Simulated Rainwater Research Articles

Enhancing Cd(II) sorption by red mud with heat treatment: Performance and mechanisms of sorption

Red mud is a waste generated from the aluminum industry in large quantities. The potential of red mud as a sorbent for beneficial reuse has been the focus of research efforts. However, the limited sorption capacity of red mud has hindered its applications in the removal of environmental pollutants. In this study, the feasibility of heat treatment in improving the sorption of toxic Cd(II) by red mud was investigated in the temperature range of 200–900 °C. Heat treatment at 500 °C resulted in the highest sorption capacity (42.64 mg g−1) and the fastest sorption rate. Further analyses revealed that heat treatment at 500 °C led to significant increases in specific surface area (32.77 m2 g−1), which likely contributed to the enhanced Cd(II) sorption performance. Notably, heat treatment at 500 °C nearly doubled Cd(II) sorption stability as compared with that of raw red mud, as demonstrated by leaching experiments with simulated rainwater. Sequential extraction and XPS analyses indicated that specific sorption was the predominant mechanism involved in Cd(II) removal by red mud heat-treated at 500 °C (RM500). The strength of specific sorption following heat treatment likely contributed to the increase in sorption stability due to the formation of inner-sphere complex (–OCdOH). Metal-metal ion exchange was identified as another sorption mechanism, which, however, likely had only a limited effect on Cd(II) sorption performance. As the final pH (6.57) of the sorption system was typically lower than the pHPZC (about 10.6) of RM500, positive charges would develop on the red mud surface and impede the retention of Cd(II) cations, resulting in weak electrostatic attraction between Cd(II) cations and red mud. In summary, heat treatment at 500 °C considerably enhanced the capacity, rate and stability of Cd(II) sorption by red mud, suggesting red mud could be optimized by heat treatment as a more effective sorbent for Cd(II) removal. These findings represent the first mechanistic characterization of Cd(II) sorption by heat-treated red mud, providing much needed insights into the potential strategies to enhance the effectiveness of red mud in the sorptive removal of toxic heavy metals.

CMAS corrosion resistance in high temperature and rainwater environment of double-layer thermal barrier coatings odified by rare earth

Abstract In order to explore the difference of CMAS corrosion resistance in high temperature and rainwater environment of single-layer and double-layer thermal barrier coatings (TBCs), and further reveal the mechanism of CMAS corrosion resistance in above environment of double-layer TBCs modified by rare earth, two TBCs were prepared by air plasma spraying, whose ceramic coating were single-layer ZrO2–Y2O3 (YSZ) and double-layer La2Zr2O7(LZ)/YSZ, respectively. Subsequently, CMAS corrosion resistance tests at 1200 °C and rainwater environment of two TBCs were carried out. Results demonstrate that after high temperature CMAS corrosion for the same time, due to phase transformation, the volume of YSZ ceramic coating in single-layer TBCs shrank and surface cracks formed, which would lead to coating failure. When LZ ceramic coating of double-layer TBCs reacted with CMAS, compact apatite phases and fluorite phases formed, the penetration of CMAS into ceramic coating was inhibited effectively. Raman analysis and calculation results show that both of the surface residual stress of ceramic coating in two TBCs were compressive stress, and the residual stress of ceramic coating in double-layer TBCs were smaller than that of single-layer TBCs. Atomic force microscopy of TBCs after CMAS corrosion show that surface of double-layer TBCs was more uniform and compact than that of single-layer TBCs. The electrochemical properties in simulated rainwater of two TBCs after high temperature CMAS corrosion showed that double-layer TBCs possessed higher free corrosion potential, lower corrosion current and higher polarization resistance than those of single-layer TBCs. Consequently, the presence of LZ ceramic coating effectively improved CMAS corrosion resistance in high temperature and rainwater environment of double-layer TBCs.

Bioavailability and mobility of arsenic, cadmium, and manganese in gold mine tailings amended with rice husk ash and Fe-coated rice husk ash.

This study was conducted to determine the effects of rice husk ash (RHA) and Fe-coated rice husk ash (Fe-RHA) on the bioavailability and mobility of As, Cd, and Mn in mine tailings. The amendments were added to the tailings at 0, 5, 10, or 20% (w/w) and the mixtures were incubated for 0, 7, 15, 30, 45, and 60days. The CaCl2 extractable As, Cd, and Mn in the amended tailings were determined at each interval of incubation period. In addition, the tailings mixture was leached with simulated rain water (SRW) every week from 0day (D 0) until day 60 (D 60). The results showed that both RHA and Fe-RHA application significantly decreased the CaCl2-extractable Cd and Mn but increased that of As in the tailings throughout the incubation period. Consequently, addition of both RHA and Fe-RHA leached out higher amount of As from the tailings but decreased Cd and Mn concentration compared to the controls. The amount of As leached from the Fe-RHA-amended tailings was less than that from RHA-amended tailings. Application of both RHA and Fe-RHA could be an effective way in decreasing the availability of cationic heavy metals (Cd and Mn) in the tailings but these amendments could result in increasing the availability of anionic metalloid (As). Therefore, selection of organic amendments to remediate metal-contaminated tailings must be done with great care because the outcomes might be different among the elements.

Talisay (Terminalia catappa) seed husk biochar for adsorption of lead (II) ions in artificially contaminated soil

Lead, a commonly found heavy metal in contaminated soil, is highly mobilized in acidic conditions resulting to rapid soil leaching. This study investigated the effectiveness of biochar derived from Talisay (Terminalia catappa) seed husks employing the long-term immobilization of Lead in an artificially contaminated soil using simulated acid rain water meant for 100 years of rain with 5% amendment rate. Before immobilization, the heating temperatures were varied at 400, 500 and 600°C to determine its optimal pyrolysis temperature. The biochar was pyrolyzed under three different temperatures: with 1-hour residence time. SEM images revealed that the degree of porosity of the biochar produced increased as the temperature increased. In addition, the biochar produced at 600°C has the highest % fixed carbon and % elemental carbon indicating stability. It then shows that Talisay seed husks are feasible materials for biochar production that can be used for the amendment of lead contaminated soil. The Freundlich and Langmuir models were used to describe the heavy metal sorption equilibrium of the biochar. Results showed that the biochar best fitted the pseudo-second-order models and Langmuir isotherm models and that the biochar displayed a favorable adsorption. Also, the immobilization experiment showed that the soil amended with biochar immobilized Pb decreasing its concentration by 99.47%. Therefore, the produced biochar is suitable for Pb remediation in contaminated soils.

Adsorption of myo-inositol hexakisphosphate in water using recycled water treatment residual.

Dissolved organic phosphorus (DOP) in rainwater runoff or other contaminated waters can cause or aggravate eutrophication of water bodies. Water treatment residual (WTR) containing spent coagulant has been shown to provide excellent adsorption capacity for inorganic phosphorus such as orthophosphate, but little information has been available on adsorption of DOPs by WTR. In this study, the adsorption characteristics of myo-inositol-1,2,3,4,5,6-hexakisphosphate (IHP), a prototype DOP in soil and stormwater, by WTR were investigated through batch adsorption equilibrium and kinetic experiments. The influences of pH and various size fractions of WTR on the adsorption capacity were tested and analyzed, and the adsorption mechanism was elucidated based on Fourier-transform infrared spectroscopy (FTIR) analysis. The experimental results showed that WTR can effectively adsorb IHP from simulated rainwater, and the IHP uptake was favored under neutral and acidic conditions. Moreover, the 1.0-2.0-mm fraction of the WTR particles was most suitable for practical application because of the well-balanced adsorption rate and capacity. The classical Langmuir isotherm model well described the equilibrium adsorption data and the pseudo-second-order kinetic model adequately interpreted the rate data. Thermodynamic analysis revealed that the adsorption is a spontaneous, endothermic, and entropy-driven reaction. The FTIR analysis indicated that adsorption of IHP on WTR is associated with the formation of ≡Al-PO3- groups and the release of -OH from WTR. A comparison of the adsorption capacities of orthophosphate and IHP on WTR suggested that binding one IHP may take two times more sites than for orthophosphate, indicating that two of the six phosphate groups in IHP were bound to WTR. This work shows that recycled WTR may be used as a low-cost adsorbent for effective removal of organic phosphate in gray water and wastewater.

Fraction distribution and leaching behavior of heavy metals in dredged sediment disposal sites around Meiliang Bay, Lake Taihu (China).

The objectives of this study were to characterize the heavy metal contamination status of surface soils sampled at two dredged sediment land disposal sites (the Baimao and Kongwan landfills) in Meiliang Bay, Lake Taihu, China, as well as to investigate the effect on their leaching behaviors due to acid rain. Among all the metals, only the nickel content in the Baimao landfill was higher than the Chinese reference value, and all metal contents were below the limit values for agricultural soils. The fraction distribution of metals by sequential extraction was similar at both sites. Cadmium had a relatively high proportion of exchangeable-carbonate fractions, while the other metals were mainly classified as residue fractions. The metals released from soils by simulated rainwater comprised less than 1% of the total soil metal content, and the effect of acid rain on heavy metal release from dredged sediments in land disposal sites was found to be negligible at both sites. All results indicate no environmental concern for the land disposal of dredged sediments and support the feasibility of beneficially reusing dredged sediment soils as a supplement to agricultural soils.

A flow injection procedure using Layered Double Hydroxide for on line pre-concentration of fluoride

This work showed a flow system designed with solenoid valves for preconcentration of fluoride using SPADNS method in water samples. The analyte was preconcentrated in a mini-column coated with Layered Double Hydroxides (LDH) used as adsorbent. Then, the fluoride ions were eluted with 0.5 mol L−1 sodium hydroxide and determined by spectrophotometry. The variables that affect the system such adsorbent mass, type of eluent, solutions flow rate, reagent concentration and pH effect were critically evaluated. Under optimized conditions, the detection limit, coefficient of variation, linear range and preconcentration factor were estimated at 15 µg L−1 (99.7% confidence level), 0.8% (500 µg L−1, n = 10), 50–500 µg L−1 and 10, respectively. The accuracy of the method was evaluated by analysis of ALPHA APS 1076 (Simulated Rain Water) certified material, the values were not significantly different at a 95% level of confidence. The method was applied for fluoride determination in water samples and the levels found were below the maximum values established by Brazilian environmental and health legislations.

Analysis of water leached from soil treated with leachate from plant biomass ash

This work analyzed water leached from soil treated with leachate from plant biomass ash. The ash was generated by industrial boilers used in the pulp and paper industry. Experiments were carried out in columns filled with soil, and the ash was then added to the soil to simulate field conditions. The ash was applied at 30 and 60 tons per hectare rate. The simulated rainwater was prepared for three scenarios: pH 3.0, 6.5 and 8.0. Each leaching experiment simulated an annual precipitation of 2,045 mm. The results showed that the parameter that demands more attention is aluminum concentration. In this context, in acidic conditions (pH 3.0) and with a significant amount of ash added (60 tons per hectare), the level of aluminum may reach the maximum level for drinking water. Despite the potential impact of aluminum, the use of ash from plant biomass in soil for agricultural purposes may serve as an alternative strategy for disposal of this waste.

English

Cypermethrin is a synthetic, pyrethroid insecticide and used for agricultural practices. The leaching of this pesticide through soil is of great concern because of the possibility of contaminating ground and surface water. The mobility of pesticide in soil being the main environmental reservoir varies among soil orders and the concept is still under investigation. Hence, this study was aimed at investigating the sorption capability of Alfisol and Inceptisol at different soil depth when leached with simulated rainwater of different pH values. The leachates were determined for cypermethrin concentration using a new UV/Visible spectrometry method. The CEC, organic matter content of Alfisol were 4.05±0.03 cmol/kg and 1.74±0.02%, while the corresponding characteristics of Inceptisol were 4.45±0.05 cmol/kg and 1.03±0.01%, respectively. pH of Alfisol and Inceptisol soil orders were 5.92 and 6.25, respectively. Simulated rainwater (pH 4) of 50, 100 and 150 mL leached out 37.0±0.1, 43.1±0.1 and 59.4±0.2% of cypermethrin, respectively from Alfisol at soil depth of 10 cm. At pH 6.8, the corresponding volumes of simulated rainwater leached out 31.8±0.1, 35.4±0.1 and 37.4±0.1% of cypermethrin, respectively. For each soil order, these proportions of sorbed cypermethrin decreased progressively as soil depth increased from 10-30 cm. The proportions of cypermethrin sorbed by Inceptisol were more than the corresponding proportions sorbed by Afisol. Afisol has high clay and organic contents, which might be responsible for its surpassing potential to sorb cypermethrin compared to Inceptisol. Key words: Pyrethroid insecticide, leaching, Alfisol-Inceptisol soil orders, simulated rainwater, UV/Visible spectrometry.

Acid pond sediment and mine tailings contaminated with metals: physicochemical characterization and electrokinetic remediation

Mine tailings and acid pond sediment from a former mining area in Canakkale (Turkey) were analyzed for physical (e.g., moisture content, particle size, specific gravity and hydraulic conductivity) and chemical parameters (e.g., organic content, pH, ORP and EC) as well as metal content and sequential extraction analysis, in an attempt to evaluate their risk as a source of contaminants. Column extraction tests were conducted to investigate the leachability under model field conditions using simulated rainwater. The toxicity characteristic leaching procedure and synthetic precipitation leaching procedure (SPLP) methods were performed to evaluate the expected concentrations in the water in contact with the solid material. The column tests proved that Fe and Pb can be released to the waterbodies in contact with the solid materials. Pb was released easier than Fe due to its content in the more labile fractions in the sequential extraction analysis. SPLP-Pb in both tailings and sediment exceeded the USEPA regulatory limit, confirming the hazardousness of those materials. Electrokinetic remediation has been tested as a possible technology for the removal of metals from mine tailings and sediment. Electrokinetics removed 20% of Pb and Fe in 9 days of treatment at 1 VDC/cm. The metal removal efficiency was very affected by metal speciation. Electrokinetics could remove metal fractions I–IV [as described by Tessier et al. (Anal Chem 51(7):844–851, 1979) especially in the closest section to the anode of the solid matrix, and the metals accumulated in the following sections. The results suggested that Fe and Pb could be effectively removed from the mine tailings and sediment if the advance of the acid front was favored and the treatment time increased. However, considering the physicochemical characterization and the results from the electrokinetic treatment, other green and more sustainable remedial strategies have to be proposed for mitigation of environmental risks of former mining areas. Instead of focusing on metal removal, the results of this work suggest that the immobilization and stabilization of metals in the site are more practical solutions. Thus, phytocapping is recommended as a practical green and sustainable method to mitigate the environmental risks of former mining areas.

Soil Nitrogen Speciation and the Relationship with Microbial Biomass Carbon in Bioretention Tanks

This outdoor research investigated the variations in soil ammonium (NH3-N), nitrite (NO2-N), nitrate (NO3-N), total organic nitrogen (TON), and microbial biomass carbon (MBC) in bioretention tanks. Two biretention tanks (tank 1#: The depth of 0–20 cm was vacant aquifer layer; 20–90 cm, filled with the planting soil; 90–105 cm, filled with gravel. tank 3#: 0–20 cm was aquifer layer, 20–50 cm, filled with the planting soil; 50–90 cm, filled with blast furnace slag and sand; 90–105 cm, filled with gravel) were used with simulated rainwater discharge experiments to obtain soil samples at intervals of 1 h before the inflow and 24 h after the end of inflow. Results indicate that soil nitrogen (N) and MBC in two bioretention tanks were mainly captured at 10∼30 cm depth in soil; the content of soil NH3-N exhibited a trend of initial decline but increase with time; the content of NO2-N varied from 0.011 to 0.024 g/kg, and the change regularity was similar with the NH3-N; different from the NH3-N and NO2-N, soil NO3-N exhibited a trend of declining; while TON exhibited a trend of declining after slightly increase. Meanwhile, the content of NH3-N and NO3-N at 50 cm depth in tank 1# was slight lower than those at 10 and 30 cm; conversely, the discrepancy at the different depths in tank 3# was small. The contents of soil NH3-N and NO2-N before inflow were less than those after inflow, but it was adverse for NO3-N. The NO3-N leaching in bioretention system is a main reason for poor N removal in runoff. The content of MBC ranged from 1.055 to 1.847 g/kg and exhibited a trend of decline after increase. Furthermore, the content of MBC and TN has good linear correlation in bioretention tanks (R 2 > 0.8), but it has general performance with TP (R 2 > 0.5). The immobilization of NH3-N, NO2-N, and NO3-N at the planting soil layer in tank 1# was greater than that in tank 3#. The N interception differences in the two tanks resulted from different infiltration rates of their underlying fillers.

Tribological Properties of AlCrCuFeNi2 High-Entropy Alloy in Different Conditions

In order to understand the environmental effect on the mechanical behavior of high-entropy alloys, the tribological properties of AlCrCuFeNi2 are studied systematically in dry, simulated rainwater, and deionized water conditions against the Si3N4 ceramic ball at a series of different normal loads. The present study shows that both the friction and wear rate in simulated rainwater are the lowest. The simulated rainwater plays a significant role in the tribological behavior with the effect of forming passive film, lubricating, cooling, cleaning, and corrosion. The wear mechanism in simulated rainwater is mainly adhesive wear accompanied by abrasive wear as well as corrosive wear. In contrast, those in dry condition and deionized water are abrasive wear, adhesive wear, and surface plastic deformation. Oxidation contributes to the wear behavior in dry condition but is prevented in liquid condition. In addition, the phase diagram of Al x CrCuFeNi2 is predicted using CALPHAD modeling, which is in good agreement with the literature report and the present study.

Studies of Leaching Characteristics of Arsenic and Antimony for Jinya Gold Mine

Jinya gold mine is a typical Carlin type gold deposit in Fengshan, China and the main gold-bearing minerals are arsenopyrite and As-bearing pyrite. The mine drainage mainly contains arsenic and antimony, which can cause pollution to the environment. In the present study, the simulated rain water was used to leach the arsenic and antimony in solid waste obtained from the mine in order to investigate the leaching characteristics of arsenic and antimony. The results indicated that a large number of arsenic and antimony dissoluted from the waste rock and tailings.

Assessment of Leaching Tests for Evaluating Potential Environmental Impacts of PV Module Field Breakage

Test methods from standard waste characterization leaching tests used in the U.S., Germany, and Japan were evaluated to determine if they can be used to help evaluate potential environmental impacts from photovoltaic (PV) module field breakage. To assess the representativeness of leaching test methods, PV module breakage types were evaluated from warranty return data. Field breakages mainly consist of various types of stress and impact fractures in which modules remain largely intact with a number of glass fractures or cracks. By breaking modules into centimeter-scale pieces and tumbling them in solvent, waste characterization leaching tests can be more aggressive than PV field breakage conditions with regard to parameters such as fragment sample size, solvent, and treatment method. An alternative test method was previously used in Japan in which modules with a predetermined number of cracks were subjected to simulated rainwater. This approach is more representative of field conditions as modules are more likely to experience cracks under field conditions than to break into pieces.

Evaluating the cement stabilization of arsenic-bearing iron wastes from drinking water treatment

Cement stabilization of arsenic-bearing wastes is recommended to limit arsenic release from wastes following disposal. Such stabilization has been demonstrated to reduce the arsenic concentration in the Toxicity Characteristic Leaching Procedure (TCLP), which regulates landfill disposal of arsenic waste. However, few studies have evaluated leaching from actual wastes under conditions similar to ultimate disposal environments. In this study, land disposal in areas where flooding is likely was simulated to test arsenic release from cement stabilized arsenic-bearing iron oxide wastes. After 406 days submersed in chemically simulated rainwater, <0.4% of total arsenic was leached, which was comparable to the amount leached during the TCLP (<0.3%). Short-term (18h) modified TCLP tests (pH 3–12) found that cement stabilization lowered arsenic leaching at high pH, but increased leaching at pH<4.2 compared to non-stabilized wastes. Presenting the first characterization of cement stabilized waste using μXRF, these results revealed the majority of arsenic in cement stabilized waste remained associated with iron. This distribution of arsenic differed from previous observations of calcium–arsenic solid phases when arsenic salts were stabilized with cement, illustrating that the initial waste form influences the stabilized form. Overall, cement stabilization is effective for arsenic-bearing wastes when acidic conditions can be avoided.

Impact of cloud microphysics and cumulus parameterization on simulation of heavy rainfall event during 7–9 October 2007 over Bangladesh

In the present study, the Advanced Research WRF (ARW) version 3.2.1 has been used to simulate the heavy rainfall event that occurred between 7 and 9 October 2007 in the southern part of Bangladesh. Weather Research and Forecast (WRF–ARW version) modelling system with six different microphysics (MP) schemes and two different cumulus parameterization (CP) schemes in a nested configuration was chosen for simulating the event. The model domains consist of outer and inner domains having 9 and 3 km horizontal resolution, respectively with 28 vertical sigma levels. The impacts of cloud microphysical processes by means of precipitation, wind and reflectivity, kinematic and thermodynamic characteristics of the event have been studied. Sensitivity experiments have been conducted with the WRF model to test the impact of microphysical and cumulus parameterization schemes in capturing the extreme weather event. NCEP FNL data were used for the initial and boundary condition. The model ran for 72 h using initial data at 0000 UTC of 7 October 2007. The simulated rainfall shows that WSM6–KF combination gives better results for all combinations and after that Lin–KF combination. WSM3–KF has simulated, less area average rainfall out of all MP schemes that were coupled with KF scheme. The sharp peak of relative humidity up to 300 hPa has been simulated along the vertical line where maximum updraft has been found for all MPs coupled with KF and BMJ schemes. The simulated rain water and cloud water mixing ratio were maximum at the position where the vertical velocity and reflectivity has also been maximum. The production of rain water mixing ratio depends on MP schemes as well as CP schemes. Rainfall depends on rain water mixing ratio between 950 and 500 hPa. Rain water mixing ratio above 500 hPa level has no effect on surface rain.

Release behaviour of cryptomeria japonica pollen allergenic cry J 1 and cry J 2 in rainwater containing air pollutants

Japanese cedar (Cryptomeria japonica) pollinosis is the most popular pollinosis in Japan. In recent years, it was reported that the most Cryptomeria japonica pollen allergenic species were scattered as fiparticles in the urban atmosphere. It is thought that allergenic fi ne particles are responsible for inducing asthma by breaking into lower respiratory tract; this phenomenon was observed in fiinvestigations during sunny days after rainfall. Hence, it is considered that the release of fiallergenic species derived from pollen grains may be induced during rainfall events. For this reason, we investigated the releasing behaviour of Cryptomeria japonica pollen allergenic species in rainwater containing air pollutants, through rainwater sampling and laboratory experiments. The pollen grain counts, pollen burst ratios, ionic concentrations and pH in each rainwater sample were measured, when rainwater samples were separately collected in Saitama City, a suburban area north of Tokyo metropolis. Additionally, three simulated rainwater (SR) samples were prepared to investigate the releasing behaviour of pollen allergenic species. In the samplings, the most pollen grains were trapped into initial rainwater (IR). Moreover, burst pollen grains were observed in many rainwater samples. Burst ratio of pollen grains were positively correlated with pH and ionic concentrations in rainwater. Therefore, it was thought that pollen grains were washed out by IR containing air pollutants. On the other hand, for the laboratory experiments, the elution of allergenic Cry j 1 and Cry j 2 was observed when pollen grains were exposed to different SR samples. A time-dependent increase of Cry j 1 was observed, but the elution of Cry j 2 was not observed from pollen grains exposed to SR samples. In particular, the elution of Cry j 1 increased by contact with SR samples under conditions of Asian dust events. The results demonstrated that the burst of pollen grains is associated with the production of fiparticles containing pollen allergenic species, and that the release of allergenic species was induced by rainwater containing air pollutants.

应用拱棚-空调法对极干旱区降水的模拟回收

PDF HTML阅读 XML下载 导出引用 引用提醒 应用拱棚-空调法对极干旱区降水的模拟回收 DOI: 10.5846/stxb201301290185 作者: 作者单位: 敦煌研究院保护所,古代壁画保护国家文物局重点科研基地;敦煌研究院保护所,古代壁画保护国家文物局重点科研基地;敦煌研究院保护所;敦煌研究院保护所;敦煌研究院保护所,古代壁画保护国家文物局重点科研基地;敦煌研究院保护所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然基金项目(41363009, 31070344, 31260136); 国家科技支撑项目(2013BAC07B02); 甘肃省科技计划项目(1308RJZF290); 敦煌研究院院级课题(201306) Application of a greenhouse air-conditioning method to simulate take-back of rainfall in an extremely arid area Author: Affiliation: The Conservation Institute of Dunhuang Academy,,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:拱棚法监测表明极干旱区存在潜水蒸发,而土壤温湿度监测表明,土壤水分具备向下运转的条件,这意味着拱棚所监测的水分可能来自降水,极干旱区并不存在深埋潜水蒸发.因此,研究降水的最终去向非常重要.为此笔者应用拱棚-空调法进行对极干旱区降雨模拟回收.结果表明,在极干旱条件下占该区85%以上频次的5 mm的降水经90 d可完全蒸发和回收.回收过程中,棚内地上50 cm 的相对湿度(RH)和绝对湿度(AH)分别较棚外增高12.10%和3.50 g/m3,这使降水的回收时间大为延长;另外,土壤内部的温湿度监测表明,洒水后30 cm土壤的温度、RH、AH分别高于棚外对照1.46 ℃、4.17%和2.50 g/m3,说明有一定数量的降水通过膜下土壤侧向流向了外部,增加了收集时间.回收实验证明极干旱区降水可完全蒸发,该区存在潜水蒸发与GSPAC(Groundwater-Soil-Plant-Atmosphere Continuum)水分的向上运转. Abstract:A preliminary greenhouse air-conditioning method demonstrates that there is phreatic water evaporation of deeply buried phreatic water in an extremely arid area. Soil-moisture monitoring shows that most daily fluctuation of moisture in the shallow soil layer of 0-60 cm enters deeper layers as water vapor; only 2‰ of this daily fluctuation water enters the atmosphere and evaporates. Monitoring of 0-500 cm soil depths shows that during May through October (the principal rainy season), temperature and absolute humidity in upper soil layers are greater than in lower layers. According to the law of water vapor migration, moisture moves from regions of higher temperature and humidity to those with lower temperature and humidity. Thus, in the aforementioned season within an extremely arid area, conditions may be suitable for rainwater vapor to move downward to the subsoil. This may mean that some rainwater does not evaporate into the atmosphere but penetrates the earth in such areas, and precipitation is likely the main source of deep soil moisture. This suggests there is no phreatic water evaporation of deeply buried phreatic water in extremely arid areas. Based on this hypothesis, a closed greenhouse with air-conditioning system was constructed in the arid area of the Mogao Grottoes in the Gobi Desert. In this greenhouse, we conducted a simulation recycling experiment of 5-mm precipitation via an air-conditioning condensation method. In this way, we first traced where rainwater went. Temperature and humidity were controlled by refrigeration and air-conditioning condensation, which made the temperature and humidity inside the greenhouse approach that of the outside. To understand characteristics of rainfall evaporation in extremely arid areas, the quantity of condensation water was monitored daily. We analyzed temperature and humidity variations, which were monitored by HOBO monitors in the soil, to understand the rainfall infiltration and evaporation process. This confirmed the ultimate flow direction of precipitation, and whether it completely evaporated. This approach was used to determine if there was phreatic water evaporation. The results showed that 5 mm of precipitation, which represented 85% of the frequency of precipitation in this area, completely evaporated. The relative and absolute humidities of the 50 cm above ground within the greenhouse were 12.10% and 3.50 g/m3 greater than outside it, respectively. These results caused the experimental time to be longer than for actual evaporation. In addition, soil temperature and humidity monitoring indicated that after water was sprinkled in the greenhouse, soil temperature, relative humidity and absolute humidity at 30 cm depth were greater by 1.46℃, 4.17% and 2.50 g/m3 than the outside control, respectively. This means that during evaporation, a certain amount of rainfall reached the outside through the greenhouse side soil, under the greenhouse film. This was another reason why the precipitation evaporation collection time was greatly extended. The collection time of 90 days may be much longer than the actual time for natural evaporation, but it confirmed the effectiveness of the rainfall recycling experiment. After complete take-back of all the simulated rainwater, soil moisture did not decline, but increased. The phreatic evaporation speed also increased, which means that precipitation pulsation has a certain control on evaporation of the phreatic water. It was demonstrated that there is phreatic evaporation, and soil water was supplemented by this water. Groundwater-Soil-Plant-Atmosphere Continuum (GSPAC) movement was upward, and the precipitation could completely evaporate. 参考文献 相似文献 引证文献

Study for Corrosion and Hydrogen Evolution Behavior of Ti-6Al-4V Alloy in Simulated Acid Rain Water

The electrochemical behavior of Ti-6Al-4V alloy was investigated using electrochemical impedance spectroscopy (EIS) measurements at the open circuit potentials and potentiodynamic polarization measurements in a simulated acid rain containing inorganic additives. The ac circuit model for Ti-6Al-4V alloy at corrosion interface in simulated acid rain containing inorganic additives was proposed, which was based on two time constants equivalent circuit. Ti-6Al-4V alloy in a simulated acid rain of pH 1.5 containing inorganic additives showed a characteristic of a capacitive behavior. The effect of different concentrations of the inorganic additives (iodate, dichromate, phosphate, and nitrate) on the corrosion of the alloy in acid rain water (ARW) was also studied. It was found that the corrosion rate decreases drastically in the solution containing iodate, dichromate, and phosphate anions; however, nitrate anions increase the corrosion rate of the alloy. The investigated inorganic additives had inhibiting effect on the corrosion of the alloy in ARW, and their efficiency decreases according to the order: iodate > dichromate > phosphate > blank > nitrate. Polarization data results are in good agreement with EIS.

Soil mobility of surface applied polyaromatic hydrocarbons in response to simulated rainfall

Polyaromatic hydrocarbons (PAHs) are emitted from a variety of sources and can accumulate on and within surface soil layers. To investigate the level of potential risk posed by surface contaminated soils, vertical soil column experiments were conducted to assess the mobility, when leached with simulated rainwater, of six selected PAHs (naphthalene, phenanthrene, fluoranthene, pyrene, benzo(e)pyrene and benzo(ghi)perylene) with contrasting hydrophobic characteristics and molecular weights/sizes. The only PAH found in the leachate within the experimental period of 26 days was naphthalene. The lack of migration of the other applied PAHs was consistent with their low mobilities within the soil columns which generally paralleled their log K oc values. Thus, only 2.3 % of fluoranthene, 1.8 % of pyrene, 0.2 % of benzo(e)pyrene and 0.4 % of benzo(ghi)perylene were translocated below the surface layer. The PAH distributions in the soil columns followed decreasing power relationships with 90 % reductions in the starting levels being shown to occur within a maximum average depth of 0.94 cm compared to an average starting depth of 0.5 cm. A simple predictive model identifies the extensive time periods, in excess of 10 years, required to mobilise 50 % of the benzo(e)pyrene and benzo(ghi)perylene from the surface soil layer. Although this reduces to between 2 and 7 years for fluoranthene and pyrene, it is concluded that the possibility of surface-applied PAHs reaching and contaminating a groundwater aquifer is unlikely.