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1.
Abiotic degradation of chlorinated solvents by reactive iron minerals such as iron sulfides, magnetite, green rust, and other Fe(II)‐containing minerals has been observed in both laboratory and field studies. These reactive iron minerals form under iron‐ and sulfate‐reducing conditions which are commonly found in permeable reactive barriers (PRBs), enhanced reductive dechlorination (ERD) treatment locations, landfills, and aquifers that are chemically reducing. The objective of this review is to synthesize current understanding of abiotic degradation of chlorinated solvents by reactive iron minerals, with special focus on how abiotic processes relate to groundwater remediation. Degradation of chlorinated solvents by reactive minerals can proceed through reductive elimination, hydrogenolysis, dehydrohalogenation, and hydrolysis reactions. Degradation products of abiotic reactions depend on degradation pathways and parent compounds. Some degradation products (e.g., acetylene) have the potential to serve as a signature product for demonstrating abiotic reactions. Laboratory and field studies show that various minerals have a range of reactivity toward chlorinated solvents. A general trend of mineral reactivity for degradation of chlorinated solvents can be approximated as follows: disordered FeS > FeS > Fe(0) > FeS2 > sorbed Fe2+ > green rust = magnetite > biotite = vermiculite. Reaction kinetics are also influenced by factors such as pH, natural organic matter (NOM), coexisting metal ions, and sulfide concentration in the system. In practice, abiotic reactions can be engineered to stimulate reactive mineral formation for groundwater remediation. Under appropriate site geochemical conditions, abiotic reactions can occur naturally, and can be incorporated into remedial strategies such as monitored natural attenuation.  相似文献   

2.
Diganta Bhusan Das 《水文研究》2002,16(17):3393-3418
Hydrodynamic modelling for analysis of groundwater flow through permeable reactive barriers (PRBs) is addressed in this paper. Permeable reactive barriers constitute an emerging technology for in situ remediation of groundwater contamination and have many advantages over the traditional ex situ treatment methods. The transport domains during groundwater flow through PRBs often may involve free‐flow or non‐porous sections. To model the fluid mobility efficiently in such situations, the free and porous flow zones (PRBs) must be studied in conjunction with each other. The present paper is devoted to the analysis of groundwater flow through combined free flow domains and PRBs. The free‐flow regime is modelled using the Navier–Stokes equations whereas the permeable barriers are simulated by either the Darcy or the Brinkman equation. In order to couple the governing equations of motions, well‐posed mathematical formulations of matching boundary conditions are prescribed at the interface between the free‐groundwater‐flow zones and the permeable barriers. Combination of the Navier–Stokes equations with the Brinkman equation is more straightforward owing to their analogous forms. However, the Navier–Stokes and Darcy equations are incompatible mathematically and cannot be linked directly. The problem is resolved in this paper by invoking validated hydrodynamical expressions for describing the flow behaviour at the interfaces between free‐flow and porous zones. Three schemes for the analyses of fluid flow in combined domains are applied to the case of groundwater flow through permeable reactive barriers and different model results are compared. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

3.
Lin L  Benson CH  Lawson EM 《Ground water》2005,43(4):582-596
This paper describes reactive transport simulations conducted to assess the impact of mineral fouling on the hydraulic behavior of continuous-wall permeable reactive barriers (PRBs) employing granular zero-valent iron (ZVI) in carbonate-rich alluvial aquifers. The reactive transport model included a geochemical algorithm for simulating corrosion and mineral precipitation reactions that have been observed in ZVI PRBs. Results of simulations show that porosity and hydraulic conductivity of the ZVI decrease over time and that flows are redistributed throughout the PRB in response to fouling of the pore space. Under typical conditions, only subtle changes occur within the first 10 years (i.e., duration of the current field experience record with PRBs), and the most significant changes do not occur until the PRB has operated for at least 30 years. However, changes can occur sooner (or later) if the rate at which mineral-forming ions are delivered to the PRB is higher (or lower) than that expected under typical conditions (i.e., due to higher/lower flow rate or inflowing ground water that has higher/lower ionic strength). When the PRB is more permeable than the aquifer, the median Darcy flux in the PRB does not change appreciably over time because the aquifer controls the rate of flow through the PRB. However, seepage velocities in the PRB increase, and residence times decrease, due to porosity reductions caused by accumulation of minerals in the pore space. When fouling becomes extensive, bypassing and reductions in flow rate in the PRB occur.  相似文献   

4.
A new in‐situ remediation concept termed a Horizontal Reactive Media Treatment Well (HRX Well®) is presented that utilizes horizontal wells filled with reactive media to passively treat contaminated groundwater in‐situ. The approach involves the use of large‐diameter directionally drilled horizontal wells filled with granular reactive media generally installed parallel to the direction of groundwater flow. The design leverages natural “flow‐focusing” behavior induced by the high in‐well hydraulic conductivity of the reactive media relative to the aquifer hydraulic conductivity to passively capture and treat proportionally large volumes of groundwater within the well. Clean groundwater then exits the horizontal well along its downgradient sections. Many different types of solid granular reactive media are already available (e.g., zero valent iron, activated carbon, ion exchange resins, zeolite, apatite, chitin); therefore, this concept could be used to address a wide range of contaminants. Three‐dimensional flow and transport simulations were completed to assess the general hydraulic performance, capture zones, residence times, effects of aquifer heterogeneity, and treatment effectiveness of the concept. The results demonstrate that capture and treatment widths of up to tens of feet can be achieved for many aquifer settings, and that reductions in downgradient concentrations and contaminant mass flux are nearly immediate. For a representative example, the predicted treatment zone width for the HRX Well is approximately 27 to 44 feet, and contaminant concentrations immediately downgradient of the HRX Well decreased an order of magnitude within 10 days. A series of laboratory‐scale physical tests (i.e., tank tests) were completed that further demonstrate the concept and confirm model prediction performance. For example, the breakthrough time, peak concentration and total mass recovery of methylene blue (reactive tracer) was about 2, 35, and 20 times (respectively) less than chloride (conservative tracer) at the outlet of the tank‐scale HRX Well.  相似文献   

5.
The Cercis siliquastrum tree leaves are introduced as a low cost biosorbent for removal of Ag(I) from aqueous solution in a batch system. FT‐IR, XRD analysis, and potentiometric titration illustrate that the adsorption took place and the acidic functional group (carboxyl) of the sorbent was involved in the biosorption process. In addition, it was observed that the pH beyond pHpzc 4.4 is favorable for the removal procedure. The effect of operating variables such as initial pH, temperature, initial metal ion concentration, and sorbent mass on the Ag(I) biosorption was analyzed using response surface methodology (RSM). The proposed quadratic model resulting from the central composite design approach (CCD) fitted very well to the experimental data. The optimum condition obtained with RSM was an initial concentration of Ag(I) of 85 mg L?1, pH = 6.3 and sorbent mass 0.19 g. The applicability of different kinetic and isotherm models for current biosorption process was evaluated. The isotherm, kinetic, and thermodynamic studies showed the details of sorbate‐sorbent behavior. The competitive effect of alkaline and alkaline earth metal ions during the loading of Ag(I) was also considered.  相似文献   

6.
Two of the biggest drawbacks of using permeable reactive barriers (PRBs) to treat contaminated ground water are the high capital cost of installation, particularly when the contaminated ground water is deep below ground surface, and the uncertainty of whether or not PRBs remain effective for the long time scales (e.g., decades) needed for many contaminant plumes. The use of an injection-extraction treatment well pair (IETWP) for capture and treatment of contaminated ground water can circumvent these difficulties, while still providing many of the same advantages offered by PRBs. In this paper, the hydraulics of IETWPs and PRBs are compared, focusing primarily on the width of the captured plume. It is demonstrated that IETWPs act as hydraulic barriers in a manner similar to PRBs, and that IETWPs provide excellent plume capture. A mathematical expression is presented for the plume capture width of an IETWP oriented perpendicular to the ground water flow direction in a homogeneous aquifer. Also discussed are other practical considerations that might determine whether an IETWP is better suited than a PRB for a particular contaminated site; these considerations include operating and maintenance costs, and the conditions under which an IETWP system can be used for in situ remediation.  相似文献   

7.
A new sorbent was prepared by loading rhodamine B on Amberlite IR‐120. Various physico‐chemical parameters such as effects of adsorbate concentration, contact time, pH, and temperature on the sorption of the dye have been studied. Thermodynamic parameters (ΔH° and ΔS°) were also evaluated for the sorption of dye. Kinetic studies revealed that the sorption of the dye was best fit for pseudo‐second‐order kinetic. The metal ion uptake in different solvent systems has been explored through column studies. On the basis of distribution coefficient (Kd), some heavy metal ions of analytical interest from binary mixtures have been separated. The limit of detection (LOD) for the Ni2+ and Fe3+ metal ions was 0.81 and 0.60 µg L?1, and the limit of quantification (LOQ) was found to be 2.72 and 2.0 µg L?1. This sorbent has also been successfully applied in the analysis of multivitamin formulation. The applicability of the modified resin in the separation of heavy metals constituting real and synthetic samples has been explored.  相似文献   

8.
MCPA (4‐chloro‐2‐methylphenoxyacetic acid) is an acidic herbicide widely used on olive crops in Spain. Due to its anionic form at natural soil pH, there is high risk of leaching and groundwater contamination by the use of this herbicide. The aim of this work was to study the effects of organoclay‐based formulations of MCPA and olive oil waste amendment on MCPA leaching in a sandy loam soil. For this purpose, batch adsorption and column leaching studies were performed. The organoclays used to prepare the clay‐based formulations of MCPA were obtained by treating Wyoming montmorillonite (SWy‐2) and Arizona montmorillonite (SAz‐1) with an amount of hexadecyltrimethylammonium (HDTMA) cation equal to 100% of the CEC of the montmorillonites. The organic residue used in this study was a solid waste from olive oil production (olive oil waste, OOW). The soil was amended with the organic residue at the rate of 10% (w/w). Batch release and column leaching studies indicated that organoclay‐based formulations of MCPA reduced the release rate and the leaching of the herbicide as compared to the use of a conventional formulation containing the herbicide in an immediately available form. The increase in soil organic matter of the soil upon amendment with the organic residue also resulted in greater adsorption and reduced leaching of MCPA in the soil. Accordingly, both the use of organoclay‐based formulations and the amendment of soil with OOW are proposed as efficient strategies to reduce extensive leaching losses associated with the application of MCPA in high‐risk scenarios, such as Mediterranean olive groves.  相似文献   

9.
Soil contamination by radioactive Cs from Fukushima Daiichi Nuclear Power Plant accident was investigated. Absorption and desorption experiments of Cs were conducted for several phyllosillicates (kaolinite, sericite, montmorillonite, vermiculite, chrysotile and biotite), zeolite and solid organic matter (dead and green leaves). The results confirmed the characteristic sorption and desorption of Cs by these materials. The 2:1 type phyllosilicate, especially, vermiculite and montmorillonite absorbed Cs well. Heated vermiculite for agricultural use and weathered montmorillonite also adsorbed Cs. Leaves also absorbed Cs considerably but easily desorbed it. In summary, the relative capacity and strength of different materials for sorption of Cs followed the order: zeolite (clinoptilolite) > 2:1 type clay mineral > 1:1 type clay mineral > dead and green leaves. Culture experiments using bacteria of both naturally living on dead leaves in Iitate village, Fukushima Pref. and bacterial strains of Bacillus subtillis, Rhodococus erythropolis, Streptomyces aomiensis and Actinomycetospora chlora were carried out. Non-radioactive 1% Cs solution (CsCl) was added to the culture media. Two types of strong or considerable bacterial uptakes of Cs were found in bacterial cells. One is that Cs was contained mainly as globules inside bacteria and the other is that Cs was absorbed in the whole bacterial cells. The globules consisted mainly of Cs and P. Based on all these results, future diffusion and re-circulation behavior of Cs in the surface environment was discussed.  相似文献   

10.
Permeable reactive barriers (PRBs) are a popular technology for passive contaminant remediation in aquifers through installation of reactive materials in the pathway of a plume. Of fundamental importance are the degree of remediation inside the reactor (residence time) and the portion of groundwater intercepted by a PRB (capture width). Based on a two-dimensional conformal mapping approach (previously used in related work), the latter is studied in the present work for drain-and-gate (DG) PRBs, which may possess a collector and a distributor drain (“full” configuration) or a collector drain only (“simple” configuration). Inherent assumptions are a homogeneous unbounded aquifer with a uniform far field, in which highly permeable drains establish constant head boundaries. Solutions for aquifer flow fields in terms of the complex potential are derived, illustrated, and analyzed for doubly symmetric DG configurations and arbitrary reactor hydraulic resistance as well as ambient groundwater flow direction. A series of practitioner-friendly charts for capture width is given to assist in PRB design and optimization without requiring complex mathematics. DG PRBs are identified as more susceptible to flow divergence around the reactor than configurations using impermeable side structures (e.g., funnel-and-gate), and deployment of impermeable walls on drains is seen to mitigate this problem under certain circumstances.  相似文献   

11.
In this paper, a novel adsorbent developed by means of granulating of natural zeolite nanoparticles (i.e., clinoptilolite) was evaluated for possible removal of the petroleum monoaromatics (i.e., benzene, toluene, ethylbenzene, and xylene, BTEX). To do this, the natural zeolite was ground to produce nanosized particulate, then modified by two cationic surfactants and granulated. The effect of various parameters including temperature, initial pH of the solution, total dissolved solids (TDS), and concentration of a competitive substance (i.e., methyl tert‐butyl ether, MTBE) were studied and optimized using a Taguchi statistical approach. The results ascertained that initial pH of the solution was the most effective parameter. However, the low pH (acidic) was favorable for BTEX adsorption onto the developed adsorbents. In this study, the experimental parameters were optimized and the best adsorption condition by determination of effective factors was chosen. Based on the S/N ratio, the optimized conditions for BTEX removal were temperature of 40°C, initial pH of 3, TDS of 0 mg/L, and MTBE concentration of 100 µg/L. At the optimized conditions, the uptake of each BTEX compounds reached to more than 1.5 mg/g of adsorbents.  相似文献   

12.
A separation procedure was developed for analysis of polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (OCPs) in urban air, while simultaneously eliminating the interfering compounds. This was carried out by optimization of a column chromatograph with regard to the eluent type (n‐hexane and n‐pentane), volume of eluent, type of sorbent material (silica gel and florisil) and activation level of the sorbent material. The determination of the level of PCBs and PAHs was carried out using gas chromatography (GC) equipped with a mass selective detector (MSD), while determination of the OCPs was carried out by GC equipped with an electron capture detector (μ‐ECD). The use of a silica gel column (10 g, 5% deactivated with H2O) with 70 mL of n‐hexane gave satisfactory separation of PCBs from PAHs and OCPs. After collecting the PCBs with 70 mL of n‐hexane, 3·20 mL of n‐hexane:ethyl acetate, (1:1, v:v) was adequate for elution of the PAHs and OCPs from the column. The primary aim of this study was to develop a multimethod for analyses of PCBs, PAHs, and OCPs in urban air as well as reducing solvent and sorbent consumption and analysis time during the clean‐up procedure compared to the US EPA standard methods (EPA methods TO‐13A for PAHs and TO‐4A for both PCBs and OCPs).  相似文献   

13.
Permeable reactive barriers (PRBs) have gained popularity in recent years as a low-cost method for ground water remediation. However, their cost advantage usually requires that these barriers remain maintenance free for a number of years after installation. In this study, sediment cores were retrieved from a pilot-scale PRB consisting of a sand and wood particle (sawdust) mixture that has been in continuous operation for 15 years treating nitrate from a septic system plume in southern Ontario (Long Point site). Reaction rates for the 15-year-old media were measured in dynamic flow column tests and were compared to rates measured in year 1 using the same reactive mixture. Nitrate removal rates in the 15-year-old media varied, as expected, with temperature in the range of 0.22 to 1.1 mg N/L/d at 6 °C to 10 °C to 3.5 to 6.0 mg N/L/d at 20 °C to 22 °C. The latter rates remained within about 50% of the year 1 rates (10.2 ± 2.7 mg N/L/d at 22 °C). Near the end of the year 15 column test, media particles >0.5 mm in diameter, containing most of the wood particles, were removed from the reactive media by sieving. Nitrate removal subsequently declined by about 80%, indicating that the wood particles were the principal energy source for denitrification. This example shows that some denitrifying PRBs can remain maintenance free and be adequately reactive for decades.  相似文献   

14.
A seaweed‐waste material resulting from the processing of Ascophyllum nodosum was previously shown to be very efficient at removing Zn(II), Ni(II) and Al(III) both in single and multi‐metal waste streams. In this study, the regeneration of the biosorbent using an acid wash resulted in the release of high metal concentrations during multiple desorption cycles. Maximum desorption efficiencies (DE) of 183, 122 and 91% were achieved for Zn(II), Ni(II) and Al(III), respectively, for subsequent metal loading cycles, significantly exceeding the desorption rates observed for conventional sorbents. The regeneration of the sorbent was accomplished with very little loss in metal removal efficiency (RE) for both single and multi‐metal systems. Values of 92, 96 and 94% RE were achieved for Zn(II), Ni(II) and Al(III), respectively, for the 5th sorption cycle in single metal aqueous solutions. A slight decrease was observed for the same metals in multi‐metal systems with maximum REs of 85, 82 and 82% for Zn(II), Ni(II) and Al(III), respectively. This study showed that the novel sorbent derived from a seaweed industrial waste would be suitable for multiple metal sorption cycles without any significant loss in RE.  相似文献   

15.
Barbro Uln 《水文研究》2003,17(4):747-758
During a 16 day period with pronounced snowmelt via surface runoff, high water concentrations (usually 0·4–0·5 mg l?1) of dissolved molybdate‐reactive phosphorus (MRP) were detected in surface runoff water from a clay soil of illite type. Other phosphorus fractions defined were: phosphorus in particles with a higher settling coefficient than 80 000 S (SPP); colloidal phosphorus caught on filters with a pore size of 0·2 µm but with a smaller settling coefficient (CPP); and dissolved phosphorus not reacting with molybdate (DUP). The order of concentrations was MRP > SPP > CPP > DUP. Nearly identical amounts of MRP, CPP, and DUP (in total 0·3 kg ha?1) were lost from a grass–clover ley and a ploughed soil. However, more of the heavier phosphorus‐containing material was lost from the ploughed area. In drainpipe water, CPP was the largest fraction (28%), and in stream water from mixed arable/forest land, MRP dominated (33%). Loss on ignition of the settling material slowly decreased from 10 to 8% (dry weight) during the snowmelt period. Total phosphorus concentrations in the material followed the runoff pattern, with slightly higher phosphorus concentrations during fast runoff. The large amounts of readily dissolved or colloidal‐bound phosphorus (70–80%) transported from this clay soil during snowmelt are discussed with regard to the use of grass buffer strips as a measure against phosphorus losses from arable land. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

16.
Agricultural soils have been analyzed to elucidate whether the trace metal distribution changes in relation to agricultural activities and to predict environmental risk. In addition to the extractability of Cu, Mn, Ni, Pb, and Zn in soils was compared by single extraction (hydrochloric acid (HCl), ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), calcium chloride (CaCl2), water (H2O)), and sequential extraction procedures. The modified Community Bureau of Reference (BCR) sequential extraction procedure (three‐step) used to extraction of metals in soil samples. The extraction capacity of the analyzed metals was found by using single extraction procedures in the order: HCl > EDTA > DTPA > CaCl2 > H2O. A single correlation analysis was used to investigate the relationship between extractable metal concentrations in soil solutions and metal accumulation in wheat grains. Simple correlation analyses indicated that the extractable Pb and Ni of soils by HCl, EDTA, and DTPA single extraction procedures were significantly correlated with the metal contents of wheat grains. For CaCl2, H2O, and BCR extraction procedures there was a relatively poor correlation between the extractable Cu, Mn, Ni, Pb, and Zn of soils and metal contents of wheat grains.  相似文献   

17.
In this study, a new sorbent is synthesized using surface imprinting technique. Cu(II)‐imprinted multiwalled carbon nanotube sorbent (Cu(II)‐IMWCNT) is used as the solid phase in the solid‐phase extraction method. After the preconcentration procedure, Cu(II) ions are determined by high‐resolution continuum source atomic absorption spectrometry. A total of 0.1 mol L?1 ethylenediaminetetraacetic acid (EDTA) is used to remove Cu(II) ions from the sorbent surface. The optimum experimental conditions for effective preconcentration of Cu(II), parameters such as pH, eluent type and concentration, flow rate, sample volume, sorbent capacity, and selectivity are investigated. The synthesized solid phase is characterized by Fourier transform infrared spectroscopy and scanning electron microscopy. The maximum adsorption capacities of Cu(II)‐IMWCNT and non‐imprinted solid phases are 270.3 and 14.3 mg g?1 at pH 5, respectively. Under optimum experimental conditions for Cu(II) ions, the limit of detection is 0.07 μg L?1 and preconcentration factor is 40. In addition, it is determined to be reusable without significant decrease in recovery values up to 100 adsorption–desorption cycles. Cu(II)‐IMWCNT have a high stability. To check the accuracy of the developed method, certified reference materials, and water samples are analyzed with satisfactory analytical results.  相似文献   

18.
Ulmus carpinifolia tree leaves were successfully used to remove Tl(I) from aqueous solution in a batch system. In order to improve the uptake capacity of sorbent, it was modified by various chemical agents such as NaOH, HNO3, NH3, NaCl, NaHCO3, and CaCl2. Among the modifiers, NaCl was the best. Equilibrium behavior of sorbent with Tl(I) was examined by the several isotherms. Considering modified U. carpinifolia equilibrium data fitted well to the Langmuir model with maximum capacity of 54.6 mg/g. The other isotherms such as: Freundlich and Dubinin‐Redushkevich (D‐R) models were also examined. The central composite design (CCD) was successfully employed for optimization of biosorption process. An empirical model was given through using response surface methodology. Also its validation was recognized by using relevant statistical tests such as ANOVA. The optimum conditions of biosorption: pH, m (amount of sorbent) and C (initial concentration) were found to be 7.9, 11.4 g/L, and 8.8 mg/L, respectively. On the other hand thermodynamic parameters: ΔG, ΔH, and ΔS were evaluated: the obtained results show that biosorption process was spontaneous and exothermic. Eventually, FT‐IR analysis confirmed that the main functional groups of sorbent have been involved through the biosorption process.  相似文献   

19.
This analysis compares decreases in soil moisture (SM) at Utah snow telemetry (SNOTEL) sites during the summer months with discharge at nearby stream gauging locations using data from water years 2008–2012. The following characteristics were evaluated: (1) the influence of the SM loss at mid‐depths (20 cm) on hydrograph recession, (2) the influence of moisture loss from deeper portions of the soil (50 cm) on late‐season baseflow and (3) the timing of this transition. Thirty‐four pairings were used between SNOTEL sites and nearby stream gauges in select locations throughout Utah, for 3–5 years each depending on data quality, to generate 143 total comparisons of soil moisture loss and stream discharge. Regressions were fairly strong (r2 > 0.8) where the SNOTEL site was in a location with slow meltout rates, ample infiltration and minimal summer precipitation. In a few cases, the correlation was remarkably strong (r2 > 0.95), even for SNOTEL sites located far from respective stream gauges (e.g. >30‐km, >1000‐m elevation difference for the best pairing). At such sites, transition timing in 2013 (between predominantly 20‐ vs 50‐cm SM loss) was well predicted from 2012 data given the similarity in water years, with discharges at the transition point less than 30% different than observed values in 2013. An index of the robustness of each pairing was generated to determine where this type of analysis might be most successful; however, results suggest that identification of high‐quality pairings may need to be site by site. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.  相似文献   

20.
In this work, 8‐hydroxyquinoline is used as the active sites in cross‐linked chitosan beads with epichlorohydrin (CT‐8HQ). The CT‐8HQ material was shaped in bead form and used for heavy metal removal from aqueous solution. The study was carried out at pH 5.0 with both batch and column methods and the maximum adsorption capacity of metal ions by the CT‐8HQ was attained in 4 h in the batch experiment. The adsorption capacity order was: Cu2+ > Ni2+ > Zn2+ for both mono‐ and multi‐component systems with batch conditions. From breakthrough curves with column conditions, the adsorption capacity followed the order Cu2+ > Zn2+ > Ni2+ for both mono‐ and multi‐component systems. The CT‐8HQ beads maintained good metal adsorption capacity for all five cycles with absorbent restoration achieved with the use of 1.0 mol L–1 HCl solution, with 90% regeneration.  相似文献   

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