The objective of this study was to investigate the possibility of using maize tassel as an alternative adsorbent for the removal of chromium (VI) and cadmium (II) ions from aqueous solutions. The effect of pH, solution temperature, contact time, initial metal ion concentration and adsorbent dose on the adsorption of chromium (VI) and cadmium (II) by tassel was investigated using batch methods. Adsorption for both chromium (VI) and cadmium (II) was found to be highly pH dependent compared to the other parameters investigated. Obtained results gave an adsorption capacity of 79.1 % for chromium (VI) at pH 2, exposure time of 1h at 25 °C. Maximum capacity of cadmium of 88 % was obtained in the pH range of 5-6 at 25 °C after exposure time of 1 h. The adsorption capacities of tassel for both chromium (VI) and cadmium (II) were found to be comparable to those of other commercial adsorbents currently in use for the removal of heavy metals from aqueous wastes. These results have demonstrated the immense potential of maize tassel as an alternative adsorbent for toxic metal ions remediation in polluted water and wastewater. 相似文献
The removal of the chromium (VI) ion from aqueous solutions with the Lewatit FO36 ion-exchange resin is described at different conditions. The effects of adsorbent dose, initial metal concentration, contact time and pH on the removal of chromium (VI) were investigated. The batch ion exchange process was relatively fast and it reached equilibrium after about 90 min of contact. The ion exchange process, which is pH dependent showed maximum removal of chromium (VI) in the pH range 5.0–8.0 for an initial chromium (VI) concentration of 0.5 mg/dm3. The equilibrium related to Lewatit FO36 ion- exchange capacity and the amounts of the ion exchange were obtained using the plots of the Langmuir adsorption isotherm. It was observed that the maximum ion exchange capacity of 0.29 mmol of chromium (VLVg for Lewatit FO36 was achieved at optimum pH value of 6.0. The ion exchange of chromium (VI) on this cation-exchange resin followed first-order reversible kinetics. 相似文献
Barium ion cross-linked alginate beads have shown great affinity to toxic hexavalent chromium ions in aqueous solution, in contrast to the traditionally used calcium alginate beads. Our adsorption experiments were carried out by the batch contact method. The optimal pH for removal was found to be pH 4. The equilibrium was established in 4 h, and the removal efficiency of chromium(VI) was found to be 95 %. The adsorption data were applied to Langmuir, Freundlich, Dubinin–Redushkevich (D–R), and Temkin isotherm equations. Both Langmuir and Freundlich isotherm constants indicated a favorable adsorption. The value of mean sorption energy calculated from D–R isoterm indicates that the adsorption is essentially physical. The high maximum chromium(VI) adsorption capacity was determined from the Langmuir isotherm as 36.5 mg/g dry alginate beads. The chromium(VI) adsorption data were analyzed using several kinetic models such as the pseudo-first-order, pseudo-second-order, intraparticle diffusion, and Elovich models, and the rate constants were quantified. Our study suggests that barium alginate beads can be used as cost-effective and efficient adsorbents for the removal of chromium(VI) from contaminated waters. 相似文献
This paper reports the potential of chemically treated wood chips to remove copper (II) ions from aqueous solution a function of pH, adsorbent dose, initial copper (II) concentration and contact time by batch technique. The wood chips were treated with (a) boiling, (b) formaldehyde and (c) concentrated sulphuric acid and characterized by Fourier transform infrared spectroscopy, scanning electron microscopy and energy dispersive analysis X-ray. pH 5.0 was optimum with 86.1, 88.5 and 93.9 % copper (II) removal by boiled, formaldehyde-treated and concentrated sulphuric acid-treated wood chips, respectively, for dilute solutions at 20 g L?1 adsorbent dose. The experimental data were analysed using Freundlich, Langmuir, Dubinin–Radushkevich and Temkin isotherm models. It was found that Freundlich and Langmuir models fitted better the equilibrium adsorption data and the adsorption process followed pseudo-second-order reaction kinetics. The results showed that the copper (II) is considerably adsorbed on wood chips and it could be an economical option for the removal of copper from aqueous systems. 相似文献
The adsorption of three copper species, the hydrated cupric ion, bisglycine Cu(II) and a Cu(II)-humic acid complex, on montmorillonite and imogolite at pH 7 was investigated by electron paramagnetic resonance (EPR) spectroscopy. The spectra of the supernatant solutions indicated that adsorption of the glycine complexes was very much less than that of the uncomplexed ion for both minerals and that montmorillonite adsorbed significantly more Cu from the humic acid solution than did imogolite. In every case the adsorbed Cu was characterized by more than one type of chemical environment and the spectral parameters show differences between the adsorbed species depending on their freedom of movement and their mode and site of adsorption. Qualitatively similar spectra were obtained when the uncomplexed ion was adsorbed on either of the mineral species and it is suggested that simple Cu(II) ions were involved and that their coordination environments comprised water molecules and hydroxyl groups. With the bisglycine Cu(II) complexes, the spectra were characterized by two components which may be accounted for by adsorption at two different types of site in the structures. In each case one component had parameters that are similar to those of the bisglycine Cu(II) in the solid state, but the second component in the spectra of the montmorillonite sample was quite different to that obtained with imogolite. The Cu(II)-humic acid complex with montmorillonite gave spectra that were similar to that from copper humate, but with imogolite the spectra from the Cu(II)-humic acid system were similar to those obtained with the uncomplexed Cu(II) ion, indicating that imogolite is able to extract copper from humic acid. 相似文献
The biosorption of chromium (VI) ions from aqueous solutions by two adsorbents viz. mango and neem sawdust was studied under a batch mode. An initial pH of 2.0 was most favorable for chromium (VI) removal by both the adsorbents. The results obtained for the final concentration of chromium (VI) and chromium (DI) at a pH range of 2–8 indicated that a combined effect of biosorption and reduction was involved in the chromium (VI) removal specially when the pH value is lower than 3. The maximum loading capacity was calculated from adsorption isotherms by applying the Langmuir model and found to be higher for neem sawdust (58.82 mg/g). Evaluation of experimental data in terms of biosorption kinetics showed that the biosorption of chromium (VI) by neem sawdust followed pseudo second-order kinetics. Therefore, the rate limiting step may be chemical sorption or chemisorption. The efficiency of this process was examined in using tannery wastewater contaminated with chromium (VI) ions in column mode. 相似文献
In this research, adsorption of chromium (VI) ions on wheat bran has been studied through using batch adsorption techniques. The main objectives of this study are to 1) investigate the chromium adsorption from aqueous solution by wheat bran, 2) study the influence of contact time, pH, adsorbent dose and initial chromium concentration on adsorption process performance and 3) determine appropriate adsorption isotherm and kinetics parameters of chromium (VI) adsorption on wheat bran. The results of this study showed that adsorption of chromium by wheat bran reached to equilibrium after 60 min and after that a little change of chromium removal efficiency was observed. Higher chromium adsorption was observed at lower pHs, and maximum chromium removal (87.8 %) obtained at pH of 2. The adsorption of chromium by wheat bran decreased at the higher initial chromium concentration and lower adsorbent doses. The obtained results showed that the adsorption of chromium (VI) by wheat bran follows Langmuir isotherm equation with a correlation coefficient equal to 0.997. In addition, the kinetics of the adsorption process follows the pseudo second-order kinetics model with a rate constant value of 0.131 g/mg.min The results indicate that wheat bran can be employed as a low cost alternative to commercial adsorbents in the removal of chromium (VI) from water and wastewater. 相似文献
An iron (III)-impregnated sorbent was prepared from sugarcane bagasse and ferric chloride solution via carbonization/activation in a muffle furnace at 500?°C for 4?h. The adsorption removal of chromium (VI) from aqueous solution by the iron (III)-impregnated sorbent was then studied in a batch system. With increasing initial chromium (VI) concentration from 25 to 130?mg/L at an adsorbent dose of 300?mg/50?mL, the amount of adsorbed chromium (VI) increased from 4.15 to 12.20?mg/g at 20?°C, from 4.16 to 12.50?mg/g at 30?°C, and from 4.16 to 13.72?mg/g at 40?°C. The dynamical data fit very well with the pseudo-second-order kinetic model, and the calculated adsorption capacities of 4.16, 8.37, and 13.37?mg/g were equal to the actual values of the experiments at the initial chromium (VI) concentrations of 25, 50, and 100?mg/L, respectively. The Langmuir isotherm could yield better fits than the Freundlich isotherm. The calculated isotherm parameters confirmed the favorable adsorption of chromium (VI) on the iron (III)-impregnated sorbent. 相似文献
In this research, spent coffee grains were modified with citric acid solutions (0.1 and 0.6 M) to increase the quantity of carboxylic groups improving its metal adsorption capacity. Added functional groups on modified and non-modified spent coffee grains were identified and quantified by attenuated total reflection Fourier transform infrared analyses and potentiometric titrations, respectively. These adsorbents were used for the removal of lead (II) and copper (II) from aqueous solutions at 30 °C and different pH in batch systems. In addition, adsorption–desorption experiments were conducted to evaluate the possibility of re-using the modified adsorbent. Potentiometric titrations data reveal that the quantity of carboxylic groups was increased from 0.47 to 2.2 mmol/g when spent coffee grains were modified with 0.1 and 0.6 M citric acid. Spent coffee grains treated with 0.6 M citric acid, achieved a maximum adsorption capacity of 0.77 and 1.53 mmol/g for lead (II) and copper (II), respectively, whereas non-modified spent coffee grains only reached 0.24 and 0.19 mmol/g for lead (II) and copper (II), respectively. Desorption of lead (II) and copper (II) achieved around 70 % using 0.1 N HCl for non-modified and modified spent coffee grains with 0.6 M citric acid. It is suggested that lead (II) and copper (II) species were adsorbed mainly on the carboxylic groups of modified spent coffee grains and these metals may be exchanged for hydrogen and calcium (II) ions during adsorption on non-modified spent coffee grains. Finally, the adsorption equilibrium was reached after 400 min for modified spent coffee grains with 0.6 M citric acid. Modified spent coffee grains are a promising option for removing metal cations from aqueous solutions due to its low cost and high adsorption capacity (about 10 times higher than the activated carbons). 相似文献
The charged sites on soil particles are important for the retention/adsorption of metals. Metallic counterions can neutralize
the intrinsic charges on the surfaces of soil particles by forming complexes. In this study, efforts have been made to determine
the effect of surface potential, pH, and ionic strength on the adsorption of four metal ions, hexavalent chromium Cr(VI),
trivalent chromium Cr(III), nickel Ni(II) and cadmium Cd(II), in glacial till soil. Batch tests were performed to determine
the effect of pH (2–12) and ionic strength (0.001–0.1 M KCl) on zeta potential of the glacial till soil. The point of zero
charge (pHPZC) of glacial till was found to be 7.0±2.5. Surface charge experiments revealed the high buffering capacity of the glacial
till. Batch adsorption experiments were conducted at natural pH (8.2) using various concentrations of selected metals. The
adsorption data was described by the Freundlich adsorption model. Overall glacial till shows lower adsorption affinity to
Cr(VI) as compared to cationic metals, Cr(III), Ni(II) and Cd(II). 相似文献
Hexavalent chromium has been proved to be the reason of several health hazards. This study aimed at evaluating the application of pomegranate seeds powder for chromium adsorption (VI) from aqueous solution. Chromium adsorption percentage (VI) increased with increasing the adsorbent dosage. Chromium adsorption capacity (VI), at pH = 2 and 10 mg/L initial metal concentration, decreased from 3.313 to 1.6 mg/g through increasing dosage of adsorbent from 0.2 to 0.6 g/100 ml. The adsorption rate increased through increase in chromium initial concentration (VI). However, there was a removal percentage reduction of chromium (VI). Chromium adsorption kinetics by different models (pseudo-first-order, modified pseudo-first-order, pseudo-second-order, Elovich, intraparticle diffusion, Boyd kinetic) was investigated as well. Studies on adsorption kinetic indicated that the experimental data were matched by pseudo-second-order model (R2 = 0.999) better. Obtained results demonstrated the pomegranate seeds can be used as an effective biomaterial and biosorbent for hexavalent chromium adsorption from aqueous solutions. 相似文献
We have used synchrotron-based soft X-ray core-level photoemission and adsorption spectroscopies to study the reaction of aqueous sodium chromate solutions with freshly fractured pyrite surfaces. Pyrite surfaces were reacted with 50 μM sodium chromate solution at pH 7 for reaction times between 1 min and 37 hr. Additional experiments were performed at pH 2 and pH 4 with 50 μM sodium chromate solutions and at pH 7 with 5 mM solutions. At chromate concentrations of 50 μM, all chromium present on the pyrite surface was in the form of Cr(III), while at 5 mM, both Cr(III) and Cr(VI) were present at the pyrite surface. Minor quantities of oxidized sulfur species (sulfate, sulfite, and zero-valent sulfur) were identified as reaction products on the pyrite surface. The amount of oxidized sulfur species observed on the surface was greater when pyrite was reacted with 5 mM Cr(VI) solutions because the rate of chromium deposition exceeded the rate of dissolution of pyrite oxidation products, effectively trapping Cr(VI) and oxidized sulfur species in an overlayer of iron(III)-containing Cr(III)-hydroxide. This work shows that pyrite, an extremely cheap and readily available waste material, may be suitable for the removal of hexavalent chromium from acidic to circumneutral waste streams. The reduced chromium ultimately forms a coating on the pyrite surface, which passivates the pyrite surface towards further oxidation. 相似文献
An investigation was undertaken regarding the adsorption of different heavy metal ions from aqueous solutions using ??-diketone-functionalized styrene divinylbenzene resin under different experimental conditions such as initial concentration of metal ions, contact time, pH, and chelating capacity. The functionalization of resin was carried out by the condensation reaction of sodium salt of ??-diketones (pentane-1,3-dione) and chloromethylated styrene?Cdivinylbenzene resin in dichloromethane. Functionalized resin beads were characterized by Fourier transform infrared spectroscopy. The batch method was employed using different metal ions solution from 5 to 15?mg/L at different contact times. The adsorption kinetics was tested for the pseudo-first order, pseudo-second order reaction at different experimental conditions. The rate constant of adsorption kinetic models were also calculated and good correlation coefficient (R2?>?0.9941) was obtained for pseudo-second order kinetic model. The maximum adsorption value obtain for lead (0.725728?mg/g), chromium (0.9199?mg/g), nickel (0.4974?mg/g), cobalt (0.6196?mg/g) and cadmium (0.6519?mg/g) at equilibrium condition, which shows that ??-diketone-functionalized styrene divinylbenzene resin is an effective adsorbent for toxic metal ions. 相似文献
Amorphous tin(VI) hydrogen phosphate (ATHP) was synthesized using the liquid phase precipitation method and served as an adsorbent to remove Pb(II), Cu(II), and Zn(II) from aqueous solutions. The ATHP was characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and nitrogen adsorption–desorption techniques. Adsorption properties were evaluated as a function of pH, reaction time, concentration of reactants, and salinity. Their equilibrium adsorption data were modeled using Freundlich, Langmuir, and Dubinin–Kaganer–Radushkevich isotherms, respectively. The results revealed that adsorption equilibrium reached within 180 min. ATHP indicated good adsorption even below the pHZPC, and best adsorption at pH 5 for Pb(II) and Cu(II) and at pH 5.5 for Zn(II) was observed. Equilibrium data fitted better to the Langmuir model for Pb(II) and Cu(II) and fitted better to the Freundlich model for Zn(II). The saturated adsorption capacities deduced from the Langmuir model were 2.425, 1.801, and 0.600 mmol/g for Cu(II), Pb(II), and Zn(II), respectively, indicating an adsorption affinity order of Cu > Pb > Zn. There is a negative correlation between the concentration of NaCl and adsorption capacity of ATHP, yet ATHP still exhibited excellent adsorption having an adsorption capacity of 19.35, 15.16, 6.425 mg/g when the concentration of NaCl was 0.6 mol/L. The free energy (E) was 12.33, 10.70, and 14.74 kJ/mol for Pb(II), Cu(II), and Zn(II), respectively. An adsorption mechanism based on ion exchange between heavy metal ions and H+ in the ATHP is proposed. Furthermore, the used ATHP was regenerated by HCl solution and the adsorbent was used repeatedly. 相似文献
Reductive precipitation of hexavalent chromium (Cr(VI)) with magnetite is a well-known Cr(VI) remediation method to improve water quality. The rapid (<a few hr) reduction of soluble Cr(VI) to insoluble Cr(III) species by Fe(II) in magnetite has been the primary focus of the Cr(VI) removal process in the past. However, the contribution of simultaneous Cr(VI) adsorption processes in aged magnetite has been largely ignored, leaving uncertainties in evaluating the application of in situ Cr remediation technologies for aqueous systems. In this study, effects of common groundwater ions (i.e., nitrate and sulfate) on Cr(VI) sorption to magnetite were investigated using batch geochemical experiments in conjunction with X-ray absorption spectroscopy.
Results
In both nitrate and sulfate electrolytes, batch sorption experiments showed that Cr(VI) sorption decreases with increasing pH from 4 to 8. In this pH range, Cr(VI) sorption decreased with increasing ionic strength of sulfate from 0.01 to 0.1 M whereas nitrate concentrations did not alter the Cr(VI) sorption behavior. This indicates the background electrolyte specific Cr(VI) sorption process in magnetite. Under the same ionic strength, Cr(VI) removal in sulfate containing solutions was greater than that in nitrate solutions. This is because the oxidation of Fe(II) by nitrate is more thermodynamically favorable than by sulfate, leaving less reduction capacity of magnetite to reduce Cr(VI) in the nitrate media. X-ray absorption spectroscopy analysis supports the macroscopic evidence that more than 75 % of total Cr on the magnetite surfaces was adsorbed Cr(VI) species after 48 h.
Conclusion
This experimental geochemical study showed that the adsorption process of Cr(VI) anions was as important as the reductive precipitation of Cr(III) in describing the removal of Cr(VI) by magnetite, and these interfacial adsorption processes could be impacted by common groundwater ions like sulfate and nitrate. The results of this study highlight new information about the large quantity of adsorbed Cr(VI) surface complexes at the magnetite-water interface. It has implications for predicting the long-term stability of Cr at the magnetite-water interface.
In this study, the adsorption behavior of Ni(II) in an aqueous solution system using natural adsorbent Peganum harmala-L was measured via batch mode. The prepared sorbent was characterized by scanning electron microscope, Fourier transform infrared spectroscopy, N2 adsorption–desorption and pHzpc. Adsorption experiments were carried out by varying several conditions such as contact time, metal ion concentration and pH to assess kinetic and equilibrium parameters. The equilibrium data were analyzed based on the Langmuir, Freundlich, Temkin and Dubinin–Radushkevich isotherms. Kinetic data were analyzed using the pseudo-first-order, pseudo-second-order and intra-particular diffusion models. Experimental data showed that at contact time 60 min, metal ion concentration 50 mg/L and pH 6, a maximum amount of Ni(II) ions can be removed. The experimental data were best described by the Langmuir isotherm model as is evident from the high R2 value of 0.988. The adsorption capacity (qm) obtained was 68.02 mg/g at an initial pH of 6 and a temperature of 25 °C. Kinetic studies of the adsorption showed that equilibrium was reached within 60 min of contact and the adsorption process followed the pseudo-first-order model. The obtained results show that P. harmala-L can be used as an effective and a natural low-cost adsorbent for the removal of Ni(II) from aqueous solutions. 相似文献
The removal of chromate from aqueous solutions, using finely ground pyrite and biotite, was investigated by batch experiments. The kinetics and mechanism of chromate reduction are discussed here. Chromate reduction by pyrite was about 100 times faster than that by biotite, and was also faster at pH 3 than 4. When pyrite was used, more than 90% of the initial chromate was reduced within 4 h at pH 4, and within 40 min. at pH 3. However, with biotite more than 400 h was required for the reduction of 90% of the initial chromate. The results indicate that the rate of chromate reduction was strongly depending on the amount and dissolution rate of the Fe(II) in the minerals. The reduction of chromate at pH 4 resulted in the precipitation of (Cr, Fe)(OH)3(s), which is believed to have limited the concentrations of dissolved Cr(III) and Fe(III) to less than the expected values. When biotite was used, the amounts of decreased Fe(II) and reduced Cr(VI) showed no stoichiometric relationship, which implies that not only was there chromate reduction by Fe(II) ions in the acidic solution, but also heterogeneous reduction of Fe(III) ions by structural Fe(II) in biotite. However, the results from a series of the experiments using pyrite showed that the concentrations of the decreased Fe(II) and the reduced Cr(VI) were close to the stoichiometric ratio of 3:1. This was because the oxidation of pyrite rapidly created Fe(II) ions, even in oxygenated solutions, and the chromate reduction by the Fe(II) ions was significantly faster than the Fe(II) ion oxygenation. When compared with the experimental sets controlled at an initial pH of 3, the pH of the biotite batch, which was not controlled, increased to 3.4. Because of the increase in the pH, Cr(VI) was not completely removed, and 25% (1.2–1.3 mg/L Cr(VI)) of the initial concentration remained for up to 1000 h. The pH increase is, in most cases, caused by the hydrolysis of clay minerals. However, in the pyrite batches, there was no difference in the variations of the chromate reduction in relation to the pH control. There was also no difference in the capacity and rate of Cr(VI) reduction in 0.01 M NaCl or Na2SO4 solutions. In the 0.01 M NaH2PO4 solution pyrite experiment, the Cr(VI) was not completely removed, despite the maintenance of the pH at 3. The dominant Fe species was about 10 mg/L Fe(III) and few Fe(II) ions existed in solution. The Fe phosphate (Fe3(PO4)2 or FePO4) coatings on the surface of pyrite prevented access of O2 or Cr(VI). Therefore, the surface coatings are likely to have caused the deterioration of the Cr(VI) reduction capacity in the NaH2PO4 solution. 相似文献
In the present research, the removal of lead(II) and copper(II) from aqueous solutions is studied, using SnO2 nanowires as new adsorbent on solid-phase extraction disk and compared with pine core and buttonwood as biosorbents. Batch adsorption experiments were performed as a function of pH, adsorption time, solute concentration and adsorbent dose for biosorbents. Also, the pH, transfer rate of solution and metal concentration were selected as experimental parameters for the removal of heavy metals by SnO2 nanowires. All of the parameters were optimized by experimental design method for sorbents. The experimental equilibrium adsorption data are tested for the Langmuir and Freundlich equations. Results indicate the following order to fit the isotherms: Langmuir > Freundlich, in case of lead and copper ions. The removal of Cu(II) and Pb(II) was performed by selected sorbents in the presence of interferences ions. This led to no remarkable decrease in the removal efficiency of SnO2 nanowires. Using the SnO2 nanowires in the wastewater treatment indicated 96.8 and 85.28% removal efficiency in only 7 min for Pb(II) and Cu(II), respectively. SnO2 nanowires were found as reusable sorbent. Therefore, SnO2 nanowires have a good potential for application in environmental protection. 相似文献
