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1.
Treatment of acid mine drainage (AMD) highly rich in sulfate and multiple metal elements has been investigated in a continuous flow column experiment using organic and inorganic reactive media. Treatment substrates that composed of spent mushroom compost (SMC), limestone, activated sludge and woodchips were incorporated into bacterial sulfate reduction (BSR) treatment for AMD. SMC greatly assisted the removals of sulfate and metals and acted as essential carbon source for sulfate-reducing bacteria (SRB). Alkalinity produced by dissolution of limestone and metabolism of SRB has provided acidity neutralization capacity for AMD where pH was maintained at neutral state, thus aiding the removal of sulfate. Fe, Pb, Cu, Zn and Al were effectively removed (87–100%); however, Mn was not successfully removed despite initial Mn reduction during early phase due to interference with Fe. The first half of the treatment was an essential phase for removal of most metals where contaminants were primarily removed by the BSR in addition to carbonate dissolution function. The importance of BSR in the presence of organic materials was also supported by metal fraction analysis that primary metal accumulation occurs mainly through metal adsorption onto the organic matter, e.g., as sulfides and onto Fe/Mn oxides surfaces.  相似文献   

2.
Mining influenced water (MIW) is often characterized by low pH (acid mine drainage) and high dissolved metal concentrations. Treatment of MIW is often required to mitigate these two characteristics. One option, which has traditionally been used only for pH neutralization, is limestone based treatment systems. However, there is field evidence that limestone systems are also effective at removing metals such as Zn and Ni. These field systems are often too complex to examine specific removal hypotheses, while certain modes of laboratory examination are too simplistic to be applied to field settings. Instead, the batch reactors used here were intentionally more complex to allow for the examination of how certain variables (pH, alkalinity, and primary metal concentrations) interact to affect Zn and Ni removal. The data herein suggest that one possible removal process for Zn and Ni is through surface interactions on the precipitated primary metals Fe and Al. The specific processes are complex and conditional, and were found to depend on pH, alkalinity, and total amount of primary metal present. Indeed the complex interplay between these variables led to an observed local maximum in Zn removal that would not be predicted from traditional surface complexation theory or observed from simpler experimental systems.  相似文献   

3.
Reactive mixtures to be used in a permeable reactive barrier (PRB) for the treatment of low quality groundwater derived from a mine waste rock storage site were evaluated. Low pH drainage water from the site contained high concentrations of sulfate and dissolved metals, including Al, Co, Ni, and Zn. Column experiments were conducted to evaluate whether mixtures containing either peat moss (as an organic carbon source) or a mixture of peat moss and granular zero-valent iron (ZVI) filings, in addition to small amounts of lime and/or limestone, were suitable treatment materials for removing these metals from the water. The experimental results showed that the mixtures promote bacterially-mediated sulfate reduction and metal removal by precipitation of metal sulfides, metal carbonate/hydroxide precipitation, and adsorption under relatively high pH conditions (pH of 7–8). Both reactive mixtures removed influent dissolved metals to near or below the limit of detection in the effluent throughout the experiment; however, influent-level concentrations of the metals of interest gradually moved through the column containing peat alone, as the pH neutralizing ability in the mixture was consumed. In contrast, the column containing both peat and ZVI showed very little breakthrough of the influent metals, suggesting that the longevity of the mixture including ZVI will be much longer than the mixture containing peat alone. The results show that both reactive mixtures should be effective in a PRB installation as long as neutral pH conditions and microbial activity are maintained. The cost to performance ratio of the two reactive mixtures will be a key factor in determining which mixture is best suited for a particular site.  相似文献   

4.
酸性矿山废水(acid mine drainage,AMD)是一类pH低并含有大量有毒金属元素的废水。AMD及受其影响的环境中次生高铁矿物类型主要包括羟基硫酸高铁矿物(如黄铁矾和施威特曼石等)和一些含水氧化铁矿物(如针铁矿和水铁矿等),而且这些矿物在不同条件下会发生相转变,如施氏矿物向针铁矿或黄铁矾矿物相转化。基于酸性环境中生物成因次生矿物的形成会"自然钝化"或"清除"废水中铁和有毒金属这一现象所获得的启示,提出利用这些矿物作为环境吸附材料去除地下水中砷,不但吸附量大(如施氏矿物对As的吸附可高达120mg/g),而且可直接吸附As(III),还几乎不受地下水中其他元素影响。利用AMD环境中羟基硫酸高铁矿物形成的原理,可将其应用于AMD石灰中和主动处理系统中,构成"强化微生物氧化诱导成矿-石灰中和"的联合主动处理系统,以提高AMD处理效果和降低石灰用量。利用微生物强化氧化与次生矿物晶体不断生长的原理构筑生物渗透性反应墙(PRB)并和石灰石渗透沟渠耦联,形成新型的AMD联合被动处理系统,这将有助于大幅度增加处理系统的寿命和处理效率。此外,文中还探讨了上述生物成因矿物形成在AMD和地下水处理方面应用的优点以及今后需要继续研究的问题。  相似文献   

5.
Vertical flow bioreactors (VFBR) are often used as a component of passive treatment systems (PTS) to treat mine drainage. One of the primary purposes of VFBR is to remove trace metals from mine drainage and retain them in the organic substrate. Elevated ionic strength may impact the performance of VFBR and affect their ability to remove trace metals. A paired-comparison study was performed to determine how products of trace metal removal may change when ionic strength is elevated due to increased concentrations of common contributors to TDS, specifically sodium and sulfate. A sequential extraction procedure (SEP) and acid-volatile sulfide/simultaneously extracted metals analyses (AVS/SEM) were used to determine dominant Cd, Mn, Ni, Pb, and Zn removal products in bench-scale VFBR. Elevated ionic strength resulted in more Pb being retained in the substrates as an insoluble sulfide and less Mn being removed via adsorption to the substrates. An increase in ionic strength had a greater impact on adsorption when sulfate reduction was inhibited, with percentages of Mn and Zn removed via this mechanism decreasing by at least half. This finding could be particularly significant at the start of VFBR operation when adsorption is expected to be the primary removal mechanism.  相似文献   

6.
Acid mine drainage was reacted with coal fly ash over a 24 h reaction time and species removal trends evaluated. The evolving process water chemistry was modeled by the geochemical code PHREEQC using WATEQ4 database. Mineralogical analysis of the resulting solid residues was done by X-ray diffraction analysis. Selective sequential extraction was used to evaluate the transfer of species from both acid mine drainage and fly ash to less labile mineral phases that precipitated out. The quantity of fly ash, volume of acid mine drainage in the reaction mixture and reaction time dictated whether the final solution at a given contact time will have a dominant acidic or basic character. Inorganic species removal was dependent on the pH regime generated at a specific reaction time. Sulphate concentration was controlled by precipitation of gypsum, barite, celestite and adsorption on iron-oxy-hydroxides at pH > 5.5. Increase of pH in solution with contact time caused the removal of the metal ions mainly by precipitation, co-precipitation and adsorption. PHREEQC predicted precipitation of iron, aluminium, manganese-bearing phases at pH 5.53–9.12. An amorphous fraction was observed to be the most important in retention of the major and minor species at pH > 6.32. The carbonate fraction was observed to be an important retention pathway at pH 4–5 mainly due to initial local pockets of high alkalinity on surfaces of fly ash particles. Boron was observed to have a strong retention in the carbonate fraction.  相似文献   

7.

Sulfide‐rich materials comprising the waste at the abandoned Montalbion silver mine have undergone extensive oxidation prior to and after mining. Weathering has led to the development of an abundant and varied secondary mineral assemblage throughout the waste material. Post‐mining minerals are dominantly metal and/or alkali (hydrous) sulfates, and generally occur as earthy encrustations or floury dustings on the surface of other mineral grains. The variable solubility of these efflorescences combined with the irregular rainfall controls the chemistry of seepage waters emanating from the waste dumps. Irregular rainfall events dissolve the soluble efflorescences that have built up during dry periods, resulting in ‘first‐flush’ acid (pH 2.6–3.8) waters with elevated sulfate, Fe, Cu and Zn contents. Less‐soluble efflorescences, such as anglesite and plumbojarosite, retain Pb in the waste dump. Metal‐rich (Al, Cd, Co, Cu, Fe, Mn, Ni, Zn) acid mine drainage waters enter the local creek system. Oxygenation and hydrolysis of Fe lead to the formation of Fe‐rich precipitates (schwertmannite, goethite, amorphous Fe compounds) that, through adsorption and coprecipitation, preferentially incorporate As, Sb and In. Furthermore, during dry periods, evaporative precipitation of hydrous alkali and metal sulfate efflorescences occurs on the perimeter of stagnant pools. Flushing of the streambed by neutral pH waters during heavy rainfall events dissolves the efflorescences resulting in remobilisation and transport of sulfate and metals (particularly Cd, Zn) downstream. Thus, in areas of seasonal or irregular rainfall, secondary efflorescent minerals present in waste materials or drainage channels have an important influence on the chemistry of surface waters.  相似文献   

8.
《Applied Geochemistry》1997,12(3):243-254
Column flow-through experiments reacting wastewater solutions with sandy loam soil samples were performed to study heavy metal attenuation by two soils with different physical and chemical properties. Reacted soil columns were leached with synthetic acid rain to study the mobility of attenuated heavy metals under leaching conditions. This study demonstrates that cation exchange, surface adsorption, chelation with solid organic material, and precipitation were the important attenuation mechanisms for the heavy metals (Cd, Cr, Cu, Mo, Ph, and Zn). Adsorption on soil hydrous oxide surfaces was the primary attenuation mechanism for Cd and Zn in both soils, and for Cu in a soil with low organic matter content. Wastewater solution pH is also an important factor that influences the retention of heavy metals. Cadmium, Cu, Cr, and Zn became mobile after prolonged application of spiked wastewater solution, either through saturation of soil adsorption sites or due to decreasing pH. Only Cr, Pb, and Mo, which are attenuated primarily through precipitation, show significant net retention by soil. Acid rain water removed heavy metals left in the column residual pore solution and weakly sorbed heavy metals in the soils, and has the ability to mobilize some strongly attenuated heavy metals, especially when the soil organic matter content is high. The results have important applications in predicting heavy metal mobility in contaminated soil, the disposal of acid mine drainage, and assessing the risks of landfall leachate leakage.  相似文献   

9.
The sediment from an acid mine drainage affected reservoir of Guizhou province of China has the iron and arsenic concentration of about 400 and 2.6 g/kg, respectively. Sediment cores were collected, and were used to study the arsenic behavior in the seriously acidified reservoir from the viewpoint of chemical thermodynamics. The limestone neutralization and ferric iron hydrolysis regulated the porewater pH from about 2.9–5.8. The reductive dissolution of As–Fe-rich (hydr)oxides under the mild acidic conditions was the main mechanism for the release of absorbed arsenic into porewater. The maximum concentrations of iron, sulfate and arsenic reached to about 2,800, 9,000 and 1 mg/l, respectively. Arsenic speciation transformation and hydrous ferric oxide (HFO) crystallization enhanced the arsenic mobility in sediment. In addition, the iron sulfide minerals diagenesis could play a role in removing the dissolved arsenic from porewater. The actual distribution of arsenic concentration in porewater was well simulated using the model of surface complexation of arsenic to HFO. Although arsenic concentration in porewater could be above 100 times higher than that of reservoir water, it was not easy to release into the reservoir water through diffusion, because the shallow sediment had relatively strong arsenic adsorption capacity, and new HFO could be generated continuously at the sediment water interface.  相似文献   

10.
Both sulfate and conductivity are useful indicators of acid mine drainage (AMD) contamination. Unlike pH, they are both extremely sensitive to AMD even where large dilutions have occurred. The advantage of using sulfate to trace AMD is that unlike other ions it is not removed to any great extent by sorption or precipitation processes, being unaffected by fluctuations in pH. These two parameters are also closely associated as would be expected, as conductivity is especially sensitive to sulfate ions. Therefore, as sulfate analysis is difficult in the field, conductivity can be used to predict sulfate concentration in both AMD and contaminated surface waters using regression analysis. Most accurate predictions are achieved by using equations given for specific conductivity ranges or AMD sources. There is also potential to use conductivity to predict approximate concentrations of key metals when the pH of the water is within their respective solubility ranges.  相似文献   

11.
The removal of Cd, Cu, Ni and Zn from dilute mine water by using several geological materials including pure limestone, sand, carbonaceous limestone and brecciated limestone was performed on a laboratory scale. The results showed that to add geological materials in combination with sodium carbonate injection would notably enhance the efficiency of heavy metal removal to varying degrees. Pure limestone was found the best one among the four materials mentioned above for removing heavy metals from mine water. The removal efficiencies of pure limestone when it is ground as fine as 30–60 meshes are 58.6% for Cd, 100% for Cu, 47.8% for Ni, and 36.8% for Zn at 20°C. The optimum pH is about 8.9 to 9.1. The mechanism of higher effective removal, perhaps, is primarily due to co-precipitation under the control of calcite-related pH value. According to this research, Na2CO3 injection manners, including slug dosing and drip-wise, seemed to have little impact on the efficiency of heavy metal removal.  相似文献   

12.
放射性核素在地下介质中迁移机理与模型研究   总被引：5，自引：0，他引：5  
介绍了铀尾矿库的物理、化学概念模型和其中重金属、放射性核素迁移的一般过程 ;论述了沉淀作用、络合作用和胶体作用对放射性核素迁移的影响 ;重点讨论了描述吸附作用的离子交换模型和表面络合模型的建模机理 ;对定量模拟放射性核素迁移行为的 Kd模型、表面络合模型及“反应 -运移模型”的应用进行了评述。  相似文献   

13.
The objective of the present study is to evaluate the absorption efficacy of H. fusiformis biochar (HFB) for the removal of phenol and heavy metals from single and mixed solute systems of these species under different experimental conditions. The effects of contact time, pH change, initial phenol concentration, and heavy metal concentration on the adsorption capacity of HFB were investigated. The kinetics and equilibrium models of sorption of the components of the single and mixed solute systems on HFB were also studied. The experimental data were fitted to kinetic and equilibrium models. The batch experiments revealed that 360 min of contact time was sufficient to achieve equilibrium for the adsorption of both phenol and heavy metals. The adsorption of phenol and nickel by HFB followed the pseudo-second-order kinetic model, which was quite adequate for describing the adsorption mechanism. The equilibrium data for the adsorption of phenol and heavy metals fit well to the Langmuir model with regression coefficients of R 2 > 0.819. The maximum Langmuir adsorption capacities were 10.39, 12.13, 22.25, 2.24, 2.89, and 22.03 mg/g for phenol, Ni2+, Zn2+, Cu2+, Pb2+, and Cd2+, respectively. Moreover, HFB exhibited optimal sorption under slightly acidic conditions at pH 6. The HFB used in the present study exhibited higher adsorption capacity for the removal of phenol and heavy metals from aqueous solutions compared to documented sorbents. These results demonstrate that HFB is potentially useful for alleviating the harmful effects of phenol and heavy metal in wastewater treatment systems.  相似文献   

14.
The chemical and physical treatment mechanisms by which crab shell removes metals from mine impacted water (MIW) were evaluated under anaerobic and biologically limited conditions in closed systems and kinetic tests. Raw (R-SC20) and deproteinized (DP-SC20) crab shell were tested and compared to limestone to quantify the contribution of chitin-associated minerals and proteins to alkalinity generation and metal precipitation. Single-metal closed systems (initial Mn and Fe = 0.18 mM and Al = 0.34 mM) containing 5 g/L of either R- or DP-SC20, yielded an increase in pH from 3 to 9.2-10.2, generation of 0.83-1.87 mM of alkalinity, and resulted in ?95% removal of metals within 72 h. In contrast, 5-125 g limestone/L only raised the pH to 7.8-8.3, produced lower alkalinity (0.56-0.63 mM), and resulted in less metal removal (?85%). In kinetic tests with 5 g-DP-SC20/L, removal of ?95% of the initial metal load was achieved after 0.5, 6, and 48 h for Al, Fe, and Mn, respectively. Geochemical calculations (PHREEQC) indicate that limestone-treated systems were close to equilibrium with calcite (CaCO3), whereas octacalcium phosphate (Ca4H(PO4)3) appears to be a controlling phase in systems treated with R- and DP-SC20. The probable mechanisms for Mn removal are the precipitation of rhodochrosite (MnCO3) and/or sorption. In the case of Al and Fe, geochemical calculations point to the precipitation of hydroxides; however, visual observations in Fe systems suggest the formation of green rust, a precursor of other, more stable phases like goethite or lepidocrocite. Several factors may account for the faster changes observed with R- and DP-SC20 compared to limestone: increased dissolution and degree of supersaturation, the presence of phosphates, the release of organic compounds, and a significantly larger surface area. These results are the first to verify and quantify the capacity of crab shell-associated minerals to treat MIW under biologically limited conditions.  相似文献   

15.
Adsorption of copper, cadmium and nickel at low concentrations on goethite was studied in the presence of the simple organic ligands oxalate, salicylate, and pyromellitate. The experimental metal adsorption behavior was compared to calculations with a surface complexation model to evaluate the most important interactions. Oxalate mostly decreased Cu and Ni adsorption at high pH-values by competition between solution and surface complexation but had no effect on Cd adsorption. Cu adsorption in the presence of oxalate below pH 6 could best be described by defining a ternary complex of type A (surface-metal-ligand). Salicylate had only minor effects on metal adsorption. The adsorption of Cu in the presence of salicylate above pH 5 could be explained by a ternary complex of type A. Pyromellitate increased the adsorption of Cu and Cd in the acidic pH-range, likely by formation of ternary surface complexes of type B (surface-ligand-metal).  相似文献   

16.
Granular activated carbon produced from palm kernel shell was used as adsorbent to remove copper, nickel and lead ions from a synthesized industrial wastewater.Laboratory experimental investigation was carried out to identify the effect of pH and contact time on adsorption of lead, copper and nickel from the mixed metals solution. Equilibrium adsorption experiments at ambient room temperature were carried out and fitted to Langmuir and Freundlich models. Results showed that pH 5 was the most suitable, while the maximum adsorbent capacity was at a dosage of 1 g/L, recording a sorption capacity of 1.337 mg/g for lead, 1.581 mg/g for copper and 0.130 mg/g for nickel. The percentage metal removal approached equilibrium within 30 min for lead, 75 min for copper and nickel, with lead recording 100 %, copper 97 % and nickel 55 % removal, having a trend of Pb2+ > Cu2+ > Ni2+. Langmuir model had higher R2 values of 0.977, 0.817 and 0.978 for copper, nickel and lead respectively, which fitted the equilibrium adsorption process more than Freundlich model for the three metals.  相似文献   

17.
The purification property of pyrite was discussed by using in situ attenuated total reflection-Fourier transform infrared spectroscopy. Results showed that there might be dissolution–adsorption precipitation equilibrium of heavy metals on the surface of pyrite, which is dependent on the surface oxidation of pyrite and the neutralization reaction of carbonate within pyrite. If there was excessive carbonate within pyrite, the “dissolution” of metals would be less than that of the “adsorption precipitation,” making pyrite exhibit its purification property. Based on this property, pyrite was used to process simulated wastewater containing Pb2+, Hg2+, Cd2+, Cr(VI) and Cu2+. Results showed that the efficiencies of metal removal exceeded 96%. In addition, reflectance spectroscopy and absorption spectroscopy were also utilized to investigate the simulated metal-bearing wastewater treatment process. Analysis by diffused reflectance infrared Fourier transform spectroscopy confirmed that the superficial hydroxyl groups in pyrite reacted with metal ions during the wastewater treatment process. Reflectance spectroscopy in the visible region was used to characterize the variation in particle size and specific surface area of pyrite during the wastewater treatment process, which explained its increasing activity when reutilized. Further, analysis by absorption spectroscopy and X-ray photoelectron spectroscopy indicated that the process involved when using pyrite for the treatment of Cr(VI)-containing wastewater was an adsorption–precipitation process.  相似文献   

18.
The effects of varying operating conditions on metals removal from aqueous solution using a novel nano-size composite adsorbent are reported in this paper. Characterization of the composite adsorbent material showed successful production of carbon nanotubes on granular activated carbon using 1 % nickel as catalyst. In the laboratory adsorption experiment, initial mixed metals concentration of 2.0 mg/L Cu2+, 1.5 mg/L Pb2+ and 0.8 mg/L Ni2+ were synthesized based on metals concentration from samples collected from a semiconductor industry effluent. The effects of operation conditions on metals removal using composite adsorbent were investigated. Experimental conditions resulting in optimal metals adsorption were observed at pH 5, 1 g/L dosage and 60 min contact time. It was noted that the percentage of metals removal at the equilibrium condition varied for each metal, with lead recording 99 %, copper 61 % and nickel 20 %, giving metal affinity trend of Pb2+ > Cu2+ > Ni2+ on the adsorbent. Langmuir’s adsorption isotherm model gave a higher R2 value of 0.93, 0.89 and 0.986 for copper, nickel and lead, respectively, over that of Freundlich model during the adsorption process of the three metals in matrix solution.  相似文献   

19.
This study was performed to investigate the operating status, evaluate the problems, and discuss possible improvement methods of passive treatment systems for acid mine drainage (AMD) in South Korea. Thirty-five passive treatment systems in 29 mines have been constructed from 1996 to 2002 using successive alkalinity producing systems (SAPS) as the main treatment process. We investigated 29 systems (two for metal mines), 19 of which revealed various problems. Overflows of drainage from SAPS, wetland, or oxidation ponds were caused by the flow rate exceeding the capacities of the facilities or by the reduced permeability of the organic substance layer. Leakages occurred at various parts of the systems. In some cases, clogged and broken pipes at the mouths of the mine adits made the whole system unusable. Some systems showed very low efficiencies without apparent leakage or overflow. Even though the systems showed fairly good efficiencies in metal removal ratios (mainly iron) and pH control; sulfate removal rates were very poor except in three systems, which may indicate very poor sulfate reductions with sulfate reducing bacteria (SRB) as a means.  相似文献   

20.
The acid mine drainage (AMD) discharged from the Hejiacun uranium mine in central Hunan (China) was sampled and analyzed using ICP-MS techniques. The analyzing results show that the AMD is characterized by the major ions FeTotal, Mn, Al and Si, and is concentrated with heavy metals and metalloids including Cd, Co, Ni, Zn, U, Cu, Pb, Tl, V, Cr, Se, As and Sb. During the AMD flowing downstream, the dissolved heavy metals were removed from the AMD waters through adsorption onto and co-precipitation with metal-oxhydroxides coated on the streambed. Among these metals, Cd, Co, Ni, Zn, U, Cu, Pb and Tl are negatively correlated to pH values, and positively correlated to major ions Fe, Al, Si, Mn, Mg, Ca and K. The metals/metalloids V, Cr, Se, As and Sb are conservative in the AMD solution, and negatively-correlated to major ions Na, Ca and Mg. Due to the above different behaviors of these chemical elements, the pH-negatively related metals (PM) and the conservative metals (CM) are identified; the PM metals include Cd, Co, Ni, Zn, U, Cu, Pb and Tl, and the CM metals V, Cr, Se, As and Sb. Based on understanding the geochemistry of PM and CM metals in the AMD waters, a new equation: EXT = (Acidity + PM)/pH + CM × pH, is proposed to estimate and evaluate extent of heavy-metal pollution (EXT) of AMD. The evaluation results show that the AMD and surface waters of the mine area have high EXT values, and they could be the potential source of heavy-metal contamination of the surrounding environment. Therefore, it is suggested that both the AMD and surface waters should be treated before they are drained out of the mine district, for which the traditional dilution and neutralization methods can be applied to remove the PM metals from the AMD waters, and new techniques through reducing the pH value of the downstream AMD waters should be developed for removal of the CM metals.  相似文献   

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