First-order Rate Equation Research Articles

Study of electric field-enhanced mass transfer and Li/Mg separation of N, N-bis (1-methylheptyl) acetamide/TBP-NaFeCl4 composite membrane

Using N,N-bis(1-methylheptyl)acetamide (N503) synergized with TBP-NaFeCl4 (TFe), a ternary composite extraction membrane known as TFeN-PIM was created. Under optimum membrane phase conditions, the mass transfer properties of TFeN-PIM-Li(Ⅰ) and its Li/Mg selective separation performance by electric field augmentation were examined, and confirmed the mechanism of TFeN-PIM-Li(Ⅰ) electric field enhanced mass transfer. The findings demonstrate a homogeneous distribution of [FeCl4-] in the TFeN-PIM membrane phase and a decrease in the water contact angle as the TFe content increases. In the TFeN-PIM membrane, the cation binding order of the composite carrier was H+>Li+>Na+>Mg2+, and the mass transfer was carried out at the interface of the two phases of the membrane through the mechanism of "cation exchange-neutralization", in which Li(Ⅰ) was bonded with the carrier in the form of 2N503-LiFeCl4-2TBP, and showed a fixed-site "hopping" mass transfer characteristics under the reinforcement of electric field. The mass transfer process of the TFeN-PIM- Li(Ⅰ) system under electric field enhancement conforms to the first-order kinetic rate equation, and the voltage (5–45 V) is positively correlated with the permeability coefficient PLi(Ⅰ) but decreases the Li/Mg selectivity of TFeN-PIM. The SLi(Ⅰ)/Mg(Ⅱ) of TFeN-PIM was 9.18 at 3 V. After three cycles of 72 h cycling at 40 V, the decrease rate of PLi(Ⅰ) was <7.42 %, which showed good stability.

Experimental solubility of FeCO3 in aqueous 3–20 wt% KCl at 25–80 °C

FeCO3 is a mineral, present in both industrial and natural systems. While the solubility of FeCO3 is determining for CO2 storage, and driving for corrosion, it is not well understood. For the development of rigorous modelling, there is a lack of adequate experimental data under relevant conditions to model carbonated systems containing iron.In this work, the solid-liquid equilibrium (SLE) of the ternary system FeCO3-KCl-H2O was measured at atmospheric pressure at temperatures from 25 to 80 °C. The FeCO3 solubility was studied in aqueous KCl solutions from 3 to 20 wt%. 73 new solubility data points for the systems FeCO3–KCl–H2O are presented together with 73 oxidation data points. Results showed that less than 5% of FeCO3 is oxidized in the electrolyte system. The equilibrium concentration of FeCO3 was obtained after 5–10 days with the fastest equilibrium kinetics obtained at the highest temperature, 80 °C. Temperature had a minor impact on the FeCO3 solubility in aqueous KCl solutions. However, the FeCO3 solubility seemed to slightly decrease with temperature. The solubility data was fitted to a first-order rate equation with molality as driving, to obtain kinetic insights. The dissolution rate decreases as a function of KCl concentrations. In some cases, it was 75 % lower than in NaCl. A rate constant of approximately 0.2 1/day was obtained for most experiments. The FeCO3 solubility and kinetic data obtained in this work will allow for a deeper understanding and better prediction of CO2 corrosion and mineralization, suitable for CO2 storage.

A phenomenological kinetic flotation model: Distinct Time-Variant floatability distributions for the pulp and froth materials

A simple and easy-to-use phenomenological kinetic flotation model, strongly connected with the physics of the process, is proposed in this paper. The model explicitly contains the cell volume, aeration rate, volumetric hold-up, mean bubble size, and particle density as input variables. It can be employed to characterize the floatability distributions of the particles in the pulp and the froth separately any time during the flotation process. Two new time-dependent kinetic parameters, the bubble loading factor φ(t) and the maximum cell mass transfer capacity Ṁmax(t) also appear in the model expression. φ(t) is a measure of the degree of crowding of the bubble surfaces and accounts for the deviations from the first-order rate equation. Ṁmax(t) describes the maximum amount of mass that can be transported to the froth phase by the bubble population in the cell. Screen fractionation of each froth product collected at different time intervals during a single kinetic flotation test is sufficient to generate the data required by the model for analysis. Application of the model to this data yields directly time-dependent functions for the floatability of the particles reporting to froth Kf(t) or remaining in the cell Kp(t) for each size fraction separately, without the need for any empirical parameters. The test of the model was carried out using published kinetic flotation data from the literature.

Effect of shear ratio on rheological properties of suspension in two-step flocculation process for fine iron tailings

In the two-step flocculation process, shear has a significant impact on the rheological properties of the flocculating slurry. In this study, the orthogonal experiments of two-step flocculation process for fine iron tailings were designed. Based on the change of shear ratio, different shear rates and shear time were designed, the yield stress, plastic viscosity and maximum packing fraction of the flocculated suspension in each group were measured and calculated with a rheometer. The result of range and variance analysis shows the shear rate in the primary broken phase was the biggest factor affecting the yield stress and plastic viscosity of the flocculated slurry in two-step flocculation process. When the shear rate increased from 100 s-1 to 400 s-1, the yield stress and the plastic viscosity of the flocculated slurry increased by 7.14% and 21.30%, respectively. When the shear rate changed from 400 s-1 to 800 s-1, they decreased by 23.27% and 33.17%, respectively. Since the shear ratio in a two-step flocculation process is also related to both shear action and floc structure parameter, the shear ratio was introduced into the first-order reversible kinetic rate equation. Through establishing the relationship between the shear ratio and the floc structural parameter of flocculating suspension, a theoretical model of the shear-dependent maximum packing fraction was established. The measured values and theoretical calculated values of the maximum packing fraction in two-step flocculation experiments were in good agreement and the error was within 5%. Last but not least, the internal mechanism of the theoretical model was discussed from the microscopic point of view.

Kinetic and thermodynamic approaches on biodiesel reaction in a simultaneously cooled enhanced microwave system

Transesterification reaction kinetics of canola oil with calcined dolomite was investigated in an Enhanced Microwave System (EMS) which can work under constant, continuous microwave (MW) power and isothermal conditions. The kinetic data obtained at 65 °C were fitted into different order models depending on methanol-to-oil molar ratio (nm/no: 3–15) to estimate the most suitable kinetic model. For nm/no=9, the selected best kinetic model and reaction order with the first-order rate equation showed good fit with high correlation coefficients (R2) at different temperatures (50–65 °C) in EMS and Conventional Heating System (CHS). While the activation energy of 108.6 kJmol−1 and pre-exponential factor of 7.3x1013 min−1 were found in EMS respectively, these values were found to be lower as 24.2 kJmol−1 and 5.47 min−1 in CHS, respectively. The thermodynamic parameters (ΔG, ΔH ΔS) of the transesterification reaction were also investigated. The nature of the reaction was found non-spontaneous, endergonic, and endothermic due to positive values of ΔG, ΔH in both systems. Further, positive ΔS showed that randomness more increases in EMS than in CHS. It was seen that MW energy more effective on pre-exponential factor and thermodynamic parameters. Thus, the reaction occurred much faster in EMS than in CHS.

Synthesis of trioctyl polyvinyl chloride ammonium, membrane extraction properties, and electrodriven mass transfer behavior of Chromium (VI)

Trioctyl polyvinyl chloride ammonium (PVCTQAS) with quaternary ammonium salt content (QAS) of 25 % was synthesized by a nucleophilic substitution reaction of between polyvinyl chloride (PVC) and trioctylamine (TOA) for the first time. The mass transfer behavior of HCrO4−, CdCl3−, CoCl42−, FeCl4−, and CuCl42− metal complex anions within the plasticized PVCTQAS membrane followed a first-order kinetic rate equation. Taking the Cr(Ⅵ)-PVCTQAS system as a representative, the influences of plasticizer content and membrane thickness on the mass transfer performance were investigated, and the electrodriven mass transfer behavior of Cr(VI) was studied. The results showed that the mass transfer of HCrO4− in PVCTQASD followed a jumping mechanism, with a QAS content threshold of 22 %. In the Cr(VI)-PVCTQAS electrodriven mass transfer system, the PVCTQASD exhibited uniform electrochemical properties, and the membrane thickness had little influence on the mass transfer rate. The response of HCrO4− mass transfer rate to voltage depended on the distribution density of QAS in the membrane. The mass transfer performance of PVCTQASD with QAS between 15 % and 20 % had a high dependence on the voltage, while the permeability coefficient of Cr(VI)-PVCTQAS system became stable when the voltage exceeded 10 V after surpassing the QAS content threshold. 50 μm QAS 25 % Cr(VI)-PVCTQAS system had a treatment efficiency of 710 mg·m−2·h−1 for HCrO4− at 10 V, while maintaining exceptional selectivity and stability.

Eco-friendly PVA-chitosan adsorbent films for the removal of azo dye Acid Orange 7: Physical cross-linking, adsorption process, and reuse of the material

The treatment of wastewater requires the use of eco-friendly and cost-efficient adsorbents. A hybrid adsorbent film based on biodegradable polymers (poly(vinyl alcohol) (PVA) and chitosan (Ch) was developed to remove Acid Orange 7 (AO7), an azo dye from the textile industry present in industrial wastewaters. The polymeric absorbent material was submitted to a curing process with different time-temperature combinations which improved its physical stability in aqueous media. This result was supported by modulated differential scanning calorimetry (MDSC) and thermogravimetric analysis (TGA). ATR-FTIR also confirmed the electrostatic interactions by hydrogen bonds between PVA and Ch, as well as among the polymers and the dye. The best curing condition to reach a high removal without weight loss was the combination of 160°C-1h.Dye adsorption depended mainly on pH, adsorbent dose, contact time, temperature, and coexisting anions. The maximum removal efficiency (>91%) was achieved at pH = 2.5. The adsorption kinetics followed the Lagergren pseudo first-order rate equation and the adsorption isotherm was best described by the Redlich-Peterson model. As far as the authors know, the maximum adsorption capacity (Qm) of the adsorbent film obtained in the present work is the highest value reported in literature (Qm = 678 mg/g at 298 K and pH = 2.5). Physisorption would be the dominant mechanism at pH 4.0 while at pH 2.5 the process was conducted by chemisorption. Regeneration studies showed that composites could be used for five consecutive cycles without losing their adsorption capacity.Thus, the use of the developed eco-compatible biodegradable materials would allow easy regeneration without losing removal selectivity, a key feature in the development of environmentally friendly sorbent materials.

A Simple One-Parameter Percent Dissolved Versus Time Dissolution Equation that Accommodates Sink and Non-sink Conditions via Drug Solubility and Dissolution Volume

In vitro dissolution generally involves sink conditions, so dissolution equations generally do not need to accommodate non-sink conditions. Greater use of biorelevant media, which are typically less able to provide sink conditions than pharmaceutical surfactants, necessitates equations that accommodate non-sink conditions. One objective was to derive an integrated, one-parameter dissolution equation for percent dissolved versus time that accommodates non-sink effects via drug solubility and dissolution volume parameters, including incomplete solubility. A second objective was to characterize the novel equation by fitting it to biorelevant dissolution profiles of tablets of two poorly water-soluble drugs, as well as by conducting simulations of the effect of dose on dissolution profile. The Polli dissolution equation was derived, % ;dissolved=100%left[1-frac{left({{M}_{0}-c}_{s}Vright)}{{M}_{0}-{{c}_{s}Ve}^{{-k}_{d}left(frac{{{M}_{0}-c}_{s}V}{V}right)t}}right], where M0 is the drug dose (mg), cs is drug solubility (mg/ml), V is dissolution volume (ml), and kd is dissolution rate coefficient (ml/mg per min). Maximum allowable percent dissolved was determined by drug solubility and not a fitted extent of dissolution parameter. The equation fit tablet profiles in the presence and absence of sink conditions, using a single fitted parameter, kd, and where solubility ranged over a 1000-fold range. kd was generally smaller when cs was larger. FeSSGF provided relatively small kd values, reflecting FeSSGF colloids are large and slowly diffusing. Simulations showed impact of non-sink conditions, as well as plausible kd values for various cs scenarios, in agreement with observed kd values. The equation has advantages over first-order and z-factor dissolution rate equations. An Excel file for regression is provided.Graphical

Biodegradation mechanism of chlorpyrifos by halophilic bacterium Hortaea sp. B15

For decades, most of the developing nations have relied on chlorpyrifos for insecticidal activity in the agriculture sector. It is a common chlorinated organophosphorus pesticide that has been widely used to control insects to protect plants. This study aimed to investigate the effects of environmental characteristics such as salinity, pH, temperature, and surfactant on Hortaea sp. B15 mediated degradation of chlorpyrifos as well as enzyme activity and metabolic pathway. The highest bacterial growth (4.6 × 1016 CFU/mL) was achieved after 20 h of incubation in a 100 mg/L chlorpyrifos amended culture. The fit model and feasible way to express the chlorpyrifos biodegradation kinetics in normal condition and optimized was a first-order rate equation, with an R2 value of 0.95–0.98. The optimum pH for chlorpyrifos biodegradation was pH 9, which resulted in a high removal rate (91.1%) and a maximum total count of 3.8 × 1016 CFU/mL. Increasing the temperature over 40 °C may inhibit microbial development and biodegradation. There was no significant effect of culture salinity on degradation and bacterial growth. In the presence of non-ionic surfactant Tween 80, the maximum chlorpyrifos degradation (89.5%) and bacterial growth (3.8 × 1016 CFU/mL) was achieved. Metabolites such as 3,5,6-trichloropyridin-2-ol and 2-pyridinol were identified in the Hortaea sp. B15 mediated degradation of chlorpyrifos. According to the findings, Hortaea sp. B15 should be recommended for use in the investigation of in situ biodegradation of pesticides.

Cadmium Removal Using Bio-Electrochemical Reactor with Packed Bed Rotating Cylindrical Cathode: A Kinetics Study

The kinetics of removing cadmium from aqueous solutions was studied using a bio-electrochemical reactor with a packed bed rotating cylindrical cathode. The effect of applied voltage, initial concentration of cadmium, cathode rotation speed, and pH on the reaction rate constant (k) was studied. The results showed that the cathodic deposition occurred under the control of mass transfer for all applied voltage values ​​used in this research. Accordingly, the relationship between logarithmic concentration gradient with time can be represented by a first-order kinetic rate equation. It was found that the rate constant (k) depends on the applied voltage, the initial cadmium concentration, the pH and the rotational speed of cathode. It was increased with increasing the applied voltage and its relationship with the applied voltage obeyed an exponential formula. The rate constant (k) was decreased with increasing the initial concentration of cadmium higher than 150ppm while at low concentrations it was increased. pH and rotational speed have different effects on the rate constant. Increasing the pH from 3 to 6 increases the rate constant while a slight decrease in the rate constant occurs at pH = 7. Increasing the rotation from 100 to 500 rpm increases the rate constant; however, the rate constant became approximately constant buoyed 300 rpm.

Model development for the optimization of operational conditions of the pretreatment of wheat straw

• Biomass pretreatment experiments and model development for process design purposes. • Hydrothermal pretreatment of wheat straw not competitive. • Dilute acid pretreatment of wheat straw has monomer yields of. Y = 98 % w / w . • Machine learning and mechanistic models have good validation metrics. • The latter performs best in optimization of operation conditions under uncertainty. The underlying study presents models for the optimization of operational conditions of lignocellulosic biomass pretreatment to facilitate the conceptual process design of biorefineries. Experiments for hydrothermal and dilute acid pretreatment are performed and analyzed. The highest xylose monomer yield obtained for dilute acid pretreatment is Y Xyl = 98 % at a temperature of T = 195 °C , a reaction time of t = 18 m i n and a dilute acid concentration of C acid = 1.25 w t % . The data is used to fit a response surface model (RSM), a Gaussian process regression model (GPR), and a mechanistic model based on thermodynamic principles and first-order rate equations. All models are validated respectively with a coefficient of determination of R RSM 2 = 0.914 , R GPR 2 = 0.999 and R mech 2 = 0.988 . Each model is used in an optimization problem to predict the optimal operational conditions that maximize the xylose yield. The conditions found by the mechanistic model T = 191 . 6 ° C , t = 18 m i n , C ac = 1.13 w t % with C Xyl , m e c h = 23.47 w t % and the GPR T = 195 ° C , t = 18 m i n , C ac = 1.25 w t % with C Xyl , G P R = 23.23 w t % are in agreement and stand out compared to the RSM metamodeling approach T = 182 . 4 ° C , t = 26.2 m i n , C ac = 1.25 w t % , which yields C Xyl , R S M = 25.72 w t % . Considering the scenario of uncertainty in the feedstock composition, the optimization under this uncertainty with the mechanistic model yields slightly different conditions T = 182 . 6 ° C , t = 18 m i n , C ac = 0.84 w t % and C Xyl , m e c h , u c = 20.88 w t % . Given the underlying phenomena in the biomass pretreatment, all models have shortcomings; however, the mechanistic model is validated best overall and is thus recommended for further engineering purposes as, e.g., the conceptual process design of biorefineries.

Effects of target temperature on thermal damage during temperature-controlled MWA of liver tumor

Microwave ablation (MWA) is one among the cancer treatment techniques applied in clinical treatment. This technique is based on rising the temperature within the tissue and the radiation dose absorbed by the cells. The goal of this study is to improve the accuracy of temperature simulation during temperature-controlled MWA of liver tumor. A two-dimensional numerical model of liver tissue has been built and solved using the Finite Element Method (FEM). The bio-heat equation, the first-order Arrhenius rate equations, and the Maxwell equations are employed to simulate the cancer cells necrosis. For heat control, an input microwave power source was controlled by a proportional-integral-derivative (PID) controller to keep the target tip temperature below the preset temperature value during MWA. The effect of the target tip temperature on the applied input microwave power has been investigated in liver tissue. Further, the thermal damage fraction and the time required for complete necrosis liver cancer are also evaluated. The present results show that the specific absorption rate (SAR) and the temperature distribution are highly influenced by the target tip temperature. Optimal treatment period for total tumor ablation will offers a significant way to reduce damage to the surrounding healthy cells and providing safe use of MWA and without risk.

Effects of Initial C/N Ratio on Maturity and Stability of Compost Produced from Two-Phase Olive Mill Pomace, Poultry and Dairy Manure and Straw

Composting of two-phase olive mill pomace, poultry and dairy manure, and straw was conducted at five initial carbon/nitrogen (C/N) ratios (from 20.03 to 39.99) using 15 100-liter reactors. Compost temperature was controlled based on Rutgers aeration strategies. Composting trials lasted 19.35 days. A first-order rate equation was used to obtain the decomposition rate and compost mass ratio (the degree of advancement of the composting process). The compost stability index was calculated considering the decomposition rate and the rate of oxygen uptake per unit of dry matter loss based on biochemical oxygen demand. The nonlinear relationship between the compost stability index and the initial C/N ratio showed that a minimum value of 0.011 kg O2 day−1 kgc −1 existed at the initial C/N ratio of 28.92. The lower compost stability index indicated relatively more stable compost. The relationship between the final ratio and the initial C/N ratios indicated that the lowest final ratio of 0.26 occurred at the initial C/N ratio of 29.66. The germination index as a function of the initial C/N ratio yielded a strong negative linear relationship with R 2 of 0.95. Compost mixes with the high initial C/N ratio resulted in relatively lower germination indexes which are phytotoxic to plant growth. This study showed how the initial C/N ratio is important for compost stability and maturity.

Measuring evaporation rate constants of highly volatile compounds for use in predictive kinetic models

A kinetic model was previously developed in our laboratory to predict evaporation of compounds as a function of gas chromatographic retention index (IT). To define the initial model, evaporation rate constants were experimentally determined for compounds in the range IT = 800–1400 at temperatures from 5 to 35 °C. While the predictive accuracy was demonstrated, broader application of the model requires extension of the IT range to include more volatile compounds. However, such extension requires experimental determination of rate constants, which is challenging due to the explosive hazard and rapid evaporation of volatile compounds.In this work, rate constants of highly volatile compounds were experimentally determined and used to extend the kinetic model to predict evaporation. Prior to experimental evaporations, theoretical calculations were performed to optimize experimental parameters and to ensure that the vapor generated remained below the lower flammability limit for each compound. Compounds were then experimentally evaporated at three different temperatures (10, 20, and 30 °C) and analyzed by gas chromatography-mass spectrometry. The evaporation rate constants for each compound, corrected for condensation, were determined by regression to a first-order rate equation. These rate constants were combined with previously collected data to extend the kinetic model at each temperature. Comparison of predicted and experimentally determined chromatograms of an evaporated validation mixture indicated good model performance, with correlation coefficients ranging from 0.955 to 0.997 and mean absolute percent errors in predicting abundance ranging from 3 to 26%.

Characteristics of indoor air pollutants and estimation of their exposure dose

Rural areas of developing countries have various indoor air pollution sources along with solid fuels used for cooking. This study aims to compare five indoor air pollution sources, viz., incense stick, dhoop, mosquito coil, cigarette, and cooking fuel charcoal, with respect to their pollution potential. The monitoring of PM, CO, CO2, NO2, and particulate bound heavy metals was carried out. Dhoop (DH1) was found to be emitting the highest concentration of metal Sb among all the analyzed metals. Dhoop, incense sticks, mosquito coil, and charcoal were found to be having high pollution potential. The first-order decay rate equation indicated that the highest decay rate constant per hour was observed with dhoop (DH1) for PM10 and PM2.5 and with mosquito coil (M1) for CO. The highest half-life of PM10 and PM2.5 was observed for cigarette (CG1) and charcoal (C1) respectively indicating their slow decay in air. The average daily dose values indicated that the age group 6 to < 11 years, 11 to < 16 years, and 31 to < 51 years will be more vulnerable to PM emissions from dhoop (DH1) and incense stick (IS1). The highest hazard index was estimated for incense stick (IS1) and charcoal. Significant carcinogenic risk was observed from cigarette and charcoal. The multiple-path particle dosimetry (MPPD) model was used to estimate the deposition of PM fractions in various regions of the human body.

Beneficiation of high-ash Indian coal fines by froth flotation using bio-degradable-oil as a collector

ABSTRACT The present paper outlines the work done on beneficiation of low-rank-oxidized coal fines by flotation using a biodegradable oil (iluppai or Mahua) to reduce the ash content. Prior to flotation, characterization of the coal and the reagents were done by FTIR and SEM-EDS analysis to identify the functional groups. Batch tests were performed with biodegradable and conventional oil (Diesel) as collectors to compare the flotation performances with an Index known as ‘Separation Index’. The results of the tests conducted revealed that biodegradable Iluppai oil to be the better collector than conventional diesel oil. In the study, the effect of variables like reagent dosages and feed solid concentration was investigated for both the type of collectors. Further, the paper concludes that it is possible to reduce ash% of the low-rank-oxidized coal from a feed ash of 29.9% down up-to 16.60% using Iluppai oil with simultaneous enrichment in Gross Calorific value of coal from 5547.0 to 6861 kCal/kg. From the results obtained, an assessment of the kinetic behavior of the process is made based on the enrichment achieved in the Gross calorific value. The first-order rate equation parameters (Rx) and (k) evaluated for the GCV recovery established that the biodegradable oil as the promising collector.

A Model for the Deposition of Scale Crystals on the Surface of Clay Particles

Deposition and aggregation of scale on microbial surface leads to poor stabilization of the treatment of oilfield high-scale oily wastewater. To study the deposition characteristics of scale on the surface of microbial particles, we perform the deposition and aggregation of calcium sulfate on the surface of clay particles as simulators of microbes and establish the deposition-aggregation process model. According to the theory of crystal growth, the diffuse electric double layer theory for clay, and the charged colloid theory, the scale deposition model can be divided into induction period, formative period of scale crystal nucleation, and crystal growth period. When calcium sulfate crystals deposit and aggregate on the surface of clay particles, the zeta potential and the average particle size on the surface of the clay particles increase continuously over time and tend to increase and decrease in cycles. The scale crystals are wrapped divergently around the surface of the clay particles in a needle-like form, such that the clay suspension is in a state of high aggregation. Logarithmic value of the conductivity in the formation of scale crystal has a good linear relationship with time, which conforms to the first-order rate equation. Conductivity curves can better reflect the deposition course of scale crystal on the surface of clay particles, which is divided into the induction period (6 min), transition period (1.5 min), formative period of scale crystal nucleation (10.75 min), rapid growth period of scale crystal (8.5 min), slow growth period of scale crystal (14.75 min), and stationary phase (4.75 min), and with the formation of the scale crystal, the deposition rate constant decreases gradually from 0.00945 min−1 to 0.0001 min−1. The results uncovered that Deposition and aggregation rules of scale on the surface of clay particles and the basis for further studying on microbial surface.

Geochemical Controls on Release and Speciation of Fe(II) and Mn(II) From Hyporheic Sediments of East River, Colorado

Hyporheic zones act as critical ecological links between terrestrial and aquatic systems where redox-sensitive metals of iron (Fe) and manganese (Mn) significantly impact nutrient cycling and water quality. However, the geochemical controls on the release and speciation of Fe(II) and Mn(II) in these biogeochemical hotspots are still poorly understood. Here we conducted batch incubation experiments and analyzed Fe K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy data using sediment samples from a hyporheic zone of the East River floodplain in Colorado to understand the production, release and speciation of Fe(II) and Mn(II) in groundwater. Our results indicate that the production and release of Fe(II) and Mn(II) vary with sediment reducing conditions and subsurface positions, and the rates were determined either by a zero- or first-order rate equation. The sediments with higher Fe(II) production did not necessarily result in higher release of dissolved Fe(II), and ≥97% Fe(II) is accumulated in solid phase. We found that the majority of Fe(II) exists as siderite (FeCO3), Fe(II)-natural organic matter (NOM) complexes and ferrosmectite, and the equilibrium concentrations of dissolved Fe(II) are controlled primarily by siderite solubility, and enhanced greatly by formation of strong Fe(II)-NOM complexes as dominant aqueous Fe(II) species. By contract, dissolved Mn(II) increases slowly and linearly, and an equilibrium concentration was not reached during the incubation period, and the roles of rhodochrosite (MnCO3) and Mn(II)-NOM complexes are insignificant. Furthermore, we reviewed and calibrated the literature reported binding constants (log K) of Fe(II)-NOM complexes which successfully predicted our experimental data. This work reveals that siderite and dissolved NOM are the controlling phases in release and speciation of dissolved Fe(II), and the finding is expected to be applicable in many hyporheic zones and subsurface environments with similar geochemical conditions.

Transport mechanisms and emission of landfill gas through various cover soil configurations in an MSW landfill using a static flux chamber technique

This study evaluated the transport mechanisms and emission rates of landfill gas (LFG) from 200- (vegetated with short grass), 300- (vegetated with short grass), and 450-mm-thick (non-vegetated) interim cover soils within a municipal solid waste landfill. LFG emission and diffusion mechanisms were evaluated using static flux chambers and laboratory-scale diffusion columns. Overall, the greatest CH4 and CO2 emissions were consistently observed from the 200-mm-thick cover soil with an average flux rate of 39.2 mg m−2 h−1 and 3.07 × 103 mg m−2 h−1, respectively. In addition to CH4 and CO2, H2S migration through a 450-mm interim cover soil was also evaluated. The H2S emission rate was relatively more uniform at an average of 2.47 × 10−5 mg m−2 h−1. Long-term LFG emission was predicted using an emission model based on a first-order decomposition rate equation and compared with the static flux chamber method. The field-measured CO2, CH4 and H2S emissions were less than the estimated emissions from the emission model, by 22%, 85%, and 91%, respectively. Further, the diffusion coefficients of CH4, CO2, and H2S for the interim cover soils were determined using a laboratory-scale diffusion column test and compared with a three-parameter diffusion model. The measured and estimated diffusion coefficients for the three landfill gases were within the 10% variation limits. Based on these findings, the LFG emission rate varied depending on the physical-chemical properties of the cover soil (e.g., cover thickness, moisture content, compaction ratio, uneven distribution of soil), organic material content and age of buried refuse, and seasonal environmental conditions (such as temperature). Test results showed that fugitive CH4 emissions can be reduced one fourth by utilizing an appropriate cover soil (300-mm to 450-mm, CL) compared to cases with a thinner cover soil.

Sorption of Cd(II) and Pb(II) ions by Nanolimestone from underground water samples from Tehama region of Saudi Arabia

Powdered Nano limestone (NLS) has been investigated as an un-expensive adsorbent for heavy toxic metals removal from aqueous solutions as cadmium and lead. Batch experiments were carried out, The favorable pH for maximum metals adsorption was at 6.8 for both. The surface area increased in case of NLS up to 6.2 m2/g. The adsorption capacity calculated by Langmuir equation was 75.1 mg/g for Cd(II) and 68.4 for Pb(II) ions at pH 6.8. The adsorption capacity increased with temperature and the kinetics followed a First-order rate equation for both. The enthalpy change (ΔH0) was 25.4 Jmol−1 for Cd(II) and 20.8 Jmol−1 for Pb(II), while entropy change (ΔS0) was 41.6 JK-1mol-1 for Cd(II) and 38.7 JK-1mol-1 Pb(II), which indicate that adsorption process was endothermic and spontaneous in nature. About 25 collected samples of groundwater were tested and found to be contaminated with cadmium and lead elements with different rates, with using NLS as adsorbent able to remove both metals from the samples. All of the results suggested that the NLS is excellent nano-adsorbents for cadmium and lead contaminated water samples.