Chromium In Aqueous Solution Research Articles

Biosorption of chromium in aqueous solutions using Bivalve Mollusk Shells through central composite design (CCD) model

Pollution of water resources caused by heavy metals has been among the greatest concerns of environmentalists in recent years. Industrial wastewater contains chromium. Therefore, removing or reducing chromium from the industrial wastewater seems to be essential. In the present research, bivalve mollusk shells acted as the adsorbent. The statistical model in this research was central composite design, which analyzed the experiments. The optimal pH range for an adsorbent was about 3–5. An increase in the adsorbent dosage led to an increased efficiency. The optimal exposure time for the ion absorption mechanism of the solution was about 35 min. The absorption mechanism followed the Freundlich adsorption isotherm model. The most significant factor was found to be the independent effect of chromium initial concentration (p = 0.0007). Compared with other adsorbents such as fruit peels and the like whose availability depends on their consumption, the use of this adsorbent was economically beneficial due to its low cost and high availability.

Preparation, Characterization of Fe<sub>3</sub>O<sub>4</sub>/TiO<sub>2</sub>/CuO Nanohybrid and its Potential Performance for Chromium Removal from Aqueous Solution

Fe3O4/TiO2and Fe3O4/CuO nanohybrid nanohybrid materials have attracted widespread attention due to their scientific and technological importance as photocatalyst. Complicated process is usually used to synthesize these nanohybrid. In this study, we demonstrated a simple low-temperature sol-gel method to prepare Fe3O4/TiO2/CuO nanohybrid as photocatalyst. Hexavalent chromium was used as a model pollutant to evaluate their photocatalytic activity. The results of the photoreduction of hexavalent chromium in aqueous solution indicated that with the incorporation of CuO content in Fe3O4/TiO2nanohybrid increasing the photocatalytic performance in ultraviolet and visible region. Moreover, it is found that hydroxyl radical has an important role in photocatalytic efficiency.

Ca and Fe modified biochars as adsorbents of arsenic and chromium in aqueous solutions

This work investigated the production of Ca and Fe modified biochars in order to use them for the removal of arsenic As(V) and chromium Cr(VI) from aqueous solutions. Rice husk was impregnated with CaO at an impregnation ratio 0.114, while both rice husk and the organic fraction of municipal solid wastes were impregnated with Fe0 and Fe3+ at impregnation ratios 0.114 and 0.23. The modified biochars exhibited high As(V) removal capacity (>95%), except for the case of rice husk impregnated with Fe0, whose removal capacity reached only 58%. All modified biochars exhibited much better As(V) removal capacity compared to the non-impregnated biochars. However, the Cr(VI) removal rates were not as high as the As(V) ones. The maximum Cr(VI) removal was observed in the case of rice husk biochar impregnated with 2.3% w/w Fe3+, whereas the majority of impregnation agents examined did not manage to enhance the biochars' Cr(VI) removal ability. The equilibrium study showed that the Freundlich model can adequately describe the sorption process for the majority of samples examined. Analysis of the amount of Fe present in the equilibrium solutions suggested that the main mechanisms of As(V) and Cr(VI) removal were possibly metal precipitation and electrostatic interactions between the modified biochars and the adsorbate.

Reduction of hexavalent chromium with polyphenol-coated nano zero-valent iron: column studies

Nano zero-valent iron (nZVI) is considered as a highly efficient reductant with wide applicability in the remediation of contaminated sites, due to the small particle size, large specific surface area, and high reactivity. In this study, nZVI was synthesized by mixing Camellia Sinensis extract (green tea, GT) with a ferric iron solution. Polyphenols in the GT extract act as: (a) strong reductants, reducing thus Fe(III) to its elemental state and (b) capping agents that stabilize the Fe(0) nanoparticles and inhibit their potential rapid oxidation. The remediation potential of ZVI nanoparticles, produced with the Green Tea method (GT-nZVI), for hexavalent chromium (Cr(VI)) was evaluated by column tests. The tests were carried out using polyethylene columns, with 2.63 cm internal diameter and ~10 cm length. The columns were filled with 65 g of natural soil and pure silica sand at a ratio of 50% w/w. The reductive capacity of GT-nZVI was examined for high (5 mg L−1) concentration of hexavalent chromium in aqueous solution. The soil was initially treated in the first column by introducing 11 pore volumes of GT-nZVI suspension through the packed column while in the second column 24 pore volumes were introduced. It was found that about 210 and 420 mg of ZVI nanoparticles were retained by the soil during this stage in column I and in column II, respectively. After this step, the solution of hexavalent chromium was introduced in the columns at a flowrate of 1.2 mL min−1, in order to determine the breakthrough curve of Cr(VI) in the immobilized GT-nZVI on the soil. The total amount of reduced Cr(VI) was equal to 17 mg in column I and 33 mg in column II. Based on the available experimental data, it was estimated that a GT-nZVI-treated zone in the subsurface, with a length (L) of 0.75 m, could provide a sufficiently long contact time in order to reduce Cr(VI) levels from 5 mg L−1 to less than 5 μg L−1, under the condition that groundwater Darcy velocity is either equal to or less than 0.1 cm min−1.

Simultaneous Determination of Trace Lead and Chromium in Water Using Laser-Induced Breakdown Spectroscopy and Paper Substrate

Toxic metals such as lead and chromium in aqueous solutions have been analyzed simultaneously by laser-induced breakdown spectroscopy (LIBS), in which the ordinary printing paper is used as a liquid absorber which was immerged into Pb(NO3)2 and Cr(NO3)3 aqueous solution to enrich the heavy metals. This method overcomes the drawbacks of splashing and low sensitivity in ordinary LIBS analysis of water, in which a laser beam is directly focused on a liquid surface. A good signal intensity and reproducibility has been demonstrated. The Pb 405.78 nm and Cr 427.48 nm spectral lines are used as the analytical lines. The variation of line intensity with immersion time was investigated. The calibration curve for quantitative measurement of Pb and Cr in water was established, and the detection limits are 0.033 mg/L and 0.026 mg/L respectively, which is about 2–3 orders of magnitude better than that in the ordinary LIBS analysis of heavy metal in solution.

Adsorptive Removal of Trivalent Chromium in Aqueous Solution Using Precipitate Produced from Aluminum Tanning Wastewater

Precipitate adsorbent was produced from aluminum tanning wastewater by alkali precipitation and characterized by XPF, XRD, and FTIR. The results showed that the main components of the precipitate were Al, Ti, and Zr. The adsorption equilibrium for Cr3+ on the precipitate was reached within 60 min. The precipitate had better removal for Cr3+ from wastewater at pH 7.0. The kinetic process of adsorption can be described by the pseudo-second-order kinetic equation, and the adsorption isotherm fitted to the Langmuir model very well. Co-existed cations (Na+, Ca2+) in aqueous solution restrained Cr3+ adsorption on the precipitate. The adsorption of Cr3+ on the precipitate was mainly through the complexation and ion-exchange mechanisms, and oxide may play a major role in Cr3+ adsorption process.

Adsorption of Cr(III) and speciation of chromium in aqueous solution using Ambrosia beetle-generated acacia polycantha frass

Acacia polycantha frass (APF) generated by boring activity of Ambrosia beetles was investigated using a batch technique for its potential to adsorb Cr(III) ions from aqueous solution. Studies were carried out to determine the effect of pH, adsorbent dose, and KBr concentration on the sorption behavior Cr(III) on the adsorbent. The adsorption process was found to be highly dependent on solution pH with maximum removal occurring at pH 11. Thermodynamic studies indicated that the sorption process was exothermic and spontaneous. Adsorption recoveries of up to 75 and 95% for a 5 mgL-1 solution were obtained for untreated and acid-treated APF respectively at room temperature. In all experiments the acid-treated adsorbent showed an apparently higher metal uptake than the untreated one. Reduction of Cr(VI) to Cr(III) in synthetic solution using hydroxylamine prior to adsorption preconcentration showed potential for studying chromium speciation. Key words: Adsorption, entropy of activation, enthalpy of activation, chromium, speciation, acacia polycantha frass.

Colorimetric Detection of Trivalent Chromium in Aqueous Solution Using Tartrate-Capped Silver Nanoparticles as Probe

This study describes a simple and highly selective method for the colorimetric detection of trivalent chromium (Cr3+) using tartrate-capped silver nanoparticles (AgNPs) as probe. The addition of tartrate to the initially prepared AgNPs gives tartrate-stabilized AgNPs ascribing to the electrostatic repulsion of the highly negatively charged tartrate ions covered on the surface of AgNPs. It is found that, in the presence of Cr3+ in aqueous solution, the aggregation of tartrate-stabilized AgNPs occurs. The color of AgNPs suspension changes from yellow to pink and the surface plasmon absorption band broadens and red shifts, which could be applied for the colorimetric detection of Cr3+ in aqueous solution. The utilization of tartrate-stabilized AgNPs as probe substantially increases the selectivity and sensitivity for colorimetric detection of Cr3+. Control experiments with the addition of over 14 other metal ions, such as Pb2+, Zn2+, Cr2O7(2-), Cd2+, Co2+, Cu2+, Al3+, Ni2+, Mn2+, Ba2+, Fe3+, Ca2+, Mg2+, Sr+ do not result in a distinct change in the color or in the spectrum of the suspension, indicating that these metal ions do not interfere with the colorimetric detection of Cr3+. Under the conditions employed here, A502/A393 (ratio of absorption value at 502 nm to 393 nm) is linear with the concentration of Cr3+ within a concentration range from 0.1 to 1.17 microM with a detection limit of 0.06 microM. This study may offer a simple, rapid and sensitive approach to colorimetric detection of Cr3+ in aqueous solution.

Photo-reduction of Hexavalent Chromium in Aqueous Solution in the Presence of TiO2as Semiconductor Catalyst

The objective of this work is to determine the optimal conditions for the reduction of the hexavalent chromium in water using the photocatalytic system TiO2/ UV. The results show that the effectiveness of this system was significantly higher compared to direct photolysis. The influence of parameters such as photocatalyst loading and initial concentration of the substrate was studied. The study of the influence of pH shows that the reduction rates are grater for acid solutions. Furthermore the experimental results show that the presence of H2O2 at small concentration (10-6M) accelerates the reduction. However at higher concentration (10-4M) H2O2 inhibits the reduction. The presence of inorganic ions such as Cl- and SO42- does not seem to have any significant influence on the reduction rate of Cr (VI).

English

  The microbial dried biomass of Thraustochytrids is used as bioadsorbent for the removal of the chromium in aqueous solution. In this investigation, three species ofThraustochydrids namely Aplanochytrium sp., Thraustochytrium sp. andSchizochytrium sp. were tested for the efficiency of chromium accumulation by culturing in chromium-incorporated medium at 30°C for one week incubation. The biomass was harvested by filtration through Whatman no.1 filter paper. The level of metal accumulation in the biomass was determined by using an inductively coupled plasma system (ICP- Optical Emission Spectrophotometer; Optima 2100DV). Finally, among the three strains, Aplanochytrium spp. was selected for the adsorption kinetics and optimization using response surface methodology. Optimization of chromium removal by dried microbial biomass was analyzed with important factors of different pH, adsorbent dosage (Aplanochytrium dried biomass), temperature and processing time with 30 batch experimental plan derived from the centre composite design (CCD) of response surface methodology. Aplanochytrium sp. dried biomass removed chromium of 69.4% in aqueous solution. Therefore, Aplanochytrium sp. dried biomass is potent for the removal of chromium in waste water treatment.   Key words: Mangroves, chromium removal, Aplanochytrium sp., biosorption, waste water treatment

Photocatalytic reduction of hexavalent chromium in aqueous solutions with zinc oxide nanoparticles and hydrogen peroxide

Photocatalytic reduction of Cr(VI) to Cr(III) in aqueous solutions under UV irradiation and ZnO semiconductor catalyst was investigated using potassium dichromate as a model compound. The effects of pH, catalyst dose (0.05−0.15 g/dm), Cr(VI) initial concentration (0.1−15 mg/dm) and hydrogen peroxide concentration on photocatalytic reduction of Cr(VI) were investigated. The reduction rate of chromium was more favorable in acidic solution. Hydrogen peroxide was added as a reduction reagent for enhancement of the photoreduction. The process of photoreduction of Cr(VI) approximately followed first-order kinetics. Drinking water samples and wastewater were collected and photocatalytically treated for reduction of Cr(VI).

Characterization of coupled NiO/TiO 2 photocatalyst for the photocatalytic reduction of Cr(VI) in aqueous solution

NiO/TiO 2 coupled photocatalysts were fabricated by sol–gel process in this study. The coupled catalyst exhibited higher response of surface photovoltage than pure TiO 2 indicating that the recombination of photogenerated electron–hole pairs was retarded by the inner electric field caused by p–n junction region. Photocatalytic reduction of hexavalent chromium in aqueous solution was studied using these NiO/TiO 2 coupled photocatalysts prepared with various NiO loadings and calcined temperatures. The coupling of NiO strongly affects the performance of coupled photocatalysts, including the retard of phase transformation of TiO 2, the decrement of particle size and the enhancement of separation efficiency of photogenerated electron–hole pairs. The addition of ethanol as a sacrificial agent significantly increased the photocatalytic activity of hexavalent chromium reduction using these NiO/TiO 2 coupled photocatalysts.

Complex Equilibria in Aqueous Solutions of Chromium(III) with Some Biological pH Buffers

In this study, we examined the complex formation of the Cr(III) ion with a variety of biological pH buffers [tris(hydroxymethyl)aminomethane (TRIS), N-[tris(hydroxymethyl)methyl]-2-aminoethanesulfonic acid (TES), N-[tris(hydroxymethyl)methyl]-3-aminopropanesulfonic acid (TAPS), N-[tris(hydroxymethyl)methyl]-3-amino-2-hydroxypropanesulfonic acid (TAPSO), N-tris(hydroxymethyl)methyl-4-aminobutane sulfonic acid (TABS), 4-morpholine ethane sulfonic acid (MES), 4-morpholine propane sulfonic acid (MOPS), 3-morpholino-2-hydroxypropane sulfonic acid (MOPSO), and 4-(N-morpholino)butanesulfonic acid (MOBS)] by potentiometric measurements at 310.15 K and ionic strength I = 0.16 mol·dm–3 KCl. The protonation constants of the biological buffers were determined and discussed, under the above conditions. The overall stability constants were obtained by the least-squares curve-fitting program HYPERQUAD 2008. As a result of the numerical treatment, a model composed of five main species CrL, CrL2, CrL2(OH), CrL2(OH)2, and ...

Reduction of hexa-valent chromium with zero-valent iron: Batch kinetic studies and rate model

Reduction of hexa-valent chromium in aqueous solution by zero-valent iron in the form of a thin plate over a pH range of 3–5.5 has been investigated. The rate of removal of Cr(VI) declines sharply at a longer time indicating passivation of the surface. A kinetic model that takes into account the direct reduction, the passivation process and the resultant decline of the ‘active’ surface area of reaction is proposed. The model parameters have been estimated by global optimization at each of the pH values. The reduction reaction conforms to 2/3-order kinetics with respect to the Cr(VI) concentration; the passivation reaction is linear in the Cr(VI) concentration. A good match of the experimental and theoretically computed concentrations as function of time was observed. The EDX of the reacted surface showed existence of a mixed oxide layer on it. A reacted plate, after cleaning of the surface, regained its original activity.

Process optimization of adsorption of Cr(VI) on activated carbons prepared from plant precursors by a two-level full factorial design

Commercial activated carbon (CAC) prepared from coconut shell and activated carbon (AC) prepared from bael fruit ( Aegle marmelos) shell (BFS) were used as adsorbents for the adsorption studies of hexavalent chromium in aqueous solution. The main and interactive effects of four different experimentally controlled environmental factors like pH, initial concentration of Cr(VI) ( C i), adsorbent dose ( m) and temperature ( T) are investigated through the model equations designed by a two-level full factorial design (FFD) in a shake-flask system. Activated carbon prepared from BFS has more removal capacity of Cr(VI) than CAC under tested conditions. The results predicted using factorial regression model showed high values of regression coefficients ( R CAC 2 = 0 .952 and R BFS AC 2 = 0 .995 ) indicating good agreement with experimental data. Main and interacting effects of different process parameters on the response (% removal of Cr) were found. Optimization of the process was carried out by using desirability ( D) function by targeting the factors to desired levels for maximum removal of Cr(VI).

Photo-reduction of hexavalent chromium in aqueous solution in the presence of zinc oxide as semiconductor catalyst

Common sources of chromium in wastewater are electroplating and leather industries. Hexavalent chromium is more toxic and carcinogenic compared to its trivalent counterpart. Conversion of Cr(VI) to Cr(III) in an aqueous medium by photocatalytic reduction using UV radiation and ZnO semiconductor catalyst has been investigated using potassium dichromate as the model compound. Effects of the process parameters such as ZnO loading (0–3 g/L) and intensity of UV radiation (0–125 W medium pressure Hg vapour lamp) on photocatalytic reduction were investigated. Initial concentration of substrate solution was varied from 40 to 120 mg/L. A comparison of the performance of the ZnO photocatalyst achieved in this study with that reported in the literature for photocatalytic and conventional processes is presented. The initial rate of the photochemical method was found to be independent of the concentration of potassium dichromate. Methanol was added as a hole scavenger for enhancement of the photo-reduction. Initial rate of photo-reduction was found to be independent of the concentration of methanol above a particular value. A probable mechanism and the corresponding kinetic model have been proposed for the photo-reduction and tested by experimental results. An alternative rate equation based on the LHHW model compares well with the mechanistic rate equation.

Adsorption of Chromium (VI) from Aqueous Solutions Using Sol-Gel Anionic Clays with Mg/ Al=7

ABSTRACTAnionic clays has been used in the adsorption of anionic species of toxic heavy metals, such as chromium (VI), which is considered to be a dangerous pollutant, due to its deleterious effects on human health such as epithelial irritation and cancer. In this work the removal of chromium in aqueous solutions using anionic clays with Mg/Al=7 was determined. The anionic clays were synthesized by the sol-gel method at pH 10 and 11.5, and were characterized by X-ray diffraction, thermal analysis, infrared spectroscopy and N2 adsorption Brunauer-Emmett-Teller (BET). By this method, anionic clay containing brucite was obtained. The solids exhibited meso-porosity, high surface areas and thermal stability until 500°C. The data obtained from the adsorption experiments of chromium fitted to the Langmuir adsorption isotherm model and the adsorbent capacity was determined using the Langmuir adsorption equation. The maximum chromium uptake was 45 mg of Cr/g sorbent and 43 mg Cr/g sorbent for anionic clays prepared to pH 10 and 11.5, respectively. The Cr saturation point was attained after eight minutes stirring time. According to chromium adsorption values, the solution pH does not have a significant affect on the adsorption capacity of the anionic clays.

Quantitative determination of hexavalent chromium in aqueous solutions by UV-Vis spectrophotometer

AbstractIn the last decade, different methods have been developed for the determination of chromium(VI) concentration in water. These methods use high cost equipment or they require a long preparation time. Because of their drawbacks, this paper describes an on-line, rapid and sensitive procedure for the determination of Cr(VI) concentrations in aqueous solutions via pH and absorption measurements. Only four Cr(VI) species are considered. The effects of pH and of total amount of chromium on the Cr(VI) speciation are investigated. The molar absorptivities of four chromium species at 371 nm are determined by minimising an objective function. The knowledge of these molar absorptivities and the measurements of pH and absorption at 371 nm lead to a rapid determination of total Cr(VI) concentration. The reliability and applicability of the method were confirmed using synthetic water samples.

Supramolecular approach to crystallization of polynuclear chromium(III) aqua hydroxo complexes: synthesis and crystal structures of complexes [Cr2(OH)2(H2O)8]4+ and [Cr4(OH)6(H2O)12]6+ with cucurbit[n]uril (n = 7, 8)

Supramolecular compounds of the compositions {[Cr2(OH)2(H2O)8](C42H42N28O14)2}-(NO3)4·18.75H2O (1) and {[Cr4(OH)6(H2O)12](C48H48N32O16)3(NO3)6·55H2O (2) were synthesized from aqueous solutions of chromium(III) nitrate and the macrocyclic cavitand cucurbit[n]uril (C6n H6n N4n O2n , where n = 7 or 8, respectively). According to the X-ray diffraction study, the polynuclear chromium aqua complexes are disposed in cavities formed by the cucurbit[n]uril molecules and are linked to these molecules through hydrogen bonds between the hydroxo and aqua ligands of the polycations and the portal oxygen atoms of the macrocycles. Compound 1 is the first example of supramolecular compounds of cucurbit[7]uril with metal aqua complexes. The isolation of the supramolecular adduct with cucurbit[8]uril 2 in the single-crystalline state allows the determination of the structure of the tetranuclear chromium aqua complex having an adamantane-like structure, [Cr4(μ2-OH)6(H2O)12]6+, which has been previously unknown in the solid state.

Different N-containing functional groups modified mesoporous adsorbents for Cr(VI) sequestration: Synthesis, characterization and comparison

Ordered mesoporous SBA-15 has been functionalized by aminopropyl, imidazole and triazole groups by one or two-step post-grafting route and investigated as adsorbents of hexavalent chromium in aqueous solutions. XRD, N 2 adsorption–desorption measurements, FT-IR, solid state NMR and element analysis techniques have been employed to prove the ordered mesoporous structures of the functionalized SBA-15 and the successful immobilization of the organic functional moieties on SBA-15. The Cr(VI) adsorption behavior on the resultant adsorbents were examined by a batchwise method. The results show that all adsorbents exhibit the fast adsorption rate and the excellent adsorption capacity. Electrostatic interaction between the adsorbents and adsorbate plays an important role in the adsorption process. Equilibrium data were well fitted to the Langmuir and Freundlich adsorption models.