Constant Initial Concentration Research Articles

Groundwater pollution containing ammonium, iron and manganese in a riverbank filtration system: Effects of dynamic geochemical conditions and microbial responses.

Bench-scale experiments were conducted to investigate the effect of hydraulic loadings and influent concentration on the migration and biotransformation behavior of three groundwater pollutants: ammonium (NH4 +), iron (Fe2+) and manganese (Mn2+). Columns packed with aquifer media collected from a river bank filtration (RBF) site in Harbin City, NE China were introduced synthetic groundwater (SGW) or real groundwater (RGW) were at two different constant flow rates and initial contaminant concentrations to determine the impact of system conditions on the fate of the target pollutants biotransformation. The results showed that the biotransformation rate of Fe2+ Mn2+, and NH4 + decreased by 8%, 39% and 15% under high flow rate (50 L d-1) compared to low flow rate (25 L d-1), which was consistent with the residence-time effect. While the biotransformation rate of Fe2+ Mn2+, and NH4 + decreased by 7%, 14% and 9% under high influent concentration compared to original groundwater. The 16S rRNA analysis of the aquifer media at different depths after experiments completion demonstrated that the relative abundance of major functional microbes iron oxidizing bacteria (IOB) and manganese oxidizing bacteria (MnOB) under higher flow rate and higher influent concentration decreased 13%, 14% and 25%, 24%, respectively, whereas the ammonium oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) exhibited minimal change, compared to the lower flow rate. Above all results indicated that both high flow rate and high concentration inhibit the biotransformation of NH4 +, Fe2+ and Mn2+. The biotransformation of Fe2+ and Mn2+ occurs primarily in the 0-40 cm and 20-60 cm depth intervals, respectively, whereas the NH4 + biotransformation appears to occur relatively uniformly throughout the whole 110cm column. The biotransformation kinetics of NH4 + in RGW and SGW, Mn2+ in RGW at different depths accords with the first order kinetics model, while Fe2+ in RGW and SGW, Mn2+ in SGW presented more complicated biotransformation process. The results should improve understanding of the transport and fate of common groundwater pollutants in riverbank filtration and other groundwater recharge environments.

The effect of HF-HNO3 chemical polishing on the surface roughness and fatigue life of laser powder bed fusion produced Ti6Al4V

Metal additive manufacturing is increasingly utilised for the production of customised components. Post-process operations are required to address the high surface roughness of as-built components which is detrimental for load-bearing applications. Parts produced by metal additive manufacturing often have complex- surfaces and geometrical features rendering mechanical finishing processes impractical. This study investigates the chemical polishing of laser powder bed fusion (LPBF) produced Ti6Al4V axial fatigue test specimens in HF-HNO3 solutions with different initial HF concentrations (1, 2, and 4 M) and a constant initial HNO3 concentration (3.17 M). Polishing efficacy was evaluated in terms of mass removal, surface roughness reduction, and resulting tension-tension fatigue strength. The 4 M HF solution resulted in both the highest mass removal and surface roughness reduction; however, when evaluated relative to resource consumption, the processing efficiency decreases more drastically than that of the 1 and 2 M HF solutions. Specimens polished in all three solutions had higher fatigue strengths and fewer surface crack initiation sites than the as-built condition. Specimens polished in 2 M solutions exhibited better fatigue performance than specimens polished in 1 M solutions while statistical significance was lacking between the fatigue strengths of specimens polished in 2 M and 4 M solutions.

Unified Soil Freezing Characteristic for Variably‐Saturated Saline Soils

AbstractFreezing and thawing of soil have a significant impact on the thermal‐hydrological processes in cold regions. Freezing point and unfrozen water content are key variables characterizing the freezing and thawing of soil. The testing results show that unfrozen water content is independent of initial water content in nonsaline silt, based on which a unified model for a soil freezing characteristic curve (SFCC) is presented. The SFCC describes the relationship between unfrozen water content and temperature for variably‐saturated saline soils. It is also demonstrated that the SFCC can describe the variation of soil freezing point with respect to water content and salt concentration. The SFCC model is validated by comparing the experimental data to the calculated result for unfrozen water content and freezing point in a variety of conditions. When the initial water content varies in saline soil, the SFCC changes with constant initial salt concentration, but it remains unchanged with constant gravimetric salt content. The SFCC model can be adopted in the simulation of thermal‐hydrological processes in arid and saline lands and coastal regions. Finally, an example of thermal‐hydrological processes was simulated with the new SFCC model to show the application of the presented model.

Carbon and nutrient accumulation in mangrove sediments affected by multiple environmental changes

In order to assess the impact of anthropogenic activities on carbon and nutrient accumulation, total organic carbon (TOC), nitrogen (TN), and phosphorus (TP) accumulation rates were examined in a 210Pb-dated mangrove sediment core from Sepetiba Bay, Brazil, a coastal region impacted by multiple environmental changes during the previous century. A 50-cm length sediment core was collected from a mangrove forest in Sepetiba Bay. Sediment subsamples were analyzed to measure TOC, TN, δ13C, and δ15N using an elemental analyzer attached to an isotope ratio mass spectrometer Thermo Finnigan Model Delta Plus XP, whereas colorimetric analysis were used to measure TP. For 210Pbex analyses, gamma-ray measurements were performed in a semiplanar intrinsic germanium high purity coaxial detector, coupled to a multichannel analyzer, whereas the sediment accumulation rate (SAR) was calculated according to the constant initial concentration (CIC) method. Also, carbon and nutrient fluxes were calculated using SAR and TOC, TN, and TP contents, whereas statistical differences were evaluated by ANOVA + Tukey HSD analysis with previous data normalization. The calculated sedimentation rate (~ 8.1 mm year−1) since the early 1900s was up to threefold higher than the global mean determined for mangrove forests (~ 2.8 mm year−1) and the regional sea level rise (~ 3.2 mm year−1). Significantly higher TOC, TN, and TP fluxes, up to nearly 1000, 90, and 15 g m−2 year−1, respectively, were observed after the water diversion from a nearby drainage basin in the 1950s and an increase in sewage effluent input, which increased in the early 1990s. After this period, lighter δ13C values (~ − 25‰) indicate an increased importance of the terrestrial organic matter source, while lower TOC:TN ratios (~ 11) and heavier δ15N values (~ + 9‰) suggest an increased influence of anthropogenic fertilization on inorganic nitrogen accumulation. The significantly higher accumulation rates during the last decades evidenced the role of mangrove sediments as sinks for anthropogenically enhanced inputs of carbon and nutrients. Also, studies on carbon and nutrient accumulation evidenced the need for further research in eutrophic coastal areas.

Evaluating electrocoagulation pretreatment prior to reverse osmosis system for simultaneous scaling and colloidal fouling mitigation: Application of RSM in performance and cost optimization

In the present research, electrocoagulation (EC) process was applied as a selected pretreatment to evaluate its effectiveness and operating cost regarding simultaneous calcium and turbidity removal in order to mitigate the scaling and colloidal fouling potential of reverse osmosis (RO) technology. The effects of the main parameters, namely, initial calcium concentration, initial turbidity, time, and current density, on EC process were assessed and optimized by employing response surface methodology (RSM). A reasonable correlation between the experimental and predicted data was found through analysis of variance (ANOVA). The highest calcium and turbidity removal efficiencies of 36 % and 93.5 %, respectively, and the minimal operating cost of 1.58 US$/m3 were obtained at the optimum time of 35.5 min and current density of 3.85 mA/cm2 with the selected constant initial calcium concentration of 250 mg/L and initial turbidity of 85 NTU. In the present study, the applicability of two pretreatments, including hybrid EC-filtration and filtration-only to RO membrane fouling was also compared. The RO recovery of the hybrid EC-filtration pretreatment improved about 25 % in comparison to that of the filtration-only pretreatment, which demonstrated the effective capability of the EC process in scaling and colloidal fouling mitigation.

Low-cost bio-based sustainable removal of lead and cadmium using a polyphenolic bioactive Indian curry leaf (Murraya koengii) powder.

There is an increasing trend of developing various low-cost biogenic sorbents for the efficient and economical removal of noxious metals . Curry leaf powder (CLP), a promising non-toxic biosorbent containing several bioactive compounds was prepared by the pulverization of the dried leaves for the effective removal of Lead (Pb) and Cadmium (Cd). Various batch sorption experiments were carried out under constant temperature (25°C), different pH (4.5-10.5), initial concentrations (50-200mgL-1), adsorbent dosages (0.10-0.40g) and contact times (0-60min) to understand the optimum experimental conditions and simultaneously evaluate the adsorption isotherms and removal kinetics of CLP. Adsorption equilibrium was established in less than an hour interval (50min). The pseudo-equilibrium process was best described by the pseudo-second-order kinetic (R2≥0.99), Freundlich and Langmuir isotherm model (R2≥0.94). The removal rate of Pb and Cd gradually increased (15.7 and 12.7mgg-1 for Pb and Cd) at 100mgL-1 of initial concentration till 60min of contact period in a single contaminant system, the effect was non-significant for multiple adsorbent dosage systems (p>0.05; t-test) though. The regeneration potential of the exhausted biosorbent was excellent upto 5 cycles with the better efficiency observed for Pb. The obtained results explicitly validated the probable utilization of CLP as a promising green adsorbent for metal removal . Future study may highlight the decontamination aspects of emerging contaminants with such green bio sorbents in large scale as well as mimicing the stomach conditions.

Large nickel isotope fractionation caused by surface complexation reactions with hexagonal birnessite

Manganese oxides are an important sink for Ni in the ocean. To explore the potential of Ni stable isotopes as a geochemical tracer, we conducted two types of sorption reactions between Ni and hexagonal birnessite in 0.05 M NaNO3 media: one where we varied pH from 5 to 8 (constant initial Ni concentration = 170 μmol/L), and a second where we varied the initial dissolved Ni concentration from 17 to 426 μmol/L (constant pH = 7.7). Isotopic measurements were made on both the solid phase and the supernatant solutions to determine the Ni isotope fractionation factors (∆60/58Nimin-aq = δ60/58Nimin − δ60/58Niaq) between the mineral and aqueous phases. Nickel extended X-ray absorption fine structure (EXAFS) spectroscopy showed Ni in two distinct bonding environments: one where Ni atoms incorporate into the MnO2 sheet and a second where Ni atoms associate with the mineral surface sharing oxygens with 3 Mn tetrahedra (TCS, triple corner sharing). As pH and net negative surface charge increase, the coordination of Ni shifts to higher proportions of incorporation. The number of structural vacancies in birnessite, which are locations for TCS coordination of Ni, are controlled by pH and increase with decreasing pH. These vacancies are preferentially occupied by lighter Ni isotopes leading to fractionation factors, ∆60/58Nimin-aq, ranging from −2.76‰ (lowest TCS) to −3.35‰ (maximum TCS). These Ni isotopic fractionation factors are among the largest observed in natural geological and biological materials to date. Our findings reveal a relationship between Ni coordination environment and pH that may ultimately be used as an isotopic geochemical tracer of past ocean conditions. However, the results are inconsistent with current isotopic fractionation factors for marine ferromanganese deposits relative to seawater and point to unaddressed processes that modify Ni isotopic fractionation for ferromanganese deposits. Further research is needed to develop Ni as an isotopic tracer.

Experimental Study of Heavy Metal Dispersion through Cohesionless Soil: a Case Study of Cd+

In this case study of cadmium metal (Cd+), an experiment has been conducted on the dispersion of heavy metals through flow in porous media. Sandy soil with a specific gravity of 2.65 has been selected as a porous medium for water contaminated with Cd+. A laboratory model has been built from glass box (0.75 m length × 0.10 m width × 0.55 m height, 10 mm thickness) in order to simulate the two-dimensional flow of the polluted water. The box is divided into three zones, namely, inlet zone (upstream), outlet zone (downstream), and sandy zone. In additional, tow adjuster valves are used to control the flow from upstream to downstream direction. Furthermore, eight points are selected in order to study the effect of time/distance ratio and to obtain acceptable results through a wide range of samples. Six of these points, P1, P2, P3, P4, P5, and P6, are fixed on the side of the model, while P7 and P8 represent the sampling points on the soil surface. The experimental model is activated using continuous flow patterns with a constant average initial concentration of Cd+ (5.899 ppm). Sampling is conducted at 5, 10, 20, 30, 40, 50, and 60 min), and the filtered samples are tested using an atomic Adsorption device. The results of the laboratory test are analyzed in order to study the variations in Cd+ concentration with vertical distance (y-axis) and horizontal distance (x-axis) and to determine the effect of hydraulic gradient on Cd+ concentration. Cd+ has higher concentration at the deeper points, so sandy soil adsorbs Cd+ at higher concentrations before reaching stability. Cd+ concentrations in points closer to the upstream zone are greater than the ones in further points due to the proximity distance from the upstream zone where the concentrations represent high values. Additionally, Cd+ concentrations in P3 at the first half are greater than the ones in P5 and P6 because the adsorption process is inactive at the beginning of running the model using continuous flow.

Modular Testing of Dinitrogen Oxide (Nitrogen Hemioxide) Catalytic Decomposition Technology for Off-Gas Cleanup Systems for Brest Spent Nuclear Nitride Fuel Reprocessing

Dinitrogen oxide N2O (nitrogen hemioxide) is one of the harmful components of the off-gases during the reprocessing of spent nitride fuel. It enters the gas phase during the dissolution of nitride fuel in nitric acid and denitration of high-activity raffinate or the bottom solution from the evaporation of intermediate-level wastes. The preferred method of neutralizing it is high-temperature catalytic decomposition. Compositions based on γ-aluminum oxide coated with catalysts were found previously. One of the compositions was checked on a semi-industrial setup. The efficiency of N2O decomposition was studied as a function of temperature. It was established that almost complete decomposition occurs at 465–480°C. The specific rate of N2O decomposition at 425–480°C was found as a function of the initial concentration. It is shown that for constant initial concentration of N2O the specific decomposition rate is almost the same in the investigated temperature interval.

Variations and influence factors of 210Pb-specific radioactivity in modern calcite depositions in a subtropical cave, South China

Although 210Pb dating has been successfully used in speleothems, the understanding of the factors impacting 210Pb variations in modern calcite depositions in karst caves is poor due to the lack of in situ monitoring. Here, we studied the 210Pb variations in drip water and modern calcite depositions at five sampling sites in Maomaotou Big Cave in Guilin, south China, through more than three years of in situ monitoring. In this work, the air 222Rn concentrations, weights and 210Pb-specific radioactivity of modern calcite depositions showed significant temporal and spatial variations. The modern calcite deposition weights and 222Rn concentrations in the air of Maomaotou Big Cave ranged from 0.02 to 6.04 g and 62.9–628 Bq.m−3 (higher values in summer-autumn and lower values in winter–spring), respectively, while the 210Pb-specific radioactivities in calcite depositions varied from 7.33 to 658.52 Bq•kg−1, with lower values reported in summer–autumn and higher values in winter–spring. The opposite seasonal trends observed for the 222Rn concentrations and 210Pb-specific radioactivity indicated that the air 222Rn concentration was not the dominant factor influencing the 210Pb-specific radioactivity in the modern calcite depositions. This study concluded that 210Pb-specific radioactivity in modern calcite depositions is mainly carried by drip water; further, the remarkable negative correlation between deposition weight and 210Pb-specific radioactivity in modern calcite depositions suggests that the Constant Initial Concentration model (CIC) is fit for recent speleothem dating in a closed system. Such important information may provide a scientific basis for cave deposition dating using 210Pb.

210Pb and 137Cs based techniques for the estimation of sediment chronologies and sediment rates in the Anzali Lagoon, Caspian Sea

137Cs and 210Pb based sediment chronology methods, along with an HPGe gamma-ray spectrometry system, were applied to estimating of sediment accumulative rates (SAR), sedimentation rate (SR) and sedimentation chronology in the Anzali Lagoon. Sedimentation chronology was calculated according to the 210Pbex based-models including; the constant rate of supply, constant initial concentration and 137Cs peak-technique. The SAR value were ranged from 0.12 g cm−2 year−1 in core-2 to 0.21 g cm−2 year−1 in core-3. The results showed that the average of SR and SAR values after 1986; interval were 22% and 54% more than between 1963 and 1986 intervals.

Adsorption-desorption of cypermethrin and chlorfenapyr on Jordanian soils

In this study, adsorption kinetic experiments were conducted on agricultural soil samples from Southern Jordan to investigate the adsorption behavior of the heavily used insecticide cypermethrin and the pesticide chlorfenapyr. Soil samples classified as sand and loamy sand with 1.77–2.02% organic matter content were collected from two locations within 0–30 cm depths in Tafilah, Jordan, and tested as adsorbents, and it was found that the adsorption of the two substances followed pseudo-second-order kinetics which implies that the adsorption process is chemisorption. The second-order rate constants were 1.01–2.03 g/mg h for cypermethrin and 11.38–13.03 g/mg h for chlorfenapyr. Adsorption isotherm experiments were also carried out at a constant temperature and variable initial adsorbate concentrations and it was found that the Langmuir model provided a slightly better fit to the adsorption data in comparison with the Freundlich model. The Langmuir maximum adsorption capacities were 8.88–9.08 mg/g for cypermethrin and 36.23–45.25 mg/g for chlorfenapyr while the Langmuir constants were 0.0123–0.0157 L/mg for cypermethrin and 0.003–0.0037 L/mg for chlorfenapyr. Higher adsorption rates were observed in the loamy sand soil due to the higher organic matter, clay, and silt contents. Nonetheless, it was concluded that the leaching potential of these substances to groundwater is low due to the physical nature of these chemicals as well as the adsorption behavior of the soil.

COD removal from disperse blue dye 79 in wastewater by using Ozone-Fenton process

Nowadays, one of the major problems that can face humankind is the water pollution. In this regard, making this natural resource a fresh and unpolluted is a major social and economic concern. However, a great attention has been given for the removal of organic pollutants discharged within wastewater by using advanced oxidation processes (AOPs) based on generation hydroxyl radicals. Among these, Ozone-Fenton (O3/H2O2/Fe2+) process used in this study as AOPs to remove chemical oxygen demand (COD) from Disperse Blue 79 (DB 79) dye in wastewater. Also, the effect of various experimental parameters such as ozone mass flow rate, mole ratio (mole H2O2/mole Fe2+), and reaction time on the COD removal efficiency of DB 79 were studied with constant initial concentration 60 mg/L of DB 79. Based on the results obtained in this study, the maximum COD removal efficiency was 85% achieved at optimum operating parameters are 288 mg/L. h ozone mass flow rate, 33.53 mole ratio (150 mg/L H2O2, 20 mg/L Fe2+), and 60 min reaction time. All Ozone-Fenton experiments were performed using Jar test apparatus at room temperature (23°C ∓ 2) and atmospheric pressure (1 atm). Finally, Ozone-Fenton offered an effective solution as AOPs for degrading pollutant especially DB 79 discharged within wastewater from various industrial processes.

Experimental and modelling studies of radiocesium sorption/desorption processes in the fixed-bed moss column

The experimental and modelling studies of the fixed-bed column filled with inanimate mosses Ptilium crista-castrensis containing background levels of 137Cs, flushed with the distilled water are presented. Fitting of the experimental results by Langmuir and Freundlich sorption models gave significant deviations. A more sophisticated two kinetic site model created for the case of non-equilibrium transport of the radiocesium solute through porous media was more suitable to describe the experimental data. It has been shown that theoretically the two site sorption model can be simplified to the conventional one kinetic site model with time dependent parameters. The radiocesium transport equation included the terms taking into account advection, dispersion and decay. General analytical solution was derived for two types of the border conditions: 1) when a constant flux of the material on the surface layer of the absorbent is known (i.e. a Cauchy type border condition); 2) a border condition with constant initial material concentrations. The mathematical solution was derived using the Laplace transformation method. In such a way, the obtained simulated profile of the radionuclide concentration distribution within the fixed-bed column with inanimate mosses showed the best-fitting to the experimental results.

Modeling of the Flows of Admixtures in a Random Layered Strip with Probable Arrangement of Inclusions Near the Boundaries of the Body

We study the random flow of admixtures in a two-phase stochastically inhomogeneous strip with the most probable arrangement of inclusions in the vicinity of the surfaces of the body. A mathematical model is formulated for the function of diffusion flow with nonzero constant initial concentration. A random diffusion flow is represented in the form of a Neumann series. The procedure of averaging of the random mass flow over the ensemble of phase configurations with arcsine distribution function is performed. The influence of the characteristics of the medium on the distribution of mass flow is analyzed. It is shown that if the diffusion coefficient of admixtures in the inclusion is higher than for the matrix, then the increase in the characteristic thickness of the layers causes a decrease in the value of the diffusion flow, whereas the mass flow in the entire body increases with the volume fraction of the inclusions.

Heat transfer analysis on progressive freeze concentration of aqueous lysozyme solution

In this study, operating conditions of progressive freeze concentration method were arranged to deal with heat transfer analysis. Progressive freeze concentration is also known as a method to remove water from the solution by freezing process. The aqueous solution of lysozyme needs a water removal technology system as the residual moisture content has a significant impact on the solid-state stability of this biopharmaceutical product. The process was carried out by a newly designed crystallizer called a multiple probe cryo-concentrator (MPCC) which is completely equipped with a controlled stirrer, adjustable cooling gas system, solution tank and a set of cooling probes. The operating condition involved in this system include operation time, t (20 to 60 min), coolant temperature, CT (-6 to -14 ?C) and stirrer speed, SS (200 to 400 rpm) at constant initial concentration of 10mg/ml. The result of overall heat transfer coefficient (Uo) at varied operating condition was analysed and obtained where coolant temperature of -8 °C, operation time of 20 min and stirrer speed of 350 rpm were found to give the highest Uo. All the operating conditions were found to contribute to the progress of ice development and removal of water in the MPCC system resulting in purity of ice and solution concentration accordingly.

A functional anionic metal–organic framework for selective adsorption and separation of organic dyes

A 3D porous anionic MOF, {[(CH3)2NH2][Zn6(μ3-OH)(μ4-O)(NSBPDC)5(H2O)2]·DMF·12H2O}n (Zn-1) (H2NSBPDC = 6-nitro-2,2′-sulfone-4,4′-dicarboxylic acid), has been synthesized and characterized. Zn-1 exhibits a rare 5-connected ‘sqp’ net and contains large 3D intersecting channels modified with functional groups. Notably, Zn-1 can adsorb cationic dyes selectively and effectively, even for large molecules including Rhodamine B and Crystal Violet. The influences of the constant time and initial concentration of MB on the adsorption capacity of Zn-1 have been studied in detail. Furthermore, the kinetic research indicates that the adsorption of MB matches well with the pseudo second-order model. In addition, the material of Zn-1 is reusable, and the adsorbed dye (MB) can be released in saturated DMF/ethanol solution of LiNO3.

Watershed diffuse pollution dynamics and response to land development assessment with riverine sediments

Sediment cores can reflect diffuse pollution history due to the accumulation of pollutants over time, therefore, the quantitative relationship between the sedimentation flux of pollutants and diffuse loads can identify the historical change. Sediment cores were collected from two river reaches in a small agricultural watershed (143 km2), and the total nitrogen (TN) and total phosphorus (TP) concentrations were determined. The sediments were dated using 210Pb isotope radioactivity and the TN and TP sedimentation flux was calculated with Constant Rate of Supply (CRS) and Constant Initial Concentration (CIC) models. Watershed loss loads were simulated using the Soil and Water Assessment Tool (SWAT) in the same temporal period. As the similar natural condition in the post-depositional period of sediments, a linear regression model was used to analyze the relationship between TN and TP sedimentation flux and the hindcast model data. The TP sedimentation flux showed a clear positive relationship with its simulated load (R2 = 0.600 and 0.664) using the CRS model, and better reflected long-term diffuse pollution loss dynamics than nitrogen. The impacts of land use change on diffuse pollution loading were identified with the combination of sedimentation flux from different reaches and watershed modeling. During the expansion of paddy land in the lower reach, the difference of TP sedimentation flux between upper and lower reaches narrowed, while gap of TN sedimentation flux increased. Base on the lateral correlations of two sections, the sediment concentration of TP was more reliable for the long term diffuse pollution assessment under land development.

Reconstructing recent changes in sediment yields from a typical karst watershed in southwest China

Southwest China is characterized by shallow soils with low soil loss tolerance (30–68 t km−2 yr-1), and this region is one of the largest contiguous karst areas in the world, notorious for its highly eroded landscapes. However, reliable information on soil erosion rates in these karst watersheds is limited due to the highly heterogonous landscape. Karst depressions are a unique geomorphologic pattern in southwest China which can trap eroded sediment similar to a reservoir or dam, and may provide a great opportunity for sediment yield estimation if the sediment chronology can be properly determined. This study used karst depression sediment deposits to reconstruct the changes in sediment yields over the past 60 years from a typical karst watershed in southwest China. Three sediment cores were collected from the depression to measure the changes in 137Cs and 210Pbex, clay, silt, and sand contents, and soil organic carbon at different depths. The results indicated that the three common 210Pbex dating models - Constant Sedimentation (CFCS), Constant Initial Concentration (CIC), and Constant Rate of Supply (CRS) - were not applicable to karst depressions, while a modified CRS model that used 137Cs age marker as reference improved determination of the sediment chronology. From 1949 to 2015, the sediment yields initially increased and then sharply decreased to a low value, which might represent a general trend of soil erosion dynamics in karst watershed of southwest China. It was noteworthy that the mean soil erosion rate after the “Grain for Green” project of 1999 was only 80 t km−2 yr-1, which also is greater than the soil loss tolerance in karst regions. This study demonstrates the potential for use of 137Cs and 210Pbex to evaluate the temporal variation in sediment yield in a typical karst watershed of southwest China and may improve karst watershed management.

Adsorptive Removal of Basic Yellow Dye Using Bigadiç Zeolites: FTIR Analysis, Kinetics, and Isotherms Modeling

The adsorptive removal efficiency of Basic Yellow Dye (Astrazon Yellow 7GLL) from aqueous solutions was studied using different types of modified zeolites in an agitated single‐stage batch experimental system. Zeolite samples consisted of mainly clinoptilolite, collected from Bigadic Region of Turkey. The optimum adsorbent amount was found as 0.5 g in the primary experiments. Then, the adsorption kinetics with a constant initial dye concentration of 50 mg/L, agitation speed of 250 rpm, and temperature of 25°C for a period of 180 min were investigated. Three kinetic models namely, pseudo‐first‐order, pseudo‐second‐order non‐linear kinetic models, and the intra‐particle diffusion were used to describe the kinetic data of adsorption process. Non‐linear fittings of the Langmuir and Freundlich adsorption isotherm models were applied to the experimental equilibrium data obtained with dye concentrations in the range of 12–550 mg/L. The adsorption capacities (Qo) of zeolite samples for basic dye were in the range of 17.8–21.2 mg/g. Different analytical methods were used to investigate the influence of the different treatments on the zeolite surface and understanding of the adsorptive removal of dye using natural and modified zeolites. It was concluded that the spectroscopic results agree with the results obtained by kinetic and adsorption experiments as the acidic pre‐treatment zeolite has the highest removal rate for dye molecules since the concentration of various active sites (oxygen species, free Al+, and Si+ sides, etc.) to increase on the surface. On the contrary, basic treatment causes the loading of the surfaces with hydroxyl groups and these interact with each other via H‐bond and causes increased removal rate. © 2018 American Institute of Chemical Engineers Environ Prog, 38: S185–S195, 2019