Simulated Acid Mine Drainage Research Articles

The Important Role of Dissolved Oxygen Supply Regulated by the Hydraulic Shear Force during the Biosynthesis of Iron Hydroxysulfate Minerals

The severity of environmental pollution from acid mine drainage (AMD) is increasingly garnering attention. In this study, the effects of hydraulic shear forces (achieved by regulating the shaking table’s rotation speed) on Fe2+ bio-oxidation and Fe3+ hydrolytic mineralization in an acidic 9K medium-FeSO4-Acidithiobacillus ferrooxidans system (simulated AMD) are investigated. Results reveal that a higher shaking speed favors a higher oxidation rate of Fe2+, whereas a very low or high shaking speed restricts the removal of Fe3+. Shaking table rotation speeds of 120–180 rpm were preferred for biomineralization treatment in the simulated AMD. As the initial concentration of Fe2+ in the system decreased from 9.67 to 0 g/L in 40 h, the dissolved O2 (DO) in the solution dropped to its lowest concentration after 20 h and then increased to its initial level between 40 and 120 h. However, the corresponding total Fe (TFe) precipitation efficiency increased with the increasing mineralization time after 40 h. The effect of O2 supply time on biomineralization revealed that DO was mainly used in Fe2+ bio-oxidation. After Fe2+ was completely oxidized by A. ferrooxidans, the precipitation efficiency of TFe was independent of the O2 supply.

Effective Treatment of Acid Mine Drainage with Microbial Fuel Cells: An Emphasis on Typical Energy Substrates

Acid mine drainage (AMD), characterized by a high concentration of heavy metals, poses a threat to the ecosystem and human health. Bioelectrochemical system (BES) is a promising technology for the simultaneous treatment of organic wastewater and recovery of metal ions from AMD. Different kinds of organic wastewater usually contain different predominant organic chemicals. However, the effect of different energy substrates on AMD treatment and microbial communities of BES remains largely unknown. Here, results showed that different energy substrates (such as glucose, acetate, ethanol, or lactate) affected the startup, maximum voltage output, power density, coulombic efficiency, and microbial communities of the microbial fuel cell (MFC). Compared with the maximum voltage output (55 mV) obtained by glucose-fed-MFC, much higher maximum voltage output (187 to 212 mV) was achieved by MFCs fed individually with other energy substrates. Acetate-fed-MFC showed the highest power density (195.07 mW/m2), followed by lactate (98.63 mW/m2), ethanol (52.02 mW/m2), and glucose (3.23 mW/m2). Microbial community analysis indicated that the microbial communities of anodic electroactive biofilms changed with different energy substrates. The unclassified_f_Enterobacteriaceae (87.48%) was predominant in glucose-fed-MFC, while Geobacter species only accounted for 0.63%. The genera of Methanobrevibacter (23.70%), Burkholderia-Paraburkholderia (23.47%), and Geobacter (11.90%) were the major genera enriched in the ethanol-fed-MFC. Geobacter was most predominant in MFC enriched by lactate (45.28%) or acetate (49.72%). Results showed that the abundance of exoelectrogens Geobacter species correlated to electricity-generation capacities of electroactive biofilms. Electroactive biofilms enriched with acetate, lactate, or ethanol effectively recovered all Cu2+ ion (349 mg/L) of simulated AMD in a cathodic chamber within 53 h by reduction as Cu0 on the cathode. However, only 34.65% of the total Cu2+ ion was removed in glucose-fed-MFC by precipitation with anions and cations rather than Cu0 on the cathode.

Experimental study on AMD treatment by SRB biodegradation in a UASB reactor

According to the water quality characteristics of acid mine drainage (AMD), sulfate removal from simulated AMD by sulfate reducing bacteria (SRB) was improved in a UASB bioreactor. In the meanwhile, the influences of C/S ratio, pH, temperature, and HRT on sulfate removal rate were analyzed to obtain the optimal operation parameters. The results show that under the optimal operation conditions of C/S = 3.0, pH = 6.5, T = 35°C, and HRT = 10 hours, the maximum removal rate of sulfate (86.3%) is reached with an influent sulfate concentration of 2 000 m/L and an effluent sulfate concentration of 274 mg/L which satisfies the local mine drainage discharge standard (500 mg/L). Different from other traditional desalting technologies, the reduction of salinity is realized in this study by removing sulfate from AMD during SRB biodegradation process.

Enhanced Monovalent Cation Biomineralization Ability by Quartz Sand for Effective Removal of Soluble Iron in Simulated Acid Mine Drainage

Acid mine drainage (AMD) is characterized by low pH, high soluble Fe, and heavy metal concentrations. Conventional lime neutralization produces large amounts of Fe(OH)2 and Fe(OH)3, which complicate subsequent disposal. Secondary iron minerals synthesized by biomineralization can reduce the concentration of soluble Fe in addition to adsorbing and removing heavy metals in AMD. Therefore, an appropriate method for improving the precipitation efficiency of Fe is urgently needed for AMD treatment. Using simulated AMD, this work analyzes the influence of quartz sand (40 g/L) on the Fe2+ oxidation and total Fe deposition efficiencies, as well as the phases of secondary iron minerals in an Acidithiobacillus ferrooxidans system including K+, Na+, or NH4+ (53.3 mmol/L). Quartz sand had no significant effect on Fe2+ oxidation and 160 mmol/L Fe2+ was completely oxidized by A. ferrooxidans in 168 h, but contributed to the oxidized product (Fe3+) mineralization, improving the total Fe removal efficiency in simulated AMD. Compared with treatments involving K+ or Na+ alone, quartz sand improved the total Fe precipitation efficiency by 26.6% or 30.2%, respectively. X-ray diffraction showed that quartz sand can promote the transformation of the biomineralization pathway from schwertmannite to jarosite with higher yields, which is important for improving the removal efficiency of heavy metals in AMD.

Nanofiltration of Simulated Acid Mine Drainage: Effect of pH and Membrane Charge

Acid mine drainage (AMD) is a severe form of environmental pollution that has the potential to contaminate surface and ground waters by introducing heavy metals and lowering the pH. The feasibility of using nanofiltration (NF) as a potentially attractive and cost-effective remediation method to treat acid mine drainage was investigated in this study. The performance of an acid-stable NF membrane focusing on the effects of the water pH and membrane charge on ion rejection was systematically studied. A single salt solution experiment showed that Mg, Cu, and Mn containing species were highly rejected at above 97%. Below the membrane iso-electric point (IEP), Mn showed an increased rejection of 99%, while Mg and Mn rejections were relatively constant within the investigated pH range of pH 2 to 7. Rejection of monovalent Cl− decreased with increasing concentration of an accompanying divalent SO42−, showing that Donnan related effects are more prominent at higher ionic concentrations. The sulfate rejection decreased drastically below pH 3 due to the formation of HSO4−, which permeated through the membrane, which can be utilized as a way of separation of the metals from the accompanying sulfur-containing compounds. For mixed salt solutions, rejection of silicate dropped from 52% to 38% when magnesium sulfate was added, owing to shielding of the membrane surface charge by Mg2+ ions. The NF process performance with a simulated AMD solution was found to be similar to that with model salt solution experiments, both in terms of ion rejection values and general pH-dependent rejection trends. The results obtained can be used as a fast preliminary tool for evaluating the feasibility of using NF for treating AMD with a given ionic composition and pH.

Recovery of Metals from Acid Mine Drainage by Bioelectrochemical System Inoculated with a Novel Exoelectrogen, Pseudomonas sp. E8.

Acid mine drainage (AMD) is a typical source of environmental pollution ascribing to its characteristics of high acidity and heavy metal content. Currently, most strategies for AMD treatment merely focus on metal removal rather than metal recovery. However, bioelectrochemical system (BES) is a promising technology to simultaneously remove and recover metal ions from AMD. In this study, both cupric ion and cadmium ion in simulated AMD were effectively recovered by BES inoculated with a novel exoelectrogen, Pseudomonas sp. E8, that was first isolated from the anodic electroactive biofilm of a microbial fuel cell (MFC) in this study. Pseudomonas sp. E8 is a facultative anaerobic bacterium with a rod shape, 0.43–0.47 μm wide, and 1.10–1.30 μm long. Pseudomonas sp. E8 can agglomerate on the anode surface to form a biofilm in the single-chamber MFC using diluted Luria-Bertani (LB) medium as an energy substrate. A single-chamber MFC containing the electroactive Pseudomonas sp. E8 biofilms has a maximum output voltage of 191 mV and a maximum power density of 70.40 mW/m2, which is much higher than those obtained by most other exoelectrogenic strains in the genus of Pseudomonas. Almost all the Cu2+ (99.95% ± 0.09%) and Cd2+ (99.86% ± 0.04%) in simulated AMD were selectively recovered by a microbial fuel cell (MFC) and a microbial electrolysis cell (MEC). After the treatment with BES, the high concentrations of Cu2+(184.78 mg/L), Cd2+(132.25 mg/L), and total iron (49.87 mg/L) in simulated AMD were decreased to 0.02, 0.19, and 0 mg/L, respectively. Scanning electron micrograph (SEM), energy dispersive X-ray spectrometry (EDXS) and X-ray diffraction (XRD) analysis indicate that the Cu2+ and Cd2+ in simulated AMD were selectively recovered by microbial electrochemical reduction as Cu0 (together with trace amounts of Cu2O) or Cd0 on the cathode surface. Collectively, data suggest that Pseudomonas sp. E8 has great potential for AMD treatment and metal recovery.

Neodymium isotopes track sources of rare earth elements in acidic mine waters

Acid mine drainage (AMD) has been proposed as a potential source of strategic rare earth elements (REEs) due to its high concentrations (>1000 µg/L) of dissolved REEs, as well as the middle rare earth element (MREE) enriched pattern exhibited by both coal mine- and metal mine-derived AMD, in which some of the most energy-critical REEs are significantly concentrated. However, the source of REEs and the origin of the MREE enrichment observed in AMD discharges is poorly understood; suggestions include dissolution of MREE-enriched surface coatings, fractionation by colloids, solid-liquid exchange reactions, incongruent dissolution of pyrite, and selective leaching of MREE-enriched phases. Filtration experiments on acidic to circumneutral AMD (unfiltered to <0.002 µm) indicate that REEs are in a dissolved state. Thus, colloids are not a significant carrier of REEs in these samples and are not responsible for the observed MREE-enriched patterns. The similarity of MREE-enriched patterns exhibited by AMD to those of laboratory sulfuric acid (simulated AMD) leachates of corresponding overburden samples suggest that these lithologies are a major contributor of REEs to AMD. Isotopes of strontium (87Sr/86Sr) and neodymium (143Nd/144Nd) in AMD discharges are distinct from whole-rock values of associated lithologies, but fall within the range of values of the leachates. Whole rocks, leachates, and AMD define a trend on a Sm-Nd isochron diagram consistent with the ∼310 Ma depositional age of the coal. These data suggest that MREE enrichment of AMD results from preferential leaching of a readily dissolvable, MREE-enriched mineral phase, most likely apatite or a related phosphate phase, that formed during or shortly after deposition of the coal and associated units.

Effect of hydraulic retention time and pH on oxidation of ferrous iron in simulated ferruginous acid mine drainage treatment with inoculation of iron-oxidizing bacteria

The effect of hydraulic retention time (HRT) and pH on the biooxidation of ferrous iron during simulated acid mine drainage (AMD) treatment was investigated. The simulated AMD was highly acidic (pH 2.5), rich in iron (about 1700 mg/L) and copper (about 200 mg/L), and contained high concentrations of sulfate (about 4700 mg/L). The biooxidation of ferrous iron was studied in a laboratory-scale upflow packed bed bioreactor (PBR). The HRT was shortened stepwise from 40 h to 20 h, 13 h, and 8 h under the acidic environment at a pH value of 2.2. Then, the influent pH value was changed from 2.2 to 1.2 at a constant suitable HRT. Physiochemical and microbial community structure analyses were performed on water samples and stuffing collected from the bioreactor under different conditions. The results indicate that the efficiency of ferrous iron oxidation gradually decreased with the decrease of HRT, and when the HRT exceeded 13 h, ferrous iron in AMD was almost completely oxidized. In addition, the best efficiency of ferrous iron oxidation was achieved at the influent pH value of 1.8. Microbial community structure analyses show that Leptospirillum is the predominant genus attached in the bioreactor, and low influent pH values are suitable for the growth of Leptospirillum.

Use of Basic Oxygen Furnace (BOF) Steel Slag for Acid Mine Drainage Treatment: A Laboratory Study

We investigated the feasibility of using alkaline basic oxygen furnace (BOF) steel slag to treat acid mine drainage (AMD). Simulated AMD was treated with different doses of slag (10, 20, 30, 40, 50, and 60 g/L) for 24 h in batch reactors. A dose of 30 g/L was considered optimal because it raised the pH to 8.6 and resulted in 99% removal of trace metals in 24 h. The pH increased to 6.36 from the initial pH of 1.5 within 0.5 h of reaction time. Approximately 95% of all trace metals were removed. Of the major cations and anions, Mg showed the highest percentage removal (72%), followed by SO4 (30%), K (8%), and Na (2.1%) at the 30 g/L dose and 0.5 h reaction time. However, Ca concentrations increased by 28% due to leaching from the slag. PHREEQC was used to predict the possible mineral phases precipitating during treatment. Calculated saturation indices indicated that Fe was removed mainly as goethite, hematite, and amorphous Fe(OH)3; Al was removed as gibbsite and amorphous Al(OH)3; Mn was removed as manganite, hausmannite, and pyrolusite; Mg was removed as Mg(OH)2; and Ca and SO4 were only minimally controlled by gypsum precipitation. Moreover, sulfate removal was increased by the precipitation of alunite, an Al-oxy hydroxysulfate mineral. Other trace elements were either co-precipitated with or adsorbed onto the Fe, Al, and Mn precipitates. Field emission scanning electron microscope analysis of the slag after interaction with the AMD revealed that metals and SO4 precipitated on the slag surface.

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.

Rejection of rare earth elements from a simulated acid mine drainage using forward osmosis: The role of membrane orientation, solution pH, and temperature variation

The high demand for the rare earth elements (REEs) in the clean technological industries implies the increased demand to produce these elements from ores and REEs containing impaired water sources such as acid mine drainage (AMD). However, the presence of these elements in AMD has increased their toxic exposure to the water environment. Herein, we investigated the role of the orientation of the membrane (such as active layer facing feed solution (AL-FS) or active layer facing draw solution (AL-DS) mode), solution pH, and temperature variation on the flux performance and rejection of three REEs (e.g., lanthanum, cerium, and dysprosium) from a simulated AMD solution using the forward osmosis (FO) process. It was found that there was a greater water flux at high pH, AL-DS mode of the FO system and high feed and draw solution temperature. FO could effectively reject all three REEs in both AL-FS and AL-DS membrane orientations mode due to steric hindrance. The rejection of these REEs in the AL-DS mode was slightly lower (82–88%) than that in the AL-FS mode (86–96%). The rejection of all REEs was noticeably influenced by solution pH in both mode. This was due to the changes in membrane surface with pH variation. The rejection of REEs increased when the temperature of the feed and draw solution was 20 and 40 °C, respectively. However, the rejection of all REEs decreased markedly when the temperature of the feed and draw solution was 40 and 20 °C, respectively. The lower rejection of these REEs was due to the enhancement of their diffusivity at a higher temperature in the feed side.

Metal ion adsorption from wastewater by g-C3N4 modified with hydroxyapatite: a case study from Sarcheshmeh Acid Mine Drainage

Hydroxyapatite (Hap) modified graphitic carbon nitride (g-C3N4) powders (Hap/g-C3N4) were prepared and characterized. The sorption activities of g-C3N4 and Hap/g-C3N4 were evaluated for the removal of Cu2+, Mn2+, Zn2+, Pb2+, Fe3+ and Cd2+ metal ions from simulated wastewater (synthetic solutions containing metal ions) and acid mine drainage from the sSarcheshmeh Copper Mine. The results indicated that the sorption capacities (SC) of g-C3N4 remarkably increased after the modification by Hap. Hap/g-C3N4 possessed higher SC than unmodified g-C3N4. So, the sorption mechanisms appear mainly attributable to the chemical interactions between the metal ions and functional groups on the Hap/g-C3N4 surface. More adsorption sites were formed on Hap/g-C3N4, which possessed abundant surface hydroxyl, phosphate and –NH2/–NH–/=N groups causing the higher efficiency of metal ion uptakes. Divalent metal cations are first adsorbed on the Hap/g-C3N4 surface and then substitution with Ca2+ ion can occur. Effect of pH evaluations confirmed that SC increased steeply with the pH increasing on both g-C3N4 and Hap/g-C3N4 adsorbents. The kinetic study demonstrated that the adsorption data were correlated well with the Langmuir isotherm model, and the adsorption process successfully followed the pseudo-second-order model.

A novel approach coupling ferrous iron bio-oxidation and ferric iron chemo-reduction to promote biomineralization in simulated acidic mine drainage.

A novel Acidithiobacillus ferrooxidans-mediated approach coupling biological oxidation and chemical reduction for treating acid mine drainage (AMD) was investigated. The results showed that controlled addition of zero valent iron (ZVI) into the coupling system did not exhibit a significant adverse influence on the bacterial activity of Acidithiobacillus ferrooxidans but markedly increased the formation of secondary Fe-minerals. Nutrition did not affect the efficiency of coupling process, except for the bacteria density of A. ferrooxidans. 2 days cyclic treatment performed better than that of 4 and 8 days. After 14 cycles of the coupling process, 89.4% of total iron (2.23 g L−1) was transferred into Fe-minerals finally. In addition, the combined system was highly effective in removing sulfate (63%) from a simulated AMD that contained soluble Cu, Zn, Al, and Mn. Valuable iron-sulfate material e.g. schwertmannite was formed with little co-precipitation of other metals. Therefore, the integration of A. ferrooxidans into the reduction by ZVI may have considerable potential in the enhancement of biomineralization efficiency, which may further decrease soluble TFe and sulfate loads in AMD before lime neutralization.

Initial pH and K+ concentrations jointly determine the types of biogenic ferric hydroxysulfate minerals and their effect on adsorption removal of Cr(VI) in simulated acid mine drainage.

It is of practical significance to promote the transformation of Fe in acid mine drainage (AMD) into ferric hydroxysulfate minerals with strong ability to remove heavy metals or metalloids. To investigate the types of biogenic ferric hydroxysulfate minerals generated in AMD by Acidithiobacillus ferrooxidans (A. ferrooxidans), different pH and K+ concentrations are tested for the formation of precipitates in media containing 160 mmol/L Fe2+. The Cr(VI) removal efficiencies of ferric hydroxysulfate minerals in AMD with different acidities are also compared. Results indicate that the mineralizing abilities of the initial pH levels (pH 3.0 > pH 2.5 > pH 2.0) and K+ concentrations (53.3 mmol/L > 3.2 mmol/L ≈ 0.8 mmol/L) differ, with cumulative Fe precipitation efficiencies of 58.7%, 58.0%, and 44.2% (K+ = 53.3 mmol/L), and 58.7%, 29.9%, and 29.6% (pH 3.0) after 96 h of A. ferrooxidans incubation, respectively. X-ray diffraction indicates that K-jarosites are formed in the treatments n(Fe)/n(K) = 0.1 and 3 at pH 2.0-3.0, while only schwertmannite is generated in a system of pH 3.0 and n(Fe)/n(K) = 200. X-ray photoelectron spectroscopy reveals that HCrO4 - may be adsorbed as an inner-sphere complex on schwertmannite when the AMD pH is 3.0.

Migration and Fate of Acid Mine Drainage Pollutants in Calcareous Soil.

As a major province of mineral resources in China, Shanxi currently has 6000 mines of various types, and acid mine drainage (AMD) is a major pollutant from the mining industry. Calcareous soil is dominant in western North China (including the Shanxi Province), therefore, clarifying the migration behavior of the main AMD pollutants (H+, S, Fe, heavy metals) in calcareous soil is essential for remediating AMD-contaminated soil in North China. In this study, the migration behavior of the main pollutants from AMD in calcareous soil was investigated using soil columns containing 20 cm of surficial soil to which different volumes of simulated AMD were added in 20 applications. Filtrate that was discharged from the soil columns and the soil samples from the columns were analyzed. Almost all of the Fe ions (>99%) from the AMD were intercepted in the 0–20 cm depth of the soil. Although >80% of SO42− was retained, the retention efficiency of the soil for SO42− was lower than it was for Fe. Cu, as a representative of heavy metals that are contained in AMD, was nearly totally retained by the calcareous soil. However, Cu had a tendency to migrate downward with the gradual acidification of the upper soil. In addition, CaCO3 was transformed into CaSO4 in AMD-contaminated soil. The outcomes of this study are valuable for understanding the pollution of calcareous soil by AMD and can provide key parameters for remediating AMD-contaminated soil.

Influence of Monovalent Cations on the Efficiency of Ferrous Ion Oxidation, Total Iron Precipitation, and Adsorptive Removal of Cr(VI) and As(III) in Simulated Acid Mine Drainage with Inoculation of Acidithiobacillus ferrooxidans

Acid mine drainage is highly acidic and contains large quantities of Fe and heavy metal elements. Thus, it is important to promote the transformation of Fe into secondary iron minerals that exhibit strong heavy-metal removal abilities. Using simulated acid mine drainage, this work analyzes the influence of monovalent cations (K+, NH4+, and Na+) on the Fe2+ oxidation and total Fe deposition efficiencies, as well as the phases of secondary iron minerals in an Acidithiobacillus ferrooxidans system. It also compares the Cr(VI) (K2Cr2O7) and As(III) (As2O3) removal efficiencies of different schwertmannites. The results indicated that high concentrations of monovalent cations (NH4+ ≥ 320 mmol/L, and Na+ ≥ 1600 mmol/L) inhibited the biological oxidation of Fe2+. Moreover, the mineralizing abilities of the three cations differed (K+ &gt; NH4+ &gt; Na+), with cumulative Fe deposition efficiencies of 58.7%, 28.1%, and 18.6%, respectively [n(M) = 53.3 mmol/L, cultivation time = 96 h]. Additionally, at initial Cr(VI) and As(III) concentrations of 10 and 1 mg/L, respectively, the Cr(VI) and As(III) removal efficiencies exhibited by schwertmannites acquired by the three mineralization systems differed [n(Na) = 53.3 &gt; n(NH4) = 53.3 &gt; n(K) = 0.8 mmol/L]. Overall, the analytical results suggested that the removal efficiency of toxic elements was mainly influenced by the apparent structure, particle size, and specific surface area of schwertmannite.

Enhanced removal of high Mn(II) and minor heavy metals from acid mine drainage using tunnelled manganese oxides

This study developed improved manganese oxide coated media based on the todorokite structure which are an effective means to remove a range of heavy metal ions from acid mine drainage (AMD) solutions. As a consequence, limitations of conventional acid mine drainage treatment wherein use of oxidants is required, substantial quantities of alkali are used and sorbents which exhibit stability issues when Fe(II) is co-present in the water, are mitigated. This study investigated three synthetic MnO2 phases: pyrolusite, cryptomelane and todorokite with a specific focus on identifying a preferred MnO2 phase for Mn(II) removal from AMD wastewaters. Pyrolusite was found to have low capacity for Mn(II) removal and was sensitive to reductive dissolution by Fe(II). Cryptomelane, similarly showed relatively small capacity for Mn(II), and also impacted by reductive dissolution. Todorokite was discovered to exhibit significant capacity for Mn(II) (75–80 mg/g) in the pH range 5.5–7; a value which increased to 130 mg/g when a lower Mn:Mg ratio todorokite material was used. The todorokite materials studied also showed resistance to reductive dissolution and a marked selectivity for Mn(II), along with further capacity for Cr(III), Cu(II), Co(II), Ni(II) and Zn(II) removal when treating simulated discharge AMD and lime-dosed AMD.

MetaCRAST: reference-guided extraction of CRISPR spacers from unassembled metagenomes.

Clustered regularly interspaced short palindromic repeat (CRISPR) systems are the adaptive immune systems of bacteria and archaea against viral infection. While CRISPRs have been exploited as a tool for genetic engineering, their spacer sequences can also provide valuable insights into microbial ecology by linking environmental viruses to their microbial hosts. Despite this importance, metagenomic CRISPR detection remains a major challenge. Here we present a reference-guided CRISPR spacer detection tool (Metagenomic CRISPR Reference-Aided Search Tool—MetaCRAST) that constrains searches based on user-specified direct repeats (DRs). These DRs could be expected from assembly or taxonomic profiles of metagenomes. We compared the performance of MetaCRAST to those of two existing metagenomic CRISPR detection tools—Crass and MinCED—using both real and simulated acid mine drainage (AMD) and enhanced biological phosphorus removal (EBPR) metagenomes. Our evaluation shows MetaCRAST improves CRISPR spacer detection in real metagenomes compared to the de novo CRISPR detection methods Crass and MinCED. Evaluation on simulated metagenomes show it performs better than de novo tools for Illumina metagenomes and comparably for 454 metagenomes. It also has comparable performance dependence on read length and community composition, run time, and accuracy to these tools. MetaCRAST is implemented in Perl, parallelizable through the Many Core Engine (MCE), and takes metagenomic sequence reads and direct repeat queries (FASTA or FASTQ) as input. It is freely available for download at https://github.com/molleraj/MetaCRAST.

Recovering Rare Earth Elements from Aqueous Solution with Porous Amine-Epoxy Networks.

Recovering aqueous rare earth elements (REEs) from domestic water sources is one key strategy to diminish the U.S.'s foreign reliance of these precious commodities. Herein, we synthesized an array of porous, amine-epoxy monolith and particle REE recovery sorbents from different polyamine, namely tetraethylenepentamine, and diepoxide (E2), triepoxide (E3), and tetra-epoxide (E4) monomer combinations via a polymer-induced phase separation (PIPS) method. The polyamines provided -NH2 (primary amine) plus -NH (secondary amine) REE adsorption sites, which were partially reacted with C-O-C (epoxide) groups at different amine/epoxide ratios to precipitate porous materials that exhibited a wide range of apparent porosities and REE recoveries/affinities. Specifically, polymer particles (ground monoliths) were tested for their recovery of La3+, Nd3+, Eu3+, Dy3+, and Yb3+ (Ln3+) species from ppm-level, model REE solutions (pH ≈ 2.4, 5.5, and 6.4) and a ppb-level, simulated acid mine drainage (AMD) solution (pH ≈ 2.6). Screening the sorbents revealed that E3/TEPA-88 (88% theoretical reaction of -NH2 plus -NH) recovered, overall, the highest percentage of Ln3+ species of all particles from model 100 ppm- and 500 ppm-concentrated REE solutions. Water swelling (monoliths) and ex situ, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) (ground monoliths/particles) data revealed the high REE uptake by the optimized particles was facilitated by effective distribution of amine and hydroxyl groups within a porous, phase-separated polymer network. In situ DRIFTS results clarified that phase separation, in part, resulted from polymerization of the TEPA-E3 (N-N-diglycidyl-4-glycidyloxyaniline) species in the porogen via C-N bond formation, especially at higher temperatures. Most importantly, the E3/TEPA-88 material cyclically recovered >93% of ppb-level Ln3+ species from AMD solution in a recovery-strip-recovery scheme, highlighting the efficacy of these materials for practical applications.

COMPETITIVE BIOSORPTION OF Pb(II), Cu(II), Cd(II) AND Zn(II) USING COMPOSTED LIVESTOCK WASTE IN BATCH AND COLUMN EXPERIMENTS

Composted livestock waste (CLW) was studied as one low-cost material to remove Pb(II), Cu(II), Cd(II) and Zn(II) from simulated acid mine drainage (AMD) by batch and column experiments. The adsorption isotherm data were well fitted by the Langmuir model. The maximum monolayer adsorption capacities were 0.5485 mmol/g for Pb(II), 0.4092 mmol/g for Cu(II), 0.2246 mmol/g for Cd(II), and 0.1879 mmol/g for Zn(II) at pH 4.0. Due to the competition effect, the adsorption capacity of the single metal ion decreased in the multiple metals system compared with single metal system. The removal equilibrium for Pb(II), Cu(II), Cd(II) and Zn(II) occurred at pH of 3.0-3.5, 4.0-4.5, 4.5-5.0 and 6.0-6.5, respectively. There was relatively high adsorption efficiency even in acid conditions (pH 2-4), especially for Pb(II). Breakthrough curves demonstrated the effectiveness of adsorption in column experiment for treatment of heavy metals in AMD. This study confirmed that CLW could be efficient for heavy metal ions removal from acid mine drainage or acidic coal refuse leachate.