Sulfidogenic biotreatment of synthetic acid mine drainage and sulfide oxidation in anaerobic baffled reactor

The treatment of synthetic acid mine drainage (AMD) water (pH 3.0-6.5) containing sulfate (3.0-3.5 g L(-1)) and various metals (Co, Cu, Fe, Mn, Ni, and Zn) was studied in an ethanol-fed sulfate-reducing 4-compartment anaerobic baffled reactor (ABR) at 32°C. The reactor was operated for 160 days at different chemical oxygen demand (COD)/sulfate ratios, hydraulic retention times (HRT), pH, and metal concentrations to study the robustness of the process. The last compartment of the reactor was aerated at different rates to study the bio-oxidation of sulfide to elemental sulfur. The highest sulfate reduction efficiency (88%) was obtained with a feed sulfate concentration of 3.5 g L(-1), COD/sulfate mass ratio of 0.737, feed pH of 3.0 and HRT of 2 days without aeration in the 4th compartment. The corresponding COD removal efficiency was about 92%. The alkalinity produced in the sulfidogenic ethanol oxidation neutralized the acidic mine water from pH 3.0-4.5 to pH 7.0-8.0. Effluent soluble and total heavy metal concentrations were substantially reduced with removal efficiencies generally higher than 99%, except for Mn (25-77%). Limited aeration in the 4th compartment of ABR promoted incomplete oxidation of sulfide to elemental sulfur rather than complete oxidation to sulfate. Depending on the aeration rate and HRT, 32-74% of produced sulfide was oxidized to elemental sulfur. This study demonstrates that by optimizing operating conditions, sulfate reduction, metal removal, alkalinity generation, and excess sulfide oxidation can be achieved in a single ABR treating AMD.     

CCB-based encapsulation of pyrite for remediation of acid mine drainage

Acid mine drainage (AMD) from abandoned coal mines continues to be one of the most significant environmental problems. Remediation of AMD requires an addition of lime source to decrease the acidity, and grouting the entire mine and encapsulating the pyrite by calcium-rich additives is often employed. Utilization of alkaline coal combustion by-products (CCBs) has gained acceptance in such remediation applications because of their cost-effectiveness. A study was conducted to investigate the effectiveness of CCBs to abate acid mine drainage by encapsulation of pyrite. Geomechanical, hydraulic, and environmental tests were performed on grouts prepared with various ratios of CCBs as well as an alternative free lime source, lime kiln dust (LKD). The results indicated that the mechanical properties of grouts were dependent on their free lime contents. Hydraulic conductivities of pyrite-grout columns were relatively high due to the coating of the pyrite rock with the grout rather than the filling of all of the void spaces, as commonly experienced in field applications. The leaching tests indicated that the presence of high amounts of lime in a grout is not solely sufficient to improve the quality of AMD, since the rate of dissolution of a high lime content grout may be slow due to its rapid hardening. Therefore, it is recommended that grouts be selected with consideration of their hardening capacities, as well as the percentage of lime content present in the mixture.     

Phosphorus removal performance of acid mine drainage from wastewater

Acid mine drainage (AMD) in Yunfu iron sulfide mine contain Fe(2+), Fe(3+), and Al(3+) up to 8000, 1700 and 1200 mg/L, respectively. Phosphorus removal from synthetic wastewater with 10mg/L of total phosphorus (TP) concentration and second municipal effluent with 3.5-4.0mg/L of TP concentration were conducted with the AMD by jar tests. Dosage of the AMD and initial pH of water are the two most important parameters affecting the performance of phosphorus removal of the AMD. The optimal phosphorus removal efficiency and residual iron ions (TFe) concentration are 97.0% and 3.0mg/L, respectively, at 1.61 Fe/P molar ratio and pH 8.03 for synthetic wastewater, and 92.1% and 0.32 mg/L, respectively, for second municipal effluent at 1.41 Fe/P molar ratio and pH 7.3. Resultant heavy metal concentration in effluents and precipitate was very low, and the risk of resultant heavy metal contamination was very small. The phosphorus removal performance of the AMD was much similar to that of ferric sulfate (FS) and polyferric sulfate (PFS), and better than that of FeSO(4). And residual TFe concentration in treated water arising from utilization of the AMD was similar to that of FeSO(4), and higher than that of FS and PFS. The AMD could be used as coagulant for phosphorus removal from wastewater directly due to the presence of Fe(2+), Fe(3+), and Al(3+) largely.     

Biological treatment of highly contaminated acid mine drainage in batch reactors: Long-term treatment and reactive mixture characterization

Passive bioreactors involving sulphate-reducing bacteria (SRB) are a practical alternative technology to treat acid mine drainage (AMD). Careful selection of the organic carbon source is important to ensure performance and long-term efficiency of the treatment. However, a rigorous and methodical characterization to predict the biodegradability of organic substrates by SRB still needs to be investigated. In the present study, four natural organic materials were thoroughly characterized to assess their ability to serve as substrates and to find a parameter that links organic carbon sources with their biodegradability. Three reactive mixtures were then comparatively evaluated for their performance to treat a highly contaminated AMD in long-term (152 days) batch experiments. All three mixtures were successful for sulphate reduction and metal (Fe, Ni, Cd, Zn, and Mn) removal (91.8-99.8%). Higher efficiencies were observed in the reactors with 30% (w/w) cellulosic wastes (maple wood chips and sawdust) which decreased sulphate concentrations from 5500 mg/L to <1mg/L, than in reactors with 2-3% cellulosic wastes, where final sulphate concentrations were in the range 2000-2750 mg/L. Organic material characterization indicated that higher C/N ratios, chemical oxygen demand (COD)/SO(4)(2-) ratios and dissolved organic carbon (DOC)/SO(4)(2-) ratios were associated with better sulphate-reducing conditions and metal removal. This work suggests that C/N and DOC/SO(4)(2-) ratios considered together are key parameters to assess the biodegradability of natural organic wastes under sulphate-reducing conditions.     

Removal of heavy metals from acid mine drainage (AMD) using coal fly ash, natural clinker and synthetic zeolites

Acid mine drainage (AMD) is a widespread environmental problem associated with both working and abandoned mining operations, resulting from the microbial oxidation of pyrite in presence of water and air, affording an acidic solution that contains toxic metal ions. The generation of AMD and release of dissolved heavy metals is an important concern facing the mining industry. The present study aimed at evaluating the use of low-cost sorbents like coal fly ash, natural clinker and synthetic zeolites to clean-up AMD generated at the Parys Mountain copper-lead-zinc deposit, Anglesey (North Wales), and to remove heavy metals and ammonium from AMD. pH played a very important role in the sorption/removal of the contaminants and a higher adsorbent ratio in the treatment of AMD promoted the increase of the pH, particularly using natural clinker-based faujasite (7.70-9.43) and the reduction of metal concentration. Na-phillipsite showed a lower efficiency as compared to that of faujasite. Selectivity of faujasite for metal removal was, in decreasing order, Fe>As>Pb>Zn>Cu>Ni>Cr. Based on these results, the use of these materials has the potential to provide improved methods for the treatment of AMD.     

反渗透处理金铜矿山酸性废水

用反渗透工艺处理某金铜矿山酸性废水,试验研究了工艺条件,结果表明,通过两段反渗透处理,水回收率可达36.79%,透过液可达标排放标准;浓缩液用硫化沉淀浮选法处理,得到含铜质量分数26.3%的铜渣,铜回收率可达74%,研究结果为矿山酸性废水治理提供了一种新思路.     

Removal and recovery of metal ions from acid mine drainage using lignite--A low cost sorbent

Acid mine drainage (AMD), has long been a significant environmental problem resulting from the microbial oxidation of iron pyrite in presence of water and air, affording an acidic solution that contains toxic metal ions. The main objective of this study was to remove and recover metal ions from acid mine drainage (AMD) by using lignite, a low cost sorbent. Lignite has been characterized and used for the AMD treatment. Sorption of ferrous, ferric, manganese, zinc and calcium in multi-component aqueous systems was investigated. Studies were performed at different pH to find optimum pH. To simulate industrial conditions for acid mine wastewater treatment, all the studies were performed using single and multi-columns setup in down flow mode. The empty bed contact time (EBCT) model was used for minimizing the sorbent usage. Recovery of the metal ions as well as regeneration of sorbent was achieved successfully using 0.1 M nitric acid without dismantling the columns.     

Copper electrowinning from acid mine drainage: A case study from the closed mine “Cerovo”

Copper removal from acid mine drainage originating from closed copper mine “Cerovo” RTB Bor, Serbia and containing approximately 1.3 g dm⁻³ of copper and a very small amount of Fe²⁺/Fe³⁺ ions, has been successfully performed by the direct electrowinning method using either a porous copper sheet or carbon felt as the cathode. A cell with a fluidised bed of inert turbulent promoters, also used in this study, may be considered as unacceptable for the purpose view, having a cell voltage between 12 and 14 V.The cells used in the electrowinning experiments were compared in terms of cell voltage, pH and copper concentration. The results showed that it is possible to remove copper successfully from the mine waters with a high degree of electrowinning—higher than 92% and with a satisfactorily average current efficiency (>60%). Depending on the process time and the applied current, a final copper concentration less than 0.1 g dm⁻³ was achieved. The specific energy consumption was approximately 7 kWh kg⁻¹ of deposited copper. A dense copper deposit was obtained when a three-dimensional electrode was used.     

In situ measurements of labile Al and Mn in acid mine drainage using diffusive gradients in thin films

The technique of diffusive gradients in thin films (DGT) can be used for in situ measurements of labile metal species in water, but the application for this method on acid mine drainage (AMD) is complicated due to reduced sampler adsorption of metals at low pH. This study evaluates the use of DGT on labile Al and Mn in AMD (pH 3.1-4.2). DGT measurements were performed both in standard solutions in the laboratory and in situ in the field. Laboratory results show that DGT can be used in water with pH as low as 3.0 for Al and 4.0 for Mn without correcting for reduced adsorption. Below pH 4.0, the adsorption of Mn showed a linearly decrease with pH to approximately 55% at pH 3.0. Taking this correction into account revealed that 84-100% of the total dissolved Al and Mn measured in the field was DGT-labile. Measurements using DGT agreed well with predictions using the speciation program WHAM VI. This study shows that the use of DGT can be extended below the previously reported pH working range for Al, and for Mn using a simple linear correction with respect to pH, and demonstrates that the technique can be applied for monitoring time-integrated labile metal concentrations at AMD sites.     

Effect of hardness on acute toxicity of metal mixtures using Daphnia magna: prediction of acid mine drainage toxicity

In this study, the effect of hardness on the combined outcome of metal mixtures was investigated using Daphnia magna. The toxic unit (TU) was calculated using modified LC(50) values based on the hardness (i.e., LC(50-soft) and LC(50-hard)). From a bioassay test, the degree of sensitivity to hardness on the toxicity changes was in the order: Cd相似文献   

煤矿瓦斯抽放监控系统数据采集模块的设计

数据采集在煤矿安全生产方面有着举足轻重的作用。在全面分析各种采集模块的基础上,提出了一种基于MSP430瓦斯监控系统数据采集的设计方案。该系统利用传感器采集现场数据,MSP430作为核心器件实时对采集数据进行处理、诊断和传信。它与过去瓦斯抽放监控数据采集模块相比,结构简单、体积小、功耗低,便于观测和处理,为进一步研发瓦斯监控数据采集模块提供新的实现方法。     

Fe2+ oxidation rate drastically affect the formation and phase of secondary iron hydroxysulfate mineral occurred in acid mine drainage

During the processes of secondary iron hydroxysulfate mineral formation, Fe²⁺ ion was oxidized by the following three methods: (1) biooxidation treatment by Acidithiobacillus ferrooxidans (A. ferrooxidans); (2) rapid abiotic oxidation of Fe²⁺ with H₂O₂ (rapid oxidation treatment); (3) slow abiotic oxidation of Fe²⁺ with H₂O₂ (slow oxidation treatment). X-ray diffraction (XRD) patterns, element composition, precipitate weight and total Fe removal efficiency were analyzed. The XRD patterns and element composition of precipitates synthesized through the biooxidation and the slow oxidation treatments well coincide with those of potassium jarosite, while precipitates formed at the initial stage of incubation in the rapid oxidation treatment showed a similar XRD pattern to schwertmannite. With the ongoing incubation, XRD patterns and element composition of the precipitates that occurred in the rapid oxidation treatment were gradually close to those in the biooxidation and the slow oxidation treatments. Due to the inhibition of A. ferrooxidans itself and its extracellular polymeric substances (EPS) in aggregation of precipitates, the amount of precipitates and soluble Fe removal efficiency were lower in the biooxidation treatment than in the slow oxidation treatment. Therefore, it is concluded that Fe²⁺ oxidation rate can greatly affect the mineral phase of precipitates, and slow oxidation of Fe²⁺ is helpful in improving jarosite formation.     

Recovery and purification of copper sulfide nanoparticles from acid mine drainage by biological sulfate reduction and microfiltration using low-cost ceramic membrane

Clean Technologies and Environmental Policy - Acid mine drainage (AMD) typically has a high amount of copper that can be recovered in pure form for different industrial applications. This study...     

Optimization of integrated chemical-biological degradation of a reactive azo dye using response surface methodology

The integrated chemical-biological degradation combining advanced oxidation by UV/H(2)O(2) followed by aerobic biodegradation was used to degrade C.I. Reactive Azo Red 195A, commonly used in the textile industry in Australia. An experimental design based on the response surface method was applied to evaluate the interactive effects of influencing factors (UV irradiation time, initial hydrogen peroxide dosage and recirculation ratio of the system) on decolourisation efficiency and optimizing the operating conditions of the treatment process. The effects were determined by the measurement of dye concentration and soluble chemical oxygen demand (S-COD). The results showed that the dye and S-COD removal were affected by all factors individually and interactively. Maximal colour degradation performance was predicted, and experimentally validated, with no recirculation, 30 min UV irradiation and 500 mgH(2)O(2)/L. The model predictions for colour removal, based on a three-factor/five-level Box-Wilson central composite design and the response surface method analysis, were found to be very close to additional experimental results obtained under near optimal conditions. This demonstrates the benefits of this approach in achieving good predictions while minimising the number of experiments required.     

Sulfide oxidation and acid mine drainage formation within two active tailings impoundments in the Golden Quadrangle of the Apuseni Mountains, Romania

Sulfidic mine tailings have to be classified as one of the major source of hazardous materials leading to water contamination. This study highlights the processes leading to sulfide oxidation and acid mine drainage (AMD) formation in the active stage of two tailings impoundments located in the southern part of the Apuseni Mountains, in Romania, a well-known region for its long-term gold-silver and metal mining activity. Sampling was undertaken when both impoundments were still in operation in order to assess their actual stage of oxidation and long-term behavior in terms of the potential for acid mine drainage generation. Both tailings have high potential for AMD formation (2.5 and 3.7 wt.% of pyrite equivalent, respectively) with lesser amount of carbonates (5.6 and 3.6 wt.% of calcite equivalent) as neutralization potential (ABA=-55.6 and -85.1 tCaCO(3)/1000 t ) and showed clear signs of sulfide oxidation yet during operation. Sequential extraction results indicate a stronger enrichment and mobility of elements in the oxidized tailings: Fe as Fe(III) oxy-hydroxides and oxides (transformation from sulfide minerals, leaching in oxidation zone), Ca mainly in water soluble and exchangeable form where gypsum and calcite are dissolved and higher mobility of Cu for Ribita and Pb for Mialu. Two processes leading to the formation of mine drainage at this stage could be highlighted (1) a neutral Fe(II) plume forming in the impoundment with ferrihydrite precipitation at its outcrop and (2) acid mine drainage seeping in the unsaturated zone of the active dam, leading to the formation of schwertmannite at its outcrop.     

Comparison and evaluation of the synthetic biopolymer poly-L-aspartic acid and the synthetic "plastic" polymer poly-acrylic acid for use in metal ion-exchange systems

Poly-L-aspartic acid (PLAsp), a biopolymer, and a similar synthetic polymer, poly-acrylic acid (PAA), each consisting of approximately 50 repeating Asp and acrylic acid monomers, respectively, were immobilized onto controlled pore glass (CPG) and evaluated for use as metal ion-exchange materials. Both polymers achieve metal complexation primarily through their repeating carboxylate side groups resulting in a similar binding trend for the metals tested (Ca(2+), Cd(2+), Co(2+), Cu(2+), Mg(2+), Mn(2+), Na(+), Ni(2+), Pb(2+)), with metal binding capacities ranging from <0.1 to 12 micromol metal/g column and <0.1 to 32 micromol metal/g column for PLAsp and PAA respectively. Cu(2+) and Pb(2+) exhibited strong binding to both materials, while the other metals demonstrated only weak or minimal binding. Both columns allowed for quantitative release of bound metals through acid stripping and experienced increased overall metal binding with increasing pH. Both systems also maintained similar structural and chemical stability when continuously exposed to neutral buffered, highly acidic, oxidizing, large molecule rich, and elevated temperature environments. The main differences between the two systems are the material cost and system biodegradability.     

Removal of chromium and toxic ions present in mine drainage by Ectodermis of Opuntia

This work presents conditions for hexavalent and trivalent chromium removal from aqueous solutions using natural, protonated and thermally treated Ectodermis of Opuntia. A removal of 77% of Cr(VI) and 99% of Cr(III) can be achieved. The sorbent material is characterized using scanning electron microscopy, energy dispersive X-ray spectroscopy, infrared spectroscopy, thermogravimetric analysis, before and after the contact with the chromium containing aqueous media. The results obtained from the characterization techniques indicate that the metal ion remains on the surface of the sorbent material. The percentage removal is found to depend on the initial chromium concentration and pH. The Cr(VI) and Cr(III) uptake process is maximum at pH 4, using 0.1g of sorbent per liter of aqueous solution. The natural Ectodermis of Opuntia showed a chromium adsorption capacity that was adequately described by the Langmuir adsorption isotherm. Finally, an actual mine drainage sample that contained Cd, Cr, Cu, Fe Zn, Ni and Pb was tested under optimal conditions for chromium removal and Ectodermis of Opuntia was found to be a suitable sorbent material. The use of this waste material for the treatment of metal-containing aqueous solutions as well as mine drainage is effective and economical.     

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Comparative energy efficiency of wastewater treatment technologies: a synthetic index approach

Improving the energy efficiency of wastewater treatment plants (WWTPs) provides notable economic and environmental benefits to society. Several studies have benchmarked the energy performance of WWTPs, but they did not take into account for differences in the wastewater treatment technologies they used, thus obscuring their relative efficiencies in removing harmful pollutants. To overcome this shortcoming, this study assessed and compared the energy efficiencies of five wastewater treatment technologies. To do so, the metafrontier approach was used in order to account for the technological differences among plants in removing pollutants. The results evidenced that energy efficiencies for WWTPs using attached-growth processes were higher than for WWTPs using suspended-growth technologies as secondary treatment. Moreover, higher pollutant removal efficiencies associated with biological removal of nutrients compensated for the higher energy requirements of this technology, making these WWTPs more energy efficient in the removal of pollutants. The results of this study provide essential information for improving the sustainability of current WWTPs and can support decision-making in the planning of new wastewater treatment facilities.