Initial Mass Concentration Research Articles

Lateral transport of soil total carbon with slope runoff and interflow: Effects of rainstorm characteristics under simulated rainfall

In order to study the characteristics of soil total carbon (TC) transport with slope runoff and interflow during rainstorms in the Zhejiang-Fujian hilly region, China. Slope gradients (5, 8, 15, 25°) and rainfall intensities (60, 90, 150 mm·h−1) were selected as the variable factors for artificially simulated rainfall experiments. Runoff samples were collected every 3 min to measure the volume and TC mass concentration, then we calculated the TC loss rates and loss gross amount. The results showed that the overall trend of TC mass concentration in slope runoff presented a high initial value that gradually decreased with the increase of rainfall duration and finally tended to be stable, and it mean mass concentration was relatively highest at all the 15° conditions. The TC loss rates presented a stability at a certain value after gradually increasing over time at gentle slopes while it led to an increasing trend when the slope was steeper, yet these trends weren't obvious at 150 mm·h−1 condition. The initial TC mass concentration was low at beginning in interflow which rose rapidly to the peak and finally continued to drop to a stable level. The shape of TC loss rate curves was similar to mass concentration curves. For both slope runoff and interflow, the slope gradient had little effect on TC mass concentration. The TC loss gross amount in the runoff (slope runoff + interflow) increased with the increase of slope gradients or rainfall intensities, which reached the maximum value at the 25°, 150 mm·h−1 condition, namely, 12.56 g, though the increase rates of TC transport decreased. The TC loss gross amount with slope runoff showed a trend of increasing first and then decreasing with increasing slope gradients, which all reached the maximum at 8° conditions, however it showed a continued rising trend as slope gradients increased in interflow. TC at 15° and 25° conditions mainly lost with the interflow, though at other slope gradients it mainly transported with the slope runoff. Similarly, the more gentle the slope gradients, the greater the proportion of the slope runoff volume in total runoff. The regression analysis showed at identical conditions, the influence of rainfall intensity on TC loss was larger than slope gradient in slope runoff while the slope gradient had a greater influence on TC loss in interflow. Correlation analysis showed that there was a significant correlation between the runoff volume and the TC loss gross amount in slope runoff and interflow (P < 0.01). There was a linear correlation between runoff volume and TC loss in slope runoff (R2 = 0.95), and power function fits the relationship between TC loss in interflow and runoff volume better (R2 = 0.66). The results provided a calculation method for estimating TC loss in runoff from bare land of weathered granite parent soil in the Zhejiang-Fujian hilly region of China.

Fractional Keller–Segel equation: Global well-posedness and finite time blow-up

This article studies the aggregation diffusion equation \[ \partial_t\rho = \Delta^\frac{\alpha}{2} \rho + \lambda\,\mathrm{div}((K*\rho)\rho), \] where $\Delta^\frac{\alpha}{2}$ denotes the fractional Laplacian and $K = \frac{x}{|x|^\beta}$ is an attractive kernel. This equation is a generalization of the classical Keller-Segel equation, which arises in the modeling of the motion of cells. In the diffusion dominated case $\beta < \alpha$ we prove global well-posedness for an $L^1_k$ initial condition, and in the fair competition case $\beta = \alpha$ for an $L^1_k\cap L\ln L$ initial condition with small mass. In the aggregation dominated case $\beta > \alpha$, we prove global or local well-posedness for an $L^p$ initial condition, depending on some smallness condition on the $L^p$ norm of the initial data. We also prove that finite time blow-up of even solutions occurs under some initial mass concentration criteria.

Investigation on focal ignition and combustion of aluminum-air suspension

The paper provides a numerical investigation on focal ignition and flame propagation in an aluminum-air suspension. The aim of the research was to determine the apparent flame propagation velocity in the aluminum-air suspension depending on the size and mass concentration of the aluminum particles. Numerical simulation showed that the smaller the particle radius the stronger the apparent burning velocity of the suspension depends on the initial mass concentration of the aluminum powder. The obtained results qualitatively correspond to the experimental data described in the scientific papers.

Non-isothermal desorption and nucleate boiling in a water-salt droplet LiBr

Experimental data on desorption and nucleate boiling in a droplet of LiBr water solution were obtained. An increase in salt concentration in a liquid layer leads to a considerable decrease in the rate of desorption. The significant decrease in desorption intensity with a rise of initial mass concentration of salt has been observed. Evaporation rate of distillate droplet is constant for a long time period. At nucleate boiling of a water-salt solution of droplet several characteristic regimes occur: heating; nucleate boiling; desorption without bubble formation; formation of the solid, thin crystalline-hydrate film on the upper droplet surface, and formation of the ordered crystalline-hydrate structures during the longer time periods. For the final stage of desorption there is a big difference in desorption rate for initial salt concentration (C0) 11 % and 51 %. This great difference in the rate of desorption is associated with significantly more thin solution film for C0 = 11 % and higher heat flux.

Kinetic modeling studies of SOA formation from &amp;lt;i&amp;gt;α&amp;lt;/i&amp;gt;-pinene ozonolysis

Abstract. This paper describes the implementation of a kinetic gas-particle partitioning approach used for the simulation of secondary organic aerosol (SOA) formation within the SPectral Aerosol Cloud Chemistry Interaction Model (SPACCIM). The kinetic partitioning considers the diffusion of organic compounds into aerosol particles and the subsequent chemical reactions in the particle phase. The basic kinetic partitioning approach is modified by the implementation of chemical backward reaction of the solute within the particle phase as well as a composition-dependent particle-phase bulk diffusion coefficient. The adapted gas-phase chemistry mechanism for α-pinene oxidation has been updated due to the recent findings related to the formation of highly oxidized multifunctional organic compounds (HOMs). Experimental results from a LEAK (Leipziger Aerosolkammer) chamber study for α-pinene ozonolysis were compared with the model results describing this reaction system.The performed model studies reveal that the particle-phase bulk diffusion coefficient and the particle-phase reactivity are key parameters for SOA formation. Using the same particle-phase reactivity for both cases, we find that liquid particles with higher particle-phase bulk diffusion coefficients have 310 times more organic material formed in the particle phase compared to higher viscous semi-solid particles with lower particle-phase bulk diffusion coefficients. The model results demonstrate that, even with a moderate particle-phase reactivity, about 61 % of the modeled organic mass consists of reaction products that are formed in the liquid particles. This finding emphasizes the potential role of SOA processing. Moreover, the initial organic aerosol mass concentration and the particle radius are of minor importance for the process of SOA formation in liquid particles. A sensitivity study shows that a 22-fold increase in particle size merely leads to a SOA increase of less than 10 %.Due to two additional implementations, allowing backward reactions in the particle phase and considering a composition-dependent particle-phase bulk diffusion coefficient, the potential overprediction of the SOA mass with the basic kinetic approach is reduced by about 40 %. HOMs are an important compound group in the early stage of SOA formation because they contribute up to 65 % of the total SOA mass at this stage. HOMs also induce further SOA formation by providing an absorptive medium for SVOCs (semi-volatile organic compounds). This process contributes about 27 % of the total organic mass. The model results are very similar to the LEAK chamber results. Overall, the sensitivity studies demonstrate that the particle reactivity and the particle-phase bulk diffusion require a better characterization in order to improve the current model implementations and to validate the assumptions made from the chamber simulations. The successful implementation and testing of the current kinetic gas-particle partitioning approach in a box model framework will allow further applications in a 3-D model for regional-scale process investigations.

Influencing Factors on the Degradation of PFOS Through VUV-SO32

The objective of this experiment was to investigate the influence of SO32-dosage, pH value, initial perfluorooctane sulfonate(PFOS)concentration as well as coexisting substances on the degradation and defluorination of PFOS by VUV-SO32- process. The results indicated that the increase of SO32- dosage could lead to rise in the concentration of active species hydrated electron(eaq-) and thus enhance the degradation and defluorination of PFOS. As the concentration of SO32- increased from 1 mmol·L-1 to 20 mmol·L-1, the degradation and defluorination rates of PFOS increased from 45% and 40% to 97% and 63%, respectively. The degradation and defluorination of PFOS were also enhanced with the increment of the solution pH values, and the defluorination was more sensitive to the pH values. In addition, more PFOS was degraded with the increase of initial PFOS mass concentration, although the degradation and defluorination rates of PFOS were reduced. When the initial PFOS mass concentration changed from 1 mg·L-1 to 50 mg·L-1, the degradation amount of PFOS after four hrs increased by about 50 times, probably due to the higher utilization proportion of eaq- at high pollutants concentration. Last but not least, the influence of co-existing substances, Cl- and HCO3-, on PFOS degradation could be neglected, whereas their effects on defluorination were observed. Defluorination of PFOS was enhanced with the increased Cl- concentration, however, increased first and then decreased with the increment of HCO3- concentration. It was also found that the presence of humic acid(HA) lowered degradation as well as defluorination of PFOS owing to the blockage of effective UV light and trapping of active species for photochemical reaction.

Removal of Reactive Dye Using New Modified Chitosan- Pandan Sorbent

This research aims to synthesise the modified Chitosan-Pandan by performing impregnated approach at which the extracted polyphenols of pandan oil was served as stabiliser. The extractions of pandan leaves were carried out using maceration process whereby ethanol (95 vol%) was used as solvent. The characterisations of the modified Chitosan-Pandan were examined using Fourier transform infrared spectroscopy (FTIR). A batch adsorption of Reactive Black 5 (RB5) from aqueous solution using the modified Chitosan-Pandan were conducted under different range of retention time (0 - 40 min), initial mass concentration dyes (0.1 - 1.0 g/L), pH solution (5 - 11), temperature (25 - 80 ± 1 ?C) and dosage of sorbent (0.1 - 1.0 g). The optimum adsorption was achieved up to 99.9 % within 30 min, 0.2 g/L initial dye concentration, 0.1 g dosage of sorbent, pH 7 and at room temperature. Compared to raw chitosan, the modified Chitosan-Pandan was proven to have better percentage removal of RB5.The results obtained shows that the modified Chitosan-Pandan has great potential to be used as a powerful novel sorbent.

Some remarks on the evaluation of m-cresol and pyridine biodegradation kinetics

Wastewater produced from petroleum and coal processing industries can be contaminated with m-cresol and pyridine, which are two hazardous compounds with significant environmental and health effects. A bacterium known as Lysinibacillus cresolivorans has been demonstrated to effectively biodegrade m-cresol and this bacterium has been utilised by researchers to study the interaction effects of m-cresol and pyridine. Some variations in the literature were observed in the experimental data of the biodegradation of pyridine, which may be attributed to inaccurate estimation of initial cell mass concentration. In this work, simulations were run in combination with an algorithm to optimise initial biomass cell concentrations to describe the biodegradation kinetics of an inhibitory system in relation to experimental data. Simulated data on predicted cell concentrations and the results of this study may facilitate full-scale bioreactor design for m-cresol and pyridine removal from wastewater resulting from petroleum and coal processing.

Long-term aging behaviors in a model soft colloidal system.

Colloidal and molecular systems share similar behaviors near to the glass transition volume fraction or temperature. Here, aging behaviors after volume fraction up-jump (induced by performing temperature down-jumps) conditions for a PS-PNIPAM/AA soft colloidal system were investigated using light scattering (diffusing wave spectroscopy, DWS). Both aging responses and equilibrium dynamics were investigated. For the aging responses, long-term experiments (100 000 s) were performed, and both equilibrium and non-equilibrium behaviors of the system were obtained. In the equilibrium state, as effective volume fraction increases (or temperature decreases), the colloidal dispersion displays a transition from the liquid to a glassy state. The equilibrium α-relaxation dynamics strongly depend on both the effective volume fraction and the initial mass concentration for the studied colloidal systems. Compared with prior results from our lab [X. Di, X. Peng and G. B. McKenna, J. Chem. Phys., 2014, 140, 054903], the effective volume fractions investigated spanned a wider range, to deeper into the glassy domain. The results show that the α-relaxation time τα of the samples aged into equilibrium deviate from the classical Vogel-Fulcher-Tammann (VFT)-type expectations and the super-Arrhenius signature disappears above the glass transition volume fraction. The non-equilibrium aging response shows that the time for the structural evolution into equilibrium and the α-relaxation time are decoupled. The DWS investigation of the aging behavior after different volume fraction jumps reveals a different non-equilibrium or aging behavior for the considered colloidal systems compared with either molecular glasses or the macroscopic rheology of a similar colloidal dispersions.

Modeling the release of Escherichia coli from soil into overland flow under raindrop impact

Pathogen transport through the environment is complicated, involving a variety of physical, chemical, and biological processes. This study considered the transfer of microorganisms from soil into overland flow under rain-splash conditions. Although microorganisms are colloidal particles, they are commonly quantified as colony-forming units (CFUs) per volume rather than as a mass or number of particles per volume, which poses a modeling challenge. However, for very small particles that essentially remain suspended after being ejected into ponded water and for which diffusion can be neglected, the Gao model, originally derived for solute transfer from soil, describes particle transfer into suspension and is identical to the Hairsine–Rose particle erosion model for this special application. Small-scale rainfall experiments were conducted in which an Escherichia coli (E. coli) suspension was mixed with a simple soil (9:1 sand-to-clay mass ratio). The model fit the experimental E. coli data. Although re-conceptualizing the Gao solute model as a particle suspension model was convenient for accommodating the unfortunate units of CFU ml−1, the Hairsine–Rose model is insensitive to assumptions about E. coli per CFU as long as the assumed initial mass concentration of E. coli is very small compared to that of the soil particle classes. Although they undoubtedly actively interact with their environment, this study shows that transport of microorganisms from soil into overland storm flows can be reasonably modeled using the same principles that have been applied to small mineral particles in previous studies.

SIGNATURES OF STAR CLUSTER FORMATION BY COLD COLLAPSE

Sub-virial gravitational collapse is one mechanism by which star clusters may form. Here we investigate whether this mechanism can be inferred from observations of young clusters. To address this question, we have computed SPH simulations of the initial formation and evolution of a dynamically young star cluster through cold (sub-virial) collapse, starting with an ellipsoidal, turbulently seeded distribution of gas, and forming sink particles representing (proto)stars. While the initial density distributions of the clouds do not have large initial mass concentrations, gravitational focusing due to the global morphology leads to cluster formation. We use the resulting structures to extract observable morphological and kinematic signatures for the case of sub-virial collapse. We find that the signatures of the initial conditions can be erased rapidly as the gas and stars collapse, suggesting that kinematic observations need to be made either early in cluster formation and/or at larger scales, away from the growing cluster core. Our results emphasize that a dynamically young system is inherently evolving on short timescales, so that it can be highly misleading to use current-epoch conditions to study aspects such as star formation rates as a function of local density. Our simulations serve as a starting point for further studies of collapse including other factors such as magnetic fields and stellar feedback.

Evaluation of Toxicity Ranking for Metal Oxide Nanoparticles via an in Vitro Dosimetry Model.

It has been argued that in vitro toxicity testing of engineered nanoparticles (NPs) should consider delivered dose (i.e., NP mass settled per suspension volume) rather than relying exclusively on administered dose (initial NP mass concentration). Delivered dose calculations require quantification of NP sedimentation in tissue cell culture media, taking into consideration fundamental suspension properties. In this article, we calculate delivered dose using a first-principles "particles in a box" sedimentation model, which accounts for the particle size distribution, fractal dimension, and permeability of agglomerated NPs. The sedimentation model was evaluated against external and our own experimental sedimentation data for metal oxide NPs. We then utilized the model to construct delivered dose-response analysis for a library of metal oxide NPs (previously used for hazard ranking and prediction making) in different cell culture media. Hierarchical hazard ranking of the seven (out of 24) toxic metal oxide NPs in our library, using EC50 calculated on the basis of delivered dose, did not measurably differ from our ranking based on administered dose. In contrast, simplified sedimentation calculations based on the assumption of impermeable NP agglomerates of a single average size significantly underestimated the settled NPs' mass, resulting in misinterpretation of toxicity ranking. It is acknowledged that in vitro dose-response outcomes are likely to be shaped by complex toxicodynamics, which include NP/cellular association, triggering of dynamic cell response pathways involved in NP uptake, and multiple physicochemical parameters that influence NP sedimentation and internalization.

The influences of mass loading and rapid dilution of secondary organic aerosol on particle volatility

Abstract. The thermally induced evaporation of secondary organic aerosol (SOA) has been characterized for SOA formed from the dark ozonolysis of α-pinene at initial mass concentrations ranging from 1 to 800 μg m−3. Temperature-dependent particle size distributions were measured using a thermodenuder and the resulting mass thermograms were compared between the SOA formed at the various SOA mass concentrations. Negligible differences were observed between the mass thermograms for SOA concentrations &lt; 300 μg m−3. At higher SOA concentrations, the observed mass thermograms indicated the SOA was actually slightly less volatile than the SOA at lower concentrations; this is likely an artifact due to either saturation of the gas phase or to recondensation during cooling. The thermograms observed when the SOA was formed at high concentrations (&gt; 380 μg m−3) and then rapidly isothermally diluted to low concentrations (1–20 μg m−3) were identical to those for the SOA that was initially formed at low concentrations. The experimental results were compared to a kinetic model that simulates particle evaporation upon heating in a thermodenuder for a given input volatility distribution and particle composition. Three cases were considered: (1) the SOA was composed of semi-volatile monomer species with a volatility distribution based on that derived previously from consideration of SOA growth experiments; (2) the initial SOA was composed almost entirely of non-volatile dimers that decompose upon heating into their semi-volatile monomer units, which can then evaporate; and (3) where a volatility distribution was derived by fitting the model to the observed mass thermograms. It was found that good agreement is obtained between model predictions and the observations when the particle composition is dominated by either compounds of low volatility or by dimers. These same models were used to simulate isothermal evaporation of the SOA and were found to be broadly consistent with literature observations that indicate that SOA evaporation occurs with multiple timescales. The use of the semi-volatile monomer volatility distribution fails to reproduce the observed evaporation. The presence of dimers and larger oligomers in secondary organic aerosol formed from products of the reaction of α-pinene and O3 has been well established in laboratory studies. However, the timescale and relative importance of the formation of oligomers or low-volatility compounds in the growth and evaporation of SOA has been debated. This study provides further support that low-volatility compounds and oligomers are formed in α-pinene + O3 in high abundances and suggests that their formation occurs rapidly upon particle formation.

Optimization of lead removal from aqueous solution using goethite/chitosan nanocomposite by response surface methodology

Abstract This work investigates goethite/chitosan nanocomposites for their use in lead removal from aqueous solutions. Goethite nanoparticles were synthesized and characterized by FTIR, DLS, and SEM. Goethite nanoparticles were identified as nanospheres with the average diameter of 10–60 nm. The optimum conditions were determined using response surface methodology (RSM) based on three-variable-three-level Box–Behnken design (BBD). The effects of three variables, i.e., initial solution pH, adsorbent mass and initial concentration of Pb(II) ions on the removal efficiency for Pb(II) ions were evaluated. The optimal conditions for the lead removal were found to be 6, 0.05 g, and 74.4 mg/L, for the initial solution pH, adsorbent mass and the initial concentration of Pb(II) ions, respectively. Under these conditions, maximum lead removal efficiency was obtained to 98.26% that was in respectable agreement with the model (97.19%). The modified quadratic model exhibited excellent stability for Pb(II) adsorption by goethite/chitosan nanocomposite. The results of adsorption study by goethite/chitosan nanocomposite revealed that Pb(II) uptake was enhanced by chitosan film using goethite nanoparticles.

Experimental investigations on carbonation of sodium aerosol generated from sodium fire in the context of fast reactor safety

Carbonation of sodium aerosols is the most important aspects to be considered for the evaluation of chemical hazards as a part of fast reactor safety studies. The sodium oxide, immediately formed as the combustion product due to sodium fire, undergoes chemical changes to NaOH, Na2CO3 and NaHCO3 upon reactions with moisture and CO2 prevailed in the atmosphere. Of which, hydroxide aerosols are highly corrosive and harmful, and it has stringent concentration limit for human exposure. Hence, in order to assess the condition for human intervention in the event of sodium fire, chemical composition of aerosols resulting from controlled sodium fires in a closed Aerosol Test Facility was investigated. The real time chemical species of aerosols generated from sodium fire and the effect of relative humidity (RH) and carbon dioxide concentration in air on carbonation have been studied. The experiments were carried out with the initial mass concentration of ∼4gm−3, RH between 20% and 90% and the CO2 concentration in surrounding environment at 390 and 280ppm. It is observed from the experimental study that aerosols are enriched with NaOH (0.8mol fraction) in the beginning stage (samples collected during first few minutes after sodium fire) when surrounding atmosphere contains any of the following compositions – (i) ∼90% RH and 390ppm CO2, (ii) ∼90% RH and 280ppm CO2 or (iii) 50% RH and 280ppm CO2 whereas they are almost equally distributed between NaOH and Na2CO3 in the beginning stage when the atmosphere has any of the compositions (i) 50% RH, 390ppm CO2, (ii) 20% RH, 390ppm CO2 or (iii) 20% RH, 280ppm CO2. Carbonation of aerosols is completed between 20min and 1h just after sodium fire depending upon the prevailing atmosphere. The present study shows that highly humid condition promotes carbonation process. Faster the carbonation process the lesser would be the chemical hazard.

A theoretical model with experimental verification for heat and mass transfer of saline water droplets

Heat transfer to and mass transfer from NaCl–water droplets are investigated both numerically and experimentally. A new model is presented and used to simulate saline water droplet evaporation. The model is robust enough to be applied for various initial concentrations and conditions of the droplet, ambient conditions, and dissolved media properties. The model is validated using experimental data obtained in this study on top of those already available in the literature. The experimental apparatus as well as the processing routines to optically measure droplet evaporation at a range of ambient conditions are presented. The droplet was suspended using a glass filament. Data were collected for droplets with an initial radius of 500 μm at three temperatures 25 °C, 35 °C, and 45 °C and three air velocities 0.5 m/s, 1.5 m/s, and 2.5 m/s to provide a comprehensive validation dataset. Based on experimental and simulation data, a correlation is presented that captures the start time of solid formation. This time plays an important role in cooling tower design as it shows the time that the outer surface of the droplet dries. Using the validated model, it is shown that for 500 μm radius droplets with 3% initial mass concentration the start time of reaching the final size is 17% less than evaporation time of a pure water droplet. Also, the net energy required to evaporate the droplet falls by 7.3% compared to a pure water droplet. For 5% initial concentration these values are 24.9% and 12.2%, respectively. Using saline water in spray-cooling has two major effects: the energy extracted from the air per unit droplet volume is reduced (which can be compensated for by increasing the liquid flow rate). Moreover, compared to the time taken for the evaporation of a pure water droplet, the period with wet surface is shorter as a result of crust formation around the saline water droplet. This allows a shorter distance between spray nozzles and heat exchangers.

Study on Removal of Trivalent Chromium from Wastewater by Banana Peel

The toxic metals released into the aquatic environment though various industrial processes are detrimental to all living species. This paper used banana peels as an adsorbent for studying heavy metal Cr(III) containing in waste water. Respectively, the effects of the adsorption dosage, temperature, contact time, pH, initial Cr(III) ions concentration and shock time on adsorption were investigated. The results showed that under the following condition: the dosage was 0.1 g, the pH value of the wastewater was 2, the temperature is 30 °C, the shock time was 2 h, the initial mass concentration of Cr(III) was about 30 mg/L, the adsorbing capacity can be 22 mg/g. The adsorption reaction is an endothermic process and mainly physical adsorption. Using banana peels to treat chromium-contained wastewater has a very good application prospect.

Effect of an internal reaction on the characteristics of high-temperature heat and mass transfer of gas suspensions of carbon particles

The high-temperature heat and mass transfer of a gas suspension of carbon particles has been simulated physically and mathematically with allowance for the chemical reaction in their pores. It is established that the internal reaction leads to a significant decrease of the ignition delay times and critical parameters determining the ignition and extinction of particles of a gas suspension. The range of the initial particles sizes and mass concentrations, corresponding to the most complete burnout of carbon fuel, is found; the effect of the internal reaction on the limits of this range is analyzed. It is shown that the way of varying the mass concentration affects qualitatively the dependences of the ignition delay on the mass concentration.

Theoretical and experimental studies on a solid containing water droplet

Heat and mass transfer to and from a single solution droplet is studied in this work. A new theoretical model to predict the evaporation behaviour of solid containing water droplets is presented. The model, implemented in MATLAB, is used to predict the process of droplet evaporation with prediction results successfully validated against data from the literature. Also, an experimental study was performed to study the evaporation of a single droplet containing NaCl and water. To investigate the influence of concentration, tests were performed with droplet having initial radiuses of approximately 0.5mm and initial mass concentrations of 3% and 5%. Results obtained from the developed model were found to be in good agreement with our experimental data. Finally, it was shown that the current model, allowing for a smooth transition from surface evaporation to crystallisation, is able to simulate the process more accurately compared to existing models in the literature which lead to a, less realistic, sharp transition.

A study on Cr(VI) reduction from aqueous solutions by bauxite

The reduction of Cr(VI) in aqueous solution by using bauxite ore was investigated. Experimental results for Cr(VI) reduction in aqueous solution depending on some factors such as time, sulfuric acid amount, bauxite dosage, initial Cr(VI) concentration, formic acid concentration, daylight and temperature were presented. The obtained results show that sulfuric acid amount, bauxite dosage and initial Cr(VI) concentration of solution are most effective parameters on the reduction process. Also, it has been found that the 60 g/L of bauxite dosage is sufficient to reduce up to 100% of Cr(VI) from acidic solution under the condition of low initial Cr(VI) mass concentrations such as 10 mg/L. The reduction reaction is completed within 30 min at 25 °C under the experimental conditions: bauxite dosage of 60 g/L, amount of sulfuric acid 40–60 stoichiometric and initial mass concentration of Cr(VI), 10 mg/L. It was determined that reduction percentage is decreasing with increasing initial Cr(VI) concentration. The chemical oxygen demand of bauxite ore was found to be 26 mg COD/g.