predict hazardous conditions and increase the understanding of the complex underlying geochemical mechanisms. Methods The proposed sensor consists of a pH sensitive iridium oxide (IrOx) layer in combination with a solid-state reference electrode. During sensor fabrication structured titanium and gold electrodes were deposited on oxidised silicon substrates using standard cleanroom techniques. IrOx was subsequently electrochemically coated on these electrodes via cyclic voltammetry. The deposition solution was prepared according to the protocol published by Marzouk [3]. In a three electrode configuration (reference: 3 M KCl Ag/AgCl, counter: platinum gauze) the prepared metal electrodes functioned as the working electrodes. Homogenous IrOx layers with a thickness around 80 nm were obtained after 100 cycles at 0.1 V/s between -0.5 V and 0.85 V or -0.7 V and 0.9 V for the gold and titanium electrodes respectively (see Figures 1 and 2).Several approaches for the construction of solid state reference electrodes (SSREs) have been presented in literature [4]. In this work, salt-saturated polymers were deposited on Ag/AgCl layers, similar to [5]. The selected polymers were either unsaturated polyester resins or UV-curing epoxy-based resins. These resins were mixed with up to 70 ma% of finely ground KCl. The resulting slurry was dropped on Ag/AgCl electrodes and cured to form the SSREs.Data collection was performed with EZO-circuits from Atlas Scientific in connection with a RaspberryPi or an ESP32-based microcontroller using I2C or serial protocols.The fabricated IrOx electrodes were characterised regarding their pH sensing performance. Their sensitivity was evaluated by recording the open circuit potential (OCP) vs. a commercial reference electrode (3 M KCl, Ag/AgCl) during a titration of a Briton-Robinson buffer with 0.5 M KOH at 25°C. Drift rates were measured in standard buffer solutions. In order to determine the SSRE’s electrochemical potential stability, OCP was recorded versus a conventional reference electrode in KCl solutions of varying concentration at 25°C. Results and Conclusions As shown in Figure 3, the IrOx electrodes exhibit a super-Nernstian pH sensitivity of around -73 mV/pH between pH 2 to 11.5. These values are comparable to published results [3]. Electrodes from several batches fabricated on different days show high reproducibility with respect to sensitivity and intercept, as indicated by the closely overlaying data points in Figure 3. These results suggest a high robustness of the coating process. The drift rate of the IrOx electrodes is less than 1 mV/h which is sufficient for the intended application. The functionality of the SSRE can be deducted from the data given in Figure 4: An uncoated Ag/AgCl electrode exhibits Nernstian behavior to changes in chloride ion concentration whereas the fabricated SSRE with a polymer coating shows a stable potential. The combination of SSRE and IrOx electrode results in a potentiometric pH sensor whose output changes with pH as shown in Figure 5. Outlook Future work will focus on improving the sensing characteristics as well as measurements in AMD samples. Eventually on-site deployment of the sensors is planned. Additionally, first experiments to transfer the electrodes to flexible and chemically inert substrates for ultimate robustness and potential applications in smart robotic skins have been conducted (see Figure 6). Acknowledgments This research has been funded by the European Social Fund (ESF) and the Free State of Saxony. (ARIDuA , project number 100310491).

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

Acid mine drainage (AMD) represents a major problem in the mining industry worldwide due to the risk of water and soil pollution. Its active treatment involves the addition of alkaline reagents such as NaOH or Ca(OH)2 to increase the pH and precipitate the dissolved metals, although substantial amounts of dissolved ions might persists. Under a remediation approach, the aim of this work was to assess the chemical and physical characteristics of treated effluent and to evaluate its ecotoxicological effects on zebrafish (Danio rerio) embryonic and larval stages, through developmental, functional, morphological, and behavioral end-points. The studied AMD sample, highly associated with pyrite, presented high sulfate and dissolved metal ions content and was submitted to the following treatment conditions: NaOH - pH 7.0 and 8.7, and Ca(OH)2 - pH 7.0 and 8.7. All neutralizing treatments resulted in a satisfactory reduction of the metals concentration, with best results achieved using Ca(OH)2 at pH 8.7; although Mn and As still remained above or very near the discharge maximum limits according to Brazilian legislation. Therefore, an additional step was employed to Mn and As adsorption by algal biomass. Regarding in-vivo toxicological assays, no significant lethality was recorded in all treated AMD groups, although adverse effects were observed in all endpoints analyzed. Ca(OH)2 groups performed closer to control than NaOH-treated groups. The additional polishing stage treatment with the algae Scenesmus sp. allowed tenuous improvements in terms of removal of residual amounts of As and Mn but not in the toxicological characteristics of treated AMD.

Quantification of Tl (I) and Tl (III) based on microcolumn separation through ICP-MS in river sediment pore water.

Thallium (Tl) is a typical toxic element, whose biological effects and geochemical behavior are closely related with its chemical speciation in the environment. In this context, the objective of the present study was to develope an effective method for separation of Tl (I) and Tl (III) based on solid-phase extraction (SPE) using anion exchange resin AG1-X8 as a sorbent and ICP-MS measurement. In this proposed method, Tl (I) and Tl (III) could be separated by selective adsorption of Tl (III)-DTPA in the resin, while Tl (III) was eluted by the solution mixed with HCl and SO2. The validity of this method was confirmed by assays of standard solutions of Tl (I) and Tl (III), as well as with spike of contaminated samples. The present study results revealed that higher concentration of Tl (I) (245.48μg/l) and Tl (III) (20.92μg/l) had been found near the acid mine drainage (AMD) sample of sediment pore water. The results revealed that Tl (I) of 61.47μg/l and Tl (III) of 9.73μg/l were present in the river water contaminated by acid mine drainage. This thallium speciation analysis implied that the dominant Tl (I) species in the river water studied might be due to the weathering of sulfide mineral-bearing rocks, mining, and smelting activities in the studied area.

Formation and prevention of pipe scale from acid mine drainage at iron Mountain and Leviathan Mines, California, USA

Pipelines carrying acid mine drainage (AMD) to treatment plants commonly form pipe scale, an Fe(III)-rich precipitate that forms inside the pipelines and requires periodic and costly cleanout and maintenance. Pipelines at Iron Mountain Mine (IMM) and Leviathan Mine (LM) in California carry acidic water from mine sources to a treatment plant and have developed pipe scale. Samples of scale and AMD were collected from both mine sites for mineralogical, microbiological, and chemical analysis. The scale mineralogy was primarily schwertmannite with minor amounts of poorly crystalline goethite. Although the bulk composition of the scale was similar along the length of the pipeline at IMM, the number of iron-oxidizing bacteria and concentrations of associated trace elements decreased along the flow path inside the pipeline. Laboratory batch experiments with unfiltered AMD from IMM and LM showed that Fe(II) oxidation was driven by microbial activity when the pH was <5. A remediation strategy of decreasing the pH to <2.2 was tested through geochemical modeling and laboratory experiments. These experiments indicated that scale formation could be prevented by decreasing the pH, which could be achieved at IMM by mixing source waters. However, the presence of Fe(III)-rich scale in a pipeline buffers the pH to higher values that may affect the efficacy of this remedial approach.

The effect of uranium, radium and thorium speciation on the removal of radioactivity from acid mine drainage using ion exchange

Acid mine drainage samples were collected from the central basin of the Witwatersrand basin in South Africa to study the removal of radioactivity. The samples were analyzed for gross alpha/beta activity, specific radionuclides, metals and anions concentration. The pH of the acid mine drainage samples was then varied and ion-exchange column experiments were carried out to remove radioactivity from acid mine drainage. The gross alpha activity ranged between 60 and 75 Bq/L and gross beta activity ranged from 56 to 70 Bq/L. The speciation of uranium, thorium and radium was modelled using Joint Expert Speciation System. The speciation had a big influence on the removal of radioactivity from acid mine drainage using ion exchange resin. The optimum pH was determined to be 8. Acid mine drainage samples treated at this pH showed gross alpha activity below the detection limit of 0.03 Bq/L for all samples and gross beta activities below 5 Bq/L for 9 of the 10 treated samples

Comparative study on the removal of toxic metal ions by advanced carbon allotropes and g-C3N4 adsorbents: a case study from Sarcheshmeh copper mine

The sorption properties of graphene oxide nanosheets (GO), functionalized multi-walled carbon nanotubes (f-MWCNTs) and exfoliated graphite like C3N4 (g-C3N4) have been studied to evaluate their potential in treating acid mine drainage (AMD). Few-layered GO nanosheets and exfoliated g-C3N4 were simply fabricated via modified Hummers’ and thermal decomposition methods, respectively. MWCNTs were functionalized in the mixture of both sulfuric and nitric acids. Fabricated nanoadsorbents were characterized by various techniques and then used for metal ion removal of prepared solutions and real AMD samples from Sarcheshmeh copper mine. To investigate the sorption activity, batch adsorption experiments were applied. GO exhibited much higher adsorption capacity toward metal ions than other adsorbents. Besides high surface area, specific groups existing on the GO surface are likely to suggest supplemental parameters, which highly improve the loading capacity in comparison to the f-MWCNTs and exfoliated g-C3N4 adsorbents. Langmuir and Freundlich kinetic models have been implemented to depict and understand the adsorption reaction of metal ions. The results showed that the sorption analysis for all metal ions obeyed the second-order kinetics, and the sorption isotherms were in agreement with Langmuir and Freundlich isotherms. Additionally, cost assessment was done. Fast adsorption kinetics, large adsorption capacity, excellent reusability and the low cost create potentials for GO and g-C3N4 nanoadsorbents to be effective at removing metal ions from aqueous solutions.

Beneficiation of pulp mill waste green liquor dregs: Applications in treatment of acid mine drainage as new disposal solution in South Africa

Abstract Acid mine Drainage (AMD) is a low pH, sulphate and heavy metal rich leachate that is produced from oxidation of sulphide bearing minerals commonly found in the host rocks of some mineral ores. The pH augmentation, and sulphate and metal removal in AMD is often achieved by adding alkaline reagents in it. CaCO3 and/or its derivatives are commonly used for this purpose due to their abundance and affordability as compared to other neutralizing reagents. The problems associated with the use of this naturally occurring reagent do not only include the emission of greenhouse gases and ecological disturbances but also include a disastrous implication of depleting their reserves. To avoid these predicaments, green liquor dregs (GLD) from two Kraft pulp manufactures in South Africa were used as alternative alkaline reagents to neutralize AMD originating from Witwatersrand goldfields in Johannesburg. These GLD samples were referred to as GLD A and B. CaCO3 was used as a reference material. The GLD samples had neutralizing values that are comparable to that of CaCO3. Thus, CaCO3, GLD A, and GLD B had a neutralizing value of, 26.0, 21.2, and 21.0% CaO respectively. Different dosages 1, 2, 6, 10, and 20 g/L of these neutralizing reagents were used to neutralize the AMD. Results of this study showed that raising the pH of AMD was possible even at a low dosages of 1 g/L. At this dosage, the acidity of the AMD sample changed from 183.36 to 21.7, 36.4, and 48.72 mg/L CaCO3, and changed the pH from 5.6 to 8.84, 8.21, and 8.0 respectively. However, the SO42− and Ec had increased from 2093 to 2360, 2538, and 2407 mg/L and from 3.6 to 4.0, 4.3, 4.2 mS/cm respectively, indicating that caution should be taken to keep these values low by keeping the reagent dosage low and being cognizant of the carbonate mineral present in GLD. The x-ray diffraction patterns of the reacted samples confirmed the presence of metal oxides and Ca and Mg compounds that were depicted by SEM/EDX micrographs. In conclusion, the results from this study showed that the pH of AMD can be raised to optimum pH process value and reduce the acidity at a low dosage, a competitive advantage over commercial CaCO3. The proposed concept can be adopted by both the mining and pulp and paper industries, for the upscaling of co-disposing GLD and AMD contaminants as an eco-friendly alternative for the CaCO3.

Cu(II) adsorption on 2-thiouracil-modified Luffa cylindrica biochar fibres from artificial and real samples, and competition reactions with U(VI)

The adsorption of Cu(II) ions by biochar fibres prior and after modification with 2-thiouracil on real and artificial samples has been studied by batch-type adsorption experiments, FTIR and XPS spectroscopy and competition reactions using U(VI) ions as competitor cations. The experimental data of the artificial samples clearly show that the modified material presents extraordinary higher affinity for Cu(II) ions even in the acidic pH range, the spectroscopic data indicate the formation of inner-sphere complexes and the competition reactions significantly higher selectivity of the 2-thiouracil modified biochar fibres for Cu(II). The 2-thiouracil-modified biochar fibres have been successfully applied to acid mine drainage (AMD) samples regarding the selective separation of Cu(II) ions from “real” samples. Regarding the desorption of copper from the biochar surface, although 100% copper recovery was achieved by eluting the metal ion using 1 M HNO3, the deterioration of the modified biochar fibers due to extensive 2-thiouracil release from the biochar surface limits the applicability of the present adsorbent in routine and large-scale applications.

The effect of saw dust in a flocculent with bentonite clay and FeSO4 in AMD treatment without addition of a neutralizer

Abstract 200 mL of synthetic acid mine drainage (AMD) was poured into five 500 mL glass beakers and treated in a jar test. The samples were dosed with 1.0–2.5 g bentonite clay, 20–60 mL of 0.025 or 0.05 M FeSO4 and 1.0–2.5 g saw dust respectively. The samples were mixed at 250 rpm for 2 minutes and reduced to 100 rpm for 10 minutes. The samples were allowed to settle for 1 hour, after which the pH, oxidation-reduction potential (ORP) and turbidity were measured (exp. A). Two other similar sets of experiments were conducted by dosing the samples with a combination of bentonite clay and FeSO4 with and without saw dust, similar treatment and measurements (exp. B and exp. C), similar treatment and measurements were conducted. The pH and the efficiencies of the flocculants containing 0.025 and 0.05 M Fe3+ in FeSO4 are similarly identical. The removal of turbid materials from the samples with FeSO4 is the lowest, followed by a combination of bentonite clay and FeSO4, whereas a combination of bentonite clay, FeSO4 and saw dust the highest. Comparative removal efficiencies between the two flocculants show that the presence of FeSO4 is relatively insignificant. The removal efficiency of a combination of bentonite clay, FeSO4 and saw dust from AMD sample is low with for Cu2+, and optimal for both Ni2+ and Fe2+ ions.

Polymeric ion exchanger supported ferric oxide nanoparticles as adsorbents for toxic metal ions from aqueous solutions and acid mine drainage.

Acid mine drainage (AMD) is a worldwide industrial pollution of grave concern. AMD pollutes both water sources and the environment at large with dissolved toxic metals which are detrimental to human health. This paper reports on the preparation of polymeric ion exchange resins decorated with hydrated iron oxides and their application for the ecological removal of toxic metals ions from AMD. The hydrated iron oxide particles were incorporated within commercial chelating ion exchange resins using the precipitation method. The synthesised hybrid resins were then characterized using appropriate spectroscopic and solid-state techniques. The metal ion levels were measured using the inductively coupled plasma-optical emission spectrometer (ICP-OES). The optimization of contact time, pH, and adsorbent dosage were conducted to enhance the efficiency of adsorption of toxic metals onto the hybrid organic/inorganic nanosorbents. Kinetics and adsorption isotherms were constructed to study the adsorption mechanisms of the adsorbents. The results showed that the dispersed Fe-O is hydrated and amorphous within the hybrid materials. The adsorption kinetics followed the pseudo-second-order shown by the high R2 values. The hybrid adsorbents were finally tested on environmental AMD samples and were able to remove toxic metals Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn at various removal degrees. Solution pH played a crucial role in the adsorption of toxic metals on hybrid iron oxide adsorbents. The hybrid TP-260 HFO had higher affinity for toxic metals than other prepared adsorbents thus has a potential for acidic mine water pollution remediation. The adsorbed Al(III) can be recovered using NaCl-NaOH binary solution from the loaded resins.

The Use of Calcium and Magnesium Hydroxides in Acid Mine Drainage Treatment

Reagent grade of calcium and magnesium hydroxides were used in this study to treat acid mine drainage (AMD) sample. AMD sample was collected from a tin tailing pond that located in Pengkalan Hulu, Perak which as pH around 2.87 ± 0.01. pH values had increased after treated with calcium hydroxide (Ca(OH)2) and magnesium hydroxide (Mg(OH)2), respectively. The maximum pH values obtained was 11.35 ± 0.01 by using 1.0 g of Ca(OH)2 at interval time 5 min. For Mg(OH)2, the highest pH value can be obtained was 7.22 ± 0.01 by using 1.0 g at interval time 30 min. The concentration of heavy metals such as aluminum, copper, iron, manganese, nickel and zinc were reduced after reaction with both materials. For examples aluminum concentration was reduced from 110.33 mg/L to 2.80 mg/L and 0.01 mg/L by using 1.0 g of Ca(OH)2 and Mg(OH)2, respectively.

Application of Response Surface Methodology and Desirability Function in the Optimization of Adsorptive Remediation of Arsenic from Acid Mine Drainage Using Magnetic Nanocomposite: Equilibrium Studies and Application to Real Samples.

A magnetic multi-walled carbon nanotube/zeolite nanocomposite was applied for the adsorption and removal of arsenic ions in simulated and real acid mine drainage samples. The adsorption mechanism was investigated using two-parameter (Langmuir, Freundlich, Temkin) and three-parameter (Redlich–Peterson, and Sips) isotherm models. This was done in order to determine the characteristic parameters of the adsorptive removal process. The results showed that the removal process was described by both mono- and multilayer adsorptions. Adsorption studies demonstrated that a multi-walled carbon nanotube/zeolite nanocomposite could efficiently remove arsenic in simulated samples within 35 min. Based on the Langmuir isotherm, the adsorption capacity for arsenic was found to be 28 mg g−1. The nanocomposite was easily separated from the sample solution using an external magnet and the regeneration was achieved by washing the adsorbent with 0.05 mol L−1 hydrochloric acid solution. Moreover, the nanoadsorbent was reusable for at least 10 cycles of adsorption-desorption with no significant decrease in the adsorption capacity. The nanoadsorbent was also used for the arsenic removal from acid mine drainage. Overall, the adsorbent displayed excellent reusability and stability; thus, they are promising nanoadsorbents for the removal of arsenic from acid mine drainage.

Physicochemical characteristics of acid mine drainage, simultaneous remediation and use as feedstock for value added products

In this study, the use of acid mine drainage as alternative source of ferric ion for the synthesis of iron nanoparticles was investigated. The physical and chemical characteristics of acid mine drainage from Navigation coal mine and the West Rand mine, South Africa were conducted. The synthesised iron nanoparticles were compared with iron nanoparticles prepared from commercial reagents by X-ray diffraction, X-ray fluorescence, scanning electron microscopy, high resolution transmission electron microscopy and Brunauer–Emmett–Teller surface area determination. The iron nanoparticles were utilised for the treatment of acid mine drainage. Experimental results showed that the characteristics of acid mine drainage samples differ from site to site due to the differences in their geological composition, chemical deposition, rate of oxidation, and availability of pyrite ores. The Toeseep acid mine drainage feedstock from Navigation coal mine was found to contain the highest concentration of iron (4219.14 mg L−1) thus; it was regarded to be a suitable source of iron, sulphate (21,317.79 mg L−1) was the predominant anion. The synthesised iron nanoparticles were crystalline and spherical in shape, with average particle size of 31.8 nm or 28.05 nm and Brunauer–Emmett–Teller surface area of 88 ± 3.16 m2 g−1 or 91 ± 3.08 m2 g−1 for the iron nanoparticles synthesised from acid mine drainage or ferric chloride, respectively. The optimisation of the iron nanoparticles dosage and contact time for the treatment of Navigation Toeseep acid mine drainage was determined to be 0.1 g and 60 min, respectively. The toxic elements in the raw acid mine drainage were removed with over 75% efficiency.

Covellite (CuS) Production from a Real Acid Mine Drainage Treated with Biogenic H2S

Acid Mine Drainage (AMD) is an environmental problem associated with mining activities, which resulted from the exposure of sulfur bearing materials to oxygen and water. AMD is a pollution source due to its extreme acidity, high concentration of sulfate, and soluble metals. Biological AMD treatment is one alternative to couple environmental amelioration for valuable dissolved metals recovery, as a new source of raw materials. Covellite (CuS) particles were synthetized from an AMD sample collected in a Brazilian copper mine, after 48 and 96 h of exposure to hydrogen sulfide (H2S) produced in a bioreactor containing acidophilic sulfate reducing bacteria (SRB). The time of exposure affected the morphology, nucleation, and size of CuS crystals. CuS crystals synthetized after 96 h of H2S exposure showed better ordination as indicated by sharp and intense diffractograms obtained by X-ray diffraction (XRD), and the predominance of placoid sheets with hexagonal habit structure as observed by scanning electrons microscopy (SEM). Energy dispersive X-ray fluorescence (EDXRF) spectrometry indicated a Cu:S molar ratio in agreement with CuS. Granulometric analysis demonstrated that 90% of CuS particles were less than 22 µm size. AMD biological treatment is a potential economical CuS recovery option for metallurgical process chain incorporation, or new industrial applications, since the alteration of synthesis conditions can produce different crystal forms with specific characteristics.

How Microbes Shape Their Communities? A Microbial Community Model Based on Functional Genes

Exploring the mechanisms of maintaining microbial community structure is important to understand biofilm development or microbiota dysbiosis. In this paper, we propose a functional gene-based composition prediction (FCP) model to predict the population structure composition within a microbial community. The model predicts the community composition well in both a low-complexity community as acid mine drainage (AMD) microbiota, and a complex community as human gut microbiota. Furthermore, we define community structure shaping (CSS) genes as functional genes crucial for shaping the microbial community. We have identified CSS genes in AMD and human gut microbiota samples with FCP model and find that CSS genes change with the conditions. Compared to essential genes for microbes, CSS genes are significantly enriched in the genes involved in mobile genetic elements, cell motility, and defense mechanisms, indicating that the functions of CSS genes are focused on communication and strategies in response to the environment factors. We further find that it is the minority, rather than the majority, which contributes to maintaining community structure. Compared to health control samples, we find that some functional genes associated with metabolism of amino acids, nucleotides, and lipopolysaccharide are more likely to be CSS genes in the disease group. CSS genes may help us to understand critical cellular processes and be useful in seeking addable gene circuitries to maintain artificial self-sustainable communities. Our study suggests that functional genes are important to the assembly of microbial communities.